Investigation of mechanical behaviour of amorphous aluminium nitride

Ultrahard ceramics have high mechanical strength, but their brittle nature often restricts their practical applications. Using molecular dynamics (MD) simulations, we investigated the mechanical properties of crystalline and amorphous aluminium nitride (a-AlN) under different loading modes. Decreased strength but improved ductility are observed in a-AlN as compared to its crystalline counterpart. We notice the failure mechanisms are very different in crystalline and amorphous AlN. At atomic scale, a self-repairing mechanism is observed, caused by repeated bond break and recovery among under-coordinated atoms in the a-AlN. Crystallization is also observed in the a-AlN during loading, contributing to the tension-compression asymmetry. It is interesting to note that the yield in a-AlN can be well described using Drucker-Prager type criterion.