ALBERT

Description: Porous shape memory alloys are a new class of advanced materials with combined advantages of both shape memory alloys and porous materials. In order to manufacture a porous shape memory alloy with the desired mechanical properties, it is important to predict its mechanical properties before fabrication. In this paper, a new unit cell model is proposed to simulate the mechanical stress-strain response of porous shape memory alloys. Microplane theory is used to attribute mechanical constitutive relations of shape memory alloys to the bulk material, and the finite element method is employed for numerical simulations. The results show a good agreement with the experimental stress-strain behavior reported in the literature. The effect of pore volume fraction on the stress-strain response is also studied using the proposed approach. Random microstructures are generated in the FE model, and the effects of randomness on the mechanical behavior of porous shape memory alloys are also investigated for different values of pore volume fraction.

Description: In the present work, Ni-WC powder was deposited on mild steel substrate to develop clads through microwave hybrid heating technique. The cladding trials were carried out in an industrial microwave applicator at 1.1 kW for 540 s. The Ni-WC composite clads were characterized for microstructure and abrasive wear performance through combination of x-ray diffraction, electron and optical microscopy, microhardness, and wear tests. Phase analysis of the Ni-WC clad indicated the presence of stable carbides such as WC, W 2 C, Ni 2 W 4 C, and Fe 6 W 6 C. The microstructure study of the clad layer revealed the presence of a uniformly distributed interlocked WC-based reinforcement embedded in the Ni-based matrix. The average Vicker’s microhardness in the clad layer was observed to be 1028 ± 90 HV, which was approximately three times the microhardness of the substrate. Abrasive wear resistance of the microwave clads was superior to the MS substrate. Abrasion was the main wear mechanism in the Ni-WC clads and the substrate samples. However, the presence of WC-based reinforcement in the composite clads reduced microcutting, resulting in enhanced wear resistance.

Description: Corrosion behavior of wrought Stellite 6B and Stellite 6K, which have similar chemical composition but contain different carbon content, in 3.5 wt.% NaCl solution and in Green Death solution is investigated using various electrochemical methods, including potentiodynamic polarization, cyclic polarization, and electrochemical impedance spectroscopy (EIS). The obtained potentiodynamic polarization curves, cyclic polarization curves, and EIS spectra for these alloys are in good agreement, showing that Stellite 6K with higher carbon content is easier corroded due to its larger volume fraction of carbides but the Cr 2 O 3 film formed on this alloy is stronger and more stable than that on Stellite 6B. Further immersion tests on these alloys show that Stellite 6K has less resistance to pitting corrosion.

Description: A solution to improve the formability of aluminum alloy sheets can consist in investigating warm forming processes. The optimization of forming process parameters needs a precise evaluation of material properties and sheet metal formability for actual operating environment. Based on the analytical M-K theory, a finite element (FE) M-K model was proposed to predict forming limit curves (FLCs) at different temperatures and strain rates. The influences of initial imperfection value ( f 0 ) and material thermos-viscoplastic model on the FLCs are discussed in this work. The flow stresses of AA5086 were characterized by uniaxial tensile tests at different temperatures (20, 150, and 200 °C) and equivalent strain rates (0.0125, 0.125, and 1.25 s −1 ). Three types of hardening models (power law model, saturation model, and mixed model) were proposed and adapted to correlate the experimental flow stresses. The three hardening models were implemented into the FE M-K model in order to predict FLCs for different forming conditions. The predicted limit strains are very sensitive to the thermo-viscoplastic modeling of AA5086 and to the calibration of the initial geometrical imperfection which controls the onset of necking.

Description: The present work is based on the study of the electrochemical response of mild steel as a function of machining configurations. The variable parameters were rake angle and turning speed, while feed rate and depth of cut remained fixed. Dynamic polarization tests and electrochemical impedance spectroscopy in 3.5% NaCl solution were done to analyze the electrochemical behavior of mild steels with the variation of rake angle and turning speed. The electrochemical response showed that the steel machined at higher speed and positive rake angle had higher resistance to charge transfer. Similarly, steel machined at lower speed and negative rake angle showed lower resistance to charge transfer. The results obtained in this study suggest that machining on mild steel should be carried out at positive rake angle and at higher speed to have smoother surface finish, strain-relieved surface grains, and subsequently better corrosion resistance, which was measured from corrosion current as determined by the Tafel extrapolation from the polarization plots.

Description: The effects of different nitrogen contents on the passivity of nickel-free stainless steels in 0.5 M sulfuric acid + 0.5 M sodium chloride solution were investigated by electrochemical impedance spectroscopy in the potential ranges of active dissolution and active-passive transition. A simplified reaction model containing adsorbed intermediates involved dissolution process, and passivation process was proposed to explain the impedance characteristics. Based on both equivalent circuit and mathematical model analysis, the effects of nitrogen on the passivity of stainless steels are discussed.

Description: The influence of heat treatment from 500 to 1100 °C on the 5 wt.% H 2 SO 4 solution-induced corrosion resistance of high-velocity oxygen-fuel sprayed WC-17Co coatings on 42CrMo steel was investigated, by using x-ray diffractometer (XRD), scanning electron microscopy (SEM)-energy-dispersive spectrometer (EDS), and polarization curve methods. XRD analysis showed decrease in W 2 C phase intensity with recrystallization of amorphous Co and generation of new Co 3 W 3 C and Co 6 W 6 C phases with heat treatment. Porosity distribution did not follow a particular pattern; it initially increased and then decreased with increasing temperature. Corrosion resistance sequence of the as-sprayed and heat-treated coatings in 5 wt.% H 2 SO 4 solution was C-5 〉 C-9 〉 C-A 〉 C-7 〉 C-11. Furthermore, microstructure and phase structure of heat-treated coatings revealed the formation of different discontinuous plate-like oxide films on the surface of the heat-treated coatings which indicated the vital effect of binder structure on the corrosion resistance.

Description: Isothermal die forging is one of near net-shape metal-forming technologies. Strict control of billet temperature during isothermal die forging is a guarantee for the excellent properties of final product. In this study, a new method is proposed to accurately control the billet temperature of complex superalloy casing, based on the finite element simulation and response surface methodology (RSM). The proposed method is accomplished by the following two steps. Firstly, the thermal compensation process is designed and optimized to overcome the inevitable heat loss of dies during hot forging. i.e., the layout and opening time of heaters assembled on die sleeves are optimized. Then, the effects of forging speed (the pressing velocity of hydraulic machine) and its changing time on the maximum billet temperature are discussed. Furthermore, the optimized forging speed and its changing time are obtained by RSM. Comparisons between the optimized and conventional die forging processes indicate that the proposed method can effectively control the billet temperature within the optimal forming temperature range. So, the optimized die forging processes can guarantee the high volume fraction of dynamic recrystallization, and restrict the rapid growth of grains in the forged superalloy casing.

Description: The hydriding-dehydriding process was used to recycle AZ40 magnesium (Mg) alloy scraps, and the microstructure nanocrystallization was realized. X-ray diffraction analysis, scanning electron microscopy, and transmission electron microscopy were carried out to characterize the microstructure. After mechanically milling in hydrogen for 72 h, matrix Mg was completely turned into nanocrystalline MgH 2 , with an average crystallite size of about 10 nm. And then, the MgH 2 phase was completely transformed into Mg again through vacuum dehydriding treatment at 300 °C for 192 min, with an average crystallite size of about 20 nm. In addition, the nanocrystalline alloy powders were hot-pressed and extruded into bars. The average grain size of the bars was about 500 nm, which had reached the size of ultrafine-grain. Meanwhile, the yield strength and ultimate tensile strength of the as-extruded bars reached about 312 and 497 MPa, respectively. The results indicate that hydriding-dehydriding process is a feasible method for recycling of Mg alloy scraps, and it is expected to have a good application prospect in preparing ultrafine-grain Mg alloys.

Description: In this study, the effect of KOH concentration on the electrochemical properties of micro-arc oxidation (MAO) coated Mg alloy AZ31B has been investigated. Also, the surface morphology and chemical composition of the MAO coatings have been characterized by scanning electron microscopy and x-ray diffraction. In MAO process, an increase in the concentration of KOH as a result of increase in the electrolyte electrical conductivity leads to a reduction in sparking which in turn improves the quality and the behavior of anodic coatings in the concentration of 2.5 M. Moreover, it can be concluded that the MAO coating shows its best protective behavior when KOH concentration is equal 2.5 M, and if the concentration is higher or lower than this value, the protective properties of MAO coating will decrease.

Description: Titanium aluminide alloys are good candidates for structural applications thanks to their low density and good balance of properties up to relatively high temperatures. However, their application is still limited by significant oxidation. Four γ-TiAl alloys with different content of aluminum and niobium were produced by electron beam melting: Ti-45Al-2Cr-2Nb, Ti-48Al-2Cr-2Nb, Ti-45Al-2Cr-8Nb, and Ti-46Al-2Cr-8Nb. The behavior of these alloys in response to oxidation in air during constant heating up to 1000 °C and isothermal oxidation for 10 h at 850 and 950 °C were studied by thermogravimetric analysis. The mass gain due to oxidation of the low Nb-containing alloys was always at least twice that of the high Nb-containing alloys. Both low and high Nb-containing alloys exhibited on their surface oxidation products of the same nature: oxides TiO 2 and Al 2 O 3 , and nitrides TiN and Ti 2 AlN. Niobium addition up to 8 at.% did not suppress the growth of rutile and promote the formation of a protective alumina layer. However, it efficiently reduced the formation of rutile, mainly responsible for the mass gain due to oxidation of γ-TiAl alloys and with tendency to spallation.

