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  • 2005-2009  (6)
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  • 1
    Electronic Resource
    Electronic Resource
    Microstructure and Indentation Size-Effect in Pure Niobium Subjected to SPD via ECAP and HPT (2008)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 584-586 (June 2008), p. 215-220 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: A commercially pure niobium has been subjected to SPD at room temperature ( ~0.11TM) via ECAP (90º, route BC) up to 16 passes and via HPT up to shear strains γ =1000. ECAP-edsamples show an equiaxed structure after 8 and 16 passes with a decreasing average grain size. Theresults show that both the microstructure and mechanical properties of ECAP-ed samples do notreach a steady state up to at least 16 passes. HPT samples show at outer region a finer structural sizebut similar hardness values at similar equivalent strains. The nanoindentation results show anevident indentation size-effect even for the most deformed samples. The hardness values at the nanolevel converge for the recrystallized, the ECAP-ed and the HPT samples. This implies that, at thenano level, when the geometrically necessary dislocation density overcomes significantly the(initial) statistically stored dislocation density, hardness depends mainly on the physical intrinsicproperties of the material (Burgers modulus, bulk modulus...) and the contribution of bulkmechanical properties (i.e., bulk yield strength) to hardness is smoothed down. Strain-ratesensitivity (SRS) of plastic strength has been also measured by means of rate-jump nanoindentationtests. The SRS is proportional to the inverse of hardness
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/19/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.584-586.215.pdf
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  • 2
    Electronic Resource
    Electronic Resource
    Grain Refinement of Pure Copper by ECAP (2008)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 584-586 (June 2008), p. 393-398 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Pure commercial Cu of 99,98 wt % purity was processed at room temperature by Equal-Channel Angular Pressing (ECAP) following route Bc. Heavy deformation was introduced in thesamples after a considerable number of ECAP passes, namely 1, 4, 8, 12 and 16. A significant grainrefinement was observed by transmission electron microscopy (TEM). Tensile and microhardnesstests were also carried out on the deformed material in order to correlate microstructure andmechanical properties. Microhardness measurements displayed a quite homogeneous straindistribution. The most significative microstructural and mechanical changes were introduced in thefirst ECAP pass although a gradual increment in strength and a slight further grain refinement wasnoticed in the consecutive ECAP passes
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/19/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.584-586.393.pdf
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  • 3
    Electronic Resource
    Electronic Resource
    Modelling of Surface Roughness (Ra and Rq) in the EDM of Reaction-Bonded Silicon Carbide (2006)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 526 (Oct. 2006), p. 151-156 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: In this work, a surface roughness study on the die-sinking electrical discharge machining(EDM) of siliconised silicon carbide (SiSiC) has been carried out. The selection of the abovementionedconductive ceramic was made taking into account its wide range of applications in theindustrial field: high temperature gas turbines, bearings, seals and lining of industrial furnaces. Thisstudy was made only for the finish stages, due to the enormous importance that a good surfacequality has over such important properties as, in the case of ceramic materials: corrosion, fatigueand wear resistance. The present study has been carried out on the influence of five design factors:intensity supplied by the generator of the EDM machine (I), pulse time (ti), duty cycle (η), opencircuitvoltage (U) and dielectric flushing pressure (P), which are the most relevant parameters to becontrolled by the EDM process machinists, over two roughness parameters such as Ra and Rq. Thestudy of the behaviour of the two previously mentioned parameters has been done by means of thetechnique of design of experiments (DOE), which allows us to carry out the previous analysisperforming a relatively small number of experiments. In this case, a 25-1 fractional factorial design,whose resolution is V, has been selected due to the number of factors considered in the study
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/13/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.526.151.pdf
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  • 4
    Electronic Resource
    Electronic Resource
