Effect of nitridation on the oxidation behavior of TiAl-based intermetallic alloys

摘要

In the present work, gas nitridation of the TiAl based alloys in an ammonia atmosphere was carried out at 800,860 and 940 deg C for different time, respectively. The nitride layers were characterized by X-ray diffraction (XRD), electron probe micro-analyzer (EPMA) and scanning electron microscopy (SEM). The composite of the nitride layers (Ti_2AlN as the inner laver and TiN as the outer layer) and the diffusing layer formed on the surface of the TiAl based alloys. The oxidation behavior of the nitrided alloys in air was studied between 800 and 1000 deg C. The scales were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis. Generally an oxide scale consisting of two lavers, an outward- and an inward-growing layer, formed. The outward-growing part of the scale consisted of mainly of TiO_2 (rutile), while the inward-growing part was composed mainly of #alpha#-Al_2O_3. Due to more #alpha#-A1_2O_3 formed in the outward-growing part, the non-nitrided alloys showed better oxidation resistance than the nitrided alloys. On the observation of the EDX measurement, the alloys nitrided at 940 deg C for 50 h grew more #alpha#-A_2O_3 with fine grains on the outer layer of its scale after 100 h exposure time at 1000 deg C. Because at its significant transient oxidation at the initial period, it displayed worse resistance. It is concluded that the high-temperature nitrided alloys exhibit better oxidation resistance at 1000 deg C.