Description: Strengthening of aluminum alloy 2219 by thermo-mechanical treatment has been compared with artificial aging. Three simple deformation modes including pre-stretching, compression, and rolling have been used in thermo-mechanical treatment. The tensile strength, elongation, fracture feature, and precipitated phase have been investigated. The results show that the strengthening effect of thermo-mechanical treatment is better than the one of artificial aging. Especially, the yield strength significantly increases with a small decrease of elongation. When the specimen is pre-stretched to 8.0%, the yield strength reaches 385.0 MPa and increases by 22.2% in comparison to the one obtained in aging condition. The maximum tensile strength of 472.4 MPa is achieved with 4.0% thickness reduction by compression. The fracture morphology reveals locally ductile and brittle failure mechanism, while the coarse second-phase particles distribute on the fracture surface. The intermediate phases θ ″ or θ ′ orthogonally precipitate in the matrix after thermo-mechanical treatment. As compared to artificial aging, the cold plastic deformation increases distribution homogeneity and the volume fraction of θ′′ or θ′ precipitates. These result in a better strengthening effect.

Description: Nano-crystalline and amorphous Co-P coatings were deposited on plain carbon steel substrates by using direct current. Effects of electrolyte pH on morphology, current efficiency, phosphorus content, hardness, and preferred orientation of the nano-crystalline coatings were investigated. Moreover, the effects of heat treatment on microstructure and hardness of the nano-crystalline and the amorphous coatings were studied. The results showed that, phosphorus content and hardness of the nano-crystalline coatings were decreased by increasing of the pH, in spite of a current efficiency enhancement to as much as 98%. Grain size and preferred orientation were also changed from 13 to 31 nm and from mostly [002] to [100] by increasing the pH from 1 to 4, respectively. Smoother coatings and higher current efficiencies were obtained by the addition of 1 g/L sodium dodecyl sulfate (SDS) to the bath. Highest hardness of the nano-crystalline and the amorphous coatings was about 600 and 750 HV, which increased and reached 760 and 1090 HV after heat treatment, respectively.

Description: In this study, the stability and microstructural evolution, including grain size and hardness of nanocrystalline Fe 91 Ni 8 Zr 1 alloyed powders, produced by ball milling, were investigated after annealing at 900 and 1000 °C for up to 24 h. Results indicate that rapid grain growth to the micron scale occurs within the first few minutes of exposure to the elevated annealing temperatures. However, despite the loss of nanocrystallinity, an extremely stable and efficient hardening effect persists, which has been found to be equal to that predicted by Hall-Petch strengthening even at the smallest grain sizes. The mechanical properties of the samples consolidated to bulk via equal channel angular extrusion at 900 °C were evaluated by uniaxial compression at room and elevated temperatures. Results reveal high compressive yield stress as well as the appearance and disappearance of a yield drop indicating the presence of coherent (GP zone like) precipitates within the microstructure. Such a hardening mechanism has implications for developing new Fe-Ni-based alloys exhibiting a combination of high strength and ductility for high temperature applications.

Description: Agglomerated TiB 2 particle and network-like structure-reinforced titanium matrix composite coatings were prepared by laser cladding of the Ni + TiB 2  + Ti preplaced powders on Ti-6Al-4V alloy. The network-like structure mainly consisted of NiTi and Ni 3 Ti. Through the experiment, it was found that the size of agglomerated particle gradually decreased with the increase of Ti content, but the number of the network-like structure first increased and then disappeared. In-situ reaction competition mechanism and the formation of network-like structure were discussed. The average micro-hardness gradually decreased with the increase of Ti content, but the average fracture toughness gradually increased. Meanwhile, the wear resistance of the coatings is higher than that of the substrate, but the wear loss of the coatings is gradually increased with the increase of Ti content.

Description: This paper investigates the effect of quenching and aging treatment on microstructure and abrasive wear of Ti-6Al-4V alloy. The as-received alloy was solution treated at 1339 K, then oil quenched, followed by aging at 823 K for 4 h (14,400 s). The microstructures of as-received and quench-aged specimens were characterized by using optical microscopy, scanning electron microscopy, energy dispersive spectroscopy, and electron backscattered diffraction techniques. The as-received specimen consisted of very fine α grains (average grain size 2 μm) with β phase uniformly dispersed throughout. The microstructure of the quench-aged specimen showed α plates (formed by the decomposition of α′ during aging). The β phase precipitated out of α′ martensite during aging and hence was dispersed uniformly in the α matrix. Ti-6Al-4V alloy was quench-aged to achieve maximum hardness with a view that the increased hardness would lead to an improvement in abrasive wear behavior. Two-body abrasive wear tests were carried out on the as-received and quench-aged specimens using pin-on-disk apparatus with SiC as abrasive media (150-grit size). The effect of sliding distance and normal load on the abrasive wear behavior was studied. The wear resistance of the as-received specimen was greater than that of quench-aged specimen, while hardness of the as-received specimen was lower than that of quench-aged specimen. The abrasive wear behavior of Ti-6Al-4V alloy has been explained based on morphology/microstructure of the alloy and the associated wear mechanism(s).

Description: In this study, in order to investigate the relationship between surface roughness and the corrosion resistance of the SS 316 LVM wires, samples have been prepared with different surface roughness by using different grits of SiC papers. In order to simulate the environment of implanted biomedical devices, a three-electrode electrochemical cell with 0.9% (by mass) NaCl solution has been used to test the corrosion resistance of the samples by potentiodynamic method and anodic polarization tests. SEM, EDS, and XPS have been performed to analyze the surfaces appearance and chemical elements on the surface before and after the corrosion. AFM was also used to get 3D images of the surface and to show the change in roughness of the samples after corrosion testing. Background-subtracted contrast-enhanced microscopy has been performed in situ to detect the pitting process happening on the surface of stainless steel samples. It was concluded that a relatively smoother surface can result in higher corrosion resistance and larger potential of stable pitting, whereas a rougher surface can easily go into stable pitting with lower pitting potentials. Rougher surfaces also showed a shorter time for the formation of stable pits. Microscopy observations illustrated more corrosion on rougher surfaces, and EDS showed more chloride ion remained on these surfaces.

Description: Superaustenitic stainless steel 654SMO was used as the experimental material to investigate the effect of heating temperatures and holding times on grain growth behavior in the temperature range of 1150-1250 °C and holding time ranging from 15 to 60 min. The contour maps of grain size and grain growth rate as a function of temperatures and times were plotted. The results of this study suggest that grains grow with parabolic trend. Grain size and its growth rate increase with increasing heating temperature, the former also increases with holding time, while the latter decreases with holding time. Both grain size and grain growth rate are more sensitive to holding time than solution temperature at temperatures below 1200 °C, which is contrary to that of at temperatures above 1200 °C. The growth behavior of grains in the tested steel is illustrated by a modified mathematical model deduced on the basis of previous empirical models, and this modified grain growth model can fit well with the experimental grain growth data obtained during solution treatment.

Description: An attempt to the modification of the microstructure and mechanical properties of affordable, Mn-containing maraging alloys is reported. These alloys have demonstrated strong age hardening but suffered with premature intergranular brittleness despite their potential applications in tooling, dies, and machinery industries. An Fe-10Ni-6Mo-3Mn-1Ti (wt.%) alloy was prepared by vacuum melting and processed by homogenization (1250 °C/48 h), cold rolling, solution annealing (950 °C/1 h), and aging treatments (500 °C/4 h). It presented tensile strength of about 2.65 GPa, a few percent of tensile elongation and a mixed ductile-brittle fracture mode. Transmission electron microscopy (TEM) revealed the precipitation of a nearly spherical phase. Crystal symmetry of the second phase precipitates was identified hexagonal close-packed corresponding reasonably to the Fe 2 Mo Laves phase having lattice parameters of a  = 0.4745 and c  = 0.7754 nm. Precipitation of a Mo-enriched second-phase particle was occasionally found at prior austenite grain boundaries but the pronounced grain boundary precipitation was never identified. Energy-filtering transmission electron microscopy using the Mo-M 4,5 post edge revealed remarkable segregation of Mo at grain boundaries.

Description: Friction stir welding was performed to join carbon steel plates at tool rotational rate of 800-1400 rpm. Microstructure and microhardness of welded specimens were evaluated across weld centerline. Torque base index, peak temperature, cooling rate, strain, strain rate, volumetric material flow rate, and width of extruded zone at weld nugget were calculated. Peak temperature at weld nugget was ~1300-1360 K. At this temperature, ferrite transformed to austenite during welding. Austenite was decomposed in to ferrite and bainite at cooling rate of ~4-7.5 K/s. The presence of bainite was endorsed by increment in microhardness with respect to base material. Ferrite grain size at weld nugget was finer in comparison to as-received alloy. With the increment in tool rotational rate strain, strain rate, total heat input, and peak temperature at weld nugget were increased. High temperature at weld nugget promoted increment in ferrite grain size and reduction in area fraction of bainite. Heat-affected zone also experienced phase transformation and exhibited enhancement in ferrite grain size in comparison to base alloy at all welding parameters with marginal drop in microhardness. Maximum joint strength was obtained at the tool rotational rate of 1000 rpm. Increment in tool rational rate reduced the joint efficiency owing to increment in ferrite grain size and reduction in pearlite area fraction at heat-affected zone.

