Surface modification of nickel-based superalloy by electrochemical selective dissolution

Abstract

In order to improve the poor machinability of nickel-based superalloys, a new strategy, the surface modification of nickel-based superalloys to remove the γ' phase in the surface layer, was proposed in this paper. A new electrochemical selective dissolution process using NaCl electrolyte was developed through theoretical analysis combined with testing and applied for surface modification. The results showed that in the NaCl electrolyte, the Cr-rich γ matrix is protected from electrochemical dissolution by a stable Cr-passive film, while the Al-rich γ' phase is exposed to electrolyte and undergoes electrochemical dissolution because the Al-passive film on its surface is eroded into AlCl3 by the Cl- ions. Through the electrochemical selective dissolution, the surface layer of nickel-based superalloy was modified into a low-hardness porous layer composed of the undissolved γ matrix, and its thickness can be well controlled by adjusting electrochemical corrosion time or electrolyte concentration. This study provides an effective pretreatment method for nickel-based superalloys to reduce the machining difficulty.