Friction And Wear Properties Of Surface Textured HA/ZrO₂ Bioceramic Coatings

Wear is one of the main reasons for the failure of artificial joints,and after the implantation of artificial joints,5 million wear particles will be produced each year,which directly affects the life of artificial joints.Hydroxyapatite and its composite bio-ceramic coating has good biocompatibility and biological activity,is an ideal material for artificial implant,however,because of coating brittleness,low intensity,poor wear resistance,it is difficult to satisfy the requirements of body load-bearing parts required,restrict its application in human load-bearing parts.Therefore,it is an important direction to improve the properties of bio-ceramic coating material,increase its wear resistance and mechanical strength and prolong its service life.In recent years,surface texture as a method to improve the surface wear resist has been widely used in hydrodynamic lubrication of surface oil film and dry wear research.Using plasma spraying technology and drilling technology of femtosecond laser processing,enhanced HA composite coatings were prepared on the surface of zirconia enhanced HA bio-ceramics coating with different diameters,surface coverage of dimple texture,using scanning electron microscopy and super depth 3D surface contour instrument to texting the surface and the section morphology of surface texture,using micro-hardness tester for measuring coating by micro hardness;UMT-3 wear test machine in a simulated human body environment in bovine serum lubricating conditions for texturing textured coating with different diameters and surface coverage of the corresponding relationship between the wear coefficient and the wear rate,get the optimal diameter and surface coverage of surface texture.The wear mechanism of textured coatings under the condition of bovine serum lubrication was investigated by observing the texture morphology of the best textured coatings under different load and speed.The main results of this paper are as follows:(1)30wt% zirconia HA composite coating on the surface of titanium alloy prepared by plasma spraying.The dimple with different diameter and regular array on the surface of the composite coating were fabricated by femtosecond laser drilling technique,then on the basis of the dimple diameter,the texture with different surface coverage was prepared.(2)Characterized the textured surface and cross-section morphologies,the overall array of textures is very neat,there is little difference in the size of the diameter of the dimple on the same specimen,There is no damage to the surface of the circumference of the texture dimple due to laser processing.The depth of different textures has some fluctuation,but the fluctuation is tiny.The micro hardness of the textured surface and laser processing area were measured,the results show that laser processing has little effect on its surface hardness,but in its processing area,the hardness of the bottom of the circular pits is obviously improved.(3)The wear experiments were carried out on the coating with different textured parameters of the lubricant as bovine serum,and the non-textured coating was tested at the same condition The experimental results show that the friction coefficient of most textured samples is less than that of the non-textured samples,the wear depth of all textured samples was less than that of the non-textured samples.The texture sample with diameter of 250?m,covering rate of 10% has the lowest friction coefficient and wear depth.(4)Load has great impact on friction coefficient and wear rate for the textured coating of covering rate 10%,dimple diameter 250?m.In bovine serum lubrication condition,the wear rate and friction coefficient increase with the increase of load.The textured coating on 4N and 8N load the wear surface morphology is smooth,have a certain luster,less surface micro cracks;at the loading of 12 N,the dimple morphology is damaged,morphology of the coating surface is rough,large surface micro cracks emerged.The wear mechanism of the best coating is micro spalling under low load.When the load is further increased,the wear mechanism of the coating is converted to the spalling failure caused by plastic deformation.(5)The friction coefficient of textured coating covered rate 10%,dimple diameter 250?m decreased with the increased of speed,and the wear rate at first decreased then increased with the speed.At low speeds,the wear morphology of the coating surface is rough,the surface has more debris and small holes,but the dimple morphology remained intact.With the increase of the speed,lubricant film's thickness increased,so the bearing capacity is improved,reducing the wear debris and pits begin to decrease,the wear surface becomes more smooth;but when the speed reached to 0.6m/s,the surface morphology of the coating is best of all the coatings,but dimple morphology is destroyed,this is because abrasive at high speed has great momentum,flowing with the lubricating fluid,which has a greater impact on the texture of circular pits,the textured morphology destroyed.(6)By studying the stribeck curve in the condition of bovine serum lubrication with different speed,the texture coating can enter the fluid lubrication stage at a lower rate than the non-textured coating,when the speed is 0.5m/s,the friction coefficient reaches the minimum value of 0.21.In summary: the textured HA bio-ceramic coatings produced by femtosecond laser processing technology has good surface morphology,hardness of dimple in processing area is improved,the wear resistance is better than non-textured coatings.In addition,the textured coating can enter the fluid lubrication state at a lower speed than the non textured coating.