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High-Temperature Behaviour of Austenitic Alloys: Influence of Temperature and Strain Rate on Mechanical Properties and Microstructural Development
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
2013 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The global increase in energy consumption and the global warming from greenhouse gas emission creates the need for more environmental friendly energy production processes. Biomass power plants with higher efficiency could generate more energy but also reduce the emission of greenhouse gases, e.g. CO2. Biomass is the largest global contributor to renewable energy and offers no net contribution of CO2 to the atmosphere. One way to increase the efficiency of the power plants is to increase temperature and pressure in the boiler parts of the power plant.

The materials used for the future biomass power plants, with higher temperature and pressure, require improved properties, such as higher yield strength, creep strength and high-temperature corrosion resistance. Austenitic stainless steels and nickel-base alloys have shown good mechanical and chemical properties at the operation temperatures of today’s biomass power plants. However, the performance of austenitic stainless steels at the future elevated temperatures is not fully understood.

The aim of this licentiate thesis is to increase our knowledge about the mechanical performance of austenitic stainless steels at the demanding conditions of the new generation power plants. This is done by using slow strain rate tensile deformation at elevated temperature and long term hightemperature ageing together with impact toughness testing. Microscopy is used to investigate deformation, damage and fracture behaviours during slow deformation and the long term influence of temperature on toughness in the microstructure of these austenitic alloys. Results show that the main deformation mechanisms are planar dislocation deformations, such as planar slip and slip bands. Intergranular fracture may occur due to precipitation in grain boundaries both in tensile deformed and impact toughness tested alloys. The shape and amount of σ-phase precipitates have been found to strongly influence the fracture behaviour of some of the austenitic stainless steels. In addition, ductility is affected differently by temperature depending on alloy tested and dynamic strain ageing may not always lead to a lower ductility.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2013. , 34 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1619
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:liu:diva-98242DOI: 10.3384/lic.diva-98242Local ID: LIU-TEK-LIC-2013:53ISBN: 978-91-7519-512-4 (print)OAI: oai:DiVA.org:liu-98242DiVA: diva2:653417
Presentation
2013-11-01, ACAS, Hus A, Campus Valla, Linköpings universitet, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2013-10-04 Created: 2013-10-04 Last updated: 2013-10-07Bibliographically approved
List of papers
1. Deformation and damage behaviours of austenitic alloys in the dynamic strain ageing regime
Open this publication in new window or tab >>Deformation and damage behaviours of austenitic alloys in the dynamic strain ageing regime
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Deformation and damage behaviours influenced by dynamic strain ageing (DSA) in three austenitic stainless steels and two nickel-base alloys have been investigated using tensile tests at elevated temperatures. The deformation and damage behaviours have been analysed using electron channeling contrast imaging and electron backscatter diffraction. The results from this study show that DSA not always reduce ductility, in fact for some materials the ductility can increase in the DSA regime. This is attributed to the formation of nano twins by DSA stimulated twinning induced plasticity. Damage mechanisms due to DSA were also investigated and discussed.

Keyword
Dynamic strain ageing, austenitic stainless steel, nickel-base alloy, TWIP, damage
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-98239 (URN)
Available from: 2013-10-04 Created: 2013-10-04 Last updated: 2013-10-04Bibliographically approved
2. Influence of deformation rate on mechanical response of an AISI 316L austenitic stainless steel
Open this publication in new window or tab >>Influence of deformation rate on mechanical response of an AISI 316L austenitic stainless steel
2014 (English)In: Advanced Materials Research, ISSN 1022-6680, E-ISSN 1662-8985, Vol. 922, 49-54 p.Article in journal (Refereed) Published
Abstract [en]

