Electrical Discharge Machining Non-Conductive Ceramics: Combination of Materials

Abstract

One of the promising processing methods for non-conductive structural and functional ceramics based on ZrO2, Al2O3, and Si3N4 systems is electrical discharge machining with the assistance of an auxiliary electrode that can be presented in the form of conductive films with a thickness up to 4–10 µm or nanoparticles - granules, tubes, platelets, multidimensional particles added in the working zone as a free poured powder the proper concentration of which can be provided by ultrasound emission or by dielectric flows or as conductive additives in the structure of nanocomposites. However, the described experimental approaches did not reach the production market and industry. It is related mostly to the chaotic development of the knowledge and non-systematized data in the field when researchers often cannot ground their choice of the material for auxiliary electrodes, assisting powders, or nano additives or they cannot explain the nature of processes that were observed in the working tank during experiments when their results are not correlated to the measured specific electrical conductivity of the electrodes, particles, ceramic workpieces or nanocomposites but depends on something else. The proposed review includes data on the main electrophysical and chemical properties of the components in the presence of heat when the temperature in the interelectrode gap reaches 10,000 °C, and the systematization of data on ceramic pressing methods, including spark plasma sintering, the chemical reactions that occur in the interelectrode gap during sublimation of primary (brass and copper) and auxiliary electrodes made of transition metals Ti, Cr, Co, and carbon, auxiliary electrodes made of metals with low melting point Zn, Ag, Au, Al, assisting powder of oxide ceramics TiO2, CeO2, SnO2, ITO, conductive additives Cu, W, TiC, WC, and components of Al2O3 and Zr2O workpieces in interaction with the dielectric fluid - water and oil/kerosene medium.

Wire Tool Electrode Behavior and Wear under Discharge Pulses

“…The occurred conditions are close to the conditions of lightning formation [20]. The temperature in the interelectrode gap achieves high value in a microsecond [21][22][23].…”

Electrical Discharge Machining of Oxide Nanocomposite: Nanomodification of Surface and Subsurface Layers

“…Powders were preliminarily mixed in a multidirectional Turbula shaker mixer (Eskens B.V., Alphen aan den Rijn, The Netherlands) in ethanol at 150 rpm for 24 h. Lyophilizer FreeZone2.5 (LabConco, Kansas, MO, USA) was used for drying of the slurries to avoid TiC agglomerates in the ceramic matrix and additional sieving [7,8]. The collector temperature was of 50 ± 2 • C, the shell temperature was of +23 ± 2 • C; the chamber pressure was of 0.02 ± 0.01 mbar.…”

“…Electrical discharge machining is a well-known technology used for processing conductive materials [1][2][3][4], while there are always developed techniques to subject the non-conductive material to electroerosive wear [5][6][7][8]. However, these techniques do not show any outstanding results due to small volumetric performance and expensive assisting materials-nanoparticles of precious or rare materials, labor-intensive techniques of conductive layers applications, etc.…”

“…It reacts with oxygen (×6) and with the formation of alumina and carbon dioxide (×3) at 650-700 • C due to its higher electronegativity (χ = 8.11 for oxygen and 5.19 for carbon). It should be noted that all acetylides are not stable at normal conditions and can explode even with a tiny move (Au 2 C 2 , the best known as initiating explosives are silver and copper acetylides-Ag 2 C 2 , Cu 2 C 2 ), and they exhibit dielectric properties [8].…”

Synthesis and Evaluation of Strengthened Copper with 3 wt. % TiC and/ or Al2O3 Prepared By SPS Technique

“…A high pulsed direct current flows through the powder material, which activates the sintering reaction. Micro-spark discharges occur in the spaces between powder particles, and plasma is generated [12]. These discharges remove absorbed gases and oxide films on powder particles [12].…”