Multi-scale Modeling and Finite Element Analyses of Thermal Conductivity of 3D C/SiC Composites Fabricating by Flexible-Oriented Woven Process

Thermal conductivity is one of the most significant criterion of three-dimensional carbon fiber-reinforced SiC matrix composites(3D C/SiC).Represent volume element(RVE)models of microscale,void/matrix and mesoscale proposed in this work are used to simulate the thermal conductivity behaviors of the 3D C/SiC composites.An entirely new process is introduced to weave the preform with three-dimensional orthogonal architecture.The 3D steady-state analysis step is created for assessing the thermal conductivity behaviors of the composites by applying periodic temperature boundary conditions.Three RVE models of cuboid,hexagonal and fiber random distribution are respectively developed to comparatively study the influence of fiber package pattern on the thermal conductivities at the microscale.Besides,the effect of void morphology on the thermal conductivity of the matrix is analyzed by the void/matrix models.The prediction results at the mesoscale correspond closely to the experimental values.The effect of the porosities and fiber volume fractions on the thermal conductivities is also taken into consideration.The multi-scale models mentioned in this paper can be used to predict the thermal conductivity behaviors of other composites with complex structures.

C/SiC/MoSi_2-SiC-Si multilayer coating for oxidation protection of carbon/carbon composites

C/SiC/MoSi2-SiC-Si oxidation protective multilayer coating for carbon/carbon （C/C） composites was prepared by pack cementation and slurry method. The microstructure, element distribution and phase composition of the as-received coating were analyzed by scanning electron microscopy （SEM）, energy dispersive X-ray spectroscopy （EDS） and X-ray diffraction （XRD）. The results show that the multilayer coating was composed of MoSi2, SiC and Si. It could effectively protect C/C composites against oxidation for 200 h with the mass loss of 3.25% at 1873 K in static air. The mass loss of the coated C/C composites results from the volatilization of SiO2 and the formation of cracks and bubble holes in the coating.

Characterization of SiC nanowires prepared on C/C composite without catalyst by CVD

SiC nanowires were prepared on C/C composite surface without catalyst by chemical vapor deposition（CVD） using CH3 SiCl3 as precursor.SEM images of the CVD-product reveal that some long nanowires have grown to tens of micrometers with some gathered as a ball.Some short nanowires agglomerate like chestnut shell with many thorns accompanied by some deposited nano-particles.XRD,Raman-spectrum and FTIR patterns indicate that the product is a typical β-SiC.TEM images show that the nanowires have a wide diameter range from 10 to 100 nm,and some thin nanowires are bonded to the thick one by amorphous CVD-SiC.A SiC branch generates from an amorphous section of a thick one with an angle of 70° between them,which is consistent with the [111] axis stacking angle of the crystal.SAED and fast Fourier transform（FFT） patterns reveal that the nanowires can grow along with different axes,and the bamboo-nodes section is full of stacking faults and twin crystal.The twisted SiC lattice planes reveal that the screw dislocation growth is the main mechanism for the CVD-SiC nanowires.

Effect of ZrC-SiC content on microstructure and ablation properties of C/C composites

C/C-ZrC-SiC composites with different ZrC-SiC contents were fabricated by precursor infiltration and pyrolysis. The effect of ceramic content on the microstructure and ablation resistance was investigated. Both the C/C-SiC and C/C-ZrC-SiC composites exhibited good ablation resistance under the plasma flame above 2300℃. Withtheincreaseof ZrC content, a continuous oxide layer and a solid Zr-Si-O mesophase were formed during the ablation. And the structure of the formed oxides layer closely linked with the contents of ZrC-SiC ceramics. The solid ZrO2-ZrC and Zr-Si-O mesophase could increase the viscosity of SiO2 moderately and improve the anti-scouring ability. The continuous SiO2-ZrO2-ZrC-SiC layer would serve as a thermal and oxygen barrier for preventing the substratefrom further ablation. The C/C-ZrC-SiC composites with 27.2%ZrC and 7.56%SiC shows superior ablation resistance, and the mass and linear ablation rates are-3.51 mg/s and-1.88 μm/s, respectively.

