Preparation And Properties Of Al₂O₃/ZrO₂/Er₃Al₅O₁₂ Composite Powders And Eutectic Ceramic

High temperature composite oxide ceramic Al₂O₃/ZrO₂/Ln₂O₃?Ln is lanthanide element,Y?has high strength,high temperature resistance,oxidation resistance and high creep resistance and other excellent performance,is expected to become a new generation of high temperature structural materials.The size of the eutectic ceramics prepared by the directional solidification method is mostly below the centimeter level.The Bridgman method is suitable for the preparation of larger eutectic ceramic blocks,but the microstructure of the materials is coarse and the phase spacing is more than 10?m,the flexure strength is low.In this paper,Al₂O₃/ZrO₂/EAG eutectic ceramics were prepared by high temperature melting method.The effects of holding time,holding temperature,isothermal solidification and the introduction of Y on the microstructure and Vickers hardness of eutectic ceramics were studied.The large size eutectic ceramic blocks had prepared successfully,whose phase spacing is on the order of microns.The precursor of the Al₂O₃/ZrO₂/EAG eutectic composite powder was prepared by chemical coprecipitation method.The precipitant with good dispersion and about 20 nm was obtained by using dilute ammonia as precipitant.The precursors were calcined and the particle size of the powders increased as the calcination temperature increased.The phase of the composite powder after calcination at 1300 oC for 2h is ?–Al2O₃,c–Er0.2Zr0.8O1.9 and c–EAG,and the particle size is about 100-200 nm.For the eutectic powders doped with Y2O₃,the Y element gradually changes from the solution in the EAG and ZrO2 phases to the YAG phase as the Y content increases.The eutectic composition of 1500 oC hot–pressed sintered ceramic has uniform distribution,grain size is about 1?m,Vickers hardness is 14.69 GPa.Al₂O₃/ZrO₂/EAG eutectic ceramics were prepared by high temperature melting method with sintered multiphase ceramics.At 1720 oC and 1770 oC respectively,the eutectic ceramics with phase spacing of about 1?m were obtained.The eutectic ceramics have a large number of hypereutectic and binary eutectic groups,and their Vickers hardness is equivalent to that of sintered bodies.By observing the indentation crack development,it is found that the toughening method of eutectic ceramics mainly has microcracking toughening,bridging toughening and interface deflection crack toughening.The large–size eutectic ceramic blocks were successfully prepared by isothermal solidification method,but the Al2O₃ precipitates a large number of internal precipitates,and the interval of the eutectic structure was 2–3?m.By changing the content of Y2O₃ in the eutectic ceramics,the microstructure of the homogeneous eutectic structure changes,and the content of Y2O₃ increases from TDI structure to lamellar structure.The microstructure of Al₂O₃/ZrO₂/EAG eutectic ceramics prepared by isothermal coagulation method at 1500 oC heat treatment is almost the same,and the Vickers hardness is slightly increased.The eutectic ceramics formed by continuous non-isothermal melting process have a continuous crack at the boundary of the colony boundary.Some of the eutectic structures are converted into equiaxed polycrystals.The ZrO2 phase is coarsened,the size is about 0.5?m,and the Vickers hardness decreases obviously.