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ZrB2, YAG and Al2O3 are widely applied because of some excellent performances, but ZrB2 is easily oxidized in the high-temperature air. To keep advantages and improve disadvantages of ZrB2, the shell-core structure A12O3-Y2O3/ZrB2 composite powders are prepared by the co-precipitation methods, the high density ZrB2-YAG-Al2O3 ceramics is prepared by the spark plasma sintering (SPS). The mechanical properties of prepared ceramics under the 20MPa sintering pressure and 4min holding time are shown, which indicates the mechanical properties are increased with increasing sintering temperature, and the increasing ratio of mechanical properties is faster at sintering temperature from 1300°C to 1700°C. When the sintering condition is 1700°C, 20 MPa and 4 minutes, the Young’s modulus and the fracture toughness are 421.8 GPa and 12.23 MPam1/2, respectively. The reinforced phase (YAG-Al2O3) is coated on the surface of ZrB2 crystal, that is to say, the YAG-Al2O3 is show on the crystal boundary, which is help for the densification and the mechanical properties. Introduction ZrB2 is posed particular interest due to the unique property combination of high refractoriness, high-electrical and high-thermal conductivity, chemical inertness against molten metals or nonbasic slags and good thermal shock resistance [1], which is became candidates for hightemperature applications where corrosion-wear-oxidation resistance is demanded. ZrB2 poses several applications such as Hall-Heroult cell cathodes for electrochemical processing of aluminium, evaporation boats, crucibles for handling molten metals, thermowell tubes for steel refining, thermocouples sleeves for high-temperature uses, nozzles, plasma electrodes, or as dispersoid in metal and ceramic-matrix composites for heaters and igniters. In addition, ZrB2 is a metallic conductor with electrical resistivity comparable with those of their parent metals. This permits to produce complex components at reduced shaping costs. ZrB2, because of its higher costs of production, has found a limited number of applications [2]. Yttrium aluminum garnet (YAG) with a chemical composition of Y3Al5O12 is an important advanced structural and functional material. Because of its relatively stable lattice structure and large thermal conductivity, it is used as a host for solid-state laser materials in luminescence systems and in the window material for a variety of lamps. YAG also has great potential application as a high-temperature engineering material because of its good high-temperature strength as well as its superior creep resistance [3-4]. To keep advantages and improve disadvantages of ZrB2, the shell-core structure A12O3-Y2O3/ZrB2 composite powders were prepared by the co-precipitation methods, the high density ZrB2-YAG-Al2O3 ceramics is prepared by the spark plasma sintering (SPS) and the microstructure and mechanical properties were investigated. 5th International Conference on Environment, Materials, Chemistry and Power Electronics (EMCPE 2016) © 2016. The authors Published by Atlantis Press 276 Materials and experimental Analytical grade of aluminum nitrate, yttrium nitrate, ammonia and commercially available ZrB2 powder (99.5% in purity) were used. ZrB2 particles were coated with Al2O3-Y2O3 composite particles via the co-precipitation method. ZrB2-YAG-Al2O3 ceramics were prepared using coated Al2O3-Y2O3/ZrB2 shell-core composite particles on the surface of ZrB2 particles with spark plasma sintering (SPS). ZrB2-YAG-Al2O3 ceramics were prepared with the SPS (Mode: SPS-1050, Japan). Phase analysis was identified by X-ray powder diffraction (XRD) (Model: D/Max-RB, Japan). Microstructure analysis was performed by scanning electron microscopy (SEM) (Model: JSM-5610LV, Japan). Mechanical properties of ZrB2-YAG-Al2O3 ceramics was tested. Results and discussion Fig.1 Sintering shrinkage curve of ZrB2-YAGAl2O3 ceramics The sintering curves for preparing 80wt%ZrB2-YAG-Al2O3 multiphase ceramic materials from different composite raw materials with the spark plasma sintering technique are shown in Fig.1. The Z-axis displacement of spark plasma sintering shows the shrinkage state of a ceramic body during the sintering process, when the value of the Z-axis displacement increases, this indicates the ceramic body is shrinking. The Z-axis displacement shows the shrinkage state of coated Al2O3-Y2O3 powders and mixed YAG powders, respectively. The composite powders with Al2O3-Y2O3 coated show a rapid shrinkage displacement from 700°C to 1000°C, where the second biggish shrinkage displacement also is shown from 1000°C to 1600°C, the Z-axis displacement is not varied basically above 1600°C. The sintering temperature curve is broken down into four parts, which include the preheating process below 700°C, the reaction process from 700°C to 1000°C, the sintering process from 1000°C to 1600°C, and the adjustment of the microstructure above 1600°C. The densification occurs mainly during the reaction process and sintering process, that is to say, the sintering processing is shown from 700°C to 1600°C. YAG is produced from 700°C to 1000°C[5-6]. The reaction temperature is lower than the 1100°C for synthesizing YAG powders from Al2O3-Y2O3 composite powders, because ZrB2 particles are changed electrically during the entire sintering process, which produces a plasma among ZrB2 particles to purify the nearby particle surfaces and increase the sintering activity. However, the Z-axis displacement for powders with YAG-Al2O3 added shows a lower shrinkage displacement below 1000°C, a larger shrinkage displacement is shown from 1000°C to 1600°C, the Z-axis displacement is not varied basically above 1700°C. The Z-axis displacement adding the different powders both show the same shrinkage state from 1000°C to 1600°C, YAG melts above 1000°C, the temperature is lowered because of the action of the plasma. Because the results of the two routes both show the Z-axis displacement is not varied basically above 1700°C, a sintering temperature of 1700°C is choosen for preparing high density ZrB2-YAG-Al2O3 multiphase ceramics (Fig.2), the microstructure of ZrB2-YAG-Al2O3 multiphase ceramics are shown in Fig.3, which indicates the density of ZrB2-YAG-Al2O3 ceramics with Al2O3-Y2O3 composite powder coated is higer than that of ZrB2-YAG-Al2O3 ceramics with YAG-Al2O3 powder mixed (Fig.3-a, b). The reinforced phase of ZrB2-YAG-Al2O3 ceramics with Al2O3-Y2O3 composite powder coated is

Influence of sintering technology on microstructure and mechanical properties of ZrB2-YAG-Al2O3 ceramics