Evolution of microstructure and properties of a novel Ni-based superalloy during stress relief annealing

In this paper, the residual stress reduction, precipitation evolution, and mechanical properties of GH4151 alloy in different annealing temperatures were studied by the scanning electron microscope (SEM), high-resolution transmission electron microscopy (HRTEM), electron backscatter diffraction (EBSD). The results show that annealing treatment can effectively reduce residual stresses. With the increase of annealing temperature from 950 °C to 1150 °C, most of the residual stresses were released from 60.1 MPa to 10.9 MPa, and the corresponding stress relaxation mechanism changed from dislocation slip dominated to both dislocation slip and grain boundary migration. Meanwhile, the annealing treatment promotes the decomposition of the Laves, accompanied by the precipitation of μ-(Mo₆Co₇) starting at 950°C and reaching a maximum value at 1050°C. The tensile strength and plasticity of the annealing alloy at 1150℃ reached the maximum(1394 MPa, 56.1%) which was 131%, 200% fold than that of the as-cast alloy (1060 MPa, 26.6%), but the oxidation process in the alloy is accelerated at 1150℃. The increase in strength and plasticity are mainly attributed to the dissolution of the brittle phase and the morphology and distribution of the γ' phase.