The Directionally Solidified Al 2 O 3 /YAG Binary Eutectic Ceramic Was Prepared By The Regional Melting Method

Ceramic material is the most rapidly developing high-tech material in the world.It has been developed from the traditional sintered ceramics to the directional solidification oxide eutectic ceramics,directional solidification oxide eutectic ceramic is caused wide attention of unique properties,such as excellent resistance to high temperature,anti-oxidation,corrosion resistance,high strength,and high hardness et al.It is considered as one of the most promising candidates for new ultra-high temperature structural materials,and may be used to make the ultra-high temperature aerospace engine in the future.Al₂O₃/YAG eutectic ceramic has been prepared with zone-melting method,the research work and results are as the following:?1?The preparation and characterization of the pre-sintered ceramic samples.The optimum sintering parameters were determined by the analysis of the density.apparent porosity,phase analysis and XRD spectra of the pre sintered ceramics.The molding pressure is 20MPa,the ball milling rate is 700rad/min,the ball milling time is 5h,the sintering temperature is 1500 degrees C,and the holding time is 2h.Under this condition,the bulk density of the sintered ceramics was 3.91g/cm3,the apparent porosity was 3.15%,the hardness was 8.52GPa,and the fracture toughness was 2.19MPa/m1/2.?2?The preparation and characterization of the eutectic ceramic.Tungsten was chosen to be the crucible material.And the crucible internal diameter was 10mm,its wall thickness was 2mm.During the directional solidification process,the outer crucible wall temperature reached 2100? the crucible movement rate was 0-10mm/h,three turns plate-shape coil is the induction coil.?3?Characterization of the eutectic ceramic.The XRD pattern shows that the eutectic consists of Al₂O₃ phase YAG phase,the same phases composition as in the pre-sintered ceramics.SEM shows that the microstructure of eutectic is typical Irregular structure.YAG was the matrix phase of eutectic ceramics,Al₂O₃ phase embedded in the matrix phase uniformly in non-continuous.?4?Effect of growth rate on microstructure and machanical properties of eutectic ceramic.With the increase of growth rate,the microstructure is finer,by measuring and calculated ?2v?80 conform to the ?2v=constant.With the increase of growth rate,the machanical properties increase gradually,the hardness of eutectic Seramics was 16.14GPa,fracture toughness was 3.10Mpa.m1/2,which was 1.89 and 1.42 times of pre-sintered ceramic.respectively.The disappearance of the pore and the interface non-crystal phase and the single crystal phase can effectively improve the hardness and fracture toughness of the material.?5?Al₂O₃/YAG/ZrO₂ three eutectic ceramics consists of Al₂O₃ phase YAG phase and ZrO₂ phases.It presents a typical irregular microstructure.The hardness and fracture toughness were calculated by indentation method,The results show that the hardness of Al₂O₃/YAG/ZrO₂ three eutectic ceramic and the eutectic of two yuan is not changed,but the fracture toughness is improved.Mainly due to the addition of ZrO₂,the generation of heterogeneous interface and the mismatch of thermal expansion coefficient prevent the expansion of the crack,thus improving the toughness.