  Total hip replacement is the most effective treatment for late stage
osteoarthritis. However, adverse local tissue reactions (ALTRs) associated with
fretting corrosion have been observed in patients with modular total hip
implants. The purpose of this study is to increase the fretting corrosion
resistance of the CoCrMo alloy and the associated metal ion release by applying
hard coatings to the surface. Cathodic arc evaporation technique (arc-PVD) was
used to deposit TiSiN and ZrN hard coatings on to CoCrMo substrates. The
morphology, chemical composition, crystal structures and residual stress of the
coatings were characterized by scanning electron microscopy, energy dispersive
x-ray spectroscopy, and X-ray diffractometry. Hardness, elastic modulus, and
adhesion of the coatings were measured by nano-indentation, nano-scratch test,
and the Rockwell C test. Fretting corrosion resistance tests of coated and
uncoated CoCrMo discs against Ti6Al4V spheres were conducted on a four-station
fretting testing machine in simulated body fluid at 1Hz for 1 million cycles.
Post-fretting samples were analyzed for morphological changes, volume loss and
metal ion release. Our analyses showed better surface finish and lower residual
stress for ZrN coating, but higher hardness and better scratch resistance for
TiSiN coating. Fretting results demonstrated substantial improvement in
fretting corrosion resistance of CoCrMo with both coatings. ZrN and TiSiN
decreased fretting volume loss by more than 10 times and 1000 times,
respectively. Both coatings showed close to 90% decrease of Co ion release
during fretting corrosion tests. Our results suggest that hard coating
deposition on CoCrMo alloy can significantly improve its fretting corrosion
resistance and could thus potentially alleviate ALTRs in metal hip implants.
