Revealing the deformation mechanisms for room-temperature compressive superplasticity in nanocrystalline magnesium

Bulk nanocrystalline (NC) Mg processed by cryomilling of commercially pure Mg powder particles followed by spark plasma sintering exhibits a compressive strain >120% at room temperature. Compressive tests at strain rates ranging from 10(-4) to 10(-1) s(-1) reveal a strain rate sensitivity (m) of similar to 0.17. Microstructural investigation reveals grain boundary migration accompanied with the ultra-large plastic deformation, which, along with the analysis of the deformation kinetics, deformation texture and dislocation structure, suggests that the excellent compressive plasticity in NC Mg mainly originates from grain boundary meditated deformation mechanisms and basal slip-dominated dislocation glide.