Effect of torsional deformation and subsequent annealing treatment on mechanical property and microstructure of MP35N superalloy

The torsional deformation and annealing treatment were carried out to regulate the microstructure and mechanical properties of MP35N alloy. In addition, the microscale mechanisms related to the mechanical behaviors were investigated. The results show that the gradient dislocation density is introduced along the radial direction during the torsional deformation. Apart from that, it can be seen clearly that not only the grains are refined but also a great number of stacking faults are induced at the surface region where the strain is maximum. The introduction of gradient structure significantly enhances the strength of sample after torsional deformation up to approximately 767 MPa, and remains considerate uniform elongation about 40% simultaneously. Subsequent annealing treatment makes no difference to the gradient structure including gradient dislocation density and grain size that were introduced during the torsional deformation. However, annealing treatment gives rise to the annihilation of a portion of dislocations in the alloy and leads to a microstructural transformation from stacking faults to nanotwins at the surface region. Considering the formation of nanotwins resulted from annealing treatment and the impact of Suzuki effect, there is a secondary-stage hardening that can partly offset the softening due to dislocation annihilation. It has been estimated that the strength provided by the secondary-stage hardening is around 76 MPa. © 2023 Central South University of Technology. All rights reserved.