Effect of Pt and Al content on the long-term, high temperature oxidation behavior and interdiffusion of a Pt-modified aluminide coating deposited on Ni-base superalloys

The present work is devoted to the effect of Al and Pt content on the oxidation behavior and interdiffusion of the industrial NiPtAl coating RT22 deposited on SCB and IN792 Ni-base superalloys. Some specimens of RT22/SCB experienced a defective aluminization resulting in one side with a lower Al content, and some specimens of RT22/IN792 had less platinum than the specification. The effect of both Pt and Al on the initial microstructure of the coating is discussed. Isothermal oxidation tests for 100 h and long-term cyclic oxidation/interdiffusion tests at 1050 °C were performed (up to 51 cycles of 300 h). It is shown that a 50 μm coating with 30 at.% Al instead of a nominal 70 μm coating with 52 at.% Al leads to the full transformation of the β phase after 6 × 300 h at 1050 °C and to the formation of large voids and spinel oxides after 35 × 300 h, but also to less surface undulations than the standard coating. A lower Pt concentration in the RT22 coating results in lower aluminization kinetics and increased spalling and Al consumption during long-term cyclic oxidation without decreasing the isothermal oxidation kinetics.