Austenitic stainless steels are often used for components in demanding environment. These materials can withstand elevated temperatures and corrosive atmosphere like in energy producing power plants. They can be plastically deformed at slow strain rates and high alternating or constant tensile loads such as fatigue and creep at elevated temperatures. This study investigates how deformation rates influence mechanical properties of an austenitic stainless steel. The investigation includes tensile testing using strain rates of 2*10-3/ and 10-6/s at elevated temperatures up to 700°C. The material used in this study is AISI 316L. When the temperature is increasing the strength decreases. At a slow strain rate and elevated temperature the stress level decreases gradually with increasing plastic deformation probably due to dynamic recovery and dynamic recrystallization. However, with increasing strain rate elongation to failure is decreasing. AISI 316L show larger elongation to failure when using a strain rate of 10-6/s compared with 2*10-3/s at each temperature. Electron channelling contrast imaging is used to characterize the microstructure and discuss features in the microstructure related to changes in mechanical properties. Dynamic recrystallization has been observed and is related to damage and cavity initiation and propagation.

Place, publisher, year, edition, pages
Trans Tech Publications Inc., 2014
Keyword
Austenitic stainless steel, elevated temperature, ageing, dynamic recrystallization
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-98240 (URN)10.4028/www.scientific.net/AMR.922.49 (DOI)
Conference
THERMEC '2013, International Conference on Processing & Manufacturing of Advanced Materials. Processeing, Fabrication, Properties, Applications. December 2-6, Las Vegas, USA
Available from: 2013-10-04 Created: 2013-10-04 Last updated: 2017-12-06Bibliographically approved
3. Mechanical Behaviours of Alloy 617 with Varied Strain Rate at High Temperatures
Open this publication in new window or tab >>Mechanical Behaviours of Alloy 617 with Varied Strain Rate at High Temperatures
2014 (English)In: Materials Science Forum, ISSN 0255-5476, E-ISSN 1662-9752, Vol. 783-786, 1182-1187 p.Article in journal (Refereed) Published
Abstract [en]

Nickel-base alloys due to their high performances have been widely used in biomass and coal fired power plants. They can undertake plastic deformation with different strain rates such as those typically seen during creep and fatigue at elevated temperatures. In this study, the mechanical behaviours of Alloy 617 with strain rates from 10-2/s down to 10-6/s at temperatures of 650°C and 700°C have been studied using tensile tests. Furthermore, the microstructures have been investigated using electron backscatter detection and electron channeling contrast imaging. At relatively high strain rate, the alloy shows higher fracture strains at these temperatures. The microstructure investigation shows that it is caused by twinning induced plasticity due to DSA. The fracture strain reaches the highest value at a strain rate of 10-4/s and then it decreases  dramatically. At strain rate of 10-6/s, the fracture strain at high temperature is now smaller than that at room temperature, and the strength also decreases with further decreasing strain rate. Dynamic recrystallization can also be observed usually combined with crack initiation and propagation. This is a new type of observation and the mechanisms involved are discussed.

Keyword
Nickel-base superalloy, twinning, Dynamic strain ageing, elevated temperature
National Category
Engineering and Technology Materials Engineering
Identifiers
urn:nbn:se:liu:diva-98241 (URN)10.4028/www.scientific.net/MSF.783-786.1182 (DOI)
Conference
THERMEC '2013, International Conference on Processing & Manufacturing of Advanced Materials. Processing, Fabrication, Properties, Applications. December 2-6, Las Vegas, USA
Available from: 2013-10-04 Created: 2013-10-04 Last updated: 2017-12-06Bibliographically approved
4. Damage and Fracture Behaviours in Aged Austentic Materials During High-Temperature Slow Strain Rate Testing
Open this publication in new window or tab >>Damage and Fracture Behaviours in Aged Austentic Materials During High-Temperature Slow Strain Rate Testing
2014 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Biomass power plants with high efficiency are desired as a renewable energy resource. High efficiency can be obtained by increasing temperature and pressure. An upgrade of the material performance to high temperature material is therefore required in order to meet the increased demands due to the higher temperature and the more corrosive environment. In this study, the material’s high-temperature behaviours of AISI 304 and Alloy617 under slow deformation rate are evaluated using high-temperature long-term aged specimens subjected to slow strain rate tensile testing (SSRT) with strain rates down to 10-6/s at 700°C. Both materials show decreasing stress levels and elongation to fracture when tensile deformed using low strain rate and elevated temperature. At high-temperature and low strain rates cracking in grain boundaries due to larger precipitates formed during deformation is the most common fracture mechanism.

