Interlayer structure of carbon fibre reinforced aluminium wires

As the extent of the interfacial reactions controls the properties of metal matrix composites, the microstructural features and the chemical composition of the interlayers in aluminium wires reinforced with unidirectional carbon fibres (volume fraction app. 55%) have been investigated. High voltage and high resolution transmission electron microscopy of fibres, matrix, and interlayers, combined with analytical methods (electron energy loss spectroscopy and energy filtered microscopy) revealed a nanometre-sized C/Al interdiffusion layer and aluminium carbide needles or platelets of 10–50 nm thickness and 50–500 nm length in the matrix material, starting from the interlayer, the extension of which strongly correlates with the duration of melt contact. The observed interlayer phenomena impose restrictions to the process parameters, as by massive interface reactions the fibre strength is degraded, and the formation of brittle reaction products such as Al₄C₃ provides sites for initiation of fibre cracking and can cause composite failure. With a newly developed continuous process, which is capable of infiltrating endless products, the fibre/melt contact duration could be reduced to less than one second resulting in carbide formation lower than 0.2 wt% as confirmed by chemical analyses. So it was possible to achieve strength values of the composite wires that are as high as the theoretical prediction.     

Interfacial properties and stability in bonded aluminium

The localized interfacial region between an aluminium substrate and an epoxy adhesive has been extensively investigated. It has been found that a transitional region exists between the substrate surface and the bulk adhesive in which the physical and/or chemical properties of the polymer differ from those of the bulk polymer. Different surface treatments prior to bonding are observed to have little effect on the formation of the transitional region. Two types of transitional layers have been identified; one extending up to 1m from the substrate interface, the other generally restricted to 10 nm from the substrate interface. Examination of regions immediately in front of a propagating crack indicate that the interfacial integrity of both an etched-bonded substrate and a pretreated-bonded substrate are maintained. In contrast, regions of the fracture surface behind a propagating crack show the existence of corrosion products on an etched substrate but not on a pretreated substrate.     

Interface reactions and bonding strength in aluminium alloy (AA-7075)-alumina diffusion bonds

Diffusion bonds between alumina and high-strength aluminium alloy (AA-7075) have been produced and studied in the present work. Direct diffusion bonding in the solid state was tested as a possible joining method for both materials. The nature of the AA7075-Al₂O₃ interface was investigated paying special attention to the chemical interaction processes between the alloying elements and the ceramic material, as well as their influence on the joint strength. SEM images and energy-dispersive microanalysis were used to determine the formation of reaction layer between both parent materials. Shear strength was used as an optimum method to evaluate the bond strength and the influence of the bonding parameters on it. A maximum shear strength of 60 MPa was achieved using bonding temperatures and pressures of 360 °C and 6 MPa, respectively, during very prolonged bonding times (100h). Fractographic studies of the failure surface gave additional information on those aspects.     

Interface structure of diffusion bonded duplex stainless steel and medium carbon steel couple

Diffusion bonding of duplex stainless steel to medium carbon steel was carried out with different temperatures for sound bonds. In the bonding process, relatively intermediate temperatures such as 750, 800, 850 and 900 °C were used with a bonding time of 30 min. In this study, microstructural changes and mechanical properties in the interface region of duplex stainless steel and medium carbon steel couples were determined. The results showed that, in interface region, Cr₂₃C₆ was formed on the stainless steel side, while ferrite formation was observed on the carbon steel side as a result of mutual diffusion of C and Cr.     

Effect of rolling temperature on interface and bond strength development of roll bonded copper/aluminium metal laminates

Copper/aluminium laminates were prepared by roll bonding at different temperatures between 350 and 500°C. The effect of the roll bonding temperature on the interface reactions and bond strength development of the laminates was investigated. It was found that the bond strength of the laminates was generally enhanced with increased roll bonding temperature up to 430°C. Optimum roll bonding conditions, in terms of maximum bond strength were identified. It is shown that the development of the optimum bonding between the metal laminates is related to the creation of physical contact between the metals in the roll bonding stage and the formation of various intermetallic phases at the interface during the subsequent sintering process. The formation of intermetallic phases is greatly affected by the diffusivity of the metallic elements across the interface. It has been identified that dissolution of the interfacial oxide layer, formed in the roll bonding stage, has a great influence on the diffusivity of metallic elements across the interface which in turn determines the bond strength development of the material.     

