骨架结构对SiC/Al双连续相复合材料的影响

用挤压铸造法制备了不同结构的SiC泡沫增强ZL109双连续相复合材料,研究了增强体骨架结构(筋的结构、泡沫孔和体积分数)对复合材料压缩性能和弯曲性能的影响。结果表明:SiC泡沫增强体的筋的结构影响了界面的结合,影响了材料的压缩性能;当筋具有三明治结构时,复合材料的强度最大;当筋具有双层结构时,复合材料的强度最低;随着SiC泡沫孔径的增大,复合材料的压缩强度、弹性模量和屈服强度都有所提高,材料的屈服应变减小,弯曲强度先升高后降低,弯曲强度在泡沫孔径为1.5 mm时达到最大值;复合材料的压缩强度随着增强体体积分数的增大而提高,屈服应变随着体积分数的增大而减小。     

SiC_p尺寸及基体强度对铝基复合材料破坏机制的影响

对粉末冶金法制备的尺寸分别为3．5,10,20μm的Sicp增强Al-Cu基复合材料的拉伸断口及EDX成分分析表明,增强相尺寸大于10μm时,复合材料的破坏归因于SiCp解理形成的裂纹;增强相尺寸为3．5μm时,复合材料的破坏则归因为SiC-Al界面撕裂形成空洞和裂纹.拉伸试验表明,小尺寸SiCp增强的复合材料具有高的拉伸强度及延伸率.低强度复合材料由于基体强度降低,塑性增加,破坏过程主要表现在拉伸载荷下SiCp附近铝基体的空洞形核、长大和聚合.     

SiCp／Mg-6Al-0．5Mn复合材料的组织与力学性能

采用压力浸渗制备了体积分数为51.5%的SiCp/Mg-6Al-0.5Mn镁基复合材料.通过力学性能测试与组织观察,研究了高体积分数SiC颗粒增强体对基体合金的显微组织与力学性能的影响.结果显示,在Mg-6Al-0.5Mn基体合金中加入体积分数为51.5%的SiC颗粒后,复合材料的压缩性能得到了大幅度的提高,室温下的抗压缩强度从329.5 MPa增大到624.8 MPa.SiCp/Mg-6Al-0.5Mn复合材料的组织致密,分布均匀,其断裂方式包括界面脱开、基体韧断和增强体开裂.SiC颗粒与基体之间发生了界面反应,生成了纳米级的Mg2Si化合物.     

粉末冶金法制备SiC_p/2024Al泡沫复合材料的表征(英文)

为了丰富泡沫材料制备工艺、推动其快速发展与广泛应用,以CaCO3为发泡剂采用粉末冶金法制备SiCp/2024Al泡沫复合材料。采用SEM和Magiscan-2A图像分析仪研究了CaCO3发泡剂和SiC颗粒的含量对发泡行为的影响,并且通过Gleeble 1500热模拟机分析了SiC颗粒的含量对压缩性能的影响。结果表明:随着发泡剂的增多,孔隙率和孔径先增加后减小。随着增强体含量的增加,孔隙率和孔径都减小。压缩曲线揭示加入增强体可以改善压缩屈服强度和吸能能力。SiCp/2024Al泡沫复合材料显示为脆性泡沫材料。     

液态模锻SiCp/2A50力学性能及腐蚀行为研究

在研究2A50及SiCp/2A50复合材料力学性能的基础上,采用失重方法和电化学方法研究了2A50及SiCp/2A50复合材料在NaCl溶液中腐蚀行为和腐蚀机理,研究了不同尺寸、不同含量的增强颗粒SiCp对复合材料力学性能和腐蚀行为影响的变化规律。研究结果表明：当增强颗粒SiCp尺寸一定时,随着增强颗粒含量的增加,复合材料的强度增加,延伸率降低,而复合材料的腐蚀速率增加;当增强颗粒SiCp含量一定时,随着增强颗粒尺寸的增加,复合材料的强度降低,而延伸率则降幅较小,复合材料的腐蚀速率增加;复合材料中增强颗粒SiCp含量的变化并没有影响材料的腐蚀电位的变化,且与基体合金的腐蚀电位变化幅度较小;合金中的第二相与增强颗粒SiCp在复试过程中作为腐蚀阴极相,共同增加了合金的腐蚀速率;增强颗粒SiCp的加入降低了合金的耐蚀性能,且所研究的5种复合材料的腐蚀速率均大于基体合金的腐蚀速率。     

