Fabrication of PyC/SiC Compound Coating on Carbon Fiber Preform and Its Effect on the Properties of Cf/Al Composite

为改善碳纤维与熔融铝合金间的润湿性、减小界面反应程度,采用化学气相沉积（CVD）法在碳纤维预制体表面沉积制备了PyC/SiC复合涂层,利用真空吸渗挤压浸渗工艺制备了Cf/Al复合材料。研究了沉积参数对碳纤维表面涂层的影响,并通过复合材料微观组织分析及材料机械性能测试来反映涂层对Cf/Al复合材料的浸渗质量和性能的影响规律。结果表明：沉积温度对涂层沉积速率影响较大,通过选择合适的沉积温度或者沉积时间,可在碳纤维表面得到厚度均匀的PyC/SiC复合涂层。碳纤维预制体表面涂层的存在可使其与基体合金润湿性良好、界面结合强度适中,形成合适的界面结合状态,有效提高浸渗质量和复合材料性能;并且当PyC涂层、SiC涂层厚度分别为0.068、0.257 μm时,复合材料性能改善效果最佳     

热生长下热障涂层残余应力及失效分析

针对典型热障涂层结构以界面开裂和涂层剥落为主要失效模式,考虑界面凹凸微观形貌特征,借助材料转换的方法实现氧化生长,利用粘弹塑性有限元法,研究了氧化层热生长和蠕变等因素对热障涂层残余应力的影响,并从应力应变循环演化的角度对热障涂层系统中微裂纹的萌生位置进行了预测。结果表明,随着氧化层厚度的增大,垂直于界面方向的残余应力迅速增大;材料蠕变对热障涂层系统应力释放作用显著;从残余应力和应变演化的角度进行评价,结构中的微裂纹会率先出现在粘接层凸峰以及陶瓷层/氧化层/黏结层界面的中间位置,仿真分析结果与试验结果一致。     

TaSi2 Oxidation Protective Coating for SiC Coated Carbon/Carbon Composites

为提高碳/碳复合材料在高温下的氧化防护性能,利用包埋技术在碳/碳复合材料表面制备了TaSi2/SiC复合涂层。通过XRD、SEM 和 EDS分析了涂层的晶相结构和形貌特征,在1773 K的空气介质中对TaSi2/SiC涂层碳/碳复合材料进行等温氧化实验。结果表明,复合涂层厚度为200 μm,涂层中含有SiC, Si 和TaSi2相,并且涂层中没有明显裂纹出现。EDS结果显示外层TaSi2相可有效地填充内层SiC涂层的空隙,使得内外两层涂层之间没有明显的界面,等温氧化实验曲线说明TaSi2/SiC复合涂层在1773 K的空气介质中可有效保护碳/碳复合材料233 h。     

界面层对近化学计量比碳化硅纤维增强碳化硅复合材料性能的影响

分别以国产近化学计量比SiC纤维和聚碳硅烷为纤维增强相和基体浸渍剂,采用聚合物先驱体浸渍裂解工艺,实现制备PyC界面层的SiC/SiC复合材料致密化.采用SEM对SiC纤维及SiC/SiC复合材料的形貌进行分析,采用三点弯曲法对材料力学性能进行测试.结果 表明,国产近化学计量比SiC纤维具有高强高模的特点,界面层厚度是...     

致密SiC涂层在水蒸气及与空气混合气氛中的氧化行为

本实验主要针对在球形燃料元件基体石墨样品上用流化床化学气相沉积工艺所制备的致密SiC抗氧化涂层,于1400℃下,对其在水蒸气及与空气混合气氛中的氧化行为进行研究与机理分析。结果表明,气氛对氧化层厚度有显著影响。单一水蒸气情况下,所得氧化层的厚度均比混合气氛的氧化层厚度薄。单一水蒸气氧化后的样品比混合气氛氧化的样品具有更平整的表面、更轻微的点状开裂和更小的线性裂纹。致密SiC涂层氧化均发生在表面,没有破坏致密层的结构。氧化机理分析表明,致密SiC涂层的表面形貌变化、裂纹的产生以及厚度变化等均与氧化竞争反应和氧化中间产物有关。致密SiC涂层在空气和水蒸气等不同环境的氧化过程中,均能在表面形成一定厚度的SiO2自愈合层,且10 h的氧化后,涂层的氧化深度仅在表层的3.5μm以内,没有破坏致密层结构。     

