Surface modification by γ-electrochemical selective dissolution for improving nickel-based superalloy machinability

A strategy to adjust mechanical properties and improve machinability of nickel-based superalloys by γ-electrochemical selective dissolution surface modification was proposed in this paper. Firstly, a new γ-electrochemical selective dissolution process using NaNO₃ electrolyte was developed through theoretical and experimental analyses. Then, the surface modification effect and mechanism of the new γ-electrochemical selective dissolution process were investigated. The results showed that during the γ-electrochemical selective dissolution process, γ' in nickel-based superalloy remained undissolved due to its stable protective film riched in Al₂O₃ and Al(OH)₃, while γ dissolved due to the broken of its protective film riched in Cr₂O₃ and Cr(OH)₃. The dissolution of γ caused the nickel-based superalloy surface layer to be modified into a porous structural layer, resulting in an effective reduction of material microhardness. Finally, the effect of γ-electrochemical selective dissolution surface modification on material machinability was studied by milling experiments. The results demonstrated that the γ-electrochemical selective dissolution surface modification can significantly reduce both cutting force and tool wear. The proposed γ-electrochemical selective dissolution surface modification strategy may have promising application prospects in the high-efficiency manufacturing of nickel-based superalloys.