Thermal expansion characteristics of cast Cu based metal matrix composites

Like any other metal/alloy, copper and its alloys also soften at elevated temperatures. Reinforcing with ceramic or carbon fibres is one of the suggested solutions to overcome this. Very limited literature is available on Cu based metal matrix composites (MMCs); none of these pertain to liquid phase fabrication. Hence, a systematic investigation was carried out on MMCs based on copper, with alumino-silicate fibres and carbon fibres as reinforcements. The MMCs thus produced exhibit a uniform distribution of reinforcement in the matrix. Coefficient of thermal expansion (CTE) values are lower than that of pure copper.     

Ageing and toughness of silicon carbide particulate reinforced Al-Cu and Al-Cu-Mg based metal-matrix composites

Metal-matrix composites (MMC) comprising powder aluminium alloys reinforced by particulate ceramic are being developed for widespread aerospace structural applications ranging from fuselage and missile components to undercarriage parts. Most interest is centred on MMCs with an Al-Cu-Mg (2124) matrix alloy. These MMCs possess high levels of specific stiffness with high specific strengths but can exhibit lower ductility and toughness than conventional unreinforced aluminium alloys.To overcome these problems the effects of alloy composition on the ageing behaviour and notched tensile properties of Al-Cu-Mg and Al-Cu based alloys reinforced with 20 wt% silicon carbide particulate have been investigated.Al-Cu-Mg MMCs gave higher strengths and moduli than unreinforced sheet. Lowering the copper and magnesium content resulted in reduced strength but did not affect the rate of age hardening. The Al-Cu-MMCs gave the lowest strengths but the absence of natural ageing may prove advantageous, enabling sheet to be formed and subsequently heat-treted to the peak strength condition.     

Effect of fabrication parameters on the microstructural quality of fibre–foil titanium metal matrix composites

The microstructure of fibre–foil Ti–6Al–4V (composition in weight per cent) and IMI 834 matrix metal matrix composites (MMCs), and corresponding foil-bonded alloys, are investigated in relation to fabrication parameters. Higher fabrication temperatures are required in IMI 834 MMCs, which results in a thicker interfacial reaction layer than in Ti–6Al–4V MMCs. The matrix microstructure in all materials is predominantly with intergranular , as a result of the slow cooling rate. MMCs reinforced with SM1240 fibres exhibit boron precipitates along foil bond lines, owing to diffusion during consolidation. Fabrication using fibre mats with 7.1 fibres per millimeter (FPM) results in an excellent microstructure in (Ti–6Al–4V)–SM1240. The larger diameter of the SM1140+fibre compared with SM1240 means that (Ti–6Al–4V)–SM1140+requires FPM significantly below 7.1 in order to produce acceptable microstructural quality. The higher residual stresses in IMI 834 MMCs result in cracking of the matrix and fibre–matrix interfacial region when a FPM of 7.1 is used. Acceptable microstructural quality is observed in IMI 834 MMCs when the FPM of fibre mats is reduced to 6.3. Interfibre cracking in IMI 834–SM1140+is enhanced by a higher matrix microhardness than the other materials. This high hardness may be caused by a high matrix carbon content.     

Thermal and dynamic mechanical analysis of polystyrene composites reinforced with short sisal fibres

The thermal behaviour of polystyrene composites reinforced with short sisal fibres was studied by means of thermogravimetric and dynamic mechanical thermal analysis. The thermal stability of the composites was found to be higher than that of sisal fibre and the PS matrix. The effects of fibre loading, fibre length, fibre orientation and fibre modification on the dynamic mechanical properties of the composites were evaluated. Fibre modifications were carried out by benzoylation, polystyrene maleic anhydride coating and acetylation of the fibre and the treatments improved the fibre-matrix adhesion. PS/sisal composites are thermally more stable than unreinforced PS and sisal fibre. The addition of 10% fibre considerably increases the modulus but the increase is found to level off at higher fibre loadings. The T_g values of the composites are lower than that of unreinforced PS and may be attributed to the presence of some residual solvents in the composites entrapped during the composite preparation. The treated-fibre composites show better properties than those of untreated-fibre composites. The Arrhenius relationship has been used to calculate the activation energy of the glass transition of the composites. A master curve is constructed based on time-temperature superposition principle.     

