液硅渗透法制备Ti3SiC2改性C/CSiC复合材料

采用浆料浸渗结合液硅渗透法原位生成高韧性Ti₃SiC₂基体, 制备Ti₃SiC₂改性C/C-SiC复合材料。研究了TiC颗粒的引入对熔融Si浸渗效果的影响, 分析了Ti₃SiC₂改性C/C-SiC复合材料的微结构和力学性能。实验结果表明: TiC与熔融Si反应生成Ti₃SiC₂是可行的, 而且C的存在更有利于生成Ti₃SiC₂; 在含TiC颗粒的C/C预制体孔隙(平均孔径22.3 μm)内, 熔融Si的渗透深度1 min内可达10.8 cm; Ti₃SiC₂取代残余Si后提高了 C/C-SiC复合材料的力学性能, C/C-SiC-Ti₃SiC₂复合材料的弯曲强度达203 MPa, 断裂韧性达到8.8 MPa·m1/2; 对于厚度为20 mm的试样, 不同渗透深度处材料均具有相近的相成分、 密度和力学性能, 无明显微结构梯度存在, 表明所采用的浆料浸渗结合液硅渗透工艺适用于制备厚壁Ti₃SiC₂改性C/C-SiC复合材料构件。      

连续碳化硅纤维增强钛基(SiCf/Ti)复合材料的制备技术及界面特性研究综述

连续碳化硅纤维(SiCf)由于具有比强度、比模量高,耐磨性、热稳定性好等性能优点,常作为增强体制备SiC纤维增强钛基复合材料。与钛合金基体相比,其具有密度更低、强度更高、疲劳蠕变性能大幅提升等优点,但横向性能却明显下降。因此,该类材料常被设计制作成单向增强性部件,广泛应用在航空航天等领域,如发动机的传动轴、整体叶环、盘类及风扇叶片等多种复合材料的结构件。碳化硅纤维增强钛基复合材料的性能主要由碳化硅纤维的性能、基体性能及纤维与基体之间的结合界面性能决定。目前批量生产的SiC纤维性能较差,界面结合状态与复合材料性能之间关系的研究开展较少,还不能为钛基复合材料构件设计提供足够的数据支持。因此,近年来研究者们主要从SiCf/Ti基复合材料力学行为的研究角度出发,探究不同基体及纤维类型、复合材料制备工艺方法、界面特性及产物对SiCf/Ti基复合材料界面结合力及破坏机制的影响,获得了大量有价值的数据,以期开发出成本低、产物稳定性好、可批量生产SiCf/Ti基复合材料的制造工艺方法。目前较为成熟的碳化硅纤维有英国DERA-Sigma公司提供的Sigma系列SiCf及美国Textron公司提供的SCS系列SiCf,后者强度最高达到6 200 MPa。SiCf/Ti基复合材料的制备工艺包括金属箔-纤维-金属箔工艺(FFF)、单层带工艺(MT)、基体-涂层纤维工艺(MCT)等,制备复合材料的工艺根据零部件的用途来定,FFF适用于制备板材等大尺寸构件,MCT适用于制备叶环、轴、管、叶片等复杂结构件。界面是增强体与基体之间的纽带和桥梁,界面结构设计、界面反应控制及反应产物均影响着界面的力学特性。在SiCf/Ti基复合材料的纤维和基体之间添加过渡层能够减缓它们之间的相互扩散及化学反应,过渡层选用反应层和惰性涂层组成的双层涂层较好。界面反应产物受涂层成分、基体组织、复合和热处理工艺、环境因素等的影响,增强纤维及基体性能、优选制备工艺、控制界面反应及产物有利于提高复合材料的力学性能。本文总结了连续SiC纤维(SiCf)增强钛基复合材料的应用研究现状,详述了SiCf/Ti基复合材料的钛合金基体材料、SiCf的种类及性能,SiCf与SiCf/Ti基复合材料的制备方法,分析了SiCf/Ti基复合材料界面结构设计及反应产物,阐明了界面力学特性与复合材料性能的关系,指出国内SiCf/Ti基复合材料发展的重点应放在高性能SiC纤维的研究与开发、界面层设计及界面与性能的关系以及复合材料分析检测手段三个方面,为SiCf/Ti基复合材料的制备及其今后的实际应用提供了参考。     

