导热PE-HD／SiC复合材料的制备及性能研究

将碳化硅（SiC）粒子和高密度聚乙烯（PE—HD）经粉末混合后制得导热复合材料。研究了SiC粒子分散状态及含量对复合材料热导率、热阻、力学性能及电绝缘性能的影响，探讨了SiC粒径对热导率的影响。结果表明：复合材料中SiC粒子围绕在PE—HD粒子周围，形成了特殊的网状导热通路；随SiC粒径增加，热导率降低；在填料体积分数为30％时，复合材料热导率、热阻、拉伸强度及冲击强度、体积电阻率和介电常数分别为1．05W／（m·K）、0．75K／W、15MPa、13．2kJ／m^2、4．6×10^15 ·Ω·cm和3．03。此外，使用少量的氧化铝（Al2O3）纤维替代SiC组成混杂填料增强的材料各项性能均得到改善，并且与纯PE-FID相比具有优良的热传导能力。     

太阳能热发电用氧化铝-碳化硅-氧化锆储热陶瓷的制备及表征

以α-Al2O3、部分稳定氧化锆(5.2%Y2O3,质量分数)和碳化硅为原料,采用无压烧成技术制备了太阳能热发电用 Al2O3–SiC–ZrO2(ASZ)储热陶瓷,研究了碳化硅和氧化锆添加量对 ASZ 储热陶瓷样品结构与性能的影响。结果表明：随着碳化硅添加量的增加,样品的力学性能、抗热震性和热物理性能均有提高;添加氧化锆可提高样品的力学性能和抗热震性能;经1280℃烧成的碳化硅添加量为50%、部分稳定氧化锆添加量为5%的样品的显气孔率、吸水率、体积密度和抗折强度分别为24.88%、10.44%、2.38 g/cm3和66.20 MPa;样品的比热容、导热系数和储热密度(600℃时)分别为1.05 kJ/(kg·K),2.26 W/(m·K)和916.91 kJ/kg。热震试验30次(室温～800℃)样品无裂纹,强度增长率为27.89%。     

三维针刺C/SiC复合材料的结构特征和力学性能

采用化学气相渗透法制备了在厚度方向上具有纤维增强的三维针刺碳纤维增强碳化硅(C/SiC)陶瓷基复合材料,复合材料的密度和气孔率分别为2.15 h/cm3和16%.三维针刺C/SiC复合材料中的针刺纤维将各层紧密结合在一起,其层间抗剪切强度显著提高,为95MPa,比二维碳布叠层C/SiC复合材料的剪切强度(35MPa)高171.4%.三维针刺C/SiC复合材料的拉伸强度和弯曲强度分别为159MPa和350MPa,断裂模式为非脆性断裂,包括:裂纹扩展、偏转,碳纤维的拉伸断裂和逐步拔出.     

掺碳SiC颗粒对MOSi2复合材料性能的影响

研究分析了掺碳SiCp/MoSi2复合材料的相组成、室温和高温力学性能、高温抗氧化性能、耐磨性能以及电阻率.结果表明(SiCp+C)/MoSi2复合材料主要由MoSi2,α-SiCp,Mo5Si3和β-SiC组成.材料的密度和相对密度分别为5.12g/cm3和91%;Vickers硬度,抗弯强度和断裂韧性分别为12.2GPa,530MPa和72MPa.m1/2;800℃的Vickers硬度为8.0GPa,1200℃和1400℃的抗压强度分别为560MPa和160MPa.材料的抗氧化性能优良.在Al2O3和SiC磨盘上表现出优异的耐磨性能.电阻率为40.2μΩ.     

