| 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. |
- Lundberg, Mattias, 1985-
(författare)
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Residual stresses, fatigue and deformation in cast iron
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The complex geometry of cylinder heads in heavy-duty diesel engines makes grey iron or compact graphite iron a preferred material choice due to its price, castability, thermal conductivity and damping capacity. Today’s strict emission laws have increased the demands on engine performance and engine efficiency. This means that material properties such as fatigue resistance need to be improved. Shot peening is often used to improve the fatigue resistance of components and the benefits of shot peening are associated with the induced compressive surface stresses and surface hardening. How different shot peening parameters can affect fatigue strength of grey and compact graphite iron has been investigated within the project underlying this thesis. To do this, X-ray diffraction (XRD) was utilized for residual stress measurements, scanning electron microscopy (SEM) for microstructural characterizations and mechanical fatigue testing for mechanical quantifications. The ultimate aim of this work has been to increase the fatigue resistance of cast iron by residual stress optimization.XRD measurements and SEM examinations revealed that the shot peening parameters shot size and peening intensity significantly influence residual stresses and surface deformation. Residual stress profiles, similar to the one general considered to improve the fatigue strength in steels, were obtained for both grey and compact graphite iron. Uniaxial push-pull fatigue testing on grey iron with these shot peening parameters reduced the fatigue strength with 15–20 %. The negative effect is likely related to surface damage associated with over peening and relatively high subsurface tensile residual stresses. With very gentle shot peening parameters, the uniaxial fatigue strength were unaltered from the base material but when subjected to bending fatigue an increase in fatigue strength were observed. An alternative way to increase the fatigue strength was to conduct a 30 min annealing heat treatment at 285 XC which increased the fatigue strength by almost 10 % in uniaxial loading. The improvement could be an effect of favourable precipitates forming during the annealing, which could hinder dislocation movement during fatigue.Measuring residual stresses using XRD and the sin2 -method demands accurate X-ray elastic constants (XEC) for meticulous stress analysis. The XEC referred to as 1~2s2 should therefore always be calibrated for the specific material used. The experiments conducted revealed that the XEC value is independent of the testing method used in this work. A small correction from the theoretical value should be applied when the material contains small amounts of residual stresses. The amount of residual stresses has a great impact on the XEC and thus on the stress analysis. Concluding that proper analysis of residual stresses in cast iron is not straight forward.
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| 3. |
- Lundberg, Mattias, et al.
(författare)
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Surface Integrity and Fatigue Behaviour of Electric Discharged Machined and Milled Austenitic Stainless Steel
- 2017
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Ingår i: Materials Characterization. - : Elsevier. - 1044-5803 .- 1873-4189. ; 124, s. 215-222
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Tidskriftsartikel (refereegranskat)abstract
- Machining of austenitic stainless steels can result in different surface integrities and different machining process parameters will have a great impact on the component fatigue life. Understanding how machining processes affect the cyclic behaviour and microstructure are of outmost importance in order to improve existing and new life estimation models. Milling and electrical discharge machining (EDM) have been used to manufacture rectangular four-point bend fatigue test samples; subjected to high cycle fatigue. Before fatigue testing, surface integrity characterisation of the two surface conditions was conducted using scanning electron microscopy, surface roughness, residual stress profiles, and hardness profiles. Differences in cyclic behaviour were observed between the two surface conditions by the fatigue testing. The milled samples exhibited a fatigue limit. EDM samples did not show the same behaviour due to ratcheting. Recrystallized nano sized grains were identified at the severely plastically deformed surface of the milled samples. Large amounts of bent mechanical twins were observed ~ 5 μm below the surface. Grain shearing and subsequent grain rotation from milling bent the mechanical twins. EDM samples showed much less plastic deformation at the surface. Surface tensile residual stresses of ~ 500 MPa and ~ 200 MPa for the milled and EDM samples respectively were measured.
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| 4. |
- Azeez, Ahmed, et al.
(författare)
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Characterisation of Deformation and Damage in a Steam Turbine Steel Subjected to Low Cycle Fatigue
- 2019
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Ingår i: Structural Integrity Procedia. - : Elsevier BV. ; , s. 155-160
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Konferensbidrag (refereegranskat)abstract
- The increased use of renewable energy pushes steam turbines toward a more frequent operation schedule. Consequently, components must endure more severe fatigue loads which, in turn, requires an understanding of the deformation and damage mechanisms under high-temperature cyclic loading. Based on this, low cycle fatigue tests were performed on a creep resistant steel, FB2, used in ultra-supercritical steam turbines. The fatigue tests were performed in strain control with 0.8-1.2 % strain range and at temperatures of 400 °C and 600 °C. The tests at 600 °C were run with and without dwell time. The deformation mechanisms at different temperatures and strain ranges were characterised by scanning electron microscopy and by quantifying the amount of low angle grain boundaries. The quantification of low angle grain boundaries was done by electron backscatter diffraction. Microscopy revealed that specimens subjected to 600 °C showed signs of creep damage, in the form of voids close to fracture surface, regardless of whether the specimen had been exposed to dwell time or been purely cycled. In addition, the amount of low angle grain boundaries was lower at 600 °C than at 400 °C. The study indicates that a significant amount of the inelastic strain comes from creep strain as opposed to being all plastic strain.
