Fretting-corrosion mechanisms of Ti6Al4V against CoCrMo in simulated body fluid under various fretting states

Ti6Al4V alloy–CoCrMo alloy pair is commonly applied for modular head–neck interfaces for artificial hip joint. Unfortunately, the fretting corrosion damage at this interface seriously restricts its lifespan. This work studied the fretting corrosion of Ti6Al4V–CoCrMo pair in calf serum solution. We established this material pair’s running condition fretting map (RCFM) regarding load and displacement, and revealed the damage mechanism of this material pair in various fretting regimes, namely partial slip regime (PSR), mixed fretting regime (MFR), and gross slip regime (GSR). The damage mechanism of Ti6Al4V alloy was mainly abrasive wear induced by CoCrMo alloy and tribocorrosion. Adhesive wear (material transfer) also existed in MFR. The damage mechanism of CoCrMo alloy was mainly abrasive wear induced by metal oxides and tribocorrosion in GSR and MFR, while no apparent damage in PSR. Furthermore, a dense composite material layer with high hardness was formed in the middle contacting area in GSR, which reduced the corrosion and wear of Ti alloys and exacerbated damage to Co alloys. Finally, the ion concentration maps for Ti and Co ions were constructed, which displayed the transition in the amount of released Ti and Co ions under different displacements and loads.