化学气相渗透法制备2维和2.5维C/SiC复合材料及其拉伸性能

采用化学气相渗透法制备了2维和2.5维碳纤维增强碳化硅(carbon-fiber-reinforced silicon carbide,C/SiC)复合材料,沿经纱(纵向)和纬纱(横向) 2个方向对2种复合材料进行了室温拉伸性能测试,并从预制体结构和原始缺陷分布的角度对比分析了两者力学性能之间的差异.结果表明:两种C/SiC复合材料均表现出明显的非线性力学行为,在经纱方向和纬纱方向上,2维C/SiC复合材料力学性能表现为各向同性,而2.5维C/SiC复合材料力学性能则表现出明显的各向异性:经纱方向上2.5维C/SiC复合材料的拉伸强度和拉伸模量(326 MPa,153 GPa)均高于2维C/SiC复合材料的(245 MPa,96 GPa),纬纱方向上的(145 MPa,62 GPa)均低于2维C/SiC复合材料的(239 MPa,90 GPa).两种复合材料的拉伸断裂行为均表现为典型的韧性断裂,并伴有大量的纤维拔出.两种复合材料中纱线断裂均呈现出多级台阶式断裂方式,但其断裂位置并不相同.2.5维C/SiC复合材料中由于经纱路径近似于正弦波,弯曲程度较大,在纱线交叉点处造成明显的应力集中,因此经纱多在纱线交叉点处断裂;而纬纱由于其路径近乎直线,应力集中现象不明显,因此纬纱断裂位置呈随机分布.2维C/SiC复合材料中经纱和纬纱由于其路径类似于2.5维C/SiC复合材料中的经纱,因此其断裂位置也多在纱线交叉点处.微观结构观察表明不同的编织结构是造成两种复合材料在不同方向上力学性能差异的主要原因.     

太阳能吸热器用莫来石--碳化硅陶瓷的原位合成(英文)

采用半干压成型和无压烧成技术,原位合成了用于太阳能热发电吸热器的莫来石结合碳化硅(SiC)吸热陶瓷。研究结果表明:经1 520℃烧成的样品B2(粒径≤61μm SiC 72%,粒径≤20μm SiC 18%,工业氧化铝4.64%,苏州高岭土5.36%)的综合性能最佳,其显气孔率、吸水率、体积密度和抗折强度分别为28.40%、13.35%、2.13g/cm3和44.20MPa;热震试验30次(1 100℃~室温,风冷),样品无裂纹,强度增加率达52.30%;在1 300℃氧化100h后,样品的氧化增重为25.43mg/cm2,氧化动力学常数为1.80×10--7kg2/(m4·s)。物相分析表明,样品的相组成为碳化硅、莫来石、石英和刚玉。显微结构分析表明,原位合成的莫来石结合于碳化硅颗粒间,赋予样品较好的抗折强度。热震试验30次后,可在样品中观察到更加致密的结构,碳化硅晶粒被树枝状微晶紧密联接,改善了样品的抗热震性。莫来石--碳化硅复相陶瓷可作为塔式太阳能热发电吸热器的潜在应用材料。     

掺碳SiC颗粒对MoSi_2复合材料性能的影响

研究分析了掺碳SiCp/MoSi2 复合材料的相组成、室温和高温力学性能、高温抗氧化性能、耐磨性能以及电阻率 .结果表明 :(SiCp+C) /MoSi2 复合材料主要由MoSi2 ,α -SiCp,Mo5Si3和 β -SiC组成 .材料的密度和相对密度分别为 5.1 2 g/cm3和 91 % ;Vickers硬度 ,抗弯强度和断裂韧性分别为 1 2 .2GPa ,530MPa和 7.2MPa·m1 / 2 ;80 0℃的Vickers硬度为 8.0GPa ,1 2 0 0℃和 1 40 0℃的抗压强度分别为 560MPa和1 60MPa .材料的抗氧化性能优良 .在Al2 O3和SiC磨盘上表现出优异的耐磨性能 .电阻率为 40 .2 μΩ·cm .与非增强MoSi2 相比 ,材料的各种力学性能有大幅度的提高     

