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Aluminum-based composites containing 0.1-0.7 wt.% graphene were produced by the powder metallurgical process. The microstructure of the nanocomposites was studied using LM, SEM, EDS, TEM, and XRD. A relatively uniform distribution of graphene nano-platelets and compacted agglomerates in composites with different graphene contents was found. A mechanical bond between the nano-platelets and the aluminum matrix was established. Under the conditions used, neither particles nor nanoparticles of Al4C3 are formed. The microhardness and mechanical properties were studied. It was found out they are the highest in the composite containing 0.1% graphene. The change of these properties with the graphene content increasing has the same character. Agglomeration of GNPs occurs in all composites containing graphene, but a part of GNPs remain in a dispersed, non-agglomerated state. The microhardness and mechanical properties depend on this part of individual GNPs. It was proven that the observed increase in the yield strength of the studied composites is due to Orowan's strengthening mechanism. The fracture mechanism of GNPs de-bonding and pull-out from the aluminum matrix of the composite was experimentally proved. [ABSTRACT FROM AUTHOR]

The influence of the volume fraction of nano-sized TiCN reinforcement additive on the mechanical properties and the microstructure of Al-based composite was studied. It was found that the addition of nano-sized TiCN particulates into the Al-matrix leads to a substantial improvement of the mechanical properties of the composite, TiCN-Al. However, the obtained results showed that the strengthening effect depends on the volume fraction of the additive; It was found, that beyond a certain volume fraction of the additive, instead of improving, the mechanical properties of the composite deteriorate. Based on these results a conclusion was drawn that at least two mechanisms, acting concurrently, are operative in the composite, one toward improving the mechanical properties, while the other toward their deterioration. A hypothesis, that the mechanical properties deteriorate due to the development of cracks in the composite' matrix proved to be correct. Based on the hypothesis a dependence, coupling together the composite's yield strength with the volume fraction of the reinforcement, was proposed and tested. It is shown, that the worked out dependence fits well the obtained experimental data. The effect of the reinforcement agglomeration on the yield strength of the composite is explained and discussed. [ABSTRACT FROM AUTHOR]