Atomic Scale Origin of Metal Ion Release from Hip Implant Taper Junctions
Millions of patients per year receive a hip implant as treatment for end-stage arthritis. These hip implants often consist of a cobalt alloy (Co-30Cr-5Mo) femoral head and a titanium alloy (Ti-6Al-4V) femoral stem. In-vivo fretting corrosion at the head-neck taper junction can lead to release of metal ions (specifically Co and Cr from the cobalt alloy) and metal wear particles, creating adverse local and systemic effects in the patient. Correlative transmission electron microscopy / atom probe tomography reveals the mechanism of nano-structural and atomic scale chemical alterations in the subsurface of titanium alloy subjected to in-vitro fretting under conditions similar to those occurring in-vivo in the hip . The fretting motion promotes tribocorrosion and hence Co-ion release from the more wear resistant cobalt alloy.