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Design of Modern High Nb-Content gamma-gamma' Ni-Base Superalloys.

Record Type:	Language materials, manuscript : Monograph/item
Title/Author:	Design of Modern High Nb-Content gamma-gamma' Ni-Base Superalloys./
Author:	Antonov, Stoichko.
Description:	1 online resource (217 pages)
Notes:	Source: Dissertation Abstracts International, Volume: 79-02(E), Section: B.
Subject:	Materials science. -
Online resource:	click for full text (PQDT)
ISBN:	9780355428162

Design of Modern High Nb-Content gamma-gamma' Ni-Base Superalloys.
Antonov, Stoichko.

Design of Modern High Nb-Content gamma-gamma' Ni-Base Superalloys. - 1 online resource (217 pages)

Source: Dissertation Abstracts International, Volume: 79-02(E), Section: B.

Thesis (Ph.D.)--Illinois Institute of Technology, 2017.

Includes bibliographical references

Certain elemental additions to Ni-base superalloys can significantly improve properties when added in high contents, but can quickly deteriorate the high temperature structural integrity and stability of the alloy, when solubility limits are exceeded and secondary phases are formed. Improved understanding of solubility limits of various elements in high refractory content Ni-base supralloys is therefore essential to improved alloy design. The morphology, formation, and composition of precipitate phases in a number of experimental alloys spanning a broad range of compositions were explored and compositional relationships were developed. The effect of increasing Nb alloying additions on formation and long term stability of topologically close packed (TCP) phases, as well as assessment of grain boundary phase compositions and local segregation along it before and after a 1000 hour thermal exposure at 800°C, was studied via electron microscopy and atom probe tomography (APT). Beneficial secondary phase precipitation, such as carbides and borides, was also studied through B, Hf and C doping. Elemental boron was observed to segregate to the grain boundary and phase interfaces, but did not form borides. APT studies on MC carbides of the alloys revealed the formation kinetics and morphological differences between NbC and Hf doped NbC, which were further explained using density functional theory (DFT) calculations of the formation energies of different facets of the MC carbide. Detailed electron microscopy and APT techniques were then used to systematically quantify the chemical and morphological instabilities that occur during aging of polycrystalline gamma-gamma' Ni-base superalloys containing elevated levels of refractory alloying additions. The morphological changes and splitting phenomenon associated with the secondary gamma' precipitates were related to the discrete chemical compositions of the secondary and tertiary gamma' along with the phase compositions of the gamma matrix and the gamma precipitates that form within the secondary gamma' particles. In addition, compositions of the constituent phases were measured in four high Nb-content gamma-gamma' Ni-base superalloys and the results were compared to thermodynamic database models from Thermo-Calc. Results were also used to predict the solid solution strength behavior of the four alloys. Finally, creep behavior of high Nb-content gamma-gamma' Ni-Based superalloys was related to the formation of secondary phases mainly at grain boundaries. As secondary phases form, their brittle nature leads to crack formation, which can propagate under the tensile load and lead to premature failure of the alloy.

Electronic reproduction.
Ann Arbor, Mich. :
ProQuest,
2018

Mode of access: World Wide Web

ISBN: 9780355428162Subjects--Topical Terms:

557839
Materials science.
Index Terms--Genre/Form:

554714
Electronic books.

Design of Modern High Nb-Content gamma-gamma' Ni-Base Superalloys.
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264 0 $c 2017
300 $a 1 online resource (217 pages)
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500 $a Source: Dissertation Abstracts International, Volume: 79-02(E), Section: B.
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502 $a Thesis (Ph.D.)--Illinois Institute of Technology, 2017.
504 $a Includes bibliographical references
520 $a Certain elemental additions to Ni-base superalloys can significantly improve properties when added in high contents, but can quickly deteriorate the high temperature structural integrity and stability of the alloy, when solubility limits are exceeded and secondary phases are formed. Improved understanding of solubility limits of various elements in high refractory content Ni-base supralloys is therefore essential to improved alloy design. The morphology, formation, and composition of precipitate phases in a number of experimental alloys spanning a broad range of compositions were explored and compositional relationships were developed. The effect of increasing Nb alloying additions on formation and long term stability of topologically close packed (TCP) phases, as well as assessment of grain boundary phase compositions and local segregation along it before and after a 1000 hour thermal exposure at 800°C, was studied via electron microscopy and atom probe tomography (APT). Beneficial secondary phase precipitation, such as carbides and borides, was also studied through B, Hf and C doping. Elemental boron was observed to segregate to the grain boundary and phase interfaces, but did not form borides. APT studies on MC carbides of the alloys revealed the formation kinetics and morphological differences between NbC and Hf doped NbC, which were further explained using density functional theory (DFT) calculations of the formation energies of different facets of the MC carbide. Detailed electron microscopy and APT techniques were then used to systematically quantify the chemical and morphological instabilities that occur during aging of polycrystalline gamma-gamma' Ni-base superalloys containing elevated levels of refractory alloying additions. The morphological changes and splitting phenomenon associated with the secondary gamma' precipitates were related to the discrete chemical compositions of the secondary and tertiary gamma' along with the phase compositions of the gamma matrix and the gamma precipitates that form within the secondary gamma' particles. In addition, compositions of the constituent phases were measured in four high Nb-content gamma-gamma' Ni-base superalloys and the results were compared to thermodynamic database models from Thermo-Calc. Results were also used to predict the solid solution strength behavior of the four alloys. Finally, creep behavior of high Nb-content gamma-gamma' Ni-Based superalloys was related to the formation of secondary phases mainly at grain boundaries. As secondary phases form, their brittle nature leads to crack formation, which can propagate under the tensile load and lead to premature failure of the alloy.
533 $a Electronic reproduction. $b Ann Arbor, Mich. : $c ProQuest, $d 2018
538 $a Mode of access: World Wide Web
650 4 $a Materials science. $3 557839
655 7 $a Electronic books. $2 local $3 554714
690 $a 0794
710 2 $a ProQuest Information and Learning Co. $3 1178819
710 2 $a Illinois Institute of Technology. $b Mechanical, Materials and Aerospace Engineering. $3 1180353
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=10606995 $z click for full text (PQDT)