Study On Microstructure And Properties Of Carbon Nanotubes Reinforced Copper Matrix Composites By Friction Stir Processing

Carbon nanotubes reinforced copper matrix (CNTs/Cu) composites with the volumefraction of0.9%to3.4%were fabricated by friction stir processing (FSP). Studied themicrostructure and properties of the CNTs/Cu composites, analyzed the impact ofdifferent CNTs content on the microstructure and properties of the composites. On thisbasis, investigated the fracture mechanism, wear mechanism and strengthen mechanismof the composites.The results show that, with the volume fraction of CNTs is0.9%, the obtainedcomposites forming the best, and the forming of the composites tends to become worsewith increasing volume fraction of CNTs, also the reunion tendency of CNTs graduallyincrease. By surface scanning on the center of friction stir zone of the composites can bedrawn, CNTs in the composites distribution is uniform overall, but partial existence thephenomenon of segregation.The addition of CNTs have improved the hardness of the CNTs/Cu composites, andthe average hardness of the composites gradually increased with increasing volumefraction of CNTs, but the hardness distribution uniformity becomes worse. Tensilestrength of the CNTs/Cu composites relative to the T2copper has improved to someextent, but elongation have a certain degree of reduction, and with the increase of CNTsvolume fraction, the tensile strength and elongation of the CNTs/Cu composites trend togradually decreased. Fracture of the composites presents the characteristics of ductilefracture, the fracture mechanism is CNTs and the copper matrix combination ofinterface debonding, resulting in composites play a bridging role of CNTs on the tensilefracture surface with a lot of pull out, and the reunion of the CNTs and the distributionat the grain boundaries largely affect the CNTs and the copper matrix interfacialbonding strength. The addition of CNTs in the composites can effectively improve thewear properties, and with increasing volume fraction of CNTs, the wear loss of thecomposites gradually reduced and finally stabilized. The wear loss of the compositesgradually increased with increasing the pressure load. The addition of CNTs can form alayer of self-lubricating membrane on the wear surface of the composites, which willplayed a good lubricating antifriction effect on the composites, the main wearmechanism of the composites is self-lubricating membrane shedding and dynamic repair,accompanied by a certain amount of abrasive wear. The conductivity of the composites obtained by FSP through the addtion of CNTs relative T2copper has decreased to someextent, and showed a downward trend with increasing volume fraction of CNTs, butdecreased slightly, the obtained composites is also a good conductive material.The formation interface of the CNTs and the copper matrix is mechanicalcombination, and the distribution of CNTs in the composites plays the role of bridgingthe matrix. Damage and local deformation of CNTs in the composites weaken thestructural integrity of the CNTs, limits the superior performance of CNTs in thecomposites has played to some extent, and the reunion of the CNTs is largely restrictedthe improvement of the performance of the composites. The composites grain size incenter of friction stir zone gradually become smaller with the CNTs volume fractionincreases. The strengthening mechanism of the composites including: the CNTs bearingand load transfer, the fine grain strengthening, dislocation strengthening and dispersionstrengthening.