Entire-servicing-temperature tensile behaviors of a Re-free Ni-based single crystal superalloy with balanced ductility and strength at intermediate temperature

Abstract

To reduce the use of Re in single crystal (SX) superalloys, a low-cost Re-free SX superalloy has been developed in this work, and its tensile behaviors under entire-service-temperature conditions were delved in detail. According to the tensile test results, the yield strength (YS) of the experimental alloy exceeds the average level of 2nd-generation SX superalloys. Particularly, the YS and elongation of the experimental alloy at 760 °C is 1292 MPa and 16.9 %, respectively, showing a synergistic improvement in strength and ductility at intermediate temperature. By TEM characterization, stacking faults (SFs) expanding within γ' phase and penetrating γ/γ' phases are believed to improve the ductility, while dislocations cross-slipping and SFs interactions in γ' phase play a key role in improving YS and work hardening. At high temperatures, dislocations can climb over the degraded γ' phase with the help of thermal activation. Moreover, dislocation pairs dragging by APBs replace SFs in γ' phase under lower APB energy. As plentiful dislocations cut into γ' phase, the flow stress decreases with plastic accumulation. Overall, the strength-ductility equilibrium depends on the competition among various dislocation configurations and their interactions with γ/γ' phases. The findings from this work are helpful to provide mechanistic guidelines to design novel low-cost SX superalloys.