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Abstract: The erosion resistance of the needled carbon/carbon composite leading edge was investigated by exposure to the solid rocket motor (SRM) plume. The erosion morphology and microstructure were examined and associated erosion mechanisms discussed. The composite leading edge was severely damaged with large recession and erosion rate after exposure. The results suggest that the erosion behavior was determined by the weak needling structure of the leading edge windward with small thickness in the severe environment of the plume impingement. Erosion mechanisms were combined effects of thermochemical ablation by oxidizing species and thermomechanical erosion by both aerodynamic force and alumina particles. The former weakens the strength of the composite while the latter contributes primarily to high erosion rate in the oxy-lean SRM plume environments. [Copyright &y& Elsevier]

Abstract: The ablation of pierced C/C composite nozzles was investigated via hot-fire testing by an oxygen/ethanol combustion gas generator simulating combustion environments of the liquid rocket engine. Ablation microstructures and mechanisms of the composite nozzle were discussed. The results showed that both linear ablation rate and mass ablation rate increased with increasing mass ratio of oxygen/ethanol. The ablation of the pierced C/C composite was attributed to the heterogeneous reactions between carbon and oxidizing species and could be interpreted by the thermochemical ablation model. The ablation rate of the composite was determined by both chemical kinetics and diffusion. The ablation of the composite resulted in cone-shape carbon fibers and shell-shape matrix with pits and grooves left on the surfaces. [Copyright &y& Elsevier]

In situ synthesis technology was adopted to fabricate SiC reinforced Ti3SiC2 composite by displacement reaction of Si and TiC powders. The formation of SiC particles as reinforcements with elongated or equiaxed shape distributed in Ti3SiC2 matrix. The average size of SiC equiaxed particles was about 2 μm and that of elongated ones was in the range of 5–8 μm in length and 2 μm in width. TiC with about 1 μm in size was also found in the composite. The particles of SiC or TiC inhibited the grain-boundary migration of Ti3SiC2 resulting in a fine Ti3SiC2 matrix with a grain size of 10 μm. Differential scanning calorimetry showed that Si reacted drastically with TiC at 1340 °C with release of heat. The presence of TiC in the Ti3SiC2/SiC composite should be attributed to decomposition of Ti3SiC2 at 1500 °C rather than the loss of Si during reaction process that resulted in unreacted TiC left. Reaction paths in the present experiment were postulated on the basis of Ti–Si–C system and reaction model of Mo2C–Si to understand the mechanism of the formation of Ti3SiC2 and SiC. [Copyright &y& Elsevier]

Ti3SiC2/SiC composite has been synthesized by in situ displacement reaction of Si and TiC powders. Its relative density is >98%. Its Vickers hardness was measured to be 8.7 GPa. Its flexural strength and the fracture toughness were 505 MPa and 5.3 MPa·m1/2, respectively. Scanning electron micrograph (SEM) and transmission electron micrograph (TEM) were used to observe the microstructure of the composite. Mechanisms for its high flexural strength and fracture toughness were discussed, respectively. The composite shows a better oxidation resistance than monolithic Ti3SiC2 at high temperatures. The oxidation layers were comprised of an outer layer with coarse TiO2 grains and an inner layer with a mixture of fine-grained SiO2 and TiO2. Its weight gain is only about 7.9 mg/cm2 at 1200 °C in air for 21 h. However, that of Ti3SiC2 is 30 mg/cm2. The results suggested that the in situ formation of SiC improved its oxidation resistance. [Copyright &y& Elsevier]

The oxidation behavior of Ti3SiC2 with additive-Al2O3 was studied over the temperature range of 1000–1500 °C in air. Ti3SiC2 based composite has a good oxidation resistance at below 1100 °C. The oxidation kinetics followed a parabolic and a linear law respectively at different oxidation stages. Morphology of oxidation products was observed from the oxidized surface by scanning electron microscope (SEM). Oxides were identified by X-ray diffraction (XRD) and energy-dispersive spectroscopy (EDS). The existence of additive-Al2O3 influenced the morphology of oxides and the oxidation behavior of Ti3SiC2. The formation of pores or cavities at high temperature provided the channels for diffusion of oxygen and accelerated the oxidation behavior of Ti3SiC2 based composite. The effects related to the morphology and microstructure features on the oxidation kinetics are discussed. [Copyright &y& Elsevier]