Structure, mechanical and tribological properties of self-toughening TiSiN/Ag multilayer coatings on Ti6Al4V prepared by arc ion plating

Hardness and elastic modulus of TiSiN coating (C1) and TiSiN/Ag multilayer coatings with different thickness of individual Ag layers of 33.87nm (C2), 30.01nm (C3), 26.67nm (C4), 22.22nm (C5) and 10.67nm (C6), together with SEM micrographs of indention morphologies after Vickers indentation tests. [Display omitted] •TiSiN/Ag multilayer coatings design for microstructure was shown by cross-sectional SEM micrographs.•The TiSiN/Ag multilayer coatings showed a significantly improved toughness compared with the TiSiN coating.•The individual Ag layers as a self-lubricating.•TiSiN/Ag multilayer coating (individual Ag layers of 22.22nm) exhibits high hardness, H/E and H3/E*2 values and excellent wear resistance. The TiSiN/Ag multilayer coatings deposited on Ti6Al4V alloy substrate using the multi-arc ion plating system. All multilayer coatings had a same total thickness of about 2.5μm, and the TiSiN layer had a fixed thickness and the Ag layer had different thicknesses. Evidence concluded from X-ray diffraction, scanning electron microcopies, X-ray photoelectron spectroscopy revealed that nanocrystallites and amorphous microstructure of nc-TiN and amorphous Si3N4 for individual TiSiN layers, where amorphous Si3N4 around nanocrystallites TiN boundaries, and ductile nanocrystallites silver clusters and metallic silver for individual Ag layers which can limit continuous growth of single (200) preferential orientation coarse columnar TiN crystal. In addition, the TiN grain size presented a decreasing trend with the decrease of the thickness of Ag layers. The TiSiN/Ag multilayer coatings showed a significantly improved toughness compared with the TiSiN coating. The individual Ag layers of nano-multilayer coatings, not only as a self-lubricating but also as a barrier which inhibited micro cracks propagation, the formation of threading defects throughout all coatings, cause energy dissipation by passing through the interface zones without making the coating fail and at the same time prevented the aggressive seawater through the micro-pores. Moreover, improved toughness, excellent wear resistance together with high hardness, H/E and H3/E*2 values were found for the TiSiN/Ag multilayer coating with the individual Ag layers of 22.22nm.