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

Abstract

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.

Optimization of MWCNTs/Al nanocomposite fabrication process parameters for mass density and hardness

“…61,62 The hardness value of the nanocomposite is improved with increasing compaction pressure and sintering temperature due to the strong interfacial bond between the reinforcement material and the shearing of load by f-MWCNTs within the Al matrix. 63 The increase in the performance characteristics with increasing milling duration up to the threshold value can be attributed to the uniform dispersion of f-MWCNTs in the Al matrix and the strengthening effect of the Al matrix. 64 Further increasing of milling duration, that is, beyond the threshold value, may cause serious damage to the MWCNTs, which leads to a decrease in their performance characteristics.…”

Bredigite-CNTs Reinforced Mg-Zn Bio-Composites to Enhance the Mechanical and Biological Properties for Biomedical Applications

“…This happens during the SPS process, strengthening the bond and making it more resistant to failure under load [ 15 , 16 ]. the presence of CNTs as nanofillers in composites with unique properties, such as very high Young’s modulus, can also accelerate charge transfer from matrix to reinforcement [ 17 , 18 , 19 , 20 , 21 ]. On the other hand, according to the Orowan mechanism, the reinforcing particles act as a barrier to the free dislocations movement in the matrix, increasing their resistance to deformation [ 11 ].…”

“…The scheme in Figure 8 shows that the presence of bredigite nanoparticles can play an important role in pinning CNTs to grain boundaries due to the dendritic surface and the resulting stronger bonds. On the other hand, smaller grain sizes were created in nanocomposites, which led to grain refinement [ 21 ]. Therefore, when stress is applied to the composite, CNTs can act as a bridge and partially prevent crack propagation [ 21 ].…”

“…On the other hand, smaller grain sizes were created in nanocomposites, which led to grain refinement [ 21 ]. Therefore, when stress is applied to the composite, CNTs can act as a bridge and partially prevent crack propagation [ 21 ].…”

“…Carbon nanotubes (CNTs) are attracting a great deal of attention as nanofillers due to their unique properties, such as high Young’s modulus (1TPa) and strength (30 GPa) [ 20 ]. CNTs are one of the best reinforcements for Mg matrix composites [ 20 , 21 ]. Ding et al [ 22 ] for example, added CNTs to Mg in powder metallurgy and observed significant improvements in mechanical properties compared to pure Mg [ 22 ].…”