Improvement of antibacterial activity and mechanical properties of titanium alloy by TiAlN/Ag gradient multilayer coatings

Abstract

Silver coating has an excellent antibacterial activity but low mechanical properties, e.g., microhardness. In order to improve simultaneously the antibacterial activity and surface hardness of titanium alloys, TiAlN/Ag multiple coatings with different gradient distributions in thickness were prepared on titanium alloys by unbalanced magnetron sputtering. The coatings with gradient thickened TiAlN–Ag cosputtered upper layers had a much stronger antibacterial activity, 99.82% in antiseptic Escherichia coli, than those with the gradient thinned upper layers. With increasing gradient cycles of the multiple coatings, the antibacterial activity decreased, whereas the hardness increased. The alternate growth of TiAlN and TiAlN–Ag layers may repeatedly provide an excellent comprehensive antibacterial activity (99.23% for Escherichia coli) and hardness (two times TC4 alloy) for a long term.