Fabrication Conditions, Microstructures and Mechanical Properties of P/M Processed 2XXX Al-SiCW Composites

The powder metallurgy fabrication of 2XXX Al composites reinforced with SiC whiskers was studied by investigating the evolution of microstructure and its relation to the mechanical properties. In this study, SiC whiskers and gas-atomized aluminum powders were mixed by fluid zone mixer, consolidated by vacuum hot press, and then extruded. The optimum condition for consolidation was 620°C and 50 MPa, at which fully densified pore-free billets were obtained. The composites with relatively homogeneous microstructures were produced by extrusion at 450–500°C under the extrusion pressure of 700–1000 MPa. The mechanical properties of the extruded bars were found to be comparable with those of the composites processed by Advanced Composite Materials Corp. The optimum fabrication conditions have been proposed for producing composites of improved mechanical properties through elimination of coarse intermetallic particles, uniform distribution of reinforcements, and minimization of whisker breakage. The possibility of using particulates rather than whiskers, and the modification of the alloy matrices for high temperature applications are also discussed in relation to the distribution of reinforcements and the optimization of the consolidation temperature.     

增强体含量对SiC_W/SiC层状陶瓷复合材料强韧性的影响

采用流延-化学气相渗透(TC-CVI)工艺制备SiC晶须(SiC_W)/SiC层状陶瓷复合材料,研究了SiC_W含量对层状陶瓷复合材料力学性能和微观结构的影响,探讨了SiC_W/SiC层状陶瓷复合材料的强韧化机制。结果表明:TC-CVI工艺能够有效提高复合材料中晶须含量(40vol%),减少制备过程对晶须损伤,所制备的SiC_W/SiC层状陶瓷复合材料具有合适的层内及层间界面结合强度。随着SiC_W含量增加,层状陶瓷复合材料的密度和力学性能均有明显提高。含40vol%晶须的SiC_W/SiC层状陶瓷复合材料的密度、弯曲强度和断裂韧性均比含25vol%晶须的分别提高了8.4%、30.8%和26.7%。断口形貌中能够观察到层间及层内的裂纹偏转,层内的裂纹桥接和晶须拔出等,这些为主要的增韧机制。高含量SiC_W及合适的层间和层内界面结合强度,对提高SiC_W/SiC层状陶瓷复合材料强韧性有明显作用。     

碳化硅晶须补强氧化铝复合材料的制备及其力学性能

本论文利用商用γ-Al₂O₃粉体和上海硅酸盐所制备的碳化硅晶须,通过热压工艺来制备碳化硅晶须补强氧化铝复合材料．当晶须含量为30vol％时,室温下复合材料的抗弯强度为812±38MPa,断裂韧性为8．8±0．1MPa·m^1／2;在1200℃、Ar气氛下,分别为560±61MPa和6．1±0．4MPam^1／2．在氮气氛下,由于晶须的损伤易导致材料的力学性能下降．添加剂可降低复合材料的烧结温度,但不利于其力学性能．显微结构观察发现,不同温度下,AS复合材料的增韧机理有变化．     

Microstructure and mechanical properties of SiC<Subscript>P</Subscript>/SiC and SiC<Subscript>W</Subscript>/SiC composites by CVI

37.2 vol.% SiC_P/SiC and 25.0 vol.% SiC_W/SiC composites were prepared by chemical vapor infiltration (CVI) process through depositing SiC matrix in the porous particulate and whisker preforms, respectively. The particulate (or whisker) preforms has two types of pores; one is small pores of several micrometers at inter-particulates (or whiskers) and the other one is large pores of hundreds micrometers at inter-agglomerates. The microstructure and mechanical properties of 37.2 vol.% SiC_P/SiC and 25.0 vol.% SiC_W/SiC composites were studied. 37.2 vol.% SiC_P/SiC (or 25.0 vol.% SiC_W/SiC) consisted of the particulate (or whisker) reinforced SiC agglomerates, SiC matrix phase located inter-agglomerates and two types of pores located inter-particulates (or whiskers) and inter-agglomerates. The density, fracture toughness evaluated by SENB method, and flexural strength of 37.2 vol.% SiC_P/SiC and 25.0 vol.% SiC_W/SiC composites were 2.94 and 2.88 g/cm³, 6.18 and 8.34 MPa m^1/2, and 373 and 425 MPa, respectively. The main toughening mechanism was crack deflection and bridging.     

