1993 Volume 42 Issue 476 Pages 490-495
Fine alumina powder prepared by an ammonium alum method was encapsulated in a stainless steel mold with the dimensions of O.D. 22φ∼I.D. 10φ×30hmm. The mold containing alumina was preheated at 1200 or 1300°C for about 8 minutes, and then immediately press-forged under uniaxial compressive load. The particle size of the starting powder (0.15μm) grew to about 0.2 or 0.3μm during the preheating, and a modarately dense polycrystal with the grain size of 0.2 or 0.3μm was obtained by the masstransport mechanism promoted during the deformation. The hot-forged polycrystalline alumina, however, did not show satisfactory hardness, because of some stored residual stress around the grain boundary. A polycrystalline alumina with excellent hardness was obtained after annealing the hot-forged body at a relatively law temperature of 1000 to 1100°C for 24 hours. The densification mechanisms of alumina powder during the hot-forging and annealing processes were investigated through microstructural observations by TEM and SEM.
