【作者】 刘长霞；

【导师】 张建华； 张??；

【作者基本信息】 山东大学 ， 机械制造及其自动化， 2007， 博士

【摘要】 本文首次将透辉石和Al-Ti-B中间合金用于增韧补强无压烧结Al₂O₃基陶瓷材料，通过注浆—冷等静压—液相反应—温度梯度无压烧结工艺，研制成功两种新型Al₂O₃基大型结构陶瓷导轨材料。对其组分设计、力学性能、微观结构、增韧机理、摩擦磨损特性和机理等进行了系统的研究；提出了透辉石和Al-Ti-B中间合金对Al₂O₃基陶瓷材料的晶粒细化机理；建立了Al₂O₃基大型结构陶瓷导轨材料的烧结动力学模型。提出了Al₂O₃基大型结构陶瓷导轨材料的设计目标和添加相的选择原则，确定透辉石和Al-Ti-B中间合金为增强相；分析了添加相与基体材料之间的物理化学相容性，计算了添加相的极限体积含量。利用X射线衍射分析了Al₂O₃基大型结构陶瓷导轨材料的相组成；根据复合陶瓷材料烧结模型和晶粒变化模型，初步确定了Al₂O₃基大型结构陶瓷导轨材料的烧结温度和保温时间。通过注浆—冷等静压—液相反应—温度梯度无压烧结工艺，研制成功两个系列的新型Al₂O₃基大型结构陶瓷导轨材料：Al₂O₃／透辉石（AD）和Al₂O₃／Al-Ti-B／透辉石（ABD）。AD陶瓷导轨材料的最佳力学性能参数为：硬度15.57 GPa、抗弯强度417 MPa、断裂韧性5.2 MPa·m^1／2。ABD陶瓷导轨材料的最佳力学性能参数为：硬度16.02 GPa、抗弯强度370 MPa、断裂韧性5.11 MPa·m^1／2。试验研究了添加相含量对AD和ABD陶瓷导轨材料力学性能的影响，AD陶瓷导轨材料中透辉石的最佳含量为3 vol．％；ABD陶瓷导轨材料中透辉石和Al-Ti-B中间合金的最佳含量分别为6 vol．％和4 vol．％。探讨了烧结温度和保温时间对AD和ABD陶瓷导轨材料力学性能的影响，得出了AD和ABD陶瓷导轨材料的最佳烧结工艺参数：即烧结温度为1520℃、保温时间分别为140 min和180min。对无压烧结Al₂O₃基结构陶瓷导轨材料的微观结构及其增韧机理进行了研究，探讨了烧结工艺及透辉石含量对AD和ABD陶瓷导轨材料微观结构的影响，研究结果表明，烧结温度对Al₂O₃基结构陶瓷导轨材料微观结构的影响较明显，主要表现为其断口晶粒出现异常长大；随着烧结温度提高，陶瓷导轨材料的晶粒生长驱动力增加，其断口平均晶粒尺寸增大。延长保温时间，Al₂O₃基结构陶瓷导轨材料晶粒尺寸基本不变，但其断裂模式发生变化。纯Al₂O₃陶瓷材料晶粒形状规则，基本呈现圆形，晶粒发育不完善，晶粒间存在较多的空隙或孔洞，晶界结合强度较弱，其断口断裂模式以沿晶断裂为主。AD和ABD陶瓷导轨材料的微观组织均匀细化，结构致密，晶粒为不规则的角状，断口出现韧窝，呈现明显的韧性断裂方式，空隙或孔洞基本已经消除。透辉石和Al-Ti-B中间合金的加入改变了Al₂O₃基结构陶瓷导轨材料的断裂模式，在其烧结过程提供液相，液相通过流动填补基体空隙或孔洞，降低了陶瓷导轨材料的孔隙率；同时，添加相与Al₂O₃基体之间界面反应的发生使其晶粒之间的结合力加强；AD陶瓷导轨材料增韧机制为晶粒细化强化以及裂纹偏转、弯曲和分支，ABD陶瓷导轨材料增韧机制主要包括晶粒细化效应、分散相小颗粒对裂纹的钉扎、裂纹弯曲和扭转以及微裂纹增韧和裂纹分岔。分析并讨论了透辉石和Al-Ti-B中间合金对Al₂O₃基结构陶瓷导轨材料的晶粒细化机理。透辉石中的MgO在烧结过程中与Al₂O₃发生界面反应生成镁铝尖晶石薄层，包裹在Al₂O₃粒子表面，使Al₂O₃晶粒之间的质点扩散受到抑制，从而抑制晶界移动，达到晶粒细化的效果。过多的尖晶石相易使Al₂O₃晶粒异常长大，并造成陶瓷导轨材料坯体气孔率高。本文中透辉石添加量小于6 vol．％时能够形成适量镁铝尖晶石，并有效抑制Al₂O₃晶粒的发育生长。Al-Ti-B中间合金的晶粒细化作用主要来自于其对金属Al优良的晶粒细化特性，微小的Al颗粒在氮化之前有充分的时间聚集在Al₂O₃颗粒周围，抑制Al₂O₃晶粒发育生长。同时AlN、TiN相是在制备过程中原位生成的，而且粒度小至纳米级，分布在Al₂O₃晶粒周围，抑制其发育生长。提出了Al₂O₃基大型结构陶瓷导轨材料液相—反应烧结致密化物理模型。通过绘制1gΔL／L₀～1gt图，用最小二乘法计算了Al₂O₃基大型结构陶瓷导轨材料的表观激活能，并判断其液相烧结机理为扩散机制控制。根据烧结温度和保温时间对陶瓷导轨材料线收缩率的影响，建立了Al₂O₃基大型结构陶瓷导轨材料的烧结动力学方程；纯Al₂O₃陶瓷材料的烧结特征指数n约为2.5，其烧结过程中的物质迁移机制由体扩散控制；AD和ABD陶瓷导轨材料的烧结特征指数n值介于2.5与3.0之间，其烧结过程中的物质迁移机制既有体扩散，也有晶界扩散。采用温度梯度无压烧结工艺试制了规格为900 mm×70 mm×70 mm的Al₂O₃基大型结构陶瓷导轨。对Al₂O₃基大型结构陶瓷导轨材料摩擦磨损特性进行理论预测，建立了基于拉伸应力的摩擦磨损模型；对无压烧结制备的Al₂O₃基大型结构陶瓷导轨材料的摩擦磨损性能进行了试验研究，并对其磨损表面微观形貌进行了观察和分析，探讨了Al₂O₃基大型结构陶瓷导轨材料的磨损机理。研究结果表明，透辉石和Al-Ti-B中间合金的加入有利于改善复合陶瓷导轨材料的摩擦特性和耐磨损性能；干摩擦条件下，AD和ABD陶瓷导轨材料的摩擦系数均随着载荷和转速的增加而降低；AD和ABD陶瓷导轨材料的摩擦系数低于纯Al₂O₃陶瓷；油润滑条件下，纯Al₂O₃陶瓷的摩擦系数为0.02～0.07，AD和ABD陶瓷导轨材料的摩擦系数为0.01～0.05，能够获得塑料导轨材料在油润滑条件下的摩擦系数。纯Al₂O₃陶瓷磨损率的数量级为10^-15 m³／N·m，AD和ABD陶瓷导轨材料磨损率的数量级为10^-16 m³／N·m；纯Al₂O₃陶瓷的磨损机理为脆性断裂和晶粒剥落，AD和ABD陶瓷导轨材料的磨损机理为机械冷焊、塑性变形、微断裂和晶粒剥落。更多还原

【Abstract】 As a vitally important innovation in this dissertation, diopside and Al-Ti-B master alloys are introduced in pressureless sintered alumina matrix ceramic materials to improve their performances. The author develops two series of new composites, which are Al₂O₃/diopside （AD） and Al₂O₃/Al-Ti-B/diopside （ABD）, respectively, by using the technology of vacuum slip casting, isostatic cool pressing, liquid sintering, reactive sintering, and temperature gradient pressureless sintering in turn. The mechanical properties, microstructures and wear behaviors of the new fabricated composites are discussed and analyzed. The toughening mechanisms and wear mechanisms are researched as well as the grain refining performance of diopside and Al-Ti-B master alloys towards alumina matrix ceramic materials. Sintering kinetics models of large-scale advanced alumina matrix structural ceramic guideway materials are presented.The design objectives of large-scale advanced alumina matrix structural ceramic guideway materials and selecting principles for additives are proposed. Diopside and Al-Ti-B master alloys are chosen as additives. Gibbs free energy of the reactions taken place between additives and alumina are calculated in order to analyze the chemical