Tribological behavior of aged UHMWPE under water-lubricated condition

Ultra-high molecular weight polyethylene (UHMWPE) is commonly used to make water-lubricated bearing in industrial application. The Water-lubricated bearing components often experience boundary and mixed lubrication during operation, which induces the aging of UHMWPE material, affecting the mechanical and tribological properties of UHMWPE. This investigation aims to study how the wear resistance of UHMWPE is affected by aging. A CBZ-1 tribo-tester was used to conduct the sliding wear tests between UHMWPE pins and ZCuSn(10)Zn(2) discs rubbing pair under water lubrication. The comparison analyses of the shore hardness, friction coefficients, wear mass loss and worn surface morphologies were elevated. Also, the Raman spectrum, Infrared spectrum and the change of elements of aged UHMWPE samples were examined. The results showed that the accelerated aging had a significant effect on the mechanical and tribological properties of UHMWPE. Especially, compared with the original sample the average friction coefficient increases by 65.96% under 720 h, 80 degrees C aging condition. Moreover, accelerated aging also resulted in a fracture of molecular chains and chemical oxidation reaction of UHMWPE, the concentration of O element increased to 12.803% when the aging condition was 720 h, 80 degrees C, which was closely correlated with the deterioration of its wear resistance. The main wear mechanisms were fatigue wear and abrasive when the aged temperature was 40 degrees C, 60 degrees C and the aged time was 120 h, 240 h and 360 h. At the 80 degrees C, 480 h and 720 h aged conditions, the main wear mechanisms between rubbing pair were adhesin wear and fatigue wear. The knowledge gained herein will be useful for optimizing and designing water-lubricated material in extreme conditions to prolong the service life of water-lubricated bearings.