致密SiC涂层在水蒸气及与空气混合气氛中的氧化行为

本实验主要针对在球形燃料元件基体石墨样品上用流化床化学气相沉积工艺所制备的致密SiC抗氧化涂层,于1400℃下,对其在水蒸气及与空气混合气氛中的氧化行为进行研究与机理分析。结果表明,气氛对氧化层厚度有显著影响。单一水蒸气情况下,所得氧化层的厚度均比混合气氛的氧化层厚度薄。单一水蒸气氧化后的样品比混合气氛氧化的样品具有更平整的表面、更轻微的点状开裂和更小的线性裂纹。致密SiC涂层氧化均发生在表面,没有破坏致密层的结构。氧化机理分析表明,致密SiC涂层的表面形貌变化、裂纹的产生以及厚度变化等均与氧化竞争反应和氧化中间产物有关。致密SiC涂层在空气和水蒸气等不同环境的氧化过程中,均能在表面形成一定厚度的SiO_2自愈合层,且10 h的氧化后,涂层的氧化深度仅在表层的3.5μm以内,没有破坏致密层结构。     

热处理对C/C复合材料Mo-Si-N系涂层抗氧化性能的影响

以Mo粉和Si粉为原料,采用熔浆法在氮气环境中制备了C/C复合材料的Mo-Si-N系抗氧化涂层,并对涂层1400℃预氧化热处理前后的组织结构和氧化行为进行了研究.结果表明,Mo-Si-N涂层除具有与Mo-Si系涂层相同的SiC底层和MoSi2/Si主结构层外,还形成了厚度不均匀的Si3N4/SiC/Si表面层.Mo-Si-N系涂层具有1400℃稳定抗氧化能力和1450℃长时间氧化防护潜力;经1400℃预氧化热处理后,涂层的最高抗氧化温度达到了1500℃,氧化12小时后重量损失率小于1wt%.     

SiC纤维表面扩散障碍涂层对SiCf/Ni复合材料界面反应的影响

分别采用高温氧化和真空电弧离子镀法在SiC纤维表面制备出C-Al2O3和SiO2-Al2O3复合涂层,通过真空热压法制备出SiCf/Ni复合材料.经过850-950℃,150 h真空热处理后,复合涂层很好地保护了纤维的完整性,涂层中的Al2O3层与基体Ni界面结合良好,有效地阻挡了SiCf/Ni界面处元素互扩散.C-Al2O3涂层的C层出现了扩散现象,但涂层基本保持完整;SiO2-Al2O3涂层中SiO2层与纤维结合界面处萌生裂纹.C-Al2O3与SiO2-Al2O3复合涂层相比具有更好的阻挡界面处元素互扩散的作用.     

Fatigue Behavior and Damage Evolution of SiC Fiberreinforced Ti-6Al-4V Alloy Matrix Composites

研究SiC纤维增强钛基复合材料(SiCf/Ti-6Al-4V)室温疲劳行为和损伤演化机制。疲劳试验条件:载荷控制、应力比0.1和加载频率10 Hz。采用疲劳断裂试验建立最大加载应力为600~1200 MPa内SiCf/Ti-6Al-4V的S-N曲线。采用疲劳中止试验以及SEM显微分析研究应力水平对SiCf/Ti-6Al-4V疲劳损伤演化的影响。结果表明,SiCf/Ti-6Al-4V疲劳损伤萌生模式与演化过程与应力水平密切相关。在高应力水平(Smax=1000 MPa),纤维开裂是主要损伤萌生模式。一旦2或3根纤维断裂后,纤维裂纹和基体裂纹开始联接并形成宏观扩展裂纹。在中等应力水平(Smax=800 MPa),基体裂纹萌生与扩展是主要损伤模式。多条基体裂纹萌生于试样外表面棱边和离外表面附近试样内部开裂的纤维基体界面处。基体裂纹均沿垂直于加载方向扩展,且大部分纤维未断裂并纤维桥接基体裂纹。在低应力水平(Smax=600 MPa),仅在C涂层和界面反应层之间和C涂层内部观察到局部界面脱粘现象。     

