Tensile Mechanical Behavior and Failure Mechanism of a Plain-Woven SiCf/SiC Composites at Room and Elevated Temperatures

Ceramic matrix composites (CMCs) are the preferred materials for solving advanced aerospace high-temperature structural components;it has the comprehensive advantages of higher temperature (~1500˚C) and low density. In service environments, CMCs exhibit complex damage mechanisms and failure modes, which are affected by constituent materials, meso-architecture and inhere defects. In this paper, the in-plane tensile mechanical behavior of a plain-woven SiCf/SiC composite at room and elevated temperatures was investigated, and the factors affecting the tensile strength of the material were discussed in depth. The results show that the tensile modulus and strength of SiCf/SiC composites at high temperature are lower, but the fracture strain increases and the toughness of the composites is enhanced;the stitching holes significantly weaken the tensile strength of the material, resulting in the material is easy to break at the cross-section with stitching holes.

连续SiCf/TC17复合材料室温偏轴拉伸性能研究

采用磁控溅射法结合热等静压工艺制备SiCf/TC17复合材料,通过SEM观察试样的断口形貌,研究了复合材料在室温的偏轴拉伸性能及断裂机制。结果表明:纤维偏轴角度在0°~2°间,复合材料轴向性能变化较小,拉伸强度稳定在1960~1987 MPa;纤维偏轴角度再增大时(>2°),材料拉伸强度近似呈单调线性降低,由1870 MPa降至1797 MPa。纤维偏轴角度较小时(≤2°),平坦区基体与纤维断裂面平整,且两者的断裂面平行。纤维/基体界面没有明显的脱粘破碎迹象;纤维偏轴角度较大时(>2°),部分纤维存在“斜切断裂”,纤维拔出距离变长,且不再与基体的断裂面保持在同一平面,基体撕裂损伤严重。依据断口形貌结合局部承载模型,详细论述了SiCf/TC17复合材料两种拉伸失效的断裂过程。纤维偏轴角度较小时(≤2°),裂纹萌生于纤维间距较小的反应层,在界面处钝化或偏转进而形成不同截面的平坦区,当纤维超过承载能力极限,试样整体断裂;纤维偏轴角度较大时(>2°),“拉-剪”耦合效应导致C涂层与反应层间的界面脱粘破碎形成裂纹源,裂纹加速反应层受损或导致界面脱粘致使纤维断裂,当基体及剩余纤维超过承载能力极限,试样整体断裂。

Electromagnetic wave absorption and mechanical properties of SiC nanowire/low-melting-point glass composites sintered at 580°C in air

Si C nanowires are excellent high-temperature electromagnetic wave (EMW) absorbing materials. However, their polymer matrix composites are difficult to work at temperatures above 300℃, while their ceramic matrix composites must be prepared above 1000℃ in an inert atmosphere. Thus, for addressing the abovementioned problems, SiC/low-melting-point glass composites were well designed and prepared at 580℃ in an air atmosphere. Based on the X-ray diffraction results, SiC nanowires were not oxidized during air atmosphere sintering because of the low sintering temperature. Additionally, SiC nanowires were uniformly distributed in the glass matrix material. The composites exhibited good mechanical and EMW absorption properties. As the filling ratio of SiC nanowires increased from 5wt%to 20wt%, the Vickers hardness and flexural strength of the composite reached HV 564 and 213 MPa, which were improved by 27.7%and 72.8%, respectively, compared with the low-melting-point glass. Meanwhile, the dielectric loss and EMW absorption ability of SiC nanowires at 8.2–12.4 GHz were also gradually improved. The dielectric loss ability of low-melting-point glass was close to 0. However, when the filling ratio of SiC nanowires was 20wt%, the composite showed a minimum reflection loss (RL) of-20.2 dB and an effective absorption (RL≤-10 dB) bandwidth of2.3 GHz at an absorber layer thickness of 2.3 mm. The synergistic effect of polarization loss and conductivity loss in SiC nanowires was responsible for this improvement.

