Effect of Laser Power on Microstructure and Mechanical Properties of W/HEA/Cu Laser Welded Joints

In this study, pure tungsten (W) and pure copper (Cu) blocks were welded using laser beam welding with a high-entropy alloy (HEA) (FeCoNiCrCu) as the intermediate layer. The effects of laser power (1500, 1750, and 2000 W) on the microstructure, hardness, strength, and toughness of the composite welded joints were investigated. Results indicated that under optimized process parameters (1750 W, 2 mm/s), the fusion zone near the Cu side, close to the heat source, exhibited a microstructure with a Cu-rich phase matrix dispersed with irregularly sized round and fine dendritic crystals. Additionally, Fe, Co, Ni, and Cr were uniformly distributed within the Cu matrix, and a fine-grained Cu region was observed at the lower part of the interface near the Cu side. The HEA intermediate layer near the W side exhibited a morphology of elongated and uniform equiaxed grains. At the interface on the W side, NiW and Ni4W phases were formed. The hardness of the joint increased gradually from the Cu side to the W side, and the interaction region between the HEA intermediate layer and the base materials (Cu and W) expanded with increasing laser power. With increasing laser power, the fracture morphology transitioned from equiaxed dimples to elongated dimples and then to a combination of equiaxed and elongated dimples. The shear strength of the W/HEA/Cu laser welded joints initially increased and then decreased, reaching a maximum of 187 MPa at 1750 W.