Microstructure and tribological properties of TiTaHfNbZr high entropy alloy coatings deposited on Ti-6Al-4V substrates

We report on the microstructure and tribological behavior of equimolar TiTaHfNbZr high entropy alloy (HEA) thin films deposited on the biomedical Ti-6Al-4V substrates by RF magnetron sputtering. Results of nanoindentation and sliding wear experiments were evaluated along with the microstructure and topographical information obtained from scanning electron microscopy and atomic force microscopy. The findings clearly demonstrate that the TiTaHfNbZr HEA not only forms a homogenous and dense coating mechanically compatible with the Ti-6Al-4V substrates, but also provides a significantly enhanced surface protection against wear and cracking, which could prove valuable especially in long-term orthopedic implants that bear dynamic contact loading, such as in the cases of hip or knee joints.