SiCp／Al复合材料的微观结构与界面

对用压力铸造法制造的碳化硅颗粒增强铝合金（ＳｉＣｐ／Ａｌ）复合材料的微观结构和界面进行了研究。结果表明：碳化硅颗粒在复合材料中均匀分布，复合材料的基体中有较高的位错密度，碳化硅颗粒中有少量的层错。研究还发现ＳｉＣｐ／Ａｌ复合材料中界面结合良好，没有反应物生成，并且在界面处没有发现孔隙存在。在复合材料拉伸断口上没有发现裸露的碳化硅颗粒，说明在复合材料拉伸破坏时ＳｉＣｐ－Ａｌ界面没有开裂，反映了压铸ＳｉＣｐ／Ａｌ复合材料中良好的界面结合。     

Reactions at the Al/SiO2/SiC layered interface

Electron spectroscopy and thermodynamic modelling have been used to examine reactions at the Al/SiO₂/SiC layered interfaces at 800 °C. The reactions have been examined as a function of oxide thickness. Three regimes have been isolated: (i) where there is no oxide present aluminium and SiC react to produce Al₄C₃ and free silicon; (ii) where there is a thin oxide present the initial products are aluminosilicates and amorphous alumina; however, once the SiO₂ is consumed, Al₄C₃ emerges as a product; (iii) where a thick oxide is present only aluminosilicate and alumina are formed.     

Measurement of interface strength in Al/SiC particulate composites

Fracture in particulate-reinforced metal-matrix composites is initiated by particulate cracking and interface decohesion, and crack propagation occurs through the matrix, particulate and interface. A ‘critical stress partition’ model is described which considers the proportions of matrix, particulate and interface for which the fracture stress is exceeded. Tensile tests and microhardness measurements are reported for SiC/Al metal-matrix composites having particulate volume fractions of 0–20%. Measurements of the fractions of cracked and interface-debonded particulate before and after final fracture are combined with the fracture model to calculate the interface strength, σ_int′. The values of σ_int′ obtained are 469 MPa for uncoated SiC particulate and 438 MPa for particulate coated with a thin layer of Al₂O₃ to prevent interface reaction. The tensile results indicate that the weaker interfaces promote interface debonding and increase percent elongation.     

无压浸渗制备SiC/Al电子封装材料的结构与性能

将粒度为F280的SiC颗粒振实后直接无压浸渗液态AlSi12Mg8铝合金,制备出高SiC含量的铝基复合材料,并对其结构和性能进行了研究。结果表明:采用该方法制备的SiC/A1复合材料内部组织结构均匀致密,无明显气孔等缺陷,界面产物主要为Mg₂Si,MgO,MgAl₂O₄;平均密度为2.93 g·cm^-3,抗弯强度在320 MPa以上,热膨胀系数为6.14×10^-6～9.24×10^-6 K^-1,导热系数为173 W·m^-1·K^-1,均满足电子封装材料要求。     

Development of Some Fundamental Research of SiC_W/Al Composites in HIT PartⅠ Microstructure and SiC/Al Interface of SiC_W/Al Composites

The microstructure of SiC whisker reinforced aluminium alloy (SiC_w/Al) composite is reviewed,andthe SiC-Al interface in SiC_w/Al composite is especially discussed,The main contents aremorphology of the aluminium matrix in SiC_w/Al composite;microstructures and defects of SiCwhiskers in SiC_w/Al composite and bonding mechanisms of the SiC-Al interface in SiC_w/Al com-posite.     

Stress carrying capability and interface fracture toughness in SiC/6061 Al model materials

Abstracts are not published in this journal This revised version was published online in November 2006 with corrections to the Cover Date.     

Influence of microstructure of fibre/matrix interface on mechanical properties of Al/SiC composites

Abstract

The relationship between microstructure and mechanical properties of composites of squeeze cast Al–Cu and Al–Cu–Mg reinforced with 25 vol.-%SiC whiskers was investigated. Tensile test results were compared with values calculated using a modified rule of mixtures (ROM). The results were found to be in good agreement for the Al–Cu matrix composite, whereas a relatively large discrepancy was observed for the Al–Cu–Mg matrix composite. It was concluded from microstructural observations that this difference resulted from a reduction of the whisker strength due to more pronounced decoration of the interfaces by oxides and spinels. For the Al–Cu–Mg composite, the effect of interfacial phases on the composite strength must betaken into account when the modified ROM is applied.