SiC纤维增强Ti-6Al-4V复合材料的疲劳行为及损伤演化研究（英文）

研究SiC纤维增强钛基复合材料(SiCf/Ti-6Al-4V)室温疲劳行为和损伤演化机制。疲劳试验条件:载荷控制、应力比0.1和加载频率10 Hz。采用疲劳断裂试验建立最大加载应力为600~1200 MPa内SiCf/Ti-6Al-4V的S-N曲线。采用疲劳中止试验以及SEM显微分析研究应力水平对SiCf/Ti-6Al-4V疲劳损伤演化的影响。结果表明,SiCf/Ti-6Al-4V疲劳损伤萌生模式与演化过程与应力水平密切相关。在高应力水平(Smax=1000 MPa),纤维开裂是主要损伤萌生模式。一旦2或3根纤维断裂后,纤维裂纹和基体裂纹开始联接并形成宏观扩展裂纹。在中等应力水平(Smax=800 MPa),基体裂纹萌生与扩展是主要损伤模式。多条基体裂纹萌生于试样外表面棱边和离外表面附近试样内部开裂的纤维基体界面处。基体裂纹均沿垂直于加载方向扩展,且大部分纤维未断裂并纤维桥接基体裂纹。在低应力水平(Smax=600 MPa),仅在C涂层和界面反应层之间和C涂层内部观察到局部界面脱粘现象。     

The concept of a strong interface applied to SiC/SiC composites with a BN interphase

Strong interfaces have been shown to allow improvement of the mechanical properties of ceramic matrix composites (CMC). The concept of a strong interface has been established in SiC/SiC composites with pyrocarbon (PyC) or multilayered (PyC/SiC) fiber coatings (also referred to as interphases). The present paper reports an attempt directed at applying the concept of a strong interface to SiC/SiC composites with a BN coating (referred to as SiC/BN/SiC). Fiber bonding and frictional sliding were investigated by means of push-out tests performed on 2D-composites as well as on microcomposite samples, and tensile tests performed on microcomposites. The stress–strain behavior of the SiC/BN/SiC composites and microcomposites is discussed with respect to interface characteristics and location of debonding either in the coating or in the fiber/coating interface.     

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     

Effects of dip-coated BN interphase on mechanical properties of SiCf/SiC composites prepared by CVI process

BN interphase was successfully synthesized on SiC fiber fabrics by dip-coating process using boric acid and urea as precursors under N₂ atmosphere. The morphology of BN interphase was observed by SEM, and the structure was characterized by XRD and FT-IR spectra. The SiC_f/SiC composites with dip-coated BN interphase were fabricated by chemical vapor infiltration (CVI) process, and the effects of BN interphase on the mechanical properties of composites were investigated. The results show that the SiC fibers are fully covered by BN interphase with smooth surface and turbostratic structure (t-BN), and the thickness is about 0.4 μm. The flexural strengths of SiC_f/SiC composites with and without BN interphase are about 180 and 95 MPa, respectively. Compared with the as-received SiC_f/SiC composites, the composites with BN interphase exhibit an obvious toughened fracture behavior. From the microstructural analysis, it can be confirmed that the BN interphase plays a key part in protecting the fibers from chemical attack during matrix infiltration and weakening interfacial bonding, which can improve the mechanical properties of SiC_f/SiC composites remarkably.     

SiC Coatings for Carbon/Carbon Composites Fabricated by Vacuum Plasma Spraying Technology

SiC coatings for carbon/carbon (C/C) composites have been prepared by the combination process of vacuum plasma spraying technology and heat treatment. The SiC coatings were formed by the reaction of C/C substrates with as-sprayed silicon coatings deposited by vacuum plasma spraying. The preparation temperature and the thickness of original silicon coatings have great influence on the microstructure and the thickness of the synthesized SiC coatings. The results indicated that a continuous and dense SiC coating has been produced on the surface of C/C substrates. The SiC coatings prepared at 2073 K with the silicon coatings of 230 μm thickness, exhibited a low mass loss of 2.56% in the plasma jet with temperature about 2473 K and duration of 420 s in atmosphere. The present results implied that vacuum plasma spraying technology combined with heat treatment was an acceptable method for synthesis of protective SiC coatings for C/C composites.     

