Deposition temperature influence on the wear behaviour of carbon-based coatings deposited on hardened steel

Abstract

This paper presents an evaluation regarding the influence of substrate material characteristics and deposition parameters on the tribological behaviour of carbon-based coatings. Chromium nitride ceramic interlayers and carbon-based thin films were deposited by magnetron sputtering on hardened AISI 5115 (16MnCr5) case hardening steel. The physical vapour deposition (PVD) deposition was performed at three different temperatures: 180 degrees C, 200 degrees C and 250 degrees C. The chemical composition of the samples was assessed by Rutherford Backscattering Spectroscopy (RBS), the structure by X-ray Diffraction (XRD), and the surface morphology by Atomic Force Microscopy (AFM). The surface chemistry was analysed by X-ray Photoelectron Spectroscopy (XPS) and Raman Spectroscopy. The coatings are homogeneous, amorphous, with a smooth surface. The mechanical behaviour has been assessed on a pin-on disk rotational tribometer (wear characteristics), on a micro scratch tester (adhesion to the substrate), by ball-cratering (film thickness) and by nanoindentation (hardness and the modulus of elasticity). A strong correlation has been observed between the substrate characteristics and, more importantly, the deposition temperature, and the mechanical properties of the assembly. The fracture toughness is positively influenced by the presence of the ceramic chromium nitride interlayer. The modulus of elasticity and friction coefficient (both in dry and lubricated conditions) are decreased for higher deposition temperatures, however the higher deposition temperature negatively affects the mechanical characteristics of the steel substrate.