Formation and oxidation behavior of Ni2Al3 coating on heat-resistant Ti-alloy

A nickel aluminide coating process, developed on heat resistant Ti alloy by electroplating a Ni film followed by high Al activity pack cementation, forms a duplex layer structure, an outer Ni2Al3 layer and an inner TiAl3/TiAl2/TiNiAl2 layer. The coated Ti-alloy was oxidized in air for up to 3,600 ks (1,000 h) under thermal cycling between room temperature and 1023 K. A protective Al2O3 scale formed with little oxide exfoliation and the oxidation amount was 6 g/m2 after the 3,600 ks oxidation. It was found that after 3,600 ks oxidation at 1023 K the coating layer structure was essentially unchanged, similar to the as-formed, except that the TiAl3 layer had changed to TiAl2.