Stress-accelerated softening in bulk nanocrystalline Mg-Gd-Y-Zr alloys

Abstract

Exploring the microstructure and mechanical property evolution of metallic structural materials during stress annealing has scientific and engineering significance since these materials are usually used to bear coupled thermo-mechanical loads in their service life. Here, we report a stress-accelerated softening phenomenon in bulk nanocrystalline Mg-Gd-Y-Zr alloys. Transmission electron microscopy observation indicates that, compared with static annealing, stress annealing accelerates the grain coarsening and precipitation of the grain boundary β phases. The precipitation of β phases results in the depletion of intragranular solute atoms, which therefore weakens the solid solution strengthening effect. The stress-assisted β phase precipitation and grain coarsening lead to the accelerated softening of nanocrystalline Mg-Gd-Y-Zr alloys. That is, the mechanical properties of nanocrystalline Mg-Gd-Y-Zr alloys subjected to coupled thermo-mechanical loads deteriorate more rapidly compared with the statically-annealed alloys.