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| 5. |
- Azeez, Ahmed, et al.
(författare)
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Low cycle fatigue life modelling using finite element strain range partitioning for a steam turbine rotor steel
- 2020
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Ingår i: Theoretical and applied fracture mechanics (Print). - : Elsevier. - 0167-8442 .- 1872-7638. ; 107
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Tidskriftsartikel (refereegranskat)abstract
- Materials made for modern steam power plants are required to withstand high temperatures and flexible operational schedule. Mainly to achieve high efficiency and longer components life. Nevertheless, materials under such conditions experience crack initiations and propagations. Thus, life prediction must be made using accurate fatigue models to allow flexible operation. In this study, fully reversed isothermal low cycle fatigue tests were performed on a turbine rotor steel called FB2. The tests were done under strain control with different total strain ranges and temperatures (20 °C to 625 °C). Some tests included dwell time to calibrate the short-time creep behaviour of the material. Different fatigue life models were evaluated based on total life approach. The stress-based fatigue life model was found unusable at 600 °C, while the strain-based models in terms of total strain or inelastic strain amplitudes displayed inconsistent behaviour at 500 °C. To construct better life prediction, the inelastic strain amplitudes were separated into plastic and creep components by modelling the deformation behaviour of the material, including creep. Based on strain range partitioning approach, the fatigue life depends on different damage mechanisms at different strain ranges at 500 °C. This allows for the formulation of life curves based on either plasticity-dominated damage or creep-dominated damage. At 600 °C, creep dominated while at 500 °C creep only dominates for higher strain ranges. The deformation mechanisms at different temperatures and total strain ranges were characterised by scanning electron microscopy and by quantifying the amount of low angle grain boundaries. The quantification of low angle grain boundaries was done by electron backscatter diffraction. Microscopy revealed that specimens subjected to 600 °C showed signs of creep damage in the form of voids close to the fracture surface. In addition, the amount of low angle grain boundaries seems to decrease with the increase in temperature even though the inelastic strain amplitude was increased. The study indicates that a significant amount of the inelastic strain comes from creep strain as opposed of being all plastic strain, which need to be taken into consideration when constructing a life prediction model.
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| 6. |
- Azeez, Ahmed, et al.
(författare)
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Low Cycle Fatigue Modelling of Steam Turbine Rotor Steel
- 2019
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Ingår i: 9th International Conference Materials Structure & Micromechanics of Fracture (MSMF9). - : Elsevier. ; , s. 149-154, s. 149-154
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Konferensbidrag (refereegranskat)abstract
- Materials in steam turbine rotors are subjected to cyclic loads at high temperature, causing cracks to initiate and grow. To allow for more flexible operation, accurate fatigue models for life prediction must not be overly conservative. In this study, fully reversed low cycle fatigue tests were performed on a turbine rotor steel called FB2. The tests were done isothermally, within temperature range of room temperature to 600 °C, under strain control with 0.8-1.2 % total strain range. Some tests included hold time to calibrate the short-time creep behaviour of the material. Different fatigue life models were constructed. The life curve in terms of stress amplitude was found unusable at 600 °C, while the life curve in terms of total strain or inelastic strain amplitudes displayed inconsistent behaviour at 500 °C. To construct better life model, the inelastic strain amplitudes were separated into plastic and creep components by modelling the deformation behaviour of the material, including creep. Based on strain range partitioning approach, the fatigue life depends on different damage mechanisms at different strain ranges. This allowed the formulation of life curves based on plasticity or creep domination, which showed creep domination at 600 °C, while at 500 °C, creep only dominates for higher strain range.
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| 7. |
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| 8. |
- 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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| 9. |
- Calmunger, Mattias, et al.
(författare)
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Characterisation of creep deformation during slow strain rate tensile testing
- 2015
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The strain-rate dependent deformation of the superalloy Haynes 282 during slow strain-rate tensile testing (SSRT) at 700 C has been investigated. The stress-strain response is remarkably well described by a simple constitutive model over a wide range of different strain-rates. The microstructure development is characterised and related to the influence of both strainrate dependent and independent deformation. Damage and cracking similar to what has been observed previously during conventional creep testing of Haynes 282 was found and explained. The model and the microstructure investigations show that the deformation and damage mechanisms during SSRT are essentially the same as under creep.
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| 10. |
- Calmunger, Mattias, et al.
