Anodic Dissolution Behavior of DD6 Nickel-Based Single Crystal Superalloy for Electrochemical Machining Applications

Abstract

Abstract Nickel-based single crystal superalloys have been widely used in turbomachinery components. Electrochemical machining (ECM) is an essential method for shaping such high-performance alloys. Understanding the fundamentals of ECM for these alloys is crucial for the design and optimization of the process. This study investigated the anodic dissolution of DD6 nickel-based single crystal superalloy in concentrated NaCl and NaNO3 electrolytes under ECM conditions. Polarization curves showed a passive-transpassive transition behavior in both electrolytes. Galvanostatic experiments demonstrated unique current efficiency characteristics contradicting the empirical ECM knowledge. Surface analyses revealed that the anomalous current efficiency of >100% in the NaNO3 electrolyte results from the falling of γ’ phases from anodic surfaces due to the preferential dissolution of the γ matrix phase. The transition from selective to uniform dissolution with increased current density and reduced electrolyte flow velocity leads to decreased current efficiency in NaNO3 electrolyte. The removal of both γ and γ’ phases depends entirely on electrochemical dissolution in NaCl electrolyte, ensuring that current efficiency maintains a normal value. A schematical anodic interface model was proposed to describe the dissolution behavior.