浇注温度对SiC泡沫/SiCp/Al混合复合材料力学性能的影响

采用挤压铸造法制备出SiC泡沫／SiCP混合增强铝基复合材料，研究了不同浇注温度对复合材料力学性能的影响及影响机制,结果表明，随着浇注温度的升高，材料的压缩强度降低，弯曲强度先升高后降低，弯曲强度在770℃达到最大值．浇注温度的升高对弹性模量没有影响，但增加了材料压缩时的塑性应变．浇注温度的升高增强了复合材料的界面结合，增加了材料中的气孔，而材料的界面和气孔综合作用决定了复合材料的断裂机制．     

微米级SiC颗粒对铝基复合材料拉伸性能与强化机制的影响

为了研究微米级碳化硅颗粒(SiCp)尺寸对中体积分数SiCp增强铝基复合材料的拉伸性能与强化机制的影响,用粉末冶金工艺制备体积分数为30%的SiCp/2024Al复合材料,利用OM,SEM,万能材料试验机等对材料微观结构和拉伸性能进行了研究。结果表明,复合材料的拉伸强度随着SiCp尺寸的减小而增大。当SiCp尺寸为3μm时,复合材料的断裂主要以界面处的基体合金撕裂为主;当SiCp尺寸为25μm和40μm时,复合材料的断裂以SiCp解理断裂为主;当SiCp尺寸为8μm和15μm时,复合材料的断裂方式是以界面处的基体合金撕裂和SiCp的断裂共同作用。3μm SiCp增强复合材料相对密度不高、SiCp分布不均匀但其拉伸强度最大,主要原因为受力时小SiCp极少断裂和小颗粒效应导致基体的显微组织强化。     

热压烧结SiCp/ZL101A复合材料显微组织研究

采用真空热压烧结在不同工艺参数下制备SiC颗粒体积分数分别为10%,20%,30%,40%的SiCp/ZL101A复合材料,研究烧结温度、保温时间等工艺参数对SiCp/ZL101A复合材料显微组织的影响以及SiC含量对SiC颗粒在基体ZL101A中分布均匀性的影响,同时对SiCp/ZL101A复合材料界面进行透射电镜显微分析。结果显示,随着烧结温度的增加,组织致密度增加,气孔数量及尺寸减小;保温时间的增加导致复合材料平均晶粒尺寸的增加;随着SiC颗粒体积分数的增加,SiC颗粒在基体ZL101A中分布均匀性变差;固相烧结法制备的SiCp/ZL101A复合材料中没有出现界面反应现象。     

SiC 粒子尺寸对 SiCp/铸铁表面复合材料组织及冲蚀磨损性能的影响

采用负压消失模(V-EPC)铸渗方法制备了 SiCp/铸铁表面复合材料,并在自制的射流式冲蚀磨损试验机上研究了 SiC 粒子尺寸对其冲蚀磨损性能的影响.结果表明,通过粘接剂和添加剂的加入,阻止了 SiC 粒子遇到高温铁液的分解,并实现了 SiC 粒子与铸铁间的冶金结合.随着 SiC 粒子尺寸的增加,SiC 粒子与铸铁基体的结合强度增大,使其抵抗浆料中石英砂粒子的冲击能力增大,从而提高了 SiCp/铸铁表面复合材料的冲蚀磨损性能.     

SiCp尺寸对铝基复合材料拉伸性能和断裂机制的影响

对粉末冶金法制备的不同尺寸SiCp增强铝基复合材料的拉伸性能进行了研究.结果表明,小尺寸SiCp（<7μm）复合材料断裂以界面处基体撕裂为主,强度较高.大尺寸 SiCp增强复合材料断裂以 SiCp解理为主,强度较低,但塑性比小尺寸颗粒增强复合材料要高.体积分数为17％,尺寸为7μm颗粒复合材料拉伸性能最好.     

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.