Metallurgical aspects of sliding wear of fcc materials for medical applications

Worn surfaces of biomedical fee alloys X2CrNiMo18-15-3, CoCr29Mo6, X13CrMnMoN18-14-3 are generated by sliding wear in order to understand the mechanisms, which bring about small wear particles. Depending on the acting wear mechanisms the debris is produced by different sites of crack initiation and paths of crack propagation. Thus, the subsurface deformation mechanisms are investigated as well. This investigation revealed that the worn surfaces of all three materials consist of a nanocrystalline layer underneath which appearances of cyclic deformation are visible. With respect to the stacking fault energy X13CrMnMoN18-14-3 as well as the CoCr29Mo6 depict sliding bands, stacking faults, and strain induced epsilon-marten site bringing about a sufficient support of the nanocrystalline layer. Thus, 80 to 500 nm fine globular and lamellar wear particles are just torn off this layer. In contrast to this, X2CrNiMo18-15-3 shows cell walls in distances of about 50 p in below the worn surfaces, which act as sites for crack initiation and propagation. The mean wear particles are about an order of magnitude bigger and range from 20 to 250 pin. Due to the fact that the nanocrystalline layer is not supported by the material underneath it has no distinct positive effect on the wear rate.