Microstructure, wear and high temperature oxidation resistance of nitrided TiAl based alloys

Gas nitridation of the TiAl based alloys in ammonia atmosphere was investigated in the present work. The scales of the nitrided alloys were characterized by X-ray diffraction (XRD) and electron probe microanalysis (EPMA). The evaluation of the surface hardness, wear and high-temperature oxidation resistance of the nitrided TiAl alloy was performed to compare with those of non-nitrided alloys. The results showed that the nitrided films composed of Ti2AlN as the inner layer and TiN as the outer layer on the surface of the alloys. Mechanical tests showed that the nitridation could obviously increase the surface hardness and the sliding wear resistance of the TiAl alloys. However, owing to the limited thermodynamical stability of the nitrides at high temperature in air, nitridation prior to the oxidation increased the high temperature oxidation rates of the TiAl alloys.