Electrolyte Jet Machining of Titanium Alloys Using Novel Electrolyte Solutions

Electrolyte Jet Machining (EJM) is a non-contact machining process whereby material is removed through highly localised electrochemical dissolution. Throughout the development of this technique, difficulties have been reported in the processing of titanium alloys due to the formation of an electrochemically inert non-conductive passivating layer. In this study, various electrolytes are investigated for the purpose of establishing more stable machining and controlled removal of the passivating layer. Surface finish, material removal rate and pit formations using solutions of sodium halides (bromide, chloride and fluoride respectively) are compared with those obtained using the more commonly used sodium nitrate solution. The concentration of electrolyte is varied in order to appraise the efficacy of each solution. Machined features produced are subject to typical characterisation methods. The removal mechanism for overcoming the passivating layer and the development of more stable machining regimes are explored. Sodium chloride machining is shown to increase mass removal rates by over 100% at concentrations less than 2.5 M compared with that achievable using the commonly used sodium nitrate electrolyte. Doping sodium chloride electrolytes with sodium fluoride decreases the overcut effect in machined pits by half compared with the pits formed in chloride, bromide, and nitrate electrolytes.