Sintering is a process to fabricate ceramics from solid particles with the application of heat. The superplastic sinter-forging of porous preform is an actual and reasonable application of ceramics superplasticity. It is desirable to know how the powder compact shrinks and deforms in order to adjust the shape of products to the precision required. The continuum model has been developed for the deformation response of powder compact to applied external stress and the internal thermodynamic driving force, i.e., the sintering stress. It is known empirically that the deformation can be described by uniaxial viscosities and viscous Poisson’s ratios. These parameters are all functions of density and microstructure, and they can be extracted from mechanical tests. Beyond such empirical approach, it is necessary to establish a solid theoretical grounding for determining these parameters directly from the knowledge of microstructure. It is possible when we assume some idealized particle arrangements as models. The purpose of this paper is to present a general method to determine the sintering stress tensor and the viscosity tensor from the knowledge of three-dimensional microstructure of particle-pore systems. We derive the viscosity tensors by assuming that grain boundary diffusion is the dominant transport mechanism that leads to shrinkage. We show the role of grain boundary sliding on the viscous shear modulus and the visous Poisson’s ratio.
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