A comparison of the growth kinetics and scale morphology for three superalloys at 930°C in air and low PO2 environments

This study assessed the oxidation behavior of three commercial alloys in air and low partial pressures of oxygen (P-O2). The kinetics of oxidation in air were compared with values obtained in an atmosphere of low P-O2. The low partial pressure of oxygen was of the order of 10(-16) atm at 930 degrees C and was generated using an H-2/4% H2O mixture. The nature of the corrosion products, structure, morphology, and composition were assessed and characterised using scanning electron microscopy (SEM), X-ray mapping and scanning Auger microscopy (SAM). The results were compared with those obtained for 99.99% pure chromium. Parabolic kinetics were Exhibited by all of the alloys, with the overall k(p) values being of the order constant for chromia-forming alloys. Large variations in the morphologies of the oxide scales were observed as a result of oxidation in the high and low P-O2 environments.