R Bermejo et al Composites Science and Technology 67(2007)1930-1938 Table l ic physical and mechanical characterization of the monolithic samples after sintering at 1550C for 2 h Density (% Young modulus(GPa) m-ZrO2(vol % ATZ 390±10 3.2±0.2 士30 AM 280±30 90-95 士20 Predicted and obtained thicknesses for the two laminated systems fabricated in this work. Predicted thickness has been calculated with the casting time and shrinkage Thick Thin Ratio Thick Thin Ratio Thick Thin 3±999±5543 560±859±69.52 ATZ Thick Layer MZ Thin laver the ones predicted for the thin layers(between 7% and l0%0) Fig 3. Kinetic curves for the ATZ and aMz slips and representation of A close-up of the thin layers is shown in Fig. 5 for both the predicted times to obtain thick ATZ and thin amz layers of 630 um laminate systems. The sharp interface between layers and and 63 um, respectively the homogeneous dispersion of the different phases can also be inferred. In the micrograph showing laminate B 55 um were prepared. They are referred to as systems B and (Fig. 5a) the edge crack can be clearly observed, thus sug- C respectively, in this investigation. A general view of the gesting the presence of high compressive residual stresses cross section for laminates B and C is presented in Fig. 4, within such layer. This phenomenon also indicates that where the bright thin layers correspond to AMZ and the the thickness of the internal AMZ layers in laminate B dark thick ones to ATZ composition. It can be appreciated over the critical thickness(te) value, above which the edge the uniform thickness achieved for both thin and thick lay cracks are induced, and thus crack bifurcation phenome- ers.Table 2 lists the predicted and measured thickness of non at failure is likely to occur [13, 21]. On the other hand, the ATZ and AMZ layers, and the corresponding thickness the SEM micrograph of laminate C(Fig. 5b) shows no ratio for each type of layered system. The predicted thick- edge crack in the centre of the compressive layer, i.e. the ness was calculated taking into account the shrinkage mea- AMZ layer thickness in this case must be lower than"tc sured in the monolithic samples. After SEM examination In order to evaluate and quantify the residual stresses of the laminates. it can be seen that the thickness of the developed in the laminates during cooling, the difference thick layers presents a lower relative error(about 2-3%), in strain for ATZ and AMZ was analysed from the data with respect to the experimentally obtained values, than recorded in the dilatometric experiments(Fig. 6).It was ATZ ATZ AMz ATZ ATZ AMZ AIZ ATZ AMZ AMZ AMZ Fig 4. Cross section of the laminates fabricated with a thickness ratio of (a)5.4 and (b)9.5. The bright thin layers are of AMz whereas the thick dark ones55 lm were prepared. They are referred to as systems B and C respectively, in this investigation. A general view of the cross section for laminates B and C is presented in Fig. 4, where the bright thin layers correspond to AMZ and the dark thick ones to ATZ composition. It can be appreciated the uniform thickness achieved for both thin and thick lay￾ers. Table 2 lists the predicted and measured thickness of the ATZ and AMZ layers, and the corresponding thickness ratio for each type of layered system. The predicted thick￾ness was calculated taking into account the shrinkage mea￾sured in the monolithic samples. After SEM examination of the laminates, it can be seen that the thickness of the thick layers presents a lower relative error (about 2–3%), with respect to the experimentally obtained values, than the ones predicted for the thin layers (between 7% and 10%). A close-up of the thin layers is shown in Fig. 5 for both laminate systems. The sharp interface between layers and the homogeneous dispersion of the different phases can also be inferred. In the micrograph showing laminate B (Fig. 5a) the edge crack can be clearly observed, thus sug￾gesting the presence of high compressive residual stresses within such layer. This phenomenon also indicates that the thickness of the internal AMZ layers in laminate B is over the critical thickness (tc) value, above which the edge cracks are induced, and thus crack bifurcation phenome￾non at failure is likely to occur [13,21]. On the other hand, the SEM micrograph of laminate C (Fig. 5b) shows no edge crack in the centre of the compressive layer, i.e. the AMZ layer thickness in this case must be lower than ‘‘tc’’. In order to evaluate and quantify the residual stresses developed in the laminates during cooling, the difference in strain for ATZ and AMZ was analysed from the data recorded in the dilatometric experiments (Fig. 6). It was Table 1 Basic physical and mechanical characterization of the monolithic samples after sintering at 1550 C for 2 h Material Density (%) Young modulus (GPa) m-ZrO2 (vol.%) KIC (MPam1/2) Strength (MPa) ATZ 99.5 390 ± 10 – 3.2 ± 0.2 422 ± 30 AMZ 98.5 280 ± 30 90–95 2.6 ± 0.2 90 ± 20 Fig. 3. Kinetic curves for the ATZ and AMZ slips and representation of the predicted times to obtain thick ATZ and thin AMZ layers of 630 lm and 63 lm, respectively. Fig. 4. Cross section of the laminates fabricated with a thickness ratio of (a) 5.4 and (b) 9.5. The bright thin layers are of AMZ whereas the thick dark ones are of ATZ. Table 2 Predicted and obtained thicknesses for the two laminated systems fabricated in this work. Predicted thickness has been calculated with the casting time and shrinkage System Predicted Measured % Error Thick Thin Ratio Thick Thin Ratio Thick Thin B 550 110 5 533 ± 9 99 ± 5 5.4 3 10 C 550 55 10 560 ± 8 59 ± 6 9.5 2 7 1934 R. Bermejo et al. / Composites Science and Technology 67 (2007) 1930–1938