浆料浸渍辅助PIP工艺制备C/HfC-SiC复合材料的微观结构及性能研究

针对高速飞行器对于防热/承载一体化超高温陶瓷基复合材料的迫切需求,以及现有反应型HfC先驱体存在的成本高、效率低和致密效果差等不足,本研究将HfC亚微米粉体配制成稳定的陶瓷浆料,利用浆料加压浸渍辅助先驱体浸渍裂解(PIP)工艺制备了HfC基体均匀分布的C/HfC-SiC复合材料,探讨了HfC含量对于复合材料微观结构、力学与烧蚀性能的影响。结果表明,当HfC实际体积分数为13.1%~20.3%时,复合材料密度为2.20~2.58 g·cm^(-3),开孔率约为5%。通过单层碳布加压浸渍陶瓷浆料,HfC颗粒能够分散到纤维束内部,且在复合材料中分布比较均匀。提高HfC含量会降低复合材料纤维含量,其力学性能也呈现出降低趋势。当HfC体积分数为20.3%时,复合材料的密度、拉伸强度和断裂韧性分别为2.58 g·cm^(-3)、147 MPa和9.3 MPa·m^(1/2);经氧乙炔焰烧蚀60 s后,复合材料的线烧蚀率和质量烧蚀率分别为0.0062 mm/s和0.005 g/s,烧蚀过程中形成的熔融相Hf_(x)Si_(y)O_(z)能覆盖在材料表面,起到良好的保护作用。

Oxidation behavior of C/C composites with SiC/ZrSiO_4-SiO_2 coating

A SiC/ZrSiO4？SiO2 （SZS） coating was successfully fabricated on the carbon/carbon （C/C） composites by pack cementation, slurry painting and sintering to improve the anti-oxidation property and thermal shock resistance. The anti-oxidation properties under different oxygen partial pressures （OPP） and thermal shock resistance of the SZS coating were investigated. The results show that the SZS coated sample under low OPP, corresponding to the ambient air, during isothermal oxidation was 0.54% in mass gain after 111 h oxidation at 1500 ° C and less than 0.03% in mass loss after 50 h oxidation in high OPP, corresponding to the air flow rate of 36 L/h. Additionally, the residual compressive strengths （RCS） of the SZS coated samples after oxidation for 50 h in high OPP and 80 h in low OPP remain about 70% and 72.5% of those of original C/C samples, respectively. Moreover, the mass loss of SZS coated samples subjected to the thermal cycle from 1500 ° C in high OPP to boiling water for 30 times was merely 1.61%.

C/SiC复合材料数据库及机器学习性能预测平台的设计与开发

以MySQL Workbench 8.0为数据库平台,采用三层浏览器/服务器架构,利用PyCharm 2022开发了一套基于Web界面和机器学习技术的C/SiC复合材料数据库系统,该系统包括材料数据库和机器学习模型2部分,具有对材料组分结构、制备工艺、试验性能等材料研发各阶段的信息查询、添加、修改、删除、搜索以及支持信息管理、设计分析视图、案例推理辅助设计、用户与系统管理等功能。基于神经网络回归算法训练机器学习模型,利用材料微观结构参数预测材料力学性能,对不同微观结构参数的影响权重进行评价,并部署在系统平台中;通过Web用户界面调用机器学习模型,对预留的验证集数据进行拉伸模量和弯曲模量预测。结果表明:机器学习模型预测材料力学性能的精度达到95%左右,训练出来的预测模型具有良好的精度与泛化能力。

SiC-ZrC复相超高温陶瓷改性C/C复合材料的研究进展

SiC-ZrC复相超高温陶瓷改性C/C复合材料的制备工艺原理与单一陶瓷相改性C/C复合材料的工艺原理基本相同,但SiC-ZrC复相陶瓷具有耐高温、温域宽(1600~2500℃)、抗氧化、工艺适应性好等优点,在测试和应用中表现出优异的力学性能和抗烧蚀性能,能够有效填补目前高温段热防护材料的空缺,因此已经成为C/C复合材料基体掺杂改性的重要选择,在航天飞行器防热领域极具应用潜力。本文针对C/C-SiC-ZrC复合材料的发展潜力和应用空间,从制备工艺、结构特征以及性能特点三个方面综述了C/C-SiC-ZrC复合材料当前的研究进展,分析了制备工艺对复合材料微结构和性能的影响规律,提出了基于工程应用C/C-SiC-ZrC防热材料的发展建议。

