X-Ray Measurement of Residual Stresses in Ceramics and Strength Evalution

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1. The X-ray elastic constants of sintered alumina were measured for the diffraction planes (1.0.10), (220), (2.1.10), (146), and (4.0.10). The order of the magnitude of E/(1+<nu>) (E=Young's modulus, =Poisson's ratio) for each plane agreed with the theoretical value obtained from the elastic constants of a single crystal on the basis of Reuss model. The magnitude itself was smaller than the predicted value because of porosity.2. The X-ray diffraction planes switable for an accurate measurement of residual stresses in four engineering ceramics were determined as follows: (2.1.10) for <alpha>-Al_2O_3, (411) and (323) for <beta>-Si_3N_4, (213) and (2.0.15) for SiC (6H), and (133) for 3%mol Y_2O_3-ZrO_2.3. The X-ray elastic constant, E/(1+<nu> of alumina and silicon nitride was measured by using the synchrotron radiation source. X-ray diffraction was recorded with a position sensitive detector. The measured value agreed well with that obtained from an ordinary method utilizing the parallel beam method of characteristic X-rays.4. The residual stresses measured on as-fired, lapped and ground surfaces of ceramics were all compression. The compressive residual stress in the direction perpendicular to the grinding direction was about twice the value in the grinding direction. The magnitude of the compressive residual stress got larger with increasing diamond grain size of a cutting wheel, while it was insensitive to the cutting depth. In partialy stabilized zirconia, the full width at half maximum of X-ray diffraction profiles and the amount of transformation from tetragonal to monoclinic phase increased with increasing diamond grain size of a cutting wheel.5. The size of indentation cracks was sensitive to the residual stress measured by X-rays. Fracture mechanics analysis will be necessary to assess the residual stress effect on cracking in ceramics.