    Analysis of Stress and Strain in the Equal Channel Angular Drawing Process (2006)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 526 (Oct. 2006), p. 19-24 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The equal channel angular drawing (ECAD) process is an innovative method to obtainmaterials with high plastic strain in a continuous way. This deformation is higher than thedeformation achieved by a conventional wire drawing process, for the same reduction of the crosssection, so if an adequate thermal treatment is employed later, it could be possible to obtain aninitial material with high value that could be useful in conventional manufacturing processes. Thisprocess consists in drawing a material through a die where two circular channels intersect at anangle between 90º and 135º. In this work a study using finite element of the plastic strain and thestresses that appear for one aluminium alloy AA-1370 has been carried out. Two ECAD passes havebeen made, where for the second pass the billet has been rotated 180º along the longitudinal axis.Finally, a calibrated pass has been carried out in order to obtain the billet with homogeneousdimensions in all the cross section. All the simulations have been calculated at room temperatureand by using good conditions of lubrication. In order to perform the FEM simulations, a threedimensional geometry has been used. To analyze by FEM the second ECAD pass and thecalibration pass, the deformations and stresses achieved in the previous passes have been taken intoconsideration. This has been done with the aim of achieving higher accuracy. Moreover, acomparative analysis with experimental results has been carried out
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/13/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.526.19.pdf
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  • 5
    Electronic Resource
    Electronic Resource
    Study of ECAE Process by Using FEM (2006)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 526 (Oct. 2006), p. 193-198 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: In this work, the strain field attained by using a severe plastic deformation (SPD) processcalled equal channel angular extrusion (ECAE) is studied by the finite element method (FEM). Thethree-dimensional model with circular section includes shear friction between the part and the die,the material strain hardening behaviour and a rigid-deformable contact between the billet and thedie. In the ECAE process the part is extruded through two channels with similar diameter thatintersect at an angle. When the extrusion process has been performed, the processed materialremains it cross section, so there is not any geometric limitation to achieve the desired plastic strain.There are different ways of processing the material by using the ECAE process; those ways ofprocessing are called routes. In this work two passages of route C have been simulated. Using routeC means that the billet has been rotated 180º between each passage. Deformations imparted to theprocessed material have been calculated and a comparison with experimental results has beencarried out
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/13/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.526.193.pdf
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  • 6
    Electronic Resource
    Electronic Resource
    Severe Plastic Deformation of a Commercial Aluminium-Lithium Alloy (AA8090) by Equal Channel Angular Pressing (2006)
    s.l. ; Stafa-Zurich, Switzerland
    Materials science forum Vol. 503-504 (Jan. 2006), p. 871-876 
    Details
    ISSN: 1662-9752
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The enhanced mechanical properties of crystalline materials are linked to very small grain sizes. The AA8090 is a commercial aluminium lithium alloy is referred in the metallurgical literature by its superplastic behavior linked as well to nano-grains as obtained by ECAP. On this research-work in progress, the 8090 aluminium alloy is studied after being processed in a 400 kN ECAE press up to nine passes through a 90º angle-die at 150 ºC following Route A (constant path) at a processing speed of 10 mm/min. The room temperature mechanical properties of the extruded alloy are investigated through hardness measurements and tensile tests. Elastic measurements have been carried out by means of nanoindentation and ultrasonic testing, showing that both texture and nanostructuration of the processed alloy influence on the elastic constant of the processed material. In order to understand the mechanisms involved in the SPD-ECAP process, microstructural characterisation of the alloy has been carried out using different high resolution techniques such as Transmission Electron and Atomic Force Microscopy. TEM results have also been used in order to evaluate grain size evolution. From this analysis it is possible to see that after 4 passages the initial grains have already a high degree of dislocations. Among the characterisation techniques, AFM in the surface potential mode has been used to evaluate discontinuities in the matrix and /or decohesion between matrix and precipitates. After nine ECAP passages, no signs of decohesion at the interface have been observed neither using FEG-SEM nor using AFM
    Type of Medium: Electronic Resource
    URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/11/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.503-504.871.pdf
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