Modeling of Antiphase Boundaries in L12 Structures

1986 ◽  
Vol 81 ◽  
Author(s):  
J.M. Sanchez ◽  
S. Eng ◽  
Y.P. Wu ◽  
J.K. Tien
Keyword(s):  
Antiphase Boundary ◽  
Cluster Variation Method ◽  
Variation Method ◽  
Bulk Alloy ◽  
Antiphase Boundaries ◽  
Ordered Structures ◽  
Wetting Transitions ◽  
Ordered Alloys ◽  
Disordered Layer ◽  
Cluster Variation

AbstractThe thermodynamic properties of conservative (111) antiphase boundaries in L12 ordered structures are modeled using the tetrahedron approximation of the cluster variation method. The concentration and long-range order parameter profiles are determined as a function of temperature and composition of the bulk alloy. Characteristic wetting transitions, with a macroscopic disordered layer growing from the antiphase boundary as the transition temperature is approached, are found for all cases investigated. The effectof antiphase boundaries on the disordering of ordered alloys and on the gliding of superdislocations are discussed.

First-Principles Theory of Alloy Phase Diagrams

1988 ◽  
Vol 141 ◽  
Author(s):  
Alex Zunger ◽  
L. G. Ferreira ◽  
S.-H. Wei
Keyword(s):  
Phase Diagrams ◽  
First Principles ◽  
Low Temperatures ◽  
Local Density ◽  
Cluster Variation Method ◽  
Variation Method ◽  
Interaction Energies ◽  
Ordered Structures ◽  
Cluster Variation ◽  
Dependent Interaction

AbstractTemperature-composition phase diagrams of alloys are calculated by a new method combining (i) first principles total energy calculations (at T=0) for ordered structures, using the local density formalism, with (ii) finite-temperature statistical-mechanics approach (the Cluster Variation Method) to the solution of the multi-spin Ising model, using volume-dependent interaction energies obtained from (i). Novel features, including the appearance of metastable long-range ordered compounds at low temperatures are discovered.

Real Space Multiple Scattering Description of Alloy Phase Stability

1991 ◽  
Vol 253 ◽  
Author(s):  
P. E. A. Turchi ◽  
M. Sluiter
Keyword(s):  
Multiple Scattering ◽  
Phase Stability ◽  
Antiphase Boundary ◽  
Cluster Variation Method ◽  
Real Space ◽  
Variation Method ◽  
Study Phase ◽  
Interfacial Energies ◽  
Cluster Variation ◽  
The Stability

ABSTRACTWe present a brief overview of the advanced methodology which has been recently developed to study phase stability properties of substitutional alloys, including order-disorder phenomena and structural transformations. The approach is based on the real space version of the Generalized Perturbation Method, first introduced by Ducastelle and Gautier, within the Korringa-Kohn- Rostoker multiple scattering formulation of the Coherent Potential Approximation. Temperature effects are taken into account with a generalized meanfield approach, namely the Cluster Variation Method. The viability and the predictive power of such a scheme will be illustrated by a few examples, among them: (1) the ground state properties of alloys, in particular the ordering tendencies for a series of equiatomic bcc-based alloys, (2) the computation of alloy phase diagrams with the case of fcc and bcc-based Ni-Al alloys, (3) the calculation of antiphase boundary energies and interfacial energies, and (4) the stability of artificial ordered superlattices.

Phase Diagram of Ni-Pt from Linear Muffin-Tin Orbitals Total Energy Calculations

1991 ◽  
Vol 253 ◽  
Author(s):  
C. Amador ◽  
W. R. L. Lambrecht ◽  
B. Segall
Keyword(s):  
Phase Diagram ◽  
Effective Interaction ◽  
Cluster Variation Method ◽  
Variation Method ◽  
Ordered Structures ◽  
Atomic Sphere ◽  
Sphere Approximation ◽  
Total Energies ◽  
The Difference ◽  
Cluster Variation

ABSTRACTProgress in the calculation of the phase diagram of the Ni-Pt compounds from "first-principles" is reported. Our procedure consists of: (1) calculating total energies for ordered structures as a function of volume and including internal relaxations by means of the linear muffin-tin orbitals method within the atomic sphere approximation; (2) mapping these results onto an Ising model with effective interaction parameters; and (3) calculating the phase diagram by means of the cluster variation method. We identify the elastic energy related to the difference in the Ni and Pt lattice constant as one of the major problems in this system and discuss the convergence of the cluster expansion of the energy.

Order—Disorder Behavior of Grain Boundaries in a two Dimensional Mcdel Ordered Alloy

1986 ◽  
Vol 81 ◽  
Author(s):  
Diana Farkas ◽  
Ho Jang
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Pair Interaction ◽  
Cluster Variation Method ◽  
Boundary Region ◽  
Variation Method ◽  
Two Dimensional ◽  
Interaction Energies ◽  
Disordered Layer ◽  
Cluster Variation

AbstractThe order-disorder behavior of a Σ = 5 grain boundary was investigated using a two dimensional latice gas model and the cluster variation method. It is found that a disordered layer forms in the grain boundary region at temperatures significantly below theorder—disorder temperature for the bulk. Under certain assumptions for the pair interaction energies the model predicts grain boundary compositions different from the bulk.

Coherent Phase Diagrams in the Cluster Variation Approximation

1982 ◽  
Vol 19 ◽  
Author(s):  
Didier De Fontaine
Keyword(s):  
Phase Diagrams ◽  
Cluster Variation Method ◽  
Energy Functional ◽  
Variation Method ◽  
Ordered Structures ◽  
Complex Phase ◽  
Coherent Phase ◽  
Neighbor Pair ◽  
Calculation Results ◽  
Cluster Variation

ABSTRACTCoherent phase diagrams are defined as pertaining to equilibria between phases which differ from one another merely by the distribution of different types of atoms on fixed crystallographic sites. Resulting ordered structures must then all be superstructures of one parent lattice, and corresponding phase diagrams are isomorphous to those of the Ising model with non–vanishing magnetic field. Rather complex phase diagrams can then be obtained from a single free energy functional by means of the cluster variation method. Calculated phase diagrams will be shown for the case of the fcc parent lattice with various positive and negative ratios of the values of second-to-first-neighbor pair interactions, this ratio being the only parameter which enters the calculation. Results will be compared to those of Monte Carlo calculations. The possibility of performing these first-principle calculations of coherent phase diagrams will be briefly touched upon.

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