Description: The strain-controlled low-cycle fatigue properties of gravity cast Al-Si-Cu alloys for engine cylinder heads were investigated. At strain ratios of R ε  = −2, 0, and 0.1, the cyclic stress amplitude progressively increased from initiation to the 450th cycle, and then proceeded into a steady stage until failure. At a strain ratio of R ε  = −∞, the material exhibited a continuous cyclic hardening. The hysteresis loops in this alloy for the 2nd and half-life cycle were tension/compression asymmetry, which also corresponded well to the evolution of peak/valley stress. Transmission electron microscopy analysis suggested that cyclic hardening was caused by the dislocations multiplication/tangles at strain ratios of R ε  = −∞ and 0. Besides, the presence of dislocation cross slip contributed to cyclic stabilization observed at later stage of deformation at a strain ratio of R ε  = 0. Micro-analysis of specimen fracture appearance was conducted in order to obtain the fracture characteristics and crack paths for different strain ratios. It showed that the fatigue cracks initiated basically at the internal defects in the samples. Meanwhile, at strain ratios of R   =  −∞ and 0, the fracture surface was rough with a large number of small unequiaxed dimples and some tear ridges. Moreover, the localized pores offered a preferential crack path in the samples, where they were surrounded by silicon particles. At a strain ratio of R ε  = −∞, the fatigue cracks preferentially initiated at pores rather than α-Fe phases. At a strain ratio of R ε  = 0, where fatigue crack initiation was observed at the interface between plate-like branch of α-Fe phase and aluminum matrix.

Description: Effects of liquid amine-terminated butadiene-acrylonitrile (ATBN) on the properties of bisphenol-A/aniline-based polybenzoxazine (PBA-a) composites were investigated. Liquid ATBN decreased gel time and lowered curing temperature of the benzoxazine resin (BA-a). The PBA-a/ATBN-based self-lubricating composites resulted in substantial enhancement regarding their tribological, mechanical, and thermal properties. The inclusion of the ATBN at 5% by weight was found decreasing the friction coefficient and improved wear resistance of the PBA-a/ATBN composites. Flexural modulus and glass transition temperature of the PBA-a composite samples added the ATBN was constant within the range of 1-5% by weight. A plausible wear mechanism of the composites is proposed based on their worn surface morphologies. Based on the findings in this work, it seems that the obtained PBA-a/ATBN self-lubricating composites would have high potential to be used for bearing materials where low friction coefficient, high wear resistance, and modulus with good thermal property are required.

Description: The structural properties of lightweight constructions can be adapted to specific local requirements using multi-material designs. Aluminum alloys and carbon fiber-reinforced plastics (CFRP) are materials of great interest requiring suitable joining techniques in order to transfer the advantages of combining the materials to structural benefits. Thus, the research group “Schwarz-Silber” investigates novel concepts to enable frontal aluminum-CFRP joints using transition structures. In the foil concept titanium foils are used as transition elements. Specimens have been produced using three-layer titanium laminates. In tensile tests, three failure locations have been observed: (1) Al-Ti seam, (2) Ti-CFRP hybrid laminate, and (3) CFRP laminate. In this paper, the fracture mechanisms of these failure modes are investigated by analyzing metallographic micrographs and fracture surfaces as well as by correlating load-displacement curves to video imaging of tensile tests. The results show that the cracking of the CFRP layers can be traced back to an assembly error. The laminate character of the titanium part tends to reduce the Al-Ti seam strength. However, two sub-joint tests demonstrate that the Al-Ti seam can endure loads up to 9.5 kN. The ductile failure behavior of the Ti-CFRP hybrid laminates is caused by plastic deformations of the titanium laminate liners.

Description: SnO 2 nanosheets with sizes around 1 μm and thickness around 30 nm have been synthesized by a template-free hydrothermal method. With the addition of urea, SnO 2 hollow microspheres with diameters of about 1 μm and shell thickness of about 200 nm were also prepared. The structures, morphologies, and optical properties of the as-prepared samples were characterized by x-ray diffraction, scanning electron microscopy, transmission electron microscopy and selected area electron diffraction, Raman spectroscopy, and ultraviolet-visible absorption spectrophotometry. The possible mechanisms for the growth of these SnO 2 nanostructures were tentatively proposed based on controlled experiments. Moreover, photocatalytic investigations revealed that the as-prepared SnO 2 samples possessed good photocatalytic activity in the degradation of rhodamine B.

Description: In order to improve the understanding of the hot deformation and dynamic recrystallization (DRX) behaviors of large-scaled AZ80 magnesium alloy fabricated by semi-continuous casting, compression tests were carried out in the temperature range from 250 to 400 °C and strain rate range from 0.001 to 0.1 s −1 on a Gleeble 1500 thermo-mechanical machine. The effects of the temperature and strain rate on the hot deformation behavior have been expressed by means of the conventional hyperbolic sine equation, and the influence of the strain has been incorporated in the equation by considering its effect on different material constants for large-scaled AZ80 magnesium alloy. In addition, the DRX behavior has been discussed. The result shows that the deformation temperature and strain rate exerted remarkable influences on the flow stress. The constitutive equation of large-scaled AZ80 magnesium alloy for hot deformation at steady-state stage (ɛ = 0.5) was \( \dot{\upvarepsilon } = 1.394 \times 10^{12} [\sinh (0.018\upsigma )]^{5.043} \exp ( - 169.610/RT). \) The true stress-true strain curves predicted by the extracted model were in good agreement with the experimental results, thereby confirming the validity of the developed constitutive relation. The DRX kinetic model of large-scaled AZ80 magnesium alloy was established as X d  = 1 − exp[−0.95((ɛ − ɛ c )/ɛ*) 2.4904 ]. The rate of DRX increases with increasing deformation temperature, and high temperature is beneficial for achieving complete DRX in the large-scaled AZ80 magnesium alloy.

Description: For a better understanding of the thermal fatigue behavior in compacted graphite cast iron (CGI), the cyclic thermal shock test is carried out through alternating induction heating and water quenching. The optical and scanning electron microscopy observations are used to examine the cracks and oxidation behavior on the cross section and heating surface of the material specimen, respectively. The results show that the thermal cracks in CGI initiate at the graphite phases mostly, and the multi-sourced thermal cracks would result in stable cracks morphology finally through crack shielding effect. In the oxidation analysis, it is found that the oxidation of graphite is selective, and the graphite is the potential channels for oxygen diffusion from the outside into the matrix, resulting in local oxidation of matrix around graphite and continuous oxygen diffusion paths in the microstructure. Thermal cracks nucleate from the oxidation holes at graphite caused by decarburization, and they prefer to propagate and coalesce by penetrating the oxide bridges.

Description: Air plasma-sprayed Ni-20Cr coating on stainless steel (AISI-304) substrate was re-melted using CO 2 laser to remove the inherent defects, i.e., porosity, splat boundaries, and oxides of air plasma-sprayed coating. The (1) uncoated, (2) air plasma-sprayed, and (3) laser-re-melted specimens were exposed to cyclic oxidation at 900 °C for a hundred cycles run. The oxidation products were characterized using XRD and SEM. Weight changes were determined after every 4th cycle; Uncoated samples showed severe oxidation indicated by substantial weight loss, whereas air plasma-coated samples demonstrated noticeable weight gain. However, oxidation resistance of laser-cladded samples was found to be significantly improved as the samples showed negligible weight change; porosity within the coating was minimized with an improvement in interface quality causing reduction in delamination damage.

Description: In the present study, corrosion inhibition influence of novel cationic surfactant (CS) with imidazole structure (1-methyl-3-octadecane imidazolium hydrogen sulfate) on low carbon steel in 1 M HCl was investigated by implementing weight loss, potentiodynamic polarization, and electrochemical impedance spectroscopy (EIS) techniques. Increasing the amount of surfactant adequately leads to an increment of the inhibition efficiency of novel CS. According to the obtained results from EIS measurements, inhibition efficiency was about 34% in the presence of 1 ppm surfactant, increasing to about 96.8% at the 25 ppm (near critical micelle concentration) surfactant concentration. Also the effects of temperature and the synergistic effect between surfactant and NaHSO 4 salt were studied. The inhibition efficiency increased with the increase of NaHSO 4 concentration and reached the maximum value near 0.1 M and experienced a plummet in the temperature range of 30-50 °C. Potentiodynamic polarization measurements revealed that the surfactant acts as mixed-type inhibitors. Results obtained from weight loss, polarization, and impedance measurements are in proper agreement and confirmed the fact that this surfactant is an excellent inhibitor for low carbon steel in 1 M HCl environment. The surface morphology of inhibited and uninhibited metal samples was investigated by atomic force microscope (AFM) and field emission scanning electron microscope (FE-SEM).

Description: The phase transformation temperature of nickel titanium (NiTi) shape memory alloy (SMA), which is commonly used in biomaterial fields, is strongly influenced by aging heat treatments. In this study, we apply a new aging heat treatment under loading conditions to near-equiatomic NiTi SMA wires to investigate its effect on phase transformation temperatures. We determine changes in the phase transformation temperatures via differential scanning calorimetry measurements. We analyze transformation temperatures, hysteresis properties, and enthalpy changes and discuss significant results with the help of micrographs. Moreover, we evaluate our results using two-way analysis of variance, axiomatic design methods, and customary analysis in order to make reliable inferences. We observe a significant difference between first and second heating-cooling cycle results for NiTi SMA samples on the basis of austenitic transformation temperatures. Consequently, we are able to theorize correlations between design parameters and functional requirements.

