The Surface Modification Of CoCrMo Alloy By Plasma Immersion Ion Implantation Deposition

CoCrMo alloy has been extensively used in orthopedic implants for its excellent biocompatibility and mechanical property, but its application is limitied for the potential toxiticy of Co and Cr ions. Thus, CoCrMo alloy surface modifications have attracted a lot of researcher's attention in order to reduce the Co and Cr ions releaseIn this study, CoCrMo was modificated by the high frequency and low voltage ionic nitriding, and DLC were deposited on CoCrMo alloy by plasma immersion ion implantation and deposition. The effect of different gas pressure and the power of radio frequency were considered in the study. The effect of the Ar content of the C2H2—Ar mixed gas and the voltage on the structures and properties of DLC films have been investigate. Finally, DLC film was fabricated on the nitrided CoCrMo, and the biotribological behaviors of CoCrMo and counter part UHMWPE were investigated in bovine synovia lubrication.After the nitriding process, the microstructure and composition were characterized with X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The thickness of the modified diffusion layer was investigated by scanning electron microscopy (SEM). The corrosion resistance of nitriding layer was characterized by electrochemical corrosion test. Raman spectroscopy and X-ray photoelectron spectroscopy were ultilized to characterize the structure of the DLC film. The adhesion strength were examined by WS-97 scratch tester. Surface hardness and wear resistance of the two modificated layers were performed by HXD-1000 microhardness meter and CSEM ball-on-disk-type equipment. The wear tracks of DLC/UHMWPE pairings in biotribological behaviors were acquired by optical micrographs and SEM.It was found that surface property of the CoCrMo alloy could be extensively improved through plasma immersion ion implantation and deposition. Plasma nitriding on CoCrMo can enhance mechanical properties apparently but decrease corrosion resistance. The micro compositons of the nitrided layers were Cr2N,CrN and Co2N. The thickness of nitriding layer increased with the increasing of the gas pressure and radio power, and mechanical properties enhanced, in other words, lower gas pressure and higher radio power were of great benefit to the property of the nitriding layer. The results also indicted that, Ar fraction in the C2H2-Ar gas mixture and the base voltage have important effects on the structure and the adhesion of the a-C:H films, and DLC films can improve corrosion resistance. When Ar fraction in the C2H2-Ar gas mixture is less than 50%, the a-C:H film microstructure transfer from graphite-like to diamond-like which contains higher sp binding, the adhesion strength and wear resistance decreased but the hardness decreased with the increment of Ar fraction. However, when Ar fraction in the C2H2-Ar gas mixture is beyond 50%, the film will contain more sp2 bonding and exhibit higher adhesion strength and wear resistance but lower hardness with the increment of the Ar fraction. With the increase of the bias voltage, C-C bonds were promoted from sp3 to sp2 due to the bombardme(?) of ion, as a result, hardness decreased and the adhesion strength, but little effects on corrosion resistance due to bias-voltage. The CoCrMo treated both nitriding and depositing DLC can decrease wear abrasion for both of the pairings.