| Zirconia-toughened alumina (ZTA) ceramics have received widely used in the fields including high temperature service, machine and electronics due to their excellent strength, high hardness, good corrosion resistance and low price. But, the improvement of alumina ceramic by the single phase strengthening and toughening is not enough, and greatly limited its applications as advanced engineering materials in aerospace vehicles, architecture and so on. However, multi-component synergistic strengthening ZTA and coupling effects of multiple toughening mechanisms will be the emphases of research and development direction of improving and enhancing the various performances of ZTA ceramics.In this study, measures were adopted to improve the sinter ability and microstructure and enhance the various properties of ZTA ceramics, which included adjusting the system constituent and sintering process. The compounds ZrOCl2·8H2O, A1(NO3)3·9H2O, Y(NO3)3·6H2O, La(NO3)3·6H2O and NH4HCO3were used as initial reactants, and co-precipitation method was used to prepare ZTA composite powders with La2O3or CeO2-addition. Samples were detected for phase analysis by XRD and the micros true ture was examined using SEM. In addition, the combined TG-DTA technique was carried out to detect the thermo-dynamic behavior of ZTA composite powders. The effects of different pretreatment processes, calcining temperature and different kinds of rare earth oxide with various amounts were studied. Rare earth doping ZTA composites were prepared by two different methods of microwave sintering and conventional sintering. Their mechanical properties (Vickers hardness, bending strength, fracture toughness) and microstructure were carefully studied. The effects of preparation process and rare earth oxide on the ZTA composite performance were investigated, and the related mechanism were analyzed and discussed.The results were shown as follow. It is an efficient way to prepare ultrafine and well-dispersed La2O3/CeO2doped ZTA composite powders (about100nm) with purely tetragonal zirconia and alpha alumina-by co-precipitation method, using hydro thermal crystallization (180℃,5h), and microwave calcination (1000℃,5min) for La2O3doped composite powders and microwave calcination (1200℃,5min) for CeO2doped composite powders. The XRD diffraction and TG-DTA characterizetion for the samples showed that the phase transition temperature for alumina was retarded in La2O3or CeO2doped samples. The effects of two different methods of microwave sintering and conventional sintering and different sintering temperatures on the ZTA composite relative density were investigated. The samples prepared by microwave sintering can be sintered to full density and the optimized sintering process was1550℃for30min. For insight into the influence of La2O3or CeO2, various properties for a series of samples with different rare earth oxide contents were studied. For samples with La2O3inclusion, the optimal mechanical properties are achieved by doping of1.5mol.%La2O3, with relative density, Vickers hardness, bending strength and fracture toughness being99%,17.2GPa,420MPa and7.1MPa-m1/2, respectively. That can be explained that LaAl11O18plate-like crystals are formed in situ in the ZTA matrix when a certain amount of La2O3is added, and improved fracture toughness is attributed to the crack deflection and crack bridging by plate-like grains. For the CeO2added composites, the enhanced sintering of the samples obtained by a small amount of sintering additives (2.5mol.%CeO2) is beneficial to improve density of the composites. The optimal mechanical properties are achieved by doping of0.5mol.%CeO2, with relative density, Vickers hardness and bending strength being93%,16.27GPa and450MPa respectively. The main reason for improvement is that a small amount of CeO2is used as the sintering aid and stabilizer. |
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