| 1. |
- Ahlström, Johan, 1969, et al.
(författare)
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Modified Railway Wheel Steels: Production and Evaluation of Mechanical Properties with Emphasis on Low-Cycle Fatigue Behavior
- 2009
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Ingår i: Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science. - : Springer Science and Business Media LLC. - 1073-5623. ; 40A:7, s. 1557-1567
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Tidskriftsartikel (refereegranskat)abstract
- Railway wheels are exposed to high mechanical and thermal loads. The objective of this study has been to develop wheels that are more resistant to damage from these loads. Fourteen different materials have been produced in the form of full-scale railway wheels. Parameters that have been varied include the chemical composition, production processes, and heat treatment. The materials have been investigated microstructurally and by hardness, tensile, and impact toughness testing. In addition, the low-cycle fatigue (LCF) behavior has been characterized at room temperature and at subzero temperatures. The results indicate improvement in microstructure and mechanical properties for some materials and it is probable that these materials would endure better in service. © The Minerals, Metals & Materials Society and ASM International 2009.
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| 2. |
- Altenkirch, J., et al.
(författare)
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Mechanical Tensioning of High-Strength Aluminum Alloy Friction Stir Welds
- 2008
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Ingår i: Symposium on Neutron and X-Ray Studies for Probing Materials Behavior held at the 137th TMS Annual Meeting and Exhibition. - : Springer Science and Business Media LLC. - 1073-5623. ; 39A, s. 3246-3259
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Konferensbidrag (refereegranskat)abstract
- The extent to which in-situ global mechanical tensioning (GMT) can be used to modify the residual stress state in friction stir (FS) welds is investigated in this article. Residual stress distributions have been determined by synchrotron X-ray and neutron diffraction for four sets of FS welds in high-strength AA7449-W51 and lithium containing AA2199-T8 aerospace aluminum alloys subjected to a systematic range of GMT levels. For the cases studied, the results indicate that the level of residual stresses present in the as-welded state is a function of the alloy. The rate of residual stress reduction brought about by GMT, however, is basically alloy independent; indeed, it is essentially linear with respect to the GMT load, so that the tensioning required to reduce the weld stresses to zero can be calculated directly from the stresses present in the untensioned case. For thin plates, proximity to the yield stress in the hot-softened zone means that a guideline rule is that 1 MPa of tensioning during welding reduces the tensile stress by approximately 1 MPa. The GMT was found to be less effective at greater depths in thick plates. Furthermore, a reduction in bending distortion and an increase in angular distortion was observed with increased GMT, while no effects on the weld microstructure and hardness were observed.
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| 3. |
- Arai, Y., et al.
(författare)
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In-situ observed dynamics of peritectic solidification and delta/gamma transformation of Fe-3 to 5 At. Pct Ni alloys
- 2005
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Ingår i: Metallurgical and Materials Transactions. A. - : Springer Science and Business Media LLC. - 1073-5623 .- 1543-1940. ; 36A:11, s. 3065-3074
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Tidskriftsartikel (refereegranskat)abstract
- The characteristics of liquid -> delta ferrite and delta ferrite -> gamma austenite transformation in Fe-3.50 at. pct Ni alloy, and of the peritectic solidification of Fe-4.83 and 5.01 at. pct Ni alloys, have been dynamically observed in situ with a confocal scanning laser microscope (CSLM) combined with an infrared image furnace (IIF). The unique sequence, morphologies, and rates of these transformations have been determined at a temperature gradient of 4 K/mm and growth rates of 2 to 3 mu m/s, in unidirectional solidification experiments. These observations have been discussed in terms of the constitutional undercooling description of solidification theory.
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| 4. |
- Cong, D Y, et al.
(författare)
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Crystal structures and textures in the hot-forged Ni-Mn-Ga shape memory alloys
- 2006
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Ingår i: Metallurgical and Materials Transactions. A. - 1073-5623 .- 1543-1940. ; 37A:5, s. 1397-1403
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Tidskriftsartikel (refereegranskat)abstract
- Three ferromagnetic shape-memory alloys with the chemical compositions of Ni53Mn25Ga22, Ni48Mn30Ga22, and Ni48Mn25Ga22Co5 were prepared by the induction-melting and hot-forging process. The crystal structures were investigated by the neutron powder diffraction technique, showing that Ni53Mn25Ga22 and Ni48Mn25Ga22Co5 have a tetragonal, I4/mmm martensitic structure at room temperature, while Ni48Mn30Ga22 has a cubic, L2(1) austenitic structure at room temperature. The development of textures in the hot-forged samples shows the in-plane plastic flow anisotropy from the measured pole figures by means of the neutron diffraction technique. Significant texture changes were observed for the Ni48Mn25Ga22Co5 alloy after room temperature deformation, which is due to the deformation-induced rearrangements of martensitic variants. An excellent shape-memory effect (SME) with a recovery ratio of 74 pct was reported in this Ni48Mn25Ga22Co5 polycrystalline alloy after annealing above the martensitic transformation temperature, and the "shape-memory" influence also occurs in the distributions of grain orientations.
