Microstructure and tribological properties of WS x /a-C multilayer films with various layer thickness ratios in different environments

Abstract

WS x /a-C multilayer films with different layer thickness ratios and the modulation period of ~50 nm were prepared on monocrystalline silicon substrate by magnetron sputtering method. The morphology, microstructure and composition of the films were characterized by using scanning electron microscopy (SEM), X-ray diffractometry (XRD), energy dispersive X-ray spectroscopy (EDS) and Raman spectroscopy. The surface chemical states under different etching conditions were investigated by X-ray photoelectron spectroscopy (XPS) depth profile technique. The hardness, the adhesion to the substrate and the tribological properties of the films under various test environments were evaluated by means of nano-indentation, scratching tester and ball-on-disk tribometer. The results showed that a WS 2 phase with (101) preferential orientation was formed in WS x sublayer and the WC phase was not present at the WS x /a-C interface. The effects of L a-C /L WSx ratio on the microstructure of as-prepared films were negligible while the effects on the

DLC and DLC-WS2 Coatings for Machining of Aluminium Alloys

“…The base material (TiB 2 coating) can be observed only at the end of the scratch. For the maximum load, the CoF for WS 2 monolayer was as low as 0.05, which matches the findings made by other researchers [8,20,22]. The DLC-WS 2 bilayer ensured a very low CoF of around 0.07, which together with previous results from a bi-directional fracture test and with no evidence of any coating spallation or delamination over the whole 10-100 N range of loads (Figure 7), confirms its good adhesion and lubricious properties.…”

“…The coating deposited with −200 V has a significantly lower thickness equal to 45 nm, which results from shorter deposition time rather than from the bias voltage itself. The WS 2 monolayer, by contrast, is seen to have a uniform thickness and a columnar microstructure similar to that observed by other researchers [21,22]. The images of DLC-WS 2 coatings do not allow us to distinguish separate layers, although the DLC macroparticles can be noticed.…”

“…The results of the coating hardness measurement obtained using nanoindentation (average of 10 indents) are presented in Table 3. The hardness of around 2.4 GPa found for the WS 2 monolayer is higher than the one measured by other researchers [22], although the measurements were done on Si and for 3 µm thick coating. With the addition of additional DLC layers, the hardness increases to 6.6 GPa for DLC-WS 2 d, which suggests the positive effect of the interface strengthening [22].…”

“…The hardness of around 2.4 GPa found for the WS 2 monolayer is higher than the one measured by other researchers [22], although the measurements were done on Si and for 3 µm thick coating. With the addition of additional DLC layers, the hardness increases to 6.6 GPa for DLC-WS 2 d, which suggests the positive effect of the interface strengthening [22]. Figure 3 shows the bi-directional scratch test results for five DLC-coated samples together with measurements for TiB 2 as a function of a number of cycles.…”

“…The combination of energetic deposition by FVCA and magnetron sputtering resulted in the DLC layers being doped into the structure rather than combined into the multilayer. This can have a positive effect on the hardness of the coatings, as Yang et al [22] suggested that destroying the columnar morphology of WS 2 can improve the adhesion and hardness, leading to better wear resistance. Nevertheless, while the total deposition time was the same for all of the DLC-WS 2 coatings, the total thickness varies and is the lowest for the highest number of layers.…”