Effect of Ta Addition on the Microstructure and Tensile Properties of a Ni-Co Base Superalloy

Herein, the effect of Ta addition (0 and 2 wt pct) on the tensile properties of a Ni-Co base superalloy was investigated in the temperature range of 23–900 °C. The results revealed that the addition of Ta improved the strength of the superalloy at all experimental temperatures and increased the plasticity at 760 °C. In addition, the microstructural observations indicate that Ta addition promoted the precipitation of γ ′ precipitates, as well as the precipitation of (Ta, Ti)-rich MC carbides. The addition of 2 wt pct Ta promoted twinning and, thus, transformed the fracture mechanism of the alloy from an intergranular brittle fracture to a mixed ductile and brittle fracture at 760 °C. Furthermore, the tensile properties and the related microstructures, deformation mechanisms, and fracture mechanisms of the experimental alloys are discussed. Finally, we demonstrated that the combined effect of the increase in the grain boundary strength, the reduction in the critical resolved shear stress, and the promotion of twinning induced the synchronous improvement of strength and plasticity of the alloy at 760 °C.