The Nature of Ductile Phase Toughening in Ni/#alpha#-Al_2O_3 Metal-Ceramic Composites

摘要

Metal-ceramic composites (cermets) combine theadvantageous properties of ceramics, namely high temperaturestability and creep resistance, with the engineering-friendlytraits of metals, such as high fracture toughness and gracefulfailure. However, optimization of the ductile phase tougheningof cermets requires both a precise understanding of themechanisms involved and the adoption of appropriate models inorder to predict the microstructure that would be most effectivefor a given system. One such system of interest isnickel/alumina. Hence, Ni/#alpha#-Al_2O_3 composites ofvarying metal contents and morphologies have been preparedthrough a number of different insitu techniques. The fracturetoughness of the various composites was determined byperforming a work-of-fracture analysis on chevron-notchedthree-point bend specimens while the composite microstructureswere quantitatively characterized using scanning electronmicroscopy and ASTM standards. Several ductile phasetoughening models were examined in order to determine themechanical mechanisms at work in the cermets and to establishcriteria for optimizing their fracture behavior.