Effect of self-lubricating carbon materials on the tribological performance of ultra-high molecular weight polyethylene

For over five decades, ultra-high molecular weight polyethylene (UHMWPE) has been the standard material for total knee replacements (TKR). Zero wear of the UHMWPE would be ideal; however, due to the natural knee movements, wear damage to the UHMWPE articulating surface is inevitable. The generated wear debris results in joint mechanical instability, reduced joint mobility, increased pain, and implant loosening. Because of these issues, the research on the materials in TKRs has increased their survival rate for up to 20 years; however, in younger patients, the durability of the UHMWPE component decreases due to increased physical activity. Hence there is a constant need for highly wear-resistant tribological pairs for TKRs. Carbon-based materials have an excellent balance between lubricating and mechanical properties and have shown great promise in tribological applications. This study used self-lubricating cubic titanium carbide (c-TiC) and multiwalled carbon nanotubes (MWCNTs) to improve the UHMWPE wear resistance further. The combination of carbon-based materials decreased the material loss by about 41.7 % compared to the UHMWPE vs. bare steel ball tribological pair. The improvement, attributed to the c-TiC self-lubricating coating surface, is close to 5 %. Cold flow and burnishing were the predominant wear mechanisms observed in all the systems; more subtle wear processes were detected for the sliding couple with c-TiC self-lubricating coating. Meanwhile, polymer delamination and micrometer-sized debris formation were the main wear mechanisms in the UHMWPE-MWCNT vs. bare steel ball system. The adhesion work obtained from the electronic structure calculations shows a more significant interfacial interaction of the CNTs on the c-TiC surface. This interaction can be associated with the layer formation that protects the surface from wear and friction.