Microstructure and Tensile Behavior of Ni-Cr-W Base Superalloys at Elevated Temperatures

Abstract:

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

Key words:Ni-Cr-W base superalloy; microstructure; fracture; mechanical twins; tensile properties