Transient liquid phase bonding of 2124 aluminium metal matrix composite

Abstract

The transient liquid phase (TLP) bonding of particle reinforced aluminium metal matrix composites (MMCs) using copper interlayers often results in the segregation of SiC particles to the bond region, and this has the effect of producing bonds with poor mechanical strengths. In this preliminary study, the TLP bonding of a 2124 aluminium alloy MMC is investigated using nickel interlayers, and the initial results show that good bonds are produced with no effect on the SiC dispersion in the matrix. The absence of segregation is attributed to the high diffusivity of the nickel in the aluminium MMC, which produces rapid isothermal solidification at the bonding temperature. Bond shear tests show that near parent metal strengths are possible when thin nickel interlayers are used, and failure occurs at the MMC/bond interface. When thick interlayers are used, failure is predominately through the centre of the bondline.     

Transient liquid phase diffusion bonding of Al/Mg2Si metal matrix composite

As-cast Al/Mg₂Si metal matrix composite was joined by transient liquid phase diffusion bonding using Cu interlayer at various bonding temperatures and durations. This metal matrix composite contained 15% Mg₂Si and was produced through in situ technique by gravity casting. Specific diffusion bonding process was applied as a low vacuum technique. The microstructure of joints consisted of Al-α, CuAl₂ and Mg₂Si or Al-α and Mg₂Si depending on bonding temperature and duration. The maximum shear strength was achieved when samples were bonded at 580 °C for 120 min. Micro-hardness and compositional homogeneity of joints across the bonded interface were improved with increasing the bonding duration at 560 °C and had no significant changes at 580 °C.     

Transient liquid-phase insert metal bonding of Al2O3 and AISI 304 stainless steel

Transition liquid-phase insert metal bonding of Al2O3 and AISI 304 stainless steel based materials is investigated. This joining technique allows the continuous replenishment of the active solute which is consumed by the chemical reaction that occurs at the ceramic/filler metal interface. Replenishment is facilitated by employing a sandwich of filler materials comprising tin-based filler metal and amorphous Cu50Ti50 or NiCrB interlayers. During Al2O3/AISI 304 stainless steel bonding, the highest shear strength properties are produced using a bonding temperature of 500 °C. Thick reaction layers containing defects form at the ceramic/filler material interface when higher bonding temperatures are applied. Bonding at temperatures above 500 °C also increases the tensile residual stress generated at the periphery of Al2O3/AISI 304 stainless steel joints. The shear strength of joints produced using NiCrB interlayers markedly increased following heat treatment at 200 °C for 1.5 h. Heat treatment had little influence on the shear strength of the joint produced using Cu50Ti50 interlayers. This revised version was published online in November 2006 with corrections to the Cover Date.     

Strength analysis of random short-fibre-reinforced metal matrix composite materials

A theory to analyse the strength of composite materials with randomly oriented short fibres has been developed. The short fibres are assumed to be uniformly distributed and randomly oriented in three dimensions. The non-homogeneous deformation within the composite has been taken into account in the strength calculation. The influences of thermal stress in the short fibres, the short-fibre dispersion hardening and the dislocation density in the matrix on the composite strength have all been estimated, and the strengthening mechanisms involved are discussed. A comparison with previous strength theory suggests that the present theory gives a better agreement with experimental data, and can be used to explain some experimental phenomena that remain unsolved.     

A boundary element analysis of metal matrix composite materials

The numerical modelling of metal matrix composites is an important part of the research now being conducted on these materials. Due to the numerical complexity of a fully three-dimensional analysis, two-dimensional approximations are normally used with finite element methods. While these analyses are informative, they cannot treat complex particle shapes or examine three-dimensional effects in the composite. The use of boundary element methods in place of the more widely used finite element methods significantly reduces the computing power necessary to obtain a solution to a given problem, making it possible to simulate fully three-dimensional geometries. In the present paper a two-dimensional form of the BEM is applied to the study of metal matrix composite materials, and its performance compared with that of similar FEM stadies. We also compare the predicted composite properties with existing and new experimental results. We conclude that the BEM is an effective tool for the analysis of this class of problems.     

