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

A new method is proposed for evaluation of local fields and overall properties of composite materials subjected to incremental thermomechanical loads and to transformation strains in the phases. The composite aggregate may consist of many perfectly bonded inelastic phases of arbitrary geometry and elastic material symmetry. In principle, any inviscid or time-dependent inelastic constitutive relation that complies with the additive decomposition of total strains can be admitted in the analysis. The governing system of equations is derived from the representation of local stress and strain fields by novel transformation influence functions and concentration factor tensors, as discussed in the preceding paper by G. J. Dvorak and Y. Benveniste. The concentration factors depend on local and overall thermoelastic moduli, and can be evaluated with a selected micromechanical model. Applications to elastic-plastic, viscoelastic, and viscoplastic systems are discussed. The new approach is contrasted with some presently accepted procedures based on the self-consistent and Mori-Tanaka approximations, which are shown to violate exact relations between local and overall inelastic strains.

Transformation field analysis of inelastic composite materials

Computational plasticity for composite structures based on mathematical homogenization: Theory and practice

The effect of local eigenstrain and eigenstress fields, or transformation fields, on the local strains and stresses is explored in multiphase elastic solids of arbitrary geometry and material symmetry. The residual local fields caused by such transformation fields are sought in terms of certain transformation influence functions and transformation concentration factor tensors. General properties of these functions and concentration factors, and their relation to the analogous mechanical influence functions and concentration factors, are established, in part, with the help of uniform strain fields in multiphase media. Specific estimates of the transformation concentration factor tensors are evaluated by the self-consistent and Mori-Tanaka methods. It is found here that although the two methods use different constraint tensors in solutions of the respective dilute problems, their estimates of the mechanical, thermal, and transformation concentration factor tensors, and of the overall stiffness of multiphase media have a similar structure. Proofs that guarantee that these methods comply with the general properties of the transformation influence functions, and provide diagonally symmetric estimates of the overall elastic stiffness, are given for two-phase and multiphase systems consisting of, or reinforced by, inclusions of similar shape and alignment. One of the possible applications of the results, in analysis of overall instantaneous properties and local fields in inelastic composite materials, is described in the following paper.

On transformation strains and uniform fields in multiphase elastic media

Metal matrix composites are an attractive choice for aerospace and automotive applications because of their high stiffness-to-weight ratio. Composites with aluminum and magnesium matrices have been investigated extensively, while less work has been carried out on steel matrix composites. In the present study the hot isostatic pressing (HIP) process of steel matrix composites is described, and the factors influencing the reinforcement distribution, interface processes, as well as the mechanical and corrosion properties, are revealed. Both stainless steels and tool steels were used as the matrix material, and the particulate reinforcements were Al 2 O 3 , TiC, Cr 3 C 2 , or TiN. The results are compared with those of the corresponding unreinforced alloys and also with those of aluminum and magnesium matrix composites. It was found that the incorporation of a relatively low volume fraction of ceramic particulate reinforcements significantly increases the wear resistance of the steel matrices, without deteriorating the corrosion properties. On the other hand, reductions in the tensile strength, ductility and toughness were observed. The superaustenitic stainless steel–TiN and hot work tool steel–Cr 3 C 2 composites may offer the best combination of properties.

Processing and properties of particulate reinforced steel matrix composites

Part 1 Strengthening mechanisms: plasticity theories for fibrous composite materials, G.J.Dvorak strengthening of metal matrix composites due to dislocation generation through CTE mismatch, R.J.Arsenault strengthening behaviour of in situ composites, T.H.Courtney. Part 2 Mechanical properties: tensile and compressive properties of metal matrix composites, R.J.Arsenault mechanical behaviour of metal matrix composites under high strain rates and impact loadings, M.Taya creep behaviour of metal matrix composites, M.Taya. Part 3 Fracture and fatigue: fracture toughness of particulate metal matrix composites, D.L.Davidson fatigue of metal matrix composites, K.K.Chawla fatigue of discontinuously reinforced metal matrix composites, J.K.Shang and R.O.Ritchie. Part 4 Physical and chemical properties: dynamic mechanical properties, A.Wolfenden and J.M.Wolla thermal expansion of metal matrix composites, T.A.Hahn electrical conductivity in continuous fibre composites, J.E.Schoutens corrosion, P.P.Trzaskoma.

R.K. Everett

Papers

Metal matrix composites : mechanisms and properties