TiAlの酸化特性に及ぼす窒素イオン注入の影響

抄録

TiAl was implanted with nitrogen and its effect on cyclic oxidation behavior of TiAl has been investigated in purified oxygen at 1200 K and in static air at 1100 K. The nitrogen implantation was carried out at room temperature, 973 K or 1173 K. The acceleration voltage was 50 kV and the ion dose was 10²⁰ m^-2 or 10²¹ m^-2. For the specimen implanted with nitrogen at room temperature with a dose of 10²¹ m^-2, the nitrogen distributed into the depth of about 200 nm with a maximum concentration at about 120 nm, and the concentration changed gradually in the penetration depth. The implantation of nitrogen resulted in the formation of Ti₂AlN. The amount of the nitride was larger for the implantation carried out at room temperature than that at 973 K or 1173 K because of the nitrogen diffusion into the matrix during high temperature implantation. The nitrogen implantation deteriorates the oxidation behavior of TiAl in oxygen due to enhanced scale spallation, while the cyclic oxidation behavior of the nitrogen-implanted specimen in air was comparable to that of TiAl without implantation. From the specimen oxidized in oxygen for a very short period, small amount of Ti₂N was detected along with TiO₂ by X-ray diffraction, indicating that the nitride formed by implantation is not stable during oxidation. The scale formed on the specimen oxidized in oxygen had thick outer layer of TiO₂ and stratified inner layer with micro pores. This scale structure seems to be responsible for the lower scale strength. The present results suggest that nitride layer formed by implantation is not continuous thus ineffective for improvement of the oxidation resistance of TiAl.