Manufacturing and analysis of VNbMoTaW refractory high-entropy alloy fabricated by selective laser melting

Abstract

Refractory high entropy alloys (RHEAs) have provided a new research direction for the development of structural materials with high-temperature characteristics due to their excellent heat tolerance and mechanical properties. Along these lines, in this work, bulk VNbMoTaW RHEA on a tungsten substrate was fabricated by enforcing the selective laser melting (SLM) technique. The impact of the laser scanning speed on the surface morphology, internal defect, microstructure and mechanical properties of the VNbMoTaW RHEA specimen were thoroughly investigated. The extracted results showed that the pores and cracks were the main sources of defects within SLMed VNbMoTaW RHEA. Interestingly, the pores disappeared when a lower scanning speed was applied. However, the manifestation of cracks was inevitable regardless of the employed scanning speed. The microstructure of the VNbMoTaW RHEA was observed in cross-section, indicating the existence of a columnar dendritic structure, which revealed the existence of a strong epitaxial growth along the building direction. In addition, the typical microstructure feature of the VNbMoTaW RHEA on the top surface was cellular structure. The average microhardness of the VNbMoTaW RHEA fabricated by the SLM method was about 664 HV, which was 1.3 times higher than that processed by arc-melting (525 HV). Moreover, the surface of the VNbMoTaW RHEA specimen was subjected to tensile residual stress, which gradually decreased as the laser scanning speed was increased. The VNbMoTaW RHEA specimens prepared by SLM exhibit higher compressive strength than the corresponding specimens, which were prepared by enforcing the vacuum arc melting procedure.