Plasma wind tunnel testing of ultra-high temperature ZrB2–SiC composites under hypersonic re-entry conditions

The resistance to oxidation and optical properties of a hot-pressed ZrB2–SiC composite were studied under aero-thermal heating in a strongly dissociated flow that simulates hypersonic re-entry conditions. Ultra-high temperature ceramic models with a blunt or sharp profile were exposed to high enthalpy flows of an N2/O2 gas mixture up to 10 MJ/kg for a full duration of 540 s, the surface temperatures approaching 2100 K. Stagnation-point temperatures as well as spectral emissivities were directly determined using an optical pyrometer. Microstructural features of the oxidized layers were correlated to optical properties through computational fluid dynamics calculations which allow for numerical rebuilding of key parameters like surface temperatures, wall heat fluxes, shear stresses or concentrations of the species composing the reacting gas mixture. Gradients of temperature on the surfaces facing the hot gas flow established different boundary conditions that led to the formation and evolution of distinct layered oxide scales.