SiC微粉含量对2D-SiC_f/SiC复合材料力学性能影响

对PIP法制备2D-SiC_f/SiC复合材料成形浆料中惰性填料SiC含量对2D-SiC_f/SiC复合材料孔隙率、纤维体积分数以及力学性能影响进行研究.研究表明,SiC微粉含量较低时,浆料粘度过低,导致层间存在较大气孔,纤维体积分数不高,致使复合材料力学性能不佳,当SiC微粉含量过高时,浆料粘度过大,层间基体厚度增加,纤维体积分数下降,并且浸渍效率降低,孔隙率增大,复合材料力学性能下降.当SiC微粉含量为33.3%时,复合材料具有较低的孔隙率和较高的纤维体积分数,复合材料具有较好的力学性能,弯曲强度和断裂韧性分别达到211.7 MPa和8.56 MPa·m~(1/2).     

反应烧结SiC制备SiC/B4C复合材料的研究

基于反应烧结SiC制备出相对密度较高的SiC/B4C复合材料,并探讨原料中C含量对SiC/B4C复合材料物相、显微结构、体积密度、力学性能的影响。结果表明,SiC/B4C复合材料的相组成为B4C、SiC、Si、B13C2和B12.97Si0.03C2。SiC/B4C复合材料的显微组织为:SiC相和B4C相均匀分布,游离Si填充在B4C相和SiC相的空隙处,且形成了连续相。随着原料中C含量的增加,复合材料的力学性能整体呈现先增加后降低的趋势。原料中C最佳添加量为10%(质量分数),对应SiC/B4C复合材料的维氏硬度、抗弯强度和断裂韧性分别为24.4GPa、361.3MPa和4.41MPa·m1/2,复合材料开口气孔率和体积密度分别为0.19%和2.58g/cm3。     

聚合物先驱体组分对SiC/SiBCN复合材料性能的影响

以SiC纤维为增强相,SiBCN复相陶瓷先驱体为浸渍剂,采用聚合物先驱体浸渍裂解工艺制备了SiC/SiBCN复合材料。采用SEM和力学性能测试对SiC/SiBCN复合材料氧化前后组分、形貌及力学行为进行了分析。试验表明,随着SiBCN复相陶瓷先驱体中聚硼氮烷(PBN)含量的增加,先驱体陶瓷产率先增加后降低,SiC/SiBCN复合材料1000℃/20 h氧化后的弯曲强度保留率亦先增加后降低。这主要归因于SiBCN复相陶瓷先驱体中PBN含量的增加有利于先驱体分子交联程度增加,更容易形成稳定的三维网络结构。此外,材料孔隙率以及SiBCN复相陶瓷的氧化行为也成为影响SiC/SiBCN复合材料氧化稳定性的重要因素。     

SiC/MoSi2复合材料500℃氧化行为研究

研究了不同SiC体积分数（30%-50%）的SiC/MoSi2复合材料低温500℃的氧化性能。结果表明：SiC/MoSi2复合材料在低温（500℃）时具有优异的抗氧化性能,氧化500h没有发生氧化粉化现象。复合材料的氧化增重随SiC体积分数的增加而减少。复合材料表面的抗氧化保护层均匀致密,材料内部缺陷少,材料内部晶界没有发生Mo与Si的氧化,材料的抗低温氧化性能得到显著提高。     

ZrB_2+SiC陶瓷高温氧化过程中SiC耗尽层的形成机制研究

ZrB_2+SiC陶瓷在高温氧化过程中会形成一层多孔的SiC耗尽层.本文首先计算了在高温氧化过程中的主要氧化产物.通过对氧化过程中相变机制的分析,利用质量守恒、固体区域体积守恒并结合反应速率方程,研究了SiC耗尽层的形成与演化过程,给出了孔隙率随温度的变化规律.结果表明:氧化过程中生成相的体积膨胀及SiC的初始体积含量是影响SiC耗尽层孔隙率的主要因素.对计算结果的分析解释了试验中发现的在低SiC含量下不出现耗尽层,以及氧化层破坏的现象.     

高能球磨法制备SiC/Al复合材料

采用高能球磨法制备了SiC颗粒增强Al基复合材料,研究了SiC含量对该复合材料力学性能的影响。结果表明,SiC/Al复合材料的硬度、屈服强度以及抗拉强度随SiC含量的增加而增大,而伸长率随之减小;SiC/Al复合材料呈延性断裂和脆性断裂混合断裂;随着SiC含量的增加,材料延性断裂特征减少。     

