Microstructural evolution of hybrid aluminum matrix composites reinforced with SiC nanoparticles and graphene/graphite prepared by powder metallurgy

The dispersion of ceramic nanoparticles is of significance to the microstructure and properties of particulate reinforced metal matrix composites.In this study,two hybrid enhancers,SiC-graphite and SiC-graphene nanosheets(GNSs),were incorporated into aluminum matrix composites using powder metallurgy.The dispersion of the reinforcements and microstructural evolution of the composites were characterized by using Scanning Electron Microscopy,X-Ray Diffraction,Transmission Electron Microscopy,and Raman spectroscopy.The results show that thin GNSs accelerated the deformation of the aluminum particles,and defects were introduced into the carbonaceous phases during the ball milling process.Al_4 C_3 needles generated during hot pressing,and were observed to bridge the aluminum grains.Compared with graphite,GNSs were more uniformly dispersed throughout the composite,which in turn restrained grain growth.As a result,a nanostructured composite(57.7 nm) was successfully produced upon the addition of SiC-GNSs.     

机械合金化改善反应合成Ti3SiC2的条件

为改善Ti3SiC2的合成条件，利用机械合金化的方法处理原料粉末，并与通常采用的原始粉末直接混合粉末进行比较分析。结果表明，机械合金化有助于合成Ti3SiC2。根据DTA曲线确定合理的烧结工艺，对合成产物进行的XRD、断口的SEM以及EDAX分析，进一步证实了机械合金化粉末可以在较低的温度下(温度降低25℃)、较短的时间(时间缩短20％)内通过反应合成得到Ti3SiC2。     

多热源合成SiC热源数目判定模型

多热源合成SiC冶炼炉炉体尺寸大,一次性生产原材料消耗大,用实验手段难以预测给定条件下的热源数目等参数。通过对冶炼炉温度场的数学分析及数值模拟,以合成SiC温区断面面积比率最大为原则,提出了多热源合成SiC热源数目的判定模型,给出了实例,并通过工业实例对模型进行了验证。热源数目的预测,可以为SiC工业生产提供理论指导。     

合成SiC晶须的热力学及生长机理的研究

对稻壳合成 Si C晶须 (简称 Si CW)及 Si C颗粒 (简称 Si Cp)进行热力学分析 ,确定了基元反应。在稻壳合成 Si CW的反应中 ,Si Cp的生成是不可避免的     

Preparation and properties of multi-wall carbon nanotube/SiC composites by aqueous tape casting

MWCNTS/SiC composites were fabricated by aqueous tape casting.High solid content(50 vol%) SiC slurries with sintering additives and multi-wall carbon nanotubes(MWCNTs) as reinforcements were prepared using Tetramethylammonium hydroxide as the dispersant.The stability of MWCNTs/SiC slurries was studied and characterized in terms of zeta potential and rheology measurements.The relative density of the composite was about 98%after hot-pressing at 1850°C(at 25 MPa in Ar for 30 min) .The hardness of the composites decreased with the increase in MWCNTs content.The flexural strength and the fracture toughness were 742.17 MPa and 4.63 MPa·m 1/2,respectively when the MWCNTs content was 0.25 wt%.Further increase in MWCNTs content to 0.50 wt%did not lead to the increase in mechanical properties.Most of MWCNTs were found to be located at SiC grain boundaries and the pull out of the MWCNTs was observed.     

二氧化硅微粉对炭素捣打料显微结构及性能的影响

以冶金焦粉为主要原料,改性中温沥青粉为结合剂,添加二氧化硅微粉混合成型,于220℃下干燥、1 550℃下埋炭烧成炭素捣打料.测定烧成样的耐压强度、体积密度和导热系数,采用XRD和SEM分析试样物相及显微结构.结果表明,添加了二氧化硅微粉的试样经1 550℃热处理,可原位反应生成碳化硅晶须,二氧化硅微粉初期添加量越大,所生成的碳化硅晶须越多,试样的体积密度、耐压强度和导热系数越高；当二氧化硅微粉添加量为8.5％时,试样的碳化硅晶须生成量减少,导热系数降低.     

镁合金表面氩弧熔覆Al-Si基SiC复合涂层组织及耐磨性

采用氩弧熔覆方法作为镁合金材料表面强化,是一项全新技术,在AZ31B镁合金基体表面制备10%Si C粉末+Al-Si合金粉末的复合涂层,利用X射线衍射仪、光学显微镜和扫描电子显微镜分析涂层的物相组成和显微组织;利用显微维氏硬度计和干滑动摩擦磨损实验机测试复合涂层在室温下的显微硬度和摩擦磨损性能。结果表明:氩弧熔覆涂层与基体界面具有良好的结合,无气孔、夹杂、裂纹等缺陷;熔覆层主要由Mg2Si、Mg2C3、Mg17Al12、Al3.21Si0.47等物相组成;熔覆层内部主要由黑色块状组织组成,尺寸为2~5μm;由于在氩弧熔覆过程中生成了新的物相使得涂层的显微硬度提高,涂层平均硬度可达2.5 GPa,是AZ31镁合金基体的4倍;基体的平均摩擦系数约为0.7,10%Si C氩弧熔覆层摩擦系数约为0.57,摩擦系数明显降低;熔覆涂层的相对耐磨性较基体提高近5倍。     

调制场法测量纳微颗粒荷电量和粒径

纳微颗粒前驱物的荷电性和粒径将直接影响生成物的形貌和物理性质,尽管现代实验技术可以对它们进行准确测量,但样品处理过程可能已破坏了前驱物的真实性质.通过密立根油滴实验技术改造,提出了调制电场纳微颗粒荷电量和粒径测量技术.从理论上采用迭代方法推导出纳微颗粒带电量和粒径的实验定量分析公式.通过不用粒径量级分析,进一步证明了调制电场技术方法的合理性和可行性.     

SiC_p－Si_3N_4基复合材料及其力学性能

研究了ＳｉＣ片晶（ＳｉＣｐ）强化Ｓｉ３Ｎ４基复合材料及其力学性能和增韧机理。研究结果表明，加入ＳｉＣｐ使Ｓｉ３Ｎ４材料的强度明显提高，并在ＳｉＣｐ含量（ＳｉＣｐ）＝０．２０（ＳｉＣｐ的体积分数）时有一峰值，ＳｉＣｐ加入量进一步增加使强度有较大降低。ＳＥＭ观察表明，裂纹偏转、片晶桥接是主要增韧机理，片晶拔出、基体细化等亦对断裂韧性的增加作出贡献，其作用与晶须增韧的机理相似。     

高温气冷堆包覆燃料颗粒的化学气相沉积

我国正在建造１０ＭＷ高温气冷堆，包覆燃料颗粒的研制是高温气冷堆的关键技术之一。ＴＲＩＳＯ型包覆燃料颗粒是由燃料核芯、疏松热解碳层、内致密热解碳层、碳化硅层和外致密热解碳层组成。采用化学气相沉积方法，选用乙炔、丙烯、甲基三氯硅烷和氢气作为反应气体，在直径为５５ｍｍ锥形流化床包覆炉中制备包覆燃料颗粒。本文系统地研究了工艺参数和性能之间的关系，摸索出疏松热解碳层、致密热解碳层和碳化硅层的最佳包覆工艺条件，总结出经验公式，用扫描电镜观察了包覆燃料颗粒的微观结构，制备出满足设计要求的ＴＲＩＳＯ型包覆燃料颗粒。