A new theory of work hardening in dispersion-hardened single crystals—by which we mean soft crystals containing hard non-deforming particles of a second phase—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 dislocations. The theory predicts a relation between stress and strain (eqn. (9)) 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.

Work hardening of dispersion-hardened crystals

Loop and void damage during heavy ion irradiation on nanocrystalline and coarse grained tungsten: Microstructure, effect of dpa rate, temperature, and grain size

Strength of iron during allotropic transformation

It is shown, using electrical resistance measurements and transmission electron microscopy, that the annealing behaviour of copper quenched from high temperature is similar to that of silver, provided that care is taken in both cases to avoid contamination by oxygen. To achieve this, copper was quenched from an atmosphere of carbon monoxide. The results obtained under these conditions suggest that the divacancy is the principal defect retained in copper after quenching from high temperatures. The temperatures at which stacking-fault tetrahedra anneal out in silver and gold were studied by transmission microscopy. In silver, tetrahedra are stable up to at least 930°c. The stability of tetrahedra in gold depends on their size, being greater the larger the tetrahedra. Finally it has been shown that dislocation loops, not tetrahedra, predominate as the clustered vacancy defect in gold if, after quenching from high temperature to 0°c, the gold is rapidly upquenched to 100°c.

The annealing of vacancies and vacancy aggregates in quenched gold, silver and copper

The long-range elastic interactions between dislocations and loops, both prismatic and shear, have been calculated for an isotropic medium. From the energy of interaction the magnitude and directio...

R.S Barnes

Papers

Stress-generated prismatic dislocation loops in quenched copper