Characterization of Ni–CNTs Nanocomposites Produced by Ball-Milling

2021

Materials

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Nickel nanocomposites reinforced by carbon nanotubes (Ni-CNTs) are one of the possible candidates for applications in highly demanding industries such as the automotive and aerospace industries. As is well known, one of the limitations on the use of some materials in these applications is thermal stability. Some components in these industries are frequently subjected to high temperatures, which is crucial to understanding their microstructures and, consequently, their mechanical properties. For this reason, the main objective of this research is to understand the microstructural evolution of Ni-CNTs nanocomposites when subjected to heat treatment. The nanocomposites with varying levels of CNT content were produced by powder metallurgy, and unreinforced nickel was used for comparison purposes under the same conditions. The dispersion of CNTs, a critical aspect of nanocomposites production, was carried out by ultrasonication, which already proved its efficiency in previous research. The heat treatments were performed under high vacuum conditions at high temperatures (700 and 1100 °C for 30 and 120 min, respectively). Microhardness tests analyzed the mechanical properties while the extensive microstructural evaluation was conducted by combining advanced characterization techniques such as scanning electron microscopy (SEM) with electron backscatter diffraction (EBSD), transmission electron microscopy (TEM), and high-resolution TEM. The obtained results are promising and show that the presence of CNTs can contribute to the thermal stability of the Ni-CNT nanocomposites produced.

Section: Resultssupporting

confidence: 78%

“…For the nanocomposite, LAGB density is higher. Previous research [ 24 , 25 , 28 ] has already shown that after sintering, nanocomposites reveal more LAGB than the metal without reinforcement due to the CNTs’ influence in increasing the dislocation density. It was expected that with the heat treatments, LAGB density would decrease.…”

Section: Resultsmentioning

confidence: 99%

Heat-Treated Ni-CNT Nanocomposites Produced by Powder Metallurgy Route

2021

Materials

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“…While for the Ni sample, grains without dislocations were observed, the nanocomposites are characterized by the presence of plastic deformation related to the presence of dislocation cells. As already mentioned in previous works [39,41,42], this plastic deformation occurs during the powder metallurgy route that for the nanocomposites is not eliminated in the last step of the process-sintering. During sintering, the dislocation rearrangement did not occur in the same way for the nanocomposites and for the Ni sample without reinforcement.…”

Section: The Influence Of Different Cnts On Mmnc Productionmentioning

confidence: 86%

“…For a more in-depth characterization of the produced nanocomposites, the EBSD technique was used to study crystal and microstructural characteristics with high resolution via the analysis of different types of maps and figures using the TSL OIM Analysis 5.2 software (EDAX Inc., Mahwah, NJ, USA). Prior to the map elaboration, the obtained raw data were submitted to a dilatation clean-up, as previously mentioned in other works [40,42], assuming a value of 15 • as grain angle tolerance and a minimum of two points for the grain size definition. This step is essential to avoid the wrong indexation of isolated points or a low confidence index, mainly located at grain boundaries, preventing incorrect results and, consequently, conclusions.…”

Section: Methodsmentioning

confidence: 99%

Effect of Morphology and Structure of MWCNTs on Metal Matrix Nanocomposites

2020

Materials

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The effect of using different carbon nanotubes (CNTs) on the production of nanocomposites was evaluated in this work. The investigated CNTs were multi-walled carbon nanotubes (MWCNTs) with different morphologies and structures. The main objective was to relate the results reported by numerical simulation with the results obtained experimentally in order to validate these methodologies. A detailed characterization of CNTs was carried out to establish the different main characteristics, such as inner and outer diameters, defects, structure and the number of walls. Metal matrix nanocomposites were produced using the powder metallurgy route. The experimental results show that the morphology and structure of MWCNTs have a significant effect on the dispersion process for nanocomposite production. Straight CNTs with a larger diameter and with few defects allow for the production of nanocomposites with uniform dispersion and strong interface bonding, leading to a higher hardness value. In addition, the CNT introduction into a metal matrix induces a change in the deformation behavior that plays an important role in the strengthening mechanisms. Although some aspects are not considered in the molecular dynamic (MD) simulation, such as the CNT random orientation and CNT agglomeration, some comparative relationships can be performed in order to validate some methodologies. While the structure and morphology of the CNTs have a significant influence on the dispersion process, the influence of the diameter and the functionalization treatment on the properties of the nanocomposites is also identified. The experimental results show that the decrease in the diameter of the CNTs and the use of functionalized CNTs also contribute to the obtention of lower mechanical properties of the nanocomposites, as is pointed out in the results of MD carried out in nanocomposites.

“…Carneiro et al [102,103] showed that introducing CNTs into metallic matrices induces an increase in the low-angle grain boundaries associated with the dislocation density. The nanocomposites were produced via powder metallurgy, and during the mixture and dispersion, the authors reported an increase in plastic deformation.…”

Section: Strain Hardeningmentioning

confidence: 99%

Strengthening Mechanisms in Carbon Nanotubes Reinforced Metal Matrix Composites: A Review

2021

Metals

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Carbon nanotubes (CNTs)-reinforced metal matrix composites are very attractive advanced nanocomposites due to their potential unusual combination of excellent properties. These nanocomposites can be produced by several techniques, the most reported being powder metallurgy, electrochemical routes, and stir or ultrasonic casting. However, the final mechanical properties are often lower than expected. This can be attributed to a lack of understanding concerning the strengthening mechanisms that act to improve the mechanical properties of the metal matrix via the presence of the CNTs. The dispersion of the CNTs is the main challenge in the production of the nanocomposites, and is independent of the production technique used. This review describes the strengthening mechanism that act in CNT-reinforced metal matrix nanocomposites, such as the load transfer, grain refinement or texture strengthening, second phase, and strain hardening. However, other mechanisms can occur, such as solid solution strengthening, and these depend on the metal matrix used to produce the nanocomposites. Different metallic matrices and different production techniques are described to evaluate their influence on the reinforcement of these nanocomposites.