Transmission electron microscopy analysis of worn alumina hip replacement prostheses

Explanted worn alumina orthopaedic hip replacements show characteristic wear regions, ranging from severe wear, dominated by intergranular fracture, to regions in which minimal damage has occurred during articulation. The surface damage accumulation mechanisms are complex and not fully understood. This paper presents a detailed transmission electron microscopy (TEM) study of the surface damage accumulation mechanisms following in vitro tested worn alumina hip replacement prostheses. TEM of focused ion beam cross-section samples indicated extensive surface dislocation activity, which is restricted in the outer grain layer. Except for one example of basal slip, all slips were found to be on pyramidal planes. Both inter- and transgranular cracks were observed in regions of high wear. Grooves, largely associated with third-body abrasion, were generally associated with extensive dislocation activity. Three types of wear debris were seen from the worn surface, namely: granular wear debris, nanocrystalline wear debris and oblong wear debris. Wear debris were shown to arise from grain pull-out and severe plastic deformation at the surface. The observations allow a mechanistic model of the damage accumulations leading to wear and ultimately failure.