Constrained sintering of YSZ/Al2O3 composite coatings on metal substrates produced from eletrophoretic deposition

Yttria stabilized zirconia/alumina (YSZ/Al2O3) composite coatings were prepared from electrophoretic deposition (EPD), followed by sintering. The constrained sintering of the coatings on metal substrates was characterized with microstructure examination using electron microscopy, mechanical properties examination using nanoindentation, and residual stress measurement using Cr3+ fluorescence spectroscopy. The microstructure close to the coating/substrate interface is more porous than that near the surface of the EPD coatings due to the deposition process and the constrained sintering of the coatings. The sintering of the YSZ/Al2O3 composite coating took up to 200h at 1250 degrees C to achieve the highest density due to the constraint of the substrate. When the coating was sintered at 1000 degrees C after sintering at 1250 degrees C for less than 100 h, the compressive stress was generated due to thermal mismatch between the coating and metal substrate, leading to further densitication at 1000 degrees C because of the 'hot pressing' effect. The relative densities estimated based on the residual stress measurements are close to the densities measured by the Archimedes method, which excludes an open porosity effect. The densities estimated from the hardness and the modulus measurements are lower than those from the residual stress measurement and the Archimedes method, because it takes account of the open porosity. (c) 2006 Elsevier Ltd. All rights reserved.