The Research Of Plasma Nitriding And DLC Films Duplex Treatment On CoCrMo Alloy

Abstract:CoCrMo alloy has been extensively used in artificial joint for its excellent biocompatibility and wear resistant, but its application is limited for the potential toxiticy of Co and Cr ions which were produced by wear. Thus, in order to increase the wear resistance of CoCrMo and decrease Co and Cr ion release, surface modification is necessary to CoCrMo alloy.In this study, CoCrMo was modified by plasma nitriding and DLC films. The effect of doped elements, the thickness of DLC films and the high energy Cr ion bombard CoCrMo substrate before deposition DLC films on the surface and cross-section morphology, adhesion, hardness and friction and wear properties of DLC films were considered in the study. The effect of the nitridation temperature on the phase structure, the thickness of the nitrided layer, microhardness and wear resistance of CoCrMo alloy have been investigate. The surface and cross-section morphology, hardness, adhesion and wear resistance of duplex treatment sample and non-duplex treatment sample were investigated. The friction and wear behavior of duplex sample and CoCrMo alloy under lubrication of Hank’s solution and0.9%NaCl solution respectively was investigated.The thickness of DLC films, doped elements (W/Ti) and high-energy ion bombardment have great effect on properties of DLC films. The hardness, adhesion and wear resistance of W-DLC were significantly higher than that of Ti-DLC. When the thickness of W-DLC was2.00μm, W-DLC films were achieved highest adhesion (41.6N). The adhesion of W-DLC is increased50.7%by cathodic arc high energy Cr ion bombard CoCrMo alloy, which the adhesion strength was up to62.7N. The optimum preparation process for DLC thin films:W-DLC films, the thickness of W-DLC was2.00μm, the cathode arc high energy Cr ion bombard CoCrMo substrate before deposition DLC films.There was a layer of CrN on the CoCrMo alloy after plasma nitriding, which improved the hardness and wear resistance of CoCrMo alloy significantly. With the nitriding temperature increasing, the hardness of CoCrMo was first increased and then decreased, the thickness of nitride layer was increased and the wear rate of CoCrMo was first decreased and then increased. The hardness and wear resistance of CoCrMo was the highest when CoCrMo was plasma nitriding at600℃.The adhesion, hardness and wear resistance of duplex treatment samples were significantly better than the non-duplex treatment samples, which the adhesion strength and the hardness were up to62.7N and2329HV respectively. The wear resistance of W-DLC/CoCrMo is increased by one order of magnitude after CoCrMo plasma nitriding.The W-DLC film has good friction-reduction performance. The coefficient of friction reduced85.0%、82.2%and90.4%than CoCrMo alloy under dry sliding and Hank’s solution and0.9%NaCl solution respectively. The wear rate of W-DLC film o was reduced by3orders of magnitude compared with CoCrMo alloy in the same condition. The sliding wear plays a main role in W-DLC films and combined little of abrasive wear in those. The wear mechanisms of CoCrMo substrate are Oxidation, adhesive and abrasive wear.