Preliminary study to determine the sintering stress from microstructural analysis of green parts

Abstract

Solid-state sintering theory predicts shrinkage kinetics assuming the two-sphere model. Spheres are of equal diameter, undeformed and smooth. The actual condition of powder particles in cold compacted green parts deviates very much from this model: particles have a broad size distribution and an irregular surface profile, they are not spherical and plastically deformed. Therefore the sintering stress cannot be directly correlated to the particle radius, as made in the two-sphere model. The actual neck curvature radius should be therefore determined. In this work, a first attempt to determine sintering stress experimentally is presented. Iron green parts produced by cold isostatic pressing were pre-sintered in order to provide a minimum consolidation avoiding densification. By means of image analysis, the microstructure was investigated to characterise the particle and the pore morphology, and in particular their profiles. A geometrical model of the pore morphology was proposed, from which the radii of curvature in correspondence of the neck regions may be calculated.

Keywords:

• Sintering stress
• Green parts