GwangSeok Kim

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 μm. 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 μm 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.

The Characteristics and Thermal Stability of CrN/AlSiN Multilayer Coatings

CrN/AlSiN multilayer coatings with bilayer period (Λ) between 2.3 nm and 8.0 nm were synthesized from Cr and AlSi (Si=20 and 66 at.%) targets by using a closed-field unbalanced magnetron sputtering (CFUBMS) and their crystal structure, chemical composition and mechanical properties have been investigated by glow discharge optical emission spectroscopy (GDOES), Xray diffractometry (XRD), X-ray photoelectron spectroscopy (XPS) and nano-indenter. In order to evaluate the thermal stability of the coatings annealing treatments for 30 min at temperature between 800 °C and 1000 °C were performed in air. The thermal stability of the CrN/AlSiN multilayer coatings was improved with increasing Si content. In case of the coating with Si content of 18.2 at.%, a superior thermal stability was exhibited even after annealed at 1000 °C and the relatively high hardness of 25 GPa was maintained without a significant decrease in hardness. The reduced oxidation rate of the coatings at high temperature could be attributed to the formation of the amorphous Si3N4 phase around the crystalline AlN phase.