Abstract
Carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) with exceptional mechanical, thermal, chemical, and electrical properties are enticing reinforcements for fabricating lightweight, high-strength, and wear-resistant metal matrix composites with superior mechanical and tribological performance. Nickel–carbon nanotube composite (Ni-CNT) and nickel–graphene nanoplatelet composite (Ni-GNP) were fabricated via mechanical milling followed by the spark plasma sintering (SPS) technique. The Ni-CNT/GNP composites with varying reinforcement concentrations (0.5, 2, and 5 wt%) were ball milled for twelve hours to explore the effect of reinforcement concentration and its dispersion in the nickel microstructure. The effect of varying CNT/GNP concentration on the microhardness and the tribological behavior was investigated and compared with SPS processed monolithic nickel. Ball-on-disc tribological tests were performed to determine the effect of different structural morphologies of CNTs and GNPs on the wear performance and coefficient of friction of these composites. Experimental results indicate considerable grain refinement and improvement in the microhardness of these composites after the addition of CNTs/GNPs in the nickel matrix. In addition, the CNTs and GNPs were effective in forming a lubricant layer, enhancing the wear resistance and lowering the coefficient of friction during the sliding wear test, in contrast to the pure nickel counterpart. Pure nickel demonstrated the highest CoF of ~0.9, Ni-0.5CNT and Ni-0.5GNP exhibited a CoF of ~0.8, whereas the lowest CoF of ~0.2 was observed for Ni-2CNT and Ni-5GNP composites. It was also observed that the uncertainty of wear resistance and CoF in both the CNT/GNP-reinforced composites increased when loaded with higher reinforcement concentrations. The wear surface was analyzed using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analysis to elucidate the wear mechanism in these composites.
Highlights
Metal matrix composites (MMCs), consisting of a metal matrix reinforced with highstrength ceramic reinforcement, exhibit a very high strength to weight ratio and can be employed at elevated temperatures and severe working conditions due to a synergetic combination of metallic properties, such as high toughness, strength, and ductility, as well as ceramic properties, such as high hardness, high tensile strength, and low coefficient of thermal expansion, with excellent resistance to wear and corrosion
Peaks related to carbon are not visible in the Ni-0.5CNT composite sample, mainly owing to the relatively lower content of carbon nanotubes (CNTs) in these composites, which is beyond the detectable resolution of X-ray diffraction (XRD)
A similar pattern was visible in Ni-graphene nanoplatelets (GNPs) composites, and peaks corresponding to crystallographic planes of face centered cubic (FCC) nickel and hexagonal closest packed (HCP) carbon are the only peaks visible in the XRD pattern in spark plasma sintering (SPS)-processed pure Ni and nickel–graphene nanoplatelet composite (Ni-GNP) composites
Summary
Metal matrix composites (MMCs), consisting of a metal matrix reinforced with highstrength ceramic reinforcement, exhibit a very high strength to weight ratio and can be employed at elevated temperatures and severe working conditions due to a synergetic combination of metallic properties, such as high toughness, strength, and ductility, as well as ceramic properties, such as high hardness, high tensile strength, and low coefficient of thermal expansion, with excellent resistance to wear and corrosion This attractive set of properties with various reinforcing agents and processing routes makes MMCs a favorable material for various applications in the automotive and aerospace industries [1,2,3]. The need for novel material with high-performance surface engineering applications has become the primary enticement for developing carbon-based nanomaterial-reinforced metal matrix composites Carbonaceous reinforcements, such as carbon nanotubes (CNTs), graphene nanoplatelets (GNPs), and carbon fibers, have attracted substantial attention as a potential solid lubricant reinforcement in the metal matrix owing to their exceptional mechanical, thermal, chemical, and electrical properties [6,7,8]. These intrinsic properties make metal matrix nanocomposites reinforced with CNTs/GNPs a latent candidate for numerous high-strength structural and surface engineering applications
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