(författare)
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Characterization of austenitic stainless steels deformed at elevated temperature
- 2017
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Ingår i: Metallurgical and Materials Transactions. A. - : Springer-Verlag New York. - 1073-5623 .- 1543-1940. ; 48A:10, s. 4525-4538
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Tidskriftsartikel (refereegranskat)abstract
- Highly alloyed austenitic stainless steels are promising candidates to replace more expansive nickel-based alloys within the energy-producing industry. The present study investigates the deformation mechanisms by microstructural characterisation, mechanical properties and stress-strain response of three commercial austenitic stainless steels and two commercial nickel-based alloys using uniaxial tensile tests at elevated temperatures from 400 C up to 700 C. The materials showed different influence of temperature on ductility, where the ductility at elevated temperatures increased with increasing nickel and solid solution hardening element content. The investigated materials showed planar dislocation driven deformation at elevated temperature. Scanning electron microscopy showed that deformation twins were an active deformation mechanism in austenitic stainless steels during tensile deformation at elevated temperatures up to 700 C.
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| 11. |
- Calmunger, Mattias, et al.
(författare)
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Creep and Fatigue Interaction Behavior in Sanicro 25 Heat Resistant Austenitic Stainless Steel
- 2016
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Ingår i: Transactions of the Indian Institute of Metals. - : Springer. - 0972-2815 .- 0975-1645. ; 69:2, s. 337-342
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Tidskriftsartikel (refereegranskat)abstract
- Sanicro 25 is a newly developed advanced high strength heat resistant austenitic stainless steel. The material shows good resistance to steam oxidation and flue gas corrosion, and has higher creep rupture strength than other austenitic stainless steels available today. It is thus an excellent candidate for superheaters and reheaters for advanced ultra-super critical power plants with efficiency higher than 50 %. This paper provides a study on the creep–fatigue interaction behavior of Sanicro 25 at 700 °C. Two strain ranges, 1 and 2 %, and two dwell times, 10 and 30 min, were used. The influences of dwell time on the cyclic deformation behavior and life has been evaluated. Due to stress relaxation the dwell time causes a larger plastic strain range compared to the tests without dwell time. The results also show that the dwell time leads to a shorter fatigue life for the lower strain range, but has no or small effect on the life for the higher strain range. Fracture investigations show that dwell times result in more intergranular cracking. With the use of the electron channeling contrast imaging technique, the influences of dwell time on the cyclic plastic deformation, precipitation behavior, recovery phenomena and local plasticity exhaustion have also been studied.
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| 12. |
- 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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| 13. |
- 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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| 14. |
- Calmunger, Mattias, et al.
(författare)
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Deformation and damage behaviours of austenitic alloys in the dynamic strain ageing regime
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 15. |
- 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
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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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| 16. |
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| 17. |
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| 18. |
- 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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| 19. |
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| 20. |
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| 21. |
- 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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| 22. |
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| 23. |
- 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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| 24. |
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| 25. |
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| 26. |
- 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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| 27. |
- Calmunger, Mattias, 1986-
(författare)
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On High-Temperature Behaviours of Heat Resistant Austenitic Alloys
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 28. |
- Calmunger, Mattias, et al.
(författare)
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Surface Phase Transformation in Austenitic Stainless Steel Induced by Cyclic Oxidation in Humidified Air
- 2015
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Ingår i: Corrosion Science. - : Pergamon Press. - 0010-938X .- 1879-0496. ; 100, s. 524-534
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Tidskriftsartikel (refereegranskat)abstract
- The formation of α’ martensite at the surface of an AISI 304 stainless steel subjected to cyclic heating in humidified air is reported. The α’ martensite formed during the cooling part of the cyclic tests due to local depletion of Cr and Mn and transformed back to austenite when the temperature again rose to 650 °C. The size of the α’ martensite region increased with increasing number of cycles. Thermodynamical simulations were used as basis for discussing the formation of α’ martensite. The effect of the α’ martensite on corrosion is also discussed.
