【作者】 黄水根；

【导师】 李麟；

【作者基本信息】 上海大学 ， 材料学， 2003， 博士

【摘要】 掺杂CeO₂、Y₂O₃和Al₂O₃的ZrO₂基结构陶瓷，具有极好的韧性、强度和热稳定性，然而ZrO₂陶瓷的力学性能及显微组织与陶瓷的成分，制备工艺密切相关，特别是原料的成分组成决定了材料的相构成和机械性能。因此研究多元ZrO₂陶瓷的热力学性质，精确的相图计算无疑起着非常重要的作用。鉴于采用普通的实验方法很难获得二元高温氧化物体系的平衡相图，更无法得到高温下三元系的平衡相图，又因为ZrO₂-CeO₂陶瓷在高温和还原性气氛下具有明显的还原现象，材料的相结构和力学性能会出现明显的变化，而目前又缺少外界氧气分压、工作温度和成分对试样相结构的定量关系和对力学性能影响的定性关系。本文将采用当今国际上通用的相图计算方法—CALPHAD，收集大量的实验数据和热力学数据，根据各相的晶体结构，构建适当的热力学模型，利用Thermo-Calc和Lukas程序优化和估算多个三元氧化锆体系的高温平衡相图、ZrO₂-CeO₂陶瓷在不同氧分压下的热力学性质。同时利用估算的相图，指导设计了CeO₂-Y₂O₃-ZrO₂／Al₂O₃复合陶瓷的成分，制备出具有中试意义的氧化锆结构陶瓷。 首先利用相图计算技术和置换溶液模型重新优化计算了ZrO₂-CeO₂、ZrO₂-Y₂O₃相图、估算了CeO₂-Y₂O₃系的热力学性质，得到与实验数据相吻合的计算相图。根据计算的热力学参数，外推出多个ZrO₂-CeO₂-Y₂O₃系的高温等温截面相图，首次建立了该系的热力学数据库。温度为2073K的等温截面再现了实验信息。利用计算的等温截面相图得到在1723K，成分为12mol％CeO₂-ZrO₂陶瓷为全四方相，而3mol％Y₂O₃-ZrO₂含有11mol％立方相。采用实验分析方法很难定量分析四方相和立方相的含量，传统上认为12mol％CeO₂-3mol％Y₂O₃-ZrO₂陶瓷为全四方相，而本工作相图计算结果则认为该成分陶瓷含有30.9mol％的立方相，为该成分陶瓷极低的韧性提供了合理的理论依据，并建议同行们不必再对该材料进行开发研究。 基于ZrO₂-CeO₂陶瓷独特的相变特征，分别利用置换溶液模型和化合物能量模型优化和估算了ZrO₂-CeO₂陶瓷在高温或低氧分压还原性气氛下的热力学性质，构建了ZrO₂-CeO₂-CeO_1.5系的等温截面，再现了不同氧分压和工作温度下，CeOZ一Ceol.，中组元CeO:、CeO，:的氧化还原关系。并采用（ZrOZ，CeOZ，CeO，5）和（Zr+’，ce十“，ce+3）l（O一，va）2模型外推出非化学计量比相<zr!一zCezOZ一、>杂赡堋Ｔ诠?上首次指出在高温，大气气氛下烧结ZrOZ一CeOZ陶瓷时，陶瓷易还原的热力学依据。计算结果表明，当CeO:部分还原后，四方相区大大减小，四方相中稳定剂含量也随着CeO!.5的生成而降低，使低温下的马氏体相变更易启动，从而为ZrOZ一CeOZ陶瓷在还原性气氛具有极高韧性提供理论依据。 利用置换溶液模型，合理地优化了A12O3一CeO:和A12o3一Zr仇二元系相图，并利用几何模型外推，估算了ZrOZ一CeOZ一A12O3系的多个高温等温截面。估算的相图与温度为1673K和1873K的实验相图非常吻合。 基于计算的多个ZrOZ一Ceq一YZO3系截面相图，为获得优化的相组成，选取了合理的成分，利用粉末涂层法制备Ceq和YZq液相稳定ZrOZ/A12O〕纳米粉末。经冷等静压后，在1450oC下无压烧结1一4小时后，获得高密度结构陶瓷。并利用扫描电镜和衍射分析研究材料的显微结构和相组成，采用压痕法测定和计算了材料的维氏硬度和断裂韧性。成分为12mol%Ce氏一2.swt%A12O3一ZrOZ陶瓷具有极高的韧性，达13.53MPa.m’/2，硬度为847k留mm“，陶瓷由弥散的超细A12o:粒子和粒径均匀的等轴四方相晶粒组成。添加A1203后，其强度和韧性明显优于12mol%Ce仇一TZP陶瓷。继续添加3mol%YZO3后，材料的韧性急剧降低，只有2.02MPa.m’‘“，不具有3Y-TzP陶瓷的高硬度和12ce一TzP陶瓷高韧性的综合性能。根据计算相图，该组织中含有30.9%mol的立方相，并且四方相固溶过多的稳定剂，相变增韧效益在低温下很难发生。当YZ仇的含量从3mol%降低到lmol%，并加入适量的CeO:和2一3诚%A12O3，陶瓷的韧性发生显著改变。稳定剂含量愈低，材料的韧性愈好。成分为lmol%CeOZ一Zmol%YZO3一ZrOZ/2喊%A1203陶瓷的韧性为5.94MPa.m’‘2，硬度为1126kg/mm，，经高速研磨和长时间热处理后，均没有生成单斜相，热稳定性好，该陶瓷的综合性能己经超过商业用陶瓷。继续降低YZO:含量，并增加CeO:含量，能获得高韧性和良好热稳定性组合的先进陶瓷。成分为4mol%Ce仇一1 mol%YZO3一ZrOZ/2诚%A12O3陶瓷的韧性为14.34MPa.m’2，硬度为95Ikg/mmZ，成分为6mol%ce02一lmol%Y203一zr02/2似%A12O3陶瓷的韧性为9.12MPa.m’月，硬度为10llkg/mmZ，这些陶瓷的力学都超过了同类商业用陶瓷，具有中试意义。 根据计算的ZrOZ一CeOZ一A12O3系相关系，为获得优化的相组成，采用商业用的12mol%CeOZ一丁ZP陶瓷粉，掺杂2.5一20叭%A12O3以抑制四方相晶粒的长大，通过球磨、压制、烧结后，分析了陶瓷的显微组织和力学性能。超细而弥散分布的A12O3粒子，均匀分布在四方相晶界处，有效地抑制了四方相晶粒生长和改善了陶瓷的硬度和韧性。在1723K下无压烧结4小时后，1更多还原

