Abstract
The combination of powder metallurgy and ball milling method has been widely regarded as the most beneficial route for producing multi-walled carbon nanotubes (MWCNTs)-reinforced aluminum matrix composites. In this study, the effects of different milling times (1, 2, 4, and 8 h) on the structural, morphological, and crystallographic properties of MWCNTs-reinforced Al7075 composite powders were characterized by particle size analyzer, Raman spectroscopy, scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), and X-ray diffraction (XRD). After the morphological and structural characterization of the milled powders, the microstructural and mechanical properties of the hot-pressed composites were evaluated using an optical microscope, SEM, density, and Brinell hardness measurements. Considering milled powder characterization, the MWCNTs were gradually distributed and embedded within the matrix as the milling time increased. Milling for 8 h resulted in a minimum level of particle size (11 µm) with shortened and uniformly dispersed CNTs. Brinell hardness of the composite increased from 91 to 237 HB -a ⁓%160 after 8 h of milling. Such a remarkable increment in hardness could be attributed to several concurrent strengthening effects related to dispersion, solution, grain refinement, and Orowan looping mechanisms. However, relative density results revealed that the composite produced by 2 h milled powders exhibited the highest density (%99.96). The observed differences between hardness and density results were ascribed to powders’ deteriorated packing and sintering behavior due to an increment in the hardness of particles and variation in particle size range and morphology, which resulted from following different milling protocols.
Highlights
Metal matrix composites (MMCs) have emerged due to the ineffectuality of traditional monolithic metals and their alloys in achieving a combination of various crucial features that are prerequisites in today’s production technologies [1]
The effects of ball milling time on the dispersion behavior of CNTs within the Al7075 matrix system were investigated within the framework of strengthening mechanisms and via ball milling
The influence of ball milling time on the structural and crystallographic properties of mixing powders and their impacts on the microstructural evolution, hardness, and relative density of produced CNT–Al7075 composites was thoroughly characterized by particle size analysis, particle size distribution, scanning electron microscopy (SEM), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), optic microscopy analyses, and hardness and density measurements
Summary
Metal matrix composites (MMCs) have emerged due to the ineffectuality of traditional monolithic metals and their alloys in achieving a combination of various crucial features that are prerequisites in today’s production technologies [1]. Among various MMCs, Al-based metal matrix composites (AMCs) have received more attention than conventional metal-based alloys thanks to their high specific mechanical properties, good machinability characteristics, lightweight, economical, and effortless accessibility. Aluminum metal matrix nanocomposites (AMNCs), which are reinforced with different nanoreinforcement materials (oxide, carbide, nitride), have fascinated many researchers due to their superior overall properties as compared to the AMCs [3]. These properties have stemmed from the grain refinement mechanism provided by homogeneously distributed nano-sized reinforcements into the matrix. Providing good interfacial bonding between the matrix and the reinforcement element is another main issue, directly or indirectly affecting the performance, fabrication, and application areas of materials [9]
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