连续SiC纤维增强金属基复合材料研究进展

SiC纤维增强金属基复合材料具有高的比强度、比刚度、耐腐蚀、耐高温等优异的综合性能,在实际应用中具有广阔的前景。本文主要总结了SiC纤维增强金属基复合材料的研究进展,分别阐述了SiC纤维增强铝基、钛基、铜基、镍基复合材料存在的问题、解决办法及应用现状。最后指出了限制复合材料实际应用的几点因素,包括:成本问题、界面问题、各向异性以及缺少质量检测评估体系。     

SiCw／Al—12Ti复合材料裂纹扩展的SEM原位观察

利用带缺口三点弯曲试样，原位观察了SiC品须含量不同的Al－12Ti基复合材料的裂纹扩展过程结果表明，随SiCw增加，裂纹由优先治Al3Ti颗粒／Al界面萌生与扩展转变成在Al3Tip内部和靠近SiCw端部的SiCw／Al界面萌生与扩展SiCw／Al-12Ti的强化机制以SiCw的桥接、拔出和诱导裂纹偏转强化为主，同时，SiCw与Al3Tip起到较好的互补强化作用     

Hybrid composites – Metallic and ceramic reinforcements influence on mechanical and wear behavior

This experimental study is concerned with the influence of metallic (Ti) and ceramic (SiC) reinforcements in an aluminumfsilicon (AlSi) alloy, when regarding tensile properties and wear behavior. Several micron sized particulate reinforced composites were produced by hot-pressing technique: AlSi–SiC and AlSi–Ti composites and AlSi-(Ti–SiC) hybrid composites.Regarding tensile properties, all composites presented higher ultimate tensile strength (UTS) than the AlSi matrix, with the highest UTS being attained by a hybrid composite (AlSi-11.25%Ti–5%SiC).Regarding wear behavior, reciprocating pin-on-plate wear tests were performed for unreinforced AlSi; AlSi–Ti composites and AlSi-(Ti–SiC) hybrid composite against a gray cast iron (GCI) counterface. The wear mechanisms for all the tested tribopairs are presented and discussed. It was observed that the wear behavior of the AlSi–Ti/GCI and also AlSi-(Ti–SiC)/GCI tribopairs are improved when compared with the AlSi/GCI system. AlSi-11.25%Ti-5%SiC hybrid composite exhibited the highest improvement in wear rate.     

SiCf/Ti复合材料的研制

概述了国外碳化硅连续纤维增强钛基复合材料的研制、性能及应用情况，并对箔压法制备SiCf/Ti复合材料的工艺及材料性能进行了研究。结果表明，本研究采用FFF法制作的SiCf/Ti复合材料能达到国外同类材料水平。此外，本研究还对SiCf/Ti复合材料各主要制作工艺进行了分析比较，认为真空等离子喷涂工艺是较有前途的。     

In situ joining of titanium to SiC/Al composites by low pressure infiltration

A method of in situ joining of titanium to SiC/Al composites by low pressure infiltration was proposed. The effect of infiltration temperature on microstructure and bending strength of in situ joining composites was investigated and the best infiltration temperature was confirmed to be 710 °C. The interfacial region of SiC/Al/Ti composites was consisted of Ti substrate, Al–Ti interfacial layer, Al layer and SiC/Al composite. The bending strength of SiC/Al composites kept nearly constant as the infiltration temperature changed while that of SiC/Al/Ti composites was influenced significantly by the infiltration temperature. The fracture occurred at the Al–Ti and Al–SiC/Al interfaces alternately as infiltrated at 670 °C. But as the infiltration temperature was increased to 710 °C, the fracture occurred only at the Al–SiC/Al interface which shows a great interfacial bonding at the Al–Ti interface. The formation of Al–Ti brittle intermetallics and the effect of crystallization and grain coarsening are two possible reasons which lead to the decrease of bending strength when the infiltration temperatures were increased from 710 °C to 730 °C.     

