In order to establish a suitable technical process of sintering the cermets in a hydrogen molybdenum furnace the cermets of TiC-Co system containing 5 to 30% metallic cobalt as a bond were studied.
Being the early part of the series of our study on the subject, which has been carried out in 1956, some points of the results have to be revised from the present point of view. Nevertheless, it contains some important problems which should be solved before establishing the method of the statistical control.
To begin with, the method of purifying hydrogen reported in the previous paper (Studies on the titanium carbide cermets sintered in a molybdenum furnace of hydrogen atmosphere) was improved for easy operation and control. Then, the relations of the mixing and forming processes to the best sintering temperature were studied. It looks like to be unnecessary to use the pressure more than 3 ton/cm2. Preliminary pressing of mixed powder gave a higher bending strength of the sintered cermet. The longer mixing times as well as the blending more than two grain sizes, has proved to give the better results especially when small amount of metallic cobalt. The best sintering temperature for any specimen containing Co from 5 to 30% may be found out as the points of maximum in the curves representing the relation of the compacting pressure to the transverse rupture strength at different sintering temperatures. The bulk density of the cermet tends to approach to a certain constant value irrespective of the compacting pressure. This value depends only on the Co content as long as the cermet was fired at a temperature near the best sintering temperature. In the present series of experiments the specimen containing 25% cobalt gave the greatest bending strength at room temperature.