Materials Science Forum Vols. 702-703

Abstract: Copper of different purity levels (4N, 5N) produced by High Pressure Torsion (HPT) with varying processing parameters is investigated utilizing the radiotracer technique. While the degree of deformation is constant, the effect of the applied quasi-hydrostatic pressure and of the impurity concentration on the as deformed samples is analysed. By applying the radio tracer method micro structural aspects are revealed that are not easily accessible by conventional methods. The measurements indicate the formation of a percolating porosity during the HPT process as a function of the applied pressure and (although less pronounced) of the impurity concentration.

Abstract: Different initial texture of ring rolled AA 2014 alloy was processed to one pass in Equal Channel Angular Extrusion (ECAE) at room temperature. The material flow/deformation characteristics as well as the degree of grain refinement, as a function of different initial grain morphological orientation are studied. Macroscopic and microscopic investigation by Optical Microscope (OM) confirms the significant variation in the shearing characteristics of grains in the billets in each orientations. OM observations also suggested that the severity of deformation was more in middle portions of the extruded billets. TEM observations made on the samples also confirmed the existence of regions which had undergone the different degree of dynamic recovery and recrystallisation after passing through shear deformation zone.

Abstract: The effect of processing routes during Equal Channel Angular Pressing (ECAP) of the Al alloy 2014 with regard to the evolution of microstructure and texture heterogeneity has been studied. The solution treated alloy (768 K for 1 hr) was subjected to ECAP through routes A, BA, BC and C using a die with inter-channel angle 90° upto 5 passes. Texture evolution was studied in the top, middle and bottom of the billets processed through routes A, BA, BC and C. Processing by route A resulted in a stronger texture evolution because of monotonic increase in strain with the number of passes. In route A, texture heterogeneity is more than the routes BC and BA. In routes BC and BA, the texture evolution in outer region near to surface of the billet changes their orientation as the passes increases possibly creating a stronger texture evolution at the top and bottom different from the centre of billet. The heterogeneity in texture evolution is the least less in route C, due to the reversal of shear.

Abstract: Equal channel angular pressing (ECAP) in magnesium alloys due to the severe plastic shear deformations provides both grain refinement and the slope of the initial basal texture at 40-50 ° to the pressing direction. Such changes in microstructure and texture contribute to the improvement of low-temperature ductility and deformability of the alloys. On the basis of analysis of data from various researchers, the main structure and texture factors affecting on the ductility increase of the Mg-Al-Zn-Mn alloys were defined.

Abstract: Interstitial-Free steel (IF-steel) sheets were severe plastically deformed using a continuous equal-channel angular extrusion/pressing technique called “Equal-Channel Angular Sheet Extrusion (ECASE). After processing, texture development as well as microstructural alteration and tensile properties were investigated. The microstructural investigations revealed that the processed sheets exhibited a dislocation cell and/or subgrain structures with mostly low angle grain boundaries. It was also observed that the strength of the processed sheets increased substantially after ECASE processing in the expense of ductility. It was shown that the ECASE has moderate influence on the texture of IF-steel sheets through route A. Intially there was θ partial fiber which changes to {110}θ with straining.

Abstract: It is possible to produce a nanocrystalline, multilayered composite structure with enhanced mechanical properties by assembling three 316L surface nanostructured stainless steel plates by roll bonding. The Surface Mechanical Attrition Treatment (SMAT) was first used to generate nanocrystalline layers on the elementary plates so that their mechanical properties were improved. They were then assembled through co-rolling. A composite structure of nanocrystalline layers of high strength alternating with more ductile layers was obtained to achieve both high strength and ductility. Microscopy observations and EBSD measurements were carried out and the bonding interfaces were analysed in detail to explore the mechanisms involved during the SMAT/Co-rolling duplex process.

Abstract: An α-β alloy (β~8% in the stress relieved condition) of Ti-5Ta-1.8Nb has been subjected to severe plastic deformation (SPD) by cryo-rolling. The grain size of α-Ti could be reduced significantly from ~ 8µm to 100 nm and less by cryo-rolling. Extensive plastic deformation leads to grain fragmentation through the formation of defect clusters. The fragmented grains exhibit deformation texture. High resolution transmission electron microscopy (HRTEM) confirmed the presence of low and high angle grain boundaries. The role of substitutional atoms (Ta, Nb) in producing lattice strains and altering the projected potential from the atomic columns has been discussed. Although, the minor phase, β (bcc-Ti) is evident in the starting alloy, it was not observed after SPD, possibly due to extended solid solution formation (Gibbs–Thomson effect) in the fine grains or due to the stress induced transformation of the α-Ti phase.

Abstract: Grain refinement of aluminum deformed by equal channel angular pressing is strongly dependent on the amount of strain. The refinement process at low to high strain level involves elongation of the existing grains by shear deformation, their subdivision into bands and subgrain formation within bands, intersection of the bands during subsequent passes and finally conversion of the subgrains to grains by continuous dynamic recrystallization process. At room temperature the conversion of subgrains to grains takes place by progressive lattice rotation.

Abstract: During high rate severe plastic deformation (HRSPD), strain and strain-rate are not the only external factors that determine microstructural transformations in materials, temperature-rise due to heat generation from deformation processes, also plays an important role. Temperature may influence the microstructure directly by controlling grain growth kinetics and it may also have an indirect effect through the interactive effect on material behavior, which in turn, influences strain and strain-rate parameters. This complex thermomechanics of HRSPD can lead to myriad of microstructure and consequently, material properties and phenomenon. These deformation parameters can be utilized as a ‘fingerprint’ for the resulting microstructure, and the properties and phenomenon related to it. Here, we capture some of these microstructural transformations by relating grain and sub-grain sizes, to the deformation parameters. In doing so, we find evidence of continuous dynamic recrystallization operative under these HRSPD conditions, where the interplay of strain, strain rate and temperatures offer varying degrees of multimodality in the grain-size distributions.

Abstract: FCC materials were subjected to large strain deformation by three techniques: equal channel angular pressing (ECAP), plane-strain machining and friction stir processing (FSP). Based on the orientation imaging mapping (OIM) analysis of the deformed regions, the most likely microstructure refinement mechanisms have been identified for each of the techniques and compared among one another.