Description: Micromechanical response of silicon carbide particle dispersed Al/Mg/Ti/Cu composite, synthesized by powder metallurgy technique was investigated. A correlation between their microhardness and nanomechanical properties at submicron length scale was established. Hardening effect of SiC particles on the hardness, elastic modulus, recovery index, and plastic energy of the matrices was prominent and may be due to the interactions between geometrically necessary and statistically stored dislocations along with their impediment with dispersoids-matrix interface. The elastic recovery obtained from nanoscratch measurement was also correlated with the recovery parameter, which was derived from the nanoindentation of the composite compacts.

Description: Residual stresses introduced by manufacturing processes such as casting, forming, machining, and welding have harmful effects on the mechanical behavior of the structures. In addition to the residual stresses, weld toe stress concentration can play a determining effect. There are several methods to improve the mechanical properties such as fatigue behavior of the welded structures. In this paper, the effects of ultrasonic peening on the fatigue life of the high-temperature seamless steel pipes, used in the petrochemical environment, have been investigated. These welded pipes are fatigued due to thermal and mechanical loads caused by the cycle of cooling, heating, and internal pressure fluctuations. Residual stress measurements, weld geometry estimation, electrochemical evaluations, and metallography investigations were done as supplementary examinations. Results showed that application of ultrasonic impact treatment has led to increased fatigue life, fatigue strength, and corrosion resistance of A106-B welded steel pipes in petrochemical corrosive environment.

Description: The present study deals with the static and dynamic microstructural evolution of a high-Mn twinning-induced plasticity steel. Static recrystallization (SRX) is considered through cold rolling followed by annealing with different holding times. Dynamic recrystallization (DRX) was explored by hot compression tests at different temperatures and strain rates. The microstructural observations demonstrated that new grains nucleate at the prior grain boundaries and grain size decreased when cold rolling was followed by annealing. Additionally to the grain size reduction due to the SRX, nucleation sites for DRX increased. It is shown that flow stress level increased as a result of grain refinement caused by static and DRX.

Description: Phase transformation during heating in homogenized Ti-22Al-(27- x )Nb- x Zr ( x  = 0, 1, 6) alloys is monitored by dilatometry, differential scanning calorimetry (DSC), and detailed metallographic examination. Moreover, the dissolution of α 2 into the B 2 /β matrix is investigated and discussed. In Ti-22Al-27Nb alloy, the sequence of phase transformation during heating can be concluded as follows: B 2 /β → O, B 2 /β + α 2  → O, B 2 /β + O→ B 2 /β + O + α 2 , B 2 /β + O + α 2  →  B 2 /β + α 2 , and B 2 /β + α 2  →  B 2 /β. For Ti-22Al-21Nb-6Zr alloy, it is B 2 /β → α 2  + O, O + α 2  +  B 2 /β →  B 2 /β + α2, and then α 2 dissolves into B 2 matrix. There are considerable shifts in the maxima of the transformation rates in B 2 /β + O+α 2  →  B 2 /β + α 2 and B 2 /β + α 2  →  B 2 /β transformed region to the higher temperatures with increasing x value. In the stage of B 2 /β + α 2  →  B 2 /β, there is a deceleration of reduction in α 2 phase with increasing temperature for Ti-22Al-(27- x )Nb- x Zr ( x  = 0, 1, 6) alloys. And for Ti-22Al-21Nb-6Zr, the dissolution rate of α 2 phase is accelerated.

Description: The scanning vibrating electrode technique (SVET) has been used to study the in-situ corrosion phenomena on AA2024T3 aluminum alloy. Three distinct sequential stages of corrosion attack, with time, on the alloy have been revealed (0-75, 75-180 min, and after 180 min). The increase and decrease in the intensity of the anodic activities at the surface of the alloy, which give a corresponding increase and decrease in the net current density values, with time, are responsible for the stepwise changes in the corrosion stages. The work also revealed mild etch-like attack regions on the surface of the alloy after the immersion test.

Description: The injection-molded metallic glass soft magnet is prepared from the powder of melt-spun ribbon of Fe 36 Co 36 B 20 Si 4 Nb 4 glassy alloy and Nylon 6,6 of wt.% from 5 to 20 via the polymer injection molding technology. The product is characterized by the SEM, mechanical, and magnetic test. The results indicate that this type of materials has comparable mechanical properties and morphological feature with the conventional injection-molded NdFeB magnet and exhibits excellent soft magnetic behaviors. The magnetic properties of the injected magnets are compared with the raw metallic glass, solvent-casted resin bonding magnets, and thermal-treated magnets to confirm that the processing temperature of Nylon injection does not affect the magnetism. The injection technology is a practical processing method to be applied on the metallic glass for potential usage.

Description: Static recrystallization (SRX) behavior of a nitrogen-alloyed ultralow carbon austenitic stainless steel was studied on a Gleeble-1500D thermal-simulator by two-step hot compression tests. Deformation temperatures of 1173-1473 K, deformation strains of 0.051-0.105, strain rates of 0.01-1 s −1 , and inter-step times of 1-100 s were selected as the deformation conditions to investigate the effects of deformation parameters on SRX behavior. Besides, the influences of initial grain size on SRX behavior were studied. The results show that deformation temperature and strain have greater influences on SRX behavior than strain rate and initial grain size. Based on true stress-true strain data obtained from the experiments, SRX kinetics equation was determined. In addition, the established SRX kinetics equation was introduced into finite element simulation software DEFORM-3D to perform the two-step compression deformation. Furthermore, SRX kinetics equation was modified for improving the accuracy of finite element simulation, and the modified SRX kinetics equation was verified.

Description: In this work, effects of pH value on the electrochemical and stress corrosion cracking (SCC) behavior of X70 pipeline steel in the dilute bicarbonate solutions were investigated using electrochemical measurements, slow strain rate tensile tests and surface analysis techniques. Decrease of the solution pH from 6.8 to 6.0 promotes the anodic dissolution and cathodic reduction simultaneously. Further decrease of the pH value mainly accelerates the cathodic reduction of X70 pipeline steel. As a result, when the solution pH decreases form 6.8 to 5.5, SCC susceptibility decreases because of the enhancement of the anodic dissolution. When the solution pH decreases from 5.5 to 4.0, SCC susceptibility increases gradually because of the acceleration of cathodic reactions.

Description: On the basis of hot rolling practice, the effects of thermomechanical control process parameters on the evolution of austenite grain size before the deformation at non-recrystallization zone were investigated in detail. The inflections in the strain hardening rate versus true stress curves show that the dynamic recrystallization (DRX) has initiated for different deformation conditions studied in the present work. But the volume fractions of the equiaxed grains in the specimens which were immediately water quenched to room temperature after deformation are different from each other. Moreover, the main refinement mechanisms for different deformation conditions have been differentiated. It is interesting to note that the austenite grain size can be refined significantly with increasing the strain from 0.0 to 0.5 for different deformation temperatures. However, when the strain increases to 0.8, the austenite grain size cannot be further refined for the higher deformation temperature range, while the austenite grain size can be further refined for the lower deformation temperature range. In addition, the effect of strain rate on the austenite grain refinement is vigorous for the higher deformation temperatures. Moreover, the empirical equation to estimate the austenite grain size for different deformation parameters was established.

Description: Nanosized In 2 O 3 powders with different particle sizes were prepared by the microemulsion synthetic method. The effects of particle size on the gas-sensing and catalytic properties of the as-prepared In 2 O 3 were investigated. Reductions in particle size to nanometer levels improved the sensitivity and catalytic activity of In 2 O 3 to i -C 4 H 10 and C 2 H 5 OH. The sensitivity of nanosized In 2 O 3 (〈42 nm) sensors to i -C 4 H 10 , H 2 and C 2 H 5 OH was 2-4 times higher than that of chemically precipitated In 2 O 3 (130 nm) sensor. A nearly linear relationship was observed between the catalytic activity and specific surface area of In 2 O 3 for the oxidation of i -C 4 H 10 and C 2 H 5 OH at 275 °C. The relationship between gas sensitivity and catalytic activity was further discussed. The results of this work reveal that catalytic activity plays a key role in enhancing the sensitivity of gas-sensing materials.

Description: The evolution of micro-texture below the machined surface is computationally modeled and experimentally verified. The orientation distribution functions of the grains below the surface were represented in spectral form. The microstructure descriptor coefficients were derived, and their change with respect to the change in the cutting feed rate was computationally calculated and monitored. Micro-texture experimental observations conducted by electron back-scatter diffraction technique verify the modeling outputs. Continuation of changing the process parameter was done by finite element method, and the evolution in texture was investigated by computational modeling. The process path function which correlates micro-texture evolution and cutting feed rate, was obtained by applying the principle of orientation conservation in the Euler space. As a result of the major finding of this work, i.e., derivation of process path functions, the evolution of texture as a function of the material feed rate is numerically determined without any need to texture modeling or finite element analyses.

