碳纳米管增强泡沫铝基复合材料的制备与性能调控机理

Al foams have received a considerable amount of attention in recent years because of their many advantages, such as low density, relatively high specific strength, and energy absorption properties. Due to the low density and the remarkable mechanical, thermal, and electrical properties, carbon nanotubes (CNTs) have been regarded as the ideal reinforcement for composite materials. However, up to now there are limited successful cases about the introduction of CNT resulting in significant improvement of the mechanical properties of the metallic matrix, due to CNTs' nature of being easy agglomeration. In this project, a novel route was developed to fabricate CNT-reinforced Al matrix composite foams by in-situ chemical vapor deposition, ball milling of a short time and a space-holder method, which resolves the bottleneck problems of difficulties in the uniform dispersion of CNTs in the matrix and the control of structural parameters of composite foams (diameter and morphology of pore, porosity). The aim of this study is to obtain CNT/Al composite foams with high specific strength, energy absorption and damping properties. So, the effect of the structural parameters of composite foams, the dispersion and content of CNT reinforcement, and the interface between CNTs and Al on the properties of compression,energy absorption and damping will be studied. Furthermore, the enhanced mechanism of CNTs and the property control rules of Al matrix composite foams will be explored. The research results will provide a theoretical basis for further developing the novel and high performance CNT/Al composite foams.

泡沫铝具有质轻、较高比强度、吸能减震等优点，作为一种结构与功能一体化的新型材料，得到人们的广泛关注。碳纳米管（CNTs）以其优异的力学、物理性能而被视为是复合材料理想的增强体，然而CNTs易于团聚的特性阻碍了CNTs增强泡沫铝基复合材料的制备和发展。本项目提出采用"原位合成-短时球磨-填加造孔剂法"制备CNTs增强泡沫铝基复合材料的新思路，可有效解决CNTs增强相在基体内分散不均、复合泡沫的结构参数（孔径、孔形状、孔隙率）难以控制等技术瓶颈，力图获得高比强度、高吸能、高阻尼的CNTs/Al泡沫复合材料。通过研究复合泡沫的结构参数，CNTs的微观结构、分布与含量，以及CNTs与泡沫铝基体界面结合对泡沫复合材料压缩、吸能和阻尼性能的影响，揭示CNTs的增强机理以及CNTs/Al泡沫复合材料的性能调控规律，为开发新型高性能泡沫铝基复合材料的研究奠定理论基础。

泡沫铝具有质轻、高比强度、阻尼减震、吸能隔热等优点，作为一种结构功能一体化的新型材料，已经越来越多地应用于航空航天、汽车等领域。颗粒或纤维增强相在泡沫铝基体中的加入，可以充分发挥泡沫铝和增强相的各自优势，获得材料综合性能的提高。本项目采用“原位合成—短时球磨—填加造孔剂法”制备了碳纳米管（CNTs）增强泡沫铝基复合材料，有效解决了CNTs在泡沫铝基体中分散不均的核心问题，系统研究了制备参数和增强相含量对材料性能的影响，得到如下结论：通过控制原位化学气相沉积法反应时间（≤60min），可以实现CNTs质量含量在0~3.5%范围内的精确控制。采用400rpm，90min的球磨工艺，可以实现CNTs均匀分散嵌入泡沫孔壁基体，在此过程中CNTs结构未明显损伤。冷压压强500MPa，烧结温度650℃，烧结时间3h是泡沫铝基体最佳致密化工艺。孔隙率显著影响了复合泡沫的性能，随着孔隙率降低复合泡沫压缩与吸能性能明显提高。在0.8~2 mm的范围内，孔径对于复合泡沫压缩性能影响很小。随CNTs含量的增加，复合泡沫铝的压缩和吸能性能均不断提高；当CNTs含量为3.0%时，复合泡沫铝的屈服强度为18.1 MPa，吸能量为15.8 MJ/M3，分别为纯泡沫铝的2.3和4.6倍。然而，当CNTs含量高于3.0%时，复合泡沫铝压缩和吸能性能有所下降。此外，随着CNTs含量的增加，复合泡沫的阻尼性能显著增强，3.0%-CNTs/Al复合泡沫的阻尼值在400℃时达到0.37，为泡沫铝的3.0倍。阻尼测试结果发现，随着测试频率的增加，复合泡沫铝的阻尼性能呈下降的趋势；而随着孔隙率和测试振幅的增加，复合泡沫铝的阻尼性能均显著增强。CNTs/Al复合泡沫的压缩和吸能性能增强主要源于CNTs自身优异力学性能以及其通过界面直接承载作用。位错阻尼机制，界面阻尼机制和CNTs高的本征阻尼，以及这几个因素间的相互耦合作用是CNTs/Al复合泡沫阻尼性能提高的原因。