Toughening behavior in ceramics and cermets

The development of high strength (greater than or equal to 1 GPa), high toughness (greater than or equal to 10 MParootm) ceramic systems is being examined using two approaches. In silicon nitride, toughening is achieved by the introduction of large prismatic shaped grains dispersed in a fine grain matrix. For the system examined herein, both the microstructure and the composition must be controlled. A distinctly bimodal distribution of grain diameters combined with controlled yttria to alumina ratio in additives to promote interfacial debonding is required. Using a cermet approach, ductile Ni3Al-bonded TiC exhibited toughening due to plastic deformation within the Ni3Al binder phase assisted by interfacial debonding and cleavage of TiC grains. The TiC-Ni3Al cermets have toughness values equal to those of the WC-Co cermets. Furthermore, the TiC-Ni3Al cermets exhibit high strengths that are retained in air to temperatures of similar to1000degreesC.