Fabrication of Copper Matrix Composites Reinforced with Carbon Nanotubes Using an Innovational Self-Reduction Molecular-Level-Mixing Method

Abstract

An innovational self-reduction molecular-level-mixing method was proposed as a simplified manufacturing technique for the production of carbon nanotube copper matrix composites (CNT/Cu). Copper matrix composites reinforced with varying amounts of (0.1, 0.3, 0.5 and 0.7 wt%) carbon nanotubes were fabricated by using this method combined with hot-pressing sintering technology. The surface structure and elemental distribution during the preparation of CNT/Cu mixing powder were investigated. The microstructure and comprehensive properties of the CNT/Cu composites were examined by metallography, mechanical and electrical conductivity tests. The results revealed that the CNT/Cu could be produced by a high temperature reaction at 900 degrees under vacuum, during which the carbon atoms in the carbon nanotubes reduced the divalent copper on the surface to zero-valent copper monomers. The decrease in the ratio of D and G peaks on the Raman spectra indicated that the defective spots on the carbon nanotubes were wrapped and covered by the copper atoms after a self-reduction reaction. The prepared CNT/Cu powders were uniformly embedded in the grain boundaries of the copper matrix materials and effectively hindered the tensile fracture. The overall characteristics of the CNT/Cu composites steadily increased with increasing CNT until the maximum at 0.7 wt%. The performance was achieved with a hardness of 86.1 HV, an electrical conductivity of 81.8% IACS, and tensile strength of 227.5 MPa.

Keywords: carbon nanotube; copper matrix composite; mechanical and electrical conductivity; molecular-level mixing; self-reduction.

Figure 1

Principle of molecular-level-mixing method.

Figure 2

(a) Infrared spectra of powder and raw CNT powder after sonication; (b) Magnified band pictures of the spectra at 300–800 cm⁻¹.

Figure 3

XRD patterns of the composites at different reduction temperatures (80 °C, 280 °C, 800 °C, 900 °C). The PDF file numbers are as follows. Copper (Cu): PDF#89-2838; Copper Oxide (Cu₂O): PDF#77-0199; Cuprite, syn (CuO): PDF#78-0428;.

Figure 4

Raman spectra of sample powders processed after raw powder, ultrasonic mixing, oxidation, and self-reduction.

Figure 5

SEM morphology image of CNT/Cu composite powder (a) 10,000× (b) 20,000× (c) The EDS layered energy spectrum image, where the main components are Cu (blue), O (green), and C (red). It can be observed that a large area was covered by carbon, accounting for 90%. The uniformly attached spherical clusters are Cu elements, accounting for about 8%. The surface of the CNT was slightly oxidized, accounting for about 2%.

Figure 6

TEM images of CNT/Cu composite powder at (a,b) 900 °C (c) Copper atoms under multiple carbon tubes. Neatly arranged and uniformly oriented carbon tube stripes against a white background. (d) Black round copper on a bent carbon tube uniformly wrapped around the surface. (e,f) The boundary junction between copper and carbon tube was tightly fitted, with large lattice stripes of copper clearly visible.

Figure 7

Metallographic pictures of surface-modified carbon nanotube reinforced copper matrix composites with different CNT contents of (a) 0.1 wt%; (b) 0.3 wt%; (c) 0.5 wt%; (d) 0.7 wt%.

Figure 8

Histogram of density, hardness, conductivity, yield strength, and tensile strength of samples with different CNT content of 0.1 wt%, 0.3 wt%, 0.5 wt%, and 0.7 wt%.

Figure 9

Stress–strain curve of samples with different CNT content of 0.1 wt%, 0.3 wt%, 0.5 wt%, and 0.7 wt%.

Figure 10

Fracture morphology of CNT/Cu composites with different CNT content of (a) 0.1 wt%; (b) 0.3 wt%; (c) 0.5 wt%; (d–f) 0.7 wt%.