Analysis of Dimensional Changes During Sintering of Fe—Cu

Abstract

The dimensional changes of Fe–Cu compacts during sintering are of considerable interest for the production of sintered parts. Previous investigations of the swelling and shrinkage behaviour were mostly based on dilatometric measurements and led to partially contradictory results. In the present investigation Fe and Cu powders of ideal sphericity were compacted to densities of up to 93%, sintered for different times, and then rapidly cooled. The simultaneous measurement of density and microstructural parameters permitted the quantitative distinction of the swelling mechanism of Fe–Cu compacts into four main contributions; I penetration of the melt between Fe particles and II along the grain boundaries; III diffusion of Cu into the Fe particles from the particle surface; and IV diffusion of Cu into the Fe grains from the grain boundaries. Whereas the penetration between the Fe particles is the result of pure capillary forces the penetration along grain boundaries is thought to be a special case of solution-reprecipitation.

Particle rearrangement during sintering of Fe–Cu compacts could be separated into two stages. Primary particle rearrangement, just after the melt phase occurs, leads to rapid densification of loose packed and slightly compacted specimens. In highly compacted specimens it can be neglected. The penetration of the melt along the grain boundaries leads to disintegration of the Fe particles, which enables densification by rearrangement of the individual grains of the Fe particles.