喷射共沉积SiCp／Al复合材料的组织与力学性能

用喷射共沉积技术制备了含３５ｖｏｌ％ＳｉＣ的ＳｉＣｐ／Ａｌ复合材料，用扫描电镜观察了这种复合材料沉积态的孔隙和ＳｉＣ颗粒分布。在拉伸实验机上测量了不同工艺条件下制备的ＳｉＣｐ／Ａｌ的应力－应变曲线，用扫描电镜观察了雾经前先抽真空，再充氮气保护工艺条件下得到的ＳｉＣｐ／Ａｌ经热压后拉伸试样的断口形貌，实验结果表明，沉积态复合材料孔隙数量较少，尺寸较小，ＳｉＣ分布均匀，雾化前抽真空并充氮气，热压均可提     

SiC颗粒强化铝基复合材料及其断裂韧性

介绍了ＳｉＣ颗粒强化铝基复合材料的性能及一些应用，阐述了ＳｉＣ颗粒的体积百分比对ＳｉＣ颗粒强化的６０６１铝合金复合材料的断裂韧性及断裂机理的影响。     

颗粒形状及基体热处理对SiCp/LD2 断裂韧性的影响

对普通SiC颗粒和钝化处理过的SiC颗粒增强LD2铝复合材料的研究表明,颗粒经钝化处理后,几乎去除了很尖锐的部分,使颗粒呈近等轴状,但颗粒的形状对两种热处理态的复合材料(热挤出态和T6态)的断裂韧性K     

新型液态搅拌铸造SiCp／A1复合材料

新型液态搅拌铸造ＳｉＣｐ／Ａ１复合材料本课题从ＳｉＣ颗粒预处理入手，利用研制的新型液态机械搅拌装置，制备了ＳｉＣ颗粒均匀分布并与基体结合紧密的铸造ＳｉＣＰ／Ａ１复合材料。ＳｉＣ颗粒尺寸５—２０μｍ，基体铝合金可以是铸造铝合金，也可以是形变铝合金。所制...     

SiC铝基复合材料的制备技术和界面问题

综述了ＳｉＣ颗粒增强铝基复合材料的制备工艺及其在制备过程中的界面反应和表面处理问题。     

可取代飞机用镍合金的MoSi2复合材料

据悉 ,美国国家航空航天局刘易斯研究中心目前正在研究拟用ＭｏＳｉ2 复合材料取代目前飞机发动机所用的镍基超耐热合金材料。这种ＭｏＳｉ2 复合材料 (3 0 %～ 50 %Ｓｉ3Ｎ4颗粒 )含有一种ＳｉＣ基纤维。据研究人员称 ,这种复合材料与镍基超耐热合金相比较 ,其高温氧化性能更好 ,材料密度更低 ,熔化温度更高。其制备方法是 :将ＭｏＳｉ2 和Ｓｉ3Ｎ4混合制成混合粉末试样 ,经真空热压(实 )后再热等静压 ,制成仅含基体材料的全致密态板型。试样按不同取向含有多种 (股 )ＳｉＣ基纤维 ,并在 1 40 0℃温度下进行化学、热机械加工和显微结构试验…     

荷兰推出全新半导体处理技术

荷兰飞利浦电子集团近日宣布 ,推出全新的处理技术———ＱＵＢｉＣ4′Ｇ′。该技术完美结合了超高速硅锗技术、无源元器件集成以及备受业界好评的ＱＵＢｉＣ4ＢｉＣＭＯＳ处理技术的衬底隔离和密集ＣＭＯＳ逻辑功能。飞利浦已成功采用该技术生产世界首个单 12 5Ｇｂｐｓ光交叉点交换ＴＺＡ2 0 6 0。低噪音值和低电流消耗等先进性能使ＱＵＢｉＣ4′Ｇ′适于先进的射频和微波应用。荷兰推出全新半导体处理技术     

