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The A15 to bcc phase transition is simulated at the atomic scale based on an interatomic potential for molybdenum. The migration of the phase boundary proceeds via long-range collective displacements of entire groups of atoms across the interface. To capture the kinetics of these complex atomic rearrangements over extended time scales we use the adaptive kinetic Monte Carlo approach. An effective barrier of 0.5 eV is determined for the formation of each new bcc layer. This barrier is not associated with any particular atomistic process that governs the dynamics of the phase boundary migration. Instead, the effective layer transformation barrier represents a collective property of the complex potential energy surface. DOI: 10.1103/PhysRevLett.116.035701 Many properties of bulk materials are determined by internal interfaces. As only small amounts of interface active elements are required to modify the stability and mobility of interfaces, interface properties are a focus in alloy design. In Ni-based superalloys [1], for example, refractory elements such as Re, Mo, or W are added to suppress creep. These elements can induce the formation of topologically close-packed (TCP) phases [2] that are not coherent with the cubic and single-crystalline superalloy material. The TCP phases are detrimental to the mechanical properties of the alloys and thus their formation needs to be avoided or retarded. In addition to a detailed knowledge of the structure and stability of the interfaces between TCP phases and the host material it is key to obtain insight into the kinetics of the migration of the phase boundaries.Simulating the kinetics of complex phase boundaries in solid-solid phase transformations up to experimental time scales remains one of the great challenges in the atomistic modeling of materials. Molecular dynamics (MD) simulations are limited to time scales that are orders of magnitude shorter than experimental ones. To observe phase boundary migration on such short time scales unrealistically high driving forces are required that can alter the underlying atomistic mechanisms. Another challenge is presented by the collective atomic displacements at the interface that are too complex to use a lattice based kinetic Monte Carlo [3,4] approach to follow the dynamics over extended time scales. To capture the kinetics of complex phase boundaries we have to go beyond standard atomistic simulation techniques. One possibility is to use accelerated MD [5] if a suitable bias potential can be defined (hyperdynamics), very large computational resources are available (parallel replica dynamics), or the important reaction rates can be assumed to follow an Arrhenius form to a high temperature where they can be observed directly with MD (temperature accelerated dynamics).In this study we present the application of adaptive kinetic Monte Carlo (AKMC) [6] to interface migration between different phases. The AKMC approach allows for simulations of atomic systems over long time scales by focusing on the dynamics of rare events. The m...

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