Abstract
Tungsten carbide (WC) and Tungsten carbonitride (WCN) coatings are deposited by reactive high-power impulse magnetron sputtering (HiPIMS) with various nitrogen gas flow rates. The characteristics of discharge current and plasma optical emission of HiPIMS are recorded by oscilloscope (OSC) and optical emission spectroscopy (OES). The results exhibit that the peak discharge currents and the intensities of optical emission spectra lines are significantly influenced by the addition of nitrogen. The elemental concentration, microstructure, mechanical and tribological properties in ambient temperature and high temperature of deposited coatings are investigated by a wide variety of techniques such as energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), nano-indentation measurement, scanning electron microscope (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and ball-on-disk tribometer. The results show that WC/WCN coatings with different microstructures, mechanical properties and tribological properties have been produced by controlling the flow rate of N2. Meanwhile, with the N2 flow rate increasing from 0 sccm to 24 sccm, (101) diffraction peak shifts to low angle. Moreover, (102) and (110) peaks’ intensities and the angle of (101) peak of β-W2C phase of the deposited WCN coatings decrease and disappear, and the average grain size decreases from 8.9 nm to 6.4 nm. XPS results show that the intensities of C=N, W–N, W–C–N, and N–O peaks increase while the intensity of C–W peak decreases. The deposited coatings change from slight columnar type to a typically dense and featureless structure, and the surface roughness decreases from Ra 11.6 nm at 0 sccm to Ra 5.7 nm at 24 sccm. The variation of nitrogen flow also plays a role in the mechanical properties of the coatings. It is found that the maximum hardness and elastic modulus of 35.6 GPa and 476.5 GPa appear at 16 sccm N2 flow rate. The results of wear tests demonstrate the addition of nitrogen slightly deteriorates tribological properties at room temperature (25 °C), but can remarkably improve tribological properties at high temperature (400 °C) of WC/WCN coatings deposited with an appropriate flow rate of nitrogen.
Highlights
Owing to a lot of excellent properties such as high hardness, low friction coefficient, good chemical stability and high wear resistance, tungsten carbide (WC) coatings serving as one of the protective coatings for mechanical components and cutting tools have attracted increasing critical attention and become a research focus in modern manufacturing industry [1,2,3,4,5]
Each sample is tested for 10 times to minim of the nitrogen gas flow rate from 0 to 24 sccm, the target voltage remains stable (Figure 2a) while the peak discharge current first rises up from 61.5 A at 0 sccm to 77.6 A at 16 sccm, decreases to 61.6 A at 24 sccm (Figure 2b)
The broadening of peaks reflects a decrease of the average grain size from 8.9 nm to 6.4 nm with the N2 flow rate increasing from 0 sccm to 24 sccm
Summary
Owing to a lot of excellent properties such as high hardness, low friction coefficient, good chemical stability and high wear resistance, tungsten carbide (WC) coatings serving as one of the protective coatings for mechanical components and cutting tools have attracted increasing critical attention and become a research focus in modern manufacturing industry [1,2,3,4,5]. Through making use of high power impulse magnetron sputtering (HiPIMS) technique Shen et al [9] deposited diamond like carbon films on AISI 304L austenitic stainless using Ar and N2 as precursors at room temperature. The results showed that the Nitrogen-doped diamond like carbon coating exhibited better tribocorrosion properties. The results show that nitrogen doping can improve the film adhesion and the wear resistance significantly. The results show that all Mo–S–N films exhibit higher hardness, oxidation resistance temperature and tribological properties at room temperature, 200, and 400 ◦ C. The addition of nitrogen into protective coatings proves to be effective for their properties improvement, such as wear resistance, corrosion resistance, oxidation resistance, adhesion strength and tribological property. The mechanical properties and the influence of nitrogen at room temperature and high temperature of WCN films have not been studied systematically. A comparison of the results with those WCN coatings for a reference pure WC sample is provided
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