| Oxide eutectic ceramics is a kind o f composite material wit h a superfine microstructure, in which each phase is intertwined, and coupled growth. Such a microstructure makes it possess the properties of high-temperature resistance, high strength and ductilit y for wide applications as high- temperature components in aviation and aerospace industries. However, the particle size, morphology, uniformity and dispersibility of raw oxide ceramic powders will affect significantly on the microstructure and mechanical properties of oxide eutectic ceramics.Precursor powders of alumina/yttria- stabilized zirconium oxide are synthesized with a chemical coprecipitation method by tailoring the precipitant content, p H value, dispersant and temperature to evaluate their influences on the powder size, morphology and dispersion of the precursor powders. The morphology, phase structure, and uniformity of the powders were characterized by using TG- DTA, XRD, SEM and TEM analyses. By means of chemical coprecipitation process, The alumina/yttria- stabilized zirconium oxide powders have been prepared, which have a particle size of about 100 nm in the aspect of scale. However, the shape of the oxide powders is difficult to be controlled, while the dispersion as well as the uniformity of the composite powders are needed to further improve.Through heating of alcohol- aqueous salt solut ions the precursor powder s with a spherical shape and a particle size of about 600 nm are synthesized. A uniform temperature fie ld without introducing a mechanical interference in solut ion has an important influence on the uniformity and dispersion of the composite powders. By using a microwave assisted heating method, the precursor powders with a spherical shape, favorable dispersion and a particle size of about 400 nm can be achieved. After the precursor was calcined at different temperatures, the composite powders are investigated by means of XRD, SEM and TEM, which consist of α- Al2O3 and Zr0.92 Y0.08 O1.92, distributed uniformly in the composite particles. The composite oxide particles remain spherical and well- dispersive, and their average particle size is about 200 nm in the aspect of scale.Dense Al2O3/Zr O2(Y2O3) bulk ceramics were prepared by the hot pressing process. The sintering densification curve indicates that, the bulk ceramics are densified rapidly in a sintering temperature range of 1400 to 1600 o C. When the sintering temperature is above 1500 o C, a reaction between Zr O2 and Y2O3 takes place to produce a small amount of Zr3 Y4O12. Different phases of α-Al2O3 and Zr O2(Y2O3) are distributed uniformly in Al2O3/Zr O2(Y2O3) ceramics with a grain size of about 1~2μm. In addition, the Zr O2 grains are finer than the Al2O3 grains.The mechanical properties of Al2O3/Zr O2(Y2O3) ceramics sintered at different temperatures by hot pressing were further evaluated. The Al2O3/Zr O2(Y2O3) ceramic sintered at 1500 o C has the best mechanical properties, which has a relative density of 98.3%, a flexural strength of 1363 MPa, and a corresponding fracture toughness of 10.01MPa·m1/2. After SEM observations of the fracture surface, the strengthening and toughening mechanis m of Al2O3 /Zr O2(Y2O3) ceramic are proposed. The main strengthening mechanism of Al2O3/Zr O2(Y2O3) ceramic is intragranular particle strengthening, while the tâ†'m transformation of Zr O2 phase makes a contribution to the high fracture toughness of the sample. |
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