Studies of the influence of surface pre-treatment on the integrity of alumina scales on MA 956

Quasi-isothermal and cyclic oxidation experiments at 1100 °C in air have been performed on a oxide dispersion strengthened (ODS) alloy MA 956 in order to investigate the effects of prior surface treatments on the integrity of the alumina scales formed. Three surface conditions: (i) as received with pre-oxidised and Al2O3 grit blasted, (ii) 800 grit SiC ground surface, and (iii) lathe turned surface—have been studied. Effects of these surface treatments on the growth kinetics of the scales, their morphologies, defect structures and spallation behaviour have been investigated for exposure times up to 5000 h (quasi-isothermal) and 3500 h (cyclic). The scale failure mechanisms involved have been identified and modelled. Good scale/substrate adhesion was observed for both flat and concave surfaces. Scale spallation occurred by a buckling mechanism. For the lath turned samples finite element (FE) modelling allowed the development of a predictive methodology for scale failure.