Oxidation mechanism of carbon fiber reinforced hafnium carbide composite in plasma wind tunnel

Ceramic matrix composite is widely applied in thermal protection system (TPS) of space vehicles to resist ul-trahigh temperature aerodynamic heating. In this work, a novel carbon fiber reinforced hafnium carbide matrix composite (C-f/HfC) is fabricated, and its potential serving as TPS material is studied inside an inductively coupled plasma wind tunnel. The oxidation mechanism of the as-fabricated C-f/HfC is thus revealed in the dissociated air flows with different heat fluxes, based on the temperature profiles and the microstructural evo-lutions of HfO2 oxide scale. The results suggest a transition in the oxidation activity of C-f/HfC at 1650-1700 degrees C in reduced pressure (<10 kPa), from reaction-control to diffusion-control, due to the accumulation of porous HfO2 oxide scale. When its thickness beyond a critical value, inner diffusions of oxidized species dominate the oxidation activity of C-f/HfC. The thicker the HfO2 is, the weaker the oxidation of C-f/HfC can be in dissociated air plasmas. The oxidation mechanism endows C-f/HfC with an excellent thermal protection property at ultrahigh temperatures (>= 2000 degrees C). However, when the oxidation temperature >= 2700 degrees C, due to strong melt and evaporation, the continuity of HfO2 is interrupted, which results in degradation of the oxidation blockage ability. As a result, C-f/HfC is strongly ablated in the dissociated air plasmas. This infers that C-f/HfC can be applied in TPS by preventing strong melt and dissipation of HfO2, and it is suggested to control the surface temperature of C-f/HfC lower than 2700 degrees C in reduced pressures. This work may forward the advance of the novel material in the TPS of future space vehicles.