Effect of aluminium concentration on phase formation and radiation stability of Cr2Al x C thin film

Near-stoichiometric and under-stoichiometric Cr2Al x C (x = 0.9 and 0.75) amorphous compositions were deposited onto a silicon substrate at 330 K in a layer-by-layer fashion using magnetron sputtering from elemental targets. The film thickness was 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 focused ion beam milling. Near-stoichiometric Cr2AlC thin films consisted of nano MAX phase after crystallization at 873 K. Under-stoichiometric Cr2Al x C (x = 0.75) thin films contained MAX phase along with nanocrystalline chromium aluminides after crystallization at 973 K. Irradiations with 320 keV xenon ions was performed at 623 K using a TEM with an in-situ ion irradiation (MIAMI) facility. Nanocrystalline films of near-stoichiometric Cr2AlC irradiated up to 83 displacements per atom (dpa) showed no observable changes. Also, irradiation of under-stoichiometric nanocrystalline thin films up to 138 dpa did not show any observable amorphization, and recrystallization was observed. This radiation resistance of near- and under-stoichiometric thin films is attributed to the known self-healing property of Cr2Al x C compositions further enhanced by nanocrystallinity.