Particulate Metal Matrix Composites Research Articles

Low-volume-fraction particulate preforms for making metal-matrix composites by liquid metal infiltration

A preform technology for making particulate metal-matrix composites with a low particulate volume fraction (as low as 18%) by liquid metal infiltration is provided. This technology used a non-combustible reinforcement (SiC) as the primary particulate and combustible particles (carbon) as the secondary particulate in the preform. The secondary particulate was removed from the preform by oxidation prior to liquid metal infiltration.

Fatigue damage and its localization in particulate metal matrix composites : Li, C. and Ellyin, F. Mater. Sci. Eng. A (1996) 214 (1–2), 115–121

Damage tolerant fatigue design in MMCs relies on the assessment of initial and final damage states and on the determination of damage accumulation rates. Fibre reinforced MMCs tend to have inherent manufacturing defects in the form of micro-cracks or broken fibres due to the relaxation of matrix residual stresses and due to machining. For most materials the final outcome of damage accumulation is either crack arrest or failure. In MMCs however, another type of damage accumulation is the unstable crack growth which can be considered as an alternative failure condition. The domains of these three damage zones and the bounds for arrest, failure and unstable crack growth are established within the confines of a damage map. Within these bounds, fatigue damage accumulates at a rate dictated by the degree of fibre bridging, fibre/matrix debonding and fibre failure. A micro-mechanical model for crack propagation which incorporates explicitly these mechanisms is presented and used to estimate a practical limit of failure-safe fatigue crack growth for a SCS6/Ti-15-3 composite.

Modeling of solidification of metal-matrix particulate composites with convection

A multiphase model for the alloy solidification of metal-matrix particulate composites with convection is developed. Macroscopic transport equations are written for each phase, with unknown parameters modeled through supplementary relations pertinent to the solidification of a binary alloy matrix containing a stationary solid phase and generally nonstationary spherical particles. The model is applied to various one- and two-dimensional systems containing an Al-7 wt pct Si/SiC composite. One-dimensional sedimentation results in nonclustering and clustering particle systems show good agreement with experiments. One-dimensional composite solidification results illustrate the effect of particle clustering and cooling direction on the final macroscopic particle distribution. Two-dimensional results in various unreinforced and reinforced systems illustrate macroscopic particle segregation and its effect on buoyancy-driven melt convection and species macrosegregation. Results indicate a nearly uniform particle distribution for relatively small particles due to negligible particle settling prior to entrapment. For relatively large particles, significant particle settling prior to entrapment results in large denuded and packed zones in the casting. Fluid flow and macrosegregation during solidification are substantially reduced in the presence of particles, due to the relatively large interfacial drag exerted on the liquid by the stationary mush and particle phases.

Wear behavior of As-cast ZnAl27/SiC particulate metal-matrix composites under lubricated sliding condition

Wear behavior of As-cast ZnAl27/SiC particulate metal-matrix composites under lubricated sliding condition

The friction and wear of Cu-based silicon carbide particulate metaal matrix composites for brake applications

The purpose of this study was to investigate the tribological characteristics of several Cu-based SiC particulate metal matrix composites (pMMCs) synthesized from copper-coated SiC particles. Pin-on-disk tests were done to compare the wear and friction properties of hemispherically lipped pMMC pins with those for grey cast iron machined from an automotive brake rotor. The sliding counterfaces in the tribotests were semi-metallic and low metallic friction materials of the type used in commercial brake pads. Against both of these counterfaces, the pMMCs exhibited lower wear rates than cast iron. It was also observed that the friction coefficients of the pMMCs against the friction material counterfaces were comparable with those for cast iron. Wear mechanisms for the CuSiC pMMC materials were studied using scanning electron and optical microscopy of the wear scars. The influence of SiC particle size and type of friction material counterface on tribological behavior of the pMMCs was also studied, as was the effect of various interfacial coatings designed to improve bonding of the matrix to the particles. A model of the wear of this pMMC material, taking into account the various material parameters, will be presented.

