| 1. |
- Lundberg, Mattias, et al.
(författare)
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In-situ SEM/EBSD Study of Deformation adn Fracture Behaviour of Flake Cast Iron
- 2013
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Konferensbidrag (refereegranskat)abstract
- Cast irons’ position as an important engineering material is un-disputed. They are widely used in many important industrial applications such as the automotives and workshop machinery. Nevertheless, fracture mechanisms in cast irons are not fully understood. In this study the fracture path and non-linear elastic behaviour of a fully pearlitic flake cast iron under uniaxial tensile loading have been investigated in a Scanning Electron Microscope (SEM) equipped with an Electron Backscattering Diffraction (EBSD) detector. The tensile load was applied via a specially made sample stage. Under uniaxial tensile loading the graphite flakes act as notches or cracks and therefore the fracture process starts at one or many graphite tips. The crack can propagate in many different ways, at the graphite and matrix interface, through the graphite, at the interface between cementite and ferrite or through the pearlitic grains. At the point where the stress strain curve deviates from its linear path plastic deformation at graphite tips can be noticed. Interface cracking between graphite and the matrix also starts at this point.
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| 2. |
- Calmunger, Mattias, et al.
(författare)
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Advanced Microstructure Studies of an Austenitic Material Using EBSD in Elevated Temperature In-Situ Tensile Testing in SEM
- 2014
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 3. |
- Calmunger, Mattias, et al.
(författare)
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Damage and Fracture Behaviours in Advanced Heat Resistant Materials During Slow Strain Rate Test at High Temperature
- 2013
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- As a renewable energy resource, biomass or biomass co-firing in coal-fired power plants with high efficiency are desired which corresponding to elevated temperature and high pressure. An upgrade of the material performance to austenitic stainless steels is therefore required in order to meet the increased demands due to the higher temperature and the more corrosive environment. These materials suffer from creep and fatigue damage during the service. In this study, these behaviours are evaluated using slow strain rate testing (SSRT) with strain rate down to 1*10-6/s at temperature up to 700°C. The influence of temperature and strain rate on strength and ductility in one austenitic stainless steel and one nickel base alloys are investigated. The damage and fracture due to the interaction between moving dislocations and precipitates are studied using electron channelling contrast imaging (ECCI) and electron backscattering diffraction (EBSD). The deformation and damage mechanisms active during SSRT are essentially the same as under creep. The influence of dynamic strain ageing (DSA) phenomena that appears in the tested temperature and strain rate regime is also discussed, DSA is intensified by increased temperature and decreased strain rate.
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| 4. |
- Calmunger, Mattias, et al.
(författare)
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Damage and Fracture Behaviours in Aged Austentic Materials During High-Temperature Slow Strain Rate Testing
- 2014
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 5. |
- Calmunger, Mattias, et al.
(författare)
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Deformation behaviour in advanced heat resistant materials during slow strain rate testing at elevated temperature
- 2014
-
Ingår i: Theoretical and Applied Mechanics Letters. - : American Institute of Physics (AIP). - 2095-0349. ; 4:041004
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Tidskriftsartikel (refereegranskat)abstract
- In this study, slow strain rate tensile testing at elevated temperature is used to evaluate the influence of temperature and strain rate on deformation behaviour in two different austenitic alloys. One austenitic stainless steel (AISI 316L) and one nickel-base alloy (Alloy 617) have been investigated. Scanning electron microscopy related techniques as electron channelling contrast imaging and electron backscattering diffraction have been used to study the damage and fracture micromechanisms. For both alloys the dominante damage micromechanisms are slip bands and planar slip interacting with grain bounderies or precipitates causing strain concentrations. The dominante fracture micromechanism when using a slow strain rate at elevated temperature, is microcracks at grain bounderies due to grain boundery embrittlement caused by precipitates. The decrease in strain rate seems to have a small influence on dynamic strain ageing at 650°C.
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| 6. |
- Calmunger, Mattias
(författare)
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High-Temperature Behaviour of Austenitic Alloys : Influence of Temperature and Strain Rate on Mechanical Properties and Microstructural Development
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 7. |
- Calmunger, Mattias, et al.
(författare)
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Influence of deformation rate on mechanical response of an AISI 316L austenitic stainless steel
- 2014
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Ingår i: Advanced Materials Research. - : Trans Tech Publications Inc.. - 1022-6680 .- 1662-8985. ; 922, s. 49-54
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 8. |
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| 9. |
- Calmunger, Mattias, et al.
(författare)
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Influence of High Temperature Ageing on the Toughness of Advanced Heat Resistant Materials
- 2013
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Konferensbidrag (refereegranskat)abstract
- 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.
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| 10. |
- Calmunger, Mattias, et al.
(författare)
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Mechanical Behaviours of Alloy 617 with Varied Strain Rate at High Temperatures
- 2014
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Ingår i: Materials Science Forum. - : Trans Tech Publications Ltd. - 0255-5476 .- 1662-9752. ; 783-786, s. 1182-1187, s. 1182-1187
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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