| 1. |
- Gustafsson, David, 1983-
(författare)
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Constitutive and fatigue crack propagation behaviour of Inconel 718
- 2010
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In this licentiate thesis the work done in the TURBO POWER project Influence of high temperature hold times on the fatigue life of nickel-based superalloys will be presented. The overall objective of this project is to develop and evaluate tools for designing against fatigue in gas turbine applications, with special focus on the nickel-based superalloy Inconel 718. Firstly, the constitutive behaviour of the material has been been studied, where focus has been placed on trying to describe the mean stress relaxation and initial softening of the material under intermediate temperatures. Secondly, the fatigue crack propagation behaviour under high temperature hold times has been studied. Focus has here been placed on investigating the main fatigue crack propagation phenomena with the aim of setting up a basis for fatigue crack propagation modelling.This thesis is divided into two parts. The first part describes the general framework, including basic constitutive and fatigue crack propagation behaviour as well as a theoretical background for the constitutive modelling of mean stress relaxation. This framework is then used in the second part, which consists of the four included papers.
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| 2. |
- Gustafsson, David, 1983, et al.
(författare)
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Fatigue crack growth behaviour of Inconel 718 with high temperature hold times
- 2010
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Ingår i: Procedia Engineering. - : Elsevier BV. - 1877-7058. ; 2:1, s. 1095-1104
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Konferensbidrag (refereegranskat)abstract
- In this work, fatigue crack growth measurements have been made on center-cracked tension specimens of Inconel 718, where the focus has been to observe the effect of high temperature hold times on the fatigue crack growth behaviour of the material. The material testing has been done at three different temperatures, namely 450 °C, 550 °C and 650 °C. All testing were done in an isothermal LCF context with a standard test method for measuring the fatigue crack growth rates. © 2010 Published by Elsevier Ltd.
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| 3. |
- Johansson, Sten, et al.
(författare)
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Investigation of localized damage in single crystals subjected to thermalmechanical fatigue (TMF)
- 2010
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Ingår i: Procedia Engineering. - : ELSEVIER SCIENCE BV. - 1877-7058. ; 2:1, s. 657-666
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Tidskriftsartikel (refereegranskat)abstract
- The deformation and damage mechanisms arising during thermalmechanical fatigue (TMF) of a CMSX-4 and high-Cr single crystal super alloy, SCA425 have been investigated and a completely new failure mechanism involving recrystallization and oxidation has been discovered. The primary deformation mechanism is slip along the {111} planes. The deformation is highly localised to a number of bands, where recrystallization eventually occur during the thermalmechanical fatigue process. When the final failure occurs along these recrystallized bands it is accompanied by the formation of voids due to the presence of grain boundaries. The damage process is further enhanced by oxidation, since recrystallization occurs more easily in the gamma depleted zone under the oxide scale. The macroscopic as well as the microscopic damage and fracture mechanisms are varying with alloy and heat treatment. The aim of this work is to further investigate, discuss the local damage mechanisms responsible for TMF damage. Of special interest is the localisation of damage into twins and extremely localized rafted deformation bands.
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| 4. |
- Leidermark, Daniel, et al.
(författare)
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Fatigue crack initiation in a notched single-crystal superalloy component
- 2010
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Ingår i: Procedia Engineering. - : Elsevier. - 1877-7058. ; 2:1, s. 1067-1075
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the fatigue crack initiation in notched single-crystal test specimens of material MD2 is investigated and analysed. A critical plane approach is adopted, in which the total strain ranges on the discrete slip planes are evaluated. Furthermore, a Coffin-Manson type of expression is used to describe the number of cycles to fatigue crack initiation. This relation is determined from a set of smooth test specimens loaded uniaxially in the [001], [011] and directions at 500 °C with Rε=−1. The numerical procedure is then applied to a series of experiments, in which notched single-crystal test specimens were exposed to uniaxial cyclic loading in the [001] direction at 500 °C with Rε=0.
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| 5. |
- Leidermark, Daniel, et al.
(författare)
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Tension/Compression asymmetry of a single-crystal superalloy in virgin and degraded condition
- 2010
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Ingår i: Acta Materialia. - : Elsevier. - 1359-6454 .- 1873-2453. ; 58:15, s. 4986-4997
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Tidskriftsartikel (refereegranskat)abstract
- The mechanical behaviour at room temperature of a single-crystal superalloy exposed to long term ageing at elevated temperature has been investigated, a topic important for the material’s resistance to thermal-mechanical fatigue. Specimens with several different crystallographic orientations were plastically deformed in either tension or compression before and after the long term furnace exposure. While the thermally activated degradation of the microstructure causes a reduction in yield limit of up to 25% for specimens initially deformed in the |001 and |011| directions, none or only moderate reduction was seen for specimens initially deformed along the |111| direction. This can be explained by the strong correlation between yield limit reduction and the amount of γ coarsening. By introducing an isotropic degradation function in a newly developed crystal plasticity model, the constitutive behaviour of both virgin and degraded materials has been described with good agreement with the experimental results.
