基于晶粒破碎-焊合的碳纳米管增强铝基块体复合材料的制备及力学行为研究

The potential excellent properties of carbon nanotubes(CNTs) in aluminum matrix composites are far less than it should have contributed. The reason has been proposed to be that affected by factors such as the contamination on the surface of metallic particles and the aggregation of CNTs during the mixing process. Based on the principle that metal particles with clean surfaces can be welded when compressed at high temperature, CNTs reinforced aluminum bulk composites will be fabricated directly in the isolation state between the basic metal and ambienc by using a patented "Rotational Extrusion Alloying" composites fabrication technology. The CNTs/Al composites are fabricated undergoing the process of the breaking of bulk aluminum matrix, the mixing of metallic particles with CNTs, and the welding of metallic particles composited with CNTs in plastic deformation without other auxiliary processings. The microstructure evolution of aluminum matrix reinforced with different contents of CNTs under severe plastic deformation， the effect factors of composites density, the distribution of CNTs in aluminum matrix, the interface between CNTs and aluminum will be investigated experimentally by changing processing parameters in this project. The research will overcome the key problem of the homogenous dispersion of CNTs in aluminum matrix with high concentration and reveal the strengthening mechanism of CNTs reinforced aluminum composites, as well as the mechanical properties and strengthening mechanism of composites under the combined action of CNTs and the secondary precipitates. The study of fundamental problems will develop a new design and processing method of CNTs reinforced metal matrix composites which can sufficiently exploit the excellent properties of CNTs on the macroscopic levels.

碳纳米管在铝基复合材料中远未发挥其性能优势，被认为与粉体混合过程中粉体颗粒表面受污染和碳纳米管团聚等因素有关。项目依据具有"洁净"表面金属颗粒在高温下受压时可以焊合的原理，采用旋转摩擦挤压的方法，使块体金属在不与环境气氛接触的条件下"破碎-与碳纳米管混合-金属颗粒在固态下焊合"，直接形成碳纳米管增强铝基块体复合材料。项目采用实验研究方法，通过改变制备过程参数，研究大变形条件下含CNTs的铝基体组织演变、影响复合材料致密性的因素；碳纳米管在铝基复合材料中的分布、以及碳纳米管与铝基体间的界面状态，突破碳纳米管含量高时其在铝基体中分散的难题，揭示碳纳米管增强铝基复合材料的强化机理；同时，研究铝合金作为基体相时，碳纳米管与铝合金第二相强化共同作用时复合材料的性能与强化机理。最终获得能有效利用碳纳米管性能的金属基复合材料的设计与制备方法，在宏观尺度上充分发挥和利用碳纳米管的优异性能。

依据具有"洁净"表面金属颗粒在高温下受压时可以焊合的原理，采用旋转摩擦挤压（简称RFE）方法，开发了用固态加工方法制备块体复合材料的装备；通过改变过程参数，制备了多种基材(纯铝1060、AA7075、5A06、ZL114)、不同CNTs添加量的铝基复合材料，研究了大变形条件下，影响复合材料致密性的因素及复合材料基体组织演变，CNTs在复合材料中的分布、CNTs与铝基体间的界面状态；测试分析了CNTs与铝合金中第二相的分布特征及复合材料的性能，揭示了CNTs增强铝基复合材料的强化机理。. 结果表明，RFE加工可获得尺寸较大、成分较均匀、材料晶粒细小的块体CNTs增强铝基复合材料块体复合材料，可改善CNTs添加量增加时其在铝基体中分散的难题。CNTs的加入对CNTs/Al复合材料的织构具有弱化作用。RFE态复合材料晶粒中的大角度晶界数量呈先增加后减少的趋势；铝基材经RFE加工后织构强度较原始态有所减弱，加入CNTs后，复合材料的织构变弱，晶体取向呈随机分布；随着CNTs添加量的增加，复合材料的织构越来越弱，CNTs对复合材料的织构强度具有弱化作用。CNTs与Al基体之间发生了界面反应，生成了Al4C3相， Al4C3薄层对CNTs与Al基体的界面起到了一定的润湿作用，这种润湿作用有助于提高复合材料的耐磨性；CNTs的添加使铝基材的高温性能得到明显提高，随着CNTs添加量的增加，复合材料的高温强度逐渐提高但高温塑性降低，复合材料的疲劳性能逐渐提高且高于基材。350℃热轧温度、80%变形量及4道次轧制有利于CNTs/Al复合材料获得最优的力学性能和良好的表面成形；热轧诱使CNTs出现沿着轧制方向取向的趋势，使复合材料得到强化，RFE态复合材料进行合适工艺的热处理可以有效地提高其力学性能。CNTs的加入导致CNTs/7075Al复合材料中沉淀第二相分散性变差，尺寸变得粗大，随着CNTs添加量的增加，复合材料中晶粒变得细小，但时效析出的沉淀相数量减少，析出相的颗粒的尺寸变大。复合材料的强化机制为第二相强化、CNTs强化、细晶强化共同作用的协同强化，其中细晶强化和CNTs强化提高了复合材料的硬度，沉淀第二相强化效果减弱。