碳纳米管增强Nb/Nb5Si3复合材料的制备及强韧化机制研究

Nb/Nb5Si3 in situ composite has high melting point, high stiffness, low density and excellent specific mechanical properties at high temperature. However, low fracture toughness at room temperature and poor deformability even at elevated temperature hinder their applications like many other intermetallic compounds. Carbon nanotubes have a very high theory strength, It was reported that the addition of carbon nanotubes could greatly improve the mechanical behaviors of metal-based composites. It is discovered in study at present that the addition of CNTs could improve the strength and fracture toughness of Nb/Nb5Si3 in situ composite. .Therefore, the Nb/Nb5Si3 in situ composites will be fabricated by SPS in this project. The relationships between preparation, properties, microstructure and fracture characteristics of CNTs reinforced Nb/Nb5Si3 in situ composites are studied. The interface bonding behavior and characteristics between CNTs and matrix are investigated by analyzing the shape, size and the distribution of CNTs and interfacial structure.Toughening and reinforcing mechanism of CNTs on Nb/Nb5Si3 in situ composites are studied by analyzing fracture morphologies and crack propagation of the composites. The results made a base for thermo-structural material in aviation, aerospace and national defense industry.

Nb/Nb5Si3复合材料具有高熔点、高刚度、低密度和极高的高温强度等优点，同时其较差的室温韧性和冷加工能力阻碍了它作为高温结构材料的应用。碳纳米管（CNTs）具有超强的力学性能，可以极大改善复合材料的强度和韧性。在前期研究中发现掺杂CNTs对Nb/Nb5Si3复合材料的强度和断裂韧性都有一定的影响。因此，本项拟采用放电等离子烧结技术制备Nb/Nb5Si3复合材料，引入CNTs作为弥散相来提高Nb/Nb5Si3复合材料的强度和断裂韧性；研究CNTs增强Nb/Nb5Si3复合材料的制备、性能、显微结构以及断裂特征的相互关系；分析CNTs增强相的形态、尺寸、分布及不同相之间的界面结构，研究CNTs相与基体界面结合行为与特征；分析复合材料的断面形貌、压痕裂纹扩展情况，探讨CNTs对Nb/Nb5Si3复合材料增韧补强的作用效果与机制，为其在航空、航天和国防等领域高温结构材料中应用奠定基础。

本项目以Nb粉和Si粉原料，采用放电等离子烧结技术制备Nb/Nb5Si3 复合材料，引入CNTs 作为弥散相来提高Nb/Nb5Si3 复合材料的强度和断裂韧性。研究了CNTs的表面处理工艺、加入量和制备工艺对Nb/Nb5Si3复合材料的组织和性能的影响，探讨CNTs 对Nb/Nb5Si3 复合材料增韧补强的作用效果与机制，并建立SPS 原位合成制备Nb/Nb5Si3复合材料过程中电场、温度场和化学反应的数理模型，通过数值模拟优化了其SPS原位合成工艺。CNTs的引入可以有效的提高Nb/Nb5Si3复合材料的室温强度和韧性，但对其相组成影响不大，只是在其结合界面处会发生一定的反应生成Nb4C3相。通过对CNTs进行表面处理可以有效改善CNTs的分散性和界面结合性能，CNTs在Nb/Nb5Si3 复合材料中分布更均匀，性能也更好。其中表面镀镍效果最好，当加入量为4wt.%时室温断裂韧性可以提高一倍，强化作用以桥联机制为主；表面非共价修饰效果次之，加入量为3wt.%时达到最大值，提高了约68%，强化作用以拔出机制为主；表面酸化处理效果最差，加入量为2wt.%时就达到最大值，提高了约31%，强化作用也是以拔出机制为主。