Modelling the effect of pressure on the critical shear stress of MgO single crystals

Abstract

A hierarchical multi-scale model was used to study the effect of high pressure on the critical shear stresses of MgO. The two main slip systems, ½⟨110⟩{110} and ½⟨110⟩{100}, were considered. Based on a generalised Peierls–Nabarro model, it is shown that the core structure of ½⟨110⟩ screw dislocations is strongly sensitive to pressure. Mostly planar and spread in {110} at ambient pressure, the core of screw dislocations tends to spread in {100} with increasing pressure. Subsequently, an inversion of the easiest slip systems is observed between 30 and 60 GPa. At high pressure, the plasticity of MgO single crystals is expected to be controlled by ½⟨110⟩{100} slip systems, except at high temperature where both slip systems become active. Pressure is also found to increase the critical resolved shear stresses and to shift the athermal temperature toward higher temperatures. Under high pressure, MgO is thus characterised by a significant lattice friction on both slip systems.

Keywords:

• dislocation core modelling
• kink-pair mechanism
• high pressure

Acknowledgements

Computational resources have been provided by IDRIS (project 101685). As this study is part of the Diup project, authors acknowledge the support of the French ANR program. The authors are grateful to B. Devincre (LEM-ONERA) for helpful discussions and to two anonymous referees who reviewed this work for useful guidance.