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The mechanisms of wear in ultra-high-molecular-weight polyethylene (UHMWPE) acetabular cups were investigated on both laboratory simulator-tested cups and a clinically retrieved component. Two different levels of wear process were identified: one characterized by the formation and detachment of platelet-like flakes from initial machining marks, and the other by the formation of fine ripple and fibrils by repeated passes of microscopic asperities on the femoral head. Both wear processes could be described by a criterion of critical plastic strain. A theoretical model was developed to account for the generation of the microscopic wear particles based on such a critical strain criterion. Its predictions of the dependence of the UHMWPE wear rate on surface roughness and applied load were in excellent agreement with previously published experimental correlations.

The surfaces of SUS304L stainless steel and pure iron specimens prepared by a lapping method were treated with argon ion bombardment, and then diffusion bonding was carried out. The effect of argon ion bombardment treatment on the properties of diffusion bonding joint was investigated by the tensile tests of joints and microstructure analyses of the fractured surfaces. The results showed that the argon ion bombardment treatment before bonding was effective to clean the bonding surface and reduce the inclusions at the bonded interface, so that the tensile strength of the bonded joints was improved and bonding temperature was lowered. The joint properties of pure iron were more excellent than those of SUS304L stainless steel. The amount of the inclusions at the joints with argon ion bombardment treatment depended on affinity of oxygen to metal.KEY WORDS: argon ion bombardment; diffusion bonding; SUS304L stainless steel; pure iron; microstructure; inclusion; oxide film.