化学气相渗透2.5维C/SiC复合材料的拉伸性能

采用等温减压化学气相浸渗(isothermal low-pressure chemical vapor infiltration,ILCVI)工艺制备了在厚度方向上具有纤维增强的2.5维(2.5 dimensional,2.5D)碳纤维增强碳化硅多层陶瓷基复合材料,从而使一端封口的防热结构部件的制备成为可能.ILCVI致密化后,复合材料的密度、孔隙率分别为1.95～2.1 g/cm3和16.5%～18%.沿经纱和纬纱两个方向对2.5D C/SiC复合材料进行室温拉伸实验.结果表明:复合材料在纵向和横向的拉伸应力-应变均表现为明显的非线性行为.复合材料具有较高的面内拉伸性能,纵横向的拉伸强度分别为326MPa和145MPa,断裂应变分别为0.697%和0.705%.复合材料的拉伸断裂为典型的韧性断裂,经纱和纬纱的断裂都表现为纤维的多级台阶式断裂以及纤维的大量拔出.     

纤维束丝数对平纹编织C/SiC复合材料力学性能的影响

通过对2种丝束平纹编织碳纤维布增强SiC（C/SiC）复合材料的力学性能实验,研究了纤维束丝数（1 k和3 k）对复合材料性能的影响.实验结果表明：1 k C/SiC复合材料的拉伸模量、拉伸强度、压缩模量、压缩强度、面内剪切强度和弯曲强度分别为90.8 GPa,281.8 MPa,135.8 GPa,452.2 MPa,464.3 MPa和126.8 MPa,分别比3 k C/SiC高39%,15.8%,25%,132%,29.3%和30.2%.纤维束粗细不同是导致纤维束弯曲度和复合材料孔隙率差异的主要原因,对压缩强度的影响最大,对拉伸强度的影响最小.     

氧化铝料浆预浸料结合PIP工艺制备SiC/Al2O3-SiC陶瓷基复合材料及性能研究

连续碳化硅纤维增强碳化硅陶瓷基复合材料（SiC/SiC）具有低密度、耐高温、低氚渗透率和优异的辐照稳定性的优点，在航空、航天、核能等领域具有广泛的应用前景。本文针对PIP工艺制备SiC/SiC复合材料周期长、孔隙率较高及易氧化的问题，通过料浆预浸料工艺在基体中引入氧化铝陶瓷形成SiC/Al2O3-SiC复相基体复合材料，并对复合材料制备工艺过程、微观形貌及力学性能进行系统表征。分析结果表明，SiC/Al2O3-SiC复相基体复合材料制备周期较传统PIP工艺大幅度缩短，且复合材料孔隙率明显降低，从11.6%左右降低至6%，拉伸强度为316.5MPa，提升了12.3%，弯曲强度与SiC/SiC相当，但层间剪切强度较低，仅为16.3MPa，有待进一步提高。     

A Process for Cf/SiC Composites Using Liquid Polymer Infiltration

A continuous carbon fiber/silicon carbide matrix composite material has been produced by a low-cost process. In this process the space in a two-dimensional carbon fiber preform is filled with a SiC powder by a pressure infiltration method. High particle packing densities are achieved within the fiber preform in this way. The compact body is heat-treated at 400°C to form a porous framework, which is then infiltrated with a liquid preceramic polymer, Ceraset^TM SN. Subsequently the infiltrated polymer is pyrolyzed in argon at 1300°C. The microstructure of the final composite is characterized, and mechanical properties of these composites are discussed.     