COMPARISON OF FATIGUE AND CREEP BEHAVIOR BETWEEN 2D AND 3D-C／SiC COMPOSITES

The differences of tension-tension fatigue and tensile creep characters of 2D-C/SiC and 3D-C/SiC composites have been scrutinized to meet the engineering needs. Experiments of tension-tension fatigue and tensile creep are carried out under vacuum high temperature condition. All of the high temperature fatigue curves are flat; the fatigue curves of the 2D-C/SiC are flatter and even parallel to the horizontal axis. While the tension-tension fatigue limit of the 3D-C/SiC is higher than that of the 2D-C/SiC, the fiber pullout length of the fatigue fracture surface of the 3D-C/SiC is longer than that of the 2D-C/SiC, and fracture morphology of the 3D-C/SiC is rougher, and pullout length of the fiber tows is longer. At the same time the 3D-C/SiC has higher tensile creep resistance. The tensile curve and the tensile creep curve of both materials consist of a series of flat step. These phenomena can be explained by the non-continuity of the damage.     

Subcritical crack growth in CVI SiCf/SiC composites at elevated temperatures: effect of fiber creep rate

Subcritical crack-growth studies in SiC_f/SiC composites were conducted with composites reinforced with Hi-Nicalon fibers over a broad temperature range for comparison to earlier studies on materials reinforced with Nicalon-CG fibers. Composites with a 0/90 plain weave architecture and carbon interphase were tested in argon from 1173 to 1473 K. Crack growth data obtained in inert environments are consistent with a proposed fiber-creep-controlled crack-growth mechanism. Measured crack-growth activation energies and time–temperature exponents in argon agree with fiber creep-activation energies and nonlinear creep equations for both fiber types. Estimates of local strains during crack growth are in reasonable agreement with estimated fiber creep strains for the given times and temperatures. The increased creep resistance of Hi-Nicalon fibers is reflected in reduced crack-growth rates for composites containing those fibers.     

ZrC-SiC-MoSi2涂覆C/C-SiC-ZrC陶瓷基复合材料在氧乙炔焰下的烧蚀行为及机理(英文)

为进一步提高C/C复合材料在不同烧蚀环境下的烧蚀性能,采用浆料刷涂法在C/C-SiC-ZrC陶瓷基复合材料上制备Zr含量分别为34%和60%(质量分数)的ZrC-SiC-MoSi₂涂层,并且利用氧乙炔焰研究涂层C/C-SiC-ZrC复合材料在3种不同氧气及乙炔流量下的烧蚀行为。结果表明：随着Zr含量的增加,涂层内部的ZrC和SiC颗粒尺寸明显减小,且颗粒分布更加均匀。Zr含量为60%的涂层线烧蚀率随氧气和乙炔流量的增加而增加,而Zr含量为34%的涂层线烧蚀率随氧气和乙炔流量的增加,先增加后降低。此外,详细讨论ZrC-SiC-MoSi₂涂层在不同条件下的烧蚀机理。随着氧气和乙炔流量的增加,主要的烧蚀机制由氧化变为氧化和蒸发的结合作用,最后变为氧化、蒸发及剥蚀的结合作用。     

Influence of heat treatment on the internal friction of 2D-C/SiC composites

The internal friction of two-dimensional C/SiC composites (2D-C/SiC) was investigated in air by means of three-point bending forced vibration, compared with the specimens after heat treatment. The result shows that the effects of PyC interface between carbon fibers and SiC matrix play an important role on the internal friction characters of 2D-C/SiC composites, which leads to some unique internal friction phenomena in 2D-C/SiC composites. After the heat treatment, the PyC interface produces damage that make internal friction increased and dynamic modulus decreased. The heat treatment makes the internal friction of 2D-C/SiC composites more insensitive to temperature and frequency, and more sensitive to amplitude.     

界面对浆料浸渍裂解Cf／SiC复合材料性能的影响

利用强制脉冲CVI工艺在2．5D纤维编织体上沉积C—SiC双层界面，然后通过浆料浸渍裂解方法得到了Cf／SiC复合材料，并考察界面中C层、SiC层厚度变化对Cf／SiC复合材料性能的影响。界面中C层、SiC层厚度变化对浸渍过程影响不大，得到的Cf／SiC复合材料密度基本相当，约2．0g／cm^3。但随C层厚度的增加，强度减小；随着SiC层厚度的增加，强度增加，到达一定厚度后，其强度几乎不变，为290．0MPa。在C层厚度为50nm，SiC层厚度为600nm时，表现出强的非脆性断裂。