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Influence of W in solid solution on the creep rate of nickel
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties.ORCID iD: 0000-0002-4408-9698
KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Properties.ORCID iD: 0000-0002-8494-3983
2019 (English)In: Proceedings Of The Asme Pressure Vessels And Piping Conference, 2018, / [ed] Qian, H; Brongers, M; Uddin, M, ASME International , 2019Conference paper, Published paper (Refereed)
Abstract [en]

Ni and Ni-W binary alloys are basis for nickel based superalloys. For most nickel based superalloys, strengthening mechanisms include both solid solution hardening and precipitation hardening. W is a vital element to create solid solution hardening and to improve the creep strength. In spite of its wide usage to strengthening of high temperature alloys, the mechanisms for solid solution hardening are not fully quantified. From the assumption that it is due to the attraction of solute atoms to dislocations and formation of Cottrell atmosphere to slow down the motion of dislocations, a fundamental model has been formulated previously. In the present paper, the model is expanded by taking the stacking fault energy and strain induced vacancies into account. Important parameters in the model are the variation of the lattice constant and the shear modulus with alloying content. Models for these variations have been formulated as a function of solute content. Another important parameter is the maximum interaction energy between the dislocations and the solutes. The model can satisfactorily predict both the large difference in creep rate between pure Ni and Ni-W alloys and the comparatively smaller differences between the three investigated Ni-2W, Ni-4W and Ni-6W alloys.

Place, publisher, year, edition, pages
ASME International , 2019.
Keywords [en]
LATTICE-PARAMETERS; BEHAVIOR; MODELS
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-248107DOI: 10.1115/PVP2018-84286ISI: 000460998900048Scopus ID: 2-s2.0-85056875021OAI: oai:DiVA.org:kth-248107DiVA, id: diva2:1307734
Conference
ASME 2018 Pressure Vessels and Piping Conference, PVP 2018, Prague, Czech Republic, 15-20 July 2018
Note

Part of proceedings ISBN: 978-0-7918-5167-8

QC 20190429

Available from: 2019-04-29 Created: 2019-04-29 Last updated: 2022-06-26Bibliographically approved
In thesis
1. Creep modeling and first-principles investigation of high-temperature alloys
Open this publication in new window or tab >>Creep modeling and first-principles investigation of high-temperature alloys
2021 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Stainless steels and nickel-based superalloys are materials that have been widely used to manufacture components servicing at high temperatures. Creep strength is one of the most important properties in such conditions. High creep strength generally comes from a combination of solid solution hardening, precipitation hardening and dislocation hardening. However, some details of the mechanism of solid solution hardening are still not fully understood. The present thesis can be separated into two parts.

In the first part, fundamental creep models are used in an investigation of creep rate of nickel-based alloys. The fundamental models are based on dislocation theories without using any adjustable parameters to describe the creep data. All parameters in the models have been derived from experimental data or using computational approaches such as ab initio methods. In the models, the effects of stacking faults, strain-induced vacancies and pipe diffusion have been taken into account. 

W is a vital element to create solid solution hardening and improve creep strength of nickel-based alloys. W readily dissolves in nickel to form a solid solution and to provide a significant effect on the creep strength. Moreover, many ternary and more complex systems of nickel-based alloys are developed starting from Ni-W solid solutions. The developed models can describe the dramatic reduction of the creep rate due to W, which has not been possible in the past. The reduction has a close correlation with the stacking fault energy and drag stress.

In the second part, the exact muffin-tin orbital method combined with the coherent potential approximation has been interfaced with a quasi-harmonic Debye model to predict the elastic and other thermodynamic properties of selected metallic alloys at high temperature. The knowledge of such properties is very useful in modeling the behavior of materials servicing at high temperatures. However, few experimental studies have been focused on measurements of thermo-mechanical properties at such temperatures. Ab initio methods based on density functional theory is an alternative way to obtain information about thermo-mechanical properties. 

Therefore, in the present work, ab initio based studies of the elastic and thermodynamic properties of pure nickel, nickel-based solid solutions and Fe25Cr20NiMnNb austenitic stainless steel have been performed. Although the modeling technique cannot fully reproduce the temperature dependencies in some of the considered cases where experimental data are available, the computed values of such properties as shear moduli, thermal expansion coefficients and entropy are close to the experimentally derived values.

Abstract [sv]

Rostfria stål och nickelbaserade superlegeringar används i stor utsträckning för att tillverka komponenter som utnyttjas vid höga temperaturer. Kryphållfastheten är en viktig egenskap i dessa tillämpningar. En hög kryphållfasthet år i allmänhet resultatet av en kombination av bidrag från fast lösning, partiklar och dislokationer. Vissa aspekter av lösningshärdning är inte klarlagda tidigare. Denna avhandling utgörs av två delar.

I den första delen används grundläggande krypmodeller för att undersöka kryphastigheten hos nickelbaslegeringar. De grundläggande modellerna är baserad på dislokationsteorier och inga justerbara storheter användes för att beskriva krypdata. Alla parametrar i modellen härleds från experimentella data eller med beräkningsmetoder som ab initio. I modellen beaktas effekter av staplingsfel, deformationsinducerade vakanser och diffusion längs dislokationer. I avhandlingen visas att de har stor inverkan på krypbeteendet hos nickelbaslegeringar. 

W har visats vara ett viktigt element för att skapa lösningshärdning och höja kryphållfastheten. Många ternära och mer komplexa nickelbaslegeringar är baserade Ni-W-lösningar. Modellerna i avhandlingen kan beskriva hur W dramatiskt minskar kryphastigheten bl.a. på grund av inverkan av staplingsfelsenergin.

I den andra delen görs beräkningar för egenskaper av betydelsen för kryphållfasthet med hjälp av ab initio metoder. Den exakta muffin-tenn-orbitalmetoden har kombinerats med den koherenta potentialapproximationen och en kvasi-harmonisk Debye-modell för att förutsäga elastiska och termodynamiska egenskaper vid höga temperaturer. Med hjälp av ab initio metoder kan värden för egenskaper erhållas där experimentalla data saknas. 

I avhandlingen studeras elastiska och termodynamiska egenskaper med hjälp av ab initio metoder hos ren nickel, nickelbaserade fasta lösningar och Fe25Cr20NiMnNb austenitiskt rostfritt stål. Även om modellerna inte kan reproducera temperaturberoendet i alla behandlade fall, så har värdena för skjuvmodulen, värmeutvidgningskoefficienten och entropi erhållits, som ligger nära dem från experimentella observationer.

Place, publisher, year, edition, pages
Stockholm, Sweden: KTH Royal Institute of Technology, 2021. p. 223
Series
TRITA-ITM-AVL ; 2021:4
Keywords
Austenitic stainless steels, Nickel-based superalloys, Fundamental creep models, EMTO-CPA method, Quasi-harmonic Debye model, Thermo-mechanical properties, High temperatures.
National Category
Materials Engineering
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-290595 (URN)978-91-7873-786-4 (ISBN)
Public defence
2021-03-15, https://kth-se.zoom.us/j/66589542927, Stockholm, 09:00 (English)
Opponent
Supervisors
Available from: 2021-02-22 Created: 2021-02-19 Last updated: 2022-06-25Bibliographically approved

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Zhang, JingSandström, Rolf

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