compatibility of large-scale advanced alumina matrix structural ceramic guideway materials. The compositions of the new fabricated composites are analyzed by using the technology of X-ray diffraction analysis. The maximum volume content of additives are predicted as well as the sintering temperature and holding time of large-scale advanced alumina matrix structural ceramic guideway materials.Vacuum slip casting and isostatic cool pressing are used to shape the guideway green bodies The technology of liquid sintering, reactive sintering, and temperature gradient pressureless sintering are used to fabricate large-scale advanced alumina matrix structural ceramic guideway materials. The sintering processing parameters to prepare large-scale advanced alumina matrix structural ceramic guideway products are optimized. The experimental results, obtained by testing mechanical properties of typical specimens, indicate that by using sintering processing parameters of 1520°C and 140min, composite with introduction of 3 vol.% diopside shows better comprehensive performances, the hardness, bending strength and fracture toughness of the composite reach 15.57 GPa, 417 MPa and 5.2 MPa·m^1/2, respectively. At the sinter temperature of 1520℃and with the holding time of 140min, composite with addition of 4 vol.% Al-Ti-B master alloys and 6 vol.% diopside shows better comprehensive performances, the hardness, bending strength and fracture toughness of which reach 16.02 GPa, 370 MPa and 5.11 MPa·m^1/2, respectively.Microstructures and toughening mechanisms of pressureless sintered large-scale advanced alumina matrix structural ceramic guideway materials are studied by using scanning electron microscopy （SEM） technology. The influences of sintering processing parameters and diopside content on microstructures of AD and ABD composites are discussed and analyzed. It can be discovered from the investigation that, the grain size of large-scale advanced alumina matrix structural ceramic guideway materials increases with increasing the sintering temperature. The grain size, however, retains unchanged when given an extended holding time and the fracture mode changes with increasing the holding time. The grain shapes of pure alumina are regular and almost circular. There appear interspaces or cavities among the grains owing to incomplete developing of alumina grains. The grain boundaries of pure alumina are observable and the fracture mode is mainly intergranular failure, most likely resulting from the interfacial weakness. There are significant microstructural differences among ceramic guideway materials and pure alumina. Evidently, AD and ABD composites show a finer and more homogeneous distribution of alumina grains and additive particles compared with pure alumina, which indicates the introduction of diopside and Al-Ti-B master alloys may restrain the growth of alumina grains. The grain shapes of ceramic guideway materials are irregular and almost like an anvil horn. Interspaces or cavities almost are almost eliminated. The introduction of diopside and Al-Ti-B master alloys changes the fracture mode of large-scale advanced alumina matrix structural ceramic guideway materials, provides liquid phases in the sintering process, decreases air holes or interspaces in bodies, increases the binding energy of grain boundaries in virtue of interface reactions with alumina. The toughening mechanisms of AD composites are grain-refining effect, crack deflection, crack inflection and crack branch. The toughening mechanisms of ABD composites are grain-refining effect, pin of finely particles to cracks, deflection and torsion of cracks, microcrack toughening and divarication of cracks.The refining performances of diopside and Al-Ti-B master alloys are discussed and analyzed. MgO will react with alumina and produce MgO·Al₂O₃, which will enwrap alumina grains and restrain alumina grain boundaries form moving. Small amount of MgO·Al₂O₃ （less than 6 vol.