Role of diffusion in material mixing during steel-copper laser powder bed fusion: A numerical study

Material mixing mechanisms in multi-material laser powder bed fusion (LPBF) are critical for mitigating defects and optimizing interfacial properties. This study employs a multiphysics modeling framework to investigate the role of diffusion in material concentration changes at a copper-steel interface during LPBF, focusing on mesoscopic phenomena. Simulations of a single-track 316L-CuCr1Zr process reveal that diffusion plays a negligible role in melt pool dynamics due to the short timescales and spatial constraints inherent to LPBF. Analytical solutions support this argument and confirm that material transport, rather than diffusion, governs mixing phenomena. These findings clarify the limitations of diffusion-based models and highlight the need for alternative numerical strategies to accurately predict interfacial mixing in multi-material LPBF simulations.