Sintering stresses and distortion produced by density differences in bi-layer structures

The variations in green density that arise when a powder is consolidated gives rise to strain rate incompatibility between regions that can result in densification stresses and or warpage during sintering. In order to quantify the effect of the green density variations, the shrinkage behavior of model bi-layers with a tailored density difference was analyzed. The methodology previously developed for co-firing of layered structures was applied to bi-layers for the case in which the layers do not differ in composition but in density. Alumina tapes with green densities of 1.96 and 2.34 Mg/m3 were fabricated by tape casting and consolidated into bi-layers. The shrinkage characteristics of the individual layers were characterized and the uniaxial viscosity of the layers with the two starting densities were determined as a function of the degree of densification using cyclic loading dilatometry. The distortion in the bi-layer configurations was experimentally measured and was shown to be in good agreement with the analytical calculations.