The effect of fibre orientation of the dry sliding wear of borsic-reinforced 2014 aluminium alloy

The effect of fibre orientation on the dry sliding wear of continuous B(SiC) fibre reinforced aluminium alloy composites was investigated using a pin-on-disc wear testing machine. The metal-matrix composites (MMC) samples were tested in the normal (N), parallel (P) and antiparallel (AP) orientations sliding against a steel counter disc at a fixed speed of 1 m s^–1 under loads of from 12 to 60 N.The results showed that for the matrix alloy and MMCs, the average wear increased linearly with load. Wear of the MMCs was insensitive to fibre content but for composites with fibre contents at or above the minimum of 16 vol% used for this work, the wear rate was about 18% of that of the unreinforced matrix. Fibre orientation had a minor effect on wear rate; the N orientation gave the lowest wear rate with the AP orientation slightly higher and the P orientation significantly higher.The average coefficients of friction of the MMCs in N and AP orientations decreased linearly with increased wear rate and non-linearly with increased load, but the P orientation was insensitive to either variable.It was concluded from these results and a metallographic examination that the mechanism of wear of MMCs was essentially oxidative wear of the matrix. The hard fibres modified this to slightly different degrees depending on their orientation relative to the wear surface and sliding direction.     

Investigation of microstructure and mechanical properties of steel fibre–cast iron composites

Abstract

The aim of the present experimental study was to investigate improvement of the toughness and strength of grey cast iron by reinforcing with steel fibres. The carbon content of the steel fibres was chosen to be sufficiently low that graphite flakes behaving as cracks were removed by carbon diffusion from the cast iron to the steel fibres during the solidification and cooling stages. To produce a graphite free matrix, steel fibres with optimum carbon content were used and the reinforced composite structure was cast under controlled casting conditions and fibre orientation. Three point bend test specimens were manufactured from steel fibre reinforced and unreinforced flake graphite cast iron and then normalising heat treatments were applied to the specimens at temperatures of 800 and 850°C. The fracture toughness and strength properties of the steel fibre reinforced material were found to be much better than those of unreinforced cast iron. The microstructures of the composite at the fibre–matrix transition zone were examined.     

δ-Al2O3短纤维/铝合金复合材料的拉伸强度及断裂机理

用挤压铸造方法制备了"Saffil"短纤维增强的Al-5.5Mg、Al-5.5Zn基复合材料,纤维体积分数分别为10%、15%、20%。金相分析表明:纤维近似呈二维随机分布。在室温及300℃下测试了基体及MMCs的拉伸强度,并对断口进行了SEM分析。分析和讨论不同情况下的断裂机理及强度预测公式。     

Ageing behaviour and toughness of silicon carbide particulate reinforced Al-Li-Cu-Mg-Zr metal matrix composites

The effects of lithium content on the ageing characteristic and notched tensile properties of particulate reinforced Al-Li-Cu-Mg-Zr based metal matrix composites (MMCs) have been investigated. MMC sheet containing 20 wt% silicon carbide particulate produced by a conventional powder metallurgy route aged at a similar rate as unreinforced sheet, and the highest strengths were achieved in samples containing 2–2.5 wt% Li. A proprietary processed 8090 Al-Li alloy MMC sheet aged more rapidly, however, and gave considerably higher strengths. The toughness of Al-Li-Cu-Mg-Zr MMC sheet, as indicated by the notched tensile behaviour, can be improved by reducing the lithium content albeit at the expense of strength.     

Young’s modulus of cast HMS 2112-C f composite—prediction and ultrasonic evaluation

Various models for the prediction of strengthening mechanism of metal matrix composites (MMCs) containing either fibres or particulates are analysed. Assuming that the matrix strengthening by dislocations could be treated as equivalent to the effect of different volume fraction of dispersoids, as well as by considering the effect of morphology of reinforcement on the Young’s modulus, an expression for Young’s modulus for MMCs has been derived. The Young’s modulus values thus predicted, using this model, have been validated by ultrasonically-derived values of Young’s modulus of an Al-alloy matrix composite containing 5, 8 and 12 wt% chopped carbon fibre (C _f) dispersoids, in as cast and extruded conditions. Further, the theoretically- and ultrasonically-derived Young’s modulus of cast Al-alloy-C _f composites with 5 and 8 wt%C _f have been found to be comparable with the reported values of Young’s modulus for these weight fractions.     

The sliding wear behavior of TiCp/AZ91 magnesium matrix composites

The AZ91 metal matrix composites (MMCs) reinforced with 5, 10 and 15 wt.% TiC particulates are fabricated by TiC_p–Al master alloy process combined with mechanical stirring. The effects of TiC particulate content, applied load and wearing time on the sliding wear behaviors of the composites were investigated using MM-200 wear testing apparatus. The results show that the wear resistance and friction coefficient of the composites increased and decreased with increase of the TiC particulate content, respectively. The wear volume loss and friction coefficient of the reinforced composites as well as the unreinforced AZ91 matrix alloy increased with increase of applied load or wearing time, but the increase rates of the reinforced composites in two performance is lower than those of the unreinforced AZ91 matrix alloy. Furthermore, the sliding wear behavior of the composites and the unreinforced AZ91 matrix alloy is characterized by ploughing, adhesion and oxidation abrasion.     

