Kinetic Study of the Competitive Growth Between θ-Al2O3 and α-Al2O3 During the Early Stages of Oxidation of β-(Ni,Pt)Al Bond Coat Systems: Effects of Low Oxygen Partial Pressure and Temperature

An oxidation study of β-(Ni,Pt)Al commercial bond coat systems was carried by means of TGA analysis during isothermal treatments at temperatures from 1273 K to 1423 K (1000 °C to 1150 °C). The effect of oxygen partial pressure on their oxidation kinetics was studied and complemented by photo-stimulated luminescence spectroscopy and SEM. Pre-oxidation treatments performed on as-aluminized samples at 10−5 atm O2 did not accelerate the θ-Al2O3 → α-Al2O3 transformation, even after 5 hours of oxidation relative to samples oxidized in 0.21 atm O2, with the exception of the sample treated at 1273 K (1000 °C), where apparently α-Al2O3 nucleation started earlier for the sample treated at a low pO2.