Effects of Ta Addition on the Microstructure and Mechanical Properties of CoCu_0.5FeNi High-Entropy Alloy

In this work, the alloying effects of Ta element on the microstructure evolution and mechanical properties of CoCu_0.5FeNiTa_x (x = 0-0.6 at.%) high-entropy alloys were studied. The microstructure changed from single solid solution to hypoeutectic, then to eutectic, and finally to hypereutectic with the increase in Ta content, which is because Ta element facilitates the Laves phase to form. The volume fraction of hard and brittle Laves phase increases with the Ta content, which increases the yield strength, Vickers hardness and theoretical density but decreases the plastic strain. The CoCu_0.5FeNiTa_0.1 alloy with a single FCC solid solution structure shows the optimal balance between density and ductility. The theoretical density and tensile fracture strain can reach 8.94 g/cm³ and 36.3%, respectively.