The effect of electrospark deposition using zirconium electrodes on structure and properties of nickel-containing alloy obtained selective laser melting

Abstract

Protective coatings were applied by electrospark deposition (ESD) using zirconium electrodes to improve the performance of the Ni-containing alloy obtained using the selective laser melting (SLM) technology. The kinetics of mass transfer was studied in 5 different frequency-energy processing modes. An analog-to-digital converter was used to determine the average number of pulse discharges, single-pulse energy, and the total energy of pulse discharges for 1 min of processing (ΣЕ) for all the modes used. In low-energy processing modes (ΣЕ = 1459÷2915 J), a weak mass transfer was observed, and the cathode weight gain was recorded only in the first minutes. As the processing time increased, a decrease in the substrate weight was observed. The roughness of coatings (Ra) varied in the range of 3.9–7.2 μm. In high-energy modes (ΣЕ = 5197÷17212 J), due to intense electrode heating, a steady cathode weight gain was observed, but the formed coatings featured by increased roughness: Ra = 7.4÷8.6 μm. The Ra parameter for the original SLM samples was 10.7 μm. The formed coatings featured by a thickness of 15–30 μm, high continuity (up to 100 %), hardness of 9.0–12.5 GPa, elastic modulus of 122–145 GPa, and friction coefficient of 0.36–0.49. The ESD processing promoted an increase in wear resistance of the SLM alloy by 7.5–20 times, and oxidation resistance by 10–20 % (t = 1150 °C, τ = 30 h). It was found that the coating obtained in the low-energy ESD mode with energy ΣЕ = 2915 J featured the best performance (hardness, modulus of elasticity, roughness, wear resistance and oxidation resistance).