Improvement of copper alloy properties in electro-explosive spraying of ZnO-Ag coatings resistant to electrical erosion

Abstract

The electroerosion resistant coatings of ZnO-Ag system have been obtained for the first time on the surface of the electrical contact of the electromagnetic starter CJ20. The formation of the coatings of ZnO-Ag system was produced due to the processing of the electrical contact surface by plasma formed at electrical explosion of silver foil with the weighed sample of ZnO powder. The nanohardness, Young modulus, wear resistance, friction coefficient and electroerosion resistance of the formed coatings have been investigated. After the electroerosion spraying the wear resistance of the modified layer increases ≈1.3 - fold as compared to the annealed copper. The nanohardness of the sprayed coating is ≈3.8 - fold larger than that of the annealed copper. By the electroerosion resistance the coating is consistent with the requirements of standards. The investigation into the electroexplosion coating of ZnO-Ag system was done by the methods of scanning electron microscopy, transmission electron microscopy and atomic-force microscopy. The structure of the coating is formed by the cells of high-velocity crystallization. The cell dimensions vary within 150 nm–400 nm. The cells are separated by the interlayers of the second phase whose thickness varies within 15–50 nm. Bu the method of atomic-force microscopy the separate particles of ZnO of different shape with size of 10–15 nm located chaotically in the silver matrix were revealed as well as the spherical particles of ZnO with size of 2–5 nm. The total thickness of the coating amounts to 60 nm.