Mechanical properties of TiN thin film coatings on 304 stainless steel substrates

Abstract

Titanium nitride (TiN) film was deposited on 304 stainless steel using a hollow cathode discharge ion-plating (HCD-IP) technique. Film thickness and N/Ti ratio were controlled. The depth profile of the composition was determined by secondary ion spectroscopy (SIMS). The results showed that the compositions of the films were uniform for the films deposited at the same deposition conditions. The purpose of this study is to investigate the variation of structure and mechanical properties of the TiN films with different film thickness. The preferred orientations of TiN films were determined using X-ray diffraction (XRD). The dominant preferred orientation of the TiN coatings for the deposition conditions was (111), especially for the films thicker than 1 μm. The residual stress of the TiN films was also measured by XRD using sin 2 Ψ method. The residual stress was ranging from −5.93 to −2.70 GPa, varying with film thickness. Hardness of the films was measured by nanoindentation. The hardness values were ranging from 14.9 to 33.6 GPa, increasing with the film thickness. The ultimate interfacial shear stress between TiN/304SS was determined by in-situ strip tension of the TiN-coated specimens in a scanning electron microscope (SEM) chamber. The limiting thickness for the effective measurement of interfacial shear strength by the in-situ strip tension method is close to 0.5 μm. N/Ti ratios of the thin films were all at 0.8 measured using both X-ray photoelectron spectrometer (XPS) and Rutherford backscattering spectrometer (RBS). The packing factors of TiN films, calculated from the results of RBS, were 0.62–0.99, increasing with film thickness and leveling off at a thickness above 1.2 μm.