Tribocorrosion Behavior Of Dlc-Coated Cocrmo Alloy

Metal ion release is one of major problems of metal-on-metal (MOM) joint implants during practical application. The carcinogenicity and toxicology of elevated metal ions have been attracted wide attention. The generation of the metal ions mainly comes from corrosion process of metal materials, especially under tribocorrosion process. In order to improve the corrosion resistance and wear resistance of metal joint material, the surface modification method has been raised. The Diamond-like carbon (DLC) film is considered to be one of the promising materials for surface modification. This is due to its excellent wear resistance and chemical stability. Therefore, in this study the DLC-coated CoCrMo alloy was chosen as main study object and with CoCrMo alloy as contrast sample the tribocorrosion behavior of DLC-coated CoCrMo alloy at friction interface was discussed.The DLC film was deposited on CoCrMo alloy by using a filtered cathodic vacuum arc technique (FCVA). The tribocorrosion behavior of DLC-coated CoCrMo alloy was studied in PBS,25%(v/v) bovine calf serum, albumin (20mg/ml) and globulin (6mg/ml) solution by using a tribometer with an integrated electrochemical cell. During rubbing process the open circuit potential (OCP), polarization curves were tested and the electrochemical impedance spectroscopy (EIS) before and after friction was also measured.The results showed that during rubbing process DLC film can improve corrosion resistance of CoCrMo alloy. The DLC-coated CoCrMo alloy has nobler open circuit potential and lower polarization current compared with CoCrMo alloy during sliding process. And higher impedance value before and after friction were also exhibited on DLC-coated CoCrMo alloy. In addition, the results also indicated that in test solution the tribocorrosion behavior of DLC-coated CoCrMo alloy and CoCrMo alloy is different. This distinction comes from differences of surface physical and chemical properties between DLC-coated CoCrMo alloy and CoCrMo alloy. Compared with CoCrMo alloy, the less protein was adsorbed on poor hydrophilic DLC surface. Furthermore, the DLC-coated CoCrMo surface has lower metal ion concentration. This is because the chemically inert DLC film can effectively prevent CoCrMo substrate corrosion. Therefore, the difference of solution composition and corrosion state (OCP state and anode polarization state) has little impact on the tribocorrosion process of DLC-coated CoCrMo alloy at friction interface. The inhibition of DLC film on reactive ion transfer process is the major controlling factor of electrochemical reaction. But for CoCrMo alloy the major controlling factor of electrochemical reaction is the electrode reaction activation process and the influence of solution composition and corrosion state on CoCrMo alloy tribocorrosion process is significant.Therefore, for DLC-coated CoCrMo alloy in different test solution the impedances difference is small, and the friction coefficient is similar, all about0.2. And under different corrosion state (OCP state and anode polarization state) the DLC-coated CoCrMo all showed a better corrosion resistance in PBS and bovine calf serum solution than that in PBS albumin/globulin-containing solution. But for CoCrMo alloys, surface adsorption of proteins and phosphate can significantly affect the impedances value. And the corrosion state change can obviously influence corrosion resistance of CoCrMo alloy in protein containing solution under sliding process. Under OCP state in PBS albumin/globulin-containing solution the competition between protein and phosphates could weaken inhibition effect of absorbed layer on reactive ions, which lead to lower and unstable OCP value during friction process compared with PBS and bovine calf serum solution. However, when CoCrMo alloy under anodic polarization potential state (0.1v-0.5v), the concentration of metal ions on surface increased which can weaken competition effect between protein and phosphate and strengthen action between protein and metal ions. The complex organicmetal film could be formed on the CoCrMo alloy in protein-containing solution which could retarded the metal ions further released and this lead to a smaller passive current. Furthermore, the results of friction force curves in different test solution showed that the protein can significantly influence the friction interface composition of CoCrMo alloy, but for DLC-coated CoCrMo the effect of protein is not prominent. For DLC-coated CoCrMo, generated friction force primarily derived from the relative movement between counterpart and the DLC film.