On The Fabrication Of Alumina-based Bulk Ceramic Materials Via A Novel Technique Of Melt Casting Under Ultra-High Gravity Field

Textured Al₂O₃ ceramics, Al₂O₃ based eutectics and transparent YAG ceramics are important advanced caramics rapidly developed in recent years, which are top representation of preparation technology of ceramics. The textured Al₂O₃ has improved mechanical performance, due to the well-arranged grains can reduce the inner stress; Because the elimination of amorphous phase in the interface, net and fine microstructure can be realized by designing eutectic composite, the Al₂O₃ based eutectics have increased mechanic performance at elevated temperature, which led to the elevated temperature structural applications on turbine components in aviation engine; The transparent YAG ceramics possess high optical and mechanical properties. Especially, the Nd3+ doped YAG has been successfully utilized as laser medium, and KW level laser output was achieved, which make the transparent YAG ceramic become a hot reaearch field. From the view of light physics, if the textured and fine microstructure can be achieved via a new fabrication technique, the optical and mechanical properties will be further improved. Therefore, for the purpose of scientific research and practical application, it is significant to explore a simple and efficient preparation technique of above-mentioned materials.Melt casting under ultra-high gravity delivered by ourselves is a new method of preparing oxide ceramics. Its main principle is to integrate the combustion synthesis with ultra-high gravity technology, firstly, the eleveted temperature metal/ceramic melts can be achieved by heat generated from thermite combustion reaction, then oxide ceramic product can be separated from mixture melt and rapidly solidified, finally the dense ceramic bulk can be produced.In order to prove as-mentioned technology route, three aspects works were performed: firstly, equipment of melt casting under ultra-high gravity was designed and built; secondly, textured Al₂O₃ ceramics, Al₂O₃ based eutectics and transparent YAG ceramics were fabricated by melt casting under ultra-high gravity according to appropriate combustion synthesis systems; thirdly, the process of fabrication was analysized and numerically simulated.The equipment of melt casting under ultra-high gravity was designed and built for the first time, several difficulties were overcome, such as balance during high speed rotation and igniting combustion synthesis at the same time and so on. Presently, the equipment can serve as high as 5000g～10000g of ultra high gravity field, and the maximum load of carried reactor reach 1000ml, the maximum size of as-fabricated sample isΦ80mm.Using Al/NiO as reagents, fabrication of textured Al₂O₃ via melt casting under ultra-high gravity was researched. The results showed that with the increase of ultra-high gravity coefficient (G), the intensity of separation increased, till thoroughly separation was realised, and the density of as-produced ceramics gradually increased, the maximum value is 97%; The microstructure of as-produced ceramics showed that each grain had apparent faceted feature, and the excellent arrangment was found among grains; the ration envaluation was performed by introducing texture coefficient, accordingly, the mechanism of texture development was researched.Fabrication of Al₂O₃/YAG, Al₂O₃/ZrO₂ and Al₂O₃/YAG/ZrO₂ eutectics via melt casting under ultra-high gravity was researched. The results showed that the density of as-produced eutectics were higher than 99%, the synthesis and simultaneous densification were realized. The microstructure observation showed that the interlamellar spacing of Al₂O₃/ZrO₂ and Al₂O₃/YAG/ZrO₂ reach nano-meter and sub-micrometer, respectively.Therefore, compound ceramic materials with ultra-fine microstructure could be achieved by combining melt casting under ultra-high gravity with designing eutectic system. Using Al/NiO/Y₂O₃ as raw reagents, fabrication of YAG ceramic material via melt casting under ultra-high gravity was researched. Effect of different reagents on phase separation, densification was researched by accounting adiabatic temperature; The density of YAG sample fabricated under 1000g reached 99.30%, and the sample showed translucent.