Place, publisher, year, edition, pages
Trans Tech Publications Inc., 2014
Series
Key Engineering Materials, ISSN 1662-9795
Keyword
High-temperature, ageing, slow strain rate, biomass power plant, austenitic stainless steel, nickel base alloy and dynamic strain ageing
National Category
Materials Engineering
Identifiers
urn:nbn:se:liu:diva-96028 (URN)10.4028/www.scientific.net/KEM.592-593.590 (DOI)000336694400133 ()
Conference
MSMF7 Materials Structure & Micromechanics of Fracture , July 13, Brno, Czech Republic
Available from: 2013-08-13 Created: 2013-08-13 Last updated: 2015-11-30Bibliographically approved
5. Advanced Microstructure Studies of an Austenitic Material Using EBSD in Elevated Temperature In-Situ Tensile Testing in SEM
Open this publication in new window or tab >>Advanced Microstructure Studies of an Austenitic Material Using EBSD in Elevated Temperature In-Situ Tensile Testing in SEM
Show others...
2014 (English)Conference paper, Published paper (Refereed)
Abstract [en]

In this study an advanced method for investigation of the microstructure such as electron backscatter diffraction (EBSD) together with in-situ tensile test in a scanning electron microscope (SEM) has been used at room temperature and 300°C. EBSD analyses provide information about crystallographic orientation in the microstructure and dislocation structures caused by deformation. The in-situ tensile tests enabled the same area to be investigated at different strain levels. For the same macroscopic strain values a lower average misorientation in individual grains at elevated temperature indicates that less residual strain at grain level are developed compared to room temperature. For both temperatures, while large scatters in grain average misorientation are observed for grains of similar size, there seems to be a tendency showing that larger grains may accumulate somewhat more strains.

Place, publisher, year, edition, pages
Trans Tech Publications Inc., 2014
Series
Key Engineering Materials, ISSN 1662-9795
Keyword
Austenitic stainless steel, electron backscatter diffraction, in-situ tensile test, Schmid factor, grain wsize and slip system
National Category
Engineering and Technology Materials Engineering
Identifiers
urn:nbn:se:liu:diva-97015 (URN)10.4028/www.scientific.net/KEM.592-593.497 (DOI)000336694400111 ()
Conference
MSMF7 Materials Structure & Micromechanics of Fracture, July 1-3, Brno, Czech Republic
Available from: 2013-09-03 Created: 2013-09-03 Last updated: 2015-11-30Bibliographically approved
6. Influence of High Temperature Ageing on the Toughness of Advanced Heat Resistant Materials
Open this publication in new window or tab >>Influence of High Temperature Ageing on the Toughness of Advanced Heat Resistant Materials
2013 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Advanced biomass, biomass co-firing in coal-fired and future advanced USC coal-fired power plants with high efficiency require the materials to be used at even higher temperature under higher pressure. The reliability and integrity of the material used are therefore of concern. In this study, the influence of ageing at temperatures up to 700°C for up to 3 000 hours on the toughness of two advanced heat resistant austenitic steels and one nickel alloy are investigated. The influence on toughness due to differences in the chemical composition as well as the combined effect of precipitation and growth of the precipitates has been analysed by using SEM techniques. The fracture mechanisms that are active for the different ageing treatments are identified as a function of temperature and time. Local approach methods are used to discuss the influence of the precipitation and growth of precipitates on the toughness or fracture in  the different aged materials.

Keyword
high-temperature, ageing, toughness, austnitic stainless steel, incke base alloy
National Category
Engineering and Technology Materials Engineering
Identifiers
urn:nbn:se:liu:diva-95440 (URN)
Conference
13th International Conference on Fracture (ICF13), June 16-21, Beijing, China
Available from: 2013-07-03 Created: 2013-07-03 Last updated: 2013-12-13Bibliographically approved

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  • Other style
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  • Other locale
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Output format
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