Effect of aluminium concentration on phase formation and radiation stability of Cr2AlxC thin film

Near stoichiometric and under stochiometric Cr2AlxC (x=0.9 and 0.75) amorphous compositions were deposited onto silicon substrate at 330 K in a layer-by-layer fashion using magnetron sputtering from elemental targets. The film thickness found to be 0.9 μm and 1.2 μm for the near and under stoichiometric compositions respectively. A transmission Electron Microscope (TEM) heating holder was used to heat thin sample lamellae prepared using focussed ion beam milling. Near stoichiometric Cr2AlC thin films consisted of nano MAX phase after crystallisation at 873 K. Under stoichiometric Cr2AlxC (x=0.75) thin films contained MAX phase along with nanocrystalline chromium aluminides after crystallisation at 973 K. Ion irradiations with 320 keV xenon ions were performed at 623 K using a TEM with in-situ ion irradiation (MIAMI) facility. Near stoichiometric Cr2AlC nanocrystalline films irradiated up to 83 displacements per atom (dpa) showed no observable changes. Also, irradiations of under stoichiometric nanocrystalline thin films up to 138 dpa did not show any observable amorphisation and recrystallization was observed. This radiation resistance of near and under stoichiometric thin films is attributed to the known self-healing property of Cr2AlxC compositions further enhanced by nanocrystallinity.