Fretting wear behavior of micro-arc oxidized Ti6Al4V articulating against ZTA and CoCrMo for taper junctions in artificial hip joints

Fretting wear at taper junctions of artificial hip joints is a major cause of allergy, prosthesis loosening, and even revision surgery. Micro‑arc oxidation (MAO) of Ti6Al4V for femoral stems offers a practical and promising approach to mitigating this problem. However, the fretting wear behavior between MAO‑Ti6Al4V and femoral head materials remains unclear. In this study, a high‑quality ceramic coating was first fabricated on Ti6Al4V by MAO. Fretting wear tests were then conducted under conditions representative of service environments of taper junctions in artificial hip joints. The fretting wear behavior and mechanisms of MAO‑Ti6Al4V/ZTA and MAO‑Ti6Al4V/CoCrMo pairs, as well as the respective contributions of the substrate and counterbody to material loss, were systematically investigated. The results demonstrated that, for both pairs, MAO treatment significantly reduced the fretting friction coefficient and wear rate of Ti6Al4V alloy, thereby providing effective protection and indicating considerable potential for clinical application in taper junctions. Moreover, the MAO‑Ti6Al4V/CoCrMo pair exhibited three‑body wear and a more pronounced micro‑cutting effect under the gross slip regime (GSR) and mixed fretting regime (MFR), which led to greater material loss and induced fatigue damage. In contrast, the MAO‑Ti6Al4V/ZTA pair was associated with lower fretting damage and superior fretting wear resistance. Notably, in the MAO‑Ti6Al4V/CoCrMo pair, the majority of material loss originated from CoCrMo, whereas in the MAO‑Ti6Al4V/ZTA pair, material loss occurred predominantly in MAO‑Ti6Al4V. For potential future clinical application, when MAO‑Ti6Al4V/CoCrMo pairs are employed at taper junctions, particular attention should be paid to the wear state of CoCrMo femoral heads.