An experimental study of the sintering kinetics of tungsten powder has been made in the temperature range 1100-1600°C. The effects of particle size, compacting pressure, sintering atmosphere, sintering temperature and sintering time upon the rate of sintering were examined.
Isothermal changes in the length, volume and density of the compacts were measured and the results were evaluated in terms of the usual degree of sintering parameter, δ , a new volume parameter, V, and by the linear shrinkage method. Of these parameters, it was found that the most reliable information was obtained by use of the volume parameter.
It was found that the activation energy for sintering tungsten powder was 102 ± 2 kcal/mole which is consistent with a mechanism which involves grain boundary diffusion. The increase in fine particle size of the tungsten powder increases the sintering rate.
The kinetics of isothermal grain growth during sintering were also examined in the temperature range 1100 to 1650°C. No grain growth was observed at temperatures below 1400°C,however, above this temperature the grain diameter increased at a rate proportional to sintering time, t 1/3. The activation energy of 94 kcal/mole obtained for this process is in reasonable agreement with that derived for densification.
The sintering of tungsten powder in the presence of a nickel - copper binder phase was examined in the temperature range 1200 to 1600°C. The effects of compacting pressure, particle size, volume of liquid binder phase, the composition of the binder phase and the sintering temperature and time were evaluated.
The kinetics were examined in terms of the volume parameter and it was found that as the concentration of binder phase was reduced from 11% to 7% the apparent activation energy increased from 69 to 80 kcal/mole. These activation energies are consistent with a solution precipitation mechanism.
The average growth of tungsten particles was examined as a function of sintering time in W - 3 Ni - 8 Cu and W - 7 Ni - 4 Cu alloys at temperatures between 1200 and 1500 °C and it was found that the mean grain size increased at a rate which was proportional to sintering time, t 1/3, The activation energy for grain growth measured by this technique is 67 kcal/mole in both systems and is in good agreement with those of 68 kcal/mole determined by the Greenwood 119 equation and 70 kcal/mole derived for liquid phase sintering experiments carried out under the same conditions.