Compositional and Hollow Engineering of Silicon Carbide/Carbon Microspheres as High-Performance Microwave Absorbing Materials with Good Environmental Tolerance

Microwave absorbing materials(MAMs)characterized by high absorption efficiency and good environmental tolerance are highly desirable in practical applications.Both silicon carbide and carbon are considered as stable MAMs under some rigorous conditions,while their composites still fail to produce satisfactory microwave absorption performance regardless of the improvements as compared with the individuals.Herein,we have successfully implemented compositional and structural engineering to fabricate hollow Si C/C microspheres with controllable composition.The simultaneous modulation on dielectric properties and impedance matching can be easily achieved as the change in the composition of these composites.The formation of hollow structure not only favors lightweight feature,but also generates considerable contribution to microwave attenuation capacity.With the synergistic effect of composition and structure,the optimized SiC/C composite exhibits excellent performance,whose the strongest reflection loss intensity and broadest effective absorption reach-60.8 dB and 5.1 GHz,respectively,and its microwave absorption properties are actually superior to those of most SiC/C composites in previous studies.In addition,the stability tests of microwave absorption capacity after exposure to harsh conditions and Radar Cross Section simulation data demonstrate that hollow SiC/C microspheres from compositional and structural optimization have a bright prospect in practical applications.

管状C/SiC复合材料高温空气氧化行为与宏细观建模研究

氧化损伤是影响火箭发动机用C/SiC复合材料喷管寿命的主要因素之一。为准确评估C/SiC复合材料喷管的氧化损伤,本研究以近似喷管结构的管状C/SiC复合材料为实验对象,研究了管状C/SiC复合材料在高温(900~1300℃)空气环境下的氧化行为,包括其组成、结构及力学性能的演变规律,发现管状C/SiC复合材料在该高温空气环境下表现出受扩散控制的氧化特征,质量与剩余强度随时间呈幂函数下降趋势,下降速率与温度正相关。在此基础上,从氧化动力学与传质学理论角度出发,建立了管状C/SiC复合材料细观/宏观尺度氧化模型,模拟了管状C/SiC复合材料高温空气氧化过程,并预测了材料的质量与剩余强度。模型预测结果与实验数据拟合程度较高,可为C/SiC复合材料喷管的寿命评估提供参考。

沉积热解炭与树脂炭比例对C/C-SiC复合材料弯曲强度的影响

以针刺整体炭毡为坯体,采用树脂浸渍和化学气相沉积混合的方法制备得到相同密度的C/C多孔体,采用熔硅浸渗(RMI)制得C/C-SiC复合材料。研究了沉积热解炭与树脂炭比例对基体显微结构及弯曲性能的影响。结果表明:随着沉积得到的沉积热解炭含量增加,C/C-SiC复合材料基体内部孔隙率先降后升,而密度、弯曲强度先增后减。当沉积热解炭与树脂炭的比例为1∶1时,C/C-SiC复合材料密度与弯曲强度最高,分别达到2.03 g/cm^(3)和240 MPa。

Fabrication of Y_2Si_2O_7 coating and its oxidation protection for C/SiC composites

Yttrium silicate （Y2Si2O7） coating was fabricated on C/SiC composites through dip-coating with silicone resin ＋ Y2O3 powder slurry as raw materials. The synthesis, microstructure and oxidation resistance and the anti-oxidation mechanism of Y2Si2O7 coating were investigated. Y2Si2O7 can be synthesized by the pyrolysis of Y2O3 powder filled silicone resin at mass ratio of 54.2：45.8 and 800 °C in air and then heat treated at 1400 °C under Ar. The as-fabricated coating shows high density and favorable bonding to C/SiC composites. After oxidation in air at 1400, 1500 and 1600 °C for 30 min, the coating-containing composites possess 130%-140% of original flexural strength. The desirable thermal stability and the further densification of coating during oxidation are responsible for the excellent oxidation resistance. In addition, the formation of eutectic Y-Si-Al-O glassy phase between Y2Si2O7 and Al2O3 sample bracket at 1500 °C is discovered.

