連續(xù)碳纖維增強莫來石基復合材料的性能與失效行為研究
發(fā)布時間：2018-08-05 14:25
【摘要】：莫來石(Mullite)陶瓷具有密度低、熱膨脹系數(shù)低、抗熱震性好、耐高溫、抗氧化等優(yōu)點,在高溫結(jié)構(gòu)和熱防護領(lǐng)域具有廣闊的應(yīng)用前景,但室溫下較差的力學性能限制了它的應(yīng)用。本文在前期研究基礎(chǔ)上,以碳纖維布疊層縫合預制件為增強體,以符合莫來石化學計量比的Al2O3-SiO2溶膠為原料,通過浸漬-干燥-熱處理技術(shù)路線制備C/Mullite復合材料。論文探究了Al2O3-SiO2溶膠的燒結(jié)收縮行為和莫來石化行為,在對復合材料工藝進行初步優(yōu)化的基礎(chǔ)上,重點研究分析了C/Mullite復合材料的本征性能,以及在模擬應(yīng)用環(huán)境中的失效行為。所用Al2O3-SiO2溶膠的固含量和陶瓷產(chǎn)率分別為30.7wt.%和18.3wt.%。經(jīng)過1300℃熱處理后,溶膠莫來石化基本完成。凝膠粉末的壓片在熱處理時,線收縮率隨著熱處理溫度增大而升高,溫度越高越有利于粉末燒結(jié)。經(jīng)初步優(yōu)化,建立了能夠避免復合過程中碳纖維布分層開裂的工藝路線。以優(yōu)化的工藝路線制備得到表觀密度、總孔隙率、開孔率分別為2.19g·cm-3、13.4%和11.3%的C/Mullite復合材料。采用不同測試方法表征了C/Mullite復合材料的彎曲強度,三點彎曲強度(228.9±11.0MPa)略高于四點彎曲強度(210.6±8.9MPa),服從m=30.6、λ=238.0的兩參數(shù)Weibull分布,m值較大,說明復合材料具有較好的均勻性。由于連續(xù)碳纖維的引入,復合材料具備纖維斷裂、界面脫粘、拔出等增韌機制,斷裂韌性達到11.2MPa·m1/2,是單體Mullite陶瓷的4-5倍。C/Mullite復合材料的拉伸強度和拉伸模量分別為119.9MPa和36.6GPa,X方向的壓縮強度為128.2MPa,層間剪切強度為28.1MPa。表征了C/Mullite復合材料在室溫-1400℃區(qū)間內(nèi)的熱物理性能,為材料的工程應(yīng)用提供基礎(chǔ)數(shù)據(jù)。C/Mullite復合材料的熱膨脹系數(shù)隨溫度的升高先增大后減小,在1000℃時達到最大值4.83×10-6K-1;1300℃以后,由于基體進一步燒結(jié)收縮,熱膨脹系數(shù)呈現(xiàn)為負值。C/Mullite復合材料的比熱容隨溫度的升高而增大,溫度高于1200℃后趨于穩(wěn)定,在1200℃時達到最大值1.547J·g-1·K-1,室溫時最小,為0.756J·g-1·K-1。C/Mullite復合材料的熱擴散率隨溫度升高呈下降趨勢,高溫時趨于平穩(wěn),室溫熱擴散率最高,為1.1mm2·s-1,700℃時最低,為0.707mm2·s-1。C/Mullite復合材料的熱導率基本上隨溫度升高而增大,室溫時熱導率為1.859W·m-1·K-1,1200℃時復合材料熱導率達到最大,為2.325W·m-1·K-1。分別研究了C/Mullite復合材料在高溫惰性、高溫氧化以及高溫水汽條件下的性能演變行為。在1200℃和1400℃惰性氣氛中熱處理1h后,復合材料具有較好的耐高溫性能,質(zhì)量保留率分布別為99.4%和99.2%,強度保留率分別為103.1%和84.6%,當溫度升高到1600℃時,由于基體晶粒粗化以及纖維與基體間的碳熱還原反應(yīng),質(zhì)量和強度保留率分別顯著下降到82.8%和29.3%。C/Mullite復合材料具有較好的抗氧化性能,在1200℃-1600℃靜態(tài)空氣中氧化30min后,強度保留率均在75%左右,復合材料氧化是從材料表面逐漸向內(nèi)部擴展的過程。C/Mullite復合材料經(jīng)過1000℃水汽考核30min后,強度保留率為71.3%,當水汽考核溫度升高到1200℃和1400℃時,復合材料性能保留率顯著下降,不到45%,纖維與基體在高溫條件下受到水汽的嚴重腐蝕,生成揮發(fā)性物質(zhì)導致復合材料失效。研究了C/Mullite復合材料在空氣中的抗熱震性能,復合材料的質(zhì)量損失隨熱震次數(shù)增加呈近線性關(guān)系增大,經(jīng)過1200℃?室溫和1400℃?室溫條件下10次熱震(保溫10min)后,復合材料強度保留率僅分別為43.9%和25.4%。熱震過程中碳纖維的氧化以及由于纖維與基體之間因熱膨脹系數(shù)不匹配而產(chǎn)生的熱應(yīng)力是復合材料失效的主要原因。初步研究了C/Mullite復合材料的抗燒蝕性能,在氧乙炔焰(中心區(qū)溫度2727℃)下考核30s后,復合材料的質(zhì)量燒蝕率和線燒蝕率分別為0.049 g·s-1和0.12 mm·s-1。由于火焰溫度過高,莫來石基體分解生成Al2O3和SiO2,在熱流以及機械沖刷的作用下,大量SiO2流失。研究成果為后續(xù)進一步優(yōu)化制備工藝和提升綜合性能提供了有益借鑒。
[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.
【學位授予單位】：國防科學技術(shù)大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TB332
本文編號：2166064
[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.
【學位授予單位】：國防科學技術(shù)大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TB332
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