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  • 1
    Electronic Resource
    Electronic Resource
    FATIGUE BEHAVIOUR OF THREE VARIANTS OF THE ROLLER BEARING STEEL SAE 52100 (1992)
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 15 (1992), S. 0 
    Details
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Stress-controlled, low-cycle, push-pull fatigue tests were performed on three variants of the bearing steel SAE 52100 with slightly different compositions and heat treatments. The experiments demonstrated differences in the cyclic plastic behaviour of differently hardened steels (bainitically-hardened and martensitically-hardened, respectively), whereas the two martensitic variants, which differ in composition, behaved very similarly. Bainitically-hardened SAE 52100 steel exhibited initial hardening followed by cyclic softening above a stress amplitude level of 1200 MPa. In contrast, the martensitically-hardened variants showed a pronounced cyclic hardening. The deformation behaviour of the martensitically-hardened bearing steel in a monotonic tensile test and during the first cycles can be well understood on the basis of the transformation of retained austenite. This process leads to an onset of plastic deformation at lower stresses compared to the bainitically-hardened bearing steel. As a result of the subsequent cyclic hardening of the martensitic variants, the CSS curves are almost identical for the differently hardened conditions under investigation. Additional tests under pulsating compression documented that a high negative mean stress enhances the cyclic plasticity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1460-2695.1992.tb00062.x
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  • 2
    Electronic Resource
    Electronic Resource
    CYCLIC STRESS-STRAIN RESPONSE AND MICROSTRUCTURE UNDER VARIABLE AMPLITUDE LOADING (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 19 (1996), S. 0 
    Details
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract— In order to study the cyclic stress-strain behaviour under variable amplitude loading in terms of dislocation glide character and microstructure, various metals and alloys were cyclically loaded in single-step tests and in an incremental step test (IST). The cyclic stress-strain curves (CSS curves) which correspond to the different loading conditions were compared and the shapes of the hysteresis loops were analysed with respect to Masing or non-Masing behaviour.As expected, cyclic loading with constant amplitude leads to the formation of a characteristic dislocation arrangement that depends on the amplitude applied. The amplitude-related microstructure corresponds to the observation that Masing behaviour was not found in single-step tests. However, in the IST a state of saturation, or at least approximate saturation, is attained after some or many loading blocks. In the case of single-phase polycrystalline materials, wavy slip behaviour was found to be a prerequisite for the fulfilment of Masing behaviour. Then, the CSS curve, obtained by means of IST, intersects that of the single-step tests at an intermediate amplitude. Planar-slip materials show very similar CSS curves in spite of considerable differences in the dislocation arrangements for different testing modes. The behaviour of particle-hardened alloys depends very strongly on the relative effectiveness of the precipitates as obstacles for dislocation motion and can be understood analogously to single-phase materials on the basis of the resulting dislocation glide character.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1460-2695.1996.tb00971.x
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  • 3
    Electronic Resource
    Electronic Resource
    THE INFLUENCE OF HYDROGEN ON THE FATIGUE BEHAVIOUR OF THE BETA-TITANIUM ALLOY Ti-3Al-8V-6Cr-4Mo-4Zr (1996)
    Oxford, UK : Blackwell Publishing Ltd
    Fatigue & fracture of engineering materials & structures 19 (1996), S. 0 
    Details
    ISSN: 1460-2695
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: In order to characterize the influence of hydrogen on the mechanical properties of β-titanium alloys, monotonic tensile and strain-controlled fatigue tests were performed on samples of the metastable alloy Ti-3Al-8V-6Cr-4Mo-4Zr in uncharged (0.5 at.% hydrogen) and hydrogen-charged (3-4 at.% hydrogen) conditions. The hydrogen was introduced into the material during the last 8 h of an ageing treatment (28 h at 482°C) from the gas phase, whereas the reference (uncharged) specimens were annealed completely in vacuum. The results of the mechanical tests indicate that hydrogen slightly increases the strength of the alloy in monotonic as well as in cyclic loading. Under tensile loading the fracture strain decreases as a result of hydrogen. Under cyclic loading both charged and uncharged conditions show initial softening followed by a saturation state. The cyclic lifetime at a constant total strain amplitude, however, is not reduced by the hydrogen charging. The effect of hydrogen on the mechanical behaviour can be interpreted and understood on the basis of microstructural observations that reveal a hydrogen-induced change in the precipitation state. This indirect influence of hydrogen on the microstructure, which leads to a reduction of the mean size of the α-precipitates, in combination with a slight decrease on the volume fraction of the α-phase, seems to dominate over any direct intrinsic hydrogen effect
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1460-2695.1996.tb00178.x
