Phase-field simulation of microstructure evolution during friction stir welding of 304 stainless steel

Abstract

Dynamic recrystallization (DRX) is the most significant metallurgical phenomenon during friction stir welding (FSW) and friction stir processing (FSP). In order to simulate the microstructure evolution during FSW, the phase-field method was applied. For this purpose, the growth and shrinkage of a nucleus in the matrix of a grain using the DRX mechanism models was simulated using the phase-field method. In order to have suitable parameters for microstructure modeling, the finite element method (FEM) was used for numerical simulation of the FSW process, including thermal, computational fluid dynamics (CFD) and mechanical simulations. The phase-field simulation of DRX microstructure evolution was performed based on the FEM results. The simulation results were validated by being compared to the experimental findings reported by other researches. It was found that the rotating speed plays a significant role in the formation of the final microstructure in the process. Grain size distribution is nearly interdependent of the nucleation rate, growth and therefore, recrystallized fraction areas. Grain boundary fraction was also predicted by post-processing of the simulation results. It was also found that the rotating speed affecting the nucleation and growth rate significantly affected the grain boundary fraction in FSW process.