Stress-induced amorphization promotes grain boundary sliding in olivine

Stress-induced amorphization has recently attracted attention as a potential deformation mechanism in ceramics, semi-conductors or minerals. Its activation is promoted when conventional plasticity, e.g. driven by dislocations, is inhibited. However, the mechanisms underlying this phenomenon are still unclear. Based on quantitative in situ TEM tensile testing of small-sized olivine bi-crystals, we demonstrate that stress-induced amorphization and grain boundary sliding can be activated under high stresses at room temperature in specimens with high angle grain boundaries. Low angle grain boundaries are less prone to this phenomenon. Varying the iron content in olivine demonstrates that iron inhibits amorphization and, consequently, promotes brittle failure. This contrast with the accepted view that iron promotes ductility but at high temperatures. These findings coming from natural minerals provide a novel approach regarding the control of the mechanical properties of hard materials at low temperatures.