Damping performance of SiC nanoparticles reinforced magnesium matrix composites processed by cyclic extrusion and compression

This work dealt with the damping performance and its underlying mechanism in SiC nanoparticles reinforced AZ91D composite(SiC_(np)/AZ91D)processed by cyclic extrusion and compression(CEC).It was found that the CEC process significantly affects the damping performance of the composite due to alterations in the density of dislocations and grain boundaries in the matrix alloy.Although there would be dynamic precipitation of the Mg17Al12 phase during processing which increases the phase interface and limits the mobility of dislocations and grain boundaries.The results also showed that the damping capacity of 1%SiC_(np)/AZ91D composite continuously decreases with adding CEC pass number and it consistently increases with rising the applied temperature.Considering the first derivative of the tanδ-T curve,the dominant damping mechanism based on test temperature can be divided into three regions.These three regions are as follows(i)dislocation vibration of the weak pinning points(≤T_(cr)),(ii)dislocation vibration of the strong pinning points(T_(cr)∼T_(V)),and(iii)grain boundary/interface sliding(≥T_(V))

Effect of C/Mo Duplex-coating on Thermal Residual Stresses in SiCf/Ti2AlNb Composites

Three-dimensional finite element physical models considering the layered distribution of materials at the interface were developed to study the effect of the coating system on distributions of thermal residual stresses in SiCf/Ti2AlNb composites.Two coating systems were comparatively studied,namely C coating and C/Mo duplex-coating.The thermal residual stresses after 1 080 ℃/1 h solution treatment and 800 ℃/20 h ageing treatment in the composites were also analyzed.The experimental results show that Mo coating can decrease thermal residual stress magnitude in the matrix.However,it would increase the thermal residual stresses in the interfacial reaction layer of TiC.The change of radial thermal residual stress in TiC layer is inconspicuous after solid solution and ageing treatment,but the hoop and axial thermal residual stresses increase obviously.However,the heat treatment can obviously reduce hoop and axial thermal residual stresses of the matrix,which is benefit to restrain the initiation and propagation of cracks in the matrix.

SiC/SiC复合材料层板低速冲击及其剩余强度试验研究

高速飞行器中的陶瓷基复合材料结构在服役过程中不可避免地会遇到低速冲击问题,低速冲击后的损伤形式以及剩余承载能力是影响飞行器结构安全的关键问题。本研究以二维编织SiC/SiC复合材料板件为研究对象,在不同能量下开展了低速冲击试验,分析了低速冲击载荷下试验件的表面损伤状态,通过计算机断层扫描技术观察了试验件内部的损伤形貌,结合冲击过程中的冲击响应曲线以及应变历史曲线,分析了SiC/SiC复合材料低速冲击过程的损伤机理。针对含勉强目视可见损伤的试验件开展了冲击后剩余强度试验,研究了勉强目视可见损伤对SiC/SiC复合材料剩余承载性能的影响。结果表明,在低速冲击载荷的作用下,试验件的表面损伤主要包括无表面损伤、勉强目视可见损伤、半穿透损伤以及穿透损伤,试验件的内部损伤主要有锥形体裂纹、纱线断裂以及分层损伤。低速冲击损伤会严重影响SiC/SiC复合材料的剩余性能,虽然试验件损伤勉强目视可见,但其剩余压缩强度为无损件81%,剩余拉伸强度仅为无损件的68%。

基于数字图像相关方法的SiCf/SiC陶瓷基复合材料力学行为表征

SiCf/SiC陶瓷基复合材料具有低密度、耐高温、高比强度等优异特性,是新一代先进航空发动机热端部件的理想材料。为实现SiCf/SiC复合材料在服役环境下的可靠应用,亟须开展复合材料力学行为表征研究。与引伸计、应变片等其他测试方法相比,数字图像相关方法(digital image correlation,DIC)具有非接触式、全场测量和可操作性强等优点,能够实现对复杂耦合环境下复合材料损伤断裂等力学行为的原位表征,因而受到广泛关注。本文系统梳理和总结DIC在SiCf/SiC复合材料室温拉伸、弯曲、爆破等力学测试中的应用进展,介绍DIC在SiCf/SiC复合材料力学加载过程的高温测量,最后对应用于SiCf/SiC复合材料的DIC表征技术进行了总结及展望。

Ti预处理的SiC_(f)/SiC与镍基高温合金复合铸件的界面组织与强度

由SiC_(f)/SiC复合材料与K403镍基高温合金熔体制备的一体化铸件,冷却到室温时会出现自行断裂。通过采用Ti粉埋覆包渗工艺在1100℃下对SiC_(f)/SiC表面进行预处理,并在适当工艺下与K403镍基高温合金熔体进行陶瓷型精密铸造,成功实现SiC_(f)/SiC与K403镍基高温合金的一体化成形和界面的牢固结合。结果表明:Ti预处理层平均厚度为17μm左右,Ti向SiC_(f)/SiC渗透、扩散和反应,形成含TiC,Ti3SiC2,Ti5Si3Cx,SiC相的显微组织;经过与高温镍基金属液复合铸造后,预处理层演变成厚约120μm的界面反应层,其典型界面组织为Ni2Si+C+Al4C3+MC(M主要含Ti及少量的Cr,Mo,W)。预处理层的存在减轻Ni与SiC的有害石墨化反应,缓解高温金属液对SiC_(f)/SiC的热冲击,形成的界面反应层降低热膨胀系数失配造成的热应力,使得SiC_(f)/SiC与K403一体化铸件结合界面的室温剪切强度达到63.5 MPa。