SiCp/Al Composites Fabricated by Modified Squeeze Casting Technique

A cost effective method was introduced to fabricate pure aluminum matrix composites reinforced with 20% volume fraction of 3.5 μm SiC particles by squeeze casting followed by hot extrusion. In order to lower volume fraction of the composites, a mixed preform containing pure aluminum powder and the SiC particles was used. The suitable processing parameters for the infiltration of pure aluminum melt into the mixed preform are： melt temperature 800℃, preform temperature 500℃, infiltration pressure 5 MPa, and solidification pressure 50 MPa. Microstructure and properties of the composites in both as-cast and hot extruded states were investigated. The results indicate that hot extrusion can obviously improve the mechanical properties of the composite.     

Mechanical properties of a zircon matrix composite reinforced with silicon carbide whiskers and filaments

The influence of a silicon carbide whisker reinforcement on room temperature mechanical properties of a monolithic zircon ceramic and zircon composites uniaxially reinforced with silicon carbide monofilaments was studied in a flexure mode. The strength of a monolithic zircon was increased by the addition of whisker reinforcement, but the composite failure was still brittle in nature. In contrast, zircon composites reinforced with SiC whiskers and filaments showed toughened composite-like behaviour and produced higher first matrix cracking strength and toughness than the composites reinforced with only SiC filaments. In addition, the whisker reinforcement had insignificant influence on the ultimate strength of filament-reinforced composites. These results were related to changes in measured fibre-matrix interfacial properties, which indicated that composites with high first matrix cracking strength and toughness can be designed and fabricated via independently tailoring the matrix and the fibre-matrix interfacial properties.     

碳化硅晶须和颗粒增强铝基复合材料的时效行为EI

综述了近年来碳化硅晶须（ＳｉＣｗ）和碳化硅颗粒（ＳｉＣｐ）增强铝基复合材料（ＳｉＣｗ（ｐ）／Ａｌ）时效行为的研究发展状况。主要包括碳化硅晶须与颗粒对基体时效硬化动力学、基体沉淀脱溶过程的影响规律和作用机制，以及影响ＳｉＣｗ（ｐ）／Ａｌ复合材料时效特性的因素。     

PROCESSING AND PERFORMANCE OF SEVERAL SiC WHISKER-REINFORCED Al2O3 MATRIX COMPOSITES

The influence of different SiC whiskers on the processing and performance of Al₂O₃ matrix composites were investigated. Three types of commercial SiC whiskers produced in the United States were used. The composites contained 30 v/o of SiC whisker and were consolidated by both hot pressing (HP) and hot pressing followed by hot isostatic pressing (HP/HIP) techniques. The microstructure, mechanical properties, fracture behavior and toughening mechanisms of the composites were evaluated. The results show that the whisker types and processing techniques have profound effect on the densification and the properties of the composites.     

SiCp/Ti Nanocomposites Fabricated Under High Pressure

Nanoscale SiC particulate reinforced Ti matrix composites were successfully synthesized under high pressure. The reaction behaviour of the SiC particles and Ti matrix during fabrication processes was studied using XRD and TEM methods. The influence of pressure and temperature on the reaction was determined. The highly densified and well bonded SiC _p/Ti composites can be fabricated without interaction by adjusting the production conditions. Their microhardnesses were measured.     

碳化硅晶须增强铝复合材料的研究

本文工作集中于SiC_w/Al复合材料的制备、材料的微观结构分析和高温瞬时拉伸试验三方面。结果表明,用高压铸造法制造SiC_w/Al复合材料是可行的。用该方法制得的复合材料造价低廉,界面结合良好,具有优良的室温、高温强度和足夠的塑性。      

碳化硅颗粒增强铝基复合材料颗粒表面改性技术研究现状

SiC颗粒增强铝基复合材料因具有高的比强度、比刚度、耐磨性及较好的高温稳定性而被广泛应用于航空航天、电子、医疗等领域,但由于SiC颗粒高熔点、高硬度的特点以及SiC颗粒与铝基体间存在界面反应,碳化硅铝基复合材料存在加工性差、界面结合力不足等问题,已无法满足航天等领域对材料性能更高的要求,因此开展如何改善基体与颗粒之间界面情况的研究对进一步提升复合材料综合性能具有重要的科学意义。结合国内外现有研究成果,总结了SiC颗粒与铝基体界面强化机制、界面反应特点、表面改性技术原理及数值建模的发展现状,结果表明,现有经单一表面改性方法处理后的增强颗粒对铝基复合材料性能的提升程度有限,因此如何采用新的手段使复合材料性能进一步提升将成为后续研究热点,且基于有限元数值模拟方法进行复合材料设计也是必然趋势。最后针对单一强化性能提升有限的问题,提出了基于表面改性的柔性颗粒多模式强化方法,同时针对现有的技术难点展望了后续的研究方向,以期为颗粒增强复合材料的制备提供理论参考。     

