Al₂₀₂₄-CNTs composites by mechanical alloying

Abstract

Carbon nanotubes (CNTs) were dispersed by mechanical milling into a 2024 aluminum alloy (Al 2024 ) in order to produce composites and study the influence of CNTs content over the mechanical and microstructural behavior of them. The time of milling was set to 5 h [1] and the addition of CNTs was of 0.0 to 5.0 wt. %. Powders obtained from milling process were cold compacted and then sintered under argon atmosphere by 2h with 5ºC/min for heating and cooling rates. The microstructural analysis was carried out by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). In the other hand, their mechanical performance was evaluated by microhardness Vickers. Microhardness values from several aluminum commercial alloys reported in literature were compared with these experimental results.CNTs used as material reinforced are shown in Figs. 1(a,b). Diameters of ~80 nm and lengths of ~0.8 mm were observed. Fig. 1c displays the microstructure after sintering process. It can be observed a well dispersion Al 2 Cu phase produced by low cooling rate in sintering treatment. Figs. 1 (d,e) present bright field TEM micrographs from the composites with 1.0 and 5.0 wt.%, respectively. CNTs are observed in Fig. 1f from the composite with 1.0 wt.% of nanotubes. A second phase characterized as Al 4 C 3 is shown in Fig. 1g. Fig. 2a shows the results from XRD of the Al 2024 -CNTs composites as a function of the CNTs content. An increase in the peaks intensity attained to the aluminum carbides (Fig. 1e, marked with circles, and 1g) is observed as function of the CNTs content. However no variation was observed for the Al 2 Cu intensity peaks. The presence of CNTs after milling process and sintering heat treatment was verified by TEM as is shown in Fig. 1g.The mechanical characterization of the composites indicates that a rapid increament in mechanical properties is observed as a function of the addition of the CNTs (Fig. 2b). The maximum Vickers hardness value (219.74 VHN) observed in this work was reached by the sample with 5.0 wt.% of CNTs, this value represents ~346% (170.56 hardness units) over the pure Al hardness value. The composite with 3

Deformation and strengthening mechanisms of a carbon nanotube reinforced aluminum composite

“…During the EDS analysis all the main alloying elements (i.e., Al, Cu, Mg, and Mn) were considered, however only Cu-containing particles were present ( Fig.4(b)). Similar results were reported by Bustamante et al [16] who studied the microstructure of a 5.0 wt.% CNT/2024Al composite after sintering, and observed a good dispersion of Al 2 Cu coarse particles due to the low cooling rate in the sintering process. The presence of this phase will be further confirmed via XRD phase analysis.…”

“…The formation of Al 4 C 3 could also be related to the shortening of CNTs as shown in Fig.5(a), leading to an increasing number of carbon atoms at the CNT tips which would enhance the probability of CNT-Al reactions during severe plastic deformation at high temperatures. Bustamante et al [16] showed the XRD results of CNT/2024Al composites as a function of CNT content, and observed that the magnitude of the Al 4 C 3 peaks increased with increasing CNT content, while the intensities of the Al 2 Cu peaks varied less significantly. This was in good agreement with the XRD results shown in Fig.6 about the appearance of small Al 4 C 3 peaks in the composite and the persistence of Al 2 Cu compared with the base alloy.…”

“…(16), its significance is implicitly accounted for since it is directly linked to the strengthening behavior of the composite through the grain refinement [68]. As presented in Equ.…”

“…As presented in Equ. (16), grain boundary (GB) strengthening is influential on the enhancement of CYS due to the refinement of the average grain size of the composite [53]. In addition to the load transfer, thermal mismatch and Orowan looping which are supposed to be present concurrently, the significance of the HallPetch effect was extended to account for the Zener pinning.…”

“…While some limited microstructural studies on the CNT reinforced Al composite were reported in the literature [7,16,17], three-dimensional electron backscatter diffraction (EBSD) investigations along different observational planes of the composite are not available, to the authors' knowledge. While the compressive micro-strains were noted to occur in the CNT reinforced composites [17][18][19], which would result in X-ray diffraction peak broadening, no actual quantification of the resultant lattice change is reported.…”