Wear behaviour of an Al–12% Si alloy reinforced with a low volume fraction of SiC particles

Aluminium–silicon alloys reinforced with low volume fractions of SiC particles were prepared by the compocasting process. The wear behaviour of the unreinforced Al–12Si alloy and metal-matrix composites (MMCs) was investigated by using a block-on-ring test at room temperature under dry conditions. The results showed that the addition of a low volume fraction of SiC particles (2–8 vol%) is a very effective way of increasing the wear resistance of the matrix alloy. Metallographic examinations revealed that the wear zone of the Al–12Si alloy consists of both hardened and deformation layers. The depth of the hardened layer depended on the applied load and was in the vicinity of 10–50 μm. The formation of the hardened layer was related to the alignment and redistribution of fragmented eutectic phase to the surface region during sliding wear. Furthermore, the delamination of debris from the hardened layer was responsible for a higher wear loss observed in the Al–12Si alloy. The thickness of the hardened layer formed on the MMC specimens was reduced considerably by the incorporation of fragmented SiC particles. This layer exhibited higher hardness and wear resistance than that developed in the unreinforced alloy.     

Fabrication of (TiB<Subscript>2</Subscript> − TiC)<Subscript>p</Subscript>/AZ91 magnesium matrix hybrid composite

Magnesium MMCs reinforced with TiB₂−TiC particulates were fabricated successfully via a master alloy route using a low cost Al-Ti-B₄C system as starting material system. Microstructural characterization of the (TiB₂−TiC)/AZ91 composite shows relatively uniform distribution of TiB₂ and TiC particulates in the matrix material. Moreover, the results show that the hardness and wear resistance of the composites are higher than those of the unreinforced AZ91 alloy.     

Tensile behaviour of powder metallurgy processed (Al–Cu–Mg)/SiCp composites

Abstract

The tensile behaviour of Al–Cu–Mg alloy matrix composites produced by a powder metallurgy process was investigated as a function of particle size in the as extruded, homogenised, and peak aged conditions. The tensile behaviour of the corresponding matrix alloy which was produced in a similar manner, designated as Control, was also studied. There was a significant increase in the 0.2% yield strength of Control and all the metal matrix composites (MMCs) after homogenisation treatment (53–68%) and peak aging (93–109%), as compared to their values in the as extruded condition. The ultimate tensile strength (UTS) of Control as well as the MMCs also increases considerably after homogenisation treatment (39–70%), however, subsequent peak aging did not result in any further increase in UTS in case of any of the MMCs. It was found that the finer the reinforcement size, the higher the 0.2% yield strength and UTS in all the conditions. On the other hand, ductility decreased considerably after homogenisation treatment and subsequent peak aging. The results are discussed in the light of dislocation strengthening as well as reinforcement damage.     

Fatigue behaviour in hybrid hollow microspheres/fibre reinforced composites

This article presents the results of a current study concerning the influence of the addition of short fibres on the fatigue behaviour of syntactic foams. The material was obtained by vacuum-assisted resin transfer moulding adding hollow glass microspheres to an epoxy resin acting as binding matrix. Specimens with microsphere contents up to 50% and fibre reinforcement up to 1.2% in volume were tested at three-point bending at room temperature. Foams show significantly lower static and fatigue strength than an epoxy matrix. A significant decrease in the absolute strength with filler increase was observed, and even specific strength decreases for low filler contents and is nearly constant for the higher filler contents. Fatigue strength also decreases with the increase in filler content. The addition of glass fibre reinforcement produces only a slight improvement in flexure strength, while the addition of carbon fibres promotes an important improvement; a hybrid composite containing 0.9% carbon fibre is about 30% stronger than unreinforced foams. An improvement in fatigue strength more than 30% was obtained by the addition of small percentages of glass or carbon fibre.     

The compression strength of composites with kinked,misaligned and poorly adhering fibres

Experiments carried out on pultruded fibre reinforced polyester resins show that, at moderate fibre volume fractions, the compressive strength of aligned fibre composites depends linearly on the volume fraction. The strength falls off when the fibre volume fraction,V _f=0.4 with Kevlar and high strength carbon fibres. The effective fibre strength atV _f<0.4 is much less than the tensile strength but it is close to the tensile strength with E-glass fibres and high modulus carbon fibres. Poor adhesion between fibres and matrix reduces the compressive strength, as does kinking the fibres when the fibre radius of curvature is reduced to below 5 mm. Misalignment of the fibres reduces the compressive strength when the average angle of misalignment exceeds about 10° for glass and carbon fibres. However, with Kevlar no such reduction is observed because the compression strength of Kevlar reinforced resin is only a very little better than that of the unreinforced resin.     

