Perm National Research Polytechnic University, Perm, Russia:

S. A. Oglezneva, Professor at the Department of the Mechanics of Composite Materials and Structures, Director of the Research Center for Powder Materials, Doctor of Technical Sciences, e-mail: ogleznevasa@pstu.ru
S. E. Porozova, Professor at the Department of the Mechanics of Composite Materials and Structures, Doctor of Technical Sciences, Associate Professor
N. D. Ogleznev, Associate Professor at the Department of Innovative Technology in Mechanical Engineering, Candidate of Technical Sciences
M. N. Kachenyuk, Associate Professor at the Department of the Mechanics of Composite Materials and Structures, Candidate of Technical Sciences

Copper and graphite currently serve as electrical engineering materials. For example, either can be used to make electrodes and contacts. Composite materials (including copper-graphite composites) offer better performance — i.e. relative electroerosion resistance and productivity. However, the scope of their application is limited and further research into them is necessary. This research aims to examine the effect of mechanical alloying of the copper – themally expanded graphite powder system followed by spark plasma sintering on the structure of particles and materials and on their physico-mechanical properties. The experimental study into the structure and properties of composite powder materials involved using the methods of X-ray phase analysis, Raman spectroscopy, atomic-force spectroscopy, metallography, spark machining, etc. Powders of high-conductivity copper PMS-1 (per GOST 49-60–75) and thermally expanded graphite produced by Novomet-Sealur were used to make the composite materials. The compositions included 1 wt. % (4 vol. %) of graphite. The process involved mechanical alloying for 1, 2 and 3 hours in a SAND planetary mill (Russia) with the powder-to-balls weight ratio of 1:25. The process resulted in the structural breakdown of graphite and the formation of solid solutions of carbon in copper. Following the process of spark plasma sintering in a Dr. Sinter SPS-1050 unit (Japan) at 900 ^oС, the latter experienced partial decomposition. This paper demonstrates the role of copper in the restoring of graphite structure during mechanical alloying. Copper-based materials have been developed which have lower electrical resistivity than copper. Intercalates formed in graphite may serve as one of probable mechanisms for decreasing the electrical resistivity. A larger copper-graphite phase contat area and a higher deformation degree of graphite during mechanical alloying lead to higher electrical resistivity in composite materials. A correlation was established between the relative spark erosion wear and the electrical resistivity in copper-graphite composite materials. Thus, the relative spark erosion wear of the best compositions was 20–30% lower than in the case of cast copper M1. The feasibility of using copper-graphite EDM electrodes can be reached due to reduced cost of the EDM electrodes that offer high wear resistance combined with higher performance.
This research was funded by the Ministry of Education and Science of Russia under the programme of the World-Class Science & Education Centre Rational Use of Mineral Resources.

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