High-fidelity level-set modeling of diffusive solid-state phase transformations for polycrystalline materials

TL;DR

The paper presents a generalized global level-set framework to model diffusive solid-state phase transformations in multiphase polycrystalline materials under complex thermomechanical processing. It combines a diffuse-interface level-set approach with a coupled diffusion equation for solute partitioning, solute-drag effects, and interface kinetics, all embedded within a ThermoCalc data-driven driving-pressure description. Key contributions include a robust coupling strategy to ThermoCalc, a flexible nucleation model with site selection and shielding, and a unified treatment of solute redistribution and interface migration across multiple phases, validated against sharp-interface and phase-field benchmarks and demonstrated on large-scale 2D microstructures and ternary alloys. The framework also demonstrates applicability to other diffusive phenomena such as particle coarsening, illustrating its versatility for industrially relevant multiphase microstructures and enabling future 3D extensions and experimental validation.

Abstract

The formation of microstructures in metallic alloys during hot metal forming involves simultaneous metallurgical complex phenomena. Traditional high-fidelity numerical frameworks used on the polycrystalline scale tend to focus on single-phase microstructures or isolate phase transformations from grain boundary migration mechanisms. The level-set method is highlighted as effective in proposing a global framework for modeling multiphase polycrystalline materials and diffusive solid-state phase transformations. This framework includes novel techniques for efficient large-scale microstructural representation, strong coupling with ThermoCalc software for real-time thermodynamic data, application for ternary alloys and beyond by taking solute drag aspects, and the use of advanced nucleation models. Numerous applications are then illustrated.

Figures (36)

• Figure 1: Biphasic microstructure indicating the underlying the level-set representation
• Figure 2: General overview of the ThermoCalc coupling with the numerical model
• Figure 3: Illustration of spherical nuclei of $\alpha$ phase (blue) nucleating in a 2D parent $\gamma$ phase
• Figure 4: Characterization of computational nodes for grain boundary nucleation in a 2D context
• Figure 5: Characterization of nucleation sites for grain corner nucleation: eligible nodes (green), shielded ineligible nodes (red)