Numerical and Experimental Validation of Microstructural Alterations and Hardness Variation During Laser Impact Welding for Ni/Ni Joining

This study develops a novel 2D Lagrangian finite element (FE) model for laser impact welding (LIW) of Ni/Ni joints, incorporating a hydrodynamic plasma pressure model to simulate realistic loading conditions during flyer deformation. Unlike conventional approaches applying force or velocity boundary conditions, this method enables accurate prediction of bonding morphology and metallurgical evolution. A user-defined subroutine implements a physically based plasticity model for Nickel 201, allowing the simulation of dislocation density evolution and hardness changes. Bonding criteria based on equivalent plastic strain (PEEQ), shear stress and critical flyer velocity are used to distinguish between welded and unwelded regions. The model shows strong agreement with experimental data, capturing trends such as decreased weld length with increasing flyer thickness (25 - 75 µm), enhanced dislocation density and grain refinement due to dynamic recrystallization. This integrated numerical framework offers a predictive tool for optimizing LIW process parameters and joint quality.