Microstructure and properties of monolayer, bilayer and multilayer Ta2O5-based coatings on biomedical Ti-6Al-4V alloy by magnetron sputtering

In recent years, tantalum pentoxide (Ta2O5) ceramic coating has attracted considerable attention in the modi-fication of implants due to its excellent biocompatibility, high corrosion resistance, and good wear resistance. However, the poor adhesion to the substrate degrades its performance and may become a significant obstacle to its clinical application. In the paper, Ta2O5 monolayer, Ta2O5/Ti bilayer, and Ta2O5/Ta2O5-Ti/Ti multilayer coatings were prepared on the Ti-6Al-4V alloy by magnetron sputtering. The microstructure, chemical composition, residual thermal stress, adhesion strength, mechanical properties, tribological behaviors, and corrosion resistance of the coatings were investigated and compared. The results showed that these deposited coatings were composed of an amorphous nano-Ta2O5 phase, and their surfaces were smooth, dense, and homogeneous without any cracks. Ta2O5/Ta2O5-Ti/Ti coatings exhibited lower thermal residual stress than that of the Ta2O5 and Ta2O5/Ti coatings, which could be attributed to the decrease of the coefficient of thermal expansion (CTE) mismatch between the Ta2O5 film and Ti-6Al-4V substrate due to the introduction of the Ta2O5-Ti/Ti doubleinterlayer. Moreover, Ta2O5/Ta2O5-Ti/Ti coating was significantly superior to Ta2O5 and Ta2O5/Ti coatings in the adhesion strength, mechanical properties, and wear resistance. These Ta2O5-based coatings can provide excellent corrosion protection for Ti-6Al-4V alloy in simulated body fluids (SBF). The Ta2O5 monolayer coating samples showed the best corrosion resistance, mainly due to its thick out-layer Ta2O5 film. These experimental results provide a feasible way to improve the performances of Ta2O5 coating on Ti-6Al-4V alloy.