MST/1242     

Ni/Al涂层反应烧结界面组织与特性

将Ni-Al混合粉在不引起反应的条件下喷涂到Q235钢基材表面,H2作为保护气氛,加热到993K,并随炉冷却制备试样.实验结果表明,界面处的硬度明显高于基材和涂层的硬度约32HV,界面结合强度比烧结前增加了2～3倍.SEM和EDX分析表明:界面有约为101μm的Ni-Fe扩散区,扩散区内EDX曲线存在4～5tμm宽的台阶,证实Fe/Ni界面区有新相生成,初步认为是Ni3 Fe有序固溶体.     

Microstructure and toughening mechanism of the 3Y-TZP/Al2O3 composite reinforced by SiC whiskers

Microstructures of 10 vol% SiC whisker reinforced 3Y-TZP (3vol% yttria stabilized tetragonal zirconia polycrystals) composite with addition of 5 wt% Al₂O₃ have been investigated using electron microscopy. The investigation focused not only on the morphology of the composite but also on the martensitic transformation of ZrO₂. The results from high resolution electron microscopy (HREM) observations show that the boundaries between whiskers and the matrix are, in general, clean; however, in some areas, little glassy phases exist. The habit plane of t/m ZrO₂ during the transformation was found at c _t//a _m in the present observations. The processes of t m transformation in various conditions have been discussed. The fact that no whisker pull-out was found during material breakage indicates that the toughening of this composite would come mainly from a t/m transformation toughening mechanism, as well as crack deflection and bridging. Finally, a fracture strength enhancing mechanism is discussed.     

Microstructure and phase constitution near the interface of Cu/Al vacuum brazing using Al-Si filler metal

Brazing of Cu to Al using Al-Si filler metal has been carried out by vacuum brazing technology. The microstructure and the phase constitution in Cu/Al joint were studied by means of metallography, electron probe microanalyser (EPMA) and X-ray diffraction (XRD). Experimental results obtained showed that two kinds of intermetallic compounds (IMCs) are formed near the interface of copper and brazing seam region and those are Cu₃Al₂ and CuAl₂ phases. Moreover, ε-Cu₁₅Si₄, Al-Si and CuZn₂ are formed on the α-Al solid solution in the brazing seam region. Technology parameters of vacuum brazing were: brazing temperature T=590-610 °C, vacuum level 10⁻³ Pa, holding time t=5-10 min.     

碳/碳化硅刹车材料的显微结构分析

采用反应熔体渗透法(reactive melt infiltration, RMI)制备了碳/碳化硅(C/SiC)刹车材料, 利用X射线衍射分析了材料组成, 并通过光学、扫描电子和透射电子显微镜从不同尺度观察了刹车材料的微观结构. 结果发现, 反应生成的SiC是面心立方的β-SiC, 主要分布在胎网层、针刺纤维附近以及无纬布层的纤维束间; 残余的单质Si分布在SiC的颗粒间. SiC在SiC-Si界面上, 以大约5～15μm的粗大颗粒存在; 而在SiC-C界面上, 以粒径100nm左右的细小颗粒存在.     

Microstructure and microchemistry of silicon particles formed during electrical-discharge machining

The structure and morphology of particles representing the byproduct of electrical-discharge machining (EDM) were analyzed using transmission electron microscopy (TEM). The EDM process involved high-efficiency and high-accuracy fine boring of a single-crystal silicon ingot by high-frequency electrical spark discharges. As the silver electrode advanced, spark-discharge-melted or vaporized small particles of the silicon workpiece were produced and the particles were flushed away and collected in deionized water. Standard TEM and analytical electron microscopy (AEM) observations were carried out. Bright-field (BF) images, diffraction, and energy-dispersive X-ray spectrometry (EDXS) data were obtained to completely characterize the EDM particles. BF images indicated the presence of large silicon particles decorated by smaller silver particles originating from the electrode as the byproducts of the EDM processing. Analysis of the particle-size distribution resulted in an average silicon particle size of about 500 nm decorated by smaller silver particles of an average size of about 65 nm. EDXS spectra depicted individual silicon and silver particles with characteristic peaks that identify the elements present. Selected-area electron diffraction (SAED) pattern confirmed the presence of crystalline silicon. Finally, a set of SAED patterns, EDXS profiles, and TEM images is included that fully describe the particles' chemistry, structure, and morphology, respectively.     