【Abstract】 Ceria-yttria co-doped zirconia-based multi-components ceramics, with superfine alumina dispersed in the matrix, possess excellent fracture toughness, strength and thermal stability. However, the mechanical properties and microstructure are strongly dependent on the composition and the fabrication procedure, especially the composition of zirconia containing multi-component ceramics. Therefore, precise phase diagrams of zirconia-based multi-components systems can be considered as the "map" for the development of advanced ceramics. Due to the experimental difficulties, the phase diagrams and thermodynamic data of zirconia systems are very limited and dispersive. Further more, the constitutes of phases and mechanical properties of ZrO2-CeO2 system change drastically when it is under the reduced atmosphere and elevated temperatures. The thermodynamic properties of ZrO2-CeO2-Ce2O3 system is very important to obtain the quantitative relation among oxygen pressure, temperature, composition, phase constituents and mechanical properties. In this paper, with the calculation technique CALPHAD, phase diagrams of ZrO2-CeO2-Y2O3, ZrO2-CeO2-Al2O3, ZrO2-CeO2-Ce2O3 systems are optimized and extraploated by Thermo-Calc and Lukas Programme with suitable thermodynamic models and experimental data. Meanwhile, the thermodynamic properties of ZrO2-CeO2 system under reducing atmosphere is also assessed with substitutional and compound energy model. Based on the calaculated phase diagrams, different compositions of CeO2-Y2O3-ZrO2/Al2O3 are selected and ceramics with commercial meaning are fabricated with the powder coated method.First, comprehensive descriptions of experimental information and thermodynamic properties in the binary systems, ZrO2-CeO2, ZrO2-Y2O3, and CeO2-Y2O3 are given and thermodynamic models of these systems are discussed. The calculated phase diagrams of binary systems are consistent with the experimental data. With the substitutional model (ZrO2,CeO2,YO1.5), the thermodynamic databese of ZrO2-CeO2-Y2O3 is constructed, and with muggianu’s formula, the isothermal sections are extraploated under different temperatures. The experimental section at 2073K is well reproduced bythe thermodynamic calcualtion. From the calcuated phase diagrams, 12 mol% CeO2-ZrO2 is in the tetragonal phase range, 3mol%Y2O3-Zr02 is with 11 mol% cubic phase, 12mol%CeO2-3mol%Y2O3-ZrO2 has 30.9mol% cubic phase, which is totally different from the tradional idea that considers it as a full tetragonal phase. The calculated result provides the theoretic basis for the weak fracture toughness of this composition.Using compound energy model and substitutional model, the thermodynamic properties of <CeO2-y>in CeO2-Ce2O3 and <Zr1-zCezO2-x>in Zr02-CeO2-Ce2O3 system are evaluated. The evaluation is based on the optimization of ZrO2-CeO2 and ZrO2-CeO1.5 systems, as well as the miscibility gap in CeO1.5-CeO2 system. The model parameters are evaluated through fitting the selected experimental data by means of thermodynamic optimization. A set of parameters with thermodynamics self-consistency is obtained that satisfactorily described the complex relation between y in <CeO2-y >and the partial pressure of oxygen at different temperatures, also the interdependence among miscellaneous factors such as temperature, oxygen partial pressure, the reduction amount of CeO2 as well as the nonstoichiometry in cubic phase <Zr1-zCezO2-x> The calculated results seem to be reasonable when put into the explanation of pressure-less sintering of CeO2-stabilised ZrO2 powder compacts under a controlled oxygen partial pressure.ZrO2-CeO2-Al2O3 system has been assessed with CALPHAD technique using PARROT procedure. The experimental information on the ZrO2-Al2O3, Al2O3-CeO2 systems as well as the isothermal sections of the ternary system at 1673K and 1873K are well reproduced. No alumina dissolves into the tetragonal zirconia phase from the calculated phase diagram.Different compositions are selected from the calculated isothermal section at 1723K of ZrO2-CeO2-Y203 system. With更多还原