Thermo-compression bonding of alumina ceramics to metal

Alumina ceramics and Kovar with aluminum interlayer are pressed together under vacuum at temperatures around 600°C for joining. This process produces mechanically strong ceramic to metal bonds in one step in an economic manner. In order to arrive at the optimum conditions for solid-state bonding, effects of bonding temperature, pressure and time on the bond strength have been studied. Bonding kinetics is also elucidated. Irradiation of 99% Al₂O₃ ceramics by 4–5 MV X-rays has been found to increase the bond-strength sharply from 33 to 60 MPa with a dose of 15 k Rads for bonding temperatures around 540°C. The apparent activation energy for the bonding process (Q _B) depends strongly on the type of alumina ceramics. Irradiation of alumina ceramics (99%), prior to joining with Kovar, accelerates the solid-state bonding by reducing (Q _B) from 209 to 76 kJ/mole.     

Kinetics of transient liquid phase diffusion bonding process for joining aluminium metal matrix composite

Abstract

The mechanism and kinetics of the transient liquid phase diffusion bonding process in a 6061–15 wt-%SiCp composite at 570°C, 0·2 MPa, with 200 μm thick copper foil interlayer, has been investigated by microstructural characterisation of the bond region using optical microscopy, scanning electron microscopy and electron probe microanalysis. The kinetics of isothermal solidification, representing the displacement of the solid/liquid interface y (in micrometres) as a function of time t (in seconds), followed a power law relationship y?=?157t^0·07. According to this kinetic equation, the effective diffusivity of copper in the composite system was found to be ～10⁶ times higher than the lattice diffusivity, indicating the dominance of short circuit diffusion through the defect rich particle/matrix interface.     

The mechanical properties of friction welded aluminium-based metal–matrix composite materials

The optimum joining parameters for the friction joining of aluminium-based metal–matrix composite (MMC) materials are examined. The properties of MMC/MMC, MMC/alloy 6061 and alloy 6061/alloy 6061 joints are derived following detailed factorial experimentation. The mechanical properties of the joints are evaluated using a combination of notch tensile testing and also conventional tensile and fatigue testing. The frictional pressure has a statistically-significant effect on the notch tensile strength of joints produced in all base material combinations. The upset pressure has only a statistically-significant influence on the notch tensile strength properties of alloy 6061/alloy 6061 joints. The notch tensile strengths of MMC/alloy 6061 joints are significantly lower than MMC/MMC and alloy 6061/alloy 6061 joints for all joining parameter settings. The fatigue strength of MMC/MMC joints and alloy 6061/6061 joints are also poorer than the as-received base materials. This revised version was published online in November 2006 with corrections to the Cover Date.     

Fatigue performance of alumina reinforced metal matrix composites

Abstract

The room temperature fatigue performance of two Saffil reinforced metal matrix composites manufactured by squeeze forming is assessed. For the composite with an LM 13 matrix, introduction of Saffil does not result in an increase in the ultimate tensile strength, and the fatigue performance is inferior to the unreinforced alloy. By contrast, the composite with a 6082 type matrix exhibits a markedly superior ultimate tensile strength and stiffness compared with the unreinforced equivalent and this is coupled with an improved overall fatigue performance.

MST/767     

Numerical analysis of fibre bridging and fatigue crack growth in metal matrix composite materials

The analysis of bridged crack configurations in unidirectional fibre-reinforced composites is relevant to a variety of crack growth problems, including the fatigue of metal matrix composites and the study of fibre failure in the wake of a bridged matrix crack. Details of numerical procedures for predicting fibre stresses and their effect on crack tip stress intensity factors are presented here to provide a useful overview of how standard bridging calculations are done. Results are presented and discussed in the context of predicting fatigue crack growth with fibre failure in metal matrix composites.     

