Strengthening and weakening in the processing of ultrafine-grained metals

Abstract

It is now well established that ultrafine-grained (UFG) metals, with average grain sizes below 1 µm, may be produced by applying severe plastic deformation to bulk metals using processing procedures such as equal-channel angular pressing (ECAP) and high-pressure torsion (HPT). Generally, these procedures lead to a significant strengthening in the material but there are some examples where processing by ECAP or HPT produces a significant weakening. This report examines examples of both strengthening and weakening in the processing of UFG metals.K e y w o r d s : equal-channel angular pressing, high-pressure torsion, severe plastic deformation, ultrafine grains

Microstructure and mechanical properties of a Zn-0.5Cu alloy processed by high-pressure torsion

“…Only one dual-phase eutectoid Zn-22Al alloy has been investigated after HPT processing, and then the presence of a second phase leads to significant grain refinement to ~350 nm after 5 turns under a pressure of 6.0 GPa [17][18][19][20][21]. In contrast to pure zinc, the dual-phase Zn alloy exhibits a strain softening behavior [22]. Besides the conventional alloys, Zn-Mg hybrids produced by HPT processing have been recently reported [23,24].…”

An investigation of the limits of grain refinement after processing by a combination of severe plastic deformation techniques: A comparison of Al and Mg alloys

“…This was first reported in the HPT processing of high purity aluminum [59] but the same effect, termed hardening with recovery, has been observed also in other materials [60]. This leads to the possibility that SPD processing may produce either a strengthening or a weakening effect [61]. For example, significant weakening was reported in several materials including the Zn-Al and Pb-Sn alloys by increasing the equivalent strain in processing by HPT [62][63][64].…”

Recent Developments in the Processing of Advanced Materials Using Severe Plastic Deformation

“…However, in some materials, such as pure Al [13], the material may initially harden and then soften to a saturation value in the behavior termed with recovery and in other materials, such as the Bi-Sn eutectic alloy [14], the material softens to a lower saturation level in the behavior termed with weakening [12]. There are various microstructural effects that account for these different types of behavior [15].…”