連續(xù)碳纖維增強(qiáng)莫來(lái)石基復(fù)合材料的性能與失效行為研究
[Abstract]:Mullite (Mullite) ceramics have the advantages of low density, low thermal expansion coefficient, good thermal shock resistance, high temperature resistance, anti oxidation and so on. It has a broad application prospect in the field of high temperature structure and thermal protection, but the poor mechanical properties at room temperature limit its application. On the basis of the previous research, the preform is sutured with carbon fiber layer as an augmented body. The C/Mullite composite was prepared by impregnation drying heat treatment technology with the Al2O3-SiO2 sol which conforms to the mullite stoichiometry. The paper explored the sintering shrinkage behavior of Al2O3-SiO2 sol and the behavior of the mullite. On the basis of the preliminary optimization of the composite technology, the C/Mullite composite was studied and analyzed. The intrinsic properties of the material and the failure behavior in the simulated application environment. The solid content and the ceramic yield of the Al2O3-SiO2 sol are 30.7wt.% and 18.3wt.%. respectively after heat treatment at 1300 degrees C. The sol mullite is basically completed. The line shrinkage of the gel powder increases with the increase of heat treatment temperature, and the temperature is higher. It is beneficial to powder sintering. After preliminary optimization, a process route to avoid layered cracking of carbon fiber cloth in the composite process is established. The apparent density, total porosity and opening rate are 2.19g. Cm-3,13.4% and 11.3% C/Mullite composites respectively. C/Mullite composite is characterized by different testing methods. The bending strength of the material, three point bending strength (228.9 + 11.0MPa) is slightly higher than that of four point bending strength (210.6 + 8.9MPa), obeying m=30.6, Weibull distribution of the two parameter of lambda =238.0, and the m value is larger. It shows that the composite has better uniformity. The composite material has fiber fracture, interfacial debonding and pulling out mechanism because of the introduction of continuous carbon fiber. The fracture toughness is 11.2MPa. M1/2. The tensile strength and tensile modulus of the 4-5 times.C/Mullite composite of the single Mullite ceramics are 119.9MPa and 36.6GPa respectively. The compressive strength of the X direction is 128.2MPa, and the interlayer shear strength is 28.1MPa. characterized by the thermal physical properties of the C/Mullite composite in the -1400 room temperature range of room temperature, which is the engineering of the material. The thermal expansion coefficient of.C/Mullite composite material increased first and then decreased with the increase of temperature, reaching the maximum value of 4.83 x 10-6K-1 at 1000 C. After 1300 C, the thermal expansion coefficient presented as negative value.C/Mullite composite material increased with the increase of temperature, and the temperature was higher than 1200. The maximum value of 1.547J. G-1. K-1 at 1200 C, the minimum temperature at room temperature, the thermal diffusivity of 0.756J. G-1 / K-1.C/Mullite composite material decreasing with the temperature, the high temperature tends to be stable, the temperature diffusivity of the room temperature is the highest, which is the lowest in 1.1mm2 s-1700 C. It is the thermal conductivity base of the 0.707mm2 s-1.C/Mullite composite material. As the temperature increases, the thermal conductivity of the composite is maximum at room temperature of 1.859W. M-1. K-11200. 2.325W. M-1. K-1., respectively, to study the behavior of C/Mullite composites under high temperature inert, high temperature oxidation and high temperature water vapor. After heat treatment of 1H at 1200 and 1400 C in inert atmosphere, the properties of the composites are recovered. The material has good high temperature resistance, the distribution of mass retention rate is 99.4% and 99.2%, the retention rate of strength is 103.1% and 84.6% respectively. When the temperature rises to 1600, the retention rate of mass and strength decreases to 82.8% and 29.3%.C/Mullite composites, respectively, due to the grain coarsening of the matrix and the carbon thermal reduction reaction between the fiber and the matrix. With good oxidation resistance, after oxidation of 30min in static air at 1200 -1600 C, the retention rate of the strength is about 75%. The oxidation of the composites is gradually expanding from the surface of the material to the interior of the material. The.C/Mullite composite material is examined by water vapor at 1000 C for 30min, the retention rate of the strength is 71.3%, when the assessment temperature of water vapor rises to 1200 and 140. At 0 C, the performance retention of the composites decreased significantly, less than 45%, and the fiber and matrix were seriously corroded by water vapor under high temperature. The formation of volatile compounds resulted in the failure of the composites. The thermal shock resistance of C/Mullite composites in the air was studied. The mass loss of the composites increased linearly with the increase of the number of thermal shock. After 10 thermal shocks (10min) at room temperature and 1400? Temperature at room temperature and room temperature, the strength retention of the composites is only 43.9% and 25.4%., respectively, the oxidation of carbon fibers in the thermal shock process and the thermal stress caused by the mismatch of thermal expansion coefficient between the fiber and the matrix are the main reasons for the failure of the composites. The preliminary study of C/Mull is made of C/Mull. The ablative properties of ite composites were evaluated by 30s at oxygen acetylene flame (2727 centigrade temperature). The mass ablative rate and line ablation rate of the composites were 0.049 G. S-1 and 0.12 mm. S-1., respectively, because of the high temperature of the flame. The Mullite Matrix decomposed into Al2O3 and SiO2, and a large amount of SiO2 loss was studied under the effect of heat flow and mechanical scour. The results provide a useful reference for further optimizing the preparation process and improving the comprehensive performance.
【學(xué)位授予單位】:國(guó)防科學(xué)技術(shù)大學(xué)
【學(xué)位級(jí)別】:碩士
【學(xué)位授予年份】:2015
【分類號(hào)】:TB332
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