Electrochemical micromachining of passive electrodes - Application to bulk metallic glasses

Electrochemical micromachining (ECMM) is a method for micro-forming of metallic materials independent of their hardness and without inducing significant heat into the work piece. Thus, it appears to be well suited for micro-shaping of bulk metallic glasses (BMGs). On the example of a Fe-based BMG, Fe65.5Cr4Mo4Ga4P12C5B5.5, the capability of ECMM exploiting the transpassive dissolution regime is discussed. The glassy alloy exhibits spontaneous passivity in aqueous acidic electrolytes. Due to its low Cr content the electrochemical behaviour during the ECMM is not comparable to that of stainless steel and therefore, established experimental conditions are not applicable. The electronic behaviour of the ECMM setup is discussed in relation with the electrochemical reactions during the machining. Resultant, different ways of machining the glassy Fe65.5Cr4Mo4Ga4P12C5B5.5 alloy in an aqueous acidic electrolyte are derived and ways to enhance the electric efficiency are discussed: the addition of an oxidant to the machining electrolyte and the application of a Schottky diode in the electronic setup.