High Temperature Fatigue Failure Behavior of Alloy718 Superalloy Coated with WC-12Co Alloy by HVOF Thermal Spraying

In order to explore a potential ability of WC-12Co coating for high temperature application, the mechanical properties and high cycle fatigue property of the HVOF sprayed Alloy718 were investigated at high temperature. It was found that the microstructure and Vickers hardness of WC-12Co coating were significantly changed and decreased during the thermal exposure at 650°C associating with progressings of oxidation and carbonization, while they were not significant in case of thermal exposure at 480°C even after 100hrs. The high cycle fatigue (HCF) tests indicated that the life of the coated specimen was almost comparable to that of the bare specimen at 480°C, while the life degradation of coated specimen was pronounced at 650°C. The delamination and the spallatoin of coating layer were seen at early stage of fatigue loading at 650°C. It was suggested that the HCF life degradation at 650°C for coated specimen was attributed to the stress concentration on the roughened substrate surface which was promoted by the blast process and was exposed by the spallation of coating layer.