Nanoindentation and nanoscratch studies of submicron nanostructured Ti/TiCrN bilayer films deposited by RF-DC co-sputtering method

摘要

In this study, submicron nanocrystalline TiCrN films (141 nm, +/- 8 nm) are deposited on titanium-coated steel substrates, maintained at a temperature of 300 degrees C. The bilayer films are prepared via an RF-DC co-sputtering system under different nitrogen flow rates (7, 10, 15, and 18 sccm). The compositional, nanostructural, mechanical, and morphological properties of the bilayer films are characterized by energy-dispersive X-ray spectroscopy (EDS), grazing incidence X-ray spectroscopy (GIXRD), backscattered scanning electron microscopy (BSE), nanoindentation and nanoscratch tests, and atomic force microscopy (AFM). The EDS results reveal that the chemical composition of the top layers is Ti1Cr1+XN with -0.06 X 0.21. The GIXRD patterns show that a face-centered cubic solid solution structure with a relatively strong (111) texture has been formed on a hexagonal close-packed structure (alpha-Ti). In addition, it can be seen the crystallite size has slightly increased in the samples with higher nitrogen content while the interplanar spacing has decreased in the samples with higher chromium content. The nanoindentation and nonoscratch tests are performed under three different indentation loads (300, 500, and 1000 mu N), and the residual impressions are studied by AFM images. The results of the nanoindentation tests demonstrate that the sample with the smallest interplanar spacing, the largest crystallite size and the highest nitrogen content exhibits the highest Cube Corner hardness value. The results of the nanoscratch tests suggest that the impact of surface roughness on the friction coefficient is less dominant as the ratio of root-mean-square roughness to penetration depth decreases and that the chromium content is the factor that means the friction coefficient differences. Comparing the hardness and the friction coefficient of the samples at the load of 1000 mu N, it can be said that the hardness value has improved by 25% while the friction coefficient has lowered by 14%, with the lowest value of 0.3.