Critical examination of continuum and cross-core theories of dynamic strain aging

Dynamic strain aging (DSA) is the process by which solute atoms diffuse towards dislocations and reduce their mobility on the timescale of loading. There are two prevailing DSA theories in the literature: classical continuum theory and cross-core theory. Continuum theory was developed in the early days of dislocation theory, but has been shown to significantly overpredict both the timescale of solute segregation and the resulting strengthening. Cross-core theory was recently developed by Curtin et al. in order to address these shortcomings, and is based on a “single-atomic-hop” diffusive mechanism across the core of an extended dislocation. Whereas these two theories are thought to be distinct from one another in terms of the underlying physics, we show through numerical calculations that in reality there is no major distinction between them. Continuum theory predicts nearly the same behaviors as cross-core theory, as long as the enhanced diffusivity at the core is accounted for; the cross-core solute migration process is not distinct from bulk diffusion. Furthermore, we show that the widely accepted classical expression for solute segregation is incorrect; both the time constant and temporal scaling are in error due to a poor semi-analytical assumption.

Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA-0003525.