【作者】 郑敏；

【导师】 樊丁； 刘其斌；

【作者基本信息】 兰州理工大学 ， 材料加工工程， 2008， 博士

【摘要】 本工作利用高功率CO₂激光器,通过激光熔覆技术在Ti-6Al-4V合金表面制备了梯度生物活性陶瓷涂层,实现了钛合金的生物活化改性处理。通过光学显微镜（OM）、扫描电镜（SEM）、荧光显微镜、X射线衍射仪（XRD）、电子探针（EPMA）、同步热分析仪（TG-DSC）、电感偶合等离子体发射光谱仪（ICP）、显微硬度计等检测手段,主要开展了以下几方面研究:首先对本试验条件下的激光熔覆工艺参数进行了优化。当固定输出功率P=2.5kW、光斑尺寸D=15mm×1mm,激光熔覆扫描速度为120～160mm/min时方有可能生成HA。通过显微组织观察及显微硬度测试,结合激光熔覆传热、传质过程的分析计算,确定本工作条件下的优化工艺参数为:激光输出功率P=2.5kW,光斑尺寸D=15mm×1mm,扫描速度V=140mm/min,Ar气保护。其次对激光熔覆生物陶瓷复合涂层的组织结构进行了研究。结果表明:涂层与基材之间实现了牢固的冶金结合;由涂层至基体存在成分梯度,钛含量逐渐减少,磷、钙含量逐渐增多;涂层由HA、β-TCP、CaTiO₃等多种陶瓷相组成,熔覆粉末Ca/P为1.4时生物活性陶瓷相的生成能力更佳;凹凸不平的涂层表面除了具备典型的粒状和短杆状HA形貌特征外还出现了团絮状、蜂窝状及片状等多种微观形貌。多种形貌共存的表面使涂层的微观表面积大大增加,为新生骨组织的生长提供更多的接触面,起到更好的生物固定作用;局部出现的微孔（熔覆带中间区域孔径约为1～10μm,两侧约为100～600μm）通过组织液的微循环能使宿主骨长入材料并与之相互嵌插连成一体,对新生骨组织沿着攀附生长十分有利。本工作还研究了0.2～0.8wt.%稀土氧化物CeO₂对梯度复合涂层的影响及其催化合成机理。利用SEM、XRD、TG-DSC和显微硬度等检测手段发现:添加0.4～0.6wt.%CeO₂时涂层组织均匀,降低了熔覆层的开裂倾向性,对生成HA和β-TCP等生物活性陶瓷相具有促进作用;添加0.6wt.%CeO₂激光熔覆涂层中的断裂韧性值比未添加稀土氧化物试样略有提高,接近人体致密骨;涂层中添加0.6wt.%CeO₂的残余应力比未添加稀土氧化物涂层中的小;结合反应动力学计算,提出稀土氧化物CeO₂催化生物活性陶瓷相的可能机理:对应生物活性陶瓷相可能生成的温度范围,添加0.6wt.%CeO₂体系对应温度范围的反应活化能比未添加稀土氧化物体系的小,更易使反应物分子热激活成为可以发生有效碰撞的活化分子,使生物活性陶瓷相能在更大的温度范围内形成,提高HA和β-TCP的高温稳定性,从而促进HA等生物活性相的生成。最后,通过模拟体液浸泡和体外细胞培养实验对激光熔覆生物陶瓷复合涂层的生物活性和细胞相容性进行了测试。模拟体液浸泡实验表明,激光熔覆生物陶瓷复合涂层具备生物活性。利用SEM、XRD、EDX、ICP等检测手段发现:随着在SBF中浸泡时间的延长,涂层表面团絮状物质不断增多,磷灰石相在其表面形核并不断长大;表面沉积物以片状为主,还出现了球状、毛绒状及一些密集生长的细针状等,局部还发现了少量HA晶须（直径约0.3～0.8μm,长径比约为10～40）,这对增强涂层韧性十分有利。该涂层在SBF中浸泡后磷灰石所对应的衍射峰明显增强,CaO对应的衍射峰强度大幅降低,表明该涂层在SBF溶液中具有快速诱导磷灰石沉积的能力。而未处理的基材即使在SBF中浸泡14天后,其表面仍未生成磷灰石相的沉积物,只有残留的浸泡痕迹及生长的盐类沉积物。体外细胞培养实验表明,随细胞培养时间（2d、4d、6d）的延长,激光熔覆生物陶瓷涂层表面的细胞增殖呈现上升趋势,而且其成骨细胞增殖数量比未处理的基材及培养板对照组高,细胞生长更为旺盛,细胞毒性评级为0级（无毒）。SEM观察发现细胞很好地铺展于涂层表面,紧密贴壁,呈长梭形,形态完整饱满,伪足往外伸展明显;荧光显微镜观察发现活细胞在涂层表面存活完好且成长旺盛。这表明该涂层能够很好的被成骨细胞所接受,具有良好的细胞相容性。更多还原

