Thermal residual stress gradients in an alumina-zirconia composite obtained by electrophoretic deposition

In order to understand the mechanical behavior of layered composites with compositional gradient, it is necessary to determine their state of residual stresses. Compositionally graded materials can offer the advantage of eliminating abrupt changes in composition between layers having different thermal expansion coefficient. The existence of a compositional gradient can reduce discontinuities in thermal residual stresses, something beneficial from the point of view of the mechanical properties. We present here a study of the microstructure and state of residual stressses in a layered material made of homogeneous layers of alumina and alumina-zirconia separated by thin (less than 300 mu m) intermediate compositionally graded layers. The composite was obtained by controlled deposition of powders from solution using an electrophoretic deposition (EPD) method. The phase distribution and compositional gradient in the sintered composite were investigated using scanning electron microscopy (SEM). Thermal residual stresses generated during cooling after sintering were measured by using fluorescence ruby luminiscence piezo-spectroscopy and the profile of hydrostatic stress on alumina was determined at steps of about 300 mu m along the direction of the compositional gradient. and at steps of about 30 mu m in the compositionally graded layers. The obtained profile of hydrostatic stresses on alumina grains follows closely the profile of compositional changes along the layered composite. The presence of thin intermediate graded layers reduce significantly changes in stress in the layered composite. (c) 2005 Elsevier Ltd. All rights reserved.