Hypersonic systems require materials able to survive important heat fluxes as well as aerodynamic and mechanical loads. Current available materials suffer of a series of technological limitations, like not favorable performance and production costs, to weight ratios or inability to perform under hot ablative fluxes. Ultra-high temperature ceramics (UHTCs) are possible candidates that, upon suitable composition and microstructure tailoring, can be a suitable solution. Among them, besides the well-known Zirconium diboride, ZrB2, Titanium diboride, TiB2, can merge the weight, hardness and strength requirements. Novel ZrB2-TiB2-mixed ceramics can be a lower density solution compared to the more popular ZrB2 and HfB2 based ceramics to protect components working in extremely high temperatures from heat and hot corrosion damages while also preserving their functionality. However, the lowest oxidation resistance of TiB2 must be compensated by additional phases.
Here, a three-phase ceramic that has ZrB2 as major component, includes TiB2, and a transition metal (TM) compound, NbC, was prepared to exploit the multiple benefits of the single phases. NbC was selected in view of the low melting point of its oxide that might protect the bulk material from further oxidation.
We first present the synthesis of NbC by carbothermal reaction of its oxide, then go through the sintering process and microstructural study to investigate the role of Nb in the formation of solid solutions with Zr- and Ti- borides by local phase analysis performed by transmission electron microscopy (TEM). Mechanical properties, like nanoindentation and strength up to 1800°C, as well as oxidation at 1500°C are also conducted and compared to a Nb-free companion ceramic.