SiC泡沫／Al双连续相复合材料连续性的研究

运用挤压铸造法制备了SiC泡沫／Al双连续性复合材料，研究了SiC泡沫、复合压力和合金成分对复合材料连续性的影响。结果表明，SiC泡沫陶瓷的加入阻碍了基体合金流动，降低了复合材料的连续性。随着复合压力的增加，复合材料的连续性逐渐增强，当压力为150MPa时，复合材料的连续性最好。随着含硅量的增加，基体合金的热膨胀系数逐渐降低，基体和增强体之间的热膨胀匹配增强，复合材料中残余应力降低，复合材料的连续性增强。     

Assessment of Microwave Heating for Sintering of Al/SiC and for in‐situ Synthesis of TiC

This work describes sintering of SiC‐reinforced Al‐matrix composites and in‐situ synthesis of TiC in a powder mixture of Ti and C. In the first case, microwave energy is absorbed by SiC grains, heating the metal matrix to sintering and even melting temperature. The composite is processed at <1 kW microwave power. Microwave absorption and the heating rate increase with decreasing SiC particle size. Composites with high SiC content (70 vol.‐%) are processed at 650 °C/1 h in the microwave furnace, whereas conventional resistive heating at the same temperature did not allow sintering of the sample. In the second case, radiative energy allowed the heating of Ti/C samples up to 950 °C, and microwave assistance enhanced the reaction sintering of Ti/C powder mixtures forming TiC at the border of the Ti particles. The results are compared with conventional processing. Optical images and XRD patterns confirmed the formation of TiC for both techniques.     

高体积分数SiCp/A356复合材料的显微组织和电导率

铝基复合材料在电子封装领域存在着潜在的应用前景。为获得高体积分数的铝基复合材料,利用压力浸渗法制备了高体积分数SiC颗粒增强A356复合材料(SiC_p/A356),通过金相显微镜、XRD、SEM和EDS等分析手段对其物相、显微结构和电导率进行了表征。结果表明:用该方法制备的SiC_p/A356复合材料组织致密,颗粒分布均匀,界面结合性能较好;SiC增强颗粒与A356基体界面反应控制良好,仅有少量Al4C3脆性相生成。SiC粉体经颗粒表面氧化处理在其表面生成一层SiO_2薄膜,虽抑制了界面反应的发生,但也使复合材料的收缩减小,电阻率增大,导电性能变差。     

Thermal conductivities of Ti-SiC and Ti-TiB2 particulate composites

Composites of commercial-purity titanium reinforced with 10 and 20 vol % of SiC and TiB₂ particulates were produced by powder blending and extrusion. Heat treatments were conducted on each of these composites. The thermal diffusivities of the composites were measured as a function of temperature using the laser flash technique. Thermal conductivities were inferred from these measurements, using a rule-of-mixtures assumption for the specific heats. It has been shown that, while an enhancement of the thermal conductivity is expected to arise from the presence of both types of reinforcement, this behaviour is in fact observed only with the Ti-TiB₂ composites. The thermal conductivity of Ti-TiB₂ composites is significantly greater than that of the unreinforced matrix and rises with increasing volume fraction of reinforcement. In contrast, the conductivities of the Ti-SiC composites were considerably lower than that of the unreinforced titanium and decreased with increasing volume fraction of SiC reinforcement. These results have been interpreted in terms of the thermal resistance of the reaction layers which exist between the matrix and two types of particulate reinforcements. The faster reaction kinetics between SiC and Ti gives rise to a thicker reaction layer for a given heat treatment than that between Ti and TiB₂ and is also accompanied by a much larger volume change (– 4.6%). It is proposed that this volume decrease, giving rise to interfacial damage and a network of microcracks, is at least partly responsible for a high interfacial thermal resistance, reducing the conductivity of the Ti-SiC composite. These results indicate that TiB₂ would be preferable to SiC as a reinforcement in Ti for situations where a high thermal conductivity would be beneficial.     

