Effect of porosity on the volume changes experienced by Al-Cu compacts during liquid-phase sintering

Abstract

In the Al-Cu system a linear relationship between the end and starting porosities exists only at porosities exceeding 20%. At a smaller pore content the linearity is disturbed by the presence of an irreducible oxide phase on the aluminum particles. Decreasing the starting compact porosity results in greater growth in the first stage of sintering and smaller shrinkage in the second. The extent of the compact growth preceding the shrinkage may markedly exceed that due to copper and aluminum atom diffusion under conditions of uniform reaction of the liquid phase on all the surfaces of the particles. The anomalously large compact growth in the first stage of sintering is due to a negative regrouping of particles resulting from an uneven Kirkendall flow of material inside the particles, bringing about a change in their shape. The extent of shrinkage is not apparently linked with the structure forming during sintering, but depends on the starting porosity. Pores in a compact affect grain growth during sintering by inhibiting it.