Fretting wear behaviors of thermal sprayed hydroxyapatite (HA) coating under unlubricated conditions

Fretting damage (fretting wear and fretting fatigue) is one of the modern plagues for the orthopedic implants because the oscillatory micromovement often occurs at the interface between the implant and bone. In this investigation, the fretting wear behaviors of plasma sprayed hydroxyapatite (HA) bioceramic coatings on titanium alloy substrate were investigated under unlubricated conditions as a function of number of oscillatory cycles, normal load and amplitude. Coefficient of friction, wear volume and wear mechanisms were studied. For the different test conditions in this study, the fretting regime is gross-slip. Results showed that the fretting wear mechanisms of plasma sprayed bioceramic coatings were mainly delamination and abrasive wear, whereas the wear mechanisms of the substrate Ti alloys were oxidation, delamination as well as abrasive wear. Under unlubricated condition, the fretting wear resistance of bioceramic coatings was not as good as that of Ti-6Al-4V substrate due to the porous, lamellar and loose structure of HA coating.