Diffusion coating of a TiAl alloy using Al3Ti-based powders

To improve the oxidation resistance of a TiAl alloy, diffusion coating using Al3Ti-based powders was developed. In this technique, the coating powder was melted by heating at temperatures above the melting point without using activators such as ammonium chloride. The coating powder of Ti-75 at%Al which consisted of D0(22)-Al3Ti phase and those of Ti-65 atY6 Al-10at%Cr and Ti-60 at%Al-15 at%Cr which consisted of L1(2)-(Al,Cr)(3)Ti phase were prepared. The effect of the addition of alumina powder was also investigated. When the alumina powder was not added, all used powder adhered to the substrate and coating layer of more than 1 mm in thickness was obtained, but there were many pores larger than 100 pm. When the alumina powder was added to 20% in weight, the extra powder was readily exfoliated by scratching and the coating layer of about 20similar to60 mum in thickness was uniformly formed on the substrate surface. The thickness of the coating layer was significantly affected by the heating temperature and increased by heating at temperature of the vicinity of the melting point.