The Theory of the Critical Shear Stress and Work Hardening in Dispersion-Hardened Crystals

摘要

Part one describes models for the critical shear stress or yield stress of dispersion hardened alloys, by which we mean crystalline materials hardened by a dispersion of strong particles of a second phase; equations relating yield stress to the size and volume fraction of particles are derived, and compared with experimental results. It is shown that the stress required to bend a dislocation between particles frequently defines the flow stress. This stress is calculated, carefully avoiding many of the approximations inherent in older calculations. Part two describes work hardening in these alloys. The theory of Fisher, Hart, and Pry is able to describe work hardening of previously undeformed dispersion hardened crystals at small strains, (a few % elongation) but at larger strains it is less successful. A new theory of work hardening, applicable to larger strains is described. It is based on the fact that, if the particles do not deform plastically, and the interface between particle and matrix does not fracture, then secondary slip must occur locally round each particle when the crystal is deformed, even though the crystal may appear to deform by 'single slip.' The density of secondary dislocations rises steeply with strain, and acts as a forest impeding the movement of primary glide dislocation. The theory predicts a relation between stress and strain which is in good agreement with experimental results. Fracture of the particle-matrix interface and the importance of the strength of this interface, are discussed. (Author)