SiCf/TC17/GH4169复合材料界面结构和元素扩散研究

采用多组元两步构筑成型方法并结合热等静压技术制备了SiCf/TC17/GH4169复合材料,研究了复合材料界面微观结构组成和元素扩散规律。结果表明,在SiCf/TC17/GH4169复合材料中,SiC纤维保持完整、圆度均匀,纤维和TC17合金形成了连续致密的TiC反应层,TC17钛合金和GH4169发生元素扩散,形成了多个反应层。GH4169中Ni、Fe、Cr扩散进入TC17,形成了TiNi_(3)、Fe Cr、TiNi、Ti_(2)Ni等反应产物,TiNi_(3)和FeCr呈交错分布,TiNi和Ti_(2)Ni各自均呈连续条状分布。TC17和GH4169形成的多个反应层总厚度为25μm,加入TC17过渡组元后,能够改善SiC纤维和GH4169界面相容性,避免纤维被高温合金侵蚀。

Particle Removal Mechanism of High Volume Fraction SiCp/Al Composites by Single Diamond Grit Tool

Particle removal mechanism was presented during machining particle SiC/Al composites with diamond grinding tool. The relevant removal modes and their mechanisms were discussed considering the impact and squeezing effect of diamond grit on the SiC particle. The experimental results show that the aluminum matrix has larger plastic deformation, so the aluminum mixed with the surplus SiC particles is cut from the surface. The SiC particles can be removed in multiple ways, such as broken/fractured, micro cracks, shearing and pulled out, etc. More particles removed by shearing, and less particles removed by fractured during material removal progress can produce a better machined surface.

环境温度对二维编织SiC/SiC复合材料拉伸性能的影响研究

为了研究环境温度对陶瓷基复合材料拉伸性能的影响,在室温和800℃,1000℃,1200℃惰性气体保护环境下开展了二维编织SiC/SiC复合材料的拉伸试验。采用数字图像相关技术采集了高温环境下试件的变形数据。通过光学显微镜和扫描电子显微镜拍摄了试件的断口形貌。结果表明:800~1200℃内,二维编织SiC/SiC复合材料的拉伸应力-应变响应同样具有明显的双线性特征,初始线性段的弹性模量与室温测试结果相近,高温环境下第二线性段弹性模量低于室温环境;800~1200℃惰性气体环境下材料拉伸强度较室温环境低20%左右;温度主要影响材料中纤维与基体的结合状态和SiC纤维的强度。一方面,温度越高断口纤维拔出情况越严重;另一方面,温度越高SiC纤维强度越低,二维编织SiC/SiC复合材料强度也有所下降。

FORMING PROCESS OF HOT-EXTRUDED SiCw/6061Al COMPOSITES(Ⅰ)

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SiC nanoparticles reinforced magnesium matrix composites fabricated by ultrasonic method

SiC nanoparticles reinforced magnesium matrix composites were fabricated by ultrasonic method.The AZ91 alloy and SiC nanoparticles with the average diameter of 50 nm were used as the matrix alloy and the reinforcement,respectively.The addition of nanoparticles was 0.1%,0.3%,and 0.5%(mass fraction) of the composites.The results of microstructural evaluation and mechanical properties indicate that the nanoparticles can be dispersed into magnesium alloys efficiently and uniformly with the aid of ultrasonic vibration.As compared with the matrix alloys,the grains of composites were refined and the mechanical properties of composites were improved significantly.The SEM and DSC analyses show that the SiC nanoparticles can act as the heterogeneous nucleation of α-Mg.Also,the strengthening mechanism responsible for the composites reinforced with SiC nanoparticles was discussed.

