Processing of platelet-reinforced glass matrix composites: effect of inclusions on sintering anisotropy

The effect of rigid, i.e. non-densifying inclusions on the densification kinetics and shrinkage anisotropy during the sintering of composite glass powder compacts is investigated. The experimental study was conducted on barium-magnesium aluminosilicate (BMAS) glass composites containing Al2O3-platelets as a rigid inclusion phase. Data on axial and radial shrinkage during sintering were obtained by using heating microscopy, which allows monitoring the densification process without the exertion of external loads, which could influence the sintering kinetics. The presence of rigid platelets retarded the densification of the compacts. The sintering behavior of all samples was anisotropic, with the degree of anisotropy varying with the progress of sintering and with the platelet content. A comprehensive qualitative explanation for the effect of rigid inclusions on sintering shrinkage anisotropy for both intrinsically isotropic and anisotropic powder compacts is offered. In general, the influence of rigid inclusions on shrinkage anisotropy can be explained on the basis of the retardation effect that inclusions have on the sintering and densification kinetics of porous glass compacts. The ideas advanced in this paper form the basis for the development of a predictive theoretical model for the effect of rigid inclusions on shrinkage anisotropy of glass powder compacts during sintering. (C) 1999 Elsevier Science S.A. All rights reserved.