Arc-jet testing of LaB6 containing ZrB2-SiC materials under high enthalpy supersonic airflows

The design of hypersonic vehicles needs leading edge components with sharp profile to improve flight performances. Such components are subject to very stressful heat fluxes in corrosive plasmas from atmosphere, and temperatures exceeding 2300K for several minutes may become a projected service condition. The spectrum of possible material candidates for such extreme conditions is presently grouped within the class of ultra-high temperature ceramics (UHTCs). There has recently been a renewed interest in UHTCs, particularly in the regard of methods for enhancing the resistance to oxidation through the "in-situ" formation and growth (at high temperature) of solid refractory phases. The effects on the resistance to oxidation coming from the addition of LaB6 particulate into hot-pressed ZrB2-SiC matrices were investigated by using an arc-jet testing facility. Differently from oxidizing furnaces or oxyacetylene torches, an arc-jet facility reproduces conditions recalling those experienced during hypersonic re-entry. CFD simulations were essential to first model the test conditions of the free-stream and boundary layer, and thus match the in-situ determinations to material evolution during arc-jet testing. For surface temperature approaching 2300K, the contemporary presence of SiC and LaB6 additives did not bring obvious advantages to improve oxidation resistance of ZrB2-based matrices.