H. Hadraba et al /Ceramics International 30(2004)853-863 AL2O, Zro Zro2 alo 20 Am 20 uLm Fig. 4. Microphotographs of indentation cracks in alumina/zirconia layered composite LC HP/Y propagated perpendicular to the interface of alumina and zirconia(crack initiated in(a)alumina and in(b) zirconia) thickness range. The composites prepared as part of the densities, and their different thermal expansion. Both these present work satisfied this requirement phenomena introduce tensile stresses into Zro2 layers and From a comparison of dilatometric curves of the Al203 compression stresses into Al2O3 layers. What effect these and Zro layered composite with the curves of the individ- stresses have on the mechanical properties of the composite ual pure components it could be seen that there were at least is shown in the following paragraph two sources of the stress introduced into the composite dur- Figs. 4-6 are microphotographs of indentation cracks in ing the sintering process: the different sintering kineti yered composite materials. The effect of layer interface on individual components resulting from their different gi indentation crack propagation was studied. The indentation Ao」 ZrO2 0 20 um f indentation cracks in alumina/zirconia layered composite LC HP/Y pro d askew to terface of alumina an (a) alumina and in(b)zirconia)H. Hadraba et al. / Ceramics International 30 (2004) 853–863 857 Fig. 4. Microphotographs of indentation cracks in alumina/zirconia layered composite LC HP/3Y propagated perpendicular to the interface of alumina and zirconia (crack initiated in (a) alumina and in (b) zirconia). thickness range. The composites prepared as part of the present work satisfied this requirement. From a comparison of dilatometric curves of the Al2O3 and ZrO2 layered composite with the curves of the individ￾ual pure components it could be seen that there were at least two sources of the stress introduced into the composite dur￾ing the sintering process: the different sintering kinetics of individual components resulting from their different green Fig. 5. Microphotographs of indentation cracks in alumina/zirconia layered composite LC HP/3Y propagated askew to the interface of alumina and zirconia (crack initiated in (a) alumina and in (b) zirconia). densities, and their different thermal expansion. Both these phenomena introduce tensile stresses into ZrO2 layers and compression stresses into Al2O3 layers. What effect these stresses have on the mechanical properties of the composite is shown in the following paragraph. Figs. 4–6 are microphotographs of indentation cracks in layered composite materials. The effect of layer interface on indentation crack propagation was studied. The indentation