Aerothermodynamic response of ZrB2-based compositionally complex ultra-high-temperature ceramics in hypersonic and supersonic flow conditions

Aerothermodynamic tests were carried out on two different ultra-high temperature ceramics based on ZrB 2 -TiB 2 -SiC and doped with NbC or VC. Hemispherical specimens were exposed to subsequent hypersonic and supersonic flows of simulated air produced by an arc-jet plasma wind tunnel, at specific total enthalpies of ≈20 MJ/kg. Different test configurations were selected, employing supersonic nozzles with different expansion area ratios, to achieve Mach numbers 3 and 6. Real-time surface temperature was monitored by two-color pyrometer and infrared thermo-camera, and achieved values between 1700 and 2700 K. One-dimensional chemical equilibrium models were used to characterize the flow field inside the test rig, to have a proper description of the thermo-fluid dynamic and chemical conditions in the different test configurations, including an estimation of the aerothermodynamic loads on the specimens. Data were correlated to the microstructure evolution and oxidation mechanism depending on the presence of Nb or V.