Effect of Ta on Tensile Behavior and Deformation Mechanism of a Nickel-Based Single Crystal Superalloy

The effects of Ta on the tensile behavior and deformation mechanisms of a Ni-based single crystal superalloy were investigated in this study from room temperature to elevated temperature. The findings demonstrated that the higher content of Ta could improve the tensile properties of the alloy at different temperatures. Due to the different deformation mechanisms at various temperatures, the influence of Ta on tensile deformation varied. At room temperature, the higher content of Ta enhanced the solid solution strengthening, which would enhance the tensile strength of 6.5Ta alloy. After standard heat treatment of 6.5Ta alloy, precipitation of the secondary γʹ phase would hinder the movement of dislocations. When the temperature was elevated to 760 °C, the higher content of Ta not only promoted the interaction of stacking faults to form Lomer–Cottrell (L-C) locks that impeded dislocation motion, but also reduced the occurrence of dislocation pile-up groups, thus enhancing the yield strength. At 1120 °C, due to the narrower γ channels and higher APB energy in γʹ phase of the alloy with higher Ta addition, the processes of bypassing and shearing of dislocations were hindered, respectively. Meanwhile, the denser and more regular dislocation networks were formed in 6.5Ta alloy; and thus, the tensile strength of 6.5Ta alloy was enhanced. This study systematically investigated the effect of Ta on the tensile behavior at three different temperatures, which provided an important theoretical basis for the design of nickel-based single crystal superalloys in the future.