Reactive phase formation during electrospark treatment of the EP741NP alloy with fusible Al – Si electrode

Abstract

An appoach for hardening and smoothing surface of a nickel based alloy EP741NP using preparing low-melting structurally homogeneous electrodes by quenching the melt and certain regimes of electrspark treatment was tested. Electrodes with eutectic (Al – 12Si) and hypoeutectic (Al – 9Si) compositions were specially prepared by melt quenching, which aimed structural refinement and chemical homogenization. These electrodes were used for electrspark surface treatment of the EP741NP alloy. The wear resistance of the surface was estimated at tribological tests. It is demonstrated that reactive phase formation, i. e. synthesis of phases that are not present in either the electrode or the substrate, is achievable when applying a longer pulsed discharge during electrospark treatment. In this case, intermetallic phases (Ni3Al, AlCo) form and the surface roughness is low: Ra = 1.98 μm, which is due to plasma sparks smoothening humps and filling in cavities by melt. Smoother layers have higher wear resistance, and a higher severe wear of the counter body is indicative of their high hardness. High-frequency electrospark treatment with shorter pulse discharges leads to reactionless mass transfer of the ductile FCC Al-based solid solution resulting in a complete wear of the modified layers during tribotesting.This research was funded by the Russian Foundation for Basic Research (Project no. 19-58-18022), in part of improving the quality of surfaces obtained by additive technologies using reactive electro-spark treatment and by the Ministry of Education and Science of Russia at frame of a governmental assignment (Project no. 0718- 2020-0034) in part of microscopy investigations of structural and phase transformations.