Powder metallurgy has been widely used to produce complex net or near-net shaped parts that require minimal or no machining. A critical step in powder metallurgy is compaction, which broadly includes die-filling, pressing and ejection. During die-filling process, powder flowability is very important to approach high and uniform packing density. It is closely related to particle characteristics [1]. To optimize inter-particle flow during die-filling, particles with broad size distributions, low surface area, low surface roughness and high mass are preferred [1–5]. In the compaction of metal matrix composites, the green density invariably decreases with increasing volume fraction of reinforcement particles. These low densities often lead to insufficient strength to support secondary processing such as sintering, machining or extrusion. The inhibition of densification is largely a result of extra deformation being needed in soft particles to fill voids between hard inclusion particles [6–10]. Using plasticene spheres and various rigid inclusions, Turner and Ashby [8] found that composites with (1) high volume fractions of hard inclusions, (2) inclusion particles that are small relative to the deformable phase, and (3) high aspect ratio inclusion particles are most difficult to densify. Using metal and ceramic particles, Singh [7] found decreased density with smaller inclusion particles and illustrated that a non-deforming layer of inclusions between two deforming contactsurfaces when inclusion particle size is much less than the matrix particle sizes. Lange et al. [6] found that at higher volume fractions, inclusions can form clusters or even a continuous network shielding densification. Lastly, Li and Funkenbusch [9,10] modeled bimodal particle file distributions and argued that the smaller particles will deform more heavily. Compaction under cyclic pressure has been shown to improve density [11–17], reduce the density gradients [11,13,16], and produce a more uniform reinforcement distribution [15,16,18]. When a composite, where constituent phases have very different properties, is subjected to a change in temperature or pressure, the differences in coefficients of thermal expansion or compressibility change the sizes of both types of particles differently. This leads to an internal mismatch strain. This volume mismatch leads to large deviatoric stresses which aid plastic behavior deformation and thereby affects the consolidation of composites. The plasticity caused by volume mismatch was first seen in creep, and then was applied to consolidation of iron where the driving mismatch was developed by allotropic transformations [19,20]. The volume mismatch plasticity was reviewed in [19]. Daehn and Wagoner et al. [11–16] shown that enhanced densification and improved mechanical properties of metal matrix Scripta mater. 44 (2001) 1117–1123