New surface treatment using shot blast for improving oxidation resistance of TiAl-base alloys

A new surface treatment using shot blasts with WO3 powder has been developed. This has been most effective in improving the cyclic oxidation resistance of TiAl-base alloy in air and in a diesel engine exhaust gas atmosphere of up to 1223 K. This effect is attributed to the formation of an Al2O3 layer in an oxidation atmosphere. The above layer is supposed to be formed as follows: Since the WO3 powder is shot repeatedly during the surface treatment, a WO3 layer adhering to the substrate is formed on the surface. This layer causes the preferential oxidation of aluminum at the early stage of oxidation, resulting in the formation of a sound and continuous Al2O3 layer. The developed surface treatment gives the same oxidation resistance as that of nickel-base superalloy Inconel 713C up to 1223 K, and is applicable to complex-shape parts with as-cast skin surfaces, such as turbocharger wheels.