Study On The Torsional Fretting Tribocorrosion Behaviors Of Contact Interface Between CoCrMo And PEEK

Artificial joint implants need to bear various cyclic loads and different forms ofdamage in the human body environment, such as,fatigue, abrasion and corrosion.Separateresearch about tribology and corrosion behavior between the mating surface is difficult toreveal the biological friction corrosion behavior of the artificial joint implants. Therefore,it is of great significance to perform the research on the torsional fretting tribocorrosioncharacteristics of artificial joint implants.The difference of the surface properties and the friction and wear behaviors forPEEK and UHMWPE were investigated.Besides,the torsional fretting experimentsbetween CoCrMo pin and PEEK plate and torsional fretting corrosion experiments werecarried out.Combined with a variety of microscopic analysis means,the runningcharacteristics and damage mechanism of torsional fretting wear between CoCrMo andPEEK in different conditions were revealed.Besides,the polarization curves and corrosionelectric current can provide a better understanding of the tribocorrosion process betweenthe mating surface.The main conclusions are as follows:Firstly,the ball indentation depth of UHMWPE under tested condition was about13times of that for PEEK indicating that the creep resistance of PEEK was far superior tothat of UHMWPE;Though the water absorption of PEEK was higher than that ofUHMWPE,PEEK is still harder than UHMWPE.Under25%bovine serum lubricatingcondition,the average friction coefficient of PEEK was lightly higher than that ofUHMWPE, the worn surface of UHMWPE was wider and deeper,concluding that PEEKhad better abrasion resistance.Secondly,under different conditions,torsional fretting between CoCrMo and PEEKmainly run in the mixed slip regime and slip regime.With the increase of angulardisplacement amplitude,T-θ curve changed from elliptic to parallelogram type.Thefriction torque firstly increased and then decreased with angular displacement increase.When torsional fretting was in mixed slip regime,the worn profile of PEEK was“W”type.With the increase of load or angular displacement,the worn profile wasdeeper,wear debris agglomerated on the surface of CoCrMo.The main damagemechanism is plastic deformation and adhesive wear.When torsional fretting run in slipregime,the worn profile of PEEK was “U” type.Wear debris was dragged.The wearmechanism still is adhesive wear, and the wear degree of edge area is more serious thancentral area.With the increase of loads, the friction torque was increasing.And more materials transferred to the surface of CoCrMo pin.Thirdly, before the tribocorrosion test, passivating film formed on CoCrMo pin in25%bovine serum, resulting in corrosion electric current always maintained at a lowlevel. When the test started, the passivating film was damaged.At the same time,corrosionelectric current increased and nature eroding voltage decreased,which indicated theaccelerated erosion rates.As angular displacement amplitude increased,the passivatingfilm was more seriously damaged and corrosion electric current was higher.When loadincreased,the nature eroding voltage was lower and the passivating film was harder torecover.Finally, environment medium had an effect on torsional fretting wear betweenCoCrMo pin and PEEK plate.In distilled water, the friction torque between the matingsurface was lower compared to dry friction and torsional fretting between CoCrMo andPEEK run easily.Due to the viscosity of bovine serum,the friction torque betweenCoCrMo pin and PEEK plate is higher in25%bovine serum.Besides,T-θ curves werelonger and narrower. In two kinds of lubrication conditions.Wear debris piled up on thewear scars.Transferred wear debris on CoCrMo pin was dendritic and corrosion behaviorappeared.