Recovery of point defects in iron after low-temperature deformation

Abstract

High-purity iron was severely deformed at 77°K by rolling or drawing under liquid nitrogen. Changes in electrical resistivity were used to measure the recovery during isochronal and isothermal anneals in the temperature range 110–520°K. A sharp recovery stage was observed at 211°K for which the activation energy is 0.55 eV. The recovery followed a kinetic law of the form m (t) m (0) = exp[−(αt) n] where m (t) m (0) is the fraction of defects remaining at time t, and α and n are constants. Between 190 and 220°K, n = 0.43. The annealing stage is attributed to the migration of vacancies (or divacancies) to dislocation sinks. The rate of increase in the mole fraction of these vacancies during straining is estimated to he: ΔN v / Δϵ = 2 × 10 −7 per percent strain.