Abstract
This work presents the results of an electro-discharge machined ceramic composites consisting of a base non-conductive ceramic component such Al 2 O 3 , to which is added sufficient amounts of an electro-conductive ceramic nanoparticles such as TiC, TiNC, NbNC, TaNC, and SiC (whiskers) to achieve an electrical resistance of less than about 100W.cm. With these compositions intricate geometries and features as holes, chamfers, slots, angles, changing radii and complex curves can be electro-discharge machined (EDM) into the ceramic body after Pulsed Electrical Current Sintering (PECS) to achieve maximum density and mechanical properties. In EDM, the electrically conductive workpiece or ceramic blank is eroded by electric discharges or sparks which on a small scale generate localized shock waves and intense heat.The four compositions studied were in the same proportion for all raw materials: alumina 42 (vol %) + conductive material (TiC, TiNC, NbNC, and TaNC) 22 (vol %) + SiC w 36 (vol %). Processing was carried out mixing raw materials in the suitable proportions in a polypropylene container with zirconia balls and isopropanol media for 72 hours in order to guarantee the homogeneity of the final compositions. The powders were dried and introduced into a PECS furnace for sintering to 1650°C (100 MPa/2 min). The diameters of the pieces obtained were 20 and about 40 mm and 7 mm thickness.SiC whiskers reinforced electrically conductive ceramic compositions provide a fully dense material with optimal mechanical properties. The capability of electro-discharge machining obtains good surface quality, chip-free edges, dimensional accuracy and complex shapes. The fracture toughness is improved two to three fold over individual ceramic components. Strength and hardness is also increased. Some composites were tested as a cutting tool to machine IN-718 nickel-base superalloy industrial laminating cylinders. The composites were formed and electro-discharge machined to a standard size cutting insert.
Highlights
Materials for cutting tools inserts fall into several well-known categories
We present results of the mechanical behaviour of several compositions of a base nonconductive ceramic component such as Al2O3 to which is added sufficient amounts of several electroconductive ceramic components such as TiC, TiCN, TaCN, NbCN to achieve an electrical resistance of less than about 100 ohm centimeters specific resistance
The following raw materials were used as starting powders: 1) TM-DAR grade D-Al2O3 powder (Taimei Chemicals Co., Japan) with a specific surface area of 14.6 mgr-1 and an average grain size of 150 nm; 2) Titanium carbide (TiC) from Hubei Minmetals Trading Corporation Limited (China) with an average grain size of 40 nm; 3) XCN (X=Ti, Nb, Ta) of nanometric grain size synthetized by mechanically induced selfsustaining reaction (MSR) following the procedure of Córdoba, et al [9]; 4) Silicon carbide whiskers (SiCw) from Tokai (Japan)
Summary
Materials for cutting tools inserts fall into several well-known categories These include high speed steels, cast alloys of cobalt and chromium, sintered carbides and ceramic materials such as alumina. Ceramic materials are used in especially difficult applications They have high hardness, chemical inertness and wear resistance even at elevated temperatures. Main trends in research of ceramic materials are shifting from high purity single phase like Al203 to multiphase composite ceramics, and nowadays extensive research is done to identify all the combinations which would satisfy the requirements: high hardness, high toughness, high temperature resistance and inertness toward machining part. The main advantage of EDM is the machining of ceramics is its ability to produce high-complexity shapes, independently of the mechanical properties of the material (hardness, brittleness, flexural strength, etc.). The combination of mechanical activation and the SPS has been shown to be suitable for the production of materials having nanostructure and a controlled consolidation level
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