Properties of titanmm-aluminide layer formed by low pressure plasma spraying

TiAl alloyed powder was sprayed onto a substrate surface by the low pressure plasma spraying (LPPS) process. The microstructure and properties of sprayed TiAl layers were examined and compared with those of a TiAl bulk plate. As-sprayed TiAl layer consisted of γ fine grains whose average grain size was 90 nm including a small amount of α2. The sprayed layer had a hardness value of 589 Hv at room temperature and above 400 Hv even at 1073 K. Although the hardness value dropped to 225 Hv at 1173 K, it was still comparable to that of a TiAl bulk plate at room temperature. The microstructure and mechanical properties of the sprayed TiAl layers changed only slightly when exposed to a high temperature of up to 973 K for 48 h. Although the hardness values of sprayed TiAl layers decreased to 350 Hv when annealed at 1273 K for 24 h and more because of the occurrence of grain growth, the hardness values were significantly higher than that of a TiAl bulk plate. Tensile strength above 400 MPa, which was almost equal to that of a TiAl bulk plate, was obtained for sprayed TiAl layers both in as-sprayed and annealed (at 1273 K for 24 h) conditions. Therefore, sprayed TiAl layers were found to be a feasible hardfacing layer at elevated temperatures.