Mechanical properties of hot pressed SiCp and B4Cp/Alumix 123 composites alloyed with minor Zr

In the present study, effect of Zr addition on the microstructure and wear behavior of aluminum alloy composites (AMCs) reinforced with B4Cp and SiCp particles fabricated via hot pressing were investigated. The samples for the study composed of unreinforced aluminum alloy (Alumix 123) and the composites reinforced with 10% B4Cp and % SiCp were prepared by hot isostatic pressing (HIP) method. Similarly, all the samples alloyed with 0.2% Zr were also produced in order to make a comparison. The produced samples were evaluated for microstructural properties and mechanical tests for hardness, tensile and bending strength were performed. Wear test was carried out at 5 mm/s sliding speed under 3.0 N load for the all kind of hot pressed produced samples. The hot pressed composite microstructures have a more uniform distribution of the reinforcements. After HIP process, the composites were successfully produced with high density (>99%). The addition of Zr increased the yield and tensile strength of the samples. The highest strength value was found for the sample Al 123 matrix alloy with Zr. Evaluation of microstructures showed that copper and zirconium dispersed equally within the matrix microstructure without agglomeration. For the composite samples, Al3Zr, appeared as white precipitate, were inspected around B4C and SiC particles. The composite containing SiC particles and Zr had wear resistance value superior to those of the other counterparts.     

Fabrication,characterization and mechanical properties of SiC-whisker-reinforced Y-TZP composites

The microstructure and mechanical properties of hot-pressed yttria-stablized tetragonal zirconia polycrystals (Y-TZP) reinforced with up to 30 vol % SiC whiskers were investigated. The homogeneously dispersed and fully dense SiC whisker/Y-TZP composites were fabricated by wet-mixing the constitutents and uniaxially hot-pressing the resulting powder. The grain size of the matrix depended on the whisker volume fraction and the hot-pressing temperature. The significant increase of fracture toughness of about MPa m^1/2 at 10 Vol % SiC and a small increase in strength were achieved by uniformly dispersing the whiskers in the Y-TZP matrix. Fracture surfaces revealed evidence of toughening by the mechanisms of crack deflection, pullout, and crack bridging by the whiskers and also a phase transformation of ZrO₂. The observed increase in the fracture toughness of Y-TZP due to the addition of SiC whiskers was correlated with existing models of toughening mechanisms. Good agreement was achieved between the theoretical predictions and the experimental toughness values, obtained from the Y-TZP/SiC_w composites.     

Discontinuously-reinforced aluminum matrix composites

This article reviews the literature relating to aluminum matrix composites reinforced by ceramic particles, short fibers or whiskers. The main reinforcements which have been used are presented with respect to their nature, morphology and mechanical behavior. The influence of matrix alloying elements on ceramic-metal compatibility is discussed. Most fabrication techniques which have been proposed are described and particular attention is paid to the methods suitable for large scale production. The mechanical characteristics of this kind of composite are reported and compared in relation to processing parameters. Finally, models giving a rough prediction of the mechanical behavior of the composites are discussed.     

Fabrication of carbon fibre-reinforced aluminium composites with hybridization of a small amount of particulates or whiskers of silicon carbide by pressure casting

An investigation was carried out on the fabrication of carbon fibre-reinforced aluminium matrix composites with hybridization of particulates or whiskers of silicon carbide by pressure casting. A small amount of particulates or whiskers was uniformly distributed among carbon fibres and the preforms prepared from the treated fibres were directly infiltrated by molten aluminium under applied stress. It was found that the longitudinal tensile strengths of hybrid composites were greatly improved, although their fibre volume fractions were very low compared to those of conventional composites. With this hybridization method, it is also practical to tailor the fibre volume fraction of composites from 60 to 25 vol %, which is not possible in direct infiltration of fibre preforms by pressure casting. The results obtained lead to the conclusion that particulate or whisker additions act not directly as reinforcements but as promoters to improve the infiltration performances of fibre preforms, and consequently to increase the strength-transfer efficiency of carbon fibres. The addition of particulates or whiskers can also improve other properties of the composites, such as hardness and wear resistance.     

