Identification of densification mechanisms of pressure-assisted sintering: application to hot pressing and spark plasma sintering of alumina

摘要

The identification of densification mechanism during hot uniaxial pressing is developed using an approach based on classical creep investigation. This approach is justified and generalised using continuum mechanics based sintering models. The benefit of this approach is to directly determine the densification parameters from the analysis of shrinkage rates of the porous material, rather than to transpose the creep mechanisms identified for dense material at given thermomechanical conditions to the densification progress. The suggested approach is applied to compare the densification mechanisms involved at the initial stage of sintering (i.e. for 60 % < relative density < 75 %) during hot pressing (HP) and spark plasma sintering (SPS) of a submicrometric alpha-alumina powder. From the stress exponent and activation energy values, it is shown that the main mechanism involves grain boundary sliding accommodated by dislocation motion and particle fracture in both cases. However, it appears that, in SPS, the high heating rate could reduce the existence of surface diffusion phenomena at the beginning of the consolidation process, as suggested by the higher activation energy compared to the one determined for HP.