弱放热反应TiSi2燃烧合成的研究

采用燃烧合成法合成了绝热温度为１８００Ｋ的ＴｉＳｉ２。分析了毛坯直径和初始孔隙率、Ｔｉ颗粒及预热温度对燃烧合成的影响，证实满足Φ＝９２ｍｍ，ρ＝５２％的－３００目钛粉形成的毛坯在常温才能发生自蔓延反应。利用燃烧波前沿熄淬法（ＣＦＱ）研究了ＴｉＳｉ２形成机制。当Ｔ≤１３３０℃时ＴｉＳｉ２通过扩散反应机制进行；当Ｔ〉１３３０℃时，ＴｉＳｉ２反应机制则是溶解－沉淀析出。分别利用ＸＲＤ和ＳＥＭ分别了产物及     

SiCw／ZTA（Y）陶瓷基复合材料力学性能的研究

研究了不同ＳｉＣ晶须含量对ＺＴＡ（Ｙ）陶瓷基复合材料力学性能的影响，实验结果表明，ＳｉＣ晶须能明显提高复合材料的抗弯强度和断裂韧性，晶须含量为２０ｖｏｌ％时，复合材料性能可达σｂｂ＝３８０ＭＰａ，ＫＩＣ＝９．８ＭＰａ·ｍ＾１／２，但晶须含量过高时，复合材料的强度有下降趋势。     

铁合金文摘THJ1829─1840

铁合金文摘ＴＨＪ１８２９─１８４０ＴＨＪ１８２９ＴＦ６４１．１ＴＦ６１５Ｃｒ－Ｓｉ－Ｃ系和Ｃｒ－Ｆｅ－Ｓｉ－Ｃ系中的液－固平衡［Ｌｉｑｕｉｄ－ＳｏｌｉｄＥｑｕｉｌｉｂｒｉａｉｎｔｈｅＣｒ－Ｓｉ－ＣａｎｄＣｒ－Ｆｅ－Ｓｉ－ＣＳｙｓｔｅｍｓ］，（Ｋ．Ｋｏ...     

Aspects of fracture in particulate reinforced metal matrix composites

The tensile deformation and fracture behaviour of the aluminium alloy 6061 reinforced with SiC has been investigated. In the T4 temper plastic deformation occurs throughout the gauge length and the extent of SiC particle cracking increases with increasing strain. In the T6 temper strain becomes localised and particle cracking is more concentrated close to the fracture. The elastic modulus decreases with increasing particle damage and this allows a damage parameter to be identified. The fraction of SiC particles which fracture is less than 5%, and over most of the strain range the damage controlling the tensile ductility can be recovered, indicating that other factors, in addition to particle cracking are important in influencing tensile ductility. It is suggested that macroscopic fracture is initiated by the SiC particle clusters that are present in these composites as a result of the processing. The matrix within the clusters is subjected to high levels of triaxial stress due to elastic misfit and the constraints exerted on the matrix by the surrounding particles. Final fracture is then produced by crack propagation through the matrix between the clusters.     

