A Lifetime of Research in Creep, Superplasticity, and Ultrafine‐Grained Materials

Abstract

A long‐term career at the University of Southern California, followed by an appointment at the University of Southampton, provided an opportunity to conduct extensive research into the flow behavior of polycrystalline metals. Initially, research is conducted on creep properties at elevated temperatures and it is shown that solid solution metallic alloys exhibit transitions in creep behavior with dislocation climb and viscous glide as the dominant rate‐controlling mechanisms. There are transitions between climb and glide with increasing stress and also a breakaway from the glide process at high stresses. These transitions are predicted theoretically and the results are in excellent agreement with the experimental data for a wide range of alloys. Attention is directed to the process of superplasticity and it is shown that the flow occurs by grain boundary sliding with accommodation by a limited amount of intragranular slip. Separate rate equations are developed for sliding in coarse‐grained materials and in superplastic materials where the grain sizes are generally <10 μm so that flow occurs without the development of any subgrains. Finally, attention is directed to the properties of ultrafine‐grained materials having submicrometer or nanometer grain sizes produced through the application of severe plastic deformation.

On the creep performance of the Ti‐6Al‐4V alloy processed by additive manufacturing

“…In particular, they concluded that Rachinger grain boundary sliding (GBS) was the dominant process producing the superplasticity of Ti6-Al-4V. The equilibrium subgrain size () was a key factor, because when  was greater than the mean grain size (d), the Rachinger GBS was rate controlling and resulted in a superplastic behaviour [53]. When  was smaller than d, dislocations formed subgrain boundaries, and classical climb-controlled deformation occurred.…”