Effect of particle distribution on deformation behaviour of particulate metal matrix composites

Effect of particle distribution on deformation behaviour of particulate metal matrix composites

Effect of particle distribution on deformation behaviour of particulate metal matrix composites

The deformation behaviour of particle reinforced metal matrix composites was studied in the form of single and multiple particle models with experimental and numerical approaches. The responses of these models to pure applied loading and to loading incorporating thermal residual stresses were both considered. Results indicated that two particles arranged in line with the loading direction would create a stress enhancement effect, promoting localised plastic deformation. However, the four particle models showed significant suppression of the stress enhancement effect by the creation of hydrostatic stresses in the matrix region surrounding the particles. These hydrostatic stresses were generated by strong constraint from these particles of the surrounding matrix when the interparticle distance was held below a certain threshold value. In addition, if particles were spaced beyond a certain distance whereby the non-uniform stress distribution created by the individual particles could not interact, the composite mechanical behaviour would be similar to that of a single particle composite. Finally, thermal residual stresses were found to have little or no effect on the stress response of the composites at high applied loads, but could attenuate the stress state at low load levels.

Effect of Heat Treatment and Volume Fractions of Praticle on Fatigue Crack Propagation of Al2O3/Al Alloy Composites.

In metal matrix particulate composites, factors such as the volume fraction of the particulate phase, particle size and interfacial bonding on influence the crack propagation behavior. In this study, the effects of the volume fraction of the particulate phase and heat treatment on the relationships between crack propagation rate da/dN and the stress intensity factor range ΔK, crack pass profiles and crack opening displacement COD are examined using two kinds of Al2O3/Al alloy composites and Al alloy. At the low ΔK level, da/dN decreases with the increase of the volume fraction, but with increasing ΔK level, the tendency disappears. This is mainly due to crack deflection and roughness-induced crack closure due to the presence of particles. A unique relationship is obtained between da/dN and CTOD irrespective of heat treatment and volume fraction. Thus, it can be concluded that the main factor which controls da/dN is CTOD.

Preparation of nanometer size TiC particulate reinforcements in Ti matrix composites under high pressure

Nanometer size TiC particulate reinforcements were in-situ synthesized in Ti matrix composites by mixing graphite powder and titanium powder under high pressure (2.5 ∼ 7.5 GPa) and high temperature (1073 ∼ 1573 K) conditions. The reinforcement, TiC, was formed inside the material, instead of being inserted into the matrix. Interface wettability problems of the two materials were therefore avoided, and well-bonded metal matrix particulate composites were achieved. The grain sizes of TiC, which ranged from 10 nm to 40 nm, can be controlled by changing processing condition. The relationship between the grain sizes of TiC particulates and their microhardnesses, as well as the influence of pressure and temperature on the grain sizes of TiC, is discussed.

The Effect of Interfacial Characteristics on the Mechanical Performance of Particulate, Fibrous and Layered Metal Matrix Composites - A Review of some Recent Work

The Effect of Interfacial Characteristics on the Mechanical Performance of Particulate, Fibrous and Layered Metal Matrix Composites - A Review of some Recent Work

Flow rule for the plastic deformation of particiulate metal-matrix composites

Finite element calculations are performed on models of particulate metal-matrix composites to study the applicability of a quadratic yield function and an associated flow rule. The matrix, here taken to be Al, is described by a J 2 flow rule for an isotropic material and the reinforcing particles, either SiC or TiC, are taken to be elastic. Two different types of three-dimensional models of the composite are considered: (1) a simple cubic lattice of spherical particles and (2) random digital models that are approximately isotropic. Only in the second type of model can the existence of a flow rule be established. The validity of a flow rule in random models is associated with the absence of shear planes that extend throughout the solid without intercepting any particles. Such planes can be drawn in the simple cubic lattice for some shear deformations and particle volume fractions. Localized shear bands occurring on these planes results in a shear response essentially identical to that of the unreinforced matrix material, which precludes the determination of the shear response from the uniaxial deformation of the composite.

