Brief Paper: Phase-Field Modeling of Grain Evolution and Recrystallization in Friction Stir Processing

Abstract

Abstract In this study, we develop a three-dimensional (3D) phase-field model to simulate and understand the mesoscopic grain evolution during extreme grain deformation and recrystallization in friction stir processing (FSP). FSP is a promising solid-state manufacturing technology. It uses a specially designed rotating tool that is plunged into the surface of a workpiece to generate heat and severe plastic deformation in the material without reaching its melting point. The rotating tool stirs and mixes the material along its path, leading to various microstructural changes and property enhancements. Compared to other manufacturing techniques, such as laser powder bed fusion (L-PBF), FSP produces parts characterized by improved grain refinement and reduced occurrence of defects, such as pores and hot cracks. A characteristic feature of FSP is that the velocity field introduced by the rotating tool displaces and deforms the grains. Our model captures this dynamic process through introducing the advection equation. The result is a comprehensive picture of how grains evolve and rearrange as the FSP tool traverses the material, effectively modeling the material’s microstructure. Another feature of FSP is nucleation and dynamic recrystallization (DRX) due to large grain deformation. These phenomena are simulated in our model, where the evolution of dislocation density is modeled by the Laasraoui Jonas (LJ) model, nucleation is determined by the magnitude of the dislocation energy and DRX grain growth is involved in the phase-field framework. The synergy between these models offers valuable insights into the material’s behavior and microstructural changes. In an endeavor to make these simulations more efficient and practical, the calculation is based on the JAX GPU computing platform. It significantly enhances the computational capacity, enabling a more accurate and detailed representation of grain evolution during FSP. Furthermore, this computational approach extends to the modeling of grain evolution in another manufacturing process, L-PBF, thereby allowing for a comparative analysis of grain morphology and the underlying physical mechanisms in both FSP and L-PBF. By conducting this comparative analysis, the study uncovers the distinguishing features and performance of FSP and L-PBF. It elucidates how the grain morphology differs between the two processes. This knowledge is invaluable for the manufacturing industry, as it enables engineers and scientists to make informed decisions about which process to employ for specific applications based on their unique requirements and desired material properties.