Research on the Characters of the Cutting Force in Vibration Cutting Particle Reinforced Metal Matrix Composites SiC_p/Al

In this paper, turning experiments of machining particle reinforced metal matri x composites(PRMMCs) SiC p/Al with PCD tools have been carried out. The cutting force characteristics in ultrasonic vibration turning compared with that in com mon turning were studied. Through the single factor experiments and multiple fac tor orthogonal experiments, the influences of three kinds of cutting conditions such as cutting velocity, amount of feed and cutting depth on cutting force were analyzed in detail. Meanwhile, according to the experimental data, the empirica l formula of main cutting force in ultrasonic vibration turning was conclude d. According to the test results, the cutting force is direct proportion to cutt ing depth basically according to the relation between cutting force and other fa ctors, which is similar to that of common cutting, so is the feed rate, but the influence is not so big. The influence of cutting speed is larger than that of f eed rate on cutting force because the efficient cutting time increases in vibrat ion cycle with the increase of cutting speed, which causes cutting force to incr ease. The research results indicate: (1) Ultrasonic vibration turning possesses much lower main cutting force than that in common turning when adopting smaller cutting parameters. If using larger cutting parameters, the difference will inco nspicuous. (2) There are remarkable differences of cutting force-cutting veloci ty characteristics in ultrasonic vibration turning from that in common turning m ainly because built-up edge does not emerge in ultrasonic turning unlike common turning in corresponding velocity range. (3) In ultrasonic vibration cutting, t he influence of cutting velocity on cutting force is most obvious among thre e cutting parameters and the influence of feed is smallest. So adopting lower cu tting velocity and larger cutting depth not only can reduce cutting force effect ively but also can ensure cutting efficiency. (4) The conclusions are useful in precision and super precision manufacturing thin-wall pieces.

Nano-SiC_P particles distribution and mechanical properties of Al-matrix composites prepared by stir casting and ultrasonic treatment

Nano-ceramic particles are generally difficult to add into molten metal because of poor wettability. Nano-SiC_Particles reinforced A356 aluminum alloy composites were prepared by a new complex process, i.e., a molten-metal process combined with high energy ball milling and ultrasonic vibration methods. The nano particles were β-SiC_P with an average diameter of 40 nm, and pre-oxidized at about 850 °C to form an oxide layer with a thickness of approximately 3 nm. The mm-sized composite granules containing nano-SiC_P were fi rstly produced by milling the mixture of oxidized nano-SiC_P and pure Al powders, and then were remelted in the matrix-metal melt with mechanical stirring and treated by ultrasonic vibration to prepare the composite. SEM analysis results show that the nano-SiC_P articles are distributed uniformly in the matrix and no serious agglomeration is observed. The tensile strength and elongation of the composite with 2 wt.% nano-SiC_P in as-cast state are 226 MPa and 5.5%, improved by 20% and 44%, respectively, compared with the A356 alloy.

Effect of SiC whiskers on the oxidation protective properties of SiC coatings for carbon/carbon composites

以便有效地采用唯一的高温度碳 / 碳的机械性质合成底层，原文如此，涂层增强了由原文如此，络腮胡子被包装硬化方法准备。效果原文如此，单个层的涂层和双层涂层的氧化抵抗性质上的络腮胡子被调查。原文如此络腮胡子在单个层原文如此涂层在反氧化性质上有小效果，但是显然改进热吃惊性质。有内部层的增强的涂层的双层涂层与原文如此内部层的涂层比双层涂层展出更多的完美的反氧化能力。

Oxidation Behavior of C/C-SiC Gradient Matrix Composites

Oxidation behavior of C/C-SiC gradient matrix composites and C/C composites were compared in stationary air. The results show that oxidation threshold of C-SiC materials increases with the amount of SiC particles in the codeposition matrix. Oxidation rate of C/C-SiC gradient matrix composites is significantly lower than that of C/C material. The micro-oxidation process was observed by SEM.

Oxidation behavior of CVI,MSI and CVI+MSI C/SiC composites

The oxidation behavior of chemical vapor infiltration(CVI),molten silicon infiltration(MSI)and CVI+MSI C/SiC composites at 500-1 400℃was studied.The oxidation below 900℃increased successively for CVI,CVI+MSI and MSI composites.However,the oxidation of CVI composite above 1 000 ℃was much faster thanthat of MSI and CVI+MSI composites. As active carbon atoms produced by siliconization of fibers during MSI process were oxidized first and decreased initial oxidation temperature.The initial oxidation temperature of MSI,MSI+CVI and CVI composites was 526,552 and 710℃,respectively.New active carbon atoms were generated due to the breaking of 2D molecular chains during oxidation,so the activation energy of three C/SiC composites was decreased gradually at 500-800℃with oxidation process,exhibiting a self-catalytic characteristic.

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。