A new surface treatment using shot blast with WO₃ powder has been developed. This has been very effective for improving the cyclic oxidation resistance of TiAl-base alloy in air and in an exhaust gas atmosphere of a diesel engine up to 1223K.

This effect is due to the formation of an Al₂O₃ layer in the oxidation atmosphere. The above layer is supposed to be formed as follows: Since the WO₃ powder is repeatedly shot during the surface treatment, a WO₃ layer adhering to the substrate is formed on the surface. This layer causes the preferential oxidation of aluminum during the early stage of oxidation, resulting in the formation of a sound and continuous Al₂O₃ layer.

The developed surface treatment provides the same oxidation resistance as that of the nickel-base superalloy Inconel 713C up to 1223K, and is applicable for complex-shape parts with as-cast skin surfaces, such as turbocharger wheels. Furthermore, the developed surface treatment is extremely effective for its application to other alloys such as titanium alloys and stainless steels.

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