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arXiv · 1302.1597

Low-temperature criticality of martensitic transformations of Cu nanoprecipitates in \alpha-Fe

Paul Erhart·Babak Sadigh
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Abstract

Nanoprecipitates form during nucleation of multiphase equilibria in phase segregating multicomponent systems. In spite of their ubiquity, their size-dependent physical chemistry, in particular at the boundary between phases with incompatible topologies, is still rather arcane. Here we use extensive atomistic simulations to map out the size-temperature phase diagram of Cu nanoprecipitates in \alpha-Fe. The growing precipitates undergo martensitic transformations from the body-centered cubic (BCC) phase to multiply-twinned 9R structures. At high temperatures, the transitions exhibit strong first-order character and prominent hysteresis. Upon cooling the discontinuities become less pronounced and the transitions occur at ever smaller cluster sizes. Below 300 K the hysteresis vanishes while the transition remains discontinuous with a finite but diminishing latent heat. This unusual size-temperature phase diagram results from the entropy generated by the soft modes of the BCC-Cu phase, which are stabilized through confinement by the \alpha-Fe lattice.

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Paul Erhart, Babak Sadigh. 2013-02-06. Low-temperature criticality of martensitic transformations of Cu nanoprecipitates in \alpha-Fe. https://doi.org/10.1103/physrevlett.111.025701

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