泡沫金属基复合相变材料的有效导热系数研究

为了更有效地预测泡沫金属基复合相变材料(composite phase claange material,CPCM)的导热性能,提出了一种新的CPCM相分布模型,以此为基础建立了带有空穴子模型的简化传热模型,并利用等效热阻法推导得到泡沫金属基CPCM有效导热系数的通用计算式.传热模型考虑了相变过程中相变材料(plnase change material,PCM)的体积变化和空穴分布的影响,使得有效导热系数的计算结果更加符合实际.     

Dual-nanoparticulate-reinforced aluminum matrix composite materials

Aluminum (Al) matrix composite materials reinforced with carbon nanotubes (CNT) and silicon carbide nanoparticles (nano-SiC) were fabricated by mechanical ball milling, followed by hot-pressing. Nano-SiC was used as an active mixing agent for dispersing the CNTs in the Al powder. The hardness of the produced composites was dramatically increased, up to eight times higher than bulk pure Al, by increasing the amount of nano-SiC particles. A small quantity of aluminum carbide (Al(4)C(3)) was observed by TEM analysis and quantified using x-ray diffraction. The composite with the highest hardness values contained some nanosized Al(4)C(3). Along with the CNT and the nano-SiC, Al(4)C(3) also seemed to play a role in the enhanced hardness of the composites. The high energy milling process seems to lead to a homogeneous dispersion of the high aspect ratio CNTs, and of the nearly spherical nano-SiC particles in the Al matrix. This powder metallurgical approach could also be applied to other nanoreinforced composites, such as ceramics or complex matrix materials.     

Simple and precise measurements of fibre volume and void fractions in metal matrix composite materials

A method for determining the fibre volume fraction, V _f and the void fraction, V _g, in a metal matrix composite (MMC) material is described. These quantities are determined from specimen weight measurements in air and in a liquid using a laboratory balance. For a material without voids, V _f can be determined with an uncertainty less than 0.5% with a balance precision of 0.01%. By making the same measurements before and after etching away the matrix, using the same balance precision, V _f and V _g can be determined to an uncertainty of about 3 and 6%, respectively. It is also shown theoretically that by indenting a specimen containing no fibres and only a uniform distribution of small voids, the void fraction can also be determined from weight measurements before and after indentation.     

Simulation of perforation and penetration in metal matrix composite materials using coupled viscoplastic damage model

In the first part of the two companion papers, theoretical formulation of the multiscale micromechanical constitutive model that couples the anisotropic damage mechanism with the viscoplastic deformation is presented. In the second part of these companion papers the numerical simulation of the computational aspects of the theory are elaborated. The perforation and penetration problem of metal matrix composites (MMCs) due to high impact loading is simulated. In this sense, the computational aspects of the developed theory are elaborated here. First, the verification of the developed model is performed through its numerical implementation in order to test the model predictions of the material characteristic tests. This encompasses uniaxial monotonic loading and unloading under different strain rates, uniaxial cyclic loading, and uniaxial loading and relaxation. The verified material routine of the developed model is then implemented in the explicit finite element code ABAQUS via the user defined subroutine VUMAT at each integration point in order to analyze the projectile impact and penetration into laminated composite plates.     

Thermodynamically consistent coupled viscoplastic damage model for perforation and penetration in metal matrix composite materials

Accurate modeling and efficient analysis of the metal matrix composite materials failure mechanism during high velocity impact conditions is still the ultimate goal for many researchers. The objective is to develop a micromechanical constitutive model that can effectively simulate the high impact damage problem of the metal matrix composite materials. Therefore in this paper, a multiscale micromechanical constitutive model that couples the anisotropic damage mechanism with the viscoplastic deformation is presented here as a solution to this situation. This coupled viscoplastic damage model is formulated based on thermodynamic laws. Nonlinear continuum mechanics is used for this heterogeneous media that assesses a strong coupling between viscoplasticity and anisotropic damage. It includes the strong directional effect of the fiber on the evolution of the back stress and the development of the viscoplastic strain in the material behavior for high velocity impact damage related problems.     

