Effects of the thickness of Ti buffer layer on the mechanical properties of TiN coatings

In order to improve the impact adhesion property of TiN hard coating maintaining their hardness and wear resistance, the ductile Ti buffer layer which could absorb impact energy was inserted in the middle of TiN film as well as the Ti interlayer on substrate. These TiN films were deposited using cathodic arc ion plating with various thickness of Ti buffer layers between 0.24 and 0.75 mum. The result of X-ray diffraction analyses showed that the preferred orientation of TiN is (1 1 1). The Ti interlayer grown on the substrate has the preferred orientation of (1 1 1). However, the Ti buffer layer grown on the TiN layer has a (0 0 2) plane, which establishes the epitaxial relationship with the TiN(1 1 1) plane. The elastic modulus and hardness of Ti buffer layer with 0.48 mum thickness were measured to be approximately 220 and 8.2 GPa, respectively, which were higher than values (165, 6.5 GPa) of the Ti interlayer. The results of impact adhesion test under the impact load of 2.5 kgf showed that the indentation cavity volume and circular cracks of TiN coating were greatly reduced with increasing the thickness of Ti buffer layer. This tendency can be attributed to the effective absorption of impact energy by the Ti buffer layer. (C) 2003 Elsevier Science B.V. All rights reserved.