Oxide-scale growth on Cr2AlC ceramic and its consequence for self-healing

Outward growth of oxide scale on Cr2AlC surface during multiple annealing at 1100 °C was investigated with ex situ microscopy. A dense alumina scale was formed on the surface of Cr2AlC samples after annealing for 40 h. A wedge-shaped specimen with varying thickness of oxide scale was prepared by focused ion beam slicing for further annealing. It is concluded that the outward diffusion of Al ions via grain boundaries dominates the growth of oxide scale during repeated annealing. This result is relevant to the self-healing kinetics of exposed cracks in MAX phase ceramics via cyclic heating.