Isothermal and Cyclic Oxidation of Chromia Forming Nickel-Based Superalloys

Three chromia-forming Ni-based superalloys, Astroloy, Udimet 720, and Waspaloy were oxidized in air isothermally between 750 and 1000 C and cyclically at 1000 C. In isothermal tests the oxidation rate of Udimet 720 was higher than Waspaloy and Astroloy. The higher titanium concentration in Udimet 720 resulted in higher weight gains due to greater formation of TiO2 above the chromia scale. The higher aluminum concentration in Astroloy allowed greater formation of internal oxides of alumina, which reduced the scale growth rate. Waspaloy showed a greater oxidation rate along grain boundaries forming oxide ridges and internal oxides. During cyclic tests weight loss occurred before 100 cycles but the rate of weight loss decreased and was followed by weight gain, with the best performance shown by Waspaloy. (Author)