%） can be beneficial to refine alumina grains effectively, while superfluous MgO·Al₂O₃ will bring on the abnormal grain growth of alumina and increased degree of porosity. The grain refining performance of Al-Ti-B master alloys maybe mainly attribute to its good grain refining performance towards Al. Before being nitrided, small grain size of Al may surround alumina grains and prevent them form growing with increasing the sintering temperature. At the end of the sintering process, Al is almost entirely transformed into A1N. A1N and TiN, which is produced by in situ synthesis and has a grains size of nanometer, distribute evenly over advanced alumina matrix structural ceramic guideway materials and contribute to the refining effect.Physical model about liquid sintering and reactive sintering of large-scale advanced alumina matrix structural ceramic guideway materials are proposed. The sintering densification behaviors are investigated. The apparent activated energy of large-scale advanced alumina matrix structural ceramic guideway materials is calculated by using the method of least squares. Results show that the densification of large-scale advanced alumina matrix structural ceramic guideway materials may be controlled by diffusion of ion in liquid phase. The sintering kinetic equations are deduced according to the influences of sintering temperature and holding time on linear shrinkage rate of the new fabricated composites. The sintering mechanisms are analyzed by comparing the characteristic exponent n. It is indicated that the main sintering mechanism of pure alumina may be volume diffusion （n=2.5）, and that of AD and ABD composites may be volume diffusion and grain boundary diffusion （2.5<n<3.0）. Ceramic guideway products with dimensions of 900 mm×70 mm×70 mm are fabricated by temperature gradient pressureless sintering technology.According to the tensile crack model, a simple model for tribological behaviors of large-scale advanced alumina matrix structural ceramic guideway materials, predicting the relationship between load and wear rate, is presented. The wear mechanisms of pressureless sintered large-scale advanced alumina matrix structural ceramic guideway materials are discussed by analyzing SEM micrographs of wear tracks on typical specimens. It is indicated that the introduction of diopside and Al-Ti-B master alloys in alumina matrix ceramic guideway materials improves their friction and wear properties. There shows a general decrease in friction coefficient of AD and ABD composites with increasing the normal load or rotation speed in unlubricated conditions and at room temperature. The friction coefficient of AD and ABD composites is lower than that pure alumina. The friction coefficient of pure alumina is in the range of 0.02～0.07, and that of large-scale advanced alumina matrix structural ceramic guideway materials, toughened by diopside and Al-Ti-B master alloys, is in the range of 0.01～0.05 in oil-lubricated conditions. The wear rate of pure alumina is in the order of 10^-15m³/N·m while that of alumina matrix ceramic composites toughened by Al-Ti-B master alloys and diopside （AD and ABD composites） is in the order of 10^-16m³/N·m. Abrasive wear may occur during dry sliding tests of pure alumina, and the wear mechanisms of which may be brittle fracture and grain pull-out. The dominant wear mechanisms of pressureless sintered large-scale advanced alumina matrix structural ceramic guideway materials may be mechanical interlocking and plastic deformation combined with a little micro-fracture and grain pull-out.更多还原