Theoretical And Experimental Study On Lubrication Characteristics For Textured Surface Of Artificial Joint

As the trend of aging population aggravates,the demand for artificial joints in China will increase in the future.The service life of an artificial joint depends largely on the performance of its friction and wear properties.Due to its good biocompatibility and biological activity,hydroxyapatite(HA)and its composite bioceramic coating have a very good prospect for application in the field of artificial joints.The coating itself has defects of poor wear resistance and brittleness,however.It is an important direction for the development of artificial joint materials to improve the tribological properties of ceramic coating materials and prolong the service life of the artificial joints.As a treatment method for surface modification,the surface texture has been extensively studied to prove that it can effectively improve the tribological performance of the friction surface,and is widely used in bearings,mechanical seals and other engineering fields.In order to study the effect of texture in the application of bioceramic materials,the theoretical model of hydrodynamic lubrication and mixed lubrication respectively is established,based on Reynolds equation and PC average flow model on texture surface.The finite difference method combined with numerical iteration is applied to calculate and solve the model through Matlab programming.The pressure distribution in the calculation area and the theoretical friction coefficient of texture surface are obtained,used as the criterion of tribological performance of texture surface.At the same time,the femtosecond laser processing technology is used to process the elliptical texture arrays with different arrangement patterns and the circular texture arrays with different surface coverage ratios on the surface of zirconia-reinforced HA bioceramic coating.The friction and wear test is performed on the reciprocating test platform.The three-dimensional profilometer is used to characterize the wear depth of the coating,and explore the design parameters of the coating with better wear resistance.The main work and achievements are as follows:(1)The elliptical dimples with its direction of motion of long axis parallel to its upper surface under the hydrodynamic lubrication model can generate the most extra load and the smallest friction coefficient.The friction coefficient on the surface of the circular dimples texture gradually decreases with the increase of the surface coverage.Under the cross contrast analysis,the impact of the circular dimples' surface coverage ratio and diameter on the friction coefficient,revealing that there is no interaction between them,and the same diameter at different texture surface coverage ratios has the lowest friction coefficient.(2)Under the condition of mixed lubrication,the influence of the texture shape and the surface coverage ratio on the friction coefficient is approximately the same as that under the hydrodynamic lubrication condition.And the smaller the surface coverage ratio,the greater the difference in the friction coefficient of the different shape textures studied in this paper.Considering the roughness factors on the texture surface under the condition of mixed lubrication,the friction coefficient obtained is generally higher than that under the hydrodynamic lubrication model.(3)Under the condition of bovine serum lubrication,the friction coefficient and the wear amount of the circular dimples texture sample with a surface coverage of 25% were the smallest.As the surface coverage ratio was less than 25%,the friction coefficient and the wear amount decrease with the surface coverage ratio increase.As the surface coverage ratio increased to 30%,the coating bond strength decreased,result in coating material particles fall off and participate in the wear process.So the friction coefficient and wear amount compared to that of 25% is higher.(4)Under the condition of bovine serum lubrication,the friction coefficient and the wear amount of the elliptical texture sample with the surface coverage ratio of 10%,the long axis parallel to the direction of movement of the ceramic pin and 45° with it are all smaller than those of the circular dimples texture sample on same surface coverage ratio.For the elliptical texture samples,the friction coefficient and wear amount increase with the angle increase formed by the long axis and the direction of movement of the ceramic pin.In conclusion,the surface texture processed by femtosecond laser processing technology can effectively improve the wear resistance of HA composite bioceramic coating surface,and in a certain range,the wear resistance of the coating increases with the increase of surface coverage ratio.Under the same surface coverage ratio,the elliptical dimples which its direction of motion of long axis parallel to its upper surface is better than that of the circular texture.The experimental results preliminarily verify the reasonableness of the theoretical analysis.The effect of different texture parameters on the friction coefficient of the coating surface is investigated through the theory combine with experiment in this dissertation,which provided a reference for the application of surface texture technology in the field of bio-ceramics.