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 ultrahigh temperature aerodynamic heating. In this work, a novel carbon fiber reinforced hafnium carbide matrix composite (Cf/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 Cf/HfC is thus revealed in the dissociated air flows with different heat fluxes, based on the temperature profiles and the microstructural evolutions of HfO2 oxide scale. The results suggest a transition in the oxidation activity of Cf/HfC at 1650–1700 °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 Cf/HfC. The thicker the HfO2 is, the weaker the oxidation of Cf/HfC can be in dissociated air plasmas. The oxidation mechanism endows Cf/HfC with an excellent thermal protection property at ultrahigh temperatures (≥2000 °C). However, when the oxidation temperature ≥2700 °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, Cf/HfC is strongly ablated in the dissociated air plasmas. This infers that Cf/HfC can be applied in TPS by preventing strong melt and dissipation of HfO2, and it is suggested to control the surface temperature of Cf/HfC lower than 2700 °C in reduced pressures. This work may forward the advance of the novel material in the TPS of future space vehicles.