Research Papers

Synthesis, Characterization, and ECAP Consolidation of Carbon Nanotube Reinforced AA 4032 Nanocrystalline Composites Produced by High Energy Ball Milling

[+] Author and Article Information
M. S. Senthil Saravanan

Department of Mechanical Engineering,
SBM College of Engineering and Technology, Dindigul 624005, India
e-mail: bhatranitt@gmail.com

S. P. Kumaresh Babu

Department of Metallurgical
and Materials Engineering,
National Institute of Technology,
Tiruchirappalli 620015, India

1Corresponding author.

Contributed by the Materials Division of ASME for publication in the JOURNAL OF ENGINEERING MATERIALS AND TECHNOLOGY. Manuscript received May 4, 2014; final manuscript received November 7, 2014; published online December 15, 2014. Assoc. Editor: Tetsuya Ohashi.

J. Eng. Mater. Technol 137(2), 021004 (Apr 01, 2015) (9 pages) Paper No: MATS-14-1096; doi: 10.1115/1.4029196 History: Received May 04, 2014; Revised November 07, 2014; Online December 15, 2014

In the present work, multiwalled carbon nanotubes (MWNTs) were synthesized by electric arc discharge method in open air atmosphere. The synthesized nanotubes were subjected to multistep purification followed by characterization using Raman spectroscopy and transmission electron microscopy (TEM). These carbon nanotubes (CNTs) have inner and outer diameters of the order of 3.5 nm and 16 nm with an aspect ratio of 63. AA 4032 nanocomposites reinforced with MWNTs were produced by high energy ball milling using elemental powder mixtures. X-ray diffraction (XRD) and scanning electron microscope (SEM) studies showed different phases of composite with and without CNTs. The crystallite size and lattice strain were calculated using an anisotropic model of Williamson–Hall peak broadening analysis, which showed in decreased crystallite size with increasing milling time. TEM studies reveal that the MWNTs were uniformly distributed in the matrix. Thermal stability of the nanocrystalline powders was studied using a differential thermal analyzer (DTA). The mechanically alloyed powders were consolidated using a novel method called equal channel angular pressing (ECAP) at room temperature. The consolidated samples were sintered at 480 °C in argon atmosphere for 90 min. ECAP method was investigated as an alternative to conventionally sintered powder composites. CNT addition has shown significant improvement in the hardness of the system, even though the observed density is relatively low compared with a base alloy. Thus, the results show that ECAP enables sufficient shear deformation results in good metallurgical bonds between particles at lower compaction pressures. Hence, it is proven that ECAP can be effectively used as one of the consolidation technique especially for powders that are difficult to consolidate by other means.

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Fig. 1

Schematic diagram of ECAP process

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Fig. 2

(a) Raman spectra of MWNTs and (b) TEM micrograph of MWNTs

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Fig. 3

(a) XRD pattern of milled powders at different stages and (b) XRD pattern of AA 4032 and AA 4032 with MWCNT

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Fig. 4

(a) Change in lattice parameter during different milling time and (b) grain size and strain variation with milling time

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Fig. 5

Morphology of milled powders: (a) 0 h milling, (b) 30 h milling, and (c) EDS analysis.

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Fig. 6

TEM images of AA 4032 alloy reinforced with 2 wt.% MWCNTs: (a) bright field image showing uniform distribution of MWCNTS in composite; (b) dark field image of ball milled powder particle (inset corresponding SAED pattern); and (c) particle size distribution calculated from TEM micrograph

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Fig. 7

DTA curves of Al 4032 showing the influence of MWNTs in melting peak of matrix

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Fig. 8

(a) Relative density against number of passes of the ECAP sample, (b) hardness variation of AA 4032 alloy powders, (c) TEM image of ECAP AA 4032/2% MWCNT, and (d) variation of strain with increasing number of passes




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