Process Development Of Al₂O₃/MgAl₂O₄ Eutectic Ceramics Prepared By Zone Melting

Directional solidification oxide eutectic ceramic is affected with its excellent resistance to high temperature,anti-oxidation,corrosion resistance,high strength,high hardness et al.properties.It is considered as one of the most promising candidates for new generations of ultra-high temperature structural materials,and has important application prospects on the ultra-high temperature aerospace engine.In this experiment,Al2O3/MgAl2O4 eutectic ceramic has been prepared by zone-melting method,and Compared to the performance of Al2O3/MgAl2O4/ZrO2 eutectic ceramic.This experiment mainly includes two aspects:(1)The preparation and characterization of pre-sintered ceramic.The component ratio of the eutectic ceramic and the parameters of the pre-sintered ceramic can be determined through the analysis of the pre-sintered body density,porosity,phase analysis combined with the directional solidification SEM and EDS analysis of samples.And the ratio of raw materials of pre-sintered is 90.5Al2O3/9.5MgO;With the increase of sintering temperature,the bulk density of materials increased,and its apparent porosity decreased,and it was sintered at 1500? for 2 hours,after which the volume density is 3.7g/cm3,the porosity is 2.80%,the hardness is 9.40GPa,fracture toughness is 1.88 MPa·m1/2.(2)The preparation and characterization of eutectic ceramic.The experimental process by finite element analysis simulation of graphite crucible,crucible molybdenum and tungsten crucible was combined with the actual test,which determined the use of tungsten crucible to do the directional solidification experiment.And the diameter of the crucible is 10mm,wall thickness is 2mm,crucible wall temperature is 2200?,the crucible rate is 2-6mm/h.The Al2O3/MgAl2O4 eutectic ceramics that its outer surface is smooth,and internal is translucent were prepared by the zone melting,and its high density is more than 99%.After the XRD analysis,the eutectic ceramics consists of Al2O3 phase that is the crystal morphology and MgAl2O4 phase,which grow according to the direction of(110)and(311).Microstructure of SEM show that Al2O3 is the matrix phase of eutectic ceramics,MgAl2O4 phase in a non-continuous sheet uniformly embedded in the matrix phase,and Al2O3 phase first growth.Along with the increase of the crystalline growth velocity,the solidification structure was refined,the toughness of the material was relatively improved;however the growth rate was too high to lead to the porosity could not be completely discharged so as to have the effect on materials density.The disappearance of porosity and interfacial amorphous phase and the single crystal phase effectively improve the hardness and fracture toughness of the materials.(3)The addition of ZrO2 has a great influence on the microstructure and mechanical properties of Al2O3/MgAl2O4 eutectic ceramics.Its microstructure showed that Al2O3 and MgAl2O4 are the matrix phase,ZrO2 phase as barred structure are uniformly embedded in the matrix phase,the toughness of Al2O3/MgAl2O4 eutectic ceramics could be increased by the addition of ZrO2.