Fabrication and mechanical characterization of Al2O 3/ZrO2 layered composites with graded microstructure

Abstract

Microstructure evaluation has been performed and related mechanical properties have been investigated and characterized in functionally graded materials (FGMs) using alumina and zirconia. Two kinds of FGM, one with a compositional variation from an alumina substrate to an outer layer of zirconia (AZ FGM) and an inverse one (ZA FGM), were prepared by dip-coating with substrates prepared by gel-casting. The slip composition for the coating was controlled with 10 vol.% variation. The microstructure changed from the substrate to the outer layer, showing smooth variation in hardness. The coating thickness of AZ FGM, with abnormal grain growth in the substrate, was thicker than that of ZA FGM, with grain growth inhibition, showing about 300 and about 200μm for AZ FGM and ZA FGM, respectively. Well developed cracks with anisotropic crack propagation were observed in AZ FGM, but no cracking was observed in ZA FGM. The fracture strength of monolithic materials decreased as coating layers were applied onto the monolithic materials. Based on the results of mechanical properties and microstructure evaluation, the fracture mechanism in each FGM is proposed and discussed. © 2008 American Institute of Physics.