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| 29. |
- Calmunger, Mattias, 1986-
(författare)
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Temperaturpåverkan på egenskaperna hos högtemperaturtåliga austenitiska rostfria stål KME 701
- 2018
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Rapport (refereegranskat)abstract
- Den globala ökningen av energianvändning och sammanhängande ökning i CO2-utsläpp vid förbränning har skärpt kraven på energileverantörer att i större utsträckning använda hållbara biobränslen samt att höja verkningsgraden på energiomvandlingsprocesserna. Detta kan uppnås genom att höja tryck och temperatur i biomasseldade förbränningspannor. Sådana omställningar leder oftast till nya utmaningar kopplade till materialegenskaper. I framtiden kommer behovet av reglerkraft att öka för att kompensera för väderbaserade energianläggningar, såsom sol- och vindkraft. Detta leder till att anläggningarna måste stoppas och startas betydlig oftare än nu. Det skapar ett behov av provningsmetoder som tar hänsyn till cykliska mekaniska och temperaturbaserade laster. Tillsammans med att framtidens material måste tåla högre temperaturer och tuffare miljöer, relaterat till bränsleflexibiliteten, innebär detta att befintliga austenitiska rostfria stål måste förbättras. Inte bara genom en ökning av andelen nickel och andra verksamma legeringselement utan även genom att generera ny kunskap om hur de mekaniska egenskaperna påverkas av den tuffare högtemperatursmiljön.Syftet med detta projekt var att utvärdera mekaniska beteenden relaterade till kombinerad cyklisk och statisk belastning, långtidsåldring samt cyklisk mekanisk och temperaturbelastning vid höga temperaturer. Detta uppnåddes genom att:Utvärdera kryp-utmattningsinteraktion beteendet hos pannmaterial.Utvärdera den strukturella stabiliteten hos de austenitiska rostfria stålen efter långtidsåldring vid hög temperatur.Utvärdera termomekaniska utmattningsegenskaper hos pannmaterial.Utvärdera spänningsrelaxation sprickningsbeteenden hos pannmaterial.Mekanisk provning enligt ovan har utförts och analyserats vid Linköpings universitet samt Sandvik Materials Technology för att få en ökad förståelse för hur mekaniska egenskaper påverkas av den tuffare högtemperatursmiljön som framtidens biomasseldade pannor utgör. Detta kan användas i materialutveckling samt vidare för att förbättra konstruktionen av framtidens biomasseldade pannor.Resultaten visade att:De undersökta pannmaterialen uppvisar kryp-utmattningsinteraktion skador och längre cykliskt liv är relaterat till högt krypmotstånd.Austenitiska rostfria stål uppvisar försprödning på grund av intermetalliska utskiljningar efter långtidsåldring vid höga temperaturer.De austenitiska rostfria stålen med högst högtemperaturshållfasthet uppvisade bäst termomekaniska utmattningsegenskaper.Mer metodutveckling och undersökning krävs för att utvärdera spänningsrelaxation sprickningsbeteendet hos pannmaterialen.
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| 30. |
- Calmunger, Mattias, 1986-, et al.
(författare)
-
Thermomechanical Fatigue of Heat Resistant Austenitic Alloys
- 2023
-
Ingår i: Procedia Structural Integrity. - : Elsevier. - 2452-3216. ; 43, s. 130-135
-
Tidskriftsartikel (refereegranskat)abstract
- Rising global energy consumption and the increase in emissions of greenhouse gases (e.g. CO2) causing global warming, make need for more sustainable power generation. This could be accomplished by increasing the efficiency of the biomass-fired power plants, which is achieved by increasing the temperature and pressure. In addition, flexible generation of power is critical if only renewable power generation is to be achieved and this will increase the number of start-and stop cycles. Cyclic condition in a long-term high temperature environment is an operation process that such materials must withstand, in order to satisfy the needs for future power generation.Commonly austenitic stainless steel are used for critical components of power plants. Because of future change in operating conditions, further investigations are needed to verify that the demands on safety for cyclic long-term usage is fulfilled. This work includes investigation of two commercial austenitic steels: Esshete 1250 and Sanicro 25. The materials were exposed to thermomechanical fatigue (TMF) in strain control under In-Phase and Out-of-Phase conditions and main testing temperature ranges of 100-650°C and 100-800°C respectively. Some of the specimens were pre-aged to simulate prolonged service condition. Mechanical test data were obtained and analysed in order to define the TMF performance of the investigated alloys. The differences in performance were discussed in relation to mechanical and microstructural characterization.
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| 31. |
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| 32. |
- Chai, Guocai, et al.
(författare)
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Influence of Dynamic Strain Ageing and Long Term Ageing on Deformation and Fracture Behaviors of Alloy 617
- 2016
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Ingår i: THERMEC 2016. - : Trans Tech Publications. ; , s. 306-311
-
Konferensbidrag (refereegranskat)abstract
- Influences of dynamic strain ageing and long term ageing on deformation, damage and fracture behaviors of Alloy 617 material have been studied. Dynamic strain ageing can occur in this alloy at temperature from 400 to 700°C, which leads to a strain hardening and also an increase in fracture strain due to plastic deformation caused by twinning. Long term ageing at 700°C for up to 20 000 hours can cause different precipitation such as γ ́, M6C (Mo-rich) and M23C6 (Cr-rich) carbides. These carbides are both inter-and intra-granular particles. The long term ageing reduces the fracture toughness of the material, but the alloy can still have rather high impact toughness and fracture toughness even with an ageing at 700°C for 20 000 hour. The mechanisms have been studied using electron backscatter detection and electron channeling contrast imaging. It shows that besides dislocation slip, twinning is another main deformation mechanism in these aged Alloy 617 materials. At the crack front, plenty of micro or nanotwins can be observed. The formation of these twins leads to a high ductility and toughness which is a new observation or a new concept for this type of material.
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| 33. |
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| 34. |
- Gebeyaw, Getiye Wodaje, et al.
(författare)
-
Effect of spatial-temporal behavior of a newly developed cooling system on carbon and stainless steel bar properties
- 2023
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report summaries the work within the project ”Effect of spatial-temporal behavior of a newly developed cooling system on carbon and stainless-steel bar properties”. The project was conducted from 2020-01-01 to 2022-12-31 and was co-produced by SSAB, Outokumpu and University of Gävle (UoG). The Knowledge Foundation, SSAB, Outokumpu and UoG financed the project.For the Swedish steel companies SSAB and Outokumpu producing special steels, it is very important to be able to control the cooling process in order to produce steel bars with excellent properties. Both steel companies also want to be able to control the cooling process so that the excellent steel properties become even over the bars’ spatial configuration.The aim of the present project is to reveal the spatial-temporal behavior of a newly developed cooling technology in order to produce steel bars with excellent properties and to control the phase transformation to achieve optimal performance of the steel bars.By using the special test rig at the UoG, detail temperature measurement mapping, invers solution and direct numerical simulation, the present project has identified and quantified several important aspects related to the quenching process, operating conditions, and temperature field development within the investigated products. The result from the proposed cooling process provides an outstanding cooling rate that is very crucial to obtain the required steel phase and thus the correct properties of the bar with different sizes. Results from this study have also shown that the cost per kg product can be reduced by tunning the process parameters such as soaking time and bar temperature before starting the cooling process.In addition, both experimental and numerical results of the material investigation show that the cooling technology has resulted in the desired phase transformation and subsequently the desired steel phases and material properties. The results show that the cooling technology and the control of the cooling parameters can be used to optimize the material properties of the bar materials.These good results and conclusions have been obtained via the deep collaboration between the SSAB, Outokumpu and UoG. The co-production, starting in the steering group planning the work along with the combination of research conducted at UoG and at the companies, have led to a successful project with great knowledge transfer in all direction during the duration of the project.
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| 35. |
- Javadzadeh Kalahroudi, Faezeh
(författare)
-
Microstructure and Fatigue Analysis of PM-HIPed Alloys : A Focus on Inconel 625 and High-Nitrogen Tool Steel
- 2024
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Nickel-based superalloys and tool steels are well-known high-performance alloys due to their extensive use in many different industries. Nickel-based superalloys have found their way into aircraft, aerospace, marine, chemical, and petrochemical industries owing to their excellent high-temperature corrosion and oxidation resistance. On the other hand, tool steels could provide a combination of outstanding corrosion and wear resistance. They can play an important role in cutting and wear applications and manufacturing plastic extrusion and food processing components.Near-net shape manufacturing using powder metallurgy (PM) and hot isostatic pressing (HIP) can serve as an efficient manufacturing process to produce these alloys. This technology can successfully tackle conventional manufacturing challenges of highly alloyed materials i.e. segregation during the casting process or cracks during hot working processes of Ni-based superalloys, and carbide segregation and formation of large and irregularly shaped carbides in wrought and hot rolled tool steels. However, the presence of precipitates on prior particle boundaries (PPBs) in Ni-based superalloys, and metallurgical defects like non-metallic inclusions in both Ni-based superalloys and tool steels may affect the fatigue performance of these PM-HIPed products.This licentiate thesis aims to investigate the microstructure and fatigue behavior of two PM-HIPed alloys i.e. Inconel 625 and high-nitrogen tool steel. The results confirm precipitation along PPBs in PM-HIPed Inconel 625; however, no effect was detected in the fractography studies of the high cycle fatigue samples, and tensile properties were comparable with wrought materials reported in the literature. On the other hand, the microstructure of PM-HIPed high-nitrogen tool steel displayed dispersed precipitates and no traces of PPBs. Moreover, in both cases, i.e. very high cycle fatigue of PM-HIPed high-nitrogen tool steel and high cycle fatigue of PM-HIPed Inconel 625, fatigue crack initiation was attributed to the presence of non-metallic inclusions, either individually or agglomerated with precipitates. This underscores the significance of the manufacturing process in fatigue performance.
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| 36. |
- Kahl, Sören, et al.
(författare)
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In Situ EBSD During Tensile Test of Aluminum AA3003 Sheet
- 2014
-
Ingår i: Micron. - : Elsevier. - 0968-4328 .- 1878-4291. ; 58, s. 15-24
-
Tidskriftsartikel (refereegranskat)abstract
- Miniature tensile-test specimens of soft-annealed, weakly textured AA3003 aluminum sheet in 0.9 mm thickness were deformed until fracture inside a scanning electron microscope. Tensile strength measured by the miniature tensile test stage agreed well with the tensile strength by regular tensile testing. Strain over the microscope field of view was determined from changes in positions of constituent particles. Slip lines were visible in secondary electron images already at 0.3% strain; activity from secondary slip systems became apparent at 2% strain. Orientation rotation behavior of the tensile load axis with respect to the crystallographic axes agreed well with previously reported trends for other aluminum alloys. Start of the fracture and tensile crack propagation were documented in secondary electron images. The region of fracture nucleation included and was surrounded by many grains that possessed high Schmid factors at zero strain. Crystal lattice rotation angles in the grains surrounding the initial fracture zone were higher than average while rotations inside the initial fracture zone were lower than average for strains from zero to 31%. The orientation rotation behavior of the tensile load axes of the grains around the fracture zone deviated from the average behavior in this material.
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| 37. |
- Lindström, Thomas, et al.
(författare)
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Fatigue Behaviour of an Additively Manufactured Ductile Gas Turbine Superalloy
- 2020
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Ingår i: Theoretical and applied fracture mechanics (Print). - : Elsevier. - 0167-8442 .- 1872-7638. ; :108
-
Tidskriftsartikel (refereegranskat)abstract
- Additive manufacturing (AM) offers new possibilities in gas turbine technology by allowing for more complex geometries. However, the fatigue performance, including crack initiation and crack propagation of AM gas turbine material, is not fully known. In addition, AM materials shows anisotropic properties due to the columnar grain growth in the building direction during the AM process, which needs to be accounted for. Also, an AM component often solidifies with a cellular dendritic structure during the manufacturing process. In the present study, the bulk material of an AM adopted nickel-based superalloy based on Hastelloy X was subjected to low-cycle fatigue (LCF) loading at room temperature. The LCF tests were conducted in strain control on additively manufactured smooth bars,with two different build orientations (with an angle of 0° and 90° relative to the building platform). The LCF results showed that the major part of the fatigue life is spent in the crack initiation phase, namely 78% to 99% of the total fatigue life. Based on the experiments, a model to predict the crack initiation life was developed that takes the anisotropic material behaviour into account. The last part of the fatigue life, the crack propagation phase, was studied on a microstructural level, where initial fractography of the ruptured LCF specimens revealed that the dendritic structure was visible on the fracture surface. It was noted that the dendritic structure could easily be mistaken for regular striations although they represent a different fracture mechanism. The fracture surfaces were therefore cross sectioned and possible correlations between fracture surface characteristics and underlying microstructure were studied using electron backscatter diffraction and electron channelling contrast imaging. The outcome showed that the dendritic structure had some effect on the LCF crack propagation behaviour by interdendritic tearing, which was discussed.
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| 38. |
- Nordström, Joakim, 1971-
(författare)
-
Deformation twinning in corrosion-resistant nickel alloys : with a rising nickel content
- 2024
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 39. |
- Nordström, Joakim, 1971-, et al.
(författare)
-
Temperature study of deformation twinning behaviour in Nickel-base Superalloy 625
- 2024
-
Ingår i: Materials Science & Engineering. - 0921-5093 .- 1873-4936.
-
Tidskriftsartikel (refereegranskat)abstract
- Deformation behaviour in the Nickel-base superalloy 625 has been studied by tensile testing at four temperatures: 295, 223, 173 and 77 K. The microstructure has been investigated using TEM, FIB-SEM, EBSD and ECCI techniques. Deformation in the alloy turns out to be a competitive course of events between at least two deformation mechanisms, namely dislocation slip and deformation twinning. Slip is the predominant deformation mechanism at higher temperatures. While at 77 K, deformation induced twinning gives an extra degree of freedom as one of the main deformation mechanisms, i.e., the material shows a twin induced plasticity, TWIP, behaviour. Ab initio calculations indicate that the influence of cryogenic/sub-zero temperatures on the stacking fault energy of this alloy can be limited and that the formation of deformation twins cannot be determined solely by the stacking fault energy. The results implies that it is the critical strain and strain hardening rate that influences the deformation twinning onset and twinning rate.
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| 40. |
- Nordström, Joakim, 1971-, et al.
(författare)
-
Temperature study of deformation twinning behaviour in nickel-base Superalloy 625
- 2024
-
Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 907
-
Tidskriftsartikel (refereegranskat)abstract
- Deformation behaviour in the Nickel-base superalloy 625 has been studied by tensile testing at four temperatures: 295, 223, 173 and 77 K. The microstructure has been investigated using TEM, FIB-SEM, EBSD and ECCI techniques. Deformation in the alloy turns out to be a competitive course of events between at least two deformation mechanisms, namely dislocation slip and deformation twinning. Slip is the predominant deformation mechanism at higher temperatures. While at 77 K, deformation induced twinning gives an extra degree of freedom as one of the main deformation mechanisms, i.e., the material shows a twin induced plasticity, TWIP, behaviour. Ab initio calculations indicate that the influence of cryogenic/sub-zero temperatures on the stacking fault energy of this alloy can be limited and therefore the formation of deformation twins cannot be determined solely by the stacking fault energy. The results implies that critical strain and strain hardening rate influences the deformation twinning onset and twinning rate.
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| 41. |
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| 42. |
- Norman, Viktor, 1988-, et al.
(författare)
-
An Accelerated Creep Assessment Method Based on Inelastic Strain Partitioning and Slow Strain Rate Testing
- 2021
-
Ingår i: Materials & design. - : Elsevier. - 0264-1275 .- 1873-4197. ; 205
-
Tidskriftsartikel (refereegranskat)abstract
- A new accelerated creep assessment method to evaluate the creep performance of metals and alloys from high-temperature tensile tests, i.e. slow-strain-rate testing (SSRT), is proposed and evaluated. The method consists of decomposing the inelastic strain into a plastic and creep component by adopting general assumptions on the inelastic strain behaviour of materials, formulated using a state variable formalism and verified by tensile tests with intermediate dwell times at constant stress. Either, the plastic and creep strain components are considered non-interacting and additive, as observed in the stainless steel AISI 316L at 600 °C. Or, as in the case of the ductile cast iron EN-GJS-SiMo5-1 at 500 °C and the nickel-base superalloy Hastelloy X at 800 °C, the components are considered unified, meaning that the effect of inelastic straining is the same irrespective of whether it is caused through creep at constant stress or by plastic deformation due to an instantaneous stress increase. Based on these assumptions, the proposed method is used to assess the creep strain from SSRT in good agreement with conventional creep test results.
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| 43. |
- Norman, Viktor, et al.
(författare)
-
On the micro- and macroscopic elastoplastic deformation behaviour of cast iron when subjected to cyclic loading
- 2019
-
Ingår i: International journal of plasticity. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0749-6419 .- 1879-2154. ; 115, s. 200-215
-
Tidskriftsartikel (refereegranskat)abstract
- The complicated constitutive behaviour of cast iron, involving a non-linear elastic regime, tension-compression stress asymmetry, varying elastic modulus and an inflection in the tension-to-compression hardening curve, is investigated using a micromechanical modelling approach. In this way, it is demonstrated that the abnormalities observed in the constitutive behaviour are qualitatively and quantitatively explained by the interaction behaviour between the matrix and graphite constituents. In initial tension, the absence of linearity is rationalised by the successive loss in load-carrying capacity of the graphite phase due to debonding, which in subsequent cycling, results in the opening and re-contact of the matrix-graphite interface. This effect is demonstrated to result in tension-compression asymmetry in stress and elastic modulus, as well as the inflection in tension-to-compression loading. The given model of explanation is validated by comparison to the experimentally acquired microscopic strain field in EN-GJV-400 at locations where stress concentrations are generated due to the matrix-graphite debonding, using high-resolution digital image correlation of scanning electron images.
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| 44. |
- Romanov, Pavel, et al.
(författare)
-
Differential Microstructure and Properties of Boron Steel Plates Obtained by Water Impinging Jet Quenching Technique
- 2024
-
Ingår i: Steel Research International. - : WILEY-V C H VERLAG GMBH. - 1611-3683 .- 1869-344X. ; 95:1
-
Tidskriftsartikel (refereegranskat)abstract
- Soil-working tools in agriculture are made of boron-containing steels with high wear resistance and hardenability. Nevertheless, these tools are subject to high impacts, abrasive wear, and fatigue and are therefore prone to failure. To combine varying levels of properties within one component in as-quenched condition can be beneficial for such products. To obtain this property variation, a component must undergo a complex and controllable cooling. Therefore, the aim of this work is to obtain a microstructure gradient along two 15 mm-thick steel plates in a newly developed test rig by water jet impingement technique to confirm its controllability and flexibility. Furthermore, a quenching simulation model is created for hardness prediction using phase transformation data from a machine learning tool. Microstructure variation is observed using light optical microscopy and the electron backscatter diffraction technique. Mechanical properties are studied through tensile tests and hardness measurements and are also compared with simulation results. The 0.27 mass% C steel sample is obtained in almost fully martensitic state transitioning to a softer ferritic/bainitic condition, while the 0.38 mass% C steel sample results predominantly into a fully hardened martensitic state and slightly shows ferritic and bainitic features along the sample. The quenching simulation model shows promising hardness prediction for both steels. A newly developed impinging jet quenching technique is used for differential quenching of 15 mm-thick boron steel sheets with the aim of obtaining microstructure and property gradients along their lengths. As a result, combinations of differential hardness profiles along with varying hardening degrees are produced and metallurgically characterized through microstructure observations and mechanical tests.
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| 45. |
- Romanov, Pavel
(författare)
-
Hardening of Carbon Steel by Water Impinging Jet Quenching Technique : Differential Cooling of Steel Sheets and Quenching of Cylindrical Bars
- 2022
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Austenitization followed by quenching is a well-known conventional heat-treating procedure which is widely used on carbon steels with the aim to obtain high strength in as-quenched condition. Such quenching is usually done by immersing a steel product into the cooling medium which provides a uniform cooling of the surface. The cooling rate can be adjusted to a certain degree on a “component” length-scale by using different cooling mediums such as water, oil, polymer solution, etc. However, certain steel products such as beams, pillars in automobile industry or different machinery parts in agriculture require a proper and controllable cooling gradient and thus mechanical property gradient within the product. It is difficult to control the cooling rates locally on the length-scale smaller than the product only by replacing the quenching medium. In addition, quenching by immersing the product into the cooling medium is accompanied by thermal stresses due to the different cooling rates of the surface and the core, and also accompanied by transformation stresses due to the volume change during phase transformations. These stresses may lead to negative effects such as undesired residual stresses or even cracks. Therefore, cooling must be properly optimized and controlled to eliminate these drawbacks. Such a controllable cooling can be performed by several impingements of the water jets onto a hot austenitized surface at certain locations. By controlling the water flow, number of jets, their locations and other parameters, the global and the local cooling rates can be optimized for a specific industrial application later on. This thesis demonstrates the potential and capability of the water Impinging Jet Quenching Technique (IJQT) to provide a flexible and controllable cooling for both differential and for uniform quenching cases. The test rig of IJQT was developed in the University of Gävle and was used to perform quenching experiments in this study: differential cooling of thick sheets and uniform quenching of bars to different depths. Differential cooling was performed on square-shaped carbon steel sheets with thickness of 15 mm, and the uniform quenching with different flow rates was performed on carbon steel cylindrical bars with 100 mm in diameter. Along with the physical experiments, Comsol Multiphysics 5.6 software was used to solve a 1D heat transfer problem to estimate the cooling rate profile along the radius of the bar. The experiments were verified by observations and characterization of the microstructure using light optical microscopy (LOM), and by examining the mechanical properties through tensile tests and hardness measurements. The results of the quenching experiments and verifications showed a high potential and flexibility of the IJQT in differential cooling case as well as in the uniform quenching case.
