C. Kaya et al. /Journal of the European Ceramic Society 29(2009)1631-1639 1635 (FEG) SEM(FX-4000, Jeol Ltd, Japan). More detailed obser vations were made using transmission electron microscopy TEM, Jeol Ltd, Japan, 4000 FX TEM) operated at 400kV, and equipped with an energy dispersive X-ray(EDX) analysis unit. Porosity and pore size were measured using a mercury pl porosimeter(Hg Por, Micromechanics Instrument Corp, USA) using a penetrometer weight of 62.79 g, and penetration volume of 6. 188 mL. The Archimedes' technique was used for density Aluminium measurements 3. Results and discussion Interface An optical microscopy image of the composite plates pro- duced after pressureless sintering at 1200C for 2 h is shown in Fig. 4a indicating that a homogeneous and macro-flaw free Coated and surface structure of the plate was obtained. The final component impregnated shown in Fig. 4a contains 12 layers with a fibre volume fraction fiber layer of 40%0. The overall thickness of the plate was x3 mm and no delamination of the layers was observed after sintering. The final sintered microstructure of the composite shown in Fig 4b con- tains 10-14 vol %o porosity which is quite low for this type of sinterable matrix precursors which are silca comp.. omposite systems. The development of complex and hi ing nano-scale alumina powders dispersed in aqueous solution mixed with nano-size colloidal Y2O3, led to full infiltration by the impregnation technique, as shown in Fig. 4b. It can be con- cluded that the matrix precursors developed display favourable rheological properties during both the impregnation and warm Fig.6. Schematic representation of the test sample arrangement to measure the pressing stages resulting in enhanced matrix infiltration and interlaminar shear strength(bonding strength) between two fibre mats. formability. In our previous research,using a combination of EPD and pressure filtration for different composite systems, for example mullite/mullite CMCs, a successful deposition was 2.7 Microstructural characterisation also achieved leading to manufacture of sintered samples with Microstructural examinations were carried out on sintered porosity levels from 15 to 20%. The present work represents an advance in the development of CMCs with lower porosity composite samples using a high-resolution Field Emission Gun using an impregnation technique combined with warm press- ing. It is expected from these results that improved sinterability and stability at moderate temperatures will ensure continued fibre integrity and matrix load translation efficiency resulting in high strength, damage-tolerant CMCs. Selected properties of the composite plates produced are given in Table 1. As shown in this table, using two different interface materials, namely NdPO4 and Zroz, quite similar mechanical properties were obtained at room temperature(four-point bending strength values of 279 and 260 MPa and tensile strength of 142 and 136 MPa, respec AE Pre amp tively). However, when the samples were subjected to bend (regain: 40 dB) strength test at 1300C, only a 5% reduction in strength was recorded for composites with NdPO4 interfaces(from 279 to 266 MPa)whereas over a 10% decrease was measured for com- Test posites with ZrO2 interfaces(from 260 to 232 MPa). Although sPecimen these two interface materials are known to be compatible with the matrix and fibres used, the difference in strength is most probably related to the possible different microstructure of the interface at high temperature. Load-displacement curves of the composite samples with the two interfaces were also recorded 中 nonitoring shown in Fis. 8. As Shown in Fig. 8a. both composites exhibC. Kaya et al. / Journal of the European Ceramic Society 29 (2009) 1631–1639 1635 Fig. 6. Schematic representation of the test sample arrangement to measure the interlaminar shear strength (bonding strength) between two fibre mats. 2.7. Microstructural characterisation Microstructural examinations were carried out on sintered composite samples using a high-resolution Field Emission Gun Fig. 7. Schematic representation of experimental set up for acoustic monitoring during tensile test. (FEG) SEM (FX-4000, Jeol Ltd., Japan). More detailed obser￾vations were made using transmission electron microscopy (TEM, Jeol Ltd., Japan, 4000 FX TEM) operated at 400 kV, and equipped with an energy dispersive X-ray (EDX) analysis unit. Porosity and pore size were measured using a mercury porosimeter (Hg Por, Micromechanics Instrument Corp., USA) using a penetrometer weight of 62.79 g, and penetration volume of 6.188 mL. The Archimedes’ technique was used for density measurements. 3. Results and discussion An optical microscopy image of the composite plates pro￾duced after pressureless sintering at 1200 ◦C for 2 h is shown in Fig. 4a indicating that a homogeneous and macro-flaw free surface structure of the plate was obtained. The final component shown in Fig. 4a contains 12 layers with a fibre volume fraction of 40%. The overall thickness of the plate was ∼3 mm and no delamination of the layers was observed after sintering. The final sintered microstructure of the composite shown in Fig. 4b con￾tains 10–14 vol.% porosity which is quite low for this type of composite systems. The development of complex and highly sinterable matrix precursors which are silica free, compris￾ing nano-scale alumina powders dispersed in aqueous solution mixed with nano-size colloidal Y2O3, led to full infiltration by the impregnation technique, as shown in Fig. 4b. It can be con￾cluded that the matrix precursors developed display favourable rheological properties during both the impregnation and warm pressing stages resulting in enhanced matrix infiltration and formability. In our previous research2,7 using a combination of EPD and pressure filtration for different composite systems, for example mullite/mullite CMCs, a successful deposition was also achieved leading to manufacture of sintered samples with porosity levels from 15 to 20%. The present work represents an advance in the development of CMCs with lower porosity using an impregnation technique combined with warm press￾ing. It is expected from these results that improved sinterability and stability at moderate temperatures will ensure continued fibre integrity and matrix load translation efficiency resulting in high strength, damage-tolerant CMCs. Selected properties of the composite plates produced are given in Table 1. As shown in this table, using two different interface materials, namely NdPO4 and ZrO2, quite similar mechanical properties were obtained at room temperature (four-point bending strength values of 279 and 260 MPa and tensile strength of 142 and 136 MPa, respec￾tively). However, when the samples were subjected to bend strength test at 1300 ◦C, only a 5% reduction in strength was recorded for composites with NdPO4 interfaces (from 279 to 266 MPa) whereas over a 10% decrease was measured for com￾posites with ZrO2 interfaces (from 260 to 232 MPa). Although these two interface materials are known to be compatible with the matrix and fibres used, the difference in strength is most probably related to the possible different microstructure of the interface at high temperature. Load–displacement curves of the composite samples with the two interfaces were also recorded for comparison at room and high temperatures (1300 ◦C), as shown in Fig. 8. As shown in Fig. 8a, both composites exhibit