Effect of atmosphere on microwave heating of titanium powder

Microwave irradiation was performed using compacted Ti powder in three types of atmosphere, namely, Ar gas, N(2) gas and air. The temperature increased slightly in the early stage of microwave irradiation and then remained almost unchanged. Thereafter, abrupt temperature rise and drop occurred. The temperature then remained almost unchanged in the late stage of microwave irradiation. The time from which the abrupt temperature rise and drop occurred was varied by the atmosphere. The maximum temperature in microwave irradiation in Ar gas was near the melting point of Ti, while those in N(2) gas and air were beyond this melting point. Although a TiO(2) layer was formed near the upper surface of the compacted powder after microwave irradiation, alpha-TiN and TiN were produced in its interior. The microwave heating behaviour and microstructure of the compacted powder after microwave irradiation depended on the atmosphere and the amount of air contamination in it.