Study On Bio-tribology Of Titanium Alloy Modified With DLC Film

With the rapid development of medical body implanted material, the technology of artificial joint replacement become the important medical method to recover the function of the patient joint and reduce the suffering of the patients. At present, the researches on the artificial joint focus on hip and knee. While the related literature and data of artificial cervical disc are less than hip and knee. What's more, the systematic study on bio-tribology behavior and wear mechanism is rare. Nowadays, the patient with cervical spondylosis is younger than before so that the artificial cervical disc is required longer life and better quality. Therefore, flexion, extension, lateral curvature and axial rotation of the artificial cervical disc are simulated in this paper and bio-tribology behavior and wear mechanism of the artificial cervical disc are researched systematically under different moving forms. Interactive mechanism is studied as well between different moving forms and this study has significant practical and theoretical value.Anodic ion beam source with unbalanced magnetron sputtering technique is used to deposit diamond-like film which contains hydrogen on the Ti6Al4 V substrate. The hardness, structure, morphology and wettability of DLC film are characterized and bio-tribology properties are tested by multi degree of freedom material abrasion tester. Meanwhile, finite element analysis is taken to analogize mechanical behavior and abrasion mechanism. Therefore, the following conclusions are concluded.Ultrahigh molecular weight polyethylene ball is prepared by high-temperature hot-press molding technology and anodic ion beam source and unbalance magnetron sputtering are used to deposit diamond-like film which contains hydrogen on the Ti6Al4 V substrate. The film appears the representative DLC film characteristic. The roughness of the surface decreases from 0.40?m to 0.28?m and the surface hardness rises by 129%. Besides, the contact angle of the surface is 37.41°, which leads to the better blood compatibility and appropriate interaction force. The film surface is relative smooth and combined closely with the substrate, none obvious crack is found on the film surface.By simulating the artificial cervical disc flexion movement of flexion, extension and lateral curvature, swing friction text is conducted. The friction coefficient of DLC film rises gradually with the increasing stress and swing angular displacement, which results in the increasing abrasion loss of UHMWPE ball and roughness after wearing. The wear forms of the DLC film modified titanium alloy are abrasive wear and adhesive wear which results that DLC film is easily fractured and spalt during friction and wear. However, comparing to the unmodified Ti6Al4 V alloy, DLC film has better abrasive resistance and the interfacial frictional force and abrasion loss decreases 77.6% and 11.2% respectively which results by the changing abrasion mechanism from the serious abrasive wear to the mainly adhesive wearBy simulating the rotation movement of the artificial cervical disc, rotation friction text is conducted. Friction rotatal torque, frictional dissipation and abrasion loss appears the increasing trend with the increasing stress and swing angular displacement. The mainly wear form of the DLC film modified titanium alloy is brittle spalling caused by stress concentration and wear forms of UHMWPE are combined influenced by adhesive wear and abrasive wear. Comparing to the unmodified Ti6Al4 V alloy, DLC film modified Ti6Al4 V alloy has better wear resistance and turns into slip zone more quickly. The friction rotatal torque of the contact interface decreases observably and the wear forms changes from serious abrasive wear into brittle spalling which results in higher abrasion loss of UHMWPE.Comparing with the swing-rotation combined movement of Ti6Al4 V alloy, the friction coefficient of swing is less than combined and rotatal friction torque is higher than combined. The abrasion loss of UHMWPE appears the trend that the sequence from high to low is rotation, combined, swing under different friction condition. On the condition of high circulation, the friction coefficient and rotatal torque of DLC film and abrasion loss of UHMWPE is lower than Ti6Al4 V apparently. The wear form of the central of the DLC film ball socket is adhesive wear and the edge is adhesive wear, whereas different parts of Ti6Al4 V ball socket are abrasive wear.Through finite element simulation, friction shear force and deformation of DLC film ball socket increase gradually with the rising load and swing angular displacement. Moreover, the displacement of DLC film socket of artificial cervical vertebra which is parallel to swing friction direction is larger than vertical friction direction. The center of DLC film socket appears frictional fatigue and fractures and drops out eventually, while local region appears brittle spalling. During rotation friction, the center of the joint socket appears adhesive zone and rotation movement area is the stick-slip mixed zone. In addition, the area of the relative slip zone, contact stress and friction shear stress on the artificial cervical intervertebral disc contact interface increases with the rising stress and rotation angular displacement which leads to the more serious wear of DLC film socket and material loss.