A Study on Microstructure and Mechanical Behavior of Cu-Al2O3 Composites: an Explanation by Deformation Theory

Abstract

Metal matrix composites (MMCs) integrate the ductility of metal and the toughness of ceramic particles. The degree of alliance of metal and ceramics constituents can be quantified in terms of interfacial activity. Cu-Al2O3 p composite materials are extensively used in resistance welding electrode, relay blades, electrical contact support, commutators for helicopter starter motor. Performance and microstructural characteristics of particle reinforced MMCs, depends on the size, shape, volume fraction, spatial distribution of the reinforcement entity and nature of the interfacial bonding. In the present investigation MMCs are prepared by powder blending, compaction followed by conventional sintering. Micro structural assessment of the specimen from SEM micrographs has been carried out. Deformation mechanism dominated by dislocation motion is emphasized comprehensively and critically by changing the reinforcement size (from micro- to nano-size) with a variation of sintering temperature. The flexural and compression tests were carried out to investigate the mechanical behaviour of MMCs. It is necessary to correlate the dislocation and deformation behaviour with reference to the changing microstructural characteristics of the composite and morphology of the particle. Dislocation generation and strain hardening of the MMCs ara explained on the basis of misfit strain, thermal misfit, lattice parameter misfit, elastic inhomogeneity misfit & allotropic misfit. The interfacial pinning (interaction between reinforced particle and dislocation) is explained on the basis of Orowan mechanism. The flow stress required for dislocation motion in an MMCs reinforced with spherical particle of radius rp with a volume fraction of f are determined from

Where G is shear modulus, b is burger vector, τf is the stress required to move dislocation in an obstacle free crystal. The viscous and collective motion of dislocations causse the dislocation –dislocation interactions and strengthening of the composite. Hardness and abrasion resistance decreases with increase in particle size. Fracture toughness rises with increases in reinforcement content and size because of bifurcation of crack by large ceramic particle.