本文選題：碳/碳復(fù)合材料 + 抗燒蝕涂層��； 參考：《西北工業(yè)大學(xué)》2015年博士論文

【摘要】：碳/碳（C/C）復(fù)合材料由于其優(yōu)異的高溫性能，在航空航天領(lǐng)域具有極其廣泛的應(yīng)用前景。但該材料在370℃以上有氧環(huán)境下的快速氧化限制了其作為航空航天熱結(jié)構(gòu)、熱防護(hù)材料的應(yīng)用，涂層技術(shù)是解決該問題的有效手段。SiC、ZrC因其高熔點(diǎn)和良好的高溫穩(wěn)定性，成為C/C復(fù)合材料表面抗燒蝕涂層的理想材料。 本文采用低壓化學(xué)氣相沉積法（Low Pressure Chemical Vapor Deposition,LPCVD）在C/C復(fù)合材料和碳纖維表面分別制備了SiC、ZrC涂層，研究了工藝參數(shù)對(duì)涂層微觀結(jié)構(gòu)的影響；通過氧乙炔焰考察和研究了涂層在循環(huán)燒蝕和不同熱流量燒蝕條件下的抗燒蝕性能和燒蝕機(jī)理；針對(duì)ZrC涂層和C/C基體之間的熱膨脹失配，設(shè)計(jì)并制備了SiC/ZrC復(fù)合涂層和SiC/ZrC/SiC多層涂層，以緩解ZrC涂層的熱膨脹失配，，提高涂層的抗燒蝕性能；采用X-射線衍射儀、掃描電鏡、透射電鏡及氧乙炔焰燒蝕等分析和測(cè)試手段對(duì)涂層的微觀結(jié)構(gòu)和燒蝕性能進(jìn)行研究，本文的主要研究內(nèi)容和結(jié)果如下： 以MTS-H2-Ar為反應(yīng)體系，采用LPCVD法在不同沉積溫度和H2/MTS摩爾比值下分別在C/C復(fù)合材料表面和碳纖維表面制備了SiC涂層，通過對(duì)涂層形貌的分析，獲得了沉積溫度和H2/MTS摩爾比對(duì)SiC涂層結(jié)構(gòu)的影響規(guī)律。隨著沉積溫度的升高， SiC顆粒生長速率逐漸加快，顆粒尺寸差別逐漸明顯，涂層表面粗糙度增加；隨著H2/MTS摩爾比的增加，SiC顆粒形核作用逐漸增強(qiáng)，顆粒尺寸逐漸減小且分布均勻，涂層致密度增加；C/C表面和碳纖維表面SiC涂層結(jié)構(gòu)均以孿晶和層錯(cuò)為主；在CVD-SiC的生長過程中，存在PAN碳纖維表面溝槽和沉積SiC層的兩種模板效應(yīng)，SiC涂層隨厚度的增加從層狀/島狀生長逐漸轉(zhuǎn)變?yōu)閷訝?島狀生長模式；氧乙炔焰燒蝕環(huán)境下，SiC涂層可以提高C/C復(fù)合材料的短時(shí)抗燒蝕性能；隨著燒蝕循環(huán)次數(shù)的增加，熱震作用導(dǎo)致SiO2層中缺陷的尺寸和數(shù)量進(jìn)一步增加，SiO2層中的微孔逐漸轉(zhuǎn)變?yōu)槠茐男缘目锥矗觿×送繉拥难趸瘬p失和火焰剝蝕損失，導(dǎo)致涂層逐漸失效。涂層燒蝕中心區(qū)域的燒蝕行為以氧化腐蝕和機(jī)械剝蝕為主，燒蝕過渡區(qū)域和邊緣區(qū)域的燒蝕行為以氧化腐蝕為主；隨著燒蝕熱流量的增加，燒蝕中心區(qū)域SiC涂層的燒蝕行為由以氧化腐蝕和機(jī)械剝蝕為主轉(zhuǎn)變?yōu)橐詺饣癁橹�，SiO2層的損耗隨著燒蝕區(qū)域逐漸遠(yuǎn)離燒蝕中心而不斷降低，試樣質(zhì)量燒蝕率和線燒蝕率明顯升高。 以ZrCl4-C3H6-Ar-H2為反應(yīng)體系，采用LPCVD法分別在C/C復(fù)合材料和碳纖維表面制備了ZrC涂層，涂層的主要成分為立方相ZrC。隨著沉積溫度升高，涂層顆粒生長速率增加，涂層生長均勻性有所降低，擇優(yōu)取向從（111）向（200）面轉(zhuǎn)變；隨著H2濃度的增加，涂層顆粒尺寸逐漸減小且變得均勻，擇優(yōu)取向從（111）向（200）向（220）面轉(zhuǎn)變，涂層致密性提高；隨著沉積位置距進(jìn)氣口距離的增加，反應(yīng)物濃度逐漸降低，涂層形核作用增強(qiáng)，顆粒尺寸逐漸減小，涂層生長均勻性增加。 