Impact of Zr content on the nanostructure, mechanical, and tribological behaviors of β-Ti-Nb-Zr ternary alloy coatings

Recent studies have dealt with Ti-based alloy coatings produced by magnetron sputtering that have promising characteristics as surface modification treatments for biomedical applications. Ti, Nb, and Zr are non-toxic and non-allergenic biocompatible metals, and the addition of Nb and Zr to Ti favored the mechanical compatibility between the alloy and the bone. In the present study, the effects of Zr content on the phase formation, morphology, texture, film growth, and mechanical and tribological properties were investigated. The coating with lower Zr content (5 at.%) presented two phases: mainly the beta (body centered cubic) phase and nanoscale precipitates of the athermal omega phase, and the presence of this omega phase counted for higher values of both the elastic modulus and hardness. The increase in the Zr content yielded the stabilization of the beta phase, and an increase in both the lattice parameter and the mean grain size, which caused a decrease in both the elastic modulus and hardness of the coatings. The increase in the Zr content also influenced the coating morphology, going from a growth characteristic of the zone I to a growth characteristic of the zone T of the structure zone diagram. Tribological tests revealed that changes in texture could bring about the deformation of the grains in the {101} orientation, causing the increase of the worn volume. No delamination of the coatings was observed. These findings indicate that the Ti-Nb-Zr ternary alloy coatings are adequate for biomedical applications.