This paper reports the mechanical property and crack propagation behavior of thin ceramics. A method to evaluate the stress intensity factor, KI, of thin ceramics was proposed. Dependence of KI values on the average grain size, d, of thin α-alumina were measured by the method. KI values of thin α-alumina decreased with increasing d values from 4.3 μm to 15.2 μm, while the KI values were almost constant for 15.2 μm≤d≤63.0 μm. The trend of KI values agreed with the dependence of fracture toughness, Kc, of bulk α-alumina. The thin α-alumina specimens after crack propagation were investigated by scanning electron microscopic electron back-scattered diffraction (SEM/EBSD) analysis. Branched cracks were hardly observed, regardless of grain size. The result indicates that the toughing mechanism do not occur in the thin α-alumina. Dependence of the transgranular fracture rate, F, and the crack deflection rate, D, on d were measured from the orientation distribution maps. However, the F values and the D values were independent of d and approximately constant. The F values and D values depend on d in bulk α-alumina. It indicates that the crack propagation behavior is varied by thinning α-alumina.