采用氧乙炔焰測(cè)試了C/C復(fù)合材料表面ZrC涂層的抗燒蝕性能并分析了其燒蝕機(jī)理。結(jié)果表明：不同沉積溫度下制備的ZrC涂層的抗燒蝕性能隨著沉積溫度的升高而提高；在1350℃溫度下制備的涂層表現(xiàn)出最佳的抗燒蝕性能；在燒蝕過程中，ZrO2層和ZrCxOy層有效地阻礙了氧氣在涂層中的擴(kuò)散并及時(shí)愈合燒蝕過程中出現(xiàn)的孔洞和微裂紋等缺陷，同時(shí)削弱了火焰對(duì)涂層的機(jī)械剝蝕作用；不同H2濃度下制備的ZrC涂層的抗燒蝕性能隨著H2濃度的升高而先提高后降低；納米結(jié)構(gòu)涂層通過納米粒子增韌涂層的作用，降低火焰對(duì)涂層的剝蝕作用，提高了涂層抗燒蝕性能；在部分涂層的燒蝕過程中生成了ZrO2納米棒，ZrO2納米顆粒在納米棒的生長中發(fā)揮了催化劑的作用并提供了納米棒的生長基底，納米棒的生長機(jī)制為V-L-S和OAG機(jī)制；在循環(huán)燒蝕條件下，ZrC涂層存在兩種燒蝕模式：表面燒蝕和內(nèi)部燒蝕。隨著燒蝕循環(huán)次數(shù)的增加，涂層中缺陷的數(shù)量和尺寸由于熱震作用而逐漸增加，涂層由表面燒蝕轉(zhuǎn)變?yōu)閮?nèi)部燒蝕，ZrC在燒蝕過程中的結(jié)構(gòu)轉(zhuǎn)變過程為ZrC→ZrCxOy→ZrO2；在不同熱流量燒蝕條件下，隨著燒蝕熱流量的增加，氧氣在涂層中的擴(kuò)散量增加，ZrC→ZrCxOy→ZrO2的轉(zhuǎn)變過程隨著熱流量的增高而加速。 通過涂層設(shè)計(jì)，采用LPCVD法在C/C表面制備SiC/ZrC復(fù)合涂層和SiC/ZrC/SiC多層涂層，內(nèi)層SiC有效的緩解了ZrC層和C/C基體的熱膨脹不匹配，增強(qiáng)了涂層和C/C基體的結(jié)合，外層SiC延緩了火焰和ZrC層的接觸，SiO2層的損耗帶走大量的熱量并降低了涂層表面溫度，進(jìn)一步提高了C/C復(fù)合材料的抗燒蝕性能。
[Abstract]:Carbon / carbon (C/C) composites have an extremely wide range of applications in the field of Aeronautics and Astronautics due to their excellent high temperature properties. However, the rapid oxidation of this material under the oxygen environment above 370 degrees centigrade limits its application as the thermal structure of Aeronautics and Astronautics and the application of thermal protection materials. The coating technology is an effective means to solve this problem,.SiC and ZrC because of its high melting. Point and good high temperature stability are ideal materials for ablative coating on the surface of C/C composite.
