Investigation of the role of silicon in TiAlSiN coating deposited on TiAl alloys during long-term oxidation

One challenge for TiAl alloys to serve above 800 ℃ is insufficient oxidation resistance. In this article, long-term oxidation of TiAlSiN coated Ti-45Al-2Nb-2Mn, Ti-48Al-2Cr-2Nb and Ti-50Al were investigated at 900 ℃. The results showed Al2O3 top layer in oxide scale which formed during earlier stage of oxidation kept protective during long-term oxidation. Presence of SiO2 layer at oxide/coating interface and segregations of SiO2 at grain boundaries were observed. Oxygen inner diffusion and titanium outer diffusion was inhibited and coating exhibited excellent oxidation resistance. Stable Ti5Si3 diffusion barrier layer formed at TiAlSiN/TiAl interface due to Si inward diffusion helped coating maintaining long-term stability.