Electron Microscope investigation of crack path selection and crack interface interactions in a W-ZrO2(Y2O3) directionally solidified eutectic (DSE)

Abstract

Metal-ceramic composites play a vital materials role in many technologically important industries due to their unique electrical, thermal and structural properties. The mechanical properties of metal-oxide materials are largely controlled by the properties of the metal-ceramic interface, specifically its structure and chemistry which govern the bonding between the constituents. For a brittle matrix composite, the fracture properties of the interface can determine the failure response of the composite as a whole.The W-ZrO2(Y2O3) directionally solidified eutectic was grown by a skull melting technique described elsewhere. Composites were grown with 10 mol % yttria and ~ 6 w% tungsten. Figure 1 is a scanning electron micrograph showing that the tungsten grows as parallel fibers approximately lujn in diameter in a zirconia matrix. Selected area diffraction of the composite (Figure 2) reveals the growth direction to be: <110>zrO2 // <11l>w.Electron microscopy of microindentation cracks, of pre-existing microcracks due to thermal expansion anisotropy and of short cracks inadvertently introduced during specimen preparation shows four different crack-interface interactions: