Effect of rescanning on the microstructure and mechanical properties of SLMed WMoTaNbV refractory high entropy alloy

Refractory high entropy alloys (RHEAs) are difficult to machine due to their extremely hardness and brittleness. Additive manufacturing, particularly selective laser melting (SLM) technique, is a feasible method for fabricating RHEA-based parts. In this paper, the processing parameters were optimized and an instant rescan strategy with the same parameters was introduced to solve the problem of insufficient energy input, poor quality and unsatisfied mechanical properties of WMoTaNbV RHEA fabricated via SLM method. The morphology, phase structure and microstructure of the as-prepared WMoTaNbV were characterized using optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and electron backscatter diffraction (EBSD). Mechanical properties were evaluated through microhardness and compressive strength tests. The effect of both building parameters and rescanning were investigated. The SLMed samples under both conditions remained single BCC phase. The sample fabricated with 350 W laser power and 600 mm/s scanning speed exhibited the fewest defects and the optimal mechanical properties. The rescanning strategy significantly increased the relative density and reduced defects. Futhermore, it not only improved the quality of the molten pool but also refined the grains, which introduced more grain boundaries, impeding dislocation motion and thereby enhancing both hardness and compressive strength.