  Direct and hybrid microwave sintering of 3Y-ZrO 2 are comparatively studied
at frequency of 2.45 GHz. Using the continuum theory of sintering, a fully
coupled electromagnetic-thermalmechanical (EMTM) finite element simulation is
carried out to predict powder samples deformation during their microwave
processing. Direct and hybrid heating configurations are computationally tested
using advanced heat transfer simulation tools including the surface to surface
thermal radiation boundary conditions and a numeric
proportional-integral-derivative (PID) regulation. The developed modeling
framework shows a good agreement of the calculation results with the known
experimental data on the microwave sintering of 3Y-ZrO 2 in terms of the
densification kinetics. It is shown that the direct heating configuration
renders highly hot spot effects resulting in non-homogenous densification
causing processed specimen's final shape distortions. Compared to the direct
heating, the hybrid heating configuration provides a reduction of the thermal
inhomogeneity along with a densification homogenization. As a result of the
hybrid heating, the total densification of the specimen is attained without
specimen distortions. It is also shown that the reduction of the sample size
has a stabilization effect on the temperature and relative density spatial
distributions.
