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Interactions and phase stability in Ni-rich binary alloys
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. (Unit of Structure)ORCID iD: 0000-0001-9354-7029
2016 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Ni-based superalloys are the important materials for gas turbines in advancedaeroplane engines . The addition of refractory elements to these superalloys,such as rhenium and tungsten, can significantly improve the hightemperatureperformance by so-called solid-solution hardening. Although thestrengthening effect of refractory elements in Ni-based superalloys have beenknown for a long time, the effective interactions among alloying componentsas well as the atomic ordering in the alloy systems are still under investigationand even under debate. In this work, we study these interactions and thisordering for two binary alloys, Ni-rich Ni-Re and Ni-rich Ni-W, by means ofab initio simulations and statistical mechanics simulations based on the IsingHamiltonian.

For the Ni-rich Ni-Re alloys, we show that the effective cluster interactionsvary substantially depending on the temperature, concentration of the componentsand the magnetic state of the matrix. The strain-induced interactionshave large contribution to the nearest-neighbor pair-interactions and some multisitecluster-interactions in the ferromagnetic and nonmagnetic states. Theordering tendency of binary Ni-Re alloy systems can be predicted in terms ofordering energy and enthalpy of formation. We show that the D1a orderedstructure should be stable at the concentration of 20 at.% Re in the Ni-rich Ni–Re alloy system. The Monte Carlo simulations of Ni-Re random alloysshow the existence with the D1a-Ni4Re ordered structure at low temperatures.

We also calculated lattice parameters for different compositions of Ni-rich Ni-W alloys, and we find that lattice parameters of random Ni-W alloys increaselinearly with the concentration of W. This is in good agreement withthe Vegard’s law predictions and experimental data. We investigated phasestability of Ni-rich Ni-W alloys in terms of the enthalpies of formation andordering energies. We find the chemical pair interactions are sensitive to themagnetic state and concentration. The calculated strain-induced interactionsare quite large for the first coordination shell, which is due to a large sizemismatch of Ni and W. Taking local lattice relaxation into account, the Ni-Wsystems were modeled by Monte Carlo method. The D1a-Ni4W ordered structurecan be observed up to 22 at.% W. In higher concentrations of W, in ourMC calculations, the DO22-Ni3W and Pt2Mo-Ni2W ordered structures can beobserved in Ni-25 at.% W alloy and Ni-33 at.% W alloy, respectively.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2016. , 65 p.
Keyword [en]
Ni-based superalloys, ab initio calculations, atomic ordering, effective interactions.
National Category
Materials Engineering
Research subject
Materials Science and Engineering; Materials Science and Engineering
Identifiers
URN: urn:nbn:se:kth:diva-189865ISBN: 978-91-7595-998-6 (print)OAI: oai:DiVA.org:kth-189865DiVA: diva2:949535
Presentation
2016-06-09, Kuben N111, Brinellvägen 23, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20160721

Available from: 2016-07-21 Created: 2016-07-20 Last updated: 2016-07-21Bibliographically approved
List of papers
1. Effective interactions and atomic ordering in Ni-rich Ni-Re alloys
Open this publication in new window or tab >>Effective interactions and atomic ordering in Ni-rich Ni-Re alloys
2016 (English)In: Physical Review B Condensed Matter, ISSN 0163-1829, E-ISSN 1095-3795, Vol. 94, no 2, 024111Article in journal, Editorial material (Refereed) Published
Abstract [en]

Interatomic interactions and ordering in fcc Ni-rich Ni-Re alloys are studied by means of first-principles methods combined with statistical mechanics simulations based on the Ising Hamiltonian. First-principles calculations are employed to obtain effective chemical and strain-induced interactions, as well as ordering energies and enthalpies of formation of random and ordered Ni-Re alloys. Based on the nonmagnetic enthalpies of formation, we speculate that the type of ordering can be different in alloys with Re content less than 10 at.%. We demonstrate that effective chemical interactions in this system are quite sensitive to the alloy composition, atomic volume, and magnetic state. In statistical thermodynamic simulations, we have used renormalized interactions, which correctly reproduce ordering energies obtained in the direct total energy calculations. Monte Carlo simulations for Ni 0.91 Re 0.09   alloy show that there exists a strong ordering tendency of the (112 0)  type leading to precipitation of the D1 a   ordered structure at about 940 K. Our results for the atomic short-range order indicate, however, that the presently applied theory overestimates the strength of the ordering tendency compared to that observed in the experiment.

Place, publisher, year, edition, pages
PRB: American Physical Society (APS), 2016
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-189867 (URN)10.1103/PhysRevB.94.024111 (DOI)000379501200002 ()2-s2.0-84978388632 (Scopus ID)
Note

QC 20160721

Available from: 2016-07-21 Created: 2016-07-21 Last updated: 2017-11-28Bibliographically approved
2. Interactions and phase stability in Ni-rich Ni-W alloys
Open this publication in new window or tab >>Interactions and phase stability in Ni-rich Ni-W alloys
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Interatomic interactions and phase transformation in Ni-rich Ni-W alloys are investigated using rst-principlesmethods and statistical thermodynamics simulations. The formation enthalpies of fcc and bcc random as wellas some fcc-based ordered structures are determined in the ferromagnetic and nonmagnetic states. The effective interactions are calculated in supercell ab initio calculations and using screened generalized perturbation method(SGPM). We find the stable fcc-based ordered structures are D1a, DO22 and Pt2Mo phases and they can be observed in the Ni-25 at.% W, Ni-25 at.% W and Ni-33 at.% W alloys, respectively. The calculated atomic short-range order results are in reasonable agreement with experiments and other theoretical investigations.

National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:kth:diva-189868 (URN)
Note

We  are working on the manuscript at present,  here we  put the main result in abstract, and detailed discussions of this manuscript can be seen in the licentiate thesis: Interactions and phase stability in Ni-rich binary alloys.

QC 20160721

Available from: 2016-07-21 Created: 2016-07-21 Last updated: 2016-07-21Bibliographically approved

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He, Shuang

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