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Advanced Microstructure Studies of an Austenitic Material Using EBSD in Elevated Temperature In-Situ Tensile Testing in SEM
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology. Sandvik Materials Technology, Sandviken, Sweden.
Linköping University, Department of Management and Engineering, Engineering Materials. Linköping University, The Institute of Technology.
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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. Vol. 592-593, 497-500 p.
Series
Key Engineering Materials, ISSN 1662-9795
Keyword [en]
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: urn:nbn:se:liu:diva-97015DOI: 10.4028/www.scientific.net/KEM.592-593.497ISI: 000336694400111OAI: oai:DiVA.org:liu-97015DiVA: diva2:645026
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
In thesis
1. High-Temperature Behaviour of Austenitic Alloys: Influence of Temperature and Strain Rate on Mechanical Properties and Microstructural Development
Open this publication in new window or tab >>High-Temperature Behaviour of Austenitic Alloys: Influence of Temperature and Strain Rate on Mechanical Properties and Microstructural Development
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:nbn:se:liu:diva-98242 (URN)10.3384/lic.diva-98242 (DOI)LIU-TEK-LIC-2013:53 (Local ID)978-91-7519-512-4 (ISBN)LIU-TEK-LIC-2013:53 (Archive number)LIU-TEK-LIC-2013:53 (OAI)
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
2. On High-Temperature Behaviours of Heat Resistant Austenitic Alloys
Open this publication in new window or tab >>On High-Temperature Behaviours of Heat Resistant Austenitic Alloys
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Advanced heat resistant materials are important to achieve the transition to long term sustainable power generation. The global increase in energy consumption and the global warming from greenhouse gas emissions create the need for more sustainable power generation processes. Biomass-fired power plants with higher efficiency could generate more power but also reduce the emission of greenhouse gases, e.g. CO2. Biomass offers no net contribution of CO2 to the atmosphere. To obtain greater efficiency of power plants, one option is to increase the temperature and the pressure in the boiler section of the power plant. This requires improved material properties, such as higher yield strength, creep strength and high-temperature corrosion resistance, as well as structural integrity and safety.

Today, some austenitic stainless steels are design to withstand temperatures up to 650 °C in tough environments. Nickel-based alloys are designed to withstand even higher temperatures. Austenitic stainless steels are more cost effective than nickel-based alloys due to a lower amount of expensive alloying elements. However, the performance of austenitic stainless steels at the elevated temperatures of future operation conditions in biomass-red power plants is not yet fully understood.

This thesis presents research on the influence of long term high-temperature ageing on mechanical properties, the influence of very slow deformation rates at high-temperature on deformation, damage and fracture, and the influence of high-temperature environment and cyclic operation conditions on the material behaviour. Mechanical and thermal testing have been performed followed by subsequent studies of the microstructure, using scanning electron microscopy, to investigate the material behaviours.

Results shows that long term ageing at high temperatures leads to the precipitation of intermetallic phases. These intermetallic phases are brittle at room temperature and become detrimental for the impact toughness of some of the austenitic stainless steels. During slow strain rate tensile deformation at elevated temperature time dependent deformation and recovery mechanisms are pronounced. The creep-fatigue interaction behaviour of an austenitic stainless steel show that dwell time gives shorter life at a lower strain range, but has none or small effect on the life at a higher strain range.

Finally, this research results in an increased knowledge of the structural, mechanical and chemical behaviour as well as a deeper understanding of the deformation, damage and fracture mechanisms that occur in heat resistant austenitic alloys at high-temperature environments. It is believed that in the long term, this can contribute to material development achieving the transition to more sustainable power generation in biomass-red power plants.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2015. 56 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1725
National Category
Metallurgy and Metallic Materials Materials Engineering
Identifiers
urn:nbn:se:liu:diva-122945 (URN)10.3384/diss.diva-122945 (DOI)978-91-7685-896-7 (ISBN)
Public defence
2015-12-21, ACAS, Hus A, Campus Valla, Linköping, 10:15 (English)
Opponent
Supervisors
Available from: 2015-11-30 Created: 2015-11-30 Last updated: 2016-12-09Bibliographically approved

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Calmunger, MattiasPeng, RuChai, GuocaiJohansson, StenMoverare, Johan

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