| 1. |
- Peng, Ru, et al.
(författare)
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In-situ Neutron Diffraction Study of the Deformation Behaviour of two High-Manganese Austenitic Steels
- 2011
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Ingår i: Materials Science Forum. - Stafa-Zurich, Switzerland : Trans Tech Publications Inc.. - 0255-5476 .- 1662-9752. ; 681, s. 474-479
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Tidskriftsartikel (refereegranskat)abstract
- In-situ neutron diffraction experiments under tensile loading were carried out to study the micromechanical behaviour of two iron-manganese based steels, a TWIP (twinning induced plasticity) steel with 30 wt% Mn and a TRIP steel (transformation induced plasticity) with 20 wt% Mn. The former was loaded to 31.3% strain and the latter to 20% strain. The 30 wt.% Mn steel had a fully austenitic microstructure which remained stable over the loading range studied, while stress induced austenite to α´- and ε-martensite transformations occur in the 20 wt.% Mn steel which initially contained an α´-martensite in addition to the austenite. The evolution of lattice strains under tensile loading differs between the two steels, reflected their different plastic deformation mechanisms. A stronger grain-orientation dependent behaviour is observed during deformation for the 20 wt.% Mn in contrast to the 30wt.% Mn steel.
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| 2. |
- Shen, Yong-Feng, et al.
(författare)
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Deformation mechanisms of a 20Mn TWIP steel investigated by in situ neutron diffraction and TEM
- 2013
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Ingår i: Acta Materialia. - : Elsevier. - 1359-6454 .- 1873-2453. ; 61:16, s. 6093-6106
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Tidskriftsartikel (refereegranskat)abstract
- The deformation mechanisms and associated microstructure changes during tensile loading of an annealed twinning-induced plasticity steel with chemical composition Fe-20Mn-3Si-3Al-0.045C (wt.%) were systematically investigated using in situ time-of-flight neutron diffraction in combination with post mortem transmission electron microscopy (TEM). The initial microstructure of the investigated alloy consists of equiaxed gamma grains with the initial alpha'-phase of similar to 7% in volume. In addition to dislocation slip, twinning and two types of martensitic transformations from the austenite to alpha'- and epsilon-martensites were observed as the main deformation modes during the tensile deformation. In situ neutron diffraction provides a powerful tool for establishing the deformation mode map for elucidating the role of different deformation modes in different strain regions. The critical stress is 520 MPa for the martensitic transformation from austenite to alpha'-martensite, whereas a higher stress (>600 MPa) is required for actuating the deformation twin and/or the martensitic transformation from austenite to epsilon-martensite. Both epsilon- and alpha'-martensites act as hard phases, whereas mechanical twinning contributes to both the strength and the ductility of the studied steel. TEM observations confirmed that the twinning process was facilitated by the parent grains oriented with < 1 1 1 > or < 1 1 0 > parallel to the loading direction. The nucleation and growth of twins are attributed to the pole and self-generation formation mechanisms, as well as the stair-rod cross-slip mechanism.
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| 3. |
- Afshari, Davood, et al.
(författare)
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An approach in prediction of failure in resistance spot welded aluminum 6061-T6 under quasi-static tensile test
- 2012
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Ingår i: Proceedings of the Institution of mechanical engineers. Part B, journal of engineering manufacture. - : SAGE Publications. - 0954-4054 .- 2041-2975. ; 226:B6, s. 1026-1032
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this article is to predict the failure load in resistance spot welded aluminum 6061-T6 sheets with 2mm thickness under quasi-static tensile test. Various welding parameters, e. g. welding current, welding time and electrode force are selected to produce welded joints with different quality. The results show that for all the samples in this study only interfacial failure mode was observed in tensile-shear test and no pull-out mode was observed. According to the failure mode, an empirical equation was used for the prediction of failure load based on nugget size and hardness of failure line. Microstructure study has been carried out to investigate microstructural changes in the welded joints. For determination of the minimum hardness, microhardness tests have been carried out to find hardness profiles. The minimum hardness value was observed for a thin layer around the nugget with large and coarse grains. The results show that by using the presented empirical equation, the failure can be predicted with a good agreement only by measuring nugget size.
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| 4. |
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| 5. |
- 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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| 6. |
- Chai, Guocai, et al.
(författare)
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Fatigue Behaviors in Duplex Stainless Steel Studied Using In-Situ SEM-EBSD Method
- 2014
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Ingår i: Procedia Materials Science. - : Elsevier. - 2211-8128. ; 3, s. 1748-1753
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Tidskriftsartikel (refereegranskat)abstract
- Austenite and ferrite in duplex stainless steels have different physical and mechanical properties. They can behave different during cyclic loading. To understand the fatigue behaviors of these two phases, an in-situ SEM/EBSD fatigue test has been performed. Flat specimens made from the specimens of pre-fatigue tested with three point bending were cyclically loaded in a scanning electron microscope via a compact test rig. By in situ/ex situ SEM/EBSD examination, slip activities and propagation of the fatigue cracks have been studied. Microstructures along the path of the fatigue crack were characterized. The different phase properties seem to lead to certain difference in the slip activity and formation of PSBs. Inhomogeneous slip activities and local strain concentrations were also found, which developed with increasing number of load cycles. Crack propagation behaviors in grain and cross the grain or phase boundaries have been discussed. Crack deflection occurs at the phase boundaries, but crack branching occurs mainly in the grains due to the dislocation slip. In-situ SEM/EBSD fatigue test confirms that crack propagation deflection and formation of crack branches can significantly reduce the crack propagation rate.
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| 7. |
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| 8. |
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| 9. |
- Chai, Guocai, et al.
(författare)
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Local Plasticity Exhaustion in a Very High Cycle Fatigue Regime
- 2012
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Ingår i: Scripta Materialia. - : Elsevier. - 1359-6462 .- 1872-8456. ; 66:10, s. 769-772
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Tidskriftsartikel (refereegranskat)abstract
- Very high cycle fatigue behaviors of four metal materials with different microstructures have been studied focusing on their damage mechanisms. It was found that the cyclic plastic deformation in the materials was highly localized in the very high cycle regime or the elastic deformation regime. This high strain localization can cause local plasticity exhaustion, which leads to a stress concentration and consequently fatigue crack initation, and finally the formation of a subsurface non-defect fatigue crack origin.
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| 10. |
- Chai, Guocai, et al.
(författare)
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Micro Fatigue Crack Propagation Behavior in a Duplex Stainless Steel Studied Using In Situ SEM/EBSD Method
- 2014
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Ingår i: 11TH INTERNATIONAL FATIGUE CONGRESS, PTS 1 AND 2. - : Trans Tech Publications Inc.. ; , s. 313-318
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Konferensbidrag (refereegranskat)abstract
- Fatigue crack propagation behaviors in a duplex stainless steel have been studied using an in-situ SEM/EBSD fatigue test and a conventional da/dN test. Crack propagation behaviors in grain, effect of Schmid factor, propagation cross the grain or phase boundaries have been discussed. Crack propagation occurs mainly in the grains with a high Schmid factor, but with very small Schmid factor. Crack deflection occurs mainly at the phase boundaries, but crack branching occurs mainly in the grains due to the dislocation slip. In-situ SEM/EBSD fatigue test confirms that crack propagation deflection can lead to a decrease in crack propagation rate. Formation of crack branches can significantly reduce the crack propagation rate, which can cause crack growth retardation in the main crack path in the worst case. The crack branches formed are usually not ideal. They can propagate almost transversely to the main crack direction with a mode II stress intensity factor, SIF, and a rate that is much higher than that of the main crack.
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