Study On Preparation Of Al₂O₃/GdAlO₃ Eutectic Ceramics By Horizontal Zone Melting

Directionally solidified oxide eutectic ceramics are considered to be one of the most promising new generation of ultra-high temperature structural materials due to their unique excellent properties at high temperature,such as thermal stability,resistance to oxidation and ablation,high temperature mechanical properties,especially high fracture toughness and creep resistance etc.The Al₂O₃/GdAlO₃ eutectic ceramics are prepared by the horizontal zone melting method.They were compared with Al₂O₃/GdAlO₃ eutectic ceramic prepared by vertical zone melting method and Al₂O₃/GdAlO₃/ZrO₂ eutectic ceramic prepared by the horizontal zone melting method.And the following conclusions were got:1.Al₂O₃/GdAlO₃ pre-sinter material was prepared and chartered.After analysis of The eutectic composition,micro-structure,density and porosity of the pre-sinter material,and the optimal experimental conditions were obtained as the sinter temperature of 1500?and the sinter time of 4h;Under these parameters,the samples were prepared with phases of Al₂O₃ and GdAlO₃,whose volume density is 5.25 g/cm³ with the porosity below 3.1%.2.Directionally solidified Al₂O₃/GdAlO₃ eutectic ceramics were prepared and chartered.The internal diameter of tungsten crucible is 10 mm and its thickness is 2 mm.At the high temperature of 2400?,the semitransparent eutectic ceramic samples with smooth surface and compact microstructure was prepared by the horizontal zone melting method at the moving rate of 1⁵ mm/h.From analysis by X ray diffraction and EDS energy spectrum,the phases of and Al₂O₃ and GdAlO₃ were observed in the samples.Compared with the material in front of melting,the eutectic ceramic exhibited a significant crystallographic orientation.From the picture of the SEM,the irregular structure with three dimension network can be found,which was composed by Al₂O₃ as the substrate phase and GdAlO₃ as the dispersed phase;With the increase of solidification rate,the micromorphology of the eutectic ceramics is gradually transformed from"Chinese character"pattern to"bar like""layered"pattern,and the eutectic spacing decreased to the minimum value 0.7?m.The eutectic ceramic had a maximum hardness of 23.36 GPa,and a maximum fracture toughness of 3.12 MPa·m^1/2.3.Al₂O₃/GdAlO₃ eutectic ceramics by Horizontal zone melting method were compared with those prepared using the Perpendicular zone melting method.At the same solidification rate,the eutectic microstructure of the sample prepared by Horizontal zone melting method exhibited regular lamellar pattern with the eutectic spacing of about 1?m.While,the eutectic microstructure of the samples prepared using Perpendicular zone melting method exhibited irregular pattern with eutectic spacing of about 2?m,which is two times of the eutectic space of the horizontal zone melting method.The hardness and fracture toughness of the former samples got an obvious improvement of 10%in compassion with the later samples.4.The addition of ZrO₂ had effects greatly on the microstructure and mechanical property of Al₂O₃/GdAlO₃ eutectic ceramics.The ZrO₂ phase is distributed on the Al₂O₃phase or boundary of Al₂O₃ and GdAlO₃ phase,which not only modified the micromorphology of GdAlO₃ eutectic,but also increased the eutectic space in the interface of Al₂O₃ and GdAlO₃ phase.This also caused the decrease of the hardness of Al₂O₃/GdAlO₃ eutectic ceramics.However,because the ZrO₂ addition could increase the toughness,the fracture toughness of the samples was improved significantly and the value increased to 6.55 MPa·m^1/2.