Stress-Induced Grain Growth in an Ultra-Fine Grained Al Alloy

Abstract

This paper reports on a study of the stress-induced grain growth phenomenon in the presence of second-phase particles and solutes segregated at grain boundaries (GBs) during high-temperature deformation of an ultra-fine grained (UFG) Al alloy synthesized via the consolidation of mechanically milled powders. Our results show that grain growth was essentially inhibited during annealing at 673 K (400°C) in the absence of an externally applied stress, whereas in contrast, grain growth was enhanced by a factor of approximately 2.7 during extrusion at 673 K (400°C). These results suggest that significant grain growth during hot extrusion was attributable to the externally applied stresses stemming from the state of stress imposed during extrusion and that the externally applied stresses can overcome the resistance forces generated by second-phase particles and solutes segregated at GBs. The mechanisms underlying stress-induced grain growth were identified as GB migration and grain rotation, which were accompanied by dynamic recovery and possible geometric dynamic recrystallization, while discontinuous dynamic recrystallization did not appear to be operative. he earned his B.S. with honors in solid mechanics from Brown University. His research interests include the synthesis and behavior of nanostructured and multi-scale materials with particular emphasis on processing fundamentals and physical behavior; thermal spray processing of nanostructured materials; spray atomization and deposition of structural materials; high temperature-high pressure atomization processes; mathematical modeling of advanced materials and processes; and additive manufacturing. He has published 515 journal and 225 conference publications on topics ranging from nanomaterials to extremely strong aluminum alloys. Prof. Lavernia has delivered more than 150 invited lectures and seminars in over 17 countries. He

Achieving excellent microformability in aluminum by engineering a unique ultrafine-grained microstructure

“…However, postmortem analysis of the stress-assisted grain growth can also be used to provide intutive evidence for the occurrence GBMP phenomena such as grain migration and rotation. Due to the unstable nature of the grain boundaries in UFG material, GBMP is accompanied by a rapid rate of stress-assisted grain growth which results in abnormal coarsening of grains to micrometer scale 34–36 . At initial stage, stress-assisted grain growth promotes plastic deformation.…”

Correlation between Microstructure and Mechanical Properties of Heat-Treated Novel Powder Metallurgy Superalloy

“…In addition, the grain growth of SH can be observed in Figure 12 during the tensile test at high temperature, and the grain size increased with an increase in the test temperature. The grain growth of SH can be ascribed to the grain boundary migration in a stressed condition at a high temperature [51]. However, the grain growth of SL during the tensile test at high temperature is not obvious, which can be seen in Figure 12.…”

Effects of annealing and extrusion on the microstructure and tensile properties of ultrafine-grained Al fabricated by spark plasma sintering

“…It has been established that to activate GDRX, the spacing between adjacent HAGBs must be reduced to a critical value which is close to the size of subgrains formed by dynamic recovery of the grains [18,19]. The subgrain size (d 0 ) can be estimated by the empirical equation [20]:…”