ZrB2-MoSi2 dual-scale composite architectures: overcoming the strength-to-toughness trade-off for high temperature structural use

Dual composite (DC) architectures 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. Composites of zirconium diboride (ZrB2) and molybdenum disilicide (MoSi2) are candidates for similar dual composite architectures for high-temperature structural use in extreme environments, due to the high-temperature ductility and oxidation resistance of MoSi2. Multiple DC architectures were prepared by hot-pressing pre-sintered granules of known volumetric amount, size and composition that are dispersed in a continuous matrix made of a different loose powder mixture. The powder technology selected to produce granules was the freeze-spray granulation. Conventional composites, using compositions representative of both the granules and the matrices, were also hot pressed for comparison. The joint research effort investigated microstructure development and mechanical properties including elastic modulus, thermal expansion, flexure strength and fracture toughness at room temperature and at 1500°C in air. The results were compared to corresponding traditional particulate sub-composites.