Formation of eutectic (γ′ + α) and α transformation in Ta-bearing high W content cast Ni-base superalloys

The microstructures of as-cast and heat treated specimens and stress rupture properties for Ta-bearing high W content cast Ni-base superalloys were investigated. The results indicate that Ta promotes the formation of eutectic (γ′ + α) in late solidification. The α phase is unstable during heating above 1260 °C and long term exposure at 1100 °C, and can transform to M6C carbides. To avoid the α phase formation, it is necessary to modify the compositions of alloys by following the principle of substitution of Ta for Al at equal atomic ratio.