鉄‐銅圧粉体の燃結時における寸法変化機構

Abstract

Anisotropy of the copper-growth was investigated by a dilatometer. Hoeganaes NC 100.24 iron powder with 5 mass% copper which was precipitated by the substitution process, or admixed as an electrolytic powder, was pressed under 490MPa to form 5mm cubes. The compacts were dewaxed in dissociated ammonia, set in a dilatometer with a support and a detecting rod made of alumina, and heated at the rate of 10K/min up to 1398K and held for 30min in vacuum. The density of the boundaries penetrated by the copper, or the boundary number/length, was measured in a mixed powder compact.Below the Ac3 transformation point of iron, both powder compacts showed shrinking tendencies in the compacting direction. The powders did not differ much from each other in dimensional changes during the Ac3 and the Ar3 transformations and the isothermal holding. The coated powder expanded in the range from the Ac3 point to the melting point of the copper. The expansion by the melting was larger for the mixed powder in both compacting and lateral directions. By adding the presintering process, the copper-growth of the mixed powder compacts was controlled to some extent.