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| 5. |
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| 6. |
- Dahle, A. K., et al.
(författare)
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Discussion of "nucleation mechanism of eutectic phases in aluminum-silicon hypoeutectic alloys"
- 2005
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Ingår i: Metallurgical and Materials Transactions. A. - : Springer Science and Business Media LLC. - 1073-5623 .- 1543-1940. ; 36:6, s. 1612-1613
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Tidskriftsartikel (refereegranskat)abstract
- A previous study tried to prove that each plate of Si in the ordinary Al-Si eutectic is nucleated individually by the action of a small iron-containing particle. The study justified the need for a more complete understanding of the Al-Si eutectic reaction in the absence of chemical modifiers in order to shed light on the complicated mechanisms operating in chemically modified Al-Si alloys. Reacting to this claim, the present authors state that the mechanisms of the ordinary eutectic reaction of Al-Si alloys have been well understood for several decades, thus a very strong evidence is required to justify a revision of that understanding. For their part, the authors of the first study justified their claim for a revision by considering results of thermal analyses, optical microscopy, scanning and transmission electron microscopy, and selected area electron diffraction (SAED) analyses and elemental X-ray mapping performed on samples of precisely controlled chemistry.
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| 7. |
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| 8. |
- Erneman, J., et al.
(författare)
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Comparison between quantitative metallography and modeling of sigma-phase particle growth in AISI 347 stainless steel
- 2005
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Ingår i: Metallurgical and Materials Transactions. A. - : Springer Science and Business Media LLC. - 1073-5623 .- 1543-1940. ; 36A:10, s. 2595-2600
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Tidskriftsartikel (refereegranskat)abstract
- A comparison was made between two experimental methods to determine the (T-phase volume fraction and three methods to model a-phase growth in a niobium-stabilized stainless steel (AISI 347). The a-phase volume fraction and precipitate size were determined in material statically aged and creep deformed at 700 degrees C with both KOH etched specimens using bright field optical microscopy (OM/BF) (conventional method) and specimens etched with oxalic acid using scanning electron microscopy and backscattered electrons (SEM/BSE) (new method). Both experimental methods used manual thresholding together with digital image analysis. The calculations were made with DICTRA software, using both the TCFE database and the SSOL database with some modification concerning the effect of silicon on the stability of sigma-phase particles. The modeled sigma-phase volume- fractions showed rather good agreement with the measured results from statically aged material using the new method. It was found that the stabilizing effect of silicon on sigma phase should be included in the thermodynamic database used for modeling.
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| 9. |
- Hedström, Peter, et al.
(författare)
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Load partitioning and strain-induced martensite formation during tensile loading of a metastable austenitic stainless steel
- 2009
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Ingår i: Metallurgical and Materials Transactions. A. - : Springer Science and Business Media LLC. - 1073-5623 .- 1543-1940. ; 40:5, s. 1039-1048
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Tidskriftsartikel (refereegranskat)abstract
- In-situ high-energy X-ray diffraction and material modeling are used to investigate the strain-rate dependence of the strain-induced martensitic transformation and the stress partitioning between austenite and α′ martensite in a metastable austenitic stainless steel during tensile loading. Moderate changes of the strain rate alter the strain-induced martensitic transformation, with a significantly lower α′ martensite fraction observed at fracture for a strain rate of 10−2 s−1, as compared to 10−3 s−1. This strain-rate sensitivity is attributed to the adiabatic heating of the samples and is found to be well predicted by the combination of an extended Olson–Cohen strain-induced martensite model and finite-element simulations for the evolving temperature distribution in the samples. In addition, the strain-rate sensitivity affects the deformation behavior of the steel. The α′ martensite transformation at high strains provides local strengthening and extends the time to neck formation. This reinforcement is witnessed by a load transfer from austenite to α′ martensite during loading.
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| 10. |
- Jaradeh, Majed, et al.
(författare)
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Differential thermal analysis and differential scanning calorimetry studies of aluminum 3003 alloys with Zn and Cu additions
- 2007
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Ingår i: Metallurgical and Materials Transactions. A. - : Springer Science and Business Media LLC. - 1073-5623 .- 1543-1940. ; 38:9, s. 2138-2147
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Tidskriftsartikel (refereegranskat)abstract
- The effect of Zn additions in the range of 0 to 5 wt pct and Cu contents of 0.15 to 1.0 wt pