Hot-Pressing and Hot-Forging of Polycrystalline Powder Particles with Unique Microstructures

Abstract

The kinetics of hot pressing and the resulting microstructure of two types of polycrystalline spherical powders (beads) were studied. The first were spherical ZrO2 beads synthesized by sintering TOSOH spray dried ZrO2 powder loose in a crucible. The average bead diameter was 51 μm and contained 0.3 μm grains. The second were Al2O3-ZrO2(1%Y2O3) synthesized by plasma spraying spray dried powders into water to quench-in a partially amorphous, partially nanocrystalline structure. The particle size was <25μm. Densification in both cases depended on creep of the beads and densification rates at 1350°C were predicted well both by equations from Helle et al.[1] for hot isostatic pressing and a finite element analysis method. The microstructure of the Al2O3-ZrO2(1%Y2O3) was much more complex but densification kinetic also followed the Helle et al.[1]equations if creep data from hot pressed specimens of the same powder were substituted into the equations rather than literature values.