Wear Property And Simulation Prediction Of Ha/ZrO₂Composite Coating In Simulated Body Fluid

Due to its excellent mechanical properties, good biocompatibility and bioactivity, the hydroxyapatite composite coating is used as a novel material for joint and bone replacement and attracted increasing attention. However, the body self-lubricating system would be destructed after implantation, resulting in wear failure of the composite coating inevitably. Meanwhile, due to the complexity of the body in vivo environment, the tribological behavior and wear loss are also changing. Thus, it is necessary to study the wear behavior of the hydroxyapatite composite coating under different working conditions. What’s more, the in vivo precise prediction of the implant is desperately required.In this dissertation, wear properties and mechanisms of plasma-sprayed HA/ZrO2composite coating are studied. The wear behaviors of the coating under different lubricants, loadings and rotational speeds are compared through the measurement and analysis of the wear rate, coefficient of friction, surface roughness and morphologies. The wear rate model of the composite coating in simulated body fluid is built basing on uniform design theory and regression analysis. The wear simulation of pin-on-disc test model and aritificial hip joint is conducted out through secondary development of ANSYS using APDL and the wear rate model of the coating, the results are compared with the experimental results and literature data. The research work is of important significance to investigate the wear properties of the composite coating and its influencing factors, optimize the design of articifical hip joint and prolong the life of the coating. The main work and achievements are as follows:1. The influences of lubricants, loadings and rotational speeds in simulated body fluid on the wear properties of HA/ZrO2composite coating are investigated using pin-on-disc wear tester. The result shows serious bruise on the worn-out surface of the coating under dry sliding and relatively good lubricating effect of simulated body fluid compared with that of physiological saline due to the deposited calcium phosphate films. The wear mechanisms are abrasion, bruise and ploughing in the simulated body fluid. There are obvious wear marks and many pits on the coating surface after wear tests. The wear process can be divided as running-in and stable wearing period. With the increasing of the load, larger and more wear particles are separated from the coating during the running-in period, and particle cutting and ploughing are aggravated at the stable wearing stage. With the increasing of the rotational speed, the wear rate decreases first and then increase during the running-in period and linearly decreases at the stable stage.2. The wear rate expressions of the composite coating between wear rate and loading and rotational speed are built during both running-in and stable period basing on uniform design theory and regression analysis. It is proven by the experimental results that the proposed models are effective in the wide range of loadings and rotational speeds.3. The wear loss of the composite coating during pin-on-disc wear test could been accurately calculated basing on the wear simulation with the wear rate prediction model. The experimental verification shows that the simulation of the wear process is accurate and the wear rate models are reliable.4. The wear simulation of artificial hip joint is carried out. The results show that the main wear areas locate on the superior surface of the acetabulum, and the super-posterior surface has the largest linearly wear loss. For the artificial hip joint with femoral head diameter of28mm and radial clearance of0.05mm, the largest wear depth is0.0244mm and the total wear volume is5.98mm3after20000wear cycles. With the increasing of wear cycle, the wear volume increases linearly but the growth rate of wear depth changes from fast to slow. With the growth of radial clearance of the hip joint, the wear volume decreases while the wear depth increases. The wear volume increases with the head diameter, while the wear depth has no significant change.