Effect of pre-deformation thermomechanical processing on the development of ultrafine grain structure during equal channel angular extrusion.

Two different microstructures, i.e., fine-grained solute depleted (FGSD) and coarse-grained solute enriched (CGSE), are prepared by thermomechanical processing. The samples are subjected to six pass equal channel angular pressing (ECAP). EBSD indicates formation of an ultrafine grained (UFG) structure within a size range of 632 nm in FGSD in comparison to 727 nm in CGSE which is attributed to more significant grain fragmentation in the FGSD sample with higher surface area of boundaries. In both as-annealed and -deformed conditions, hardness, yield strength (YS) and ultimate tensile strength (UTS) of the CGSE samples are higher than those of FGSD which is attributed to more significant solute enrichment. Elongation is found to reduce by the initial passes of ECAP and gradually improve by further processing. At a similar deformation history, the uniform elongation of the deformed CGSE samples is higher than those of the deformed FGSD samples which is attributed to more significant solute enrichment and work hardening causing a delayed necking and larger uniform elongation. However, the elongation to failure of FGSD samples after 2, 4 or 6 pass ECAP is larger than the CGSE sample with a similar deformation history which may be due to the high capacity of boundaries to accommodate dislocations and postpone fracture. [ABSTRACT FROM AUTHOR]