Fracture-resistant strong ultra-refractory structural composites with functionally designed microstructures

The paradigm shift in materials selection was to develop technologies that enables the engineer to move away from restrictive properties trade-offs, the wear-toughness-hardness to cite one of the widely known. In fact, hybrid WC-Co cemented carbide composites, otherwise known as dual composites (DC), have been shown to increase wear resistance while maintaining or increasing fracture toughness in WC-Co composites for room-temperature applications by the use of multiple, discretely segregated engineered microstructures. Another general question is whether it is possible to improve high temperature functional properties of structural ceramics with concurrent improvements of intrinsic mechanical properties such as flexure strength and fracture toughness: a positive answer would create a new paradigm of structural materials that have superior elevated temperature properties. Can DC architectures be synthesized and densified? How do DC architectures affect the intrinsic physical properties of ceramics? What are the intrinsic mechanical properties of DC ceramics? Does DC composites have improved mechanical properties at elevated temperatures? To answer these basic questions, multiple DC architectures were densified dispersing pre-sintered granules of known volumetric amount, size and composition in a continuous matrix made of different loose powder mixtures. Granules were produced by the freeze-spray granulation. Conventional composites of the only compositions representative of granules and matrices were hot pressed for comparison. Composites of zirconium diboride (ZrB2) and molybdenum disilicide (MoSi2) are candidates for similar dual composite architectures for high-temperature structural use in corrosive environments, due to the high temperature ductility and oxidation resistance of MoSi2. Microstructures were investigated and correlated to mechanical properties including elastic modulus, thermal expansion, flexure strength and fracture toughness at room temperature up to 1500 °C in air, and compared to corresponding traditional particulate sub-composites.