SOME OBSERVATIONS ON THE SHRINKAGE BEHAVIOUR OF COPPER COMPACTS AND OF LOOSE POWDER AGGREGATES

Abstract

The relative shrinkage in the radial and in the axial directions of both conventionally pressed copper powder compacts and of loose copper powder aggregates has been determined. Irregular-shaped electrolytic copper powder and flake copper powder were used. The structures of the green and of the sintered compacts and aggregates were examined metallographically. The results led to the tentative conclusion that the theories previously advanced to explain the differences in the axial and radial shrinkage of compacts and aggregates are not correct. The pores of green and sintered compacts of irregular copper powder are not necessarily disc- or lens-shaped, but rather equiaxed, and the observed difference in shrinkage cannot be attributed to the shape of the pores. On the other hand, the ratio of axial to radial shrinkage of irregular-shaped powder and of flake powder aggregates is nearly the same, in spite of the fact that the pores in the flake powder aggregates are much larger in the radial than in the axial direction. The possibility that forces other than surface-tension forces have an influence upon shrinkage behaviour is discussed.