Hierarchical Modeling of the Mechanical Behavior of High Speed Steels as Layer-Structured Particulate MMCs

High Speed Steels (HSS) produced by electro-slag remelting can be viewed as particle reinforced Metal Matrix Composites (MMCs) consisting of alternating layers of high and low inclusion volume fraction These phase arrangements require specific models to be used in analytical and numerical studies of the elastoplastic response of HSS. In the present study, a hierarchical micro-meso-macro approach is discussed, which combines the Multi-Particle Effective Field Method (MIEFM) for describing the matrix-inclusion topology at the microscale with an extended lamination theory for handling the layered geometry at the mesoscale. In addition, a Finite Element based two-dimensional method is presented, in which HSS is modeled as a material with a graded microstructure. The obtained results are discussed in terms of overall elastoplastic behavior and of damage relevant microscale fields.

Plastic flow and fracture of a particulate metal matrix composite

The effects of particle volume fraction and matrix temper on the flow and fracture characteristics of a series of particle-reinforced metal matrix composites under tensile and compressive loadings have been examined. Under compressive loading, a steady-state regime is attained in which the composite flow stress is proportional to the matrix flow stress at the same level of strain. The strength enhancement associated with the particles increases with increasing particle content and the matrix hardening exponent. The trends are consistent with predictions of finite element calculations of unit cell models, treating the particles as either spheres or cylinders with unit aspect ratio. Under tensile loading, the particles crack at a rate dependent on the intrinsic strength characteristics of the particles as well as the flow characteristics of the matrix. Particle cracking causes local softening, which reduces the work hardening rate as compared with compression deformation. This lowers both the strength and the ductility. Experimental measurements have been combined with finite element calculations to develop a damage law, incorporating the effects of the matrix strength on the particle stress. The damage law has been used to simulate the tensile flow response of the composites, using appropriate cell models under either isostrain or isostress conditions. Though the trends obtained from the simulations are in qualitative agreement with the experimental results, they tend to underestimate the flow stress. In all cases, tensile fracture is preceded by the formation of a neck. The condition at the onset of necking is consistent with the Considère criterion. Differences in necking strains between the composites and the monolithic matrix alloy have been rationalized on the basis of the rate of damage accumulation.

Fatigue damage and its localization in particulate metal matrix composites

A series of high and low cycle fatigue tests have been conducted on Al 2O 3 particulate-reinforced 6061 aluminum alloy composite(Al 2O 3/6061 Al). Fatigue damage in the composite, as observed by optical and scanning electron microscopes, is primarily in the form of particle debonding, fractured particles and matrix cracks. Mesoscale reinforcement defects, such as a clump of large particles, cause damage localization which may lead to short crack initiation and extension. The cyclic plastic strain amplitude appears to be an appropriate low cycle fatigue damage parameter as indicated by the hysteresis loop variation of strain-controlled cylindrical specimens.

Evaluation of tensile damage in particulate-reinforced MMC's by acoustic emission

Recently published research works showed that the mechanical properties of particulate reinforced metal matrix composites (MMC`s) are strongly affected by damage. It is accepted that such development of microstructural deterioration is related to reinforcement integrity (i.e. particulate cracking or matrix/reinforcement interface debonding) and that it takes place well before the final material collapse. Damage in composites can be measured by metallographic observations or by indirect methods such as by monitoring the elastic modulus changes as affected by the strain experienced. For monolithic metallic alloys, acoustic emission (AE) techniques are a useful tool for the detailed analysis of damage mechanisms and of their evolution during tensile and fatigue testing. The present paper is concerned with microstructural damage that occurs during tensile testing of MMC`s. Damage progression during loading was measured by acoustic emission technique on a Al{sub 2}O{sub 3}-Al particulate composite and on the corresponding unreinforced alloy considered for comparison purposes.

