Effect of grit-blasting on the competitive growth between θ-Al2O3 and α-Al2O3 during the oxidation of β-(Ni,Pt)Al bond coat systems

Abstract The effect of surface modification by grit-blasting of β-(Ni,Pt)Al bond coats on the growth of α-Al2O3 is here presented. Thermogravimetry tests at 1000°C, 1050°C, 1100°C, and 1150°C were performed on as-aluminized and as-grit-blasted specimens under the same oxygen partial pressure (pO2= 2.1 x 10-1 atm), where the parabolic rate constant (kp) was calculated. The oxide phase fraction was obtained from the fitting of the photo-stimulated luminescence spectroscopy (PSLS) results. A strong dependence between the surface condition of the bond coat and the α-Al2O3 phase formation was observed. The thermally treated grit-blasted samples achieved faster the steady-state (1.6 h) of the thermal growth oxide (TGO), while a treatment 2.7 times longer (4.25 h) was required for the as-aluminized specimens. This result contributes to the general understanding of the effect of the surface condition on the TGO formation during pre-oxidation treatment to promote the growth of the α-Al2O3 phase at low temperature and less time without affecting the lifetime of thermal barrier coating systems.