Microstructure evolution of polycrystalline Ti2AlN MAX phase film during post-deposition annealing

Polycrystalline Ti2AlN MAX phase films were fabricated by post-deposition annealing of Ti-Al-N film at annealing temperature in the range of 600 °C-800 °C in high vacuum. The temperature-dependent microstructure evolution from Ti-Al-N film to polycrystalline Ti2AlN film has been investigated. It was found that after post-deposition annealing above 600 °C, the as-deposited amorphous Ti-Al-N film transformed to polycrystalline Ti2AlN film. With the increase of annealing temperature from 600 °C to 700 °C, the crystallinity of polycrystalline Ti2AlN film was improved. At 800 °C, the surface Ti2AlN grains completely decomposed and transformed to TiN phase while inner grains was partial decomposed and surrounded by amorphous Al-rich phase. The polycrystalline Ti2AlN film exhibited a highest hardness of 34.1 GPa while the hardness of amorphous Ti-Al-N film was only 24.2 GPa. The mechanism of texture changes and phase transformation as well as its effect on thermal stability was also discussed.