Ordering Mechanism in Ni-Cr Alloys: Theory and Experiment

1989 ◽  
Vol 166 ◽  
Author(s):  
P.E.A. Turchi ◽  
F.J. Pinski ◽  
R. H. Howell ◽  
A.L. Wachs ◽  
M.J. Fluss ◽  
...  
Keyword(s):  
Fermi Surface ◽  
First Principles ◽  
Alloy System ◽  
Annihilation Radiation ◽  
Potential Approximation ◽  
Flat Sheet ◽  
Inverse Monte Carlo ◽  
Atomic Interactions ◽  
Effective Cluster ◽  
Theory And Experiment

ABSTRACTRecently, short range order (SRO) parameters have been extracted from the neutron diffuse scattering intensities on Ni-Cr alloys with 11 to 25 at. pct. chromium. These data were analyzed using inverse-Monte Carlo simulations to extract atomic interactions and the results suggested the existence of a well defined, flat sheet of Fermi surface normal to the [110] direction. In this paper, this suggestion is investigated with a series of calculations which are based on the first-principles Korringa-Kohn-Rostoker-coherent-potential-approximation (KKRCPA). We calculate the electronic structure and the Bloch spectral function at the Fermi energy. We then proceed to calculate the effective cluster interactions using the generalized perturbation method (GPM) and compare them with the above-mentioned experimentally deduced interactions. In addition, we present preliminary results of two-dimensional angular correlation of positron annihilation radiation (2D-ACPAR) measurements, which probe the fermiology of this alloy system. The positron experiments demonstrate the existence of well-defined features in the Fermi surface of Ni89Cr11 but our calculations still have not yet established the origin of SRO in this system.

A Comparative First Principles Study of Phase Stability in Ni-Ti and Ni-Al Alloys Around Equiatomic Composition

1990 ◽  
Vol 186 ◽  
Author(s):  
P.E.A. Turchi ◽  
M. Sluiter ◽  
F.J. Pinski ◽  
D.D. Johnson
Keyword(s):  
Electronic Structure ◽  
Internal Energy ◽  
Phase Stability ◽  
First Principles ◽  
Al Alloys ◽  
Equiatomic Composition ◽  
Potential Approximation ◽  
Dependent Part ◽  
Substitutional Alloys ◽  
Effective Cluster

AbstractElectronic structure and phase stability properties of Ni-Ti and Ni-Al around equiatomic composition are investigated with a first principles approach. The study is based upon the generalized purturbation method applied to the Korringa-Kohn-Rostoker multiple scattering formulation of the coherent potential approximation. Within this framework, effective cluster interactions which build up the configuration-dependent part of the internal energy are calculated. The strength of ordering tendencies in both bcc-based substitutional alloys is compared and contrasted in terms of hybridisation effects, in relation with experimental evidences.

First-Principles Study of Phase Stability in Pd-Rh Alloys

1990 ◽  
Vol 186 ◽  
Author(s):  
D.D. Johnson ◽  
P.E.A. Turchi ◽  
Marcel Sluiter ◽  
D.M. Nicholson ◽  
F.J. Pinski ◽  
...  
Keyword(s):  
Phase Separation ◽  
Phase Stability ◽  
First Principles ◽  
Ternary Addition ◽  
Potential Approximation ◽  
Effective Interactions ◽  
Reference Medium ◽  
Random Alloy ◽  
Substitutional Alloys ◽  
Effective Cluster

We present a study of the mixing energies and the effective cluster interactions which form the configurational part of the internal energy of Pd-Rh substitutional alloys. We discuss the tendency towards phase-separation and more generally phase stability. The effects of a substitutional ternary addition on the tendencies toward order or phase-separation are also reported. The Korringa-Kohn-Rostoker Coherent-Potential Approximation (KKR-CPA) is used to investigate the electronic structure effects and energetics of the random alloy. Moreover, we use the Generalized Perturbation Method (GPM), using the KKR-CPA random alloy as a reference medium, to investigate the effective interactions which determine phase stability. We briefly comment on other factors which may give important contributions to the total free-energy of the alloy. We also contrast the GPM with the Connolly-Williams approach for calculating phase diagrams from first-principles. Finally, we explore the inadequacies of the frozen-potential and Harris approximations to the energetics of alloying.

