In-situ Columnar Crystal Toughened Al₂o₃Ceramic Prepared Via Microwave Sintering

Al₂O₃ceramics is one of structure ceramics widely used. The primarydisadvantages of brittleness and ceramics difficulty restrict its wider application, Soit is a tide of ceramics development to prepare ceramic matrix composites. From thestructures of ceramic materials and the main factors influencing the grain shapes, thetoughening element was in-situ synthesized in Al₂O₃ceramic by the design ofmicrostructure and the new processing way. In-situ columnar crystal tougheningAl₂O₃composite ceramic materials were prepared by microwave sintering by addingNb₂O₅, La₂O₃, LaNbO₄and Nb₂O₅/La₂O₃mix powders in commercial a-Al₂O₃powder as additives,respectively. The relationship of different additives influencingthe microstructure and the mechanical properties has been studied. Also, the effect ofdifferent additives on the Al₂O₃ceramic columnar crystals was studied. The resultshave shown that:The additive of Nb₂O₅can improve the sintering properties of material, andresult on the formation of equiaxed grains with small amount of columnar crystal.The additive of La₂O₃can produce LaAl₁₁O₁₈columnar grains with the relativedensity less than90%, so that mechanical property shocking. The additive ofLaNbO₄can improve the sintering properties of material, and result on the formationof equiaxed grains with LaNbO₄phase distributed in grain boundaries.Studies on microstructure and crack propagation showed that the tougheningefficiency of the complex additive was much better than that additive Nb₂O₅, La₂O₃,LaNbO₄. In-situ columnar Al₂O₃grain and LaNbO₄phase cooperate with enhancetoughness in densifying.The addition of Nb₂O₅/La₂O₃and eliminated the resistance to the abnormalgrowth and increased the activity of grains, thus, the grains can freely grow in ananisotropy. and result on the formation of equiaxed grains with LaNbO₄phasedistributed in grain boundaries. The ceramics of complex additive have bettermechanical property than single phase additive. It was found that the grains grew toa columnar crystal as the addition content of La₂O₃was7.5Vol.%, the aspect ratio was4∶1, and the relative density was98%.