Morphological evolution and dissolution mechanisms of ?? phase in a novel HIPed P/M superalloy in hot deformation process

Isothermal compressive tests of a new hot isostatic pressed (HIPed) powder metallurgy (P/M) superalloy are performed at diverse deformation amounts, strain rates, and elevated temperatures. The impacts of hot com-pression parameters on the morphological evolution and dissolution behavior of gamma' phase are studied. Results show that the morphology of gamma ' phase changes from the various initial shapes (irregular, split-off branch, dendrite, butterfly-like, and cauliflower) to spherical, due to the overlap of the gamma'/gamma interface energy and the coherent strain energy related to lattice misfit. Besides, the dislocation accumulation leads to the increased local stress and en-hances the spheroidization behavior of gamma' phase. Increasing temperature/true strain or decreasing strain rate, the dynamic dissolution behavior of gamma' phase is obvious. It is because the dislocation/ vacancies-assisted element diffusion is rapid at high deformation temperatures/true strains, and the low strain rate can provide the enough time for element diffusion. The substantial dissolution of gamma' phase at 1140 degrees C and 1170 degrees C is also related to the deformation temperature approaching and exceeding the gamma' solvus temperature (1150 degrees C), respectively. Additionally, the decreased fraction of gamma' phase is also related to the high gamma'/gamma interfacial energy. To quantitatively describe the dissolution behavior of gamma ' phase, a dynamic dissolution kinetics model is proposed, and the corre-lation coefficient between the predicted and experimental values is 0.990. It indicates that the proposed model can precisely depict the dissolution behavior of gamma ' phase. The findings in this work can provide the theoretical guidance to optimize deformation parameters, as well as control the morphology and fraction of gamma ' phases.(c) 2023 Elsevier B.V. All rights reserved.