Electronic Structure and Phase Stability Properties of Ai-Li Alloys

1990 ◽  
Vol 186 ◽  
Author(s):  
Antonios Gonis ◽  
Patrice E.A. Turchi ◽  
Marcel Sluiter ◽  
Frank J. Pinski ◽  
Duane D. Johnson
Keyword(s):  
Phase Diagram ◽  
Electronic Structure ◽  
Perturbation Method ◽  
Multiple Scattering ◽  
Phase Stability ◽  
First Principles ◽  
Potential Approximation ◽  
Effective Interactions ◽  
Lattice Constants ◽  
Effective Cluster

AbstractRecently, the phase diagram of AI-Li alloys was calculated with the use of the Connolly-Williams method. In an effort to test the validity and to supplement the results of that study, equilibrium lattice constants and effective cluster interactions have been obtained using the generalized perturbation method within the first-principles multiple-scattering formalism of the Korringa-Kohn-Rostoker coherent-potential approximation. The implication of these effective interactions to the phase stability of these alloys is discussed.

New Pt-based Superalloy System Designed from First Principles

2008 ◽  
Vol 1128 ◽  
Author(s):  
Vsevolod I. Razumovskiy ◽  
Eyvaz I. Isaev ◽  
Andrei V. Ruban ◽  
Pavel A. Korzhavyi
Keyword(s):  
Elastic Properties ◽  
First Principles ◽  
Defect Formation ◽  
Alloy System ◽  
First Principles Calculations ◽  
Phonon Spectra ◽  
Ultrahigh Temperature ◽  
New Generation ◽  
Formation Energies ◽  
Temperature Applications

AbstractPt-Sc alloys with the γ-γ′ microstructure are proposed as a basis for a new generation of Pt-based superalloys for ultrahigh-temperature applications. This alloy system was identified on the basis of first-principles calculations. Here we discuss the prospects of the Pt-Sc alloy system on the basis of calculated elastic properties, phonon spectra, and defect formation energies.

First principles study of surface stability and segregation of PdRuRh ternary metal alloy system

2018 ◽  
Vol 671 ◽  
pp. 51-59 ◽  
Author(s):  
Susan Meñez Aspera ◽  
Ryan Lacdao Arevalo ◽  
Hiroshi Nakanishi ◽  
Hideaki Kasai
Keyword(s):  
First Principles ◽  
Alloy System ◽  
Metal Alloy ◽  
Surface Stability ◽  
First Principles Study ◽  
Ternary Metal

scholarly journals New MAX Phase Superconductor Ti2GeC: A First-principles Study

2013 ◽  
Vol 6 (1) ◽  
pp. 11-27 ◽  
Author(s):  
M. A. Hadi ◽  
M. Roknuzzaman ◽  
F. Parvin ◽  
S. H. Naqib ◽  
A. K. M. A. Islam ◽  
...  
Keyword(s):  
Optical Properties ◽  
Thermodynamic Properties ◽  
Fermi Surface ◽  
Vickers Hardness ◽  
First Principles ◽  
Elastic Anisotropy ◽  
Debye Model ◽  
First Principles Calculation ◽  
Max Phase ◽  
Specific Heats

This is the first DFT-based first-principles prediction of the detailed optical and thermodynamic properties, including Vickers hardness and Fermi surface of 211 MAX phase Ti2GeC for which superconductivity (Tc~ 9.5 K) was reported very recently. The calculated structural properties are in excellent agreement with experiments. Our results on elastic parameters indicate a slight elastic anisotropy and brittleness of the compound. The chemical bonding is seen to be a combination of covalent, ionic and metallic nature. The rather stronger covalent bonding is responsible for its high Vickers hardness of 11.6 GPa. The investigated Fermi surface is formed mainly by the low-dispersive bands, which should be responsible for the presence of superconductivity in Ti2GeC. All the optical properties are evaluated and analyzed for two different polarization directions of incident photon. The temperature and pressure dependence of primitive cell volume, thermal expansion coefficient, specific heats, bulk modulus, and Debye temperature of Ti2GeC are derived from the quasi-harmonic Debye model with phononic effect and the various implications are discussed in details.  Keywords: First-principles calculation; Vickers hardness; Optical properties; Thermodynamic properties. © 2014 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights reserved. doi: http://dx.doi.org/10.3329/jsr.v6i1.16604 J. Sci. Res. 6 (1), 11-27 (2014)

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