SiC w/BAS复合材料的显微结构及力学性能的研究

本文采用热压烧结法制备出致密的SiCw增强BAS玻璃陶瓷基复合材料．结果表明,BAS基体晶化后获得以钡长石为主晶相和莫来石为次晶相的复相BAS玻璃陶瓷．晶须的加入对BAS基体有显著的强韧化效果,加入30vol％SiCw可使材料的室温抗弯强度和断裂韧性分别由基体的156MPa和1．40MPa·m1/2提高到356MPa和4．06MPa·m1/2．TEM观察结果表明,晶须／基体界面结合良好,无界面反应物和非晶层的存在．断口形貌和压痕裂纹扩展路径的SEM观察结果表明,复合材料的主要增韧机制为裂纹偏转、晶须的拔出和桥接．     

Microstructure and mechanical properties of barium aluminosilicate glass-ceramic matrix composites reinforced with SiC whiskers

BAS glass-ceramic composites reinforced with different volume fractions (0, 10, 20, 30, 40 vol%) of SiC whiskers were successfully fabricated by a hot-pressing method. The microstructure, whisker/matrix interface structure, phase constitution and mechanical properties of the composites have been systematically studied by means of SEM, TEM, XRD techniques as well as three-point bending tests. It was demonstrated that the incorporation of SiC whiskers could significantly increase the flexural strength and fracture toughness of BAS glass-ceramic matrixes. The celsian seeds can effectively promote the hexacelsian-to-celsian transformation in BaAl₂Si₂O₈. The active Al₂O₃ added to the BAS matrix obviously reduced the amount of SiO₂ in the matrix and formed needle-like mullite. The high temperature strengths of the composites were also investigated.     

Casting particulate and fibrous metal-matrix composites by vacuum infiltration of a liquid metal under an inert gas pressure

A new method of making metal-matrix composites is reported. This method combines the essentials of three liquid-phase fabrication methods: (i) vacuum infiltration, (ii) infiltration under an inert gas pressure, and (iii) squeeze casting. In this method, the particulate or fibrous preform is placed in a mould and the matrix alloy is placed above the preform. The matrix alloy is heated to the liquidus temperature together with the mould and the preform under vacuum. Then an inert gas like argon is compressed on to the top surface of the matrix-alloy melt, forcing the melt to infiltrate the preform. The pressure is 1000 to 2500 psi. As the melt is just at liquidus temperature, it is much lower than that used in squeeze casting. Moreover, the pressure is an order of magnitude lower than that used in squeeze casting. The low temperature lessens the interfacial reaction between the matrix and the filler, while the low pressure essentially eliminates preform compression. This method has been successfully used to fabricate aluminium-matrix composites reinforced by short ceramic fibres, continuous ceramic fibres, SiC particles, Al₂O₃ particles, graphite flakes and SiC whiskers.     

SiCw/BAS复合材料的显微结构及力学性能的研究

本文采用热压烧结法制备出致密的SiC_w增强BAS玻璃陶瓷基复合材料．结果表明,BAS基体晶化后获得以钡长石为主晶相和莫来石为次晶相的复相BAS玻璃陶瓷．晶须的加入对BAS基体有显著的强韧化效果,加入30vol％SiC_w可使材料的室温抗弯强度和断裂韧性分别由基体的156MPa和1．40MPa·m^1/2提高到356MPa和4．06MPa·m^1/2．TEM观察结果表明,晶须／基体界面结合良好,无界面反应物和非晶层的存在．断口形貌和压痕裂纹扩展路径的SEM观察结果表明,复合材料的主要增韧机制为裂纹偏转、晶须的拔出和桥接．     

颗粒增强镁基复合材料的研究现状及发展趋势

综述了颗粒增强镁基复合材料的研究概况,着重介绍了颗粒增强镁基复合材料的制备技术,界面行为和制备热力学与动力学三大研究热点,另外,对颗粒增强镁基复合材料的增强机理及常温力学性能作了简单介绍,最后,对颗粒增强镁基复合材料的研究方向进行了一些看法和展望,指出原位颗粒增强镁基复合材料的制备技术交城为制备镁基复合材料的发展趋势,镁基复合材料由于具有高的比强度,比模量和良好的耐磨性、耐高温性能和减震性能,在航空航天,特别是汽车工业具有在的应用前景和广阔的市场。