Abstract
Non-equilibrium phenomena such as the disappearance of solute drag, the origin of solute trapping and evolution of disorder trapping occur during fast transformations with originating metastable phases [D.M. Herlach, P.K. Galenko, D. Holland-Moritz, Metastable solids from undrercooled melts (Elsevier, Amsterdam, 2007)]. In the present work, a theoretical investigation of disorder trapping by a rapidly moving phase interface is presented. Using a model of fast phase transformations, a system of governing equations for the diffusion of atoms, and the evolution of both long-range order parameter and phase field variable is formulated. First numerical solutions are carried out for a congruently melting binary alloy system.
Highlights
Disorder trapping is a known non-equilibrium phenomenon occurring during transformations of congruently melting ordered intermetallic compounds [1, 2]
The initial concentration distribution was taken as homogeneous, xB = 0.5, while both phase field φ and order parameter η were initialized to unity in the solid and zero in the liquid, connected by a smooth transition at the interface, which was described by a Gaussian error function with a width of 1 micron, corresponding to 10 finite difference (FD) nodes
An increase in the relaxation time τη moves the initiation of disorder trapping to smaller undercoolings
Summary
Disorder trapping is a known non-equilibrium phenomenon occurring during transformations of congruently melting ordered intermetallic compounds [1, 2] This phenomenon occurs especially during rapid crystallization of undercooled melts of intermetallics with a superlattice crystalline structure [3,4,5]. In such systems, the phase interface propagation is sluggish at small undercoolings. In addition to previous works [1,2,3, 6, 11], the present model takes into account highly rapid interface propagation at which locally non-equilibrium states in chemical composition and in atomic ordering are freezing in solid phase with an appearance of metastable states. The main focus of the present work is to analyze numeric results and to formulate conditions for disorder trapping in rapidly transforming congruently melting alloy undercooled in the liquid state
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