【作者】 周泽华；

【导师】 丁培道；

【作者基本信息】 重庆大学 ， 材料科学与工程， 2002， 博士

【摘要】 层状复合陶瓷由于具有较高的韧性而受到广泛的关注，层状复合结构设计将减小材料力学性能对缺陷的敏感性，使之成为一种耐缺陷材料，使材料的断裂韧性获得较大的提高。本文研究了表面层厚度为0.3(0.1mm，中间层厚度为5.4(0.2mm的氧化锆—氧化铝三层复合陶瓷经模压成型、无压烧结后的力学性能。为了掌握成分与性能的关系，在中心层成分为5wt％Al2O3+ ZrO2保持不变的前提下，研究了表面层成分分别为20wt％、30wt％及40wt％Al2O3+ ZrO2的层状复合陶瓷的性能变化，并对比不同成分的氧化锆—氧化铝单层复合陶瓷的力学性能，借助各种现代实验分析手段，研究了层状复合陶瓷的显微组织特征，分析了性能变化的原因和强韧化机理。研究表明：相同条件下，采用本研究设计的三层氧化锆—氧化铝复合陶瓷的硬度、强度和断裂韧性均高于单层复合陶瓷，尤其是层状陶瓷的断裂韧性较单层陶瓷提高较大，提高率约为60％；当表面层成分为30wt％Al2O3+ ZrO2时，层状复合陶瓷的整体机械性能最佳，为：(f＝786MPa，KIC＝18.37MPa·m1/2，HV＝14.99GPa。层状陶瓷的强韧化机理为层状结构热失配引起的残余应力和界面特征强韧化、氧化锆的马氏体相变增强增韧、及第二相氧化铝颗粒的弥散细晶强化的共同作用，其中层状结构对材料韧性的贡献最大。采用本组分结构设计，可获得表面层含残余压应力、中心层含残余张应力的层状复合陶瓷，表面层压应力可促进氧化锆的相变增韧，同时减缓主裂纹的能量，中心层的张应力可导致层内微裂纹的形成，以分散主裂纹的能量。目前评价陶瓷材料抗热震性的两类理论及其公式在结论上相距较大，无法对陶瓷材料的热震稳定性作出准确地预测和解释。本文分别采用残余强度法及裂纹扩展法对氧化铝—氧化锆层状及单层复合陶瓷的抗热震性进行了测定，比较了两类陶瓷的热震性能差异，根据实验结果对传统的两种陶瓷抗热震理论进行了分析和验证，并在此基础上对陶瓷材料的抗热震理论进行了修正。研究表明：相同成分下，三层复合的氧化锆—氧化铝层状结构复合陶瓷的临界抗热震温度(Tc均高于氧化锆—氧化铝单层复合陶瓷的(Tc，其中成分为30wt％Al2O3+ ZrO2的层状复合陶瓷的临界抗热震温差(Tc最高，残余强度法测定的(Tc为550℃，裂纹扩展法测定的(Tc为500℃。根据陶瓷热震的具体条件，本文首次提出了单层陶瓷和层状陶瓷的临界抗热震温度公式如下，并根据实验数据对公式进行了验证。结果证明下述公式较准确地反映了陶瓷材料抗热震性能的变化规律，材料临界抗热震温度的预测值与实验结果较为接近。<WP=5> （急冷时单层陶瓷的(Tc） （一定速度冷却时单层陶瓷的(Tc） （急冷时层状陶瓷的(Tc） （一定速度冷却时层状陶瓷的(Tc） 此外，本文首次系统地研究了氧化锆—氧化铝三层结构复合陶瓷和单层复合陶瓷与Cr12钢对磨时，在润滑介质、载荷、转速和磨损时间等参数的变化下，层状和单层复合陶瓷的摩擦磨损性能变化，并分析了性能变化的原因和不同条件下层状和单层陶瓷的磨损机理。研究表明：相同实验条件下，层状复合陶瓷的摩擦系数和磨损率总体均小于单层复合陶瓷，层状陶瓷具有较好的摩擦磨损性能的根本原因在于其良好的韧性和表面层的压应力；水润滑状态下层状及单层陶瓷的摩擦系数和磨损率均小于干摩擦状态下陶瓷的摩擦系数和磨损率，性能变化的根本原因在于磨损机制的变化，水润滑下复合陶瓷的磨损机制为微切削、微裂纹和陶瓷表面塑性变形引起的疲劳磨损及摩擦化学磨损的共同作用，而干摩擦下陶瓷的磨损机制为塑性变形引起的粘着磨损和晶粒拔出引起的磨粒磨损、表面脆断的共同作用。更多还原

