Ablation behavior of gradient ceramic-polymer composites in wind tunnel environment

Ceramic matrix composites are desirable for applications in extreme environments due to the excellent ablation resistance, but few ceramic materials can exhibit a matched load bearing capacity currently. The technological potential of functionally graded materials, such as improved ablation resistance and enhanced load-bearing capacity, has opened up the feasibility for designing highly efficient thermal protection materials. In this study, composite insulation tiles, with three-dimensional braided carbon fibers in a ceramic-polymer continuous gradient matrix, are designed and fabricated by using a temperature-controlled polymer-derived ceramic method. The ablation behavior of the specimens exposed to high-temperature high-speed wind tunnel environments has been investigated at a total enthalpy of 15.8 MJ/kg. Temperature response, morphology and composition characteristics are obtained, which allows detecting oxidation resistance and thermal stability of the gradient composites. The results showed that the formation the silicon oxide layer covering the ablated surface and the inner gradient layer composed of amorphous SiCN ceramics display a key role in resisting ablation and reducing heat conduction. Meanwhile, the underlying resin layer can display superior load-bearing capacity at environment temperatures lower than pyrolysis. The present study highlights high ablation behavior of continuous gradient ceramic-polymer composites, offering a possibility in developing thermal protection composites with good trade-off between thermal and mechanical properties.