Microstructure and wear resistant performance of TiN/Zr-base amorphous-nanocrystalline composite coatings on titanium alloy by electrospark deposition

To improve the wear resistance of titanium alloy, especially under high loading friction conditions, TiN/Zr-base amorphous-nanocrystalline composite coatings were prepared by Electrospark Deposition (ESD) on the surface of TC11. The microstructure of the coatings was examined and the fracture toughness and microhardness of the coatings were tested. The wear behavior and mechanism of the coatings under various loading conditions were investigated. The results show that the composite coating consists of two parts, one is a TiN substrate coating ( coating I) and the other is Zr-base amorphous-nanocrystalline surface coating (coating II). The former is mainly composed of TiN and Ti2N phases while the latter is mainly composed of amorphous phases, within which a large number of nanoparticles exists with diameter between 2 nm and 4 nm. These nanoparticles mainly include CuZr2, Ni2Zr3, and NiZr2, etc. The composite coatings are dense and their thickness is approximately ranging from 90 mu m to 95 mu m, bonding with substrate metallurgically. The fracture toughness of composite coatings is approximately 936 MPa m(1/2). The microhardness of the coating changes in a gradient trend. The average micro hardness of coating I and coating II are 1221.5 HV1.96 and 801.3 HV1.96, respectively. The wear tests results show that the composite coatings exhibit excellent wear resistance, especially under high loading friction conditions. The main wear mechanisms of the composite coatings are the micro-cutting wear and the multi-plastic deformation wear under low friction conditions. However, under high loading friction conditions (>8 N), the main wear mechanism of the composite coatings changed to micro-cutting wear, accompanied with a portion of micro fracture wear. The average wear rate of the composite coating is approximately 1.2-1.5 times of that of the single TiN coating and 2.6-2.7 times of that of the TC11 substrate, respectively. (C) 2016 Elsevier B.V. All rights reserved.