Effect of Cr on the oxidation behaviour of polycrystalline nickel based superalloys

Isothermal oxidation behaviour of two nickel base superalloys with different Cr contents was investigated in the temperature range of 700–800 °C. Weight–change curves show that weight loss increases with increasing temperature and a relatively lower Cr ratio corresponds to slow weight gain rate. Microscopic observations uncover that oxidation penetration attacks the alloys primarily along grain boundary especially for the lower-Cr alloy, and the penetration depth is strongly dependent on the oxidation temperature. The underlying oxidation mechanisms of the two alloys are explained using energy-dispersive x-ray spectroscopy and X-ray photoelectron spectroscopy.