Effect Of Two Methods Of Surface Modification On Physical And Chemical Properties Of Dental Casted Cobalt-Chromium Alloy

Cobalt-chromium(Co-Cr) alloy casted removable partial denture is currently widely exploited in prosthodontical field. However, Co-Cr alloy will be under various chemical and even electro-chemical reactions with surrounding materials while used in the complicated and relatively chemical active oral environment. The released metallic ions, generated from the consequent corrosions, not only affect the designed material properties, but also have negative effect on human body at different degree. There have being reports about allergic reactions induced by Co,Cr ions in European and American countries. Since the corrosion initially starts from the alloy surface, different kinds of surface modification in order to improve the anti-corrosion and bio-compatibility of material are heavily investigated. After surface modification, restorative material owns the specific properties of new surface(e.g. anti-corrosion, wear resistance and better bio-compatibility), while keeping the basic mechanical property of substrate. In this thesis, industrially mature deposition technique was utilized to deposit titanium nitride(TIN) film on Co-Cr alloy and additionally comprehensive comparisons between this deposition approach and conventionally gold-plating technique were conducted in several aspects to demonstrate the superior performance of these two surface modification methods.PartⅠPreparations of Titanium Nitride and Gold Coating on Cobalt-Chromium Alloy, and Individual Tests regarding Mechanical FunctionsObjective: sample preparation and evaluation of their mechanical properties.Materials and methods: Multi-arc ion plating and Electro-depositing were used to deposited TiN and gold coating on Co-Cr alloy respectively. Crystallographic information of individual thin films were revealed by X-ray diffraction(XRD), moreover, their surface morphology were obtained with metallurgical microscope. Mechanical properties including surface-substrate bonding force and wear resistance of deposited thin films were acquired from scratch methods and wear tests.Results: Both techniques produced compact, uniform and smooth golden thin film on the Co-Cr substrate. The purity of TiN and gold components in both films were confirmed with XRD. The averaged bonding force between TiN film and its substrate was 77 N, while only 7 N for the gold coating. Under the same experimental conditions, the weight loss of TiN coated samples was statistically less than that of gold coated and uncoated samples(P＜0.05).Conclusion: TiN film with similar color and superior mechanical properties, with respect to gold film, can be prepared by multi-arc ion plating on Co-Cr alloy.PartⅡEffect of Two Coatings on Electrochemical Corrosion of Cobalt-Chromium AlloyObjective: To investigate the effect of TiN and Au coating on electrochemical corrosion of Co-Cr alloy.Materials and methods: The electro-chemical method was used to get the electric potential of corrosion(Ecorr) of TiN, glod coated and uncoated samples in aritifical saliva environment. After importing the dynamic electric scanning parameters, the polarization curve can be obtained, which was afterwards linearly fitted to acquire the polarization resistance(Rp) and current density of corrosion(Icorr) of individual test components.Results: Compared with the control alloy without coating, the Ecorr and Rp of coated samples were higher, and the Icorr was lower. Moreover, these parameter differences were more obvious at TiN coated samples.Conclusion: The anti-corrosion performance of Co-Cr alloy is improved with TiN and Au coating, inbetween, TiN coating exhibites a superior performance than conventionally gold coating. PartⅢEffect of Two Coatings on Chemical(Marination) Corrosion of Cobalt-Chromium AlloyObjective: To investigate the effect of TiN and Au coating on chemical corrosion of Co-Cr alloy in a marination environment.Materials and methods: The groups of samples coated with TiN and gold film respectively were immersed into the same artificial saliva at 37℃for three months. During the whole immersion period, the concentration of cobalt ion in the 10 ml artificial saliva was analyzed with atomic absorption spectrophotometer after 30, 60 and 90 days. Finally, the weight change of the post- immersion samples was measured. The samples without coating were used as the controls.Results: In all the groups, Co ion concentration in the artificial saliva increased while the immersion continues. Co ion concentration from TiN film coated samples into the immersed artificial saliva was lower than that of other two kinds of samples after the same immersion time. The weight loss of TiN coated and uncoated samples was statistically smaller than that of the gold coated samples(P＜0.05).Conclusion: The anti-corrosion property of the Co-Cr alloy can be strengthened by TiN coating.