Study of the Electrochemical Dissolution Behavior of Nitinol Shape Memory Alloy in Different Electrolytes for Micro-ECM Process

Nickel-Titanium alloy (Nitinol) is an excellent shape memory alloy (SMA) for Micro electro-mechanical systems (MEMS) particularly in biomedical applications owing to its three excellent features like shape memory effect (SME), superelasticity, and biocompatibility. The fabrication of micro features on Nitinol SMAs through conventional machining has been challenging due to its temperature-dependent material transformation properties. Micro electrochemical machining (micro-ECM), a nonconventional machining method for conductive material irrespective of strength and hardness has the potential for microfeature fabrication on Nitinol. This study presents the investigation on electrochemical dissolution behavior of Nitinol in different electrolytes for micro-ECM. The influence of electrolytes on the nature of dissolution of Nitinol has been studied by fabricating microchannels in three levels of parameters containing applied voltage and electrolyte concentration. The first three electrolytes were all aqueous neutral electrolytes i.e. sodium chloride (NaCl), sodium nitrate (NaNO3), and sodium bromide (NaBr). For profound analysis of dissolution behavior and its influence on machining performance, potentiodynamic polarization (PDP) tests of Nitinol were performed in aqueous NaCl, aqueous NaNO3, and aqueous NaBr solutions. The PDP tests that are conducted here are cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The three aqueous solutions were utilized for microchannel fabrication in Nitinol through micro ECM in three levels of parameters out of which aqueous NaNO3 was successful in fabricating microchannel. Then nonaqueous electrolyte of ethylene glycol-based NaNO3 has been used to fabricate microchannels with lower depth overcut (DOC), width overcut (WOC), and length overcut (LOC) with respect to aqueous NaNO3 electrolyte.