【Abstract】 Laminated composite ceramics are attached great importance to because of their high toughness. Mechanical properties of laminated ceramics are not in relation close to flaw, and such ceramics become flaw-tolerance materials, therefore their toughness is improved more.In this paper, mechanical properties of ZrO2—Al2O3 laminated ceramics prepared by dry-pressing, pressureless-sintering were studied, which have three-layer structure and thickness of their surface and center layers are separately 0.3(0.1mm, 5.4(0.2mm. For knowing the relation of composition and properties, mechanical properties of different laminated ceramic which surface layer’s composition is separately 20wt％、30wt％ and 40wt％ Al2O3+ ZrO2 were studied under 5wt％Al2O3+ ZrO2 center layer condition, and properties of monolayer ceramics of different composition were compared; the reason of properties’ change and mechanism of strengthening and toughening were analyzed by microstructure research of laminated ceramics with the helps of lots of modern analyzing instruments. The results showed that hardness, strength and toughness of this kind of three layer composite ceramics were higher than those of monolayer ceramics under same conditions, especially toughness of laminated ceramics was higher 60％ than that of monolayer ceramics. When composition of surface layers is 30wt％Al2O3— ZrO2,the total mechanical properties of laminated ceramic were the best: (f＝786MPa，KIC＝18.37MPa·m1/2，HV＝14.99GPa. Strengthening and toughening mechanisms of laminated ceramics were from residual stress caused by different thermal-expansion of laminated structure, layer’s interface, martensite phase transformation of zirconia and dispersion of alumina grains together, in which effect of laminated structure was the most. Laminated composite ceramics of residual compressive stress in surface layers and tensile stress in center layer were brought by above laminated structure and composition. Toughening effect of phase transformation of zirconia were increased and energy of main crack were decreased by compressive stress in the surface layers, and micro-cracks were formed to decentralize energy of main crack by tensile stress in the center layer.Currently two sorts of theories and formulae of thermal-shock-resistance of ceramics are too contradictive each other to be forecasted and explained exactly. In this paper, thermal-shock-resistance of the ZrO2—Al2O3 laminated and monolayer ceramics<WP=7>were measured by residual strength method and crack extension method, difference of thermal-shock-resistant properties were compared, two sorts of traditional theories of thermal-shock-resistance were analyzed and validated according to test results, and these theories were revised based on above study. The results indicated that critical thermal-shock-resistant temperature (Tc of ZrO2—Al2O3 laminated ceramics was higher than that of monolayer ceramics under same test conditions, and (Tc of laminated ceramics which composition of surface layer was 30wt％Al2O3+ ZrO2 was the highest which was 550℃ measured by residual strength method and 500℃ by crack extension method. Formulae of critical thermal-shock-resistant temperature of ZrO2—Al2O3 laminated and monolayer ceramics were put forward firstly as follow based on practical test conditions and were validated based on test results. The results showed that rules of thermal-shock-resistance of ceramics were discovered by those formulae, and the forecast results of (Tc of ceramics were equal to test results. ((Tc of monolayer ceramics under quick cooling speed) ((Tc of monolayer ceramics under a constant cooling speed) ((Tc of laminated ceramics under quick cooling speed) ((Tc of laminated ceramics under a constant cooling speed)Besides, tribology properties of the ZrO2—Al2O3 laminated and monolayer ceramics were studied systemically under different lubrication medium, load, speed更多还原