Chemical segregation of solute elements in ultrasonically gas atomized aluminium alloy powders

A new experimental approach to the evaluation of chemical segregation of solute elements in ultrasonically gas atomized aluminium-alloy powders using X-ray spectral data of scanning electron microprobe analyser is described. The experimentally obtained chemical segregation data is compared with the conventional method of quantitative analysis and with theoretical predictions as determined from Scheil’s approach to the evaluation of elemental segregation during the solidification process. A comparison of experimental and theoretical predictions confirms the validity of the experimental approach in the estimation of solute segregation levels and also suggests that the solidification conditions considered for estimation of microchemical segregation can appropriately be applied to ultrasonically gas atomized powders.     

Influence of fine-grained structure and superplastic deformation on the strength of aluminium alloys

Samples of 1560 (Al-Mg-Mn) and 1960 (Al-Zn-Mg-Cu) alloys have been used to investigate the nature of the effect of grain size and superplastic treatment on the strength of aluminium alloys. The observed increase in the work needed for crack formation with the transition from coarse-grained (CG) to fine-grained (FG) structure is connected to a greater homogeneity of the plastic deformation in the material volume. This leads to a reduction in local stress concentrations at the sites of preferential crack initiation. The easier crack growth in FG alloys is mainly caused by a reduction in the energy for plastic deformation at the head of a long crack and also for the formation of free fracture surfaces.Deceased.     

GH3044镍基合金钎焊接头的界面组织和强度分析

采用Ni基箔片钎料对GH3044镍基合金进行钎焊连接,利用电子扫描显微镜(SEM)及能谱分析仪,对接头的界面组织进行观察和分析;采用电子万能试验机对GH3044镍基合金的钎焊接头进行抗剪试验,评价接头的室温抗剪强度.试验结果表明:当钎焊温度为1070℃,保温时间为10min时,界面处有(Cr,W)2+Ni固溶体析出,钎缝中有(Cu,Ni)固溶体组织+Ni-Mn金属间化合物层及η″+ξ′金属间化合物层生成,此钎焊工艺参数下获得的钎焊接头具有最高的室温抗剪强度319MPa.     

Microstructure and strength of Si-Ti-C-O,fibre-reinforced aluminium and aluminium alloys

Microstructures of Si-Ti-C-O fibre-reinforced aluminium and aluminium alloys were investigated by scanning electron microscopy, and both conventional and analytical transmission electron microscopy. In the latter samples, some inclusions were observed between the matrix and the fibres. From the electron diffraction, high resolution microscopy and compositional analysis by energy-dispersive X-ray, the inclusions were identified as the α-Al-Si-Fe phase. Since the longitudinal three-point bending strength decreases with the increase of iron content, it was concluded that the α-phase inclusions on the surface of the fibre contribute to the lower strength of the composites based on this alloy.     

Influence of fine grained structure and superplastic deformation on the strength of aluminium alloys

The influences of fine grained (FG) structure and superplastic deformation on the mechanical properties under quasistatic, impact and cycling loading conditions have been established for the aluminium alloys 1560 (Al-Mg-Mn), 1141 (Al-Cu-Mg-Ni-Fe) and 1960 (Al-Zn-Mg-Cu-Zr). FG materials compared with recrystallized coarse grained (CG) ones improve tensile strength and ductility and high-cycle fatigue endurance, but reduce static and impact toughnesses. The effect of grain refinement on crack resistance is directly manifested in the difficulty of crack initiation and in facilitating its growth. Blanks with FG structure, after superplastic processing, are recommended instead of CG recrystallized ones for the production of principal parts whose service life is limited by first crack appearance. In the presence of cracks, higher strength can be obtained by the use of blanks made of CG commercial semifinished products and those manufactured by traditional methods of hot die forging.     

Rotatable magnetron sputtering of aluminium in continuous and high power pulse modes using different strength magnetic arrays

This paper reports preliminary results of industrial size (152 mm target O.D.) rotatable magnetron sputtering of Al target in direct current (DC) and High Power Impulse Magnetron Sputtering (HIPIMS) modes using two standard commercially available magnetic arrays: standard strength array (as used for DC and AC processing) and a lower strength ‘RF’ array [i.e. as used for radio frequency (RF) magnetron sputtering]. A comparison of processes resulted in by combining the different magnetic arrays and power modes is made in terms of magnetic field distribution on the cathode surface, magnetron characteristics, process characteristics and deposition rates.Optical emission spectroscopy (OES) revealed enhanced sputtered Al flux ionisation in the HIPIMS discharge monitored 64 mm away from the target surface when using the ‘RF’ array. Importantly, the results of this work (at the processing conditions investigated) demonstrate that at the same average power the deposition rate of Al using HIPIMS in conjunction with the ‘RF’ array is substantially the same as that obtained for the ‘standard’ strength balanced array and DC power. This indicates that the magnetic field design of the ‘RF’ magnetic array affects favourably the sputtered flux transport perpendicular to the target surface by altering mass transport direction and minimising effects that reduce deposition rate (e.g. ion return effect). Arc rate is also reduced significantly (approximately ten times) if the low strength ‘RF’ array is used.     

