Influence of W contents on the microstructure and tribological properties of W-DLC coatings deposited by PECVD combined with magnetron sputtering

Abstract

In the field of industrial applications, reasonable selection of frictional counterparts is pivotal for reducing friction and wear. To interpret the tribological behavior of W-DLC films when interfacing with themselves and 9Cr18 steel, W-DLC coatings of varying W content were applied using sputtering of a WC target in a combined Ar and C₂H₂ atmosphere. The findings reveal that the sp³ content elevates as the WC target power intensifies, peaking at 52.5 at.% with a WC target power of 2 kW. Beyond this point, a further increase in power results in a decline of sp³ content. When W-DLC coatings of different W content are pitted against a 9Cr18 ball, the W-DLC coating with a composition of 19.4 at.% W content exhibits a notably lower friction coefficient and minimized wear rate. The tribological results for W-DLC coatings interfacing with a W-DLC coated 9Cr18 ball surpass those of an uncoated 9Cr18 ball. Moreover, the wear rates for W-DLC coatings with reduced W content, when tested against the W-DLC coated 9Cr18 ball, reduce by more than twice as compared to their performance against an uncoated 9Cr18 ball. This suggests that the transfer layer effect is subdued when W-DLC coatings interface with a W-DLC counterpart. Here, the surface texture and resilience of the coatings assume a significant role. Coatings with resilience and smoother surfaces exhibit enhanced wear resistance. A reduced difference in hardness between the W-DLC coated disc and the 9Cr18 ball makes it prone to pronounced wear. This highlights the notion that the concurrent application of similar W-DLC coatings on both the disc and ball marginally enhances wear resistance.