A generalized plane strain technique for estimating effective properties of particulate metal matrix composites using FEM

A procedure to estimate the effective elastic moduli and coefficient of thermal expansion (CTE) of particulate-reinforced metal matrix composites (MMCs) using a two-dimensional finite element method is presented. The actual microstructural geometry of the composites with randomly distributed second-phase particles is incorporated in the model. A generalized plane strain technique, realistically to describe the three-dimensional behaviour, is also incorporated in the model. The elastic moduli and the CTE, estimated using this model, agree favourably with the experimental data. The technique is shown to be superior compared to the conventional two-dimensional plane stress and plane strain approximations. Also, the results indicate that the effect of the shape of the randomly distributed second-phase particles on the effective elastic moduli is insignificant. Although the procedure is demonstrated for particulate MMCs, it can be easily extended to many other materials as well.

Comparison between the experimental and theoretical tensile behaviour of aluminium-based metal matrix composites reinforced with preforms of α-alumina platelets

In this article, the tensile behaviour of an aluminium matrix composite reinforced with new preforms of α-alumina platelets was studied both from an experimental and a theoretical point of view. The investigated composite characterized by a well-defined microstructure allowed us to establish a comparison between the experimental and theoretical evolutions and to check the ability of Eshelby-type theoretical models to assess the tensile properties of a particulate metal matrix composite. The analysis of the tensile properties was focused on the interpretation of Young's modulus and on the 0.2% proof stress of the composite, considering successively the effect of the variable parameters of the reinforcement on these two tensile characteristics. Young's moduli were assessed by an iterative Eshelby method developed in our laboratory and likely to take into account all the parameters defining the microstructure of the investigated composite; 0.2% proof stresses were analyzed by a hybrid model based both on dislocation mechanics and on the iterative Eshelby method.

Microstructure and kinetics of recrystallisation of hot deformed Al-Al<SUB>2</SUB>O<SUB>3</SUB> particulate reinforced metal matrix composite

Microstructure and kinetics of recrystallisation of hot deformed Al-Al<SUB>2</SUB>O<SUB>3</SUB> particulate reinforced metal matrix composite

Solidification shrinkage in metal matrix composites

A new test is described using simple unfed cast discs which allows a quantitative assessment of the shrinkage behaviour of cast materials in terms of (i) internal or external porosity and (ii) concentrated or dispersed porosity. The test has been applied to two different particulate metal matrix composites, and an aluminium alloy (Al—7% Si—0.4 Mg) which was common to both as the matrix alloy has also been investigated. One composite contained 7 vol% TiB2 particles and the other contained 20 vol% SiC particles. The shrinkage behaviour of the MMCs was found to be different from that of the matrix alloy. For higher section thickness castings, the matrix alloy alone developed a concentrated central shrinkage cavity, whereas the MMCs showed different behaviour. A large amount of external shrinkage was generated in TiB2 MMC, while the amount of internal shrinkage was small. For the SiC MMC, the internal and external shrinkage was similar. Generally, the internal porosity in both MMCs was found to be finer and more uniformly dispersed. The reason for the greater proportion of internal porosity in the SiC MMC compared to its TiB2 equivalent appears to be associated with the partly non-wetted surfaces of the SiC particles, whereas the chance of pore nucleation on well-wetted TiB2 particles (formed by chemical reduction in the melt) was very low. The level of internal porosity in thin-section castings was low (approximately 0.5%) for all cast materials in this study, and even for heavy sections in the cast MMCs the porosity would be tolerable for many components because it was dispersed and therefore would not by itself cause a casting to leak.

The flowability of particulate TiB2-containing metal matrix composite

This paper reports a study of the flow behaviour of a particulate TiB2-containing metal matrix composite (MMC) and a SiC particulate MMC containing the same matrix alloy, both in comparison with the unreinforced matrix alloy, Al-7Si-0.4Mg.Both the MMCs exhibited a similar extreme sensitivity to surface turbulence during casting, to the point at which it was not easily possible to produce good-quality castings using a conventional gravity-poured filling system. Further results obtained from fluidity measurements showed that the fluidity is not so different to conventional casting alloys, although the fluidity of the TiB2 MMC was slightly less good than the Al-SiC metal matrix composite, which in turn was poorer than the matrix alloy. A surprising result was that increasing the casting temperature did not significantly improve the fluidity of either of the MMCs.The relatively low fluidity and the high density of major defects appears to be associated with the high viscosity of the mixture and the fact that ...