Investigation of the electrochemical dissolution behavior of tungsten during electrochemical machining

Abstract

With the advantageous properties of a high melting point, high strength at high temperatures, low vapor pressure, and good thermal conductivity, tungsten is widely used in several advanced industrial applications. Micro structures such as micro holes and grooves are commonly prepared on the tungsten surface to enhance its heat transfer performance. Electrochemical machining (ECM) is a promising method of generating micro structures on the metal surface. Typically, an alkaline solution is employed as an electrolyte during tungsten ECM. Unfortunately, significant stray corrosion commonly occurs on the tungsten surface when high-concentration alkaline solutions (NaOH > 1 wt.%) are used. However, the machining efficiency decreases sharply when the concentration is less than 0.5 wt.%. In order to improve machining efficiency and accuracy, this paper proposes a novel mixed electrolyte consisting of NaClO3 mixed with a low concentration of NaOH for electrochemical machining of tungsten. The NaClO3 is used to increase the conductivity as well as to improve the formation of oxide films on the tungsten surface in order to avoid stray corrosion. NaOH is used to ensure continuous machining by removing the oxide film in the region being machined. The influence of the electrolyte composition and concentration on electrochemical dissolution of tungsten is analyzed by measuring the anode polarization curve and open circuit potential, and an optimized electrolyte with of 10 wt.% NaClO3 and 0.3 wt.% NaOH is identified. This optimized electrolyte enables generation of micro-through holes with inlet and outlet diameters of 500 and 410 μm, respectively, using a tube electrode with a diameter of 250 μm. The feed rate of the tool reaches 24 μm/min, which is 4 times faster than in previous studies.