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Dense silicon carbide (SiC) composites with 0–30 vol% (ZrN-TiB 2) were fabricated by using liquid phase spark plasma sintering at a relatively lower sintering temperature (1800 °C) and shorter holding time (5 min). The effects of co-addition of ZrN and TiB 2 on densification, mechanical properties, and electrical conductivity of SiC ceramics were investigated. The reinforcement significantly enhanced density of sintered composites, while the phase analysis and microstructure confirm the suppression of β→α phase transformation in the SiC matrix. The fracture toughness ranged from 4.1 to 4.6 MPa·m0.5, hardness from 19.5 to 20.3 GPa, and electrical conductivity from 4.85 ×101 to 1.25 ×103 (Ω·cm)−1. Incorporating conductive reinforcements and nitrogen additives enhanced electrical conductivity. Successful wire-EDM cutting of SiC-ZrN-TiB 2 composites demonstrate the feasible alternative to conventional machining of non-oxide ceramics with a maximum material removal rate of 8.54 mm2/min. [Display omitted] [ABSTRACT FROM AUTHOR]

High electrical conductivity and low thermal conductivity are beneficial for the electrical discharge machining performance of ceramics. In this work, B 4 C–TiB 2 composites were prepared by spark plasma sintering of B 4 C–TiC–B powder mixture. The chemical reaction between TiC and B, together with subsequent selective matrix grain growth, expelled small in-situ generated TiB 2 grains to form conductive interlayers around large B 4 C grains. The unique microstructure significantly enhances the electrical conductivity of B 4 C–TiB 2 composites, especially at low TiB 2 content, while the ultrafine in-situ formed TiB 2 grains endow the composites with low thermal conductivity. The effects of TiB 2 content on the microstructure, mechanical properties, thermal & electrical conductivity of the composites were investigated. B 4 C–20 vol% TiB 2 composite exhibits excellent comprehensive performance, including a relative density, Vickers hardness, flexural strength, fracture toughness, room electrical and thermal conductivity of 98.6%, 28.15 GPa, 656 MPa, 5.46 MPa⋅m1/2, 1.08 × 105 S/m and 19.37 W/m⋅K, respectively. [ABSTRACT FROM AUTHOR]

Boron carbide (B 4 C) composites containing 0–10 wt.% graphene nanoplatelets (GNPs) were consolidated using hot pressing at 1950 °C for 60 min under 30 MPa in an argon atmosphere. Their electrical discharge machining (EDM) characteristics were evaluated for the first time. Additionally, the effects of GNPs on the microstructure, electrical conductivity, material removal rate (MRR), and surface roughness (R a) of B 4 C composites were investigated. The results show that the B 4 C composite containing 10 wt.% GNPs exhibited the highest electrical conductivity of 4997 S·m−1 because of the formation of GNPs conductive networks. Under a fine machining condition, the MRR of the B 4 C composite was enhanced by 43.5 % (from 6.55 to 9.40 mm3 min−1) compared with that of monolithic B 4 C. Furthermore, the R a decreased to 1.12 μm, which was significantly lower than that of pure B 4 C (2.44 μm). Scanning electron microscope and energy disperse spectroscopy analysis of the EDM surfaces were used to determine that the main material removal mechanisms for B 4 C composites with less than 2 wt.% GNPs were spalling and melting. As the GNPs content increased, B 4 C grain fallout, melting, and evaporation became more dominant. The other mechanisms, including thermal shock and oxidation, are also discussed in detail. [ABSTRACT FROM AUTHOR]

Alumina zirconia (ZTA) ceramics can be made electric discharge machinable by addition of a percolating network of an electrically conductive phase. In this study the influence of NbC content on the mechanical and electrical properties as well as the ED-machinability of ZTA-NbC ceramics containing 17 vol.% zirconia and 24–32 vol.% NbC were investigated. Samples were hot pressed from mixed and milled starting powders. Surface morphology and surface roughness of wire electrical discharge machined surfaces were studied by SEM and perthometry. Cutting speed was determined to benchmark the ED-machinability. Rising NbC contents progressively impede sinterability. Maximum strength, Young’s modulus and hardness were found at intermediate NbC contents. Conductivity evidently rises with NbC content, the cutting performance showed an adverse tendency. The surface quality of the materials was improved by increasing the content of conductive phase. Additional trimming operations can reduce the mean roughness of machined surfaces to 1 μm. [ABSTRACT FROM AUTHOR]

This paper describes the observation of EDM gap phenomena through a transparent electrode from the direction normal to the machining surface using a high-speed video camera. To visualize the gap, SiC single crystal was used as the electrode material since it is optically transparent and electrically conductive. It was found that more than 70% of the working surface was occupied by bubbles generated by discharge after a few hundred pulse discharges from the start of machining. Electrical discharge occurs not only in liquid but also in bubble and at the boundary between liquid and bubble. The probability of discharge occurrence per unit area of each atmosphere was highest at the boundary between liquid and bubble. Furthermore, the probability of discharge occurrence through debris particles located at this boundary generated by the last discharge was highest. [ABSTRACT FROM AUTHOR]

