X-Ray Residual Stress Measurement and Strength Evaluation of Ceramic Coating

1.对于氧化铝爆炸涂层，衍射角2 θ与sin ^2 psi之间呈线性关系，不存在系统非线性。涂层的弹性模量随爆轰条件的变化而变化，由于多孔性，涂层的弹性模量小于块体的弹性模量。测得的残余应力为拉伸应力，且分布均匀.采用CVD法在不同基体上制备了TiC薄膜。测得的残余应力比从涂层和基材之间的热膨胀系数（CTE）的差异预测的残余应力略大。这种差异是由于内在的压力。用X射线衍射法分离重叠衍射线，测量了石墨衬底上CVD法制备的TiC-SiC复合薄膜的残余应力。复合膜中的残余应力呈三轴应力状态。面外应力σ_3的大小与面内应力σ_1和σ_2处于相同的量级。采用压痕显微断裂试验测定了TiC-SiC复合膜的断裂韧性。复合材料的断裂韧性远大于整体涂层，这是由于裂纹偏转的缘故。这种变形是由不同符号的相位应力引起的. PVD法制备的TiC薄膜织构非常发达，因此传统的sin^2psi方法不适用。220平面法线垂直于膜表面。在R曲线法的基础上，提出了一种预测微小缺陷对陶瓷断裂强度影响的新方法。

1. For alumina detonation coating, the relation between the diffraction angle 2theta and sin^2psi was linear and had no systematic non-linearity. The elastic modulus of coating changed depending on detonation condition and was smaller than that of the bulk solid because of porosity. The residual stress measured was tension and distributed uniformly in the coated film.2. TiC thin films were coated on various substrates by the CVD method. The measured residual stress was slightly more compressive than the residual stress predicted from the difference in the coefficient of thermal expansion (CTE) between coating and substrates. This difference is due to intrinsic stresses.3. The residual stress in TiC-SiC composite films coated on graphite substrates by the CVD method was measured with X-rays by separating overlapped diffraction profiles. The residual stress in the composite film showed a triaxial stress state. The magnitude of the out-of-plane stress sigma_3 was on the same order of the in-plane stresses sigma_1 and sigma_2.4. Fracture toughness of TiC-SiC composite film was measured by the indentation microfracture test. The fracture toughness of composites was much larger than that of monolithic coating because of crack deflection. This deflection was caused by the phase stresses with different signs.5. The texture was highly developed in TiC film coated by the PVD method, and so the conventional sin^2psi method is inapplicable. The 220 plane normal was perpendicular to the film surface.6. A new method for predicting the effect of small defects on the fracture strength of ceramics was pro- posed on the basis of the R-curve method.