Optimizing electrochemical micromachining parameters for Zr-based bulk metallic glass

Abstract

Bulk metallic glasses (BMGs) contain a unique combination of enhanced mechanical and chemical properties due to the absence of crystalline features, but their machining processes are still being developed. Electrochemical micromachining (ECMM) with microtool electrodes is a promising technique for microshaping BMGs without the use of elevated temperatures or deformation – both of which can induce crystallization. This work systematically studied the mechanisms and processing parameters responsible for degradation of the material surface allowing the development of a novel protocol for utilizing the ECCM technique for Zr based BMGs. Anodic polarization of Zr57Ni20Al15Cu5.5Nb2.5 BMGs in 2.94M NaNO3 and subsequent microscopy revealed that the primary corrosion mechanism during electrochemical micromachining is pitting. Through chronoamperometry the repassivation potential was determined to be 2.235V. This voltage was used to prevent spontaneous repassivation during electrochemical micromachining. The Taguchi method was used to assess the effect of electrolyte flow rate, duty cycle and pulsed voltage range. Signal-noise ratios and analysis of variance were used to optimize ECMM parameters of the electrochemical micromachining process. Through this method, an electrolyte flow rate of 0.4L/min with a duty cycle of 1:10 and a voltage range of 2.235–3V was determined to yield the optimal holes with respect to the aspect ratio, surface roughness and the rate of electrochemical micromachining of Zr-based BMGs.