MS-7-IN-1636 High temperature in-situ ceramic eutectic composite and functional glass matrix composite with a novel microstructure
We have developed unique ceramic eutectic composites, which are named Melt Growth Composites (MGC). The MGCs have novel microstructures (Fig. 1 for Al2O3/Y3Al5O12 (YAG) binary MGC and Fig. 2 for Al2O3/GdAlO3 (GAP) binary MGC), in which continuous networks of single-crystal Al2O3 phases and single-crystal complex oxide compound (YAG or GAP) interpenetrate without grain boundaries. The reconstructed three-dimensional images showed that binary MGCs have a chain structure. The existence of amorphous phases at interfaces generally leads to a reduction in the strength of the material at high temperature. Fig. 3 shows typical HREM images of the interface between Al2O3 and YAG phases in unidirectionally solidified Al2O3/YAG binary MGC. No amorphous phases are observed at the interfaces between the Al2O3 and YAG phases and relatively compatible interfaces are formed. The MGCs, therefore, have excellent high-temperature characteristics such as high temperature strength, thermal stability of microstructure and oxidation resistance in an air atmosphere at very high temperatures. We have also developed a new compositional binary MGC comprised of Al2O3 and SmAlO3 phases. The Al2O3/SmAlO3 binary MGC displays the highest high temperature flexural strength at 1773 K in conventional MGC binary systems.
On the other hand, we have recently developed functional glass matrix composites reinforced with thin discal metallic particles (cross-sectional microstructures to perpendicular to pressed plane showed in Fig. 4). The volume resistivity of the glass matrix composites can be controlled by the volume fraction and the aspect ratio of thin discal Ni-Cr alloy particles. In addition, it is achieved by simultaneous improvement of the strength and fracture toughness by microdispersion of thin discal Ni-Cr alloy particles. Therefore, several useful applications can be considered, for example, household electrical instruments as a board-shaped heater such as hot plates, etc.
In this paper, microstructural and high temperature characteristics of the binary MGCs and new functional glass matrix composites with superior characteristics of electric resistance will be briefly introduced.
We thank prof. H. Yasuda at Department of Material Science and Engineering, Graduate School of Engineering, Kyoto University for the 3 D observation of eutectic structure in the ceramic eutectic composite.
Fig. 1: SEM image showing the microstructure of a cross-section perpendicular to the solidification direction of the unidirectionally solidified Al2O3/YAG binary MGC. |
Fig. 2: SEM image showing the microstructure of a cross-section perpendicular to the solidification direction of the unidirectionally solidified Al2O3/GAP binary MGC. |
Fig. 3: HREM image of the interface between Al2O3 and YAG phases of the unidirectionally solidified Al2O3/YAG binary MGC. |
Fig. 4: Optical micrographs showing the microstructure of a cross-section perpendicular to the SPS pressed planes of the soda-lime glass matrix composite reinforced with 30 vol % Ni-Cr alloy particles with shapes of the thin disc. |