铜及其合金具备良好的力学性能、加工性能和导电、导热性能，在交通运输、集成电路、电子器件制造等方面发挥着难以替代的作用，但是导电铜材料使用时会产生热效应导致电阻增加，限制了它的功能发挥和应用范围。 超顺排碳纳米管（SACNT）具备高强度、高弹性模量、排列取向整齐和负电阻温度系数的特点，是高强高导铜基复合材料的一种理想增强体。本文采用电沉积、轧制和退火工艺制备了超顺排碳纳米管增强铜基复合材料（Cu/SACNT），系统地研究和分析了温度、加工状态和碳纳米管含量对复合材料的电学性能（电阻率、导电率、电阻温度系数）的影响。 研究结果表明：碳纳米管的引入不会明显降低铜的导电率，电镀态纯铜的室温导电率为88%IACS，Cu/5CNT的导电率为82%IACS。复合材料的电阻温度系数随碳纳米管体积分数的增加而降低，且呈线性变化，电镀态Cu/20CNT在25~50℃的平均电阻温度系数为0.0037℃-1，相比纯铜（0.0044℃-1）下降约16%，证明了本实验中，使用电沉积法在铜基体中引入碳纳米管可以改善铜电阻的温度依赖性。 在电镀态样品的基础上，制备了轧制态Cu/CNT复合材料。相比于电镀态，轧制态复合材料的导电率提高，同时保持较低的电阻温度系数，说明轧制态复合材料的（高温）导电性能更加优异。分析室温下两种状态复合材料的导电率，发现轧制后晶粒拉伸，导电方向上晶界散射减弱是轧制后导电率提高的主要原因。利用有效介质理论和混合定律计算了轧制态样品理想状态下的电导率，计算结果显示，碳管体积分数越低，实验值越接近理论值，这与高碳管体积分数样品制备时碳管分布更加混乱且容易发生团聚有关。 在轧制态样品的基础上，制备了退火态Cu/CNT复合材料。室温下，纯铜与Cu/20CNT的导电率相差11%IACS左右，升温至250℃后，该差值减少为2%IACS。当温度超过200℃时，Cu/5CNT的导电率高于纯铜。对比了不同加工状态复合材料的导电性能，发现加工状态几乎不影响电阻温度系数。结合Matthiessen’s Rule解释了该现象：铜晶格振动产生的基本电阻对温度变化更敏感，随着温度上升明显提高，而位错、晶界等缺陷引起的杂质电阻的影响较小。
Copper and its alloys play an irreplaceable role in transportation, integrated circuit, electronic device manufacturing, etc. because of their good mechanical properties, machining properties and electrical and thermal conductivity. However, conductive copper alloys will heat up in use, resulting in increased resistance, which limits its function and application. The Super-aligned Carbon Nanotube (SACNT) film, characterized by high strength, high elastic modulus, neat alignment and negative temperature coefficient of resistance, is an ideal reinforcement for high strength and high conductivity copper matrix composites. In this paper, copper matrix composites reinforced by super-aligned carbon nanotube (Cu/SACNT) were prepared by electrodeposition, rolling and annealing processes. The effects of temperature, processing state and carbon nanotube content on the electrical properties (resistivity, conductivity and temperature coefficient of resistance) of Cu/SACNT composites were systematically studied and analyzed. The results show that the introduction of carbon nanotubes did not significantly reduce the conductivity of copper, the conductivity of copper at room temperature is 88%IACS and that of Cu/5CNT is 82%IACS. The average resistance temperature coefficient of electroplated Cu/20CNT at 25~50℃ is 0.0037℃-1, which is about 16% lower than that of pure copper (0.0044℃-1). It is proved that the temperature dependence of copper resistance can be improved by introducing carbon nanotubes into copper matrix by the electrodeposition method. The rolled Cu/CNT composites were prepared from electroplated samples. Compared with electroplated samples, the electrical conductivity of the rolled composite is improved, while the temperature coefficient of resistance is lower, indicating that the rolled composite has better (high temperature) electrical conductivity. It is found that the main reasons for the increase of the electrical conductivity are the grain stretching and the weak grain boundary scattering in the direction of conduction with analyzing the electrical conductivity of the rolled composites at room temperature, The equivalent medium theory and mixing law were used to calculate the electrical conductivity of the rolled sample under the ideal state. The results show that the lower the volume fraction of the carbon tube, the closer the experimental value is to the theoretical value, which is related to the more chaotic distribution of the carbon tube and the easier to agglomerate in the preparation of the sample with high volume fraction of the carbon tubes. The annealed Cu/CNT composites were prepared from rolled samples. At room temperature, the conductivity difference between pure copper and Cu/20CNT was about 11%IACS, and at 250℃, the difference was 2%IACS. When the temperature exceeded 200℃, the conductivity of Cu/5CNT was higher than that of pure copper. The electrical conductivity of composites under different processing conditions was compared, and it was found that the processing conditions hardly affected the temperature coefficient of resistance. Matthiessen‘s Rule was used to explain the phenomenon: the intrinsic resistance generated by the lattice vibration of copper is more sensitive to temperature change, and increases significantly with the increase of temperature, while the influence of impurity resistance caused by dislocation, grain boundary and other defects is less.
