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

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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.