Design and fabrication of Ti-Zr-Hf-Cr-Mo and Ti-Zr-Hf-Co-Cr-Mo high-entropy alloys as metallic biomaterials.

Novel TiZrHfCrMo and TiZrHfCoCrMo high-entropy alloys for metallic biomaterials (bio-HEAs) were developed based on the combination of Ti-Nb-Ta-Zr-Mo alloy system and Co-Cr-Mo alloy system as commercially-used metallic biomaterials. Ti-Zr-Hf-Cr-Mo and Ti-Zr-Hf-Co-Cr-Mo bio-HEAs were designed using (a) a tree-like diagram for alloy development, (b) empirical alloy parameters for solid-solution-phase formation, and (c) thermodynamic calculations focused on solidification. The newly-developed bio-HEAs overcomes the limitation of classical metallic biomaterials by the improvement of (i) mechanical hardness and (ii) biocompatibility all together. The TiZrHfCrMo and TiZrHfCoCrMo bio-HEAs showed superior biocompatibility comparable to that of commercial-purity Ti. The superior biocompatibility, high mechanical hardness and low liquidus temperature for the material processing in TiZrHfCrMo and TiZrHfCoCrMo bio-HEAs compared with the Ti-Nb-Ta-Zr-Mo bio-HEAs gave the authenticity of the application of bio-HEAs for orthopedic implants with multiple functions.