Description: The life cycle requirements for advanced Ni alloys are very demanding and can be on the order of several hundreds of thousands of hours. Results are presented on a wrought Ni-based superalloy designed within the nominal chemistry range of Haynes 282 with a fixed amount of γ′ strengthening phase, and either low Al or Ti (within the alloy specification) to give different ratios of Ti/Al, and thus, different γ′ misfit with the γ matrix. The effect that these changes have on the γ′ misfit and its relevance to long-term microstructural stability is being explored both experimentally as well as with computational modeling with results through almost 10,000 h. The basics of the modeling approach are presented as are the procedures for evaluating the γ′ volume fractions from transmission electron microscopy (TEM) micrographs and correcting these volume fractions for truncation error due to TEM foil thickness. Results on each alloy formulation are compared and discussed with respect to possible γ′ coarsening due to the different Ti/Al ratio and what this might mean for the long-term stability of the alloy.

Description: The numerical simulation of tensile fracture behavior on Al-Cu alloy friction stir-welded joint was performed with the Gurson-Tvergaard-Needleman (GTN) damage model. The parameters of the GTN model were studied in each region of the friction stir-welded joint by means of inverse identification. Based on the obtained parameters, the finite element model of the welded joint was built to predict the fracture behavior and tension properties. Good agreement can be found between the numerical and experimental results in the location of the tensile fracture and the mechanical properties.

Description: In this work, the inhibiting effect of benzotriazole (BTA) on corrosion of X65 pipeline steel in bicarbonate solution was investigated by electrochemical measurements, including open-circuit potential, potentiodynamic polarization curves and electrochemical impedance spectroscopy, and atomic force microscopy characterization. It is found that BTA is effective to inhibit the steel corrosion, and the inhibiting efficiency is increased by the increasing inhibitor concentration. The BTA is an anodic inhibitor, which shifts the corrosion potential of the steel less negatively and decreases the anodic current density at individual potential. A layer of inhibitor film is formed on the steel surface to reduce the corrosion rate of the steel. The formed film is quite smooth, with a roughness at the nano-meter scale.

Description: This study investigates the performance of three triazole derivatives with different molecular structures as corrosion inhibitors for the copper-nickel alloy CuNi 90/10 in 3.5 wt.% NaCl solution. Inhibition behavior was systematically determined through electrochemical measurements, scanning electron microscopy, energy-dispersive spectroscopy, and Fourier transform infrared spectroscopy. In addition, adsorption behavior and the inhibition mechanism were investigated via quantum chemical calculation and molecular dynamic simulation. Experimental results indicate that the three inhibitors with triazole rings and heteroatoms exhibited excellent corrosion inhibition capabilities on the copper-nickel alloy surface through physisorption and chemisorption. In particular, 3-amino-5-mercapto-1,2,4-triazole showed the best inhibition capability according to the concentration ranges considered in the experiments. The results of quantum chemical calculation agreed with the experimental findings.

Description: The addition of silicon carbide (SiC) nanoparticles into electroless nickel (Ni)-based coatings improves both corrosion resistance and mechanical properties of the resulting Ni-P/SiC nanocomposite coatings, making them potential candidate as protective coatings in aggressive environments. Ni-P/SiC nanocomposite coatings were produced from precursor bath with small SiC loading levels (0.25 or 1.0 g/L) and characterized for morphology, corrosion resistance, and hardness. Microstructural examination using FE-SEM and AFM revealed that incorporation of uniformly dispersed SiC nanoparticles leads to smaller nodule size with fine-grain structure and low surface roughness. Electrochemical impedance spectroscopy studies in 4 wt.% NaCl solution showed that the nanocomposite coatings exhibit excellent corrosion resistance, as indicated by high charge-transfer resistance and low double-layer capacitance values of ~137 kΩ cm 2 and 19 µF cm −2 , respectively. The coatings maintained their structural integrity even after 5 days of saline bath immersion, as there was no cracking in the deposit microstructure besides formation of shallow pits and submicron-sized pores. A two-fold increase in the average hardness value was noticed from 4.5 (pure Ni-P) to 8.5 GPa (Ni-P/SiC coating) which can be ascribed to modified deposit morphology and uniformly dispersed SiC nanoparticles that act as obstacles to plastic deformation.

Description: Distortion resulting from heat treatment may cause serious problems for precision parts. A precision component made from 30CrNi3Mo steel with internal threads distorts slightly after quenching-tempering treatment. Such a small distortion results in serious difficulties in the subsequent assembly process. The distortion of the internal thread was measured using semi-destructive testing with video measuring system. Periodic wavy distortions emerged in the internal threads after heat treatment. Then both XRD analysis and hardness testing were conducted. A numerical simulation of the complete quenching-tempering process was conducted by DANTE, which is a set of user subroutines that link into the ABAQUS/STD solver. The results from the simulations are in good agreement with the measurement in distortion, microstructure field, and hardness. The effects of the technological parameters including quenchant, immersion orientation, and grooves were discussed on the basis of the simulation results. Finally, strategies to significantly decrease distortion and residual stress are proposed.

Description: The paper describes an experimental study aimed at suppressing stress corrosion cracking susceptibility of machined 304L stainless steel specimens through laser shock peening. The study also evaluates a new approach of oblique laser shock peening to suppress stress corrosion cracking susceptibility of internal surface of type 304L stainless steel tube. The results of the study, performed with an indigenously developed 2.5 J/7 ns Nd:YAG laser, demonstrated that laser shock peening effectively suppresses chloride stress corrosion cracking susceptibility of machined surface of type 304L stainless steel. In the investigated range of incident laser power density (3.2-6.4 GW/cm 2 ), machined specimens peened with power density of 4.5 and 6.4 GW/cm 2 displayed lower stress corrosion cracking susceptibility considerably than those treated with 3.2 and 3.6 GW/cm 2 in boiling magnesium chloride test. Oblique laser shock peening, performed on machined internal surface of a type 304L stainless steel tube (OD = 111 mm; ID = 101 mm), was successful in introducing residual compressive surface stresses which brought about significant suppression of its stress corrosion cracking susceptibility. The technique of oblique laser shock peening, in spite of its inherent limitations on the length of peened region being limited by tube internal diameter and the need for access from both the sides, presents a simplified approach for peening internal surface of small tubular components.

Description: The present work explores how deposition parameters affect structural and morphological characteristics of ZnNi/nano-SiC composites in order to engineer an environmentally benign corrosion-resistant coating. In this regard, ZnNi and ZnNi coatings containing SiC nanoparticles were electrodeposited from chloride bath by direct current method, and the effects of SiC concentration, deposition current density and two types of surfactant (sodium dodecyl sulfate, SDS, and hexadecyltrimethyl ammonium bromide, HTAB) were investigated. Increasing SiC nanoparticles concentration in the electrolyte enhances the SiC content of the coating and can affect the coating composition, structure and morphology. Elevation of deposition current density may reduce SiC content of the coating, yet this decline can be compensated by the addition of HTAB. Application of 11 g/L SiC nanoparticles produced a coating with a more even surface and less porosity that had the highest corrosion resistance. The presence of nanoparticles seemingly reduces the available surface for electrochemical reactions and decelerates corrosion.

Description: The effect of deep cryogenic treatment (DCT) on microstructure and mechanical properties including corrosion behavior of the squeeze-cast AE42 alloy has been investigated. For comparison, the same has also been studied on the untreated alloy. Both the untreated and deep cryogenic-treated (DCTed) alloys comprised α-Mg and Al 4 RE phases. Volume fraction of the Al 4 RE phase in the AE42 alloy reduced gradually following DCT carried out from 4 to 16 h. Ductility and UTS increase significantly with a marginal increase in YS of all the DCTed alloys. The improvement was attributed to the dissolution of the brittle Al 4 RE phase following DCT. Among the alloys employed, the best tensile properties were obtained for the 16-h DCT alloy due to its lowest content of the brittle Al 4 RE phase. Creep resistance of the DCTed alloys was lower than that of the untreated alloy owing to the presence of less amount of thermally stable intermetallic Al 4 RE phase. Wear resistance of the alloy reduces following DCT due to reduced hardness of the DCTed alloys. The untreated alloy exhibits the best corrosion resistance, whereas poor corrosion resistance of the DCTed alloys is attributed to the reduced amount of Al 4 RE phase that fails to built a corrosion resistance barrier.

Description: Based on the growing application value of the P11 alloy steel in the nuclear power field, its dynamic recrystallization (DRX) behavior was firstly investigated by means of isothermal hot compression experiments, under the conditions of a testing temperature range between 800 and 950 °C, and a strain rate range between 0.01 and 2/s. Furthermore, optical microscopy and transmission electron microscopy were also employed to analyze the effect of the mechanism of the strain rate on DRX. The results indicated that the grain size could be significantly refined with the increase of strain rate. Also, the recrystallized volume fraction was increased and the dislocation density decreased with the decrease of strain rate, for the same strain values. Subsequently, numerical simulations, under the assistance of experimental results on DRX behavior, were successfully used to study the hot push bending process and simultaneously obtain the processing parameters of the actual work-pieces. Finally, some comparative analyses were performed and discussed in parallel with the deformed actual work-pieces. The EBSD results on the deformed P11 alloy steel were emphasized for exploring the forming properties of this alloy steel.

