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A First-Principles Investigation of ...

Nataraj, Chiraag M.

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A First-Principles Investigation of Refractory Alloy Systems United by a Common Computational Framework.

Record Type:	Electronic resources : Monograph/item
Title/Author:	A First-Principles Investigation of Refractory Alloy Systems United by a Common Computational Framework./
Author:	Nataraj, Chiraag M.
Published:	Ann Arbor : ProQuest Dissertations & Theses, : 2021,
Description:	141 p.
Notes:	Source: Dissertations Abstracts International, Volume: 83-01, Section: B.
Contained By:	Dissertations Abstracts International83-01B.
Subject:	Phase transitions. -
Online resource:	https://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=28727134
ISBN:	9798534694093

A First-Principles Investigation of Refractory Alloy Systems United by a Common Computational Framework.
Nataraj, Chiraag M.

A First-Principles Investigation of Refractory Alloy Systems United by a Common Computational Framework. - Ann Arbor : ProQuest Dissertations & Theses, 2021 - 141 p.

Source: Dissertations Abstracts International, Volume: 83-01, Section: B.

Thesis (Ph.D.)--Brown University, 2021.

This item must not be sold to any third party vendors.

The cluster expansion formalism for alloys is used to investigate phenomena in several refractory alloys: Co3W (superalloy), NbTiVZr, HfNbTaTiZr, and AlHfNbTaTiZr (high entropy alloys). Density functional theory (DFT) is used to calculate the energies of many small structures which are used to construct a cluster expansion model for each alloy system. These models are then used as Hamiltonians for Monte Carlo simulations in order to explore the dependence of the antiphase boundary (APB) energy on temperature and Al and Hf impurity concentration in metastable FCC Co3W as well as phase segregation behavior in NbTiVZr, HfNbTaTiZr, and AlHfNbTaTiZr. First, the effects of Al and Hf impurities on the (111) antiphase boundary (APB) energy of metastable FCC Co3W are investigated via ab initio calculations. It is found that Hf increases the APB energy far more than Al, particularly at higher concentrations of the impurity, and both systems exhibit little variation with respect to temperature. It is further shown that at higher concentrations of Hf, and most noticeably for Co3(W0.5Hf0.5), Hf and W tend to segregate into alternating planes, unlike the corresponding Co3(W0.5Al0.5), which explains the different impacts of the two impurities on the APB energy. Finally, the ratio of (111) to (100) APB energies is studied for sacrificial W compositions to understand cross slip behavior in both ternary systems. Second, the phase segregation behavior of three key refractory high entropy alloys (NbTiVZr, HfNbTaTiZr, and AlHfNbTaTiZr) is studied using first-principles calculations. Phase segregation and intermetallic phases documented in the experimental literature are reproduced in all three high entropy alloys and thermodynamic integration is used to calculate the configurational entropy of these alloys as a function of temperature. Our results show that at low temperatures, the configurational entropy of these materials is largely independent of N, which suggests that alloy design guidelines based on the ideal entropy of mixing require further examination.

ISBN: 9798534694093Subjects--Topical Terms:

3560387
Phase transitions.
Subjects--Index Terms:

Refractory alloys

A First-Principles Investigation of Refractory Alloy Systems United by a Common Computational Framework.
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245 1 0 $a A First-Principles Investigation of Refractory Alloy Systems United by a Common Computational Framework.
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300 $a 141 p.
500 $a Source: Dissertations Abstracts International, Volume: 83-01, Section: B.
500 $a Advisor: van de Walle, Axel.
502 $a Thesis (Ph.D.)--Brown University, 2021.
506 $a This item must not be sold to any third party vendors.
520 $a The cluster expansion formalism for alloys is used to investigate phenomena in several refractory alloys: Co3W (superalloy), NbTiVZr, HfNbTaTiZr, and AlHfNbTaTiZr (high entropy alloys). Density functional theory (DFT) is used to calculate the energies of many small structures which are used to construct a cluster expansion model for each alloy system. These models are then used as Hamiltonians for Monte Carlo simulations in order to explore the dependence of the antiphase boundary (APB) energy on temperature and Al and Hf impurity concentration in metastable FCC Co3W as well as phase segregation behavior in NbTiVZr, HfNbTaTiZr, and AlHfNbTaTiZr. First, the effects of Al and Hf impurities on the (111) antiphase boundary (APB) energy of metastable FCC Co3W are investigated via ab initio calculations. It is found that Hf increases the APB energy far more than Al, particularly at higher concentrations of the impurity, and both systems exhibit little variation with respect to temperature. It is further shown that at higher concentrations of Hf, and most noticeably for Co3(W0.5Hf0.5), Hf and W tend to segregate into alternating planes, unlike the corresponding Co3(W0.5Al0.5), which explains the different impacts of the two impurities on the APB energy. Finally, the ratio of (111) to (100) APB energies is studied for sacrificial W compositions to understand cross slip behavior in both ternary systems. Second, the phase segregation behavior of three key refractory high entropy alloys (NbTiVZr, HfNbTaTiZr, and AlHfNbTaTiZr) is studied using first-principles calculations. Phase segregation and intermetallic phases documented in the experimental literature are reproduced in all three high entropy alloys and thermodynamic integration is used to calculate the configurational entropy of these alloys as a function of temperature. Our results show that at low temperatures, the configurational entropy of these materials is largely independent of N, which suggests that alloy design guidelines based on the ideal entropy of mixing require further examination.
590 $a School code: 0024.
650 4 $a Phase transitions. $3 3560387
650 4 $a Stainless steel. $3 3560388
650 4 $a Stress-strain curves. $3 3560389
650 4 $a Energy. $3 876794
650 4 $a Alloys. $3 654175
650 4 $a Thermodynamics. $3 517304
650 4 $a Materials science. $3 543314
650 4 $a Mechanics. $3 525881
650 4 $a Metallurgy. $3 535414
650 4 $a Standard deviation. $3 3560390
650 4 $a Simulation. $3 644748
650 4 $a Trends. $3 3560051
650 4 $a Methods. $3 3560391
653 $a Refractory alloys
653 $a Antiphase boundary energy
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690 $a 0346
690 $a 0794
690 $a 0348
710 2 $a Brown University. $b Engineering: Mechanics of Solids. $3 3560386
773 0 $t Dissertations Abstracts International $g 83-01B.
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793 $a English
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