A dislocation pile-up model for the yield stress of a composite

A numerical model to simulate yielding in a composite is developed for the transmission of slip across a dissimilar interface through the formation of co-planar dislocation arrays in both phases. A pileup of dislocations in t he soft phase is assumed to nucleate dislocations in the hard phase in whic h movement is dictated by lattice friction stress. The polycrystalline comp osite yield stress is calculated by determining the equilibrium positions o f the dislocation arrays as a function of the length scales, elastic consta nts and Burgers vectors in the two phases, with particular reference to mel t oxidized Al-Al2O3, in which homophase boundaries are absent, and to the c ommercially important system Co-WC. The hardness values predicted from this model are in good agreement with experimentally measured values in the abo ve systems. The implications of these results for the design of hard compos ite microstructures are elucidated. (C) 1999 Acta Metallurgica Inc. Publish ed by Elsevier Science Lid. All rights reserved.