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| 6. |
- Moverare, Johan, 1973-, et al.
(författare)
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Damage mechanisms of a high-Cr single crystal superalloy during thermomechanical fatigue
- 2010
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Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 527:3, s. 553-558
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Tidskriftsartikel (refereegranskat)abstract
- The deformation and damage mechanisms arising during thermomechanical fatigue of a high-Cr single crystal superalloy have been investigated and a completely new failure mechanism involving recrystallization and oxidation has been discovered. The primary deformation mechanism is slip along the {1 1 1} planes. The deformation is highly localized to a number of bands, where recrystallization eventually occurs during the thermomechanical fatigue process. When the final failure occurs along these recrystallized bands it is accompanied by the formation of voids due to the presence of grain boundaries. The damage process is further enhanced by oxidation, since recrystallization occurs more easily in the γ′ depleted zone under the oxide layer.
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| 7. |
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| 8. |
- Sadrossadat, Mohsen, et al.
(författare)
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Analysis of residual stress development during thermal processing of Al-Si alloys
- 2010
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Konferensbidrag (refereegranskat)abstract
- Residuals stresses can be present in almost every industrial component. Manufacturing processes such as casting, welding, and heat treatment are the most common causes of residual stresses. Thermal residual stresses could be developed in a component during heat treatment process as a result of non-uniform heating or cooling operations. In this study, experiments were carried out to develop insights into and understanding of the residual stresses that can arise during thermal treatments of Al-Si components. Due to the complexity of residual stresses analysis in real components, a common mixed-section casting was employed. In order to fulfill the requirements of performing different thermal treatments, a special cooling apparatus was designed and built. A number of the casting components of an Al-Si alloy were annealed for stress relief, and then removed from the furnace and cooled with different water flow rates. Then, the amount of accumulated residual stresses in the components was measured relaxation of stress using cutting. Thermal analysis and residual stress measurement for different thermal treatment regimes showed that by choosing a specific holding temperature before direct cooling, the value of residual stress increases linearly with flow rate of cooling. On the other hand, for a constant value of cooling water flow, ∆Tmax and residual stress level decreases when the value of base temperature of furnace decreases. Moreover, the cutting method can be a suitable method for measuring thermal residual stresses in Al-Si components and thermal analysis is a powerful technique to predict residual stresses.
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| 9. |
- Sadrossadat, Mohsen, et al.
(författare)
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The effects of solidification conditions and heat treatment on the microstructure and mechanical properties of EN-AC 44400 alloy
- 2010
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Ingår i: Materials Science Forum. - Switzerland : Trans Tech Publications. - 0255-5476 .- 1662-9752. ; 649, s. 505-510
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Tidskriftsartikel (refereegranskat)abstract
- Improved mechanical and physical properties of an Al-Si alloy as a well-known casting alloy is strongly dependent upon the morphology of silicon particles, Al grains and also type of intermetallics which are in turn a function of alloy composition, solidification rate and heat treatment. This study aims at investigating the influence of the different solidification conditions (high pressure die, gradient and sand cast) and heat treatment on the microstructure (dendrite parameters, silicon particle morphology, intermetallic compounds), mechanical properties and fracture surface appearance of Al- 9Si- 4Mn alloy. To identify the features of microstructure and fracture surface analysis, a combination of optical metallography, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) have been employed. The results show that the cooling rate has a strong effect on the evolution of intermetallics, morphology of the silicon and dendrite parameters.
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| 10. |
- Sadrossadat, Mohsen, et al.
(författare)
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The influence of casting geometry on the tensile properties and residual stresses in aluminium castings
- 2010
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Ingår i: Materials Science Forum. - Switzerland : Trans Tech Publications. - 0255-5476 .- 1662-9752. ; 652, s. 174-179
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Tidskriftsartikel (refereegranskat)abstract
- The soundness and the performance of castings are significantly affected by generation and accumulation of residual stresses. This has been proven that mechanical properties and residual stresses level of the casting components are affected by thermal gradient across the casting component during cooling and some intrinsic physical properties of the material. In the present work, microstructural development, mechanical properties, residual stress evolution and cooling curves associated with different legs of a mixed–section grid castings have been investigated employing scanning electron microscope, optical microscope, 3D measurement equipment, computerized thermal data acquisition instrument and tensile testing machine. Experimental results show that the accumulated residual stress in circular, triangular and rectangular grid shapes is increasing respectively. From the results it can be seen that there are clear influences of grid’s geometry on the microstructure and mechanical properties. The geometrical stiffness can affect a lot the residual stress level and the casting modulus has a big influence on the microstructure and mechanical properties.
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