Plastic flow in dispersion hardened materials
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I.
INTRODUCTION
INa meeting devoted to celebration of the half century since the introduction of the theory of crystal dislocations, it is appropriate to review some aspects of dispersion hardening for two reasons. First, dispersion hardening encompasses a number of problems which involve the overlap of dislocation and continuum mechanics and second, the detailed consideration of the interaction of crystal dislocations with hard rigid elastic particles is applicable to a wide range of practical processes including ductile fracture and recrystallization as well as the prediction of the changes in flow stress and dislocation storage rate due to the hard particles. In addition, it is of value to realize that in the past two decades, the utilization of dislocation theory in relation to strengthening and fracture mechanisms has progressed from the analysis of idealized two phase materials and of some existing engineering materials to the point where it is of direct relevance to the design of new synthetic microstructures. This change has been accompanied by progress in the technology and production of both fine scale powders and composite materials using techniques such as rapid solidification, plasma methods, laser processing, and electron beam technology. In the future, dispersion strengthening is likely to have a major role to play in the design of synthetic materials based on both metals and ceramics and thus, it is appropriate in this brief review to indicate some areas where current theoretical work is likely to have a direct bearing on future technological developments. The service behavior of engineering materials often requires not only a knowledge of the initial level of yield stress and work hardening, which are the problems addressed by detailed dislocation models, but a broader view of the predictions of the influence of changes in strain path, the plastic behavior under complex J.D. EMBURY is Professor, Department of Metallurgy and Materials Science, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4L7, Canada. This paper is based on a presentation made at the symposium "50th Anniversary of the Introduction of Dislocations" held at the fall meeting of the TMS-AIME in Detroit, Michigan in October 1984 under the TMSAIME Mechanical'Metallurgy and Physical Metallurgy Committees.
METALLURGICAL TRANSACTIONS A
stress states, and the rate of accumulation of microstructural damage prior to fracture. Thus, the effective utilization of current theoretical concepts involves their effective integration with more macroscopic, continuum concepts of yield surfaces, the definition of the conditions for the stability of plastic flow, and the competitive processes of fracture initiation and damage accumulation. The essential description of dispersion strengthening in systems in which elastic rigid particles are embedded in a matrix capable of undergoing plastic flow is that the resultant mechanical behavior is determined not by a simple rule of mixtures based on the stresses bome by the matrix and the particu
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