SiC纳米线对大气等离子喷涂硅涂层性能的影响

为提升C/SiC复合材料表面Si涂层的韧性及其与C/SiC复合材料的结合强度,首先以10 mm×10 mm×10 mm的C/SiC复合材料作为基体,在基体表面生成约20μm厚的SiC纳米线(SiCnws)多孔层;再用大气等离子体喷涂法分别将生长SiCnws的基体和未生长SiCnws的基体喷涂约30、60、90μm厚的Si涂层。研究SiCnws对涂层试样的结合强度和抗氧化性的影响,并借助XRD、SEM、TEM和EDS对所制备的SiCnws和SiCnws/Si涂层进行物相组成、显微结构的分析。结果表明:1)制备的SiCnws形状平直,表面光滑,取向随机,直径为100~200 nm,是沿[111]晶向择优生长的β-SiC;2)SiCnws引入到Si涂层后,SiCnws/Si涂层试样的结合强度均比相应的Si涂层试样的高,说明SiCnws增强了Si涂层与C/SiC复合材料的结合;3)从室温至1400℃经历12次热震循环后,SiCnws/Si涂层试样的质量损失率比相应Si涂层试样的低20.7%~37.2%,说明SiCnws能有效缓解热应力,抑制裂纹的形成和扩展,降低裂纹尺寸和数量,提高涂层的抗氧化性。

2D-C/SiC复合材料的面内剪切本构模型

为了表征2D-C/SiC复合材料的面内剪切行为,考虑基体开裂、界面脱粘、纤维桥连弯曲等损伤机制,提出宏细观两尺度下的含损伤体元模型;引入热失配应力的影响,在分别表征卸载弹性应变和残余应变的基础上,建立材料的温度相关面内剪切本构模型。开展室温单调加载和加卸载面内剪切实验,发现残余应变和弹性应变均随剪应力的增大逐渐增大,而卸载模量随剪应力的增大持续减小。将模型用于2D-C/SiC复合材料剪切行为的模拟,结果表明:模型对于弹性应变、残余应变、卸载模量和整体应力-应变曲线的预测值均与实验数据吻合,验证了分析模型的合理性与准确性;在此基础上,给出2D-C/SiC复合材料在不同温度下的面内剪切应力-应变关系曲线,为热结构设计提供参考。

C/SiC复合材料的烧蚀机理试验研究

C/SiC复合材料具有优异的热力学性能,在临近空间领域具有较好的应用前景。针对C/SiC复合材料的烧蚀机理理论方法开展研究,建立了C/SiC复合材料主/被动氧化烧蚀分析方法,并在传统主动和被动氧化烧蚀的基础上,对于更高温度条件则采用一种升华分解烧蚀模型。通过设计典型状态电弧风洞试验,验证了主/被动氧化模型烧蚀、升华分解烧蚀模型的准确性,试验结果表明典型状态下C/SiC复合材料无因次质量烧蚀率与理论值吻合,有关研究及结果可以为C/SiC复合材料防热设计分析提供参考。

C/SiC复合材料的人工孔发汗冷却性能分析及优化研究

C/SiC复合材料在热防护领域中应用广泛,但受制备工艺、成本等方面的限制,具有低孔隙率、小孔径的特征,在发汗冷却过程中这些微小孔隙难以支撑足够的冷却剂供应量且易发生堵塞,限制了冷却的进行。针对此问题,本文研究通过增加人工孔来改善C/SiC复合材料发汗冷却性能的可行性。建立了人工孔表征单元结构及等效模型,获得了打孔后复合材料内冷却工质的流量比及等效渗透率的变化情况,探究了打孔方式与工质流量对复合材料等效体换热系数的影响规律,并拟合了打孔后复合材料等效体换热系数经验公式。结果表明:渗透特性方面,冷却工质的主要流量分布于人工孔中;对于渗透率为1×10^(-16) m^(2)的低渗透率材料,打孔后复合材料自身工艺孔中的流量占比小于0.1%,其中的工质流动可忽略;在换热特性方面,可通过调节打孔方式改善复合材料的换热性能,相同渗透率下调节打孔方式可使体换热系数提升154%。

