Effects of Si content on microstructure and mechanical properties of TiAlN/Si3N4-Cu nanocomposite coatings

•The grain size and surface roughness decreased with the increase of Si content.•The microhardness of these coatings increased with the increasing content of Si.•The ratio H3/E2 of TiAlN/Si3N4-Cu coating of 3.39at.% Si reached the maximum value of 0.11GPa.•Indentation morphology of TiAlN/Si3N4-Cu coating contained 3.39at.% Si has fewer cracks.•TiAlN/Si3N4-Cu coating contained 3.39at.% Si has good adhesion property and wear resistance. TiAlN/Si3N4-Cu nanocomposite coatings of various Si content (0–5.09at.%) were deposited on AISI-304 stainless steel by DC reactive magnetron sputtering technique. The chemical composition, microstructure, mechanical and tribological properties of these coatings were systematically investigated by means of X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), nanoindentation tester, a home-made indentation system, a scratch tester and a wear tester. Results indicated that with increasing Si content in these coatings, a reduction of grain size and surface roughness, a transformation of the (111) preferred orientation was detected by XRD and FESEM. Furthermore the hardness of these coatings increase from 9.672GPa to 18.628GPa, and the elastic modulus reveal the rising trend that increase from 224.654GPa to 251.933GPa. However, the elastic modulus of TiAlN/Si3N4-Cu coating containing 3.39at.% Si content dropped rapidly and changed to about 180.775GPa. The H3/E2 ratio is proportional to the film resistance to plastic deformation. The H3/E2 ratio of the TiAlN/Si3N4-Cu coating containing 3.39at.% Si content possess of the maximum of 0.11GPa, and the indentation test indicate that few and fine cracks were observed from its indentation morphologies. The growth pattern of cracks is mainly bending growing. The present results show that the best toughness is obtained for TiAlN/Si3N4-Cu nanocomposite coating containing 3.39at.% Si content. In addition, the TiAlN/Si3N4-Cu coating containing 3.39at.% Si content also has good adhesion property and superior wear resistance, and the wear mechanism is mainly adhesion wear.