Strengthening mechanism for high-entropic weld of molybdenum/Kovar alloy electron beam welded joint

High-entropic weld was acquired by adding high-entropy alloy interlayer into molybdenum/Kovar alloy electron beam welded joint to optimize the mechanical properties. The tensile strength of joint was up to 358 MPa when the high-entropy alloy interlayer was 1.0 mm thick, corresponding to the increase of 87% compared to the only 191 MPa of the joint without high-entropy alloy interlayer. The microstructure of the weld was transformed from γ-Fe matrix with reticular α-Fe into the combination of pro-eutectic fcc and eutectic fcc + laves, as is expected from the increase in the volume of high-entropy alloy into the weld. The brittle reaction interface along the fusion line of molybdenum side was predominately changed after adding high-entropy alloy interlayer. The original continuous σ(FeMo) at the edge of α-Mo in reaction interface, which was responsible for the inferior bearing capacity of the joint, was gradually decreased and replaced by intermittent fine σ(FeCr) as the high-entropy alloy interlayer was thicker. The optimization of tensile strength derived from the transformation from continuous σ(FeMo) to intermittent σ(FeCr). The superior affinity of Cr to Fe and Mo compared to the affinity between Fe and Mo itself was the underlying reason for the decrease and morphology change in brittle σ.