Stress-Corrosion Cracking of Silicon Carbide Fiber/Silicon Carbide Composites

Ceramic-matrix composites are being developed to operate at elevated temperatures and in oxidizing environments. Considerable improvements have been made in the creep resistance of SiC fibers and, hence, in the high-temperature properties of SiC fiber/SiC (SiC_f/SiC) composites; however, more must be known about the stability of these materials in oxidizing environments before they are widely accepted. Experimental weight change and crack growth data support the conclusion that the oxygen-enhanced crack growth of SiC_f/SiC occurs by more than one mechanism, depending on the experimental conditions. These data suggest an oxidation embrittlement mechanism (OEM) at temperatures <1373 K and high oxygen pressures and an interphase removal mechanism (IRM) at temperatures of ≳700 K and low oxygen pressures. The OEM results from the reaction of oxygen with SiC to form a glass layer on the fiber or within the fiber–matrix interphase region. The fracture stress of the fiber is decreased if this layer is thicker than a critical value ( d > d _c) and the temperature below a critical value ( T < T _g), such that a sharp crack can be sustained in the layer. The IRM results from the oxidation of the interfacial layer and the resulting decrease of stress that is carried by the bridging fibers. Interphase removal contributes to subcritical crack growth by decreasing the fiber-bridging stresses and, hence, increasing the crack-tip stress. The IRM occurs over a wide range of temperatures for d < d _c and may occur at T > T _g for d > d _c. This paper summarizes the evidence for the existence of these two mechanisms and attempts to define the conditions for their operation.     

Reactive Hot Pressing of ZrB2–SiC Composites

A ZrB₂–SiC composite was prepared from a mixture of zirconium, silicon, and B₄C via reactive hot pressing. The three-point bending strength was 506 ± 43 MPa, and the fracture toughness was 4.0 MPa·m^1/2. The microstructure of the composite was observed via scanning electron microscopy; the in-situ -formed ZrB₂ and SiC were found in agglomerates with a size that was in the particle-size ranges of the zirconium and silicon starting powders, respectively. A model of the microstructure formation mechanism of the composite was proposed, to explain the features of the phase distributions. It is considered that, in the reactive hot-pressing process, the B and C atoms in B₄C will diffuse into the Zr and Si sites and form ZrB₂ and SiC in situ , respectively. Because the diffusion of Zr and Si atoms is slow, the microstructure (phase distributions) of the obtained composite shows the features of the zirconium and silicon starting powders.     

Temperature Dependence of Tensile Strength for a Woven Boron-Nitride-Coated Hi-Nicalon™ SiC Fiber-Reinforced Silicon-Carbide-Matrix Composite

The temperature dependence of tensile fracture behavior and tensile strength of a two-dimensional woven BN-coated Hi-Nicalon™ SiC fiber-reinforced SiC matrix composite fabricated by polymer infiltration pyrolysis (PIP) were studied. A tensile test of the composite was conducted in air at temperatures of 298 (room temperature), 1200, 1400, and 1600 K. The composite showed a nonlinear behavior for all the test temperatures; however, a large decrease in tensile strength was observed above 1200 K. Young's modulus was estimated from the initial linear regime of the tensile stress–strain curves at room and elevated temperatures, and a decrease in Young's modulus became significant above 1200 K. The multiple transverse cracking that occurred was independent of temperature, and the transverse crack density was measured from fractographic observations of the tested specimens at room and elevated temperatures. The temperature dependence of the effective interfacial shear stress was estimated from the measurements of the transverse crack density. The temperature dependence of in situ fiber strength properties was determined from fracture mirror size on the fracture surfaces of fibers. The decrease in the tensile strength of the composite up to 1400 K was attributed to the degradation in the strength properties of in situ fibers, and to the damage behavior exception of the fiber properties for 1600 K.     

Influence of Strong Fiber/Coating Interfaces on the Mechanical Behavior and Lifetime of Hi-Nicalon/(PyC/SiC)n/SiC Minicomposites

Hi-Nicalon fiber-reinforced silicon carbide matrix minicomposites (Hi-Nicalon/SiC) with nanoscale multilayered (PyC/SiC) _n fiber coatings (also referred to as interphases) have been manufactured via pressure pulse chemical vapor infiltration (P-CVI). Fiber/coating interfaces were strengthened by using treated fibers. The microstructures of the interphases as well as the propagation and deflection of cracks in the interfacial region were investigated by SEM and TEM. Interfacial shear stress was estimated using various methods based on either the width of hysteresis loops on unloading–reloading, crack spacing, or fitting of the force–deformation curve using a micromechanics-based model. Tensile behavior at room temperature and lifetime in static fatigue in air at 700°C were related to the interphase/interface characteristics.     

