Boride hierarchical composites for ultra-high temperature applications

Here we present a simple method to obtain highly refractory boride-based ceramic nano-composites. Fundamental requirement for the development of a hierarchical boride composite is the formation of a solid solution around the native MB2 boride grain during the densification stage. This can be obtained upon addition of soluble transition metal compounds. In the present case, introduction of W- or Ta-based compounds enabled to form (M,W)B2 or (M,Ta)B2shells around the original MB2 cores. Subsequent annealing at high temperature further developed the nano-texturing in the shell, where metallic W or TaC nano-particles precipitated within MB2 grains and displayed unprecedented refractoriness. Here we show the microstructural features of different diboride composite and show how these microstructural change impact on local properties measured by nanoindentation and on the ultra-high temperature strength. The unique microstructural findings reported open vast opportunities for nano-composite ceramic development, manufacturing and applications.