Effect of pre-tensile treatments on the mechanical properties and deformation mechanism of a novel Ni-based superalloy

Abstract

Stacking fault energy can be reduced by adding Co to Ni-based superalloys. In this work, a novel Ni-based superalloy was developed with 20 wt% Co content to reduce the stacking fault energy. After pre-tensile treatments, the alloy formed substructures with numerous dislocations, slip bands, and stacking faults. When the deformation reached 6%, stacking faults in different directions intersected, forming Lomer-Cottrell locks (L-C locks) at the intersections. Mechanical properties were tested at 760 °C. Compared to the standard heat-treated alloy, the yield strength of the alloy with 3% pre-tensile deformation increased by 16.2%, while the stress rupture life maintained 64.2% at 760 °C/480 MPa. The yield strength of the alloy with 6% pre-tensile deformation increased by 29.8%, and the stress rupture life maintained 74.1% at 760 °C/480 MPa. During the tensile process, the densities of stacking faults and deformation twins in the pre-tensile alloys increased, leading to increased hindrance to dislocations and consequently an increase in yield strength. The grain boundaries of the pre-tensile alloy have high dislocation density, and the dislocation recovery and recrystallization softening mechanism occurred during the stress rupture process, resulting in a lower stress rupture life than that of standard heat-treated alloy. As the deformation was increased to 6%, the simultaneous presence of M23C6 and stacking faults enhanced the pinning of dislocations and grain boundaries, improving the stress rupture life of the pre-tensile alloy.