The effect of environment on mechanical properties of coated and uncoated alloys

Combined creep and corrosion testing, as well as creep testing of pre-oxidized specimens has been used to assess the effect of oxidation on alloy creep strength. Exposure in wet air for up to 1500 h at 650°C for alloy T92 resulted in the formation of a 80 μm thick oxide scale that did not affect the alloy creep resistance. Alloy 230 creep properties were also only slightly affected by pre oxidation for 2000 h in steam at 800°C. Application of an aluminide coating protected the alloy from oxidation but decreased the substrate mechanical properties because of the weak coating mechanical properties. Stress was found to have an effect on the Fe-rich oxide grown on alloy T92 during oxidation in wet air by promoting cracking of the scale. However, no effect of the creep deformation was observed on the aluminide coating integrity. In-situ steam testing is necessary to provide relevant data for lifetime models of in-service components.