直接在粉末表面生长站立石墨烯用于制备石墨烯增强复合材料的研究

Since its discovery, graphene has attracted great attention due to its unique combination of mechanical, thermal and electrical properties. Thus, recently much work has exploited graphene as reinforcement to improve the mechanical property of a variety of host materials such as metals and ceramics. Homogeneous distribution of graphene in the metal or ceramic matrix is a key factor to get the best performance of the composites. To realize this, in the most of literatures, mixture procedures were usually carried out after separately preparing the matrix powder and graphene. The most commonly used mixture methods are ball-milling and liquid-state processing. However, both of the methods always create lots of defects in graphene and can’t well control the lateral size of the graphene sheets, which will give rise to serious degradation of the composites’ mechanical properties. Here we propose a new mixture method to overcome these drawbacks by in-situ deposition of graphene on metal or ceramic powder using plasma enhanced chemical vapor deposition (PECVD) technique. Firstly, the dependences of the lateral size and thickness of the graphene sheets on the deposition parameters will be investigated by scanning electron microscope (SEM), high resolution transmission electron microscope (HRTEM), and Raman spectroscopy. Secondly, the optimal mass fraction of graphene addition at which the strength, hardness and toughness of the composite get their respective best performance will be extensively studied. Finally, the strengthening and toughness mechanism will be discussed. This work is helpful for us to look insight into the reinforcing mechanism of graphene, and to further improve the performance of the composites.

石墨烯具有优异的力学特性，作为增强剂添加到陶瓷、金属等基体材料中，可大幅提高材料性能，在航空、电子、机械等领域有潜在的应用价值。石墨烯能否在基体材料中均匀分散是决定复合材料性能的关键因素。目前的方法是先独立制备基体材料粉末和石墨烯，再通过球磨法和液相法将两者混合均匀；然而这些方法都伴随着石墨烯产生大量缺陷、易团聚和尺寸不均一等弊端，进而降低复合材料的性能。本项目提出利用等离子增强化学气相沉积技术直接在陶瓷、金属粉末表面生长站立石墨烯这种新方法来克服上述方法的缺点，通过调控反应参数实现石墨烯的可控制备。利用扫描、透射电子显微镜及拉曼光谱等手段研究生长参数对站立石墨烯尺寸、层数和缺陷的影响；研究石墨烯的添加量对材料的抗拉强度、维氏硬度和断裂韧性等力学性能的影响；分析得到石墨烯增强增韧效应的物理机制。这一工作对于制备性能更加优异的石墨烯增强增韧陶瓷、金属复合材料具有重要的参考价值。

增材制造技术在《中国制造2025》规划中占据显要位置，处于上游的复合粉末的制备，极有可能成为下一代先进制造技术的制高点。复合粉末通过向基体粉末中添加强化相纳米材料来制备，两者均匀混合至关重要。传统的机械球磨法和液相混合法存在诸多弊端：机械球磨过程会将基体粉末碾压成扁平状，低球形度的复合粉末难以用于打印；液相混合法中大量使用的硝酸、高分子聚合物等试剂，难以洗净，成为杂质。.针对于此，本课题提出利用等离子增强气相沉积方法，在基体粉末表面原位生长增强相纳米材料，微观尺度实现两者的均匀混合。研究选择石墨烯作为增强相，开展的主要工作有：（1）实现了石墨烯在铜、铝、镍基高温合金等金属粉末表面和氧化铝、碳化硅等陶瓷粉末表面的原位生长，扫描电镜结果显示，石墨烯均匀包覆在基体粉末外表面，实现了两者的均匀混合，并且粉末球形度得到了完好保护；（2）综合利用X射线光电子能谱、扫描电镜等手段研究了石墨烯的初期生长过程。结果表明，其生长可分为面内成核和站立生长两个阶段，首先，纳米片沿平行于粉末表面方向生长，形成岛状结构；随着尺寸和层数不断增加，岛边缘卷曲，随即沿粉末表面的法向方向生长。进一步利用生长/刻蚀与温度的关系，通过调节生长温度，实现了石墨烯纳米片尺寸的均一、可控制备；700 ℃、600 ℃和500 ℃温度时，纳米片的尺寸分别为50 nm、150 nm和350 nm；（3）将石墨烯/高温合金粉末、石墨烯/氧化铝粉末利用放电等离子烧结成块体，实验结果表明，石墨烯的添加可显著提高材料的力学、电学等性能。高温合金拉伸测试结果显示，添加石墨烯试样的抗拉强度和屈服强度分别提高了9.5%和12.3%，同时，延伸率也由9%提高至13%；陶瓷电导率测试结果显示，未添加时石墨烯陶瓷样品为绝缘体，添加后，其电导率提高至0.724 S/m。

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