Nanoindentation deformation and fracture mechanisms of SiC/SiO2 thermally oxidized in plasma wind tunnel.

• SiO 2 oxide scale formed inside plasma wind tunnel maintains an amorphous microstructure. • Young's modulus and hardness of SiC/SiO 2 evolved linearly with penetration depth. • Compressive residual stress in SiO 2 may increase's its nanoindentation hardness. • SiO 2 delamination has a negligible effect on the nanoindentation response of SiC/SiO 2. Mechanical strain and delamination of surface oxide from substrate are important mechanisms leading to failure of thermal protection systems in hypersonic vehicles. In this work, the deformation and fracture mechanisms of a thermally oxidized SiC/SiO 2 , formed by dynamic oxidations inside a plasma wind tunnel, are studied by nanoindentation experiments and finite element modeling. The results show an amorphous and uniform SiO 2 formation on β-SiC at 1200∼1400 °C in the plasma flow (pressure ≈6.5 kPa), after long-term single/repeated oxidations. In the plasma environment the passive oxidation of SiC is slow, as a result the as-formed SiO 2 is very thin. The SiO 2 thickness is only ≈680 nm after 8 × 500 s dynamic oxidation. SiC/SiO 2 exhibits a strong depth dependent indentation behavior, and at a critical indentation depth, delamination of SiO 2 oxide scale is triggered. Finite element modeling helps decouple the effects of SiC substrate, residual thermal stress and interfacial delamination on the nanoindentation response of SiC/SiO 2. The results evidence that delamination has a negligible effect on the nanoindentation response, and the main contributions are the SiC substrate and residual thermal stress. This work may forward the fundamental understanding of deformation and fracture mechanisms of oxide scales on thermal protection materials in response to localized loading conditions. [ABSTRACT FROM AUTHOR]