【Abstract】 Based on high power CO₂ laser,the bioactive modified treatment of Ti-6Al-4V alloy was realized.The gradient bioactive ceramic coating was fabricated on the surface of Ti-6Al-4V alloy by laser cladding.The composite coating was investigated by optical microscopy（OM）,scanning electron microscope（SEM）, fluorescence microscope,X-ray diffraction（XRD）,electron probe microanalysis （EPMA）,thermal gravimetry and differential scanning calorimetry（TG-DSC）, Inductively Coupled Plasma（ICP） and microhardness（HV） instrumentation.The main research results are as follows.Firstly,The processing parameters of laser cladding were optimized at the experimental condition.In the condition of laser output power 2.5kW and laser beam size 15mm×1mm,the hydroxyapatite could be probably formed at laser scanning speed of 120～160mm/min.Based on microstructure observation,microhardness and analytical calculations about heat transmission and mass transfer during laser cladding,the optimal processing parameters of laser cladding were as follows:laser output power 2.5kW,laser scanning speed 140mm/min,and laser beam size 15mm×1mm.Secondly,the microstructure of laser-cladded composite coating was investigated.The results indicated that the coating was metallurgically bonded to the titanium alloy substrate by the action of laser.Gradient component was varied from coating to substrate.The content of titanium was gradually decreased and the calcium and phosphorus were gradually increased.The laser-cladded composite coating contained such bioactive phases as hydroxyapatite（HA）,β-tricalcium phosphate（β-TCP） and calcium titanate（CaTiO₃）,etc.The ability of bioactive ceramic phases formation with clad powders of Ca/P=1.4 was better than other ratio. Besides granular and rod-like morphology of the classical HA morphology,the morphology of flocculent,honeycomb and micropore existed on the surface of composite coating.The appearances of multiform morphologies on the coating made the areas of coating extremely increased.And more contact area was provided for the growth and biofixation of new bone tissue.The pores（aperture:clad belt 4～9μm; clad edge 30～80μm） existed in local zone made the host bone grow into materials by the microcirculation of tissue fluid and combined together with chimerism.These may be in favor of the osseous tissue to grow along.Thirdly,the effect of 0.2～0.8wt.%rare earth oxide CeO₂ on laser-cladded bioactive ceramic coating and the mechanism was also investigated by SEM,XRD, TG-DSC and microhardness.The results indicated that the microstructure of coating of 0.4～0.6 wt.%rare earth oxide CeO₂ was homogeneous.Moreover,the addition of 0.4～0.6 wt.%CeO₂ could reduce the tearing tendency and accelerate the formation of HA andβ-TCP bioactive phases.According to the kinetics of reaction model,the activation energy of the system of 0.4～0.6wt.%CeO₂ addition was smaller than the system of without rare earth oxide on the temperature region of bioactive ceramic phase formation.Therefore,the molecule of reaction could easily form activated molecule of effective collision.The bioactive ceramic phases could form in an extensively range of temperature.The stabilization of high temperature was enhanced and the formation of HA bioactive phases was accelerated.The Simulated Body Fluid（SBF） test indicated that the composite coating at the experimental condition was of bioactivity by SEM,XRD,Energy Dispersive X-ray analysis（EDX） and Inductively Coupled Plasma（ICP）.After soaking in SBF,the flocculent precipitates were increased on the surface of coating and the apatite phases were gradually nucleated and grew.The morphology of precipitates was mainly composed of flake-like and the globular,flocculent and acicular morphology were also appeared.Moreover,the appearance of a small quantity of crystal whisker （diameter about 400nm,slenderness ratio about 40～100） in local zone sufficiently benefited intensify toughness.The diffraction peak of apatite extremely intensified and the CaO distinctly decreased when the coating soaked in SBF.It indicated that the coating had the ability of depositing apatite quickly.However,the untreated substrate was not formed the apatite precipitates after a long soaking period of 14days.The surface was merely formed trace of soaking and some precipitation of salts.The cell cutured in vitro test indicated that cell proliferation on the surface of coating exhibited ascending tendency.The osteoblast proliferation quantity of coating was higher than the untreated substrate and the cultured plate.The cell growth on the surface of coating was more luxuriance and the cytotoxicity grade was zero.The cells were well attached and spread on the surface of the coating exhibiting spindle-shaped morphologies.The cell pasted the wall closely.And the morphology was complete and full and the pseudopod obviously spread to outward.The state of viable cell was observed by fluorescence microscope.The results indicated that the viable cell commendably spread on the bioceramic coating,keeping their healthy spindle-shaped morphologies.Furthermore,the SEM morphology was corresponding to the MTT colorimetry results of cell proliferation count.The coating was fine accepted by osteoblast and had well cell biocompatibility.更多还原