| For combined artificial hip joint, there are different forms of fretting corrosionwear on the mating surface between head and neck under the cyclic loading of bodymovement, which may induce implant failure and even endanger human health due tolong-term effects. Therefore, it is of great significance to performing the research onthe fretting corrosion characteristics of interface between prosthesis head and neck o fartificial hip joint.Galvanic corrosion between Ti6Al4V alloys and CoCrMo alloys, torsionalfretting corrosion tests with Ti6Al4V ball (pin) and CoCrMo plane and torsionalfretting corrosion experiments simulated the contact mode between prosthesis headand neck were carried out respectively in different medium. Combined with a varietyof analysis means, the running characteristics and damage mechanism of torsionalfretting corrosion between Ti6Al4V and CoCrMo in different conditions wererevealed. The main conclusions are as follows：Firstly, in saline solution, with the extension of soaking time, the galvanic currentbetween the Ti6Al4V alloys and CoCrMo alloys rised, due to spontaneous superiorcorrosion resistance and cathodic protection, the impedance value of Ti6Al4V alloysmaintained at a high value, while the impedance value of CoCrMo alloys was at leastone order of magnitude inferior to that of Ti6Al4V alloys because of dissolution ofpassive film。While in FBS, the galvanic current did not appear an obvious increasingtendency，the potential difference became small and galvanic corrosion trend ofthermodynamics was not obvious with the extension of time, the anode and thecathode were not easy to distinguish. After a long time soaking, the phenomenon ofmutual protection was observed between the two kinds of alloys.Secondly, under the pin-plane contact form, the fretting run in slip regime insaline solution, wear area covered the entire contact area, and in bovine serumsolution fretting run in partial slip regime, serious wear area was mainly located at theouter contact zone, fretting damage mainly characterized by abrasive wear andadhesive wear. Under ball-plane contact form, torsional fretting run in partial slipregime with smaller angular displacement, and in the case of larger angulardisplacement, torsional fretting run in slip regime. And with the increase of theangular displacement, the severe wear area gradually expand to center of contact area,fretting damage mainly characterized by joint action of abrasive wear, corrosive wearand adhesive wear. As we can see from the three dimensional morphology, at the edge of the wear area arc furrows were founded in saline solution. Friction torque curvescould be divided into the running-in stage, peak stage and stable stage. In two kinds ofsolution, impedance and polarization resistance obviously decreased with the increaseof normal load and the the angular displacement.Thirdly, under the taper contact form between head and neck, in the case ofrelatively smaller normal load, the friction torque values first increased and thenstable with the increase of cycles, in the case of larger normal load, friction torquevalues stabled in early stages without obvious rising stage. Corrosion potential ofCoCrMo specimens after frition showd an obviously negative shift, anodic currentincreased as well as corrosion tendency of material. When the angular displacementθ>1°, the impedance of CoCrMo alloys decreased obviously after the friction as wellas the polarization resistance, when the angular displacement θ=2°, angulardisplacement had a greater influence on the corrosion resistance of materialscompared with normal load. When the angular displacement θ=2°, the smaller normalload produce obvious slip band on the surface where serious wear happensaccompanied by corrosion damage. And in the case of larger normal load, a mass ofscratches appeared at wear surface accompanied with phenomenon of spalling andcorrosion of materials, the relative motion of surface given priority to partial slipcondition. |
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