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Deformation twinning and the role of stacking fault energy during cryogenic testing of Ni-based superalloy 625
Laboratory for Mechanics of Microstructures, Department of Metallurgical and Materials Engineering, IIT Madras, Chennai, India.ORCID iD: 0000-0003-0978-5089
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, Faculty of Science & Engineering. Alleima, Sandviken, Sweden.
Alleima, Sandviken, Sweden.
Alleima, Sandviken, Sweden.
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2024 (English)In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 898, article id 146404Article in journal (Refereed) Published
Abstract [en]

Ni-based superalloys play a crucial role in various high-temperature applications, where their exceptional mechanical properties and resistance to corrosion are highly desirable. However, their response to low temperatures, especially concerning strain hardening, microstructural evolution, and deformation mechanisms, requires further scrutiny. In this study, we investigate the influence of temperature on the stacking fault energy (SFE) and its implications on deformation twinning in Alloy 625. Uniaxial tensile tests are performed at 298 K, 173 K and 77 K. The study reveals a notable increase in strain hardening at intermediate strain levels, suggesting the activation of a secondary deformation mechanism. To gain deeper insights, crystal plasticity-based simulations using the DAMASK framework are employed, complementing the experimental outcomes. Deformation twins are consistently observed at all temperatures, albeit with a small volume fraction and thickness. The critical strain for twinning decreased with decreasing temperature. Based on the numerous literature studies, experimental and computational observations, the SFE of the material is estimated to be constant over the studied temperature range.

Place, publisher, year, edition, pages
2024. Vol. 898, article id 146404
Keywords [en]
Stacking fault energy, Deformation twinning, Cryogenic testing, Crystal plasticity
National Category
Metallurgy and Metallic Materials
Identifiers
URN: urn:nbn:se:liu:diva-203479DOI: 10.1016/j.msea.2024.146404ISI: 001219293800001OAI: oai:DiVA.org:liu-203479DiVA, id: diva2:1857917
Available from: 2024-05-15 Created: 2024-05-15 Last updated: 2024-05-31Bibliographically approved
In thesis
1. Deformation twinning in corrosion-resistant nickel alloys: with a rising nickel content
Open this publication in new window or tab >>Deformation twinning in corrosion-resistant nickel alloys: with a rising nickel content
2024 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Sanicro 28 and Alloy 625 are corrosion-resistant nickel alloys with a fully austenitic structure and a very low carbon content, which means they are both well suited for cold working. Since the millennium shift deformation twinning has been a live research issue as it enhances strength and ductility simultaneously. As nickel has been pointed out as a high stacking fault energy element and deformation twinning should be promoted by a low stacking fault energy level they have been considered as opposite poles. Nonetheless, it is known since long that deformation twins can emerge in high stacking fault face centred cubic elements at low temperatures.

In this thesis, we have investigated deformation twinning behaviour in corrosion-resistant nickel alloys. The objective is trying to distinguish between deformation twinning in TWIP steel and corrosion resistant nickel alloys regarding for instance size and bundles.

Interrupted uniaxial tensile tests have been performed at several cold working temperatures for the alloys: Sanicro 28 (31% nickel) and Alloy 625 (61% nickel). The microstructure has been characterized in homogeneous deformation volume, by scanning electron microscopy electron backscattering diffraction and electron channelling contrast imaging, transmission electron microscopy and X-ray diffraction. In one investigation fracture behaviour has also been studied with secondary electrons. Ab initio calculations, crystal plasticity modelling and DAMASK simulations have been performed to support emphasizing active deformation mechanisms.

It has been revealed that deformation twinning can occur in high Ni alloys. With increasing deformation twinning levels, the diffuse necking decreases. Ab initio calculations indicates that the initiation of deformation twins cannot be determined solely by the stacking fault energy. Distinct features were discovered at low strains that could be rejected from being neither deformation twins nor stacking faults. Level of texture increases with increasing strain and decreasing temperature and the texture modes are changed with decreasing temperature.

