Three-body abrasive wear behaviour of orthopaedic implant bearing surfaces from titanium debris

The abrasive wear behaviour of several orthopaedic bearing materials was characterized for fully conformal, reciprocating sliding contact against ultra-high molecular weight polyethylene (UHMWPE). The bearing surfaces investigated were nitrogen ion implanted Ti−6Al−4V, TiN coated Ti−6Al−4V, Ti−6Al−4V, F-799 Co−Cr−Mo, yttria-stabilized zirconia and a Zr−2.5Nb alloy with a zirconia ceramic surface. The third-body debris was introduced as either Ti−6Al−4V particles or oxidized titanium powder (black debris). The wear tests were performed in deionized water with the third-body debris entrapped between the UHMWPE and the hard bearing surface. Surface profilometry measurements, scanning electron microscopy (SEM) and optical microscopy showed the severity of damage to the hard bearing surfaces to increase with decreasing hardness. The abrasion damage to the UHMWPE increased as the roughness of the opposing, hard bearing surface increased. Surface profilometry and energy dispersive spectroscopy (EDS) also showed oxidized titanium (black debris) to form an adherent transfer layer on all of the hard bearing surfaces. Nitrogen ion implantation of Ti−6Al−4V was ineffective in reducing wear of both the Ti−6Al−4V substrate and the UHMWPE. Solid yttria-stabilized zirconia and zirconia-coated Zr−2.5Nb showed no evidence of abrasion damage and produced the least amount of UHMWPE wear. These results are attributed to the high hardness and excellent wear resistance of zirconia and the excellent wettability of ZrO₂ due to its relatively high ionic character in comparison to metals and covalently bonded compounds.