Development Process and Evolution Mechanism of Microstructures of Friction-Induced Plastic Deformation Layers on Uhmwpe

Abstract

UHMWPE is a critical material applied in artificial joint replacements due to its outstanding 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 protrudes at the edge of the groove and grows gradually and reaches stability over time, while higher rotation speed leads to faster development of protruded plastic layers. Raman spectroscopy results show increased crystallinity in the plastic deformation layers, especially at the groove edges, implying ordered distributions of microstructures. The following scratch and indentation results suggest intensely packed but anisotropic distribution of microstructures on UHMWPE. In addition, MD simulation results show that the frictional process induces ordered distributions of polyethylene chains, which increases the interaction strength between adjacent molecular chains. The compactly arranged polyethylene chains flow along the frictional direction as driven by the linearly moved Fe slab, and show the potential to separate from the undeformed substrate in UHMWPE, forming the plastic deformation layer. Higher oriented molecules at the initial stage could result in greater plastic deformations. These results provide a new insight to analyze the wear mechanism of UHMWPE, and the evolution of plastic deformation layer is closely related to the wear of UHMWPE.

Keywords: UHMWPE, Friction, Plastic deformation layer, Molecular chain orientation