Comparative Study of Coatings formed by Electrospark Alloying Using TiC–NiCr and TiC–NiCr– Eu2O3 Electrodes

Abstract

Coatings formed on steel 40Kh by electrospark alloying (ESA) using TiC–NiCr and TiC–NiCr–Eu2O3 electrodes are investigated. The coatings are deposited using an Alier-Metal 303 installation in argon under a normal pressure in the direct and opposite polarity modes. The structure, elemental composition, and phase composition of electrodes and coatings are investigated using X-ray phase analysis, scanning electron microscopy, energy dispersion spectroscopy, glow discharge optical emission spectroscopy, and optical profilometry. Mechanical and tribological properties of coatings are determined by nanoindentation and testing according to the “pin–disc” scheme, including elevated temperature in a range of 20–500°C. The tests for abrasive wear are performed using a Calowear tester, the impact resistance is studied using a CemeCon impact tester, and gas and electrochemical corrosion resistance are studied. The results show that the electrodes contain titanium carbide, the solid solution of nickel in chromium, and europium oxide in the case of a doped sample. Coating also included these phases, but the solid solution is formed based on iron. Coatings with the Eu2O3 additive are not substantially different in regards to structural characteristics, hardness, and friction coefficient, but exceed base coatings by abrasive resistance, cyclic impact resistance, and heat and corrosion resistance. An increase in impact resistance by a factor of 1.2–2.0, a decrease in the corrosion current more than 20-fold, and an almost twofold decrease in the oxidation index are observed upon the passage to doped coatings.