HIGH-TEMPERATURE GAS NITRIDATION OF TiAl BASED ALLOYS

The nitridation process of TiAl based alloys in an atmosphere of purified ammonia has been investigated. The nitridation temperature range is between 800 ℃and 940℃ and the major emphasis is at 940 ℃. X-ray diffraction and electron probe analysis show that the formed nitride scale consists of two layers, an outward-growing and an inward-growing layer. The outward-growing part of the scale consists mainly of TiN, while the inward-growing part is composed of Ti2AlN. The hardness and wear resistance of the nitrided alloys are improved and at 940 ℃ nitridation, Knoop hardness value of TiAl based alloys can reach 1286 kg/mm2.