Effect of lubricated sliding wear against CFRPEEK on the nanomechanical properties of Ag alloyed Cr/DLC thin film

Ag-doped Cr/DLC coatings were deposited on medical grade 316 LVM stainless steel using DC magnetron sputtering. Morphological study of the coating indicated the formation of island of Ag clusters owing to the inability of Ag to form carbides, which is also corroborated from the XRD analysis. The composite coating showcased elastic nature suggestive from the p-h curve obtained from the nanoindentation test. However, the coating possesses 33% ductility, which is an important virtue for stress relieving attributed to Ag in the carbon matrix. The coating registered improved adhesion due to Cr3C2 carbide formation in the interlayer. The composite coating was subjected to lubricated sliding in physiological fluid against carbon fiber reinforced PEEK (CFRPEEK) friction pair to realize a closer scenario to hip implant articulation. A lubricious film of Ag with scattered particles of PEEK was formed in the sliding interface resulting in a long run-in process during sliding. The composite coating suffered mild wear on the Ag-doped DLC top layer with few gullies of wear scar deep into the interlayer due to graphitization of carbon in the film. A statistically significant difference was observed in the hardness, H3/E2, elastic work, and plastic work; however, there was no statistically significant difference in H/E attribute between the unworn and worn surface. What is more, Raman spectra of the worn (ID/IG = 1.9 ? 0.2) and unworn surface (ID/IG = 2.1 ? 0.1) were indicative of no significant loss in the structural integrity of the composite coating.

Automated summary

Ag-doped Cr/DLC coatings were successfully deposited on medical grade stainless steel, demonstrating elastic nature and 33% ductility. The coatings showed improved adhesion and lubrication during sliding tests, but experienced mild wear and wear scar gullies due to graphitization of carbon. Additionally, there were significant differences in hardness, elastic work, and plastic work between unworn and worn surfaces, but no significant difference in the H/E attribute. Raman spectra indicated no significant loss in structural integrity of the composite coating between worn and unworn surfaces.