Hot-roll bonding of aluminium matrix composites with different volume fractions of alumina

Metal matrix composites (MMC) with volume fractions of 0.08, 0.11 and 0.14 alumina (Al₂O₃) were fabricated by roll bonding. This low-cost approach to MMC manufacture has the flexibility of controlling the volume fraction of the MMCs by varying the oxide thickness on the anodized aluminium foil, and the number of layers of these foils to be sandwiched between plain aluminium sheet as the matrix metal. The fragmentation of the laminate alumina is achieved by a series of hot- and cold-rolling operations. The resulting reinforcing alumina particles have platelet shape measuring approximately 20 m×11m×5 m instead of a stringer shape as expected. It is found that the improvement in modulus and strength did follow very closely with the rule of mixtures. A small scatter of measured data, especially the resistivity of the MMCs, was observed. This can be explained by the inefficient bonding between the reinforcing alumina and the matrix metal as demonstrated later in this study.     

Ceramic joining II partial transient liquid-phase bonding of alumina via Cu/Ni/Cu multilayer interlayers

Multilayer Cu/Ni/Cu interlayers that form a thin layer of a Cu-rich transient liquid phase have been used to join alumina to alumina at 1150 °C. The method and bonding conditions yield an assembly bonded by a Ni-rich (>94 at% Ni) interlayer at a temperature substantially lower than those normally required for solid-state diffusion bonding with pure Ni interlayers. Flexure strengths of as-bonded beams ranged from 61 to 267 MPa with an average of 160 MPa and a standard deviation of ±63 MPa. The highest flexure strengths were observed in samples where failure occurred in the ceramic. Post-bonding anneals of 10 h duration in air and gettered-argon at 1000 °C decreased the average room temperature strength to 138 and 74 MPa, respectively. In as-processed and annealed samples, varying degrees of interfacial spinel formation are indicated. Spinel formation may contribute to the scatter in as-processed samples, and the decrease in strength values resulting from annealing.     

Wear behaviour of aluminium matrix composite materials

Wear behaviour of aluminium matrix composites is characterized by the dry spindle wear test under various conditions (volume fractions of reinforcements, sliding distances and speeds). Wear resistance of composites is improved due to the presence of reinforcements, but no noticeable improvements are observed in the wear resistance with more than 20% addition of reinforcements. To analyse wear mechanisms, wear surfaces are examined by scanning electron microscopy (SEM). The major wear mechanisms of discontinuous metal matrix composites (MMC)s are strongly dependent on sliding speeds. Dominant mechanism is the adhesive-abrasive wear at low and intermediate sliding speeds, and melt wear at high sliding speeds. Weight loss is linearly increased with the sliding distance. The effect of reinforcements' orientations on wear behaviours is also discussed.     

Transient creep behavior of a metal matrix composite with a dilute concentration of randomly oriented spheroidal inclusions

The transient creep behavior of a metal matrix composite containing a dilute concentration of randomly oriented spheroidal inclusions is derived explicitly from the constitutive equation of the matrix. This theory can account for the influence of inclusion shape, elastic inhomogeneity between both phases, and the volume fraction of inclusions. The micro-macro transition is carried out by considering the mechanics of incremental creep, which discloses the nature of stress relaxation in the ductile matrix and the connection between the micro and macro creep strains. The transient creep curves of the composite are displayed with several inclusion shapes. Consistent with the known elastic behavior, spherical inclusions are found to provide the weakest reinforcing effect, whereas thin, circular discs possess the most effective strengthening shape. According to this theory and in line with the experimental data, the creep resistance of cobalt at 500°C can improve by more than 80% after adding a mere 5% of rutile particles into it.