【作者】 蔡阳；

【导师】 侯铁翠； 卢红霞；

【作者基本信息】 郑州大学 ， 材料学， 2012， 硕士

【摘要】 氧化锆增韧氧化铝陶瓷(ZTA)由于具有高强度、高硬度、耐腐蚀、价格低廉等优点,在高温、机械、电子领域得道了广泛应用。随着研究的发展,这种单一相强化、韧化氧化铝陶瓷的综合性能还是不能满足航空航天、交通运输等高端工程技术领域的需求。然而利用多元协同强化ZTA复相陶瓷以及多种增韧机制的耦合协同将成为提高ZTA陶瓷断裂韧性和抗弯强度的重要研究和发展方向。本文通过调整体系组成和改变陶瓷烧结工艺,改善ZTA陶瓷的粉体性能、烧结性和显微结构,提高材料的综合力学性能。以ZrOCl2·8H2O, Al(NO3)3·9H2O, Y(NO3)3·6H2O, La(NO3)3·6H2O, Ce(NO3)3·6H2O和NH4HCO3为主要原料,采用共沉淀法分别制备了La2O3和CeO2掺杂的ZTA复合粉体,通过TG-DTA、XRD、SEM等手段对粉体的热行为、成分与结构进行表征；并分析了不同的前期处理工艺、煅烧温度以及稀土氧化物种类、含量对复合粉体性能的影响。分别采用传统烧结和微波烧结两种方法制备了稀土掺杂ZTA复合陶瓷,通过研究组成和工艺对复合材料力学性能(维氏硬度、抗弯强度、断裂韧性)以及显微结构的影响,分析了稀上氧化物、烧结工艺对复合材料组织结构与性能的影响,并探讨了其相关机理。研究结果表明：采用共沉淀法成功的制备出了粒径为100nm左右,分散性良好的稀土氧化物掺杂ZTA复合粉体。采用水热处理和微波加热方式,对于La2O3和CeO2掺杂ZTA复合前驱粉体,分别在1000℃和1200℃微波煅烧条件下保温5min,得到了主晶相为t-ZrO2和α-Al2O3的复合粉体；La2O3和CeO2的掺杂可以影响ZTA复合粉体的相转变温度,,并改变粉体的物相成分。比较传统烧结与微波烧结两种烧结方式以及不同烧结温度下样品的致密度和力学性能,探索出了最佳的烧结工艺：微波烧结1550℃,保温30min。对于La2O3掺杂的样品,当La2O3含量为1.5mol.%时,样品的相对致密度达到99%,且力学性能最佳,分别为硬度17.2GPa,弯曲强度420MPa,断裂韧性7.1MPa·m1/2,这主要是掺杂La2O3可以使ZTA材料内部原位生成片状LaAl11O18这种片晶既可以阻碍氧化铝、氧化锆颗粒的长大,也可以借助较大的长径比诱发裂纹桥接、晶粒拔出等增韧机制来改善材料的力学性能。对于CeO2掺杂的样品,当CeO2含量为0.5mol%时,样品的相对密度达到93%,且综合力学性能最佳,分别为硬度16.27GPa,弯曲强度450MPa,这主要是由于CeO2的添加可以起到烧结助剂与稳定剂的作用,促进了ZTA复合陶瓷的致密化、提高了四方相氧化锆的稳定性。更多还原

【Abstract】 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.更多还原