Order-Disorder Processes in Crystals When Crystallizing Binary Metallic Melts

摘要

Theoretical grounds of order-disorder processes in crystals with a simple cubic lattice when crystallizing stoichiometric binary metallic melts were studied in [1-5]. These works presented mathematical models of the growth of binary crystals that accompanies the solidification of corresponding metallic melts. These models are based on time-independent master equations describing the structure and growth kinetics of binary metallic crystalline phases. It is noteworthy that, at significant supercooling of the melt-crystal system, there is a point where a disordered crystalline phase is formed at temperatures lower than the corresponding Curie temperature for the binary alloys in question. The above order-disorder effect is studied in connection with the fluctuation crystal-growth theory, where the model of the so-called two-phase transition (TPT) zone was used [6, 7]. The TPT zone separates two contiguous massive areas-a crystalline phase and the binary melt (see Fig. 1). In this model, the probability distribution functions of so-called growth monomers in TPT-zone layers were introduced and studied (see [2-5]). In the model of the concentration image of the TPT zone, these monomers are the analogues of liquid and solid metallic particles within the layers of the real TPT zone or the melt-crystal interface (see Fig. 2). As was noted in [2-5], the topological structure of the concentration image of the TPT zone affects the disordering process: the long-range order parameter η tends to zero in a way different from that for the Bragg-Williams thermodynamic order-disorder transition.