Abstract
Pressureless sintered alumina with 92% purity was quenched from 1500°C into silicon oil with the kinematic viscosity of 1, 100 and 10000cs. The residual stress distribution in the quenched ceramics was measured by the X-ray diffraction method. The increase of the bending strength of quenched ceramics was discussed on the basis of the measured residual stress. The results obtained were summarized as follows:
The compressive residual stress was formed near the surface of quenched ceramics, and its magnitude increased with decreasing viscosity of silicon oil. The bending fracture of quenched ceramics started from the material defect embedded in the surface layer with large compressive residual stresses. The bending strength increased in proportion to the amount of compressive residual stress measured on the surface. The maximum strength was obtained for the case of quenching into 1cs silicon oil. It was 531MPa which is about 1.4 times the strength of annealed specimens. The microscopic residual stress, estimated from the broadening of the X-ray diffraction profile, could reduce the stress for fracture from a small (microscopic) defect.
