Microstructural Characteristics of Al 4 C 3 Phase and the Interfaces in Al/Graphene Nanoplatelet Composites and their Effect on the Mechanical Properties

It has been thoroughly investigated Al 4 C 3 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 Al 4 C 3 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 Al 2 O 3 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.