SiC基反射镜制备工艺研究进展

空间系统用的高性能轻质反射镜的研究和应用正逐年稳定发展,本文从几种卫星反射镜材料的性能和特性出发,得出SiC及其复合材料作为反射镜材料性能最佳的结论;通过比较各种工艺制备SiC基反射镜性能,结果显示:只有CVD SiC能够作为反射镜反射光学表面.本文重点详细介绍了SiC及其复合材料反射镜制备工艺及方法特点,并对其工艺发展前景进行了展望.     

Improved Resistance to Damage of Silicon Carbide-Whisker-Reinforced Silicon Nitride-Matrix Composites by Whisker-Oriented Alignment

The effects of whisker-oriented alignment on resistance to damage of SiC( w )/Si₃N₄ composites have been investigated by the Vickers indentation method and R -curve behavior. It is shown that increasing the degree of whisker-oriented alignment decreases the lengths of Vickers impressions and indentation cracks. The results exhibit rising R -curve behaviors for the SiC( w )/Si₃N₄ composites with different degree of whisker-oriented alignment. Moreover, the initial crack length c _i, the threshold of crack growth resistance K _i, and the upper bound of crack growth resistance K _∞ change regularly with increasing degree of whisker-oriented alignment. All results suggest that the whisker-oriented alignment improves the resistance to damage of the composites, resulting in a more reliable and usable composite.     

Tribological Properties of Silicon Carbide and Silicon Carbide–Graphite Composite Ceramics in Sliding Contact

A monolithic SiC ceramic and two SiC–C composite ceramics containing 10 and 20 vol% graphite were fully densified with Al₄C₃ and B₄C as additives. The tribological properties of these materials were evaluated by sliding against sintered silicon carbide under dry conditions using two tribometers, block-on-ring and pin-on-disk, where wear occurred under low and high contact stresses, respectively. For all three materials, under low stress, worn surfaces were smooth and wear processes were dominated by tribochemical reaction; under high stress, worn surfaces were rough and wear processes were dominated by fracture and three-body abrasion. A lubricating effect of the graphite particles in the SiC–C composites was observed in all sliding tests. However, while the addition of graphite could concurrently result in a reduction in friction and an increase in wear resistance in the block-on-ring tests, the addition of graphite led to sharply enhanced wear rates despite the lowered coefficients of friction in the pin-on-disk tests. The cause for that difference was attributed to the effect of both the hardness of the materials and the contact stresses.     

Mirror Constant for Tyranno® Silicon-Titanium-Carbon-Oxygen Fibers Measured in Situ in a Three-Dimensional Woven Silicon Carbide/Silicon Carbide Composite

The strength, S , of ceramic and glass fibers often can be estimated from fractographic investigation using the fracture mirror radius, r _m, and the relationship S = A _m/( r _m)^1/2, where A _mis the "mirror constant." The present work estimates the value of A _mfor Tyranno^® Si-Ti-C-O fibers in situ in a three-dimensional woven SiC/SiC-based composite to be 2.50 ± 0.09 MPa·m^1/2. This value is within the range of 2–2.51 MPa·m^1/2 previously obtained for nominally similar Nicalon^® Si-C-O fibers.     

Influence of Thermal Conductivity and Fracture Toughness on the Thermal Shock Resistance of Alumina—Silicon–Carbide–Whisker Composites

The thermal shock resistance (indentation–quench method), fracture toughness, and thermal conductivity of three alumina–silicon–carbide–whisker composites and alumina have been investigated. A new procedure for the evaluation of thermal conductivity data is suggested, and higher room-temperature thermal conductivity than that reported in the literature is determined for silicon carbide whiskers. The ranking of the materials according to thermal shock resistance is consistent with the ranking according to fracture toughness but disagrees with the ranking according to thermal conductivity. This finding supports the analytically obtained result that, in defining thermal shock resistance, fracture toughness is more important than thermal conductivity.