An electrically conductive SiC ceramic was fabricated via hot-pressing a 72.6 wt% β-SiC, 7.6 wt% polysiloxane, 4.3 wt% phenol resin, and 15.5 wt% yttrium nitrate powder mixture. It was machined into 300-μm-thick cylindrical specimens (YN-SiC) with diameters of 3 mm. The micro-electrical discharge machining characteristics such as the number of shorts, machining time, entrance clearance, material removal rate (MRR), and debris size of the conductive SiC ceramic were compared to those of SUS304. The number of shorts for SiC was smaller than that of SUS304 because of its low electrical conductivity. As the unit discharge energy increased, the debris size and its standard deviation for YN-SiC increased, while those of SUS304 decreased. The machining time for the SiC was longer than that of SUS304 because of the increase in the number of shorts at a small discharge energy. It was also found that the entrance clearance of the SiC was the smallest at a unit discharge energy of about 7 μJ. The MRR was inversely proportional to the machining time. [ABSTRACT FROM AUTHOR]

Highlights: [•] Successful preparation of MMCs having adequate conductivity for EDM application. [•] Study on influence of process and material parameters on multiple responses. [•] Proposes a novel methodology for simultaneous optimization of multiple responses. [ABSTRACT FROM AUTHOR]

Highlights: [•] The circuit of semiconductor EDM is a typical circuit with reverse-biased diode and linear resistance in series. This circuit has three typical parameters: breakdown point, conduction angle, and breakdown angle. [•] Two diodes exist in the equivalent circuit with two metal electric feeders. One diode is forward-biased and the other is reverse-biased. The loop current will improve if the diode with larger contact area is under reverse bias. [•] The discharge voltage of semiconductor EDM is almost the same with the no-load voltage. The body resistance also decreases, which results in the continuous increase of the discharge current. [•] The nature of the plasma channel of semiconductor EDM is similar to that of metal EDM, which can be regarded as a 20V voltage regulator tube. If the work piece is connected to anode in semiconductor EDM, the diode in the conduction side is reverse-biased and the avalanche voltage is only 42V. If the work piece is connected to the cathode in semiconductor EDM, the diode in the discharge side becomes reverse-biased. The temperature in the arc plasma side is high, causing the breakdown voltage to be much higher than the theoretical calculation value 88.5V. [•] Favorable conditions for spark generation could be achieved and the process efficiency could be improved if positive polarity discharge is adopted for P-type silicon. [ABSTRACT FROM AUTHOR]

Abstract: Electrical Discharge Machining (EDM) has emerged as an outstanding approach for cutting conductive metals that are otherwise difficult or impossible to be cut with traditional machining [1]. Moreover, a survey of literature has found that a little of work was carried out in the direction of achieving optimal levels of machining parameters for the super alloy Inconel 718, among other super alloys, which are otherwise difficult to machine. The objective of the present work was to investigate the effects of various EDM input parameters as well as the influence of different tool geometry on Material Removal Rate(MRR), Tool Wear Rate(TWR) and Surface Roughness(SR) on machining of Inconel 718 material by using copper electrode. Five EDM parameters, namely pulse on time (TON), pulse off time (TOFF), peak current (A), flushing pressure (P) and electrode tool geometry (Geo), were considered here. Tool geometry of the electrodes was circle (C), square (S), rectangle (R) and triangle (T). Four different levels for the five input parameters were planned as per the L16 orthogonal array. The parameters were optimized using multi-objective optimization technique of desirability approach and the significance of each parameter was analyzed by Analysis Of Variance (ANOVA). In addition, Fuzzy Logic Model (FLM) was used to better understand the input and output responses. With the desirability approach, it was sought to optimize the values for copper electrode for maximum MRR and minimum TWR and SR. Overall, the rectangular tool geometry emerged successful. A comparison of the performances of the electrode by desirability approach and ANOVA showed that the current was the most influencing factor, followed by pulse on time and pulse off time. It was also observed that the rectangular tool geometry provided better results as compared to other tool geometries. Validation tests for FLM were carried out and show closer relationship with the experimental results. [Copyright &y& Elsevier]

Abstract: The interrelationships between the microstructure and electrical discharge machining (EDM) behaviour of B4C–TiB2 composites with respectively 30, 40 and 60vol.% TiB2 are investigated. Special attention was given to the influence of the grain size on the EDM behaviour by producing composites with an ultrafine TiB2 phase using in situ synthesis during PECS. The experimental work revealed that 40vol.% of TiB2 results in an optimal material removal rate while the surface roughness for rough cut EDM decreases with increasing TiB2 content. The finer microstructure of the ultrafine composite shows higher MRR''s and lower R a values than the commercial powder based composites. The major material removal mechanism for the PECS based composites was melting. The 3 point bending strength of all composites after grinding, EDM rough cut and EDM finish cut was not statistically different and about 800MPa. The EDM recast layer was analysed by X-ray photoelectron spectroscopy. [Copyright &y& Elsevier]

Conductive TiN/Si3N4 hot pressed composites were processed by electrical discharge machining (EDM) and their microstructure and conductivity investigated. The dependence of surface texture, surface roughness, and materials removal rate on electrical discharge machining conditions including working voltage and feed rate were also analyzed. The flexural strength and strength reliability in terms of Weibull modulus of TiN/ Si3N4 processed by EDM and conventional cutting and polishing are compared. Higher working voltage and current, as well as higher content of TiN result in greater material removal rate. Comparison of the flexural strength and Weibull modulus of the composites processed by EDM with conventional polished samples revealed that the surface with low roughness lead to an increase in strength and reliability for electrical discharge machining. [Copyright &y& Elsevier]