The Tribological Properties And Metal Ions Release Of DLC Film Deposited On CoCrMo

CoCrMo alloys are one of the most widely used materials for orthopaedicimplants due to their excellent mechanical properties, good wear resistance andoutstanding corrosion resistance. However, in the clinical application, the release andtoxicity of Co and Cr ions becomes a potential danger in joint replacement, whichinfluence the service life of artificial joint seriously. Diamond–like carbon (DLC) canbe used as a protective coating on the joint implants because of its extraordinaryproperties such as high hardness, low friction coefficient and biocompatibility, whichcan reduce the formation of wear particles and impede the metal ions released fromsubstrate. DLC deposited on the CoCrMo can improve wear resistance of CoCrMo,reduce wear debris specially, and reduce the incidence of aseptic loosening during thelong term of artificial joint implants. Furthermore, it can solve the problem of metalion release, and improve the biocompatibility of artificial joint, which is significantfor medical CoCrMo alloy used in artificial joints.The DLC film was deposited on the CoCrMo by using the composite depositiontechnology of magnetron sputtering and ion source. The fundamental characteristicsincluding composition, structure, surface topography, hardness, film thickness,binding force, contact angle and corrosion resistance and so on were investigated byusing Raman spectroscopy, X-ray photoelectron spectroscopy, scanning electronmicroscope, energy dispersive spectrometer, nanoindentation, scratch tester and otherinstruments. In addition, the stress of DLC film deposited on CoCrMo was calculatedby Abaqus. To evaluate the tribological properties of DLC, the sliding wear test ofDLC was performed on the Universal Multifunctional Tester (UMT) with theball-on-flat and pin-on-flat style under dry friction and conditions against ZrO2andUltrahigh molecular weight polyethylene (UHMWPE) respectively. Finally, theexperiments including static immersion test, blood compatibility test and cytotoxicitytest were carried out to examine the blood compatibility.The results revealed that DLC coating contained sp3could be deposited on thesurface of CoCrMo. The hardness of sample was improved but the surface of DLCexist a few pores, and the thickness was about3μm, and the binding force was4.5N.The contact angle decreased both in deionized water and saline. The corrosionpotential increased and corrosion current density decreased in saline, so thecomprehensive performance including hardness, corrosion resistance, wettability and other properties increased significantly compared to CoCrMo. Moreover, the stressincreased result from DLC film and the shear stress changed abruptly at the interfacebetween the film and substrate. The shear stress increased at both surface andinterface when friction coefficient increased, and the change of friction coefficienthad a significant effect on the value and distribution of surface, but little effect on theinterface.The value of friction coefficient was stable at about0.1when DLC deposited onthe CoCrMo sliding against ZrO2under dry, saline and bovine serum lubrication, andcompared with CoCrMo, the friction coefficient decreased and fluctuated slightly. Thewear mechanism was mainly abrasive wear when CoCrMo sliding against ZrO2, whileDLC film wear lightly, only showed light wear traces. The friction coefficient andfluctuation decreased with different degree compared with CoCrMo when slidingagainst UHMWPE. What’s more, it not only could reduce the wear rate of CoCrMo,but also reduce the wear of UHMWPE, so DLC deposited on the CoCrMo had a goodeffect on friction reduction and wear resistant behavior in sliding against both ZrO2and UHMWPE under dry, saline and bovine serum lubrication.The peeling of material and corrosion was formed on the surface of CoCrMoafter soaking in saline for nine months, while some pinholes were formed on the DLC.The release of Cr ion was slower than that of substrate, which could restrain therelease of Cr ion. On the contrary, the concentration of Co decreased significantlywith increase of time，but it all greater than the concentration of Co ion in thesubstrate. Additionally, DLC film had a better blood compatibility since that theplatelets consumption reduced from12.8%to10.2%and the hemolysis also reducedfrom1.49%to0.55%. Similarly, the cytotoxicity decreased because the absorbancevalue of DLC film increased9.8%. In summary, these results showed that DLCdeposited on the CoCrMo could effectively apply to artificial hip joints.