Enhanced mechanical and biocompatibility performance of Ti(1-)Ag(x) coatings through intermetallic phase modification

Advanced materials combining superior mechanical and biocompatibility performance are of significant interest to extend the lifetime of biomedical devices. In this work, Ag is alloyed with Ti to investigate the role of emerging TiAg intermetallic coatings with high mechanical hardness and exceptional biocompatibility. Thin films of Ti(1-x)Ag(x) were deposited on 316 L steel and glass substrates using magnetron sputtering and subsequently heat-treated to aid TiAg intermetallic development. Mechanical properties were then measured and correlated to microstructural and morphological changes in the TiAg films. In the as-grown state, the TiAg matrix developed different intermetallic structures which increased the hardness of pure Ti films from 5 to >7 GPa. After heat treatment, a peak hardness of 7.39 GPa and elastic modulus of 105 GPa was achieved for a 43 at.% Ag film due to formation of the tetragonal TiAg phase and increase of upper surface oxides which act as dislocation barriers. However, at higher Ag concentrations, heat treatment leads to agglomeration of Ag around grain boundaries and decreases the crystallite size, leading to reduction in hardness to <3 GPa. The Ti rich films also depict better cytotoxicity performance following exposure to the L929 cell line, though excellent cell viability values >98% are observed for the entire TiAg range. While leached ion concentrations lower than 100 ppb demonstrate excellent biocompatibility of this TiAg alloy system. This work demonstrates the first successful attempt to develop biocompatible TiAg thin film coatings with high mechanical hardness with the potential to extend the lifetime of medical implants.