The scientists of the Institute of Problems in Mechanical Engineering of the Russian Academy of Sciences (IPMash RAS), Peter the Great St. Petersburg Polytechnic University (SPbPU) and the Institute of Metal Research (Shenyang, China) created the world's first reliable model for predicting plastic deformation of graphene-reinforced metal alloys, which showed the importance of the graphene distribution pattern, and also revealed that the addition of graphene can increase the strength of some alloys by up to 50%.

The results of the study were published in International Journal of Solids and Structures.

Almost all the metals, which surround us, are alloys: steel, bronze, aluminum alloys, etc. The materials of which the supporting elements of structures and machines are made are called structural. Their main task is to carry a mechanical load. Studying the deformation of these metals is important for understanding how the metal will behave under load, under what stresses, how much and with what peculiar features it will deform.

The scientists have studied the composites based on metal alloys with graphene as a filler, that is, a strengthening element.
Graphene is one of the promising materials, which is a two-dimensional allotropic modification of carbon formed by a layer of carbon atoms one atom thick and with very high mechanical strength.

It was decided to strengthen with graphene the so-called “aging” alloys, in which secretions occur during heat treatment. These secretions are the hardening particles in actual fact which increase the strength of the alloy significantly and affect other mechanical properties. Such alloys have been known for a very long time and are widely used in industry.

“In our work, we theoretically obtained the so-called tensile stress-strain diagram (the dependence of the tensile stress on the tensile strain) in a wide range of deformations; practically before the beginning of the fracture process. The analysis of this diagram makes it possible to understand what mechanical properties the analyzed material has: its strength, how plastic it is or, conversely, brittle, etc.”, — told Sergey Bobylev, a leading researcher at the IPMash RAS Laboratory of Nanomaterial Mechanics and Defect Theory, Chief Researcher at the Laboratory of Mechanics of New Nanomaterials at SPbPU,

“In our work, we investigated different configurations of the composite, where the parameters of graphene varied, namely: its total amount (concentration), the nature of its distribution in the volume of the material (graphene may be located along the grain boundaries, may be inside the grains, or may be there and there in different proportions) and the geometric characteristics of graphene inclusions (dimensions). Of course, the parameters of the alloy (its chemical composition, size of secretions, etc.) can also be varied, but the main purpose of the work was to investigate the influence of graphene particularly,” explained Sergey Bobylev.

As part of this work, a theoretical model was created which calculates the mechanical properties of metal alloy/graphene composites with high reliability. This model allows you to predict the properties of composites, that helps to save on expensive experiments. In addition, the theoretical model makes it possible to identify the dependencies, which are non-obvious initially. For example, in this case, the model showed that graphene lying along grain boundaries has a key effect on the strength of the metal alloy/graphene composite, while graphene inside the grains is less important. At the same time, experiments often do not pay any attention to this factor, and many methods of composites manufacture do not even have control over where graphene will end up in the finished sample.
Using the developed model, the efficiency of adding graphene to the Al-4Cu (aluminum-copper) alloy was evaluated. It turned out that the introduction of 1% of graphene (by weight) increases the strength of an alloy by 50%.