First Stages of Oxidation of Pt-Modified Nickel Aluminide Bond Coat Systems at Low Oxygen Partial Pressure.

The θ-AlO → α-AlO phase transformation was investigated in thermally grown oxide formed on β-(Ni,Pt)Al bond coats during isothermal exposures at 900-1,200 °C in an argon atmosphere stream with the O partial pressure of 1 × 10 atm. Local curve fitting was used to evaluate the evolution of the parabolic rate constant, k, using a general kinetic model ( t = A + BΔ m + CΔ m), during the first 5 h of oxidation. All net mass-gain curves exhibited deviations from the classic parabolic model, Δ m = k t; a steady state regime was established only after 4 h of exposures, except for the sample oxidized at 1,100 °C. [ABSTRACT FROM AUTHOR]