Time-dependence of the alpha to epsilon phase transformation in iron

R. F. Smith, J. H. Eggert, D. C. Swift, J. Wang, T. S. Duffy, D. G. Braun, R. E. Rudd, D. B. Reisman, J. P. Davis, M. D. Knudson, G. W. Collins

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Iron was ramp-compressed over timescales of 3 ≤ t(ns) ≤ 300 to study the time-dependence of the α→ε (bcc→hcp) phase transformation. Onset stresses (σ α → ε) for the transformation ∼14.8-38.4 GPa were determined through laser and magnetic ramp-compression techniques where the transition strain-rate was varied between 106 ≤ μ α → ε(s-1) ≤ 5 ×108. We find σ α → ε = 10.8 + 0.55 ln (μ α → ε) for μ α → ε < 10 6/s and σ α → ε = 1.15 (μ α → ε) 0.18 for μ α → ε > 106/s. This μ response is quite similar to recent results on incipient plasticity in Fe [Smith, J. Appl. Phys. 110, 123515 (2011)] suggesting that under high rate ramp compression the α → ε phase transition and plastic deformation occur through similar mechanisms, e.g., the rate limiting step for μ > 106/s is due to phonon scattering from defects moving to relieve strain. We show that over-pressurization of equilibrium phase boundaries is a common feature exhibited under high strain-rate compression of many materials encompassing many orders of magnitude of strain-rate.

Original languageEnglish (US)
Article number223507
JournalJournal of Applied Physics
Issue number22
StatePublished - Dec 14 2013

All Science Journal Classification (ASJC) codes

  • General Physics and Astronomy


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