Effects of sic content on fatigue crack growth in

An experimental study has been conducted with the purpose of examining the fatigue crack growth characteristics of cast aluminum alloy matrix composites reinforced with different vol- ume fractions of silicon carbide particles. Particular attention has been paid to developing com- posite microstructures with similar matrix aging condition, precipitation, matrix strength, reinforcement particle size distribution, and interfacial characteristics but with different con- trolled amounts of reinforcement particles. Fatigue crack growth experiments have been con- ducted using constant stress amplitude methods with a fixed load ratio as well as constant K_max control involving a varying load ratio. The development of crack closure and the microscopic path of the crack through the composite microstructure are monitored optically and using the electron microscope in an attempt to examine the mechanisms of fatigue fracture. The results indicate that an increase in SiC content results in the suppression of striation formation in the ductile matrix. Although ductile matrix failure involving the formation of striations in the low SiC content composite or of void growth in the high SiC content composite is evident, the results also show that fracture of the reinforcement particles plays a significant role in dictating the rates of fatigue crack growth. Detailed quantitative analyses of the extent of particle fracture as a function of the reinforcement content have been performed to elucidate the mechanistic origins of fatigue resistance. The propensity of particle fracture increases with particle size and with the imposed value of stress intensity factor range. While discontinuously reinforced metal- matrix composites with predominantly matrix cracking are known to exhibit superior fatigue crack growth resistance as compared to the unreinforced matrix alloy, the tendency for particle fracture in the present set of experiments appears to engender fatigue fracture characteristics in the composite which are inferior to those seen in the unreinforced matrix material. Particle fracture also results in noticeable differences in the microscopic fracture path and causes a reduction in crack closure in the composites as compared to that in the matrix alloy. The results of this work are discussed in light of other related studies available in the literature in an attempt to develop a mechanistic perspective on fatigue crack growth resistance in metal-matrix composites.     

Effect of overaging and particle size on tensile deformation and fracture of particle-reinforced aluminum matrix composites

The effect of reinforcement particle size and overaging treatment on the tensile behavior and fracture morphology of a 2080/SiC/20 _p composite was investigated. Tensile behavior was profoundly influenced by particle size and matrix strength. The composite strength increased with a decrease in particle size, while overaging greatly reduced the strength of the composite, independent of particle size. Almost all particles on the fracture plane were fractured, and the amount of particle fracture in the composites was insensitive to overaging and particle size, due to the excellent bonding between SiC particles and the Al matrix. Fractography showed that void nucleation in the matrix of peak-aged composites took place primarily at very fine SiC particles, which were much smaller than the average SiC particle size. Subsequent failure took place by the tearing topography surface (TTS) mechanism. In the overaged composite, composites failed by a more conventional void nucleation and growth process, where void nucleation took place at coarsened S precipitate particles, resulting in smaller and more elongated voids.     

混料时间和挤压对SiC增强纯Al基复合材料显微组织和力学性能的影响

采用粉末冶金法制备SiC颗粒增强工业纯Al基复合材料,研究混料时间和挤压对复合材料显微组织和力学性能的影响。研究表明:机械混粉过程存在最佳的混料时间,混料时间为16 h时SiC颗粒分布均匀,复合材料的密度高、力学性能好。挤压可以改善复合材料的界面结合强度、减少孔洞的数量,从而提高材料的致密度和力学性能。烧结态复合材料的断裂机制以基体的脆性断裂以及增强相与基体的界面脱粘为主。挤压态复合材料的断裂以基体的韧性断裂以及SiC颗粒的脆性断裂为主,伴随着少量的基体与SiC颗粒的界面脱粘。     

Crack Growth Resistance of Hybrid Fiber-Reinforced Cement Matrix Composites

The effect of hybrid fiber reinforcement on fracture energy and crack propagation in cement matrix composites is examined. The crack in cement matrix composites is allowed to fracture under mode-I loading with three-point bending beam specimens. The influence of fiber types and their combination is quantified by using the toughness index and fracture energy. A proper hybrid combination of steel fibers and polyvinyl alcohol microfibers enhances the resistance to both the nucleation and growth of the crack. The micromechanical model of hybrid composites by using a fiber bridging law is emphasized, and the numerical model prediction closely matches the behavior obtained from the experiment. The influencing role of the material parameters in the fracture tests (e.g., the fracture toughness index and fracture energy) becomes more apparent than ones used in some conventional strength-based or fiber pullout tests, and these fracture parameters could screen the effect of fiber/microfiber reinforcement in enhancing the crack growth resistance of cementitious composites. This study demonstrates that fundamental fracture tests are effective to characterize and develop high-performance hybrid fiber–reinforced cement matrix composites.     

