In vitro biocompatibility evaluation of Ti1.5ZrTa0.5Nb0.5Hf0.5 refractory high-entropy alloy film for orthopedic implants: microstructural, mechanical properties and corrosion behavior

Abstract

In the present research, a non-equimolar Ti1.5ZrTa0.5Nb0.5Hf0.5 RHEA film with a thickness of 1.025 µm was deposited on 316L, CoCrMo, and Ti6Al4V substrates by RF magnetron sputtering system. The microstructural characterizations showed that an amorphous and compact film with a continuous and cauliflower-like morphology was developed on the substrates. The hardness and elastic modulus of the deposited film, together with its adhesion, were determined by the nanoindentation. The RHEA-coated specimens exhibited much improved surface mechanical properties as compared with uncoated ones. The results of the scratch test demonstrated that the RHEA film provides high adhesion strength on the Ti6Al4V substrate compared to 316L and CoCrMo. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) tests were carried out in phosphate buffer saline (BPS) solution at 37 ± 1 °C. In contrast to RHEA-coated 316L and CoCrMo specimens, RHEA-Ti6Al4V showed remarkable polarization resistance without any trace of pitting on its surface. According to the EIS measurement, the charge transfer resistance of the RHEA-Ti6Al4V specimen is significantly high, about 1.5 × 107 Ω cm2, owing to the strong bonding between the RHEA film and Ti6Al4V substrate.