Oxidation damage zone formed in creep fatigue crack growth of GH4169 alloy at 650 °C

In the creep fatigue crack growth of GH4169 alloy, oxidation is a prominent damage source, which is mainly manifested as the oxidation damage zone in front of crack tip. In order to investigate the property of the oxidation damage zone formed in the creep fatigue crack growth, crack growth tests of directly aged GH4169 alloy were conducted at 650 °C in air under various load conditions. Interrupted tests were performed to observe the damage characteristics at crack tip. Block tests were systematically executed to quantify the dependency of oxidation damage zone size on load and holding time. The crack propagation of the GH4169 alloy has a close relationship with grain boundary oxidation at 650 °C. An oxidation damage zone in front of crack tip includes intergranular microcracks and oxidised but uncracked grain boundaries. Its size has been calculated from transient crack growth rate and described as a function of maximum stress intensity factor and holding time. Based on oxidation damage zone size, a novel model has been developed to predict the creep fatigue crack growth rate of the GH4169 alloy at 650 °C.