Particle reinforced metal matrix composites are now being produced commerically, and in this paper the current status of these materials is reviewed. The different types of reinforcement being used, together with the alternative processing methods, are discussed. Depending on the initial processing method, different factors have to be taken into consideration to produce a high quality billet. With powder metallurgy processing, the composition of the matrix and the type of reinforcement are independent of one another. However, in molten metal processing they are intimately linked in terms of the different reactivities which occur between reinforcement and matrix in the molten state. The factors controlling the distribution of reinforcement are also dependent on the initial processing method. Secondary fabrication methods, such as extrusion and rolling, are essential in processing composites produced by powder metallurgy, since they are required to consolidate the composite fully. Other methods, suc...

Particle reinforced aluminium and magnesium matrix composites

Microstructurally inhomogeneous composites: Is a homogeneous reinforcement distribution optimal?

Heterostructured materials have been reported as a new class of materials with superior mechanical properties, which was attributed to the development of back stress. There are numerous reports on ...

https://tandfonline.com/doi/pdf/10.1080/21663831.2019.1616331

Perspective on hetero-deformation induced (HDI) hardening and back stress

Dry sliding wear of aluminium composites : A review

Strengthening mechanisms in particulate metal matrix composites

The tensile deformation and fracture behaviour of the aluminium alloy 6061 reinforced with SiC has been investigated. In the T4 temper plastic deformation occurs throughout the gauge length and the extent of SiC particle cracking increases with increasing strain. In the T6 temper strain becomes localised and particle cracking is more concentrated close to the fracture. The elastic modulus decreases with increasing particle damage and this allows a damage parameter to be identified. The fraction of SiC particles which fracture is less than 5%, and over most of the strain range the damage controlling the tensile ductility can be recovered, indicating that other factors, in addition to particle cracking are important in influencing tensile ductility. It is suggested that macroscopic fracture is initiated by the SiC particle clusters that are present in these composites as a result of the processing. The matrix within the clusters is subjected to high levels of triaxial stress due to elastic misfit and the constraints exerted on the matrix by the surrounding particles. Final fracture is then produced by crack propagation through the matrix between the clusters.

Aspects of fracture in particulate reinforced metal matrix composites

The strengthening of a particulate metal matrix composite due to quenching was studied both experimentally and theoretically. The strengthening was attributed to two mechanisms: punched-out dislocations due to CTE mismatch strain and back stress. Both mechanisms were analyzed by theoretical modeling leading to a good agreement between the experimentally observed strengthening and the prediction by the models. A parametric study revealed that the volume fraction of particulate, quenching temperature and its temperature differential and particulate size are the major variables influencing the increase in composite flow stress.

Strengthening of a particulate metal matrix composite by quenching

Resistivity and differential scanning calorimetry (DSC) techniques are used to study the kinetics of precipitation and dissolution of GPB zones and metastable phases ([delta][prime] and S[prime]) in Al-Li-Cu-Mg alloy 8090. Three stages of the precipitation sequence during aging have been analyzed. A new analytical method is developed for the DSC technique, which requires only one heating rate to obtain the kinetic parameters, and the results show good agreement with the more conventional method of varying heating rate. The low-temperature endothermic peak in the DSC thermogram is interpreted as the dissolution of Li-bearing zones, which is supported by the hardness results. The activation energy, Q, and the growth parameter, n, determined by resistivity and DSC techniques are in good agreement with previously published data.

Precipitation and dissolution kinetics in AlLiCuMg alloy 8090

The tensile fracture behavior of a cast and extruded 2014 aluminum alloy metal matrix composite (MMC) reinforced with 10, 15, and 20 vol.% aluminum oxide particles was investigated as a function of temperature between 100 and 300°C and hold time, and compared with the unreinforced alloy. In addition, the effect of aging condition was investigated in a 15 vol.% composite tested at 200°C. At lower temperature the composites have higher yield strength and UTS than the unreinforced material, and both decrease with increasing temperature. At higher temperatures all the materials have similar strength levels. The elongation is lower in the composites, decreasing with increasing level of reinforcement and increasing with increasing temperature, except at the highest temperature where all the composites are about the same. The microstructural damage in the composites also varies with temperature: particle fracture dominates at lower temperatures and interparticle voiding is the main damage feature at elevated temperatures. The time at temperature, and hence the degree of overaging, has little effect on the observed trends in the composite, in contrast with the unreinforced material where the density of voids decreases with increasing hold times. The transition temperature where the major damage changes from particle cracking to interparticle voiding increases with volume fraction and particle size, and decreases with overaging. The cracked particle density and void density both increase with strain, and the highest rate of increase occurs in the overaged material. In general, the tendency for particle cracking is reduced and for interparticle voiding is increased by any factor which permits accomodation of strain by the matrix, such as lower volume fraction of particles, small particle size, nonclustered particle distribution, and matrix softening from underaging or overaging.

Fracture at elevated temperatures in a particle reinforced composite

The work-hardening behavior of a particulate metal matrix composite (MMC) was studied in terms of the Bauschinger effect. The particulate MMC system used in this study is SiC particulate in 6061 aluminum alloy with three different aging conditions: unaged (solution-treated T4) and T4 aged at 175 °C for 4 and 8 h. The experimental results of the stress-strain behavior of the MMCs, which were processed by the casting route, are considered in terms of the Bauschinger effect, the difference (Δσf) andsum (Σσf) and of flow stresses in the forward (σtf) and backward loading (σcf) directions It was found that Δσf increases linearly with plastic strain ϵp up to some point (ϵbp) and then bends to a non-linear curve, while the relation between Σσf and ϵp gives rise to a flat curve. These results are confirmed by an analytical study based on Eshelby's model. These findings imply that the work hardening of this particulate MMC system is mainly due to back stress and not to forest dislocations or the source-shortening stress effect.

D.J. Lloyd

Papers

Aspects of fracture in particulate reinforced metal matrix composites

Strengthening of a particulate metal matrix composite by quenching

Precipitation and dissolution kinetics in AlLiCuMg alloy 8090

Fracture at elevated temperatures in a particle reinforced composite

Bauschinger effect in particulate SiC-6061 aluminum composites