Electro Conductive Alumina Nanocomposites From Different Alumina-Carbides Mixtures

Abstract

This work presents the results of an electro-discharge machined ceramic composites consisting of a base non-conductive ceramic component such Al₂O₃, 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.