Microstructure and mechanical properties of a laser welded Ti–6Al–4V titanium alloy/FeCoNiCrMn high entropy alloy with a Cu filler layer

A high-power solid-state laser was used to weld the Ti–6Al–4V titanium alloy and the FeCoNiCrMn high-entropy alloy. By adding a pure Cu filler layer for the laser welding, a strong welded joint is obtained and the average tensile strength of the laser welded Ti–6Al–4V/FeCoNiCrMn joint exceeds 140 MPa. Composition and mechanical properties of phases in the laser welded Ti–6Al–4V/FeCoNiCrMn joint were investigated by the optical microscope, the electron probe microanalysis technique, the scanning electron microscope and the nanoindentation technique. The fusion zone is mainly composed of the Cu-rich and the FeCoNiCrMn-rich regions. The Cu-rich phases can disperse brittle intermetallic compounds such as Ti–Fe, to prevent the formation of a continuous brittle compound layer, thereby improving the plasticity of the welded joint and promoting the formation of the joint. The temperature distribution model in the fusion zone was established, and combined with the element distribution and phase composition analysis results in the fusion zone, microstructure mechanism for formation of the fusion zone was proposed.