FABRICATION OF SiCp-AI COMPOSITE MATERIALS

Liquid phase fabrication methods for aluminum matrix composites reinforced with SiC whiskers, or SiC particles have been investigated and the mechanical properties of fabricated composites have been evaluated. Three kinds of liquid phase fabrication methods; hot extrusion, hot pressing and pressure infiltration, were studied. Commercial SiC whiskers and SiC powders of alpha type and beta type were used as the reinforcements for an aluminum matrix. Among the fabrication methods investigated, the best results were achieved by the pressure infiltration. The mechanical properties and the wear resistance of the fabricated composites were measured. The SiC whisker reinforced aluminum matrix composites have high strength, so that they can be used as high specific strength materials. The SiC particulate reinforced aluminum matrix composites are not strong as the SiC whisker reinforced composites. However, the SiC particulate reinforced aluminum matrix composites have a good potential for use as wear resistant material. The hardening effect of beta type particles on the aluminum matrix was larger than that of alpha type particles.     

The effect of the interface on the thermal conductivity of titanium-based composites

Thermal conductivity measurements have been made on composites of unalloyed Ti reinforced with short fibre SiC, particulate SiC and particulate TiB₂, and Ti-6Al-4V reinforced with long fibre SiC. Measurements were also made on the unreinforced matrices and on the reinforcements themselves. The results have been compared with predictions from the Hasselman and Johnson model for spherical and long fibre composites and from the Eshelby model for ellipsoids of any aspect ratio. It is shown that, while an enhancement of the thermal conductivity is expected to arise from the presence of both types of particulate, this effect is in fact produced only with the TiB₂ reinforcement. This is explained in terms of the large thermal resistance of the SiC/Ti interface, which is in turn related to the nature of the reaction layer formed there during processing. The transverse conductivity of the Ti-6Al-4V reinforced with long SiC fibres was also impaired by the high thermal resistance of the interface, but in this case the effect was less significant because of the larger diameter of the reinforcement, which reduces the frequency with which transport of heat across an interface must occur. Finally, similar characteristics were exhibited by the short SiC fibre/Ti composite, except that the axial conductivity was rather lower than expected. This effect is attributed to matrix porosity localized at the fibre ends.     

Effect of SiC Particulates on the Microstructure of Al-6Ti-6Nb Matrix Composites Fabricated by Mechanical Alloying Technique

Millimeter sized SiC (m-SiCp) and nanometer sized SiC (n-SiCp) particulates reinforced Al-6Ti-6Nb matrix composites were prepared by mechanical alloying (MA) and later hot-press sintering. Their microstructure was investigated to know the influence of the incorporated SiC particles. The secondary Al3Ti, AlNb2 intermetallics particle size, the Al matrix grain size and their submicrostructure are strongly affected, and they are correlated with the thermal stability of the composites.     

Effects of interface coating and nitride enhancing additive on properties of Hi-Nicalon SiC Fiber reinforced reaction-bonded silicon nitride composites

Strong and tough Hi-Nicalon SiC fiber reinforced reaction-bonded silicon nitride matrix composites (SiC/RBSN) have been fabricated by the fiber lay-up approach. Commercially available uncoated and PBN, PBN/Si-rich PBN, and BN/SiC coated SiC Hi-Nicalon fiber tows were used as reinforcement. The composites contained 24 vol% of aligned 14 m diameter SiC fibers in a porous RBSN matrix. Both one- and two-dimensional composites were characterized. The effects of interface coating composition, and the nitridation enhancing additive, NiO, on the room temperature physical, tensile, and interfacial shear strength properties of SiC/RBSN matrix composites were evaluated. Results indicate that for all three coated fibers, the thickness of the coatings decreased from the outer periphery to the interior of the tows, and that from 10 to 30 percent of the fibers were not covered with the interface coating. In the uncoated regions, chemical reaction between the NiO additive and the SiC fiber occurs causing degradation of tensile properties of the composites. Among the three interface coating combinations investigated, the BN/SiC coated Hi-Nicalon SiC fiber reinforced RBSN matrix composite showed the least amount of uncoated regions and reasonably uniform interface coating thickness. The matrix cracking stress in SiC/RBSN composites was predicted using a fracture mechanics based crack bridging model.     

