The influence of substrate bias voltages on structure, mechanical properties and anti-corrosion performance of Cr doped diamond-like carbon films deposited by steered cathodic arc evaporation

摘要

Cr-doped diamond-like carbon films (Cr-DLC) were deposited on 304 stainless steel (304SS) substrates by a steered cathodic arc plasma evaporation with various negative bias voltages (-50 to -550 V). The Cr layer (-90 nm), CrN layer (-400 nm), transition layer and Cr-DLC layer (-3.2 mu m.) were deposited sequentially onto the substrate. The Raman spectra showed that the sp(3)/sp(2) ratio increased when the magnitude of bias voltage increased from 50 to 450 V and then it slightly decreased with further increase in the voltage. A dome-shaped morphology was found on the film deposited at low bias voltage due to incorporation of Cr droplets into the films and low mobility of adatoms. In addition, the crack in the conical structure and boundaries between the regular film and conical structure were also observed. The size of dome-shaped morphology and surface roughness decreased with increasing the bias voltage, which is attributed to enhanced surface mobility, increase in re-sputtering events above the droplets, and repulsion of droplets at higher bias voltages. The hardness significantly increased from 8.3 to 25.3 GPa when the bias voltage was increased from 50 to 450 V and then slightly decrease to 23.7 GPa as further increased to 550 V. The best corrosion current density of the film deposited at 450 V was 2.69 x 10(-8) A/cm(2), which is about 2-order of magnitude less than that of the bare 304SS plate (1.19 x 10(-6) A/cm(2)). The anti-corrosion properties and hardness were improved at higher substrate bias voltage due to the decrease in surface defects. The breakdown potentials of 304SS plates can be significantly improved from 0.75 V for bare samples to 1.3 V for those coated with Cr-DLC films. The passive current density of the Cr-DLC coated 304SS plate significantly decreased to around 1 x 10(-7) A/cm(2), because the pits did not penetrate through underlying Cr-DLC film. The optimum anti-corrosion performance and hardness was achieved for the samples deposited at a bias of -450 V. (C) 2015 Elsevier B.V. All rights reserved.