Residual stresses and constrained sintering of YSZ/Al2O3 composite coatings

Cr3+ fluorescence spectroscopy was used to determine the residual stresses in YSZ/Al2O3 coatings. Analysis is given with regard to the separation of the residual stresses of different origins. Variations of macro-mismatch stresses near the coating edge and as a function of coating thickness are reported. A micro-thermal stress profile was determined, which can be related to the density distribution in the coating through the thickness. A model is presented for the sintering of a thick porous coating based on a linear viscous assumption. Solutions concerning strain rate, constraint stress and coating densification are obtained. This model gives new insights into the sintering behaviour of a porous coating supported on a rigid substrate. Both theoretical analysis and experimental evidence indicate that the coating density increases while constraint stresses decrease with an increase in the distance from the bonded interface. The influences of substrate constraint on coating microstructure are also discussed. (C) 2004 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.