Description: Flexure, compressive, and shear properties of the carbon matrix in carbon/carbon (C/C) composites made via a pitch impregnation method have been determined. The pitch carbon matrix was made using the same densification cycle used in making the C/C composite. Cyclic compression tests were performed on the matrix specimens. While unloading, a reduction in modulus was observed and residual strains were observed on complete unloading. These features were attributed to the presence of damage and plasticity in the densified matrix. A J 2 plasticity model with damage was used to simulate this behavior numerically. The parameters required for plasticity and damage model were evaluated iteratively by comparing the results in experiments with simulation.

Description: Hydrogen was intentionally introduced into ultra-high strength steel by cadmium plating. The purpose was to examine the effect of cadmium plate thickness and hence hydrogen on the impact energy of the steel. The AISI 4340 steel was austenitized at 1000 °C for 1 h, water quenched, and tempered at temperatures between 257 and 593 °C in order to achieve a range of targeted strength levels. The specimens were cadmium plated with 0.00508 mm (0.2 mils), 0.00762 mm (0.3 mils), and 0.0127 mm (0.5 mils). Results demonstrated that the uncharged specimens exhibited higher impact energy values when compared to the plated specimens at all tempering temperatures. The cadmium-plated specimens had very low Charpy impact values irrespective of their ultimate tensile strength values. The model of hydrogen transport by mobile dislocations to the fracture site appears to provide the most suitable explanation of the results.

Description: Hot compression tests were performed on high titanium content 6061 aluminum alloy (AA 6061-Ti) using a Gleeble-3500 thermomechanical testing system at temperatures from 350 to 510 °C with a constant strain rate in the range of 0.001-10 s −1 . Three types of flow stress models were established from the experimental stress-strain curves, the correlation coefficient ( R ), mean absolute relative error ( MARE ), and root mean square deviation ( RMSD ) between the predicted data and the experimental data were also calculated. The results show that the Fields–Backofen model, which includes a softening factor, was the simplest mathematical expression with a level of precision appropriate for the numerical simulations. However, the Arrhenius and artificial neural network (ANN) models were also consistent with the experimental results but they are more limited in their application in terms of their accuracy and the mathematical expression of the models.

Description: Pulsed laser spot welding of intersection points of zirconium alloys straps was performed. Weld bead size, microstructure and the corrosion behavior of weld bead were investigated. With the increasing laser peak power or number of shots, the weld width of the beads increased, the protrusion decreased and the dimple increased with further increase in heat input. The fusion zone consisted of a mixture of αZr and residual βZr phases. After annealing treatment, βNb and Zr(Fe, Nb) 2 second phase particles were precipitated inter- and intragranular of αZr grains adequately. The oxide thickness of annealed weld bead was about 3.90 μm, decreased by about 18.1% relative to the 4.76 μm of as-welded specimen corroded at 400 °C and 10.3 MPa for 20 days. The corrosion resistance of annealed specimen was better than that of as-welded specimen, since the second phase particles exerted better corrosion resistance, and the content of Nb in βZr and the fraction of βZr decreased after the annealing treatment.

Description: Al 2 O 3 micro-powder was suspended in the basis electrolyte to form micro-arc oxidation (MAO) coatings on 6061 aluminum alloy by MAO. During the stage of micro-arc oxidation, Al 2 O 3 micro-powder with negative surface charge was melted by the micro-arc around the anode and incorporated into the MAO coatings. With the continuous addition of Al 2 O 3 micro-powder, the oxidation voltages rose up firstly and then decreased. The surface and cross-sectional morphologies showed that the size of micropores decreased and the MAO coatings surface got loosened following the variation in Al 2 O 3 micro-powder concentration. As a consequence of the changing coating structure, the corrosion resistance of the coatings decreased apparently. The micro-hardness of the coatings increased firstly and then decreased, opposite to the trend of the average friction coefficient. It revealed the minimum average friction coefficient of MAO coatings and maximum adhesion between the coatings and substrate when 2.0 g/L Al 2 O 3 micro-powder was added into electrolyte. There were visible cracks and peelings on the coating surface merely at 4.0 g/L after thermal shock tests. The x-ray diffraction results indicated that the addition of Al 2 O 3 micro-powder had less effect on the phase composition of MAO coatings.

Description: Microstructure and functional mechanism of friction layer need to be further researched. In the present work, the friction coefficients and wear rates are analyzed through response surface methodology to obtain an empirical model for the best response. Fitting results show that the tribological performance of Ni 3 Al matrix composites (NMCs) with graphene nanoplatelets (GNPs) is better than that of NMCs without GNPs, especially at high sliding velocities and high loads. Further research suggests that the formation of integrated friction layer, which consists of a soft microfilm on a hard coating, is the major reason to cause the differences. Of which, the wear debris layer (WDL) with a low shear strength can reduce the shear force. The ultrafine layer (UL), which is much harder and finer, can effectively avoid fracture and improve the load support capacity. Moreover, the GNPs in WDL and UL can be easily sheared and help to withstand the loads, trending to be parallel to the direction of shear force.

Description: Spark plasma sintering (SPS) is a powder metallurgy process that sinters powder materials within a short time by simultaneous application of electrical current and pressure. SPS differs from other conventional powder metallurgy processes by its heating mechanism, which is Joule heating of the sample within a graphite die. This study investigates the consolidation of aluminum powder by SPS. Different pressures were used and particle bonding evaluated by means of fracture surface analysis. Electrical resistance, obtained from online monitoring of the variation of voltage and current during the process, showed an enhanced descent at 0.3  T m , and the area under this drop was associated with ductility: the greater the area, the higher the ductility. This temperature corresponds to a significant increase in the hardness ratio of the oxide layer to aluminum, where breakdown of the oxide layer becomes easier, permitting enhanced metallurgical bonding between the powder particles.

Description: Microstructures of the heat-affected zone (HAZ) of a Gr. 91 steel weld were simulated to evaluate their effects on the creep life of the weld at elevated temperatures. The Ac 1 and Ac 3 temperatures of the Gr. 91 steel were determined by a dilatometer to be at 867 and 907 °C, respectively. An infrared heating system was employed to heat the samples to 860 (STOT), 900 (ICHAZ) and 940 °C (FGHAZ) for 1 min, followed by cooling to room temperature. The simulated specimens were then subjected to conventional post-weld heat treatment (PWHT) at 750 °C/2 h. After the PWHT, the tempered ICHAZ specimen had a shortest creep life among the specimens tested at 650 °C/60 MPa. Moreover, the simulated specimen heated to 860 °C (STOT) was more likely to fracture at 615 °C/80 MPa than others.

Description: Sliding wear tests were performed for H13 steel in atmosphere, distilled water, 3.5% NaCl, and 5% NaOH water solutions under various loads on a pin-on-disk wear tester. The results showed that for different environmental media, the wear rate of H13 steel in atmosphere was the maximum and that in 3.5% NaCl solution was the minimum. The maximum wear rate in atmosphere was caused by a larger quantity of heat produced in the friction process. In this case, the adhesive wear prevailed. In three wet environments, the mild wear prevailed due to the good lubrication and cooling capacity of media as well as corrosion product film on worn surface. In distilled water, the wear mechanism was a typical fatigue wear. On the other hand, in 3.5% NaCl and 5% NaOH solutions, corrosive wear prevailed. The minimum wear rate in 3.5% NaCl solution was attributed to the protective function of corrosion product film. On the contrary, noncompact corrosion product film in 5% NaOH solution resulted in higher wear rate.

Description: The microstructure and mechanical properties of laser-welded high-strength Mg-Gd-Y-Zr alloy in T6 condition were investigated. The network-distributed precipitates at grain boundaries were identified as the Mg 24 (Gd,Y) 5 . No significant grain coarsening was observed in the heat-affected zone. The deterioration of mechanical properties was attributed to the dissolution of precipitates in the heat-affected zone during laser welding. For the weakest part of the heat-affected zone, solid solution strengthening was the most important strengthening factor.

Description: The effect of grain size and current density on deformation behavior during electrically assisted tension of Ti-6Al-4V alloy was investigated. The microstructural variations under different conditions were observed by optical microscope, SEM and TEM. The dislocation density was quantified by x-ray diffraction technique. The decrease in grain size could increase the elongation growth and stress reduction during electrically assisted tension. Fine grain size specimens can reach higher temperature than coarse grain specimens. With increasing current density, wider and deeper dimples on the fracture surfaces were observed, and less dislocation density and pileups were found in comparison with room-temperature tension without current. The dislocation density has a 62.1% reduction at 10.48 A/mm 2 compared with room-temperature tension for 9.2 μm grain size specimens.

Description: Reported work focuses on the effect of morphology of the Fe-rich intermetallic phases on the machinability of Al-alloy containing 〉2wt.% Fe, obtained from automotive scrap. Effect of Mo addition on the microstructure, high-temperature impression creep and thereby the machinability of the Al-recycled alloy were studied. The machinability of the recycled alloy was estimated by investigating the built-up-edge (BUE) and surface roughness ( R a ). SEM-EDS and TEM-SADP studies have shown that the crystal structure (BCC) of the Al 8 Fe 2 Si phase remained unchanged; however, Mo replaced few Fe atoms with little effect on the lattice dimension. It has been found that the addition of Mo to the recycled alloy suppresses the formation of β -phase (Al 5 FeSi) by suppressing the peritectic transformation of α (Al 8 Fe 2 Si) phase. Such suppression is found to improve the high-temperature creep resistance and the machinability with the increase in the Mo addition level.

