Effect of copper content on the properties of graphite-copper composites formed using the plasma spray process

Graphite-copper composite coatings are often used for the production of electrical machines because they are characterized by stable electrical and mechanical properties. The plasma spraying method was used to form such coatings in this work, as we aimed to evaluate the influence of copper content in the initial powders on the properties of graphite-copper composite coatings. The graphite-copper coatings were deposited on stainless steel and quartz glass substrates, as the copper content of the initial powder ranged from 2 to 60%. As shown by SEM studies, at small amounts of copper (up to 10%) in the initial powder the micro-derivatives of the spherical form are formed on the coatings. Meanwhile, XRD analysis have shown that mechanical stresses due to different thermal expansion coefficients between the coating and the substrate are characteristic for graphite-copper coatings. The measurements of electrical conductivity shown that the maximum electrical conductivity (of 10 S) is obtained when the copper content in the initial powder reaches 20%. Despite the increase of the copper content in the initial powder above 20% the electrical conductivity of the coatings remain constant. The microhardness studies have shown that with the increase of copper content in initial powder from 2 to 60%, the microhardness of graphite-copper composite coatings is reduced by about 2 times, while the plasticity increase from 11 to 19% is observed.