| The wear of human joint interface could easily trigger the bone and joint diseases.According to the statistics of the World Health Organization,about 400 million people worldwide suffer from bone and joint diseases.Therefore,bone and joint diseases are considered to be the number one disability disease in the world.The damaged joint cannot be repaired naturally and the surface of bone injury is difficult to heal effectively,for the functional of bone joint loss,the artificial joint as a joint implant,is the only effective method to replace the damaged joint and tissue.At the same time,the existing artificial joints based on inert bioceramics,ultra-high molecular weight polyethylene and metal composite material,because it is difficult to build an orderly functional junction completely consistent with the bone,surface,cavity and capsule in human joints,there are still problems such as submicron abrasive wear failure,interface wear fatigue and pathogen infection,which seriously restricts the long-term service of artificial joint and hinders the improvement of joint life and reliability.In addition,the porous gradient characteristics of bone structure,the characteristic structure and heterogeneous materials of primary organisms cause excellent characteristics of drag reduction of the natural biological tissue,wear resistance,crack arrest and strength,which can provide a bionic model for the multi coupling design of artificial joints.Therefore,it is an important way and necessary means to improve the service performance of artificial joint materials by obtaining the weakening law and failure mechanism of joint materials,combined with the blocking effect of biological model on the evolution of micro defects,and carrying out the construction of wear-resistant function of bionic human joints.The wear resistance and other service properties of artificial joint materials need to be improved,and the correlation between the micromechanical behavior,damage mechanism and microstructure evolution of joint materials needs to be revealed.Based on the principles and methods of realizing the properties of wear resistance,toughening and drag reduction,this doctoral dissertation functionally coupled the"toughening"of porous gradient materials with the"wear resistance"of heterogeneous materials,contained the bionic structure design and preparation,and material coupling of artificial joint with high entropy alloy coating,and optimized the structure of the coating and porous substrate of bionic artificial joint by constructing the environment close to the service of human joints.The wear resistance of bionic artificial joint materials was effectively improved,which provided a theoretical basis for the development of new artificial joints.The main contents of this doctoral dissertation are as follows:（1）The research progress and existing problems of artificial joint structure,material and testing technology were systematically discussed.Based on the concept of coupled bionic design,taking the porous gradient structure of bone as the bionic model,two kinds of bionic artificial joint structures were designed,which were high connected topology gradient and Tyson polygon bionic artificial bone structure based on broken bone surface.The two structures were conducive to the differentiation of backbone cells and the growth of bone tissue,and realized the interface strengthening and improved the mechanical properties of structural gradient.On this basis,the titanium alloy specimens with the above two structures were prepared by additive manufacturing technology.Through stress elimination,the compressive fracture limit of the specimens was three times higher than that in the original state.The strain distribution characteristics of two kinds of compression specimens were obtained by digital speckle strain analysis method,and their fracture morphology was characterized and analyzed.The experimental results showed that the bearing capacity of high connected gradient bionic artificial bone structure was better than Tyson polygon bionic artificial bone structure.（2）In order to improve the surface properties of the specimens,a high entropy alloy hard coating for the surface enhancement of bionic structure was prepared.The main element types and ratio of high entropy alloy were optimized by thermodynamic calculation.Then Fe22Co22Ti22Ni22Al12 coating with controllable coating thickness were prepared by magnetron sputtering.On this basis,the mechanical properties of high entropy alloy coating were obtained through nano-indentation test.Combined with the characterization and analysis of its microstructure,the amorphous transformation trend of high entropy alloy from target sputtering to coating formation was revealed,and the grain refinement rate was 83.3%.After repeated application of indentation load,the high entropy coating produced local crystallization.At the same time,in order to verify the antibacterial performance of high entropy alloy coating,the common joint pathogenic bacteria staphylococcus aureus and high entropy alloy coating were cultured together to verify the antibacterial performance of the coating material against joint pathogenic bacteria.（3）According to the porous gradient structure,porous titanium alloy substrates with different pore sizes were fabricated by pressure sintering mixed with pore forming agent.The body environment of the actual service condition of the joint was constructed,and the friction tests based on body temperature,pig plasma dialysate environment and dry friction conditions were carried out respectively.The friction pair materials were articular acetabular cup material zirconia and porous titanium alloy based high entropy alloy coating material.Under the condition of dry friction,the diameter of pore forming agent was 10μm.Compared with the dense specimen,the friction coefficient of the specimen was reduced by 37%;Under the condition of plasma friction,the diameter of pore forming agent was 30μm.The friction coefficient of the specimen was 35.7%lower than that of dense titanium alloy specimen.Furthermore,through finite element simulation,the high bearing capacity of porous structure and its mechanism of improving antifriction performance were explained.（4）The comprehensive mechanical properties of porous titanium alloy based high entropy alloy coating materials were tested and analyzed.The indentation response and deformation characteristics of porous titanium alloy substrate with different pore characteristics were analyzed.A controllable residual stress release method based on secondary indentation was proposed for the residual deformation at the indicated pore defects in the preparation process.On this basis,the permeability of the specimen was obtained by the drop method.The effects of high entropy alloy coating sputtering time and coating quality on the indentation force response and progressive scratch response of bionic artificial joint materials were studied.The coating thickness corresponding to the optimal coating quality and the minimum wear volume was obtained（1.9μm）and pore forming agent diameter（10μm）.The results suggested that the bionic artificial joint material designed in this paper has excellent load-bearing,wear-resistant,antibacterial and permeability characteristics.The research was expected to provide design support for improving the service life and reliability of artificial joint,and also provide basic data for the development and application of new artificial joint. |
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