VISCOPLASTIC PHASE FIELD MODELLLING OF RAFTING IN NI BASE SUPERALLOYS

摘要

The mechanical behaviour of Ni-base superalloys depends largely on the microstructure at mesoscale. Initially, the alloy consists in cuboid precipitates separated by channels of matrix. When such a material is submitted to a creep loading at high temperature (around 1000 ℃), we observe a directional coalescence of the γ' precipitates often called rafting. The aim of this study is to propose a Phase Field model to represent in a quantitative way the change in morphology in superalloys. The misfit stresses as well as the anisotropy and inhomogeneity of elastic constants between matrix and precipitates are taken into account. Moreover several authors have pointed out the role of the plastic strain in the matrix which enables relaxation of misfit stresses between the two phases during rafting. Thus plasticity in the γ phase is introduced by the means of a viscoplastic law coupled with the Phase Field model.