Integrating experiments and simulations to correlate thermal convection and defect morphologies in the overlapping tracks of Cu–Cr alloy during laser-assisted additive manufacturing

Laser additive manufacturing (LAM) efficiently fabricates metal parts with reduced cost, time, and increased design flexibility. Its ultrafast cooling preserves metastable microstructures, extends solid solubility, and imparts unique properties unattainable via traditional methods, making it ideal for creating and refurbishing components with enhanced lifespan and performance. However, LAM faces significant challenges when applied to copper (Cu) and aluminum (Al) based alloys due to their intrinsic high reflectivity to laser beams and thermal conductivity, which result in inadequate melting, poor intermixing, and defects such as porosity, cracks, and inhomogeneities. Optimizing the process parameters to mitigate these defects from the experimental insights alone is expensive, time-consuming, and constrained by inadequate knowledge of the coupling between fluid flow, thermal transport, phase change, and microstructure evolution. To address this deficit, we report an experimentally validated multi-physics modeling approach for laser powder bed fusion of Cu–Cr alloy, valued for its high electrical/thermal conductivity and wear resistance. The influence of various process parameters on the bonding between the overlapping tracks and surface microstructure and properties is assessed. Going beyond the previously reported studies that mainly focused on optimizing the laser parameters and quantifying widths and depths of the melt pool, our results could establish an explicit interlinkage between the thermal convection and microstructural evolution, thereby probing the root causes of poor bonding in the overlapping tracks. These findings reveal the mechanism of defect formation such as balling and porosity, unveiling the control of the melt flow dynamics necessary for achieving uniformly fabricated tracks and their bonding with the underlying substrate.