Study of machinable SiC/Gr/Al composites

The effect of flaky graphite particles [with volume fraction (vf) 3–7%] on machinability and mechanical properties of SiC/Al composites were investigated. Results showed that the machinability was improved greatly with the increasing vf of graphite particles. When the vf of graphite particles was 7%, the tool life was prolonged by 130%, and the tensile strength and elastic modulus of SiC/Gr/Al composite were 365 MPa and 144 GPa, respectively. The presence of flake graphite particle acted as solid lubrication and promoted chip formation during cutting, resulting in an improved machinability.     

Effects of the SiC/Al interface reaction on fracture behavior of a composite conductor using SiC fiber reinforced aluminum for next generation power equipment

Electrical power demands are increasing every year, meaning that lightweight electric cable is needed which has high transmission capacity, high thermal resistance and low sag. Tokyo Electric Power Co., Chubu Electric Power Co. and Hitachi Cable Ltd. have been breaking new ground in the field of electric cable through the development of a SiC fiber reinforced aluminum conductor. In this work, the SiC/Al interface reaction during the manufacturing process and the electricity transmission temperature were studied by transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX) and field emission-Auger electron spectroscopy (FE-AES) for long-term reliability assessment. No reaction products were detected at the SiC/Al interface of elemental wire consisting of 7 SiC/Al preformed wires, indicating that the wire manufacturing process was reliable. An Al₄C₃ product was detected locally at the SiC/Al interface of the wire which had been thermally treated in molten Al under unfavorable conditions. The activation energy, Q, of Al₄C₃ growth at the SiC/Al interface was about 190 kJ/mol. In the temperature range of electricity transmission, Al atoms diffused into SiC fiber during heat treatment, and the amount of the diffused Al increased with increasing treatment temperature and holding time. The activation energy of Al diffusion through the SiC/Al interface to SiC fiber was about 78 kJ/mol. Strength deterioration was not induced by Al diffusion into SiC fiber, but strength strongly depended on the formation of Al₂SiO₅ compound at the SiC/Al interface above 400°C transmission temperatures. Kinetics calculations indicated that the rate of strength deterioration of the composite cable, held at 300°C for 36 years, was about 5%, so that practical use of SiC/Al composite cable should not be far in the future.     

不连续界面相Al4C3对SiC/Al复合材料界面结合影响的第一性原理及实验

采用密度泛函理论的第一性原理及实验相结合的方法,探讨了不连续界面相Al₄C₃对SiC/Al复合材料界面结合的影响,并与无界面新相生成时进行对比。研究表明,当Al(111)表面吸附C原子时,在Bridge位置上吸附C原子最为稳定;随着C覆盖率的增加,C原子吸附能逐渐减小;当界面相呈不连续分布时,界面由原来的SiC/Al转变为(SiC+Al₄C₃)/Al,界面黏着功由原来的0.851 J/m2增加至1.231 J/m2,这主要由于当C原子在Al表面吸附时,C原子和Al原子间形成共价键和离子键,且与界面处的Si原子也形成共价键,从而促进界面结合。利用第一性原理计算的SiC/Al和(SiC+Al₄C₃)/Al体系黏着功与实验值较为接近,且变化规律相同,具有较高的参考价值。      

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。      

新型复式连通SiC/390Al复合材料的制备和性能

以空心多孔SiC泡沫陶瓷为增强体,用挤压铸造法制备了新型复式连通双连续相SiC/390Al复合材料,研究了泡沫陶瓷骨架筋的结构对复合材料的影响,以及复合材料中的界面对力学性能的影响.结果表明,SiC空心多孔泡沫陶瓷与390Al复合后形成了复式连通双连续相复合材料,具有独特的互穿式界面结构,材料界面的结合优异.随着复合材料界面结合的加强和泡沫增强体的复合韧化,复合材料的屈服强度、压缩强度和弯曲强度明显提高,韧性显著增强.     

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.