微纳米结构涂层/基底体系界面力学性能的表征及测量

The interface system of the coats (elastic thin films) bonded on the matrixes is used in many fields, such as microelectronics, energy battery and aero-spaceflight, etc. Interface binding strength characterizes the stability of interfaces and reliability of the related devices. For example, the thermal barrier coatings, made of the ceramics with low thermal conductivity, is used to provide thermal insulation to interior metallic components from the hot gas stream in gas turbine engines for aircraft propulsion and power generation, once the interface between the ceramic coats and metallic matrixes fractures, and the coats flake off, the metallic components exposed in the high temperature environment will failure. The nanostructured coats have been found to have lower thermal conductivity and better thermal protection effect compared with the conventional micro-scale microstructured coats, how about the interface strength between the coats and the matrixes? To understand the question provides not only a guide in the application of the nanostructures, but also an opportunity to study the scale effect of the interface cohesive behavior. Therefore, the interface mechanical properties and its physical mechanism between the micro- and nanostructured coats and the matrixes will be studied by theoretical characterization and experimental measurement in this project. There are two important parameters in the interface cohesive zone model, which is usually used describe the mechanical behavior of the crack tip in the interface fracture process, the interface adhesive energy (fracture toughness) and the interface binding strength (fracture strength), their size effects reflect the size effect of the interface cohesive (fracture) properties. According to the thermodynamic relation among the interface adhesive energy, the surface energies of the coats and the matrixes, and the interface energy between them, the physical equation of the size-dependent interface adhesive energy will be established based on the size effect models of the surface energy and the interface energy. The interface binding strength between the micro- and nanostructured coats and the same matrixes will be measured experimentally, which will be compared with each other, the size effect of the interface strength will be obtained. Combining the interface cohesive stress function and the macro- and micro-scale characterization of the interface fracture (or separate) displacement, the trans-scale model of the interface cohesive behavior will be developed. Moreover, the interface fracture and damage mode (crack initiation and propagation characteristics) will be observed in situ under the loading by the real time three-point bending experimental measurement, the interface fracture toughness and the residual stress will be calculated, and the results will be used to compare with and validate the theoretical model.

涂层/基底体系在微电子、航空航天等领域有广泛应用，涂层与基底之间的界面强度和韧性等力学性能对相应器件的稳定性有重要影响，同时微纳米结构涂层/基底体系为研究界面力学行为的尺度效应提供了良好的契机。因此本项目拟对微纳米结构涂层/基底体系的界面力学性能展开研究。基于界面粘聚区模型，拟对反映界面性能的两个重要参量：界面粘聚能（即断裂韧度）和界面结合（断裂）强度的尺度效应进行理论表征和实验测量。根据界面粘聚能与界面断裂前后的界面能、表面能的关系，以及表界面能尺度效应的热力学模型，建立尺度依赖的界面粘聚能的物理方程。通过粘结拉伸方法测量微、纳米结构涂层/基底样品的界面结合强度，比较两者考察界面强度的尺度效应。结合界面粘聚力的函数表达及界面断裂位移的宏、微观表征，发展跨尺度的界面粘聚模型。并通过实时原位的三点弯实验，考察涂层/基底体系受载时界面及涂层的断裂损伤特征，计算界面断裂韧性及应力，印证理论模型。

涂层／基底体系在微电子、化工、航空、航天等许多领域有广泛应用，涂层与基底之间的界面强度和断裂韧度等力学性能对相应器件的稳定性有重要影响，而微纳米结构涂层体系的界面力学性能表征则为研究力学行为的尺度效应提供了很好的平台。因此本项目针对微纳米结构涂层／基底的界面力学性能展开了系统研究。首先基于表面能和界面自由能的热力学表达，建立了界面断裂能（即本征界面断裂韧度）及其尺度效应的物理模型，预测了纳米结构陶瓷涂层比传统微米结构涂层与同样合金基底间的界面断裂能减小约三分之一；并对微纳米结构涂层／基底样品开展了标准的界面拉伸实验测量，研究发现纳米结构涂层比传统涂层与同样基底间的界面强度提高约一倍；进一步刻划了涂层／基底的界面粘聚本构，指出界面临界分离位移这一界面粘聚模型中力学参数的物理意义，对应了界面材料微结构的特征尺度。在此基础上，建立了含界面粘聚模型的涂层／基底体系三点弯的有限元模型，表征了涂层／基底体系断裂模式的厚度依赖特征：薄涂层拉伸主导，涂层呈现多条横向裂纹的失效方式；厚涂层界面剪切主导，涂层与基底之间界面开裂失效；并设计了不同涂层厚度的陶瓷涂层／合金基底样品，在扫描电镜下开展了相应的原位三点弯实验，实验结果与有限元模拟结果一致。另外还建立了微纳米结构涂层在热震载荷下的总势能方程，分析了纳米结构涂层具有较高抗热震性的机制，是由于其较大的界面比例为沿微观界面断裂提供了能量条件，足以耗散在热震过程中产生的弹性应变能。