Transverse tensile behaviour of fibre reinforced titanium metal matrix composites

Four Ti MMCs have been tested in transverse tension, at ambient temperature and 600 °C. Generally, mechanical properties are reduced compared to monolithic Ti alloys. Transverse Young's modulus is, however, higher than in monolithic alloys, as a result of constraint of the matrix by the fibres.MMC proportional limits are associated with the onset of interfacial failure. Fibre coating cracking and longitudinal fibre splitting may also contribute to MMC yield and the associated acoustic emission peak. The fibre/matrix interface in IMI 834/SM1140+ appears to be weaker than in the other MMCs, resulting in a lower proportional limit and less acoustic emission. Final failure of the MMCs is generally via ductile shearing of matrix ligaments. The exception to this is IMI 834/SM1140+ in which the matrix fails in a brittle manner. This causes poor transverse tensile strength and failure strain in this MMC.A model to predict the MMC proportional limit, previously proposed by Jansson et al., has been modified to take account of the tensile strength of the fibre/matrix interface. The model previously used by Jansson et al. to predict the transverse tensile strength is acceptably accurate provided that the area fraction of matrix appearing on fracture surfaces is accurately determined.     

A study of the mechanical behaviour on fibre reinforced hollow microspheres hybrid composites

This paper presents the results of an investigation into the effects of hollow glass microsphere fillers and of the addition of short fibre reinforcements on the mechanical behaviour of epoxy binding matrix composites. Properties like flexural stiffness, compressive strength, fracture toughness and absorbed impact energy, were studied. The specimens were cut from plates produced by vacuum resin transfer moulding having a microsphere contents of up to 50% and with fibre reinforcement up to 1.2% by volume. The tests performed with unreinforced composites show that flexural and compressive stiffness, maximum compressive stresses, fracture toughness and impact absorbed energy decrease significantly with increasing filler content. However, in terms of specific values, both flexural and compressive stiffness and impact absorbed energy increase with microsphere content. The addition of glass fibre produces only a slight improvement in the flexure stiffness and fracture toughness, while increasing significantly the absorbed impact energy. In contrast, the addition of a small percentage of carbon fibres produces an important improvement in both fracture toughness and flexure stiffness, when hybrid composites with 0.9% carbon fibre are compared to unreinforced foam, but did not improved absorbed impact energy.     

Formation of interfacial voids in composites with a weakly bonded viscoplastic matrix

The formation and evolution of interfacial voids are investigated in the case of metal matrix composites (MMCs) reinforced by ceramic fibres and subjected to high compressive loads. The resulting compression flows of a viscoplastic aluminum matrix around rigid fibres are described by a nonlinear free-boundary problem. A new finite element model with boundary-fitted mesh motion is introduced to simulate the formation of interfacial voids. The fibre–matrix interface is weak and allows yielding and sliding with separation at a dynamic contact line connecting three phases. The fibre–matrix interaction is simulated via a modified O'Donovan–Tanner constitutive model and a phenomenologically defined interface potential. The shape of the interfacial surface undergoing large deformation is not known a priori and found as a part of the solution. The influence of hydrostatic stress and constitutive characteristics of the matrix on the evolution of interfacial voids and their growth rates are examined. As the transverse strain increases, the evolution of interfacial voids occurs through a sequence of convex profiles. Numerical simulations are carried out for a special case involving small values of the yield stress and the viscosity of yielded matrix in order to compare them with similar results for linear viscous solids. The numerical results are also compared with the experiments involving similar compression flows of viscoplastic model materials.     

Electrical resistivity of copper reinforced with short carbon fibres

The electrical resistivity of copper reinforced with short aligned carbon fibres has been measured in axial and transverse directions as a function of fibre content. The results have been considered in the light of predictions from the Eshelby equivalent homogeneous inclusion method for modelling of conduction. Higher resistivities, particularly for transverse current flow, were observed than is predicted on the basis of an isotropic matrix resistivity equal to that of unreinforced copper. This is thought to be explicable in terms of the effect of relatively high levels of elongated porosity present in the specimens examined.     

Squeeze-casting conditions of Al/Al2O3 metal matrix composites with variations of the preform drying process

The characteristics of the preform play a role in determining the final properties of MMCs. Effects of organic binder and microwave drying on preform microstructure have been examined by SEM. In the preform with organic binder, flocking processes are observed during drying. The preform has a uniform distribution of binder and dries quickly with microwave drying owing to its internal and volumetric heating patterns. The fundamental manufacturing process and controlling parameters of squeeze casting, including preform temperature, mould temperature, applied pressure and molten metal temperature, have been studied in Al/Al₂O₃ composites. MMCs have poor mechanical properties with too high temperatures of preform and molten metal due to thermal shocking of the preform, oxidation of the matrix and thermal damage to the fibers. Mould temperature barely affects the tensile strength of MMCs. High applied pressure reduces voids and solidifies the matrix faster. Conditions for squeeze casting to achieve optimal processing, are suggested. The tensile strength of MMCs can be improved by up to about 20% compared with the unreinforced matrix alloy.