A Damage Mechanics Model for Creep and Oxygen Embrittlement in Metals

This paper first describes a creep damage mechanics model that shows a marked performance for both steady-state creep and tertiary creep, as evidenced by comparisons with creep test results for two metallic materials. Then, using the creep damage mechanics model as a foundation, a framework is presented for treating the phenomenon of stress-accelerated grain-boundary oxygen embrittlement (SAGBO) in metals (e.g. superalloys) at elevated temperatures and under oxidizing environments. This framework establishes a combined creep and oxygen embrittlement damage model that incorporates the effect of oxygen diffusion along grain boundaries and oxidation-accelerated cavitation. The damage model has been applied to round-bar creep tests of a steel alloy that exhibits the SAGBO phenomenon. Predictions of the creep curve in air and its dependence on the bar size have been obtained based on a simplified analysis of the tests. Comparisons between model predictions and test results show that the model can capture the essential features of the SAGBO phenomenon and can adequately describe the creep and oxygen embrittlement behavior of metals such as superalloys.