The effect of a thoria dispersion on the yielding and flow of iron

A technique for the preparation of iron containing a fine dispersion of thoria particles has been developed. The method involves co-precipitation, hydrogen reduction and hot rolling in a reducing atmosphere at 1373°K. The mechanical properties of iron and iron-thoria strip have been investigated over the temperature range 77-373°K. The dispersion increased the strength and work hardening rate of iron, and reduced the ductility . The yield strength of the alloy has been explained in terms of dislocation multiplication rates and the stress dependence of dislocation velocity. The work hardening rate is regarded as a balance between the yield stress behaviour at low temperatures and recovery processes at the higher temperatures. The mechanics of neck and Luders band formation have been examined, and the observed fracture angles explained in terms of this analysis. The ductile-to-brittle transition temperature was found to be improved in the iron-thoria, as a consequence of both a finer grain size and the direct influence of the particles.Applied Science, Faculty ofMaterials Engineering, Department ofGraduat