M.S. Senthil Saravanan

Dispersion and Thermal Analysis of Carbon Nanotube Reinforced AA 4032 Alloy Produced by High Energy Ball Milling

In this work, multi-walled carbon nanotubes (MWNTs) were successfully reinforced in AA 4032 nanocrystalline matrix. The elemental powders of AA 4032 composites were mechanically alloyed in the high energy ball mill for 30 h to get nanocrystalline structure. The carbon nanotubes (CNTs) were added at the 29th hour of ball milling process. The morphological changes during milling were studied, using scanning electron microscope analysis and the distribution of the CNTs within the aluminum matrix was successfully revealed, using transmission electron microscope analysis. The results show that the CNTs are effectively distributed within the aluminum matrix without any structural damage. The variation in the melting point was studied using simultaneous thermal analyzer.

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

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.

Synthesis and Characterization of CNT Reinforced AA4032 Nanocomposites by High Energy Ball Milling

A few studies have focused on the preparation of metal matrix composites (MMC) reinforced with CNTs. In these composites there is evidence of poor interfacial bonding between the CNTs and the metal matrix, and this may be detrimental to the mechanical properties Furthermore, agglomeration of the CNTs may produce an uneven dispersion within the matrix which reduces their effectiveness. These are the challenges that need to be addressed in optimizing the synthesis of CNT metal matrix composites. In the present investigation, nanocrystalline AA4032 alloy reinforced with CNTs in different fractions was produced by high energy ball milling. The Raman spectra and TEM observations revealed multi‐walled CNTs that are used as reinforcement in the composite. TEM observations revealed nanocrystalline matrix of AA4032 alloy composite along with uniform distribution of CNTs.

Mechanical Properties and Corrosion Behavior of Carbon Nanotubes Reinforced AA 4032 Nanocomposites

Carbon nanotubes (CNTs) reinforced aluminum matrix composites were fabricated using powder metallurgy technique. The effect of nanotubes content on mechanical properties of the composites was investigated. Experimental results showed that nanotubes are homogeneously distributed in the composites. The corrosion of AA 4032 alloy based nanocomposite with CNTs was investigated by electrochemical polarization studies. CNTs-reinforced composites have shown a better corrosion resistance than parent alloy. The nanotubes content significantly affect mechanical and corrosion properties of composite.

CONSOLIDATION OF CNT-REINFORCED AA4032 NANOCOMPOSITES BY ECAP

The present work emphasizes on the synthesis of CNT-reinforced nanocrystalline AA4032 alloy powders and their consolidation by equal channel angular pressing (ECAP). Nanocrystalline AA4032 alloy reinforced with 2 wt% CNTs was produced by high-energy ball milling. The XRD analysis and TEM observation revealed the formation of nanocrystalline AA4032 alloy and uniform distribution of CNTs in the nanocrystalline matrix. The nanocomposite powders were canned in commercially pure aluminum sheath and subjected to ECAP for consolidation. More than 98% of density was achieved after four passes in route BA at the center of the can. The hardness obtained is around 218 HV5.0 after four passes in the core of alloy with 2 wt% of CNTs. Increase in hardness was significant even with minimum addition of CNTs.

Influence of Crystallite Size on Consolidation of Carbon Nanotube Reinforced AA 4032 Composite Powders by Equal Channel Angular Pressing

Equal channel angular pressing (ECAP) is the one of the promising methods of severe plastic deformation to obtain bulk ultrafine grain structures. However, ECAP can also be used for powder consolidation. In the present study, fully dense bulk AA 4032 alloy was consolidated from nanocrystalline and microcrystalline powders. These materials were processed by ECAP until four passes at ambient temperature. It is observed that hardness and densification increased significantly with increase in number of ECAP passes. Transmission electron microscopic and scanning electron microscopic examinations evidenced that crystallite size of the nanopowders are unaltered, however a significant crystallite size reduction from around 50 µm down to submicron size is observed. Moreover, higher densification is achieved in microcrystalline powders than nano powders, whereas higher hardness in the case of nanopowders compared to microcrystalline powders.