Si含量对放电等离子烧结制备(1-x)Ti3SiC2+xSiC复合材料的影响

以钛粉、硅粉和石墨粉为原料,制备出(1-x)Ti3SiC2+xSiC(x=0.1～0.8)复合材料,并利用X射线衍射仪对样品进行相组成分析.结果表明经1300℃放电等离子烧结15min后,可以得到纯净的0.9Ti3SiC2-0.1SiC和含有 微量石墨的0.2Ti3SiC2-0.8SiC复合材料,0.9Ti3SiC2-0.1SiC和0.2Ti3SiC2-0.8SiC复合材料的显微硬度分别为8.8和10.5GPa,均明显高于Ti3SiC2的(4GPa).随着SiC含量的增加,复合材料的硬度也增加,但杂质(石墨)和孔洞的含量也增多,成分为0.5Ti3SiC2-0.5SiC的复合材料在烧结过程中有少量Si流出;而当SiC含量增加到0.2Ti3SiC2-0.8SiC时,烧结过程中大量的Si流出使得复合材料无法成功烧结.     

Al含量及SiC预处理对SiCp/Ti基复合材料高温抗氧化性能的影响

通过800℃氧化试验,研究了不同Al含量以及SiC经600℃×3 h预处理后,SiCp/Ti基复合材料的氧化行为.利用SEM、EDS以及XRD分析了表面氧化层的形貌以及相组成.结果表明,未加Al复合材料氧化层的氧化产物主要为金红石TiO2,添加Al的材料中有少量Al2O3;对于SiC颗粒增强的Ti基复合材料,未加Al的抗氧化性能最好;当比较所有含Al的复合材料时,随着Al含量的增加,抗氧化性增强;对于具有相同Al含量的材料,SiC预处理可以促使界面较好结合,故可提高材料的抗氧化性.     

原位合成Ti3SiC2/SiC复合材料及其显微组织的观察

利用Si和TiC原位反应合成了Ti3SiC2/SiC复合材料.研究了不同烧结工艺参数和原料配比对形成复合材料的影响.利用X-射线衍射分析了材料的物相组成.所合成的材料中除Ti3SiC2和SiC外,还有TiC存在.利用扫描电镜和透射电镜观察了材料的微观组织,发现生成的SiC颗粒呈棒状和等轴状分布于Ti3SiC2基体中.在Ti3SiC2晶粒内部存在大量的位错和层错.     

Ti3SiC2/HAp陶瓷复合材料力学性能研究

以Ti3SiC2(10%～50%,体积分数)和HAp粉为原料,采用等离子体放电烧结(SPS)方法,在外加应力60 MPa,烧结温度1200℃条件下,制备了Ti3SiC2/HAp陶瓷复合材料.研究了Ti3SiC2含量对复合材料的硬度、抗弯强度、断裂韧性等力学性能的影响.实验结果表明,随Ti3SiC2含量的变化,复合材料的强度和韧性均得到了提高和改善.分析认为,Ti3SiC2材料的微观结构特征和增韧机制起到了重要作用.     

High-Temperature Nanoindentation of SiC/SiC Composites

JOM - The results of high-temperature nanoindentation testing on both a control and a neutron-irradiated silicon carbide matrix silicon carbide fiber composite sample are presented. The mechanical...     

Elevated-temperature effects of oxygen on SiC/SiC composites

High-temperature exposures of SiC/SiC composites to oxidizing environments can lead to substantial changes in mechanical behavior. In the work reported here, results from flexure and crack growth experiments are used to demonstrate such effects. Flexure tests of graphite-coated Nicalon-reinforced SiC previously oxidized in air at 950°C revealed that degradation of fracture resistance began after very short exposure times (less than 1 h) and could be described in terms of distinct oxidation effects on strength and fiber pullout. Crack velocities were determined as a function of applied stress intensity and time for varying O₂ levels. It was observed that crack velocities increased at 1,100°C in the presence of oxygen, which also shifted the onset of stage III (power law) growth to lower values of applied stress intensity. The crack growth observations were described using a two-dimensional micro-mechanical model developed to simulate cracks bridged by continuous fibers. Fiber creep relaxation predicted the correct crack velocity and time-dependence in argon, but other mechanisms, such as interface removal, are required to explain the data in Ar + O₂     

Flexural strength distribution of 3D SiC/SiC composite

Flexural strength of a four-step, three-dimensional (3D) braiding SiC/SiC composite was tested at room temperature. The strength distribution was studied based on Weibull distribution and Normal distribution as well as examined by the Kolmogorov test. The results indicated that the flexural failure behavior of the composite was rather brittle with a small displacement. And the statistical strength distribution of the 3D SiC/SiC composite was in agreement with two-parameter Weibull distribution of the Weibull modulus,m=8.1545 and normal distribution. And the predicated mean flexural strength of the 3D SiC/SiC composite by the two-parameter Weibull distribution was consistent with the tested value.     