改性C/SiC-ZrC复合材料热化学烧蚀仿真研究

基于C/SiC复合材料基体改性制备超高温陶瓷基复合材料,是满足高超音速飞行器对热防护系统材料所需更高要求的有效途径。基于热化学平衡理论构建了C/SiC-ZrC复合材料的烧蚀模型,选取文献中相同制备方式下两组不同体积分数的C/SiC-ZrC复合材料,并利用MATLAB计算出两组材料的无量纲烧蚀率,然后在COMSOL多物理场分析软件中建立数值仿真,将仿真结果与文献实验结果进行对比,误差分别为8.7%~16.9%和1.05%~11.07%,验证了模型的有效性。

ZrC纳米粉体改性C/C-SiC复合材料的微观结构和烧蚀性能

为改善C/C-SiC复合材料的抗烧蚀性能,以ZrC纳米粉体和Si粉为反应渗料,采用反应熔渗(reactive melt infiltration,RMI)法制备ZrC纳米粉体改性C/C-SiC复合材料。采用X射线衍射仪、扫描电镜和能谱仪等研究ZrC纳米粉体含量对C/C-SiC复合材料微观结构和烧蚀性能的影响。结果表明:随ZrC纳米粉体含量增加,复合材料的孔隙率增大,而密度变化不大。ZrC纳米粉体一部分弥散分布在SiC基体中,一部分则发生了团聚。烧蚀30 s后,ZrC纳米粉体摩尔分数为6%时,复合材料的质量烧蚀率和线烧蚀率最低,分别为2.0 mg/s和3.9μm/s。随ZrC纳米粉体含量增加,烧蚀过程中形成的ZrO_(2)含量增多,对SiO_(2)的钉扎作用明显增强,能有效提升C/C-SiC复合材料的抗烧蚀性能。

2.5D C/SiC复合材料铣削材料去除的实验研究

为了探究2.5D C/SiC复合材料铣削加工的材料去除特性,分别选用端铣刀和鱼鳞铣刀对2.5D C/SiC复合材料开展普通铣削和超声振动辅助铣削实验。分析了四种铣削工况下切削力、切削温度的变化规律,研究了0°、90°和z向针刺纤维的去除特性。结果表明,相比于传统端铣刀和普通铣削,鱼鳞铣刀和超声振动辅助铣削分别可以显著地降低切削力和切削温度。超声振动辅助铣削可以使纤维的整体去除变为破碎去除,减小表面缺陷。鱼鳞铣刀和超声振动辅助铣削的组合工艺方式可以较大程度地降低表面缺陷、切削力和切削温度,提高工件表面质量,为2.5D C/SiC复合材料低损伤铣削提供了可行性。

C/SiC复合材料单颗磨粒切削有限元仿真及磨削实验分析

为了探究C/SiC复合材料的去除机制,建立了三维C/SiC复合材料单颗磨粒微观切削有限元模型。借助Abaqus有限元分析软件,使用BrittlecCracking模型、Johnson-Holmquist 2模型和内聚力模型分别被用来模拟碳纤维,SiC陶瓷及界面层的材料属性,并以此建立三相微观切削模型来分析不同切削速度和切削深度下的材料加工变形规律和切削力变化趋势。同时参考C/SiC复合材料锥形电镀金刚石工具加工表面形貌实验进行辅助分析。结果表明:C/SiC复合材料的切削过程主要表现为碳纤维的脆性去除;随着切削速度的增加,界面层的破坏程度减少且切削力降低;随着切削深度增加,切削力增加且界面层损伤程度增大。这些结果为进一步了解碳纤维复合材料切削时的材料去除机理提供了一定的借鉴意义。