Microstructure and tensile behavior of Ni-Cr-W base superalloys at elevated temperatures

The microstructure and the tensile deformation behavior between 200°C and 900°C of solution strengthened Ni-Cr-W base superalloy were studied by OM, SEM, TEM and a high temperature tensile testing machine. The results show that there are only two phases of γ and M₆C in the matrix. Lots of stacking faults are formed in the superalloy microstructure. With the increasing temperature, ultimate tensile strength and yield strength decrease slowly when the temperature is below 650°C. When the temperature is above 650°C, ultimate tensile strength decrease rapidly and yield strength almost keep invariable. The elongation and reduction in cross-section of the superalloy change little below 650°C, but both of them increase rapidly when the temperature is higher than 650°C. Serration stress-strain curves are induced by mechanical twins mechanism in the temperature range of 400~700°C. The fracture is of ductile dimple fracture mode. The cracks are initiated mainly in the interface between γ and M₆C.