| Laminated ceramics is a kind of high strength ,high toughness ceramics developed from pearl and shell. Based on the design ways of multilayered ceramics, this paper produced a three-layer Al2O3/ZrO2 ceramics---30wt%Al2O3+ZrO2 or 45wt%Al2O3+ZrO2 in the two surfaces, 5wt%Al2O3+ZrO2 in the center. With the helps of transmission electronic microscopy, scan electronic microscopy, X-Ray diffractometry and mechanical property instruments, the relationship of the process ,microstructure and mechanical property of the three-layer Al2O3/ZrO2 ceramics was systematically studied at home and abroad, which provided a theoretical basis for composition, macro-structure and micro-structure of the multilayered ceramics design.In order to overcome the sintering anisotropy of the laminated ceramics, we used non-pressure sintering process, adjusted the surface compositions, adopted wave interface structure and lowered the heating rate, and finally obtained >98% relative density. Further study showed that the product of 45wt% Al2O3+ZrO2 surface composition has high mechanical properties: 682 MPa bending strength,15.56GPa hardness , 20MPa·m1/2 fracture toughness, higher 30～50% than those of monolayer ceramics. The laminated Al2O3/ZrO2 ceramics had a feature of R-curve, and a decrease in the sensitivity of the strength to the size of surface cracks. When the surface cracks length were over 600um,the bending strength was over 400MPa.Indentation thermal shock test showed that the critical temperature difference of the three-layer Al2O3/ZrO2 ceramics was 400℃,higher 150℃ than those of monothic ceramics, which had nothing to do with the thickness of the laminated ceramics. Using 40×40×8mm laminated ceramics as the side wall in Φ250mm twin-rolling casting technics, the results showed that the laminated ceramics has some superior properties,which may be used in the high-temperature bad condition.Under the condition of the moderate surface compressive stress, the transformation from t-ZrO2 to m-ZrO2 during sintering was greatly restrained, which increased the contents of transformable tetragonal ZrO2, made the grains much fine ; the surface fracture appearance was changed from the fracturing along and through the grain boundaries of the monothic 5wt%Al2O3+ZrO2 ceramics to the latter one. Further observation showed the crack ways deflected along the interfaces of multilayered ceramics .All of these greatly strengthened the effects of the t-ZrO2 on toughness increasing during transformation. We can conclude from TEM experiments and analyses that surface compressive stresses didn't change the orientational relation between tetragonal and monoclinic phase, while (100)m//(010)t still existing.According to the stress analyses for layers ,when the tensile stress>200～250MPa,cracks occur. A critical delamination character λ was given , when λ<1, cracks did not occur. λ>1,cracks occurred and became more and more. The experimental data of two methods -indentation method and indentation-fracture method to measure fracture toughness of the ZrO2 laminated ceramics showed that the data from the later method had 55% higher than the former data. The analyse for the driving force of the indentation cracking in the ZrO2 laminated ceramics showed that neither the contribution of transformation drive force, nor the restrains for the surface cracks of the compressive stress were considered in the traditional indentation theory, so the value of fracture toughness measured by the indentation method was usually lower than the practical value for the transformation toughening laminated ceramics.Using Indentation-fracture method to measure annd calculation, the data is more correct.
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