Description: This study is the first attempt to investigate the influence of severe plastic deformation (SPD) treatment on material surface behavior under intensive erosive conditions. Samples of aluminum alloy 1235 (99.3 Al) before and after high-pressure torsion (HPT) were subjected to intensive erosion by corundum particles accelerated via air flow in a small-scale wind tunnel. Velocity of particles varied from 40 to 200 m/s, while particle average diameter was around 100 μm. Surface roughness measurements provided possibility to compare surface properties of both materials after erosion tests. Moreover, SPD processing appeared to increase noticeably the threshold velocity of the surface damaging process. Additionally, structural analysis of the fracture surfaces of the tested samples was carried out.

Description: Functionally graded aluminum foam (FG Al foam) is a new class of Al foam in which the pore structure varies over the foam, resulting in corresponding variations in the mechanical properties of the foam. In this study, FG Al foam plates were fabricated by a friction powder sintering (FPS) process with a traversing tool that is based on a previously developed sintering and dissolution process. The variation of the mechanical properties was realized by setting the volume fraction φ of NaCl in the mixture to 60, 70, and 80%. Long FG Al foam plates were fabricated with a length equal to the tool traversing length with φ varying in the tool traversing direction. From x-ray computed tomography observation, it was shown that the density of the Al foam decreased with increasing φ . In contrast, almost uniform pore structures were obtained in each area. According to the results of compression tests on each area, the plateau stress and energy absorption tended to decrease with increasing φ . Therefore, it was shown that FG Al foam plates with varying mechanical properties can be fabricated by the FPS process with the traversing tool.

Description: This review sheds light on the creep properties of AZ91 magnesium alloys with a major emphasis on the influence of microstructure on the creep resistance and underlying creep deformation mechanism based on stress exponent and activation energy. Effects of processing routes such as steel mold casting, die casting, and thixoforming are considered. Roles of a wide range of additional alloying elements such as Si, Sb, Bi, Ca, Sn, REs, and combined addition of them on the microstructure modification were investigated. The reaction between these elements and the Mg or Al in the matrix develops some thermally stable intermetallic phases which improves the creep resistance at elevated temperatures, however does not influence the creep mechanism.

Description: In this study, using a nonlinear estimation of strain hardening rate versus strain, a new phenomenological constitutive equation is developed. Utilizing the presented model, three new equations were presented to determine the peak strain, critical strain for initiation of dynamic recrystallization (DRX), and transition strain associated with the maximum softening rate of DRX. Also, two temperature and strain rate-sensitive parameters were introduced to generate flow stress curve at any desired deformation conditions. The predicted results were found to be in a good agreement with the ones measured experimentally. Maximum errors in prediction of peak strain, critical strain, and transition strain were about 8, 11, and 4%, respectively. In addition, evaluation of maximum errors in prediction of flow stress indicates that the presented constitutive equation gives a more precise estimation of flow stress curves in comparison with the previous models pertaining modeling of single-peak flow stress curves.

Description: Hot compression tests of Ti-6Al-4V alloy in a wide temperature range of 1023-1323 K and strain rate range of 0.01-10 s −1 were conducted by a servo-hydraulic and computer-controlled Gleeble-3500 machine. In order to accurately and effectively characterize the highly nonlinear flow behaviors, support vector regression (SVR) which is a machine learning method was combined with genetic algorithm (GA) for characterizing the flow behaviors, namely, the GA-SVR. The prominent character of GA-SVR is that it with identical training parameters will keep training accuracy and prediction accuracy at a stable level in different attempts for a certain dataset. The learning abilities, generalization abilities, and modeling efficiencies of the mathematical regression model, ANN, and GA-SVR for Ti-6Al-4V alloy were detailedly compared. Comparison results show that the learning ability of the GA-SVR is stronger than the mathematical regression model. The generalization abilities and modeling efficiencies of these models were shown as follows in ascending order: the mathematical regression model 〈 ANN 〈 GA-SVR. The stress-strain data outside experimental conditions were predicted by the well-trained GA-SVR, which improved simulation accuracy of the load-stroke curve and can further improve the related research fields where stress-strain data play important roles, such as speculating work hardening and dynamic recovery, characterizing dynamic recrystallization evolution, and improving processing maps.

Description: Effects of the normalizing treatment on microstructural evolution, mechanical properties, and impact fracture behavior of 20MnV low alloy cryogenic as-rolled steel were evaluated. The results indicate that grain boundary carbide and acicular ferrite of the as-rolled steel were eliminated and a large amount of nanoscale VC precipitates were observed after 860 °C normalizing treatment. The as-normalized steel had lower strength, higher elongation, and impact absorbed energy than as-rolled steel. The optimal comprehensive mechanical property, especially the superior cryogenic toughness with impact absorbed energy values at −20 and −50 °C were 62 and 40 J, respectively, was obtained at 860 °C. The as-rolled steel contained shearing crack and necking crack simultaneously, while 860 °C as-normalized steel only contained deflecting necking crack, indicating the significant improvement of the toughness.

Description: In the present work, residual stresses distribution in the gas nitrided AISI 4140 sample has been studied using finite element (FE) simulation. The nitrogen concentration profile is obtained from the diffusion-controlled compound layer growth model, and nitrogen concentration controls the material volume change through phase transformation and lattice interstitials which results in residual stresses. Such model is validated through residual stress measurement technique—micro-ring-core method, which is applied to the nitriding process to obtain the residual stresses profiles in both the compound and diffusion layer. The numerical and experimental results are in good agreement with each other; they both indicate significant stress variation in the compound layer, which was not captured in previous research works due to the resolution limit of the traditional methods.

Description: Butt weld joints are prepared using pulse current gas tungsten arc welding out of thin sheets of AISI 1008 steel using various combinations of pulse parameters. During welding, the welding speed was kept high, but with the increase of welding speed the mean current was also increased to get the required weld joint at the constant heat input. The use of pulse current has led to improvement in mechanical and metallurgical properties of weld joints. It has resulted in less development of humping which is a common problem with high-speed welding. The undercut or dipped weld face is not observed severe. The tensile strength and hardness are enhanced by 12.5 and 12%. The increase of tensile strength and hardness is justified through TEM micrograph showing the presence of dislocation.

Description: To develop an optimised manufacturing method of fly ash-reinforced metal matrix composites, the preliminary tests were performed on the cenospheres selected from fly ash (FA CS ) with halloysite nanotubes (HNTs) addition. The preform made out of FA CS with and without the addition of HNT (with 5 and 10 wt.%) has been infiltrated by the pure aluminium (Al) via adapted gas pressure infiltration process. This paper reveals the influence of HNT addition on the microstructure (analysis was done by computed tomography and scanning electron microscopy combined with energy-dispersive x-ray spectroscopy), thermal properties (thermal expansion coefficient, thermal conductivity and specific heat) and the mechanical properties (hardness and compression test) of manufactured composites. The analysis of structure-property relationships for Al/FA CS -HNT composites produced shows that the addition of 5 wt.% of HNT to FA CS preform contributes to receiving of the best mechanical and structural properties of investigated composites.

Description: A Fe-Al-Cr alloyed layer was deposited onto the surface of Q235 low-carbon steel via double glow plasma surface metallurgy (DGPSM) to improve the steel’s wear resistance. After the DGPSM treatment, the Fe-Al-Cr alloyed layer grown on the Q235 low-carbon steel was homogeneous and compact and had a thickness of 25 µm. The layer was found to be metallurgically adhered to the substrate. The frictional coefficient and specific wear rate of the sample with a Fe-Al-Cr alloyed layer (treated sample) were both lower than those of the bare substrate (untreated sample) at the measured temperatures (25, 250 and 450 °C). The results indicated that the substrate and the alloyed layer suffered oxidative wear and abrasive wear, respectively, and that the treated samples exhibited much better tribological properties than did the substrate. The formation of Fe 2 AlCr, Fe 3 Al(Cr), FeAl(Cr), Fe(Cr) sosoloid and Cr 23 C 6 phases in the alloyed layer dramatically enhanced the wear resistance of the treated sample. In addition, the alloyed layer’s oxidation film exhibited a self-healing capacity with lubrication action that also contributed to the improvement of the wear resistance at high temperature. In particular, at 450 °C, the specific wear rate of treated sample was 2.524 × 10 −4  mm 3 /N m, which was only 45.2% of the untreated sample.

Description: The sliding wear under fretting condition, scratch adhesion, deformation behavior during micro- and nanoscratch studies have been studied for nanocomposite TiSiBC hard coating deposited on steel substrate by magnetron sputtering. The nanocomposite coatings having hardness and modulus around 30 and 300 GPa, respectively, showed a very significant decrease in fretting wear as compared to the uncoated steel. Pileup occurred along the sides of the scratch track due to plastic deformation of the substrate at the scratch load; however, cracks were not seen in films. The coefficient of friction remained 〈0.25 with increasing load. Under static load, even at 2000 gf (20 N) coating did not show crack in the film. Coated steel showed significant elastic recovery as compared to uncoated steel. The TiSiBC-coated substrate showed higher resistance to scratch, higher wear resistance, higher toughness and low coefficient of friction.

