Biofunctional TiZrNbSiMo high entropy alloy coatings deposited by hybrid HiPIMS–RF sputtering for corrosion-resistant implant surfaces

This study investigates the structural, mechanical, electrochemical, and biological performance of TiZrNbSiMo high entropy alloy (HEA) coatings deposited on 316L stainless steel and Si wafers using a hybrid HiPIMS–RF co-sputtering system. By varying the RF power applied to the Ti target (0–150 W), Ti content in the coatings was increased from 21.9 to 36.9 at. %, while all coatings retained an amorphous structure. The results indicate that the dense, featureless microstructure contributed to consistent hardness values (∼10 GPa) and excellent adhesion, with all samples exhibiting adhesion critical load, L_C3, values exceeding 30 N. Corrosion resistance was significantly enhanced, particularly in the T100 coating containing 30.9 at. % Ti, which achieved a polarization resistance 18 times higher than bare 316L SS in Ringer's solution. In vitro assays using MG-63 osteoblast-like cells confirmed excellent cytocompatibility, with enhanced cell proliferation and migration across all HEA-coated surfaces. These findings demonstrate the potential of TiZrNbSiMo HEA coatings as multifunctional protective layers for biomedical implants, offering superior mechanical durability, corrosion resistance, and biocompatibility.