| Cu matrix composites reinforced by carbon nanotubes(CNTs)have been investigated to conquer the degradation of the electrical conductivity and simultaneously enhance the mechanical strength of Cu-based conductors.The two main challenges in the previous research may be the agglomeration of nanocarbons during processing as well as the poor interfacial bonding of the composites.Surface oxidation modification is an effective method to usage these problems by improving the structure and reaction activity of the surface of CNTs.However,during the oxidation process,the CNTs generate surface functional groups accompanied by structural defects and both of the two factors should be taken into account.In this study,we investigate the dependence of oxidation treatment conditions of CNTs on properties of the copper matrix composites on the analysis of the critical problems in preparation of the composites.For this purpose,firstly,we employed a simple and rapid acid steaming method to achieve surface modification of the raw CNTs;Secondly,copper matrix composites with CNTs under different oxidation treatment time were successfully fabricated by combined use of a hetero-aggregation mixing method and spark plasma sintering;Thirdly,under the optimized CNT oxidation treatment condition,CNT/Cu composites with different CNT volume fraction were prepared.The structure and properties of the modified CNTs and the CNT/Cu composites were studied.The main results are:(1)The optimal temperature for the surface oxidation of the CNTs is 200?.Raman spectra,TEM,BET,XPS and Zeta potential measurement were employed to investigate the structure and chemical composition of the surface of CNTs.The results indicate that,with the oxidation treatment time increasing,the degree of the CNT oxidation as well as the degree of structural defects or disorders in CNTs increase,and meanwhile,the amount of the functional groups on the surface of the CNTs increases and the dispersion stability of the CNTs is improved.The electrical resistivity results of the CNTs films measured by a four-point probe method indicate that electrical conductivity of CNTs increases with the increasing of the oxidation treatment time.(2)After a moderate treatment time of 3.5h,the CNTs were inserted with enough charged groups and simultaneously maintain a moderate structure integrity.Accordingly,the prepared composite with 3.5h-treated CNTs exhibited the highest 457 Mpa tensile strength and 130 HV Vickers hardness,which is 1.6 and 2 times higher than those of the unreinforced copper prepared by the same route.At the same time,the electrical conductivity of this composite was up to the highest 92%IACS,which is 94% of the unreinforced copper.The CNT/Cu composites exhibited good combination of high strength and high electrical conductivity through an efficient control of the CNT surface modification process.(3)Low CNT volume fraction limits enhancement of the CNTs and fewer CNTs cannot adequately fill the gap of the copper matrix during the sintering process.When the volume fraction of CNTs is excessively high,the properties of the composites declined due to the increasing aggregation of the CNTs.CNT/Cu composites with CNT volume fraction of 3vol% exhibited the highest density,mechanical properties and electrical conductivity. |
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