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  • 4
    Electronic Resource
    Electronic Resource
    Influence of the solubility product on the concentration profiles of internal oxidation (1989)
    Springer
    Oxidation of metals 32 (1989), S. 111-123 
    Details
    ISSN: 1573-4889
    Keywords: internal oxidation ; carburization ; computer simulation ; finite-difference technique
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A computer-based method is used to simulate the process of penetration of a foreign element (e.g., oxygen) into an alloy connected with internal precipitation of a compound of this element with a solute in the alloy. The method employed is based on the solution of the differential equations corresponding to this high-temperature corrosion phenomenon with the help of the finite-difference technique. To demonstrate the possibilities of the calculation method, various cases were treated which differ especially regarding the thermodynamic stability of the internal precipitates. The calculated concentration profiles and penetration depths obtained are reported and discussed. In the case of internal precipitates of high stability, the results are compared with the approaches derived in the literature for internal oxidation and are used to determine the parameter ranges in which the analytical equations apply. The results obtained for the case of a less-stable compound is used to illustrate the influence of the solubility product on the concentration profiles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00665271
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  • 5
    Electronic Resource
    Electronic Resource
    Mechanisms of high-temperature corrosion in helium containing small amounts of impurities. II. Corrosion of the nickel-base alloy inconel 617 (1988)
    Springer
    Oxidation of metals 30 (1988), S. 27-51 
    Details
    ISSN: 1573-4889
    Keywords: Ni-base alloy IN 617 ; reactor helium ; oxidation ; carburization ; decarburization ; kinetics ; mechanisms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Application of the technical nickel-base alloy IN 617 in the primary circuit of the high-temperature gas-cooled reactor is limited essentially by the chemical reactions with the impurities (CO, CO2, H2, CH4, H2O) in the helium coolant. The interactions of the alloy with the reactive impurities in different helium-base gases were investigated by thermogravimetry in a gas-tight microbalance and by simultaneous measurement of the changes in gas composition by a continuous sensitive mass spectrometric analysis. The results demonstrate that the set of six reaction equations deduced in part 1 can be applied to describe the corrosion of the alloy. The occurrence of the various reactions is determined essentially by temperature. For the case of a standardized helium gas (HHT-He), three temperature regions can be distinguished. Below a critical temperature (about 1105 K), the presence of CO can cause simultaneous oxidation and carburization. Above this temperature, this reaction does not reverse itself. Rather, oxidation by CO2 and H2O takes place that shows, after a transient period, the same kinetics observed in undiluted oxygen-containing gases. At temperatures above about 1205 K, decarburization of the alloy accompanied by the production of CO takes place, leading to severe destruction of the carbide microstructure and, therefore, limiting the applicability of the material.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00656643
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  • 6
    Electronic Resource
    Electronic Resource
    Oxidation of Ni-base alloys in atmospheres with widely varying oxygen partial pressures (1986)
    Springer
    Oxidation of metals 26 (1986), S. 45-76 
    Details
    ISSN: 1573-4889
    Keywords: Ni-base alloys ; oxidation ; influence of oxygen partial pressure at high temperatures ; kinetics and mechanisms of high temperature oxidation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The oxidation behavior of the Ni-base alloys IN 617, IN 713 LC, Ni20Cr, and Ni20Cr+Si has been investigated in the temperature range from 850°C to 1000°C in air and at low-oxygen partial pressure p(O2) (10−19 to 10−16 bar). With the exception of alloy IN 713 LC, the materials show no influence of p(O2) on the oxidation mechanisms and the kinetics. This result can be explained by the formation of a dense Cr2O3 layer, the growth rate of which is controlled by the Cr ion interstitial concentration in Cr2O3 at the phase boundary oxide/alloy and the mobility of Cr ions in Cr2O3. For the alloy IN 713 LC which develops a dense Al2O3 layer in air, a modified transition mechanism at low p(O2) leads to the formation of Cr2O3 at the surface and a strong internal oxidation of Al.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00664273
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  • 7
    Electronic Resource
    Electronic Resource
    Mechanisms of high-temperature corrosion in helium containing small amounts of impurities. I. Theoretical and experimental characterization of the gas phase (1988)
    Springer
    Oxidation of metals 30 (1988), S. 1-26 
    Details
    ISSN: 1573-4889
    Keywords: Reactor helium ; carbon activity ; oxygen activity ; flow conditions ; reactions with Pt, Cr, Cr3C2, Cr2O3
