Microstructure and Mechanical Properties of (TiZrHf)₅₀(NiCoCu)₅₀ High Entropy Alloys

The microstructure and mechanical properties of pseudo-binary (TiZrHf)₅₀(NiCoCu)₅₀ high entropy alloys (HEAs) with B2 matrix were investigated in this study. The studied HEAs includes Ti₄₀Zr₁₀Ni₄₀Co₅Cu₅, Ti₃₀Zr₂₀Ni₃₀Co₁₀Cu₁₀, Ti₂₅Zr₂₅Ni_16.67Co_16.67Cu_16.67, Ti₃₀Zr₁₀Hf₁₀Ni₃₀Co₁₀Cu₁₀, Ti₂₀Zr₁₅Hf₁₅Ni₂₀Co₁₅Cu₁₅, and Ti_16.67Zr_16.67Hf_16.67Ni_16.67Co_16.67Cu_16.67. XRD and SEM analyses revealed that all studied HEAs were a mixture of B2 and C15 intermetallic phases, instead of a single solid solution, due to their highly negative enthalpy of mixing and the relatively large difference in atomic radii. The B2 matrix was found capable of forming a solid solution of all six elements in a wide composition range. The lattice constants of B2 and C15 phases increase linearly with increasing the difference in atomic radii. Additionally, the microhardness of these HEAs increases from 409 to 595 HV with the increasing difference in atomic radii as well. Compression tests demonstrated substitution of Zr with Hf can improve the ductility. In all studied HEAs, the Ti₃₀Zr₁₀Hf₁₀Ni₃₀Co₁₀Cu₁₀ HEA achieves a great balance between yield strength, ultimate compressive strength, and fracture strain of 1574 MPa, 1933 MPa, and 6.5%, respectively.