Materials Science and Engineering Seminar Series: William Soffa
L12 and L10 Ordering Revisited Using the Generalized Bragg-Williams Model: Second Nearest-Neighbor Interactions/Spinodal Decomposition/Elastic Relaxation/Third Law
Department of Materials Science and Engineering
University of Virginia
A generalized Bragg-Williams model incorporating first and second nearest-neighbor interactions is employed to re-visit issues related to L12 and L10 ordering in FCC solid solutions. The computational thermodynamics approach addresses quantitatively the interplay of ordering and clustering in the solution energetics governing the diffusional pathways leading to the precipitation of an ordered phase(L12) within a supersaturated FCC solution showing a marked impact of the higher (second) order interactions on microstructural evolution. In the case of L10 ordering the effects of elastic relaxation accompanying the cubic→tetragonal transformation are shown to change the thermodynamic order( Ehrenfest ) of the phase transition including the emergence of tricritical behavior at low temperatures. Also, in examining the (A1)→ tetragonal (L10) transformation the concept of pseudospinodal decomposition arising in recent studies of the Fe-Pd system will be discussed briefly. In both L12 and L10 ordering some considerations related to the application of the Third Law of Thermodynamics to solid solution models will be discussed.