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.