Micropatterning of Fe-based bulk metallic glass surfaces by pulsed electrochemical micromachining
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A new technique for micropatterning Fe-based bulk metallic glass surfaces is reported. The transpassive dissolution process is utilized for a defined localized material removal when using a pulsed electrochemical micromachining process. By applying submicrosecond pulses between a work piece and a tool electrode, microholes of high aspect ratio and depth of up to 100 lm can be machined into the bulk glassy Fe65.5Cr4Mo4Ga4P12C5B5.5 alloy. Two potential electrolytes are identified for the machining process. For these electrolytes, different reaction mechanisms are discussed. The possibility of machining more complex structures is demonstrated for the most promising electrolyte, a methanolic H2SO4 solution. The impact of the process parameters, pulse length and pulse voltage, on the machining gap and the surface quality of the machined structures is evaluated. I. INTRODUCTION
Bulk metallic glasses (BMGs) are very promising materials for the production of microdevices. They exhibit high strengths and hardnesses and are therefore regarded as attractive structural materials in microelectromechanical systems.1,2 Their outstanding mechanical properties are important for the applications like micromoulds3 or tools for microembossing techniques.4 Soft magnetic glassy alloys based on Fe or Co are, furthermore, the appropriate materials for micrometer-sized yokes in positioning systems2 or magnetic cores.5 However, forming microparts from BMGs is still challenging. In general, thermomechanical forming is a promising technique for shaping them.6–11 Using this method, surface patterning6,7 and the production of microparts8,9 were demonstrated. Nevertheless, this technique exhibits some disadvantages.7,8,10,11 The processing is only possible for glassy alloys exhibiting a wide undercooled liquid region at low temperatures. For thermomechanical processing, a strict temperature and atmosphere control is needed to avoid crystallization and oxidation. Therefore, a shaping technique operating at room temperature might open new possibilities for the utilization of glassy alloys. For crystalline metallic materials, different electrochemical methods operating at low temperatures were a)
Address all correspondence to this author. e-mail: [email protected] b) This author was an editor of this journal during the review and decision stage. For the JMR policy on review and publication of manuscripts authored by editors, please refer to http://www.mrs. org/jmr-editor-manuscripts/ DOI: 10.1557/jmr.2012.347 J. Mater. Res., Vol. 27, No. 23, Dec 14, 2012
developed in the past.12 In the electrochemical machining process, the shape of the cathode (tool electrode) is reproduced on the anode (work piece) by a diffusionlimited high-rate anodic dissolution. The current densities in this process can exceed 100 A/cm2, and electrolyte flow rates in the electrode gap of several meters per second are used.12 High machining rates of up to 1 mm/min are achieved. However, the accuracy is limited to about 0.1 mm.13 A more recent development is the pulsed e
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