TiC陶瓷/NiCrSiB/铸铁钎焊连接的界面组织和强度分析

采用NiCrSiB钎料对TiC陶瓷与铸铁进行钎焊连接,分析了接头的界面组织和剪切强度.结果表明:当连接规范一定时,在钎料内部、钎料与母材的界面处有TiC从TiC陶瓷侧扩散过来,同时在钎料内部和界面处有[Ni,Fe]和Ni基固溶体生成.当连接温度为1373K,连接时间为20 min时,接头的剪切强度最高可达78.6 MPa.     

Exchange diffusion phenomenon between free-silicon in reaction bonded SiC and liquid aluminium

Journal of Materials Science Letters -     

Surface energy and chemical characteristics of interfaces of adhesively bonded aluminium joints

The deleterious effects of water on the physico-chemical aspects of the durability of adhesively bonded aluminium joints has been investigated. Emphasis was placed on analytical techniques that lead to the better understanding of changes induced at the metal/epoxy interface by the presence of water. Analytical techniques such as contact angle measurements, X-ray photoelectron spectroscopy and X-ray diffraction were practical in obtaining information on the chemical composition and structure of the samples. Chemical conversion-coated samples were found to be much more stable in wet conditions compared to samples without conversion coating. The surface structure on the adherend, after extensive immersion times, was found to consist of a compact layer of bayerite with traces of gibbsite. The calculations of interfacial energy, _sl, and work of adhesion in dry and wet conditions, W _A and W _Al were carried out to evaluate the maximum bond strength. It was found that the durability of the bond in the presence of water was quite high for the XD4300/6061-T6 joint systems.     

Performance analysis of crystalline silicon solar modules with the same peak power and the different structure

Textured crystalline silicon solar cells, planar crystalline silicon solar cells, textured glass, and planar glass are commonly fabricated for crystalline silicon solar modules. Thus, there are four kinds of crystalline silicon solar modules. The photovoltaic electricity outputs of these four kinds of modules with the same peak power are different under true sunshine conditions. This discrepancy inevitably occurs due to the different materials used in modules. Using the actual optical performance of a four-layer encapsulation, a simulation was made on the reflection losses and energy outputs of the four kinds of solar modules. The computer simulation shows that the module encapsulated by textured crystalline silicon solar cells and textured glass has more energy output than others in actual uses. Even if they have equal electrical characteristics under standard test conditions of 1000 W/m², 25°C cell temperature, and 1.5 air mass, the result of simulation approximately agrees with the measured values. A quantitative analysis of energy production of the four kinds of modules with the same peak power as a function of angle of incidence and module structure is presented for the first time. Performing the measured energy production analysis for the four kinds of modules with the same peak power as a function of angle of incidence and module structure provides insight into economic analysis of PV systems and performance estimation of a photovoltaic roof within a fixed flat plate array.     

Effect of oxide additive in silicon nitride on interfacial structure and strength of silicon nitride joints brazed with aluminium

Silicon nitride ceramics with Y₂O₃ and Al₂O₃ as sintering additives were brazed with aluminium, and the brazed strength and the interfacial structure of the joints were compared with those of the joints made of additive-free silicon nitride ceramics. It is concluded that the additives in silicon nitride ceramics take part in the interfacial reaction, make the reaction layer thicker, and hence increase the brazed strength greatly.     

Workability,hardness, and strength of aluminium alloys

Abstract

Binary alloys of Al with elements of the first long period, from Ca to Zn inclusive, and also with Li, Mg, Si, Ag, Y, La, and Gd have been examined regarding their working response and tensile properties after forging and cold rolling of arc melted specimens. The results are correlated with the solid solubilities of the alloying elements and their positions in the periodic table.

MST/3059     

Effect of fibre/matrix interface structure on strength and plasticity of boron aluminium reinforced with discontinuous fibres

The variation of strength characteristics of boron aluminium were studied in relation to the structure of the fibre-matrix interface. It was found that effects of optimal discrete reinforcement of boron aluminium may be realized to a certain extent if such structural characteristics of the interface as density of interphase bonds, , are purposefully changed. In the case where =0.340, the effect of discrete reinforcement is the largest for both failure work and elongation, if the composite strength remains relatively high. Failure work of discrete reinforced boron aluminium is five times higher than that of the continuously reinforced one, but relative elongation reaches 10%.