Description: Temperature histories of structural steel deep-penetration welds are presented, which are calculated using numerical-analytical basis functions and solidification-boundary constraints. These weld temperature histories can be adopted as input data to various types of computational procedures, which include numerical models for prediction of solid-state phase transformations and mechanical response. In addition, these temperature histories can be used parametrically for inverse thermal analysis of welds corresponding to other welding processes whose process conditions are within similar regimes. The present study applies an inverse thermal analysis procedure that uses three-dimensional constraint conditions whose two-dimensional projections are mapped within transverse cross sections of experimentally measured solidification boundaries. In addition, the present study uses experimentally measured estimates of the heat effect zone edge to examine the consistency of calculated temperature histories for steel welds.

Description: The cross dissimilar welds between T92 martensitic steel and S30432 austenitic steel were crept at 625 °C with different applied stresses, and the creep deformation and microstructure behaviors were characterized. The results revealed that the creep deformation behavior of dissimilar weld joint was controlled by its martensitic T92 part due to the Ni-based filler metal employed. The fracture positions of crept dissimilar welded joints were located in base metal of T92 steel as the applied stress over than 140 MPa. The fracture type was mainly caused by plastic deformation and characterized by dimples and surface necking. In contrast, as applied stress was 〈140 MPa, fractured location was transferred into the fine-grained heat-affected zone of T92 part identified to be the intergranular brittle fracture. This phenomenon was controlled by creep deformation and related to undissolved carbides, fine grain size and constraint effect induced by creep deformation inconsistent in this zone.

Description: A triplex plasma (NiCoCrAlHfYSi/Al 2 O 3 ·13%TiO 2 )/polycaprolactone composite coating was successfully deposited on a Mg-1.2Ca alloy by a combination of atmospheric plasma spraying and dip-coating techniques. The NiCoCrAlHfYSi (MCrAlHYS) coating, as the first layer, contained a large number of voids, globular porosities, and micro-cracks with a thickness of 40-50 μm, while the Al 2 O 3 ·13%TiO 2 coating, as the second layer, presented a unique bimodal microstructure with a thickness of 70-80 μm. The top layer was a hydrophobic polymer, which effectively sealed the porosities of plasma layers. The results of micro-hardness and bonding strength tests showed that the plasma coating presented excellent hardness (870 HV) and good bonding strength (14.8 MPa). However, the plasma/polymer coatings interface exhibited low bonding strength (8.6 MPa). The polymer coating formed thick layer (100-110 μm) that homogeneously covered the surface of the plasma layers. Contact angle measurement showed that polymer coating over plasma layers significantly decreased surface wettability. The corrosion current density ( i corr ) of an uncoated sample (262.7 µA/cm 2 ) decreased to 76.9 µA/cm 2 after plasma coatings were applied. However, it was found that the i corr decreased significantly to 0.002 µA/cm 2 after polymer sealing of the porous plasma layers.

Description: Tb 2 TiO 5 neutron absorber was synthesized by ball milling and sintering. Microstructure character of ball-milled Tb 4 O 7 -17.605%TiO 2 (mass fraction, %) powders and sintered bulks was analyzed using XRD, SEM and TEM. The microhardness, coefficient of thermal expansion and thermal conductivity of sintered bulks were measured. The experiment results showed that the nanocrystalline solid solution was obtained during ball milling. After 96 h of ball milling, TiO 2 was completely solved in Tb 4 O 7 and the crystal size of Tb 4 O 7 was up to 37 nm. The bulk materials prepared by cold isostatic pressing were sintered at 1300 °C. Tb 2 TiO 5 bulks with an orthorhombic structure were obtained. The microhardness of sintered bulks, as well as the thermal conductivity, increased firstly with increasing ball milling time and then decreased. The coefficient of thermal expansion decreased initially and then increased with increasing ball milling time. For the sintered bulk with powder milled for 48 h, the highest values of both microhardness and thermal conductivity were observed, whereas the lowest coefficient of thermal expansion was exhibited. In addition, with increasing testing temperature, the thermal conductivity of sintered bulks initially fell and then rebounded while an opposite trend was found in the coefficient of thermal expansion.

Description: This paper presents new studies of the physical and mechanical characterization of PA6 matrix composites with different volume fractions of glass microspheres (10, 15, 20, 25 and 30%), which have been processed in an industrial environment. The mechanical properties of different processed composites were obtained by three-point bending tests, and the influence of the time of immersion in water in the strength and modulus was analyzed. The mechanical properties obtained in static tests and DMA tests of the processed composites demonstrated significant increases with an increasing volume fraction of the glass microspheres. In fracture toughness tests, K IC values higher than 12% were obtained. On the contrary, the immersion in water for 20 days promotes a decrease in flexural strength and flexural modulus greater than 11 and 22%, respectively. Finally, the influence of the addition of glass microspheres to the polyamide matrix was analyzed, and the increase in Tg with increasing fraction of the glass microspheres was observed.

Description: The objective of this work is to understand the different mechanisms of crack formation in dense anodes used in the aluminum industry. The first approach used is based on the qualitative characterization of the surface cracks and the depth of these cracks. The second approach, which constitutes a quantitative characterization, is carried out by determining the distribution of the crack width along its length as well as the percentage of the surface containing cracks. A qualitative analysis of crack formation was also carried out using 3D tomography. It was observed that mixing and forming conditions have a significant effect on crack formation in green anodes. The devolatilization of pitch during baking causes the formation and propagation of cracks in baked anodes in which large particles control the direction of crack propagation.

Description: AZ31-Mg 2 Si in situ composites were prepared from AZ31 Mg alloy and Si particles by a gravity casting method. Several parameters, such as Si content, normal load, and environmental temperature, were varied in order to study their effects on the composite dry sliding wear properties. Tensile properties and hardness of the composites were also investigated. The obtained results showed that the wear resistance, yield strength, and hardness of the AZ31-Mg 2 Si composites increased with size and quantity of the Mg 2 Si phase. However, when the environmental temperature increased from 25 to 190 °C, the composite wear resistance and ultimate tensile strength gradually decreased due to softening of the AZ31 matrix.

Description: In the present research work, corrosion behavior of post-weld heat-treated (PWHT) AISI 316L (X2CrNiMo 17-13-2) specimens joined by gas metal arc welding is compared with as-welded samples by using potentiodynamic polarization technique. Welded samples were PWHT at 1323 K for 480 s and quenched. Mechanical properties, corrosion behavior and microstructures of as-welded and PWHT specimens were investigated. Microstructural studies have shown grain size refinement after PWHT. Ultimate tensile strength and yield strength were found maximum for PWHT samples. Bend test have shown that PWHT imparted ductility in welded sample. Fractographic analysis has evidenced ductile behavior for samples. Potentiodynamic polarization test was carried out in a solution composed of 1 M H 2 SO 4 and 1 N NaCl. Corrosion rate of weld region was 127.6 mpy, but after PWHT, it was decreased to 13.12 mpy.

Description: In this work, corrosion inhibitors were added into an electroless nickel plating bath to realize nickel-phosphorus (Ni-P) coating deposition on magnesium alloy directly. The performance of five corrosion inhibitors was evaluated by inhibition efficiency. The results showed that only ammonium hydrogen fluoride (NH 4 HF 2 ) and ammonium molybdate ((NH 4 ) 2 MoO 4 ) could be used as corrosion inhibitors for magnesium alloy in the bath. Moreover, compounding NH 4 HF 2 and (NH 4 ) 2 MoO 4 , the optimal concentrations were both at 1.5 ~ 2%. The deposition process of Ni-P coating was observed by using a scanning electron microscope (SEM). It showed corrosion inhibitors inhibited undesired dissolution of magnesium substrate during the electroless plating process. In addition, SEM observation indicated that the corrosion inhibition reaction and the Ni 2+ replacement reaction were competitive at the initial deposition time. Both electrochemical analysis and thermal shock test revealed that the Ni-P coating exhibited excellent corrosion resistance and adhesion properties in protecting the magnesium alloy.

Description: Inherent strain analysis has been successfully applied to predict welding deformations of large-scale structural components, while thermal-elastic-plastic finite element method is rarely used for its disadvantages of long calculation period and large storage space. In this paper, a hybrid model considering nonlinear yield stress curves and multi-constraint equations to thermal-elastic-plastic analysis is further proposed to predict welding distortions and residual stresses of large-scale structures. For welding T-joint structural steel S355JR by metal active gas welding, the published experiment results of temperature and displacement fields are applied to illustrate the credibility of the proposed integration model. By comparing numerical results of four different cases with the experiment results, it is verified that prediction precision of welding deformations and residual stresses is apparently improved considering the power-law hardening model, and computational time is also obviously shortened about 30.14% using multi-constraint equations. On the whole, the proposed hybrid method can be further used to precisely and efficiently predict welding deformations and residual stresses of large-scale structures.

Description: In this study, four kinds of roughness structures were constructed on the Al alloy surface using laser marking technology. The tribological properties of the surfaces under the condition of dry friction were carefully investigated. The results indicate that the fabricated surfaces have similar compositions. The hardness of surfaces can be improved after the laser surface treatment. Besides, the texturing of surfaces can efficiently reduce friction and improve friction resistance. However, the friction-reducing mechanisms are not the same. The surfaces with lined and grating grooves can remove wear debris away from the interfaces between steel balls and surfaces, while those with irregular protrusions and micro-orifices array would be able to trap wear debris in the microstructure. Furthermore, due to the different friction mechanisms of distinct roughness structures, their friction-reducing performances are greatly affected by the actual friction conditions (sliding speed and load), which offers a guide for constructing a specific roughness structure on the Al alloy surface to improve its friction resistance efficiently.