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Long-time behavior of the $ω\to α$ transition in shocked Zirconium: Interplay of nucleation and plastic deformation

We study the thermally activated, slow conversion of the hysteretically retained $ω$ phase into stable $α$ phase in recovered samples of shocked zirconium. The $ω$-phase decays in time following an algebraic law, unlike the predictions of the nucleation-growth framework for first order transitions, and residual volume fractions of phases and dislocation densities are related by a power law. We propose an explanation for the annealing mechanism through coupled dynamics of dislocations and phase change. We find that the long-time behavior is controlled by the interplay of dislocations, shear fluctuations, and remnant volume fractions of phases, which lead to an algebraic decay in time. For late time, thermally activated quantities such as the dislocation mobility and nucleation rate set the timescale and control the algebraic behavior, respectively. At high enough temperatures this behavior is effectively indistinguishable from standard Avrami kinetics.