Design and properties of novel Ti–Zr–Hf–Nb–Ta high-entropy alloys for biomedical applications

The novel high-entropy alloys (HEAs) with compositions of (Ti_1/3Zr_1/3Hf_1/3)₁₅(Nb_1/2Ta_1/2)_x (x = 3, 5) for biomedical applications have been designed and synthesized, using the cluster formula approach. The present HEAs have a single body-centered-cubic (BCC) solid-solution structure and possess prominent mechanical properties of high compressive yield strength (834–890 MPa) and microhardness (287–293 Hv), large plasticity (>45%) under compression, as well as low Young's moduli (56–68 GPa). Also, these HEAs exhibit good bio-corrosion resistance, as revealed by a low corrosion rate at the order of 10⁻⁴ mm/year and the low passive current densities of 10⁻² – 10⁻¹ A/m², which are attributed to the formation of passive films consisting of Ti-, Zr-, Hf-, Nb-, and Ta- oxides. The high cell viability and proliferation of bone-forming MC3T3-E1 cells on the HEAs are comparable to those on the Ti–6Al–4V alloy, indicating their good biocompatibility. The present work demonstrates the great potential of these novel Ti–Zr–Hf–Nb–Ta HEAs for biomedical applications.