Tribological study of amorphous polyethylene under different rough surfaces of chromium based on molecular dynamics simulation

Due to its excellent friction and wear properties, polyethylene is often used in bearings, seals and driveline systems together with metal-coated components. Therefore, how to study the contact friction behavior and wear mechanisms of polyethylene molecular chains with metal surfaces on a microscopic scale is a current scientific problem to be solved. In this study, molecular dynamics simulations were used to investigate the changes in contact interface morphology, plastic deformation, friction temperature, and friction properties of amorphous polyethylene and chromium under different conditions. The results show that during the friction process, the movement of amorphous polyethylene chains is mainly affected by the roughness peaks on the surface of the chromium plate and the inter-chain entanglements, forming a "migration-detachment-migration" process, which leads to the generation of a plastic flow layer. The height of the roughness peak on the contact surface is critical for the regulation of frictional properties. At a normal load of 1 GPa, the number of contact atoms on the surface increased by 20% as the height of the rough peak increased to 6 Å compared to a smooth surface. During friction, the plastic flow layer thickness increased from 10 Å to 16 Å as the normal load increased from 1 GPa to 5 GPa, which is about 60% increase in the plastic flow layer thickness. And as the sliding velocity increases to 3 Å/ps, the thickness of the plastic flow layer increases by 70%, which in turn leads to higher atomic mobility and atomic wear. In addition, the modulation of chain entanglement by normal load and sliding velocity is revealed by analyzing the distribution of C-C-C bond angles, with normal load being more sensitive to the angular change of amorphous polyethylene chains. As the normal load increases, some of the C-C-C bond angles begin to shift from 110° to 115°, which in turn increases atomic wear. This study has certain theoretical guiding significance for studying the tribological behavior of amorphous polyethylene and metal.