Influence of particle size and volume percent of flaky mo particles on the mechanical properties of AI2O3/Mo composites

The influence of particle size and volume percent of Mo particles on flake-forming behavior of Mo powders during a ball milling process and three-point flexural strength and fracture toughness of A1₂O₃ composites reinforced with flaky Mo particles have been investigated. The flake-forming behavior of Mo powders mixed with A1₂O₃ powders becomes prominent with increasing Mo particle size, while remaining almost independent of Mo volume percent. The microstructure of the composites reinforced with flaky Mo particles is anisotropic, depending on the arrangement of these Mo particles in the A1₂O₃ matrix. The microdispersion of flaky Mo particles contributes remarkably to an increase in both flexural strength and fracture toughness. The flexural strength increases with decreasing Mo particle size, while the fracture toughness increases with increasing Mo particle size, which corresponds to an increase of the flake-forming tendency of these particles. Furthermore, the flexural strength and fracture toughness can be simultaneously improved by increasing the volume fraction of flaky Mo particles. The microstructural observations indicate that the improvement in strength may be attributed to a grain-refining effect due to inhibition of grain growth of the matrix by the presence of Mo particles. In addition, the improvement in fracture toughness may be due to plastic deformation of Mo particles at a crack tip, which is accelerated more by the flaky rather than the small spherical shape.     

The mode I fracture resistance of unidirectional fiber-reinforced aluminum matrix composites

The mode I fracture resistance has been measured for Al and Al/4 Mg matrix composites, unidirectionally reinforced with ceramic fibers, prepared using a squeeze casting technique. Effects of SiC particle additions have also been investigated. The Al/4 Mg system had a high toughness, whereas the Al matrix system had a relatively low fracture resistance. In all cases, the addition of particulates slightly decreased the resistance to crack growth. The fracture resistance was simulated by a ductile bridging model with plastic dissipation occurring within a zone governed by the fiber spacing. The tensile strength of these composites has been estimated, based on the resistance behavior and microstructure.     

Determination of fracture toughness and bridging tractions from crack-opening displacement measurements in particulate composites of diamond in zinc sulfide

The fracture toughness of zinc sulfide ceramic and a series of ZnS diamond particle composites was studied through measurements of crack opening displacement profiles. Five composites were fabricated using weight fractions of 10, 20 and 30% of 0–1 μm diamond particles, and 10 and 20% of 1–3 μm particles in a ZnS matrix. The cracks were grown using a novel specimen geometry and a loading technique that permitted stable crack growth even in small specimens. The fracture toughness of each material was calculated on the basis of the displacement profiles and the material properties, as opposed to the applied loads and the specimen geometry. The pure zinc sulfide material exhibited nearly ideal brittle behavior, and the toughness measurements agreed closely with other methods. The greatest toughening occurred in the 1–3 μm particle size composites, in which weak bridging tractions (⩽ 100 MPa) over a short distance along the crack (50–100 μm) could explain the reduced displacements near the crack tip. Even smaller size bridging zones (5–10 μm) may have been present in the 0–1 μm particle size composites, but elastic shielding alone can explain the observed toughening. The specimen geometry used here permitted toughness measurements using small specimens (< 5 mm) but is limited to materials having bridging zones that are less than about 250 μm.     

Characteristics of hot-pressed fiber-reinforced ceramics with SiC matrix

Silicon carbide ceramics’ matrix composites with SiC or C filaments were fabricated through hot pressing, and the effects of the filament pullout on their fracture toughness were experimentally investigated. The C-rich coating layers on the SiC filaments were found to have a significant effect on the frictional stress at the filament/matrix interfaces, through assising the filamet pullout from the matrix. Although the coating layers were apt to burn out in the sintering process of SiC matrix compposites, a small addition of carbon to the raw materials was found to be effective for the retention of the layers on the fibers, thus increasing the fracture toughness of the composites. The fracture toughness of the C filament/SiC matrix composite increased with temperature due to the larger interfacial frictional stress at higher temperatures, because of the higher thermal expansion of the filament in the radial direction than that of the matrix.