The low pressure chemical vapor deposition (Low Pressure Chemical Vapor Deposition, LPCVD) was used to prepare SiC, ZrC coating on the surface of C/C composite and carbon fiber, and the effect of process parameters on the microstructure of the coating was studied. The coating was investigated and studied under the condition of cyclic ablation and different heat flow ablation through oxygen acetylene flame. In order to alleviate the thermal expansion mismatch of the ZrC coating and improve the ablative performance of the coating, the SiC/ZrC composite coating and the SiC/ZrC/SiC multilayer coating were designed and prepared for the thermal expansion mismatch between the ZrC coating and the C/C matrix. The X- ray diffractometer, scanning electron microscope, transmission electron microscope and oxyacetylene flame ablation were used to analyze the corrosion resistance of the coating. The microstructure and ablation properties of the coating were studied by means of testing. The main contents and results of this study are as follows:
The SiC coating was prepared on the surface of C/C composite and on the surface of carbon fiber on the surface of C/C composite and carbon fiber on the surface of C/C composite with MTS-H2-Ar as the reaction system. By analyzing the morphology of the coating, the influence of the deposition temperature and molar ratio of H2/MTS to the structure of the SiC coating was obtained. With the increase of the deposition temperature, the SiC particles were produced. With the increase of the particle size, the surface roughness of the coating increases. With the increase of the H2/MTS molar ratio, the nucleation of SiC particles increases gradually, the particle size decreases and the distribution is uniform, the density of the coating increases, and the structure of the SiC coating on the surface of C/C and the surface of carbon fiber is mainly twinning and stacking, and in CVD-SiC During the growth process, there are two template effects on the surface groove of PAN carbon fiber and the deposition of SiC layer. As the thickness increases, the SiC coating gradually changes from the layer / island growth to the layered + island growth mode. Under the oxygen acetylene flame ablative environment, the SiC coating can improve the short-time anti ablation performance of the C/C composite; with the increase of the times of the ablation cycle, the SiC coating can be improved. The thermal shock causes the size and quantity of the defects in the SiO2 layer to be further increased, and the micropores in the SiO2 layer are gradually transformed into destructive holes, which aggravate the oxidation loss and the loss of the flame erosion, resulting in the gradual failure of the coating. The ablation behavior of the center area of the coating is mainly oxidized and mechanical denudation, and the transition area and edge are ablated. The ablative behavior of the rim region is mainly oxidation corrosion. With the increase of the ablation heat flux, the ablation behavior of the SiC coating in the central area of the ablation center is mainly converted from oxidation corrosion and mechanical denudation to gasification. The loss of the SiO2 layer decreases with the ablation zone gradually away from the ablation center, and the mass ablative rate and the line ablation rate of the sample are clear. Increase significantly.
With ZrCl4-C3H6-Ar-H2 as the reaction system, the ZrC coating was prepared on the surface of C/C composite and carbon fiber by LPCVD. The main component of the coating was cubic ZrC., with the increase of the deposition temperature, the growth rate of the coating particles increased, the uniformity of the coating growth decreased, the preferred orientation changed from (111) to (200) surface, with the increase of H2 concentration. Adding, the size of the coated particles gradually decreases and becomes uniform. The preferred orientation changes from (111) to (200) to (220) surface, and the coating densification increases. With the increase of the distance from the inlet to the inlet, the concentration of the reactant decreases gradually, the nucleation of the coating increases, the particle size decreases, and the uniformity of the coating increases.
The ablative properties of the ZrC coating on the surface of C/C composites were measured by oxyacetylene flame and its ablation mechanism was analyzed. The results showed that the ablative performance of the ZrC coating prepared at different deposition temperatures increased with the increase of the deposition temperature; the coating prepared at 1350 C showed the best ablative performance; in the ablation process, the corrosion resistance of the coating was improved. The ZrO2 layer and the ZrCxOy layer effectively obstruct the diffusion of oxygen in the coating and heal the holes and micro cracks in the ablation process in time, and weaken the mechanical denudation of the flame to the coating. The ablative properties of the ZrC coating prepared at different H2 concentrations increase first and then decrease with the increase of the concentration of H2; The coating was toughened by nano particles, the denudation effect of flame on the coating was reduced and the ablative performance of the coating was improved. ZrO2 nanorods were formed during the ablation process of some coatings. ZrO2 nanoparticles played the role of the catalyst in the growth of nanorods, and the growth of nanorods. The mechanism is V-L-S and OAG mechanism. Under cyclic ablative conditions, there are two kinds of ablation modes in ZrC coating: surface ablation and internal ablation. With the increase of the number of ablation cycles, the number and size of the defects in the coating gradually increase due to thermal shock, the coating changes from surface ablation to internal ablation, and the structure transformation of ZrC in the process of ablation. The process is ZrC - ZrCxOy - ZrO2, and the diffusion of oxygen in the coating increases with the increase of the ablation heat flow, and the transition process of ZrC to ZrCxOy to ZrO2 accelerates with the increase of heat flux under different heat flow ablation conditions.
Through the coating design, the SiC/ZrC composite coating and SiC/ZrC/SiC multilayer coating are prepared by LPCVD method on the C/C surface. The inner layer SiC effectively relieves the thermal expansion mismatch between the ZrC layer and the C/C matrix, enhances the combination of the coating and the C/C matrix. The outer SiC delaying the contact between the flame and the ZrC layer, the loss of the SiO2 layer takes away a large amount of heat and reduces the coating. Surface temperature further enhances the ablation resistance of C/C composites.
【學(xué)位授予單位】：西北工業(yè)大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2015
【分類號(hào)】：TB332

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