Sintering with Rigid Inclusions

Rigid inclusions retard the densification of a sintering body by creating a hydrostatic tensile stress in the matrix. Two models of this process are presented and compared with others from the literature. The composite can be represented by a composite sphere, with the core representing the inclusion. Alternatively, a self‐consistent (s‐c) calculation can be performed in which the sintering material is regarded as being surrounded by a composite matrix with a slower densification rate. The results differ only in that the shear modulus of the matrix is replaced by the shear modulus of the composite in the s‐c calculation. The stress in the inclusion cannot exceed twice the sintering pressure, unless the Poisson's ratio of the matrix is negative. Predictions of higher stresses by previous authors carry the erroneous implication that Poisson's ratio is negative. Since the predicted stresses are not large, models of this type cannot account for the experimentally observed retardation of densification of polycrystalline matrices by inclusions.