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| 46. |
- Romanov, Pavel, et al.
(författare)
-
Hardening of Cylindrical Bars with Water Impinging Jet Quenching Technique
- 2024
-
Ingår i: Steel Research International. - : Wiley. - 1611-3683 .- 1869-344X. ; 95:6
-
Tidskriftsartikel (refereegranskat)abstract
- Hardening of carbon steel products by austenitization and immersion in a quenching medium is a widely used heat treatment to obtain a hard and strong martensitic structure. To avoid the undesired consequences, such as residual stresses or insufficient hardening depth, the cooling rates must be accurately measured and controlled. This can be achieved using the impinging water jet quenching technique. The aim of this work is to perform hardening of four low-alloyed 70 mm cylindrical carbon steel bars, using impinging water jet quenching technique with different jet flow rates, and to analyze its effect on thermal evolution and residual stresses. The temperature evolution during quenching experiments is recorded and used as input to a comprehensive quenching model to predict phase transformations, final hardness, and residual stresses of cylindrical bars. All four quenching experiments result in a fully hardened martensitic state. Furthermore, a decrease in jets’ flow rate, within a certain interval, results in different thermal histories and in lower compressive residual stresses on the surface. The results from quenching simulations show promising hardness, microstructure, and residual stress predictions that are validated by hardness measurements, optical microscopy, and residual stress analysis using X-Ray diffraction method.
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| 47. |
- Romanov, Pavel, et al.
(författare)
-
Quenching of Carbon Steel Plates with Water Impinging Jets : Differential Properties and Fractography
- 2023
-
Ingår i: Procedia Structural Integrity. - : Elsevier. - 2452-3216. ; 43, s. 154-159, s. 154-159
-
Tidskriftsartikel (refereegranskat)abstract
- The demand for steel components with tailored properties is constantly growing. To obtain a specific variation of microstructures and mechanical properties along the component it must undergo a controllable cooling. One way to control the cooling rates along the component is by using different simultaneous water jet impingements on a hot austenitized surface. This can be done by a newly developed test rig for water Impinging Jet Quenching Technique (IJQT). This work discusses the effect of IJQT on mechanical properties and fracture behavior of 15 mm steel plates containing 0.27 and 0.38 mass-% carbon. The samples were cooled in a specifically designed setup of the technique to obtain simultaneous water and air cooling resulting in diverse microstructures. The mechanical property gradients of both steels were analyzed through hardness measurements and tensile tests. The fracture surfaces and the near fracture regions were observed using scanning electron microscope and light optical microscope respectively. The results from tensile tests showed that the larger part of the sample with higher carbon content was fully hardened, however smoothly transitioning to a more ductile region. The sample with lower carbon content combined various degrees of hardening and transitioned from higher to lower ultimate tensile strength values. Fracture behavior of higher carbon steel was predominantly brittle transitioning to a ductile, while the lower carbon steel had a small region showing brittle fracture transitioning to a larger region of predominant ductile fracture behavior.
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| 48. |
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| 49. |
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| 50. |
- Wärner, Hugo, 1988-, et al.
(författare)
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Creep-Fatigue Interaction in Heat Resistant Austenitic Alloys
- 2018
-
Ingår i: MATEC Web of Conferences 165 , 05001 (2018). - : EDP Sciences.
-
Konferensbidrag (refereegranskat)abstract
- This work includes an investigation of two commercial austenitic steels: UNS S21500 (Esshete 1250) and UNS S31035 (Sandvik Sanicro (TM) 25). The materials were exposed to isothermal strain controlled fatigue with load controlled dwell time at maximum strain. The testing temperature used was 700 degrees C and the test cycles were performed in tension. Mechanical test data were obtained and analysed in order to define creep-fatigue damage diagrams at failure for the investigated austenitic alloys. During the given conditions, Sanicro 25 showed superior creep-fatigue life, suffered less amount of creep elongation for the same amount of strain amplitude and dwell times compared to Esshete 1250. Both alloys showed creep-fatigue interaction damage for specific test configurations.
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