Abstract
The change in dimensions of some atomized powder compacts, 10φ×h10 mm in size, was measured with a micrometer during the production process, after pressing at 2-8 t/cm2 (196-784 MPa), after de-waxing at 500°C (773 K) for 30 min, and after sintering at 900°C (1173 K) for 5180 min. Cubes, 10 mm in size, of the compacts were also prepared as above, and used for the dilatometry.
No relation was found between the sum of the expansion by spring-back and de-waxing, and the shrinkage during sintering. A remarkable swelling appeared during de-waxing and initial sintering in atmospheres containing H2 regardless of the content of the powder lubricant. This is probably due to the pressure of the water vapour formed in reducing the oxide. Although the swelling was larger in the pressing direction than in any others, the shrinkage during sintering after the swelling was almost isotropic. The swelling seems to be the major cause of the anisotropy in the dimensional changes obtained from the sizes of green and sintered compacts.
