A Study on the Sintering of Nickel-bonded Titanium Carbides

Abstract

An experimental investigation of sintering process of nickel-bonded titanium cardides was carried out by means of dilatometric and metallographic methods.Powders of titanium carbide and nickel were ball-milled in addition with methyl alcohol for 25 hours. The average diameters of the particles after ball-milling were 2.5 microns for titanium carbide and 3 microns for nickel, respectively. Powders of seven compositions; 10, 20, 30, 40, 50 and 75 per cent nickel by weight, and titanium carbide only (100 per-cent TiC), were pressed in a graphite mold at 50kg/cm2. The linear shrinkage, during sintering, of the compacted of each powder in the graphite mold was measured in argon atomosphere with a silicon carbide dilatometer. The temperature was raised linearly at the rate of 250°C/hr up to 1500°C and kept there for 1 hour and then cooled linearly at the rate of 250°C/hr. For all compositions except the one of 75 per cent nickel, the shrinkage was slight up to 1200°C, but increased abruptly in the range 1200° to 1350°C. This abrupt shrinkage was attributed to an appearence of liquid phase in the sample. With increase of nickel content, the total shrinkage during sintering increased but the temperature at which the abrupt change begins dropped. Change in linear shrinkage during kept at 1500°C was proportional to logarithm of the sintering time.After the measurement of shrinkage, the sintered compacts were subjected to the metallographic examination. It was confirmed that the shape of carbide particles changed from spheroid to polygone with increased nickel content. The particle size and the “sphericity index” of carbide, however, did not change so much with the composition. The change in shape of the particles in the nickel-bonded titanium carbides may be attributed to the continuity of liquid phase appeared during sintering.