Mechanical instability of stressed grain boundaries during plastic deformation of zirconium carbide

Grain boundaries are the elementary carriers of mechanical stress and chemical transport in polycrystalline materials. They are responsible for most macroscopic properties of them, particularly the mechanical performance. Most models take into account the ability of grain boundaries to slide each other assuming that surfaces do not suffer any deformation. However, one fact that is normally ignored is the mechanical distortion of flat boundaries under shear stresses. Indeed, such deformation is usually very small to play a significant role on the dynamics of point defects or dislocations. In this work, we will report the presence of a notably mechanical instability of flat boundaries under shear solicitation in zirconium carbide, giving rise to a periodic transversal shift. Such effect is the driving force for dislocation nucleation and annihilation, the main mechanism for high-temperature plasticity in this carbide.