Modelling plastic deformation in BCC metals: Dynamic recovery and cell formation effects

A recently developed model for describing plasticity in FCC metals (E.I., Galindo-Nava, P.E.J., Rivera-Díaz-del-Castillo, Mater. Sci. Eng. A 543 (2012) 110-116; E.I. Galindo-Nava, P.E.J. Rivera-Díaz-del-Castillo, Acta Mater. 60 (2012) 4370-4378) has now been applied to BCC. The core of the theory is the thermostatistical description of dislocation annihilation paths, which determines the dynamic recovery rate of the material. Input to this is the energy for the formation, migration and ordering of dislocation paths; the latter term corresponds to the statistical entropy which features strongly on the solution. The distinctions between FCC and BCC stem primarily from the possible directions and planes for dislocation slip and cross-slip, as well as from the presence of the kink-pair mechanism for dislocation migration in BCC, which are incorporated to the mathematical formulation of the model. The theory is unique in describing the stress-strain response for pure iron, molybdenum, tantalum, vanadium and tungsten employing physical parameters as input; the description is made for wide ranges of temperature and strain rate. Additionally, succinct equations to predict dislocation cell size variation with strain, strain rate and temperature are provided and validated for pure iron.