A mechanism for stress-aided grain boundary oxidation ahead of cracks

A comparison of literature data indicates that intergranular oxide intrusions formed in the nickel-based superalloy RR1000 ahead of stationary cracks grow at a rate higher than that observed on flat surfaces. This is attributed to the effect on vacancy equilibria of the tensile stress that exists at the tip of the intrusion. A stress-aided oxidation rate parameter is defined that is stress dependent and varies with the nature of the oxide. The threshold condition for crack advance is also discussed.