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Helium used as a coolant in high-temperature gas-cooled reactors contains gaseous impurities that cause various corrosion effects. To determine the mechanisms of the reactions that occur in this complex gas phase, a theoretical and experimental characterization of the gas is given in part 1. To obtain estimates of the reactions that are possible in principle and to derive the basis for the interpretation of the experimental results, thermodynamic considerations on gas equilibrium and partial equilibria are presented. Because of the extremely low concentrations of the impurities, diffusion processes within the gas may become rate-controlling. This requires a consideration of the flow conditions. The reactions of Pt, Cr, Cr2O3 and Cr3C2 with helium-based atmospheres containing impurities are investigated by means of a mass spectrometric gas analysis with respect to temperature and flow rate. A set of six reactions is derived from the results and discussed in detail. The application of these equations to describe the high-temperature corrosion phenomena of a technical nickel-base alloy is dealt with in part 2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00656642
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  • 8
    Electronic Resource
    Electronic Resource
    Internal Nitridation of Nickel-Base Alloys. Part I. Behavior of Binary and Ternary Alloys of the Ni-Cr-Al-Ti System (1999)
    Springer
    Oxidation of metals 52 (1999), S. 277-298 
    Details
    ISSN: 1573-4889
    Keywords: INTERNAL NITRIDATION ; NITROGEN DIFFUSION ; NITROGEN SOLUBILITY ; π-PHASE ; THERMODYNAMIC EQUILIBRIUM CALCULATIONS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The internal-nitriding behavior of several modelalloys of the Ni-Cr-Al-Ti system in an oxygen-freenitrogen atmosphere at 800-1100°C was studied.Thermogravimetry as well as various metallographic techniques (SEM and TEM) were used. It wasshown that both the nitrogen solubility and the nitrogendiffusion coefficient are strongly affected by the Crcontent of the Ni alloy. Hence, in Ni-Cr-Ti alloys a higher chromium content leads to an increaseddepth of the internal precipitation of TiN. Nitridationof the alloying element Cr takes place only at highconcentrations of Cr. In general, the nitridation rate was found to obey Wagner's parabolic ratelaw of internal oxidation. Changes in the parabolic rateconstant with alloy composition can be understood bymeans of thermodynamic calculations in combination with microstructural observations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018843612011
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  • 9
    Electronic Resource
    Electronic Resource
    Internal Nitridation of Nickel-Base Alloys. Part II. Behavior of Quaternary Ni-Cr-Al-Ti Alloys and Computer-Based Description (1999)
    Springer
    Oxidation of metals 52 (1999), S. 299-320 
    Details
    ISSN: 1573-4889
    Keywords: INTERNAL NITRIDATION ; NITROGEN DIFFUSION ; NITROGEN SOLUBILITY ; FINITE-DIFFERENCE TECHNIQUE ; THERMODYNAMIC EQUILIBRIUM CALCULATIONS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Whereas in Part I of this study the process ofinternal nitridation was described for binary andternary alloys within the Ni-Cr-Al-Ti system, this partfocuses on quaternary Ni-Cr-Al-Ti alloys, which are similar to commercial Ni-base alloys used inhigh-temperature applications regarding their chemicalcompositions. These alloys can simultaneously form twodifferent nitride-precipitation zones consisting of TiN and AlN. In order to quantify thenitridation process, thermogravimetric measurements inan oxygen-free nitrogen atmosphere in the temperaturerange 800-1100°C were carried out and supplemented by extensive microstructural studies. Whilesingle-nitride internal nitridation can easily bedescribed by Wagner's theory of internal oxidation,modeling of the more complex internal-precipitationreactions that involves more than one nitride requires anumerical treatment of both the diffusion and thethermochemical processes in the alloy. For this purpose,a computer simulation was developed in which the commercial thermodynamic software ChemApp iscombined with a finite-difference diffusion calculation.It was shown that this calculation technique can beapplied successfully to quantitatively describe the internal-nitridation process of theNi-Cr-Al-Ti model alloys used in this study.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018895628849
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  • 10
    Electronic Resource
    Electronic Resource
    Kinetics and Thermodynamics of the Absorption of Hydrogen in β-titanium Alloys (1999)
    Springer
    Journal of thermal analysis and calorimetry 55 (1999), S. 609-617 
    Details
    ISSN: 1572-8943
    Keywords: absorption diffusion and solubility of hydrogen ; β-Ti alloys ; TG
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A thermogravimetric method was applied to study the hydrogen uptake in the near-β-titanium alloy Ti 10 2 3 and the metastable β-titanium alloy Ti 21S. The tests were performed in H2-He gas mixtures with various partial pressures of H2 at temperatures between 600 and 800°C. Basic findings such as the decreasing solubility of H2 with increasing temperature could be verified, and first information on the effects of surface conditions was gained. Thus, it could be shown that, despite the low atomic mass of hydrogen, thermogravimetry is an appropriate tool for investigation of the H2/metal interactions of titanium alloys.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1010166424053
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