Microstructural, mechanical and electrochemical characterization of TiZrTaHfNb and Ti_1.5ZrTa_0.5Hf_0.5Nb_0.5 refractory high-entropy alloys for biomedical applications

The state-of-the-art metallic biomaterials are 316L, CoCrMo and Ti6Al4V but they all suffer from known issues relating to biocompatibility, wear resistance and corrosion resistance. Therefore, there is always the motivation to identify novel superior metallic biomaterials to 316L, CoCrMo and Ti6Al4V. The concept of refractory high-entropy alloys (RHEAs) provides an interesting research direction towards developing novel metallic biomaterials, initially because RHEAs consist of purely biocompatible elements, but a systematic study of the performance of RHEAs targeting biomedical applications, while comparing to that of the state-of-the-art 316L, CoCrMo and Ti6Al4V, was not existing before and constitutes the theme of the current work. Two exemplary RHEAs that are studied in detail in this work, TiZrTaHfNb and Ti_1.5ZrTa_0.5Hf_0.5Nb_0.5, show highly promising characteristics as novel superior metallic biomaterials in that they possess a desirable combination of wear resistance, wettability and pitting and general corrosion resistance, outperforming 316L, CoCrMo and Ti6Al4V almost in all these important aspects. In addition, it is also shown in this work that how appropriate alloying in RHEAs can be utilized to fine-tune their performance as better metallic biomaterials, such as the correlation between lattice strain and corrosion resistance.