Compaction of ceramic powders

Up-to-date ceramic technology involves invention and design of new components and optimization of production processes of complex structures.

Ceramics can be formed by a variety of different methods which can be divided into three main groups, depending on whether the starting materials involve a gas, a liquid, or a solid.

Examples of methods involving gases are: chemical vapour deposition, directed metal oxidation and reaction bonding.

Since these processes permit an efficient production of parts ranging widely in size and shape to close tolerances, there is an evident interest in industry.

Currently, there is a high production rejection rate, due to the fact that manufacturing technologies are mainly based on empirically engineered processes, rather than on rational and scientific methodologies.

There is therefore a strong interest from the ceramic industry in the availability of tools capable of modelling and simulating: i) the powder compaction process and ii) the criticality of defects possibly present in the final piece after sintering.

Recently, an EU IAPP research project [1] has been financed with the aim of enhance mechanical modelling of ceramic forming in view of industrial applications.

Fig. 1 A piece (formed with M KMS-96 alumina powder) has been broken after mold ejection.
Fig. 2 Micrographs of a M KMS-96 alumina powder. The loose state is shown on the left, while granule arrangements corresponding to Phases I and II of the compaction process are shown on the centre and on the right. Note the plastic deformation of grains visible on the right.
Fig. 3 The hardening process during hydrostatic powder compaction described with the Bigoni & Piccolroaz yield surface.
Fig. 4 A mechanical model of ceramic forming correctly predicts: (left) the load/displacement curve during cold pressing, (centre) the density (void ratio) map within a formed piece and (right) the dark annular region evidenced on the bottom of a formed piece.