Research On The O₂-C₂H₂ And Ramjet Combustor Ablation Resisitance Of Al20Si/Gr Transpiring Coolant Materials

In this thesis, Al20Si/Gr transpiring coolant materials were prepared by a patent technology(ZL200810064995.2). Porous graphite was used as matrix and Al20Si was used as refrigerant. The composite was denoted by Al20Si/Gr. The flexural strength and compression strength under room temperature and high temperature were tested by multi-purpose electronic testing machines. The behavior of Al20Si/Gr transpiring coolant materials under different ablation time and cooling condition was studied by oxygen-ethane torch heating test and ramjet combustor heating test. The surface morphology and microzone component after ablation were researched by scanning electron microscope(SEM) and energy spectrometer. The surface and inner phase composition were studied by X-ray diffraction(XRD). After that, the forming process of metal oxides film, the effect of volume ablation and the ablation mechanism were disscussed.The experiment results showed that the flexural strength and compression strength of Al20Si/Gr transpiring coolant materials under room temterature were 3.5 times and 1.3 times more than that of graphite matrix respectively. With the temperature increasing, the flexural strength of Al20Si/Gr transpiring coolant materials decreased gradually. The compression strength got its minimum value at 750℃, and rebounded to 175MPa at 1000℃.Under the oxygen-ethane torch heating condition, the linear ablation rate of Al20Si/Gr transpiring coolant materials was 5.0×10^-3mm/s, the linear ablation rate of twice^-30s-ablation was 60% than that of once-60s-ablation, which was two orders of magnitude lower than that of the graphite matrix. The ablation surface morphology could be divided into three parts: central ablation area, transition region and marginal zone. As the ablation time increased to 30s, pits emerged in the central ablation area, which played an important part on the forming process of metal oxides film. Large particle metal oxides appeared in transition region. The marginal zone was made up of reticular metal oxides. During the forming process of the metal oxides film, the metal melted and absorb the heat. The metal oxides film firstly could prevent the heat transfer and oxygen transfer and then decrease the scouring effect of airflow. These three effects together increased the ablation properties of Al20Si/Gr transpiring coolant materials. During typical ablation process, the phase composition was C+Al₂O₃+SiO₂ , C+Al4SiC₄ ,C+Al4SiC₄+SiC+Al4C₃,C+SiC+Al4C₃,C+Si +Al4C₃ in sequence from surface to tail. The linear ablation rate of twice-30s-ablation was much lower than that of once-60s-ablation. The surface phase composition under twice-30s-ablation was C+Al₂O₃+ Al4SiC₄.With low-temperature, the ramjet combustor heating condition was quite different from the oxygen-ethane torch heating condition. The protective film increased the air flow scouring resistence of Al20Si/Gr transpiring coolant materials. The inner phase composition was Al,Si and C. The content of Al and Si decreased as the decreasing of the distance from ablation surface.