Abstract [sv]

Sanicro 28 och Alloy 625 är två legeringar med ett imponerande korrosionsmotstånd, ett lågt kolinnehåll och en helaustenitisk struktur. Det gör dem väl lämpade för kallbearbetning. Sedan millenieskiftet har aktivten varit mycket hög inom forskningsområdet: deformationstvillingar. TWIP (twinning induced plasticity)-effekten har den så eftertraktade egenskapen att både styrkan och duktiliteten förbättras på samma gång. Eftersom nickel har en hög staplingsfelsenergi och TWIP-effekten har uppmätts/beräknats till att aktiveras vid ett snävt och lågt värde, för densamma, har ett ökande nickelinnehåll och TWIP-effekten setts som direkta motpoler. Trots det, har man länge vetat om att deformationstvillingar också framträder, om än, vid låga temperaturer, i legeringar med kubiskt ytcentrerat gitter och hög staplingsfelsenergi.

I den här avhandlingen har vi undersökt hur deformationstvillingar utvecklas, om de ens kan bildas i korrosionsbeständiga legeringar med ett högt nickelinnehåll. Målet är att se om det finns några större skillnader i tvillingbeteendet i TWIP-stål i jämförelse med korrosionsbeständiga legeringar med ett högt nickelinnehåll. Några egenskaper vi har tänkt att undersöka är: tjocklek på tvillingarna och om tvillingarna bildas i grupper. Vi hoppas på så sätt kunna svara på den övergripande forskningsfrågan: är det möjligt att designa ett rostfritt TWIP-stål, baserat på det vanligaste legeringssystemet för rostfria austenitiska stål, nämligen: järn-krom-nickel?

Enaxliga dragprov har genomförts vid flera kallbearbetningstemperatuer; de har utförts både till brott och till förutbestämda töjningsnivåer. Legeringarna som har testats är: Sanicro 28 (31% nickel) och Alloy 625 (61% nickel). Mikrostrukturen har framför allt karakteriserats i material uttaget från volym där deformationen har varit homogen. De analysmetoder som har använts är: svepelektronmikroskopi, mer specifikt: ”electron backscatter diffraction” och ”electron channelling contrast imaging”. Transmissionselektronmikroskop och röntgendiffraktion har också använts. I en undersökning har också brottbeteende studerats med hjälp av "secondary electrons".

Ab initioberäkningar, modellering av kristallplasticitet och materialbeteende med hjälp av DAMASK har också utförts för att kunna se vilka deformationsmekanismer som är aktiva.

Vi upptäckte att deformationstvillingar faktiskt kan bildas i korrosionsbeständiga legeringar med ett högt nickelinnehåll. Den diffusa midjebildningen minskar på samma gång som andelelen deformationstvillingar ökar.

Ab initioberäkningarnas resultat indikerar också på att deformationstvillingarnas inträde inte enbart kan bestämmas med staplingsfelsenergin.

Tydliga mikrostrukturmönster upptäcktes med hjälp av transmissionsmiroskop och vid låga töjningsnivåer. De mikrostrukturmönstren kunde avfärdas från att vara både deformationstvillingar och staplingsfel. Texturnivån ökar med ökande töjningsnivå och sjunkande temperatur. Typen av textur förändras också med sjunkande temperatur.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2024. p. 43
Series
Linköping Studies in Science and Technology. Licentiate Thesis, ISSN 0280-7971 ; 1998
Keywords
Deformation twinning, Twinning induced plasticity, TWIP, Strain hardening, Corrosion-resistant alloys, Superalloys, Superaustenitic, Superaustenitic stainless steel, Dtacking fault energy, SFE, Microband-induced plasticity
National Category
Metallurgy and Metallic Materials
Identifiers
urn:nbn:se:liu:diva-203478 (URN)10.3384/9789180756877 (DOI)9789180756860 (ISBN)9789180756877 (ISBN)
Presentation
2024-06-12, C3, C Building, Campus Valla, Linköping, 10:15 (English)
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Funding agency: Tube division, Alleima AB

Available from: 2024-05-17 Created: 2024-05-17 Last updated: 2024-05-28Bibliographically approved

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