Effect of Zr on the morphology, microstructure and mechanical properties of NbTa0.5TiZrX refractory high entropy alloy fabricated by selective laser melting

Abstract

In this paper, the NbTa0.5TiZrX series refractory high entropy alloys(RHEAs) were processed by selective laser melting (SLM). NbTa0.5TiZrX alloy are observed with BCC crystal structures.The effect of Zr content on microstructure and properties of NbTa0.5TiZrX alloys was studied, as the Zr content increases, the main defects of NbTa0.5TiZrX alloy changed from lack of fusion defects to solidification cracks. Due to the different melting points of alloying elements, the elements with high melting point are enriched in the dendrite and the elements with low melting point are enriched in the inter-dendrite. As the Zr content increases, the number of cellular subgrain increases, and the number of columnar subgrain decreases. The fine equiaxed grain at the boundary of the molten pool and the coarse grain in the molten pool make the grain of the NbTa0.5TiZrX alloy with bimodal size distribution. The compressive yield strength increases with the increase of Zr content. Due to the effects of solid solution strengthening, precipitation strengthening and fine crystal strengthening, the alloy has the highest yield strength of 1320 MPa. When Zr content reaches 10 wt%, and the Compressive strain of NbTa0.5TiZrX alloy exceeds 75% at room temperature.