Nanocrystalline WC and WC/a-C composite coatings produced from intersected plasma fluxes at low deposition temperatures

Abstract

Low temperature vacuum deposition of tungsten carbide coatings, W1−yCy with compositions that varied from y=0 to 0.9, was investigated. Special attention was given to the production of nanocrystalline carbides with coatings of y>0.5. Previous attempts at producing WC with excess carbon at near room temperatures resulted in the formation of amorphous phases. In this study, crystalline WC was produced at 45 and 300 °C by the intersection of plasma fluxes from magnetron sputtering of tungsten and laser ablation of graphite. At both temperatures, formation of WC chemical bonding and nanocrystalline cubic β-WC1−x was observed using x-ray photoelectron spectroscopy and grazing angle x-ray diffraction when the carbon content was increased more than 30%. Increasing the substrate temperature to 300 °C did not affect the percentage of WC bonding, but it did promote considerable crystallization of cubic WC. As the carbon content was increased to more than 50%, a second phase consisting of amorphous carbon (a-C) was observed together with amorphitization of β-WC1−x. The a-C phase was identified as amorphous diamond-like carbon (DLC) by Raman spectroscopy. At 60–80 at. % C, a two phase structure was produced, which was composed of nanocrystalline β-WC1−x with 5–10 nm grains and amorphous DLC. The hardness of the WC/DLC composites was about 26 GPa based on nanoindentation tests. Correlation of the chemistry, microstructure, and mechanical properties of WC and WC/a-C coatings is discussed.

On the microstructure of tungsten disulfide films alloyed with carbon and nitrogen

“…Voevodin et al [24], developed pioneering films of W-S-C with high C contents deposited by MSPLD (Magnetron Sputtering Pulsed Laser Deposition) and have reached hardness values of the order of 7-8 GPa in film containing 40-50 at.% C. They suggested the existence of a nanocomposite structure consisting of WC/ DLC/WS 2 . These hardness values were neither comparable to W-C carbides (24-28 GPa) nor to WC/DLC composites (15-17 GPa) [25,26], but were significantly higher than the typical hardness of solid lubricants such as WS 2 .…”

Influence of doping (Ti, V, Zr, W) and annealing on the sp2 carbon structure of amorphous carbon films

“…In recent years several groups studied the structure of metal-containing carbon layers -mainly using Ti or W as dopant -with a focus on the bonding environment of the metal 3,[12][13][14][15][16] . Due to the deposition conditions (high particle energy, bias voltage, elevated temperature) or high metal content (>25 %) the formation of a nanocomposite is observed with nm-sized carbide crystals embedded in a matrix of (hydrogenated) amorphous carbon.…”

Synthesis and Oxidation of non-Stoichiometric Tungsten Carbide Studied by Scanning Tunneling Microscopy/Spectroscopy

“…WC 1-x seems much more likely since it is often observed in low temperature thin film depositions. 107,[110][111][112] The C1s spectra presented in Figure 44 agree with the assumption that Since the cubic carbide has been identified as dominant, the spectra in Figure 42 are likely the LDOS at the surface of this carbide. There is significant variation in the LDOS, with both metallic spectra and spectra with a small bandgap being observed.…”

“…This is not necessarily inconsistent with a single phase, as the WC 1-x has a significant homogeneity range, from x = 0 -0.4. 107 Changes in stoichiometry perturb the bonding configuration and the band structure. So these variations in the LDOS could certainly be consistent with WC 1-x with different values of x.…”