【作者】 王非；

【导师】 张凯锋；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2008， 博士

【摘要】 许多复相陶瓷均被发现具有不同程度的超塑性,利用纳米复相陶瓷的超塑性进行加工成形是实现复杂形状陶瓷零件近净成形的重要手段。Al₂O₃-ZrO₂系陶瓷材料是陶瓷复合材料的研究重点之一。这类材料具有良好的室温和高温力学性能,其在耐磨、耐高温等部件上应用广泛。本文采用真空热压烧结制备了20mol%ZrO₂（3Y）含量的3Y-TZP/Al₂O₃纳米复相陶瓷,随后进行了复相陶瓷的超塑挤压成形和压缩变形,测量、评价了超塑成形过程中的摩擦和润滑,分析了复相陶瓷的成形性能以及变形前后的力学性能和显微组织,研究了复相陶瓷的超塑变形机理。采用真空热压烧结法在1400℃、1450℃、1500℃、1550℃四个温度下制备了3Y-TZP/Al₂O₃纳米复相陶瓷。ZrO₂的添加,显著改善了材料的烧结性能,抑制Al₂O₃的晶粒生长,形成典型的晶界/晶内混合型结构。在1450℃以上烧结时,复相陶瓷的致密度可达到98%以上,但随着温度的升高,晶粒尺寸显著增加。复相陶瓷弯曲强度、断裂韧性、维氏硬度和弹性模量的最高值分别达到591MPa、7.9MPa·m1/2、18.1GPa和442.5GPa。为了评估陶瓷在高温成形过程中的摩擦特性,寻找合适的润滑剂,试验采用圆环压缩法研究了六方BN有机溶液润滑剂在1400～1600℃温度范围内,1.1×10^-4 s^-1、5.4×10^-4 s^-1和2.5×10^-3 s^-1应变速率下的摩擦润滑行为。使用BN润滑剂的摩擦因子值比较稳定,分析了其随温度和应变速率的变化情况。通过圆环压缩法还评价了复相陶瓷的流动情况,测算了真实流动应力。在1500℃、1550℃、1600℃和1650℃四个温度分别对复相陶瓷块料进行涡轮盘模拟件的超塑挤压。复相陶瓷在1600℃具有最佳的挤压性能,最大单位挤压力小于25MPa,最大压头速率达到0.14mm·min-1。由于材料本身优良的性能和BN润滑剂的有效作用,挤压过程中材料流动平稳,应变硬化较小;成形件质量良好,无明显缺陷。通过SEM和TEM分析了变形材料的显微组织和变形机理,对比测试了试样成形前后的力学性能。在1500℃对复相陶瓷坯料进行恒压25MPa超塑压缩变形。通过XRD谱、晶向指数和峰强比分析对比了变形前后ZrO₂和Al₂O₃各晶面随变形量的取向变化,结果表明变形材料织构化明显,而Al₂O₃的实测和计算ODF{110}、{113}和{300} X射线极图更加清晰地显示了织构的强度。通过SEM分析了复相陶瓷变形后在平行于压缩轴截面和垂直于压缩轴截面上晶粒尺寸、纵横比、晶粒形状因子等表面形貌和断口形貌的变化,TEM观察了变形材料的显微组织变化,进而分析复相陶瓷的主要变形机理、变形织构产生和发展的原因。测试了变形材料的力学性能,发现弯曲强度、断裂韧性和维氏硬度值随应变量的增大呈先增大后减小的趋势,研究了应变量、晶粒大小、空洞和织构化对材料力学性能的影响。更多还原

【Abstract】 Superplasticity is observed in many composite ceramics. It is an important way that superplasticity of nanocomposite ceramic at elevated temperatures is utilized to achieve near-net shape forming of ceramic components with complex shape. Al₂O₃-ZrO₂ ceramics are important ceramic composites, which own excellent mechanical properties from ambient to elevated temperature and can be widely used to fabricate many parts of resistance to wear, to high temperature, et al. In the present research 3Y-TZP/Al₂O₃ nanocomposite ceramic with 20mol% ZrO₂（3Y） content was prepared. Subsequently, the superplastic extrusion forming and compressive deformation were carried out. Moreover, the friction and lubrication during superplastic forming were evaluated and measured. The forming properties of composite ceramic, mechanical characters and microstructure before and after deformation were presented. The superplastic deformation mechanism of composite ceramic was studied.The 3Y-TZP/Al₂O₃ nanocomposite ceramics were prepared by hot pressed sintering at 1400℃, 1450℃, 1500℃and 1550℃. The addition of ZrO₂ particles was very effective in improving the sintering character of materials and hindering the grain growth of Al₂O₃. The typical inter/intra granular mixed structure was achieved. The relative density of composite ceramic was more than 98% at above 1450℃, while he grain size increased with the increasing temperature. The maximum of bending strength, fracture toughness and Vickers hardness of composites were up to 591MPa, 7.9MPa·m1/2, 18.1GPa and 442.5GPa.The ring compression test was adopted to evaluate the friction and lubrication behavior of the hexagonal BN lubricant at the temperature range of 1400～1600℃and the strain rate of 1.1×10^-4 s^-1, 5.4×10^-4 s^-1 and 2.5×10^-3 s^-1, in order to measure the friction during the superplastic forming and seek for suitable lubricant. The friction factor on the BN lubricant was very stable, which viaration was analyzed with the increase of strain rate and temperature. The ring compression test was also used to evaluate the flow behavior of composite ceramic and measure the true flow stress.Superplastic extrusion on turbine disk model was attempted at temperature of at 1500℃, 1550℃, 1600℃and 1650℃. The material showed the best formability for extrusion at 1600℃, at which the maximum extrusion pressure was less than 25MPa and the maximum punch speed was up to 0.14mm·min-1. Due to the internal good forming property of composite ceramic and effective action of BN lubricant, the material showed good flow property during extrusion and no apparent strain hardening. Deformed samples owned good quality and there were almost no apparent flaws. Through the observation for the microstructure of SEM and TEM before and after deformation, the deformation mechanism was studied. The mechanical properties of deformed samples were measured, which were also compared with sintered samples.Superplastic compressive deformation was conducted at 1500℃and a constant pressure of 25MPa. According to the analysis of XRD pattern, orientation index and peak-intensity ratio, the orientation changes of crystal planes of ZrO₂ and Al₂O₃ with the increasing strain were observed and compared. The results showed that the texture in deformed material was strong. Moreover, the measured and caculated {110}, {113} and {300} X-ray pole figures of Al₂O₃ matrix can distinctly illustrate the indensity of texture. The changes of fracture surface and surface characters in cross section parallel and perpendicular to compressive axis for deformed material, such as grain size, aspect ratio, grain shape factor and et.al, were analyzed by SEM. The microstructural evolution during deformation was observed by TEM, through which the main deformation mechanism and the forming and development of high texture were sdudied. The mechanical properties such as bending strength, fracture toughness and Vickers hardness showed the increasing tendency and then decreasing tendency with the increase of strain. The effect of strain, grain size, cavity and texture on the mechanical properties was studied.更多还原