2001 Volume 48 Issue 1 Pages 77-81
Effect of phase change from unstable phase to stable phase on densification process by pressure sintering was studied by using mechanically alloyed powders. Powder mixtures of Ti and Si having the composition of Ti-37.5mol%Si were milled for 360ks and 3600ks. The latter powder showed homogeneous microstructure and amorphous-like XRD profile, although the former showed (Ti+Si) lamellar microstructure. Milled powders were vacuum hot pressed at a heating rate of 20 K/min up to 1273 K with applying constant pressure from 10 to 200 MPa, then kept for 10.8 ks. It was observed that the density of compacts increases suddenly at the temperature range between 869K and 900K for 3600ks MAed powder. This temperature range showed good agreement with that of the phase formation from amorphous to Ti5Si3. 360 ks MAed powder densified faster during heating stage, however 3600 ks MAed powder obtained higher final density after 10.8 ks holding at 1273 K due to the very fine spherical grains. It is concluded that fine grain superplastic deformation and internal superplastic deformation act an important roll in densification of MA powder having amorphous-like structure.
