【作者】 周畅；

【导师】 武高辉；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2017， 博士

【摘要】 本文研究一种新型零膨胀材料——负膨胀颗粒增强Al基复合材料。本文利用挤压铸造方法设计并成功制备了颗粒分散均匀,高致密度的50～73vol.%ZrW₂O₈/Al-Si复合材料。利用扫描电镜（SEM）、透射电镜（TEM）、热膨胀分析仪、原位拉曼（In-situ Raman）、第一性原理模拟和三点弯曲试验等多种手段,对复合材料的微观组织及形成机理进行了系统的研究,测试了复合材料的热膨胀性能、力学性能及热循环性能,分析了相关的影响因素。并基于界面反应公式,建立了一种ZrW₂O₈/Al-Si复合材料热膨胀系数预测的方法。本文以超低膨胀（零膨胀）为目标,进行材料设计。根据Kerner模型,Turner模型和混合定律、界面反应程度、超低膨胀用ZrW₂O₈/Al-Si复合材料的增强体体积分数应在73vol.%;基于Grüneisen参数,以拉曼峰偏移为变量,得到了变温条件下复合材料内部残余应力计算方程。残余应力的计算表明,铸造态复合材料体系中存在残余应力值为183～244MPa。残余应力引发的亚稳高压相γ-ZrW₂O₈,导致负热膨胀效应大大降低。采用高温拉曼、DSC、高温XRD、理论计算和原位TEM等多种表征手段确定了200℃为热处理温度,进而减少高压相γ-ZrW₂O₈的含量,实现对复合材料膨胀性能的调控。基于界面反应动力学原理,设计采用降低制备温度、缩短保温时间工艺,实现了复合材料的界面反应控制,获得了超低膨胀性能。本文中,73vol.%ZrW₂O₈/Al-Si复合材料的平均热膨胀系数（0℃～100℃）为0.79×10^-6K^-1,符合零膨胀应用宽温区,超低膨胀的性能要求。研究了复合材料的组成和界面微观结构。SEM分析表明,铝基体连续分布在复合材料中。TEM分析表明,基体和负膨胀颗粒之间存在着一层纳米级别的界面区域。界面层与两相结合完整,界面反应随制备温度的升高而增加。低温制备条件下,纳米界面层的主要相结构为ZrW₂O₈。高温下界面层厚度增加到亚微米,并有脆性界面产物ZrO₂和WO₃生成。当制备温度从680℃升高到770℃,复合材料的力学性能由110MPa降低为80MPa。通过高分辨TEM和第一性原理从原子尺度复合材料解释了零膨胀复合材料纳米界面的形成机制,指出ZrW₂O₈晶格内的多面体间隙可以容纳基体中的铝原子,是一种自发的行为。冷热循环200次后73vol.%ZrW₂O₈/Al-Si复合材料弯曲强度,密度和弹性模量保持一致,服役性能优异。显微组织观察还表明,Al元素扩散至界面内部并呈现出单调下降的趋势。氧元素扩散至Al基体内部,并形成了少量Al,O化合物。证明ZrW₂O₈/Al界面的反应是一种扩散行为,并计算了相应的扩散速率和扩散能。基于扩散公式,引入反应程度建立了温度与时间等参数与界面反应的理论计算模型。分析了反应程度,界面层厚度,宏观热膨胀性能之间的关系。更多还原

【Abstract】 In this paper,inertial navigation for the application of background,to study a new type of zero expansion material-negative thermal expansion particles reinforced Al matrix composites.Fully dense 50～73vol.%ZrW₂O₈/Al-Si composites were designed and successfully fabricated by squeeze-casting method.The scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,thermal expansion tester,thermal conductivity tester,In-situ Raman,computer simulation and three-point bending tests were used to systematically study microstructure and mechanism of the composites.The thermophysical properties,mechanical properties and thermal cycling properties of the composites were tested,and the relevant influencing factors were analyzed.Based on the interfacial reaction formula,a method for predicting the thermal expansion coefficient of ZrW₂O₈/Al-Si composites were established here.In this paper,the goal is to design the ultra-low thermal expansion（zero thermal expansion） materials.According to the Kerner model,the Turner model and the Rule of mixed,the volume fraction of the reinforcement of the ultra-low expansion ZrW₂O₈/Al-Si composite material should be 73 vol.%.Based on the Grüneisen parameter and the Raman peak shifts,the calculated equation of the residual stress as function of temperature is obtained.The XRD and density results show that there is a large amount of metastable high-pressure phase,γ-ZrW₂O₈ in the cast composite system,reducing the negative thermal expansion effect.The high temperature Raman,DSC,high temperature XRD,theoretical calculation,in situ TEM methods were used to determine the 200℃ as the appropriate heat treatment temperature,thereby eliminate the high-pressure phaseγ-ZrW₂O₈ content,to achieve the low thermal expansion behavior.Based on the principle of interfacial reaction kinetics,the design of the interface is controlled by reducing the preparation temperature and shortening the holding time,and the ultra-low expansion performance is obtained.In this paper,the average coefficient of thermal expansion（0℃～100℃） of 73vol.%ZrW₂O₈/Al-Si composites are 0.79×10^-6K^-1,which is consistent with the application of zero expansion.The composition and interface microstructure of the composites were also studied.SEM analysis showed that the aluminum matrix was continuously distributed in the composites.TEM analysis showed that a layer of nanoscale interface was formed between the matrix and the negative expansion particles.The interface layer is combined well with the two phases.With the increase of preparation time,the interface layer thicken.Under the condition of low temperature preparation,the main phase structure of nano-interface layer is ZrW₂O₈.The thickness of the interfacial layer is increased to submicron at high temperature and the brittle interface products ZrO₂ and WO₃ are formed.The mechanical properties of the composites were reduced from 110 MPa to 80 MPa when the fabricated temperature changed from 680℃ to 770℃.The formation mechanism of the nanostructures of zero-expansion composites is explained from the atomic-scale structure by high-resolution TEM and First-principles Calculations.It is pointed out that the polyhedral gap in the ZrW₂O₈ lattice can hold the aluminum atoms in the matrix,which is proved to be a spontaneous behavior.The interstitial solid solutions eventually transform into a high-intensity,stable nano-interface.The bending strength,density and elastic modulus of 73vol.%ZrW₂O₈/Al-Si composites were consistent after 200 cycles of hot and cold cycles,and the service performance was excellent.Microstructure observation also showed that Al elements diffused into the interface and showed a monotonically decreasing trend.Oxygen elements diffuse into the Al matrix and form a small amount of Al,O compounds.It is proved that the reaction of ZrW₂O₈/Al interface is a diffusion behavior and the corresponding diffusion rate and diffusion energy are calculated.Based on the diffusion formul a,the theoretical calculation model of temperature and time parameters and interface reaction was established.The relationship between the extention of reaction,the thickness of interfacial layer and the macroscopic thermal expansion was analyzed.更多还原