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    A novel fabrication method for a TiO2 layer over CoCr alloy
    (Taylor & Francis Ltd, 2019) Cetiner, Dogukan; Paksoy, Ahmet Hilmi; Tazegul, Onur; Baydogan, Murat; Guleryuz, Hasan; Cimenoglu, Huseyin; Atar, Erdem
    This study has been initiated to form a TiO2 layer having enhanced biological properties on the surface of a CoCr alloy, which is mostly used in manufacturing of orthopaedic implants. As a novel approach, CoCr alloy samples were first coated with titanium and then oxidised in air at 600 degrees C for 60 h. Surface characterisation of the samples were made by structural surveys (scanning electron microscopic examinations, X-ray diffraction analyses), roughness and hardness measurements, bioactivity and wear tests. Results of the experiments have showed that fabrication of TiO2 as the outermost surface layer caused remarkable increment in the wear resistance and the bioactivity of the CoCr alloy.
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    Thermal Oxidation of Cold Sprayed Titanium-Based Coating Deposited on Co-Cr Alloy
    (Springer, 2018) Cetiner, Dogukan; Paksoy, A. Hilmi; Tazegul, Onur; Baydogan, Murat; Guleryuz, Hasan; Cimenoglu, Huseyin; Atar, Erdem
    This study focuses on the surface modification of a medical grade Co-Cr alloy via combining cold spray and thermal oxidation processes. After deposition of a Ti96-Al4 (wt.%) coating, samples were oxidized at 600 degrees C for 60h in air. Oxidation transformed the coating into a dual-layered structure comprising an outer oxide layer (mainly rutile) with a diffusion layer (mainly oxygen enriched titanium and Ti-Al intermetallics) beneath it. Formation of new phases made the diffusion layer brittle and prone to fracture during pull out tests. Scratch and Rockwell-C tests confirmed good adhesion between the oxide and underlying diffusion layers, having average hardness as 1297 HV and 387 HV, respectively. The dual-layer coating exhibited excellent wear performance in a 0.9wt.% NaCl solution against sliding action of alumina ball as compared to Co-Cr substrate, especially at contact pressures<1200MPa, while the maximum in vivo contact pressure is<15MPa for load-bearing orthopedic implants. Furthermore, the release of the aluminum from the dual-layer coating into 0.9wt.% NaCl solution is lower than the permissible limit stated by the International Agency for Research on Cancer.