Damage Progression and Stress Redistribution in Notched SiC/SiC Composites

The stress fields adjacent to machined notch roots were examined during tensile tests of woven SiC/SiC composites using thermoelastic stress analysis. As expected, the stress-concentration factor (SCF) at the notch roots increased with increasing notch lengths. Damage-induced stress-relief was not evident in these composites. In fact, the redistribution of stresses onto isolated fiber tows adjacent to the notch root caused an increase in the apparent SCF. Lastly, the SCF increased with mean stress. This was assumed to occur as a result of opening matrix cracks that are typically closed due to residual compressive stresses in the matrix material at near zero loads.     

Interfacial characterization of a slurry-cast melt-infiltrated SiC/SiC ceramic-matrix composite

An SiC-particulate, silicon-metal melt-infiltration-matrix composite reinforced with SiC fibers is being developed for combustor applications under the High Speed Civil Transport (HSCT) Enabling Propulsion Material (EPM) Program. A major part of this effort has dealt with the characterization and optimization of the boron nitride (BN) based fiber/matrix interface. BN was chosen as the primary interfacial material due to its inherently weak structure and thus good crack-deflecting ability, ease of deposition by chemical vapor infiltration (CVI) into woven fiber preforms, and relatively good environmental stability. Topics discussed in this paper include an overview of the differences in composite microstructure between the EPM SiC/SiC material and a more conventional CVI SiC/SiC composite material, the microstructure/property relationships for the EPM SiC/SiC composite with two different types of SiC fiber (High-Nicalon and Sylramic^™), and the effect of moist, high-temperature environments on the stability of the BN interface.     

Preparation and oxidation protection of CVD SiC/a-BC/SiC coatings for 3D C/SiC composites

An amorphous boron carbide (a-BC) coating was prepared by LPCVD process from BCl₃-CH₄-H₂-Ar system. XPS result showed that the boron concentration was 15.0 at.%, and carbon was 82.0 at.%. One third of boron was distributed to a bonding with carbon and 37.0 at.% was dissolved in graphite lattice. A multiple-layered structure of CVD SiC/a-BC/SiC was coated on 3D C/SiC composites. Oxidation tests were conducted at 700, 1000, and 1200 °C in 14 vol.% H₂O/8 vol.% O₂/78 vol.% Ar atmosphere up to 100 h. The 3D C/SiC composites with the modified coating system had a good oxidation resistance. This resulted in the high strength retained ratio of the composites even after the oxidation.     

Mullite-gadolinium silicate environmental barrier coatings for melt infiltrated SiC/SiC composites

Slurry based mullite/gadolinium silicate (Gd₂SiO₅) environmental barrier coatings (EBCs) were developed for melt infiltrated (MI) SiC/SiC composites. The coating chemically adhered well on the substrates. Thermal cycling of uncoated MI-SiC/SiC composites conducted between 1350 °C and 90 °C (one hour hot and 15 min cold) in a 96.5% H₂O-3.5% O₂ environment caused severe oxidation damage after 100 cycles resulting in the formation of dense silica layer of about 25 μm maximum thickness. Mullite/Gd₂SiO₅ EBCs provided excellent protection to MI-SiC/SiC against moisture damage with significantly less oxidation of the substrate; only about a 2 μm thick oxide layer formed even after 400 similar thermal cycles. The hair-line cracks formed at the coating/substrate interface after 400 cycles causing partial coating de-lamination.     

SiC颗粒增强Al-Fe-V-Si复合材料的SiC/Al界面形貌

采用喷射沉积工艺制备SiCp/Al-Fe-V-Si复合材料,并通过热压和热轧工艺对沉积坯进行致密化;通过高分辨电镜观察其SiC/Al界面形貌,并对比热暴露后的界面形貌。结果表明:复合材料主要存在两种SiC/Al界面,一种是厚度为3nm左右的晶态Si界面层,且在界面附近的基体中生成细小的Al4C3相;另一种是厚度为5nm的非晶态SiO2界面层,部分溶解的SiC颗粒向附近Al基体中注入游离态的Si,在界面附近形成Si的浓度梯度;两种界面都具有良好的润湿性,界面结合强度高;经640℃热暴露10h后,SiC/Al界面处生成的粗大Al4C3脆性相降低界面结合强度,从而降低复合材料的力学性能。     

纤维涂层处理SiCf/SiC复合材料

分别采用酚醛和沥青为先驱体,在连续SiC纤维表面进行涂层制备,采用SEM、表面能谱等分析手段系统研究了涂层组成、结构及其对SiC纤维力学性能的影响.以含碳涂层的SiC纤维和聚碳硅烷(PCS)为原料通过先驱体转化法(PIP)制备SiCf/SiC复合材料,对其微观结构及性能进行了表征.结果表明,经过涂层处理后,在连续SiC纤维表面涂敷了一层无定形碳,纤维表面缺陷得到改善,抗拉强度有所提高.采用碳涂层SiC纤维制备SiCk/SiC复合材料后,断裂韧性明显提高.通过涂层处理有效地改善了SiCf/SiC复合材料的韧性.