Novel Platelet Composites for Improved Mechanical Behavior

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9616668 Chan In recent years, platelet reinforced ceramic composites have emerged as viable alternatives to whisker and fiber reinforced materials for many structural applications. It is recognized that there are certain characteristics of the reinforcement phase and the matrix/platelet interface which will favor improved toughness behavior, e.g., ease of debonding at the platelet/matrix interface, high platelet volume fraction, however detailed systematic study has been limited. Based on recent work carried out at Lehigh, it is believed that a novel composite system consisting of alumina platelets coated with calcium hexaluminate (CA6) has the potential to surpass the properties of conventional platelet composites. CA6 exhibits several characteristics which make it exceptionally well-suited for the proposed application. These include the adoption of an epitaxial relationship such that the weak basal cleavage planes of CA6 align parallel to the (0001) a-alumina platelet faces, values of thermal coefficients of expansion which favor debonding, and thermodynamic stability with alumina. Mechanical characterization of both the bulk composites and the interface structures is proposed. The processing and mechanical testing will be complemented by high resolution study of debonded interfaces using TEM. The goals of the program are several-fold. One aim will be to determine the processing and microstructural parameters of the composite system which optimize the mechanical properties. On a more fundamental level, however, the proposed program will enable the direct correlation between interfacial structure, the toughness, and strength of the interface, and the mechanical behavior of the bulk composite. %%%% In recent years, platelet reinforced ceramic composites have emerged as viable alternatives to whisker and fiber reinforced materials for many structural applications. It is recognized that there are certain characteristics of the reinforcement phase and the matrix/platelet interface which will favor improved toughness behavior, however detailed systematic study has been limited. Based on recent work carried out at Lehigh, it is believed that a novel composite system consisting of alumina platelets coated with calcium hexaluminate (CA6) has the potential to surpass the properties of conventional platelet composites. The goals of the program are several-fold. One aim will be to determine the processing and microstructural parameters of the composite system which optimize the mechanical properties. On a more fundamental level, however, the proposed program will enable the direct correlation between interfacial structure, the toughness, and strength of the interface, and the mechanical behavior of the bulk composite. ***