Mechanisms and anisotropy of serrated flow in Mg-Gd single crystals

Abstract

Serrated flow has been primarily studied at the macron scale, yet the length and times scales at which the solute–meditated dislocation pinning and de-pinning processes that underlie the phenomenon occur are largely inaccessible by macroscopic tests. Moreover, direct insights into the dominant slip systems in the serrated flow regime, which is particularly critical in Mg alloys given their high plastic anisotropy, requires the use of small-scale testing methods such as microcompression. Thus, in this work, a combination of microcompression and TEM based EDS/STEM measurements have used to critically study the temperature and strain rate dependences in single crystals of pure Mg and a Mg–Gd alloy oriented for twinning, basal-, prismatic-, and pyramidal-slip. The results provide compelling evidence that the solute drag mechanism underlie serrated flow in the alloy; they also show that serrated flow in Mg alloys is markedly anisotropic. This anisotropy is caused by differences between the Burgers vector for slip/twinning, and between the impurity diffusivity along/perpendicular to the basal plane.