Prediction of microstructural changes in laser impact welding of nickel joints

This work presents a novel 2D finite element (FE) model to investigate the bonding morphology and microstructural evolution during laser impact welding (LIW) of Ni/Ni joints, considering variations in flyer thickness and target impact angle. A key innovation is the introduction of a hydrodynamic plasma pressure model that captures the progressive deformation of the flyer, providing a physically accurate alternative to conventional methods that apply node-concentrated forces or predefined velocities. The model uses equivalent plastic strain (PEEQ), shear stress and critical flyer velocity at the collision point to assess bonding quality and identify welded regions. A user-defined subroutine was developed and implemented in commercial FE software to simulate the metallurgical changes induced by severe plastic deformation during welding. This subroutine incorporates a physically based plasticity model for Nickel 201 to predict dislocation density evolution, a Zener–Hollomon-based formulation for grain refinement and a dislocation-driven hardness model to estimate local mechanical property variations. The numerical results were validated against experimental data, demonstrating the model’s effectiveness in predicting key features such as grain refinement, dislocation density evolution, hardness changes, affected layer depth and overall bond integrity. This integrated and physics-informed modeling strategy provides new insights into the interplay between process parameters and microstructural transformations in LIW. It represents a significant scientific contribution by enabling predictive simulations that support process optimization and enhance understanding of weld quality in nickel-based materials.