SiC纤维增强钛基复合材料界面反应机理

本文应用相图和扩散通道理论分析了SiC/Ti复合材料界面反应的过程及界面区微观形貌,SiC纤维的表面状态直接影响着SiC/Ti界面反应的扩散通道。在SiC纤维表面涂覆TiC,或涂覆碳基涂层使Ti₃SiC₂层优先形成,能有效地控制界面反应,保护SiC纤维,界面区中反应产物层的排列顺序不一定与扩散通道所示的相顺序一一对应。      

Microstructure and mechanical properties of cast (Al–Si)/SiCp composites produced by liquid and semisolid double stirring process

Abstract

A stirring process containing two steps, i.e. liquid and then semisolid stirring, was used to produce SiC particle reinforced aluminium matrix composites. The major advantages of this process are that full wetting of SiC particles by molten aluminium can be readily achieved at relatively low stirring rates, and undesirable Al₄ C₃ is not formed at the Al/SiC interface due to lower processing temperatures. Cast Al–Si matrix composites reinforced with 15 and 20 vol.-%SiC particles were produced in the present work. The mechanical properties of the composites were evaluated under the conditions of investment mould casting and heat treatment. For the composites obtained without employing semisolid stirring, the aggregation of SiC particles observed in the microstructure of composites resulted in quite poor mechanical properties. Observations and analyses indicated that some Al/SiC interfaces were very clean, and a reaction product of spinel MgAl₂O₄ was also found at some Al/SiC interfaces. Silicon dioxide (SiO₂ ) was found to exist on the surface of as purchased and 250°C dried SiC powders. This SiO₂ is involved in the spinel reaction at the interface between the SiC particles and the matrix in the present Al/SiC composites.     

SiC纤维增强钛基复合材料的界面改性研究现状

针对SiC纤维增强Ti基复合材料的界面反应问题,综述了国内外涂层法界面改性的研究现状,主要包括各种单涂层法、双涂层或复合涂层法及其对复合材料界面和力学性能的影响,指出了其存在的问题或不足,并预测了今后的发展趋势。     

制备工艺对热压烧结SiC/SiC复合材料结构与性能的影响

采用纳米SiC和亚微米SiC粉料作为基体形成原料,通过热压烧结技术制备了SiC/SiC 复合材料.研究了粉料颗粒、烧结温度、烧结压力对复合材料显微结构和各种性能的影响.结果显示,采用纳米碳化硅粉体可有效降低烧结温度,促进复合材料的致密化过程,在1780℃、20MPa条件下可获得性能优良的复合材料.而采用亚微米SiC粉体,复合材料的致密化过程需要较高的温度,但随着密度的增加,基体与纤维之间的作用力增强,不利于性能的提高.     

The CVD of Ceramic Protective Coatings on SiC Monofilaments for Use in Titanium Based Composites

TiB₂, TiC and TiN protective coatings have been deposited onto SiC monofilament fibers by the CVD technique using a cold-wall reactor at reduced pressure. The effect of deposition conditions on the morphology, microstructure, phase composition and adherence of the coatings were studied. The physical and chemical compatibility of these ceramic coatings with SiC filaments together with titanium-alloy matrices were assessed and compared. Dense and uniform TiB₂ coatings have been deposited successfully onto SiC monofilaments. The coating is stable on the SiC fiber and acts as an effective: barrier against the vigorous SiC/Ti-6Al-4V interfacial reaction. The adhesion of TiC on SiC fibers is comparatively weaker than the TiB₂ coating. There was no significant reaction found at the interface of TiC/Ti except at the interface of TiC/SiC. Examination of the TiN coatings showed severe cracking and spalling, hence TiN could not provide protection in a Ti-alloy matrix.