Surface morphology manipulation and wear property of bioceramic oxide coatings on titanium alloy

Different thickness and surface porosity of TiO2 coatings on Ti alloys as bio-implants appear to have a different behavioral combination of bioactivity, chemical stability and mechanical integrity. In order to study the wear properties of the coatings under extremely high loading conditions, for instance, sport impacting and crashing, a newly-developed impact-sliding testing instrument was used to simulate the impacting and sliding motions of the implants experienced with extreme contact stresses during the accidents. Traditional Pin-On-Disc (POD) tribotests were also carried out at 2 N and 5 N load conditions with maximum Hertz contact stresses of 471 and 639 MPa, respectively. The tests conducted in dry and simulated body fluid (SBF) environment were to figure out the coefficient of friction (COF) of the TiO2 coatings and the effect of the SBF on COF. The research results showed that the smooth and uniform surface was beneficial in reduction in COF and also led to a better coating performance in both dry and wet wear tests even if the coating was slightly thinner. The uniform coating had a less degree of surface failure during 1000 cycles of the impact-sliding tests at 80 N/200 N (approximate 0.8–1.2 GPa contact stress) impact-sliding forces. The coating surfaces with larger pores or higher roughness would lead to a higher friction coefficient and earlier coating failures. The test results also showed that the TiO2 coatings had a low COF of around 0.2, and the performances of thinner coatings were worse in SBF than in dry air, indicating that the SBF might have a corrosion-induced negative effect.