Development process and evolution mechanism of microstructures of friction-induced plastic deformation layers on UHMWPE

Abstract

UHMWPE is a vital material used in artificial joint replacements because of its excellent mechanical properties and wear resistance. This study systematically investigated the development process and the evolution mechanism of plastic deformation of UHMWPE. The plastic deformation layer that protrudes at the edge of the groove grows gradually and stabilizes over time, while a higher rotation speed leads to a faster development of the protruded plastic layers. Raman spectroscopy results in the worn surface show increased crystallinity in the plastic deformation layers, especially at the groove edges, implying ordered distributions of microstructures. The scratch and indentation results indicate a densely packed but anisotropic distribution of microstructures in UHMWPE. Additionally, MD simulation results indicate that the frictional process creates ordered distributions of polyethylene chains, thereby enhancing the interaction strength between adjacent molecular chains. The compactly arranged polyethylene chains flow along the frictional direction as the Fe slab moves linearly, and show the potential to separate from the undeformed substrate in UHMWPE, forming the plastic deformation layer. More PE chains aligned parallel to friction at the initial stage could result in greater plastic deformations. These results offer new insights into the wear mechanisms of UHMWPE, showing that the wear of UHMWPE is closely linked to the development of the plastic deformation layer.