TiO2纳米管阵列/Ti基体的界面特征与失效机制

In this project, the interfacial structure, interfacial properties, interfacial bonding mechanism, failure mechansim and annealing effects of TiO2 nanotube array will be studied. .Firstly, the relationship of growing characteristics including length, diameter, wall thickness and density distribution of TiO2 nanotube array to the interfacial structure will be elucidated. The interfacial structure consists of interface thickness, phase structure and diffusion layer. .Secondly, the interfacial properties including residual stress, interfacial shear strength, energy release rate, and fracture toughness under different conditions will be evaluated. The quantitative relationship between annealing parameters and interfacial properties will be given. The influencing rule of annealing to the interfacial properties of TiO2 nanotube array will be established. Moreover, physical mechanism of annealing influence to the interfacial properties will be raised..Thirdly, the interfacial bonding mechanism of TiO2 nanotube array/Ti substrate will be proposed according to the finite element analysis and stress distribution theory of bending beam..Fourthly, the failure mechanism of TiO2 nanotube array from crack consideration will be raised based on the transverse tensile test method and interfacial shear-lag model.On the basis of correlation among crack, buckling, debonding and tensile strain, the failure mechanism from buckling and debonding consideration will be presented..The purpose of this project is to achieve the interfacial fundamental theories and failure mechanism and to provide theoretical basis of fabricating technology and practical applications of TiO2 nanotube array.

本课题拟进行TiO2纳米管阵列/Ti基体的界面结构、界面性能、界面结合机理、失效机制及热处理影响的研究。首先阐明TiO2纳米管长度、直径、壁厚及密度分布等生长特性与界面厚度、相结构、扩散层等界面结构的内在关系；其次测量与评价不同热处理条件下残余应力、界面剪切强度、能量释放率、断裂韧性等界面性能并形成与热处理参数间的定量关系，构建热处理对TiO2纳米管阵列界面性能的影响规律，提出热处理影响界面性能的物理机制；然后根据弯曲梁应力分布理论并结合有限元分析，提出TiO2纳米管阵列的界面结合机理；最后通过横向拉伸法，结合界面剪滞力学模型，建立TiO2纳米管阵列基于裂纹的失效机制，并将屈曲、脱层、裂纹与应变的关系相关联，提出基于屈曲和脱层的失效机制。旨在掌握TiO2纳米管阵列的界面基础理论和失效机制，为TiO2纳米管阵列制备技术的改良与实际应用提供理论依据。

由阳极氧化法制备的TiO2纳米管薄膜，因其高度有序而显示出优异的性能，是一种应用前景广阔的新型纳米材料。本项目系统地研究了外加电压、阳极氧化时间、电解液（NH4F+乙二醇）浓度、电解液体系对纳米管阵列生长特性的影响。阐明了TiO2纳米管阵列生长特性与TiO2纳米管阵列/Ti基体界面结构的内在关系，提出了TiO2纳米管阵列的界面结合机理为强化学结合机理。随后，研究了200℃、300℃、400℃、500℃、600℃、800℃六个不同退火温度对TiO2纳米管阵列薄膜的微观结构和相结构转变的影响，TiO2纳米管的晶型发生了从无定型到锐钛矿相最后到金红石相的转变；且纳米划痕划破薄膜所需要的力随退火温度的升高不断增大，薄膜的物相转变逐渐完善，薄膜与基体的界面结合程度越来越强。研究证实了TiO2纳米管与钛基体之间存在一层肖特基界面层，该肖特基界面层厚度为纳米管管径的一半，即约30-40nm。不同退火温度的拉伸试验随应变的增加均表现出明显的裂纹起始、裂纹饱和的趋势，据此所获得的未退火、200℃、300℃、400℃、500℃、600℃退火的界面剪切强度分别为163.3MPa、370.2MPa、711.7MPa、684.5MPa、1013.2MPa、1582.6MPa，临界能量释放率、断裂韧性等界面力学性能与界面剪切强度一样均随退火温度升高而增大；综合认为，600oC退火效果最佳，其界面力学性能如下：裂纹起始应变7.0%，裂纹饱和时的裂纹密度135根/mm，界面剪切强度1582.6MPa，临界能量释放率950.2J•m-2，断裂韧性4.4MPa•m1/2。最后，从裂纹密度、屈曲密度、脱层半径的角度研究了TiO2纳米管阵列薄膜的界面失效行为，提出TiO2纳米管薄膜/Ti基体的界面失效机制分为前后连贯的五个步骤: a）裂纹出现；b）裂纹饱和，屈曲出现；c）屈曲饱和，少部分屈曲出现脱层；d）大部分屈曲已破坏，大量脱层出现；e）薄膜散裂，界面失效。这些研究成果为TiO2纳米管阵列的实际应用提供了理论依据。