Substitutional dynamic strain ageing in an iron — 1.1 at. % niobium alloy

Abstract

The mechanical properties of an Fe-1.1 at. % Nb alloy have been studied in compression over the temperature range 300 to 1100°K. The substitutional niobium atoms were responsible for dynamic strain ageing which resulted in a small peak in the temperature dependence of the flow stress, negative strain rate sensitivity, and serrated stress strain curves.

The serrations were preceded by a strain rate and temperature dependent critical strain. These dependencies were analysed using theories that have been successfully applied to substitutional strain ageing in fcc structures. The analysis showed that, unlike in fcc structures, the apparent activation energy for the onset of serrated flow increased at the faster strain rates; this was attributed to the vacancies produced by the plastic deformation rapidly annealing out due to the high temperatures involved at the faster strain rates.