【作者】 李伯琼；

【导师】 陆兴；

【作者基本信息】 大连交通大学 ， 材料加工工程， 2011， 博士

【摘要】 本文系统地研究了多孔钛的制备工艺、微观结构与其力学性能和生物化学相容性之间的关系,初步探讨和分析了孔隙结构对多孔钛的断裂机制和导电性能的影响,以期利用多孔钛独特的孔隙结构、良好的生物相容性和与骨接近的力学性能,应用于种植体等骨科临床领域。论文首先选取球形聚甲基丙烯酸甲酯作为造孔剂,采用粉末冶金法制备孔隙结构(孔隙度为10—70%,孔隙尺寸<500μm,开孔率>75%)可控的多孔钛。其孔隙分两种：尺寸为几十微米到几百微米、具有台阶表面、相互连通的宏观大孔隙和尺寸为几到十几微米分布在孔壁上近似球形的微孔。宏观大孔隙的孔隙度、孔隙尺寸及连通程度随着造孔剂体积分数及尺寸的增大而增大；与此同时,大孔隙的各向异性随孔隙尺寸的增大成线性降低。随烧结温度的升高和时间的延长,晶粒尺寸增大,孔隙尺寸和数量减小,微孔隙的形貌逐渐趋于球形。多孔钛的压缩应力-应变曲线具有线弹性阶段、塑性屈服平台和致密化阶段,而拉伸和弯曲应力-应变曲线只有线弹性特征。在三种状态下,多孔钛均发生脆性解理断裂,其主裂纹受大孔隙的控制,沿与外加载荷方向成45°角扩展。随孔隙度及孔隙尺寸的增大,多孔钛的压缩强度、拉伸强度、弯曲强度和弹性模量均降低。与MOri-Tanaka模型相比,多孔钛的弹性模量、强度与孔隙度的关系更加符合Gibson-Ashby理论计算值；其泊松比v*介于-0.92—-0.37之间,且与孔隙尺寸近似成线性关系。随烧结温度的增大,烧结时间的延长和烧结真空度的提高,多孔钛的弹性模量和强度增大。多孔钛(孔隙度为10-70%,大孔隙尺寸为100-500μm)在1 M NaOH溶液、0.1MH2SO4溶液和37℃Hank’s溶液中的阳极极化曲线均具有活化-钝化特征,而在37℃0.9% NaCl溶液中表现为自钝化特征。随孔隙度的增大和连通大孔隙尺寸的降低,多孔钛的有效表面积增大,致使其腐蚀电流密度增大,但腐蚀电位变化不大(<6%)。多孔钛的电导率随孔隙度的降低(由70%降至10%)和大孔隙尺寸的增大(由150μm增至400)而增大。两者的关系符合麦克斯韦近似理论；而微分有效媒体近似理论仅适用于平均孔径为400μm,孔隙度为40-70%的多孔钛。综合考虑孔隙度、孔隙尺寸和形态等因素对多孔钛导电性能的影响,麦克斯韦近似理论和微分有效媒体近似理论分别修正为σ=σ0(1-ε)/(1+aε+bxε)和σ=σ0(1-ε)(c+dx),式中：σ和σ0分别代表多孔钛及孔壁材料的电导率,ε代表孔隙度,x代表孔隙尺寸,a和b分别为与实验条件和与孔隙形态有关的常数,c和d分别为依赖于系统参数和孔隙形态的临界指数。更多还原

【Abstract】 The relationship between fabrication processing, microstructure and mechanical properties of porous Ti has been investigated, and the effect of pore structure on the fracture behavior and electrical conductivity of porous Ti has been also analyzed, in order to utilize the adequate porous structure, good biocompatibility and appropriate mechanical properties of porous Ti for the application in clinic orthopaedics field such as the bone substitute.Adding polymethyl methacrylate powders as pore maker, porous Ti with controllable pore structure was successfully prepared by powder metallurgy at first. The porous Ti shows a three-dimensional open-cellular structure with two types of pore:inter-connection macro-pore with stepped pore walls and a small isolated micro-pore distributed on the macro-pore walls. Porosity, macro-pore size and the open pore ratio of sintered porous Ti increase with the increasing of volume fraction and particle size of the pore maker. The pore anisotropy decreases linearly as the size of the PMMA particles used increases and hence with macro-pore size. As the increase of sintering temperature and sintering time, the grain size increases, pore size and porosity decrease and micro-pore rounds gradually.The compressive stress-strain curve of porous Ti show linear elasticity at low stresses followed by a long collapse plateau, truncated by a regime of densification in which the stress rises steeply. While the tensile and bending stress-strain curves of porous Ti both show the linear-elastic feature. Fractography shows evidence of the brittle cleavage fracture in porous Ti. The stress is prior to concentrate on the weak macro-pore wall, thus resulting in the crack and then propagation. The failure with the formation of shear bands of 45°to the stress axis due to cracking (complete fracture) of the struts on porous Ti is controlled primarily by the macro-pores. The elastic modulus and strength of porous Ti decrease with the increase of porosity and macro-pore size. Compared to Mori-tanaka model, the present experimental results are in agreement with the theory of Gibson-Ashby satisfactory. Poisson’s ratio measured is in the range of-0.92—-0.37, which is linear with macro-pore size. The elastic modulus and strength of porous Ti increase with the increasing sintering temperature, longer sintering time and higher vucuum.Electrochemical corrosion tests are performed on porous titanium in 0.1 M H2SO4,1 M NaOH and 37℃0.9% NaCl and 37℃Hank’s solutions. It is shown that the anodic polarization curves of porous titanium exhibit active-passive transition behavior in 1 M NaOH and 0.1 M H2SO4 and 37℃Hank’s solutions, while self-passivation in 37℃0.9% NaCl solution. As the porosity increases and macro-pore size decreases, the corrosion current density of porous titanium increases due to the higher effective specific area, while the corrosion potential does not change (<5%) remarkably.As the porosity increasing and the macro-pore size decreasing, the electrical conductivity of porous Ti decreases dramatically. The dependence of the electrical conductivity on the porosity could be well described by the Maxwell approximation. The differential effective medium approximation is only applicable to porous Ti with average pore size of 400μm in the porosity range of 40-70%. Taking the porosity, pore size and pore morphology into consideration, Maxwell approximation and differential effective medium approximation have been modified to beσ-σ0(1-ε)/(1+aε+bxε) andσ=σ0(1-ε)(c+dx), respectively. Where x represents pore size,εis porosity,σandσ0 are electrical conductivity of porous and solid Ti, respectively, a and b are the constant correlative to the experimental condition and pore morphology of porous materials, respectively, c and d represent the critical exponent that depend on the system parameters and pore morphology in a piecewise constant manner, respectively.更多还原