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It has been thoroughly investigated Al4C3 formed as a result of the reaction of graphene in the form of graphene nanoplates (GNPs) and aluminum from the metal matrix during annealing of an aluminum matrix composite with GNPs strengthener produced by powder metallurgical method. Carbide's microstructural and crystallographic characteristics have been determined using SEM, TEM, and HRTEM. The formation of Al4C3 depends on the annealing temperature and holding time. The carbides have rod-like shapes. They are distributed predominately at grain boundaries. The average length is 118 nm, and the average diameter is − 17 nm. The longitudinal orientation of carbides coincides with the extrusion direction and the tensile direction in most cases. The interfaces between the aluminum matrix and existing particles in the composite were estimated. The factors that lower the strength indicators of the composite are the following: i) the presence of an Al2O3 layer or shell between the carbide particles and the aluminum matrix because of the incoherent interface between the carbide and oxide; ii) the accumulation of carbide particles at grain boundaries and their unfavorable longitudinal orientation which leads to a lack of locking effect of the carbides and poor load transfer. Thus, the carbides brittle the boundaries and reduce the ductility; iii) the presence of even a tiny number of micro-sized carbides which increase the brittleness of the composite. [ABSTRACT FROM AUTHOR]

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The study investigates the effects of graphene nanoplatelets (GNPs) on the tribological properties of aluminum-based nanocomposites, both annealed after extrusion and non-annealed. It also examines the role of nanosized Al4C3 (aluminum carbide), which forms in the annealed Al/GNPs nanocomposite, on the tribological performance of the nanocomposites. The nanocomposites were fabricated using the powder metallurgy method. The microstructure of the composite materials was characterized using SEM, EDS, XRD and TEM techniques. The coefficient of friction (CF) and mass wear of the composites were measured using a pin-on-disk test under dry sliding friction conditions. The results showed that adding GNPs increased the coefficient of friction (CF) of the nanocomposites by up to 44% at 0.1 wt.% GNP, but the CF decreased by 15% at 1.1 wt.% GNP. The optimal concentration of GNPs for minimizing the CF and mass wear of Al-based nanocomposites was 0.1 wt.%. Additionally, the presence of Al4C3 in the annealed Al/GNP nanocomposite had a positive effect on the CF at low GNP concentrations, with a 38% increases at 0.1 wt.% GNP, but this effect diminished as the GNP concentration increased. The study also found that the mass wear of the nanocomposites increased with the GNP concentration, with a 46% increase in the mass wear from 0.1 wt.% GNP to 0.5 wt.% GNP and a 202% increase from 0.1 wt.% GNP to 1.1 wt.% GNP. The presence of Al4C3 also affected the mass wear, with the effect diminishing as the GNP concentration increased. The study observed an increase in the mass wear with the increase in the GNP concentrations, but the mass wear of the annealed Al/GNPs with 1.1 wt.% GNP and Al4C3 was 52% lower than the Al composite with 1.1 wt.%. Overall, this study provides insights into the role of GNPs and Al4C3 on the tribological performance of aluminum-based nanocomposites. [ABSTRACT FROM AUTHOR]

Reinforcement of aluminum and aluminum alloys with graphene has been intensively practiced by researchers in the past dozen years. The role of Al4C3, which could be produced unintentionally or purposefully during the composite production, was controversial until it was found that nano-sized carbides were beneficial for strengthening the composites. aluminum-graphene-nano-sized Al4C3 composites were produced by us using the powder metallurgical method and subsequent annealing. The microstructure was investigated using light microscopy (LM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), transmission electron microscopy (TEM), and high resolution transmission electron microscopy HRTEM. Nano-sized carbides were found at the interface aluminum-graphene. The formation of a chemical bond between aluminum and graphene during annealing was proved. Lower values of the microhardness and strength characteristics of the composites after extrusion and subsequent annealing during which nano-sized carbides are formed were found in comparison with those obtained after extrusion. It could be supposed that the annealing processes contribute more to the reduction in microhardness and strength characteristics than nano-sized carbides contribute to its increase. The presence of a strong chemical bond between the graphene and the aluminum is manifested in the failure pattern, which is characterized by graphene nano-platelets and nano-sized carbides fracture and semi-pulled out or semi-slipped Al4C3 from the matrix. [ABSTRACT FROM AUTHOR]

Dual α-β brasses are still not investigated towards the dependence of mechanical properties on the β-phase volume fraction and the average grain size. This problem is elucidated by us. The microstructural characteristics are determined using image analyses and standard scales. The mechanical properties are measured by standard testing. It was found that the medium average grain diameter of 35 μm and medium β-phase volume fraction of 56 % provide the highest values of proof strength, tensile strength, and hardness and lowest elongation. Mathematical dependencies of mechanical properties on microstructural parameters are derived and graphically depicted by means of linear interpolation. The microstructural parameters areas, in which the value of the mechanical characteristics could be predicted, are outlined. [ABSTRACT FROM AUTHOR]