Microstructural Degradation and Tensile Properties of K465 Equiaxed-cast Superalloy After Short-time Overheating

Abstract

Turbine blades of aircraft engines may suffer serious degradation caused by overheating service exposures. In this paper, microstructure characteristics and tensile properties of K465 alloy, which is an equiaxed cast superalloy and widely used in turbine blades and vanes, were investigated after overheating treatment at 1180~1270℃. The microstructure before and after overheating was also examined and quantitatively characterized using SEM, XRD and physicochemical phase analysis. The relationship between microstructural degradation after overheating and tensile properties was investigated. The results indicate that primary γ' phase, carbides and grain boundaries are gradually dissolved in K465 alloy with increasing the overheating temperature; γ' phase distributed in the interdendritic region has a higher dissolution temperature than that in the dendrite core region due to a higher content of γ' phase forming elements. Incipient melting mainly occurs at the residual eutectic region and grain boundaries at 1270℃. The tensile properties are decreased significantly with increasing the overheating temperature, the yield strength was 439MPa at 1000℃ and dramatically decreased to 85MPa and 26MPa at 1180℃ and 1240℃, respectively. The tensile properties are mainly influenced by the dissolution behaviors of primary γ' phase and γ' film along grain boundaries as well as the influence of incipient melting.

Keywords

• K465 alloy
• turbine blade
• overheating
• microstructure
• tensile property