Initial-Stage Hot-Pressing Of Monosized Ti And 90-Percent Ti-10-Percent Tic Powders
The kinetics of the initial stage of uniaxial vacuum-hot-pressing of commercially pure spherical titanium powders are investigated for temperatures between 730 and 870-degrees-C and applied pressures from 25 to 50 MPa. Densification kinetics are found to agree with models of Arzt, Ashby and coworkers for hot isostatic pressing by power law creep. The best fit with all data is for a creep exponent of 4.9 and a creep activation energy of 208 kJ mol-1. With the addition to the titanium powder of 10 vol.% TiC powder of same size, the densification rates remain in overall agreement with the same models but become from 5 to 20 times slower. Addition of the inert ceramic particles slows hot pressing kinetics in two ways: (i) by decreasing the initial density of the compact and (ii) by reducing the densification rate at interparticle contacts. It is shown that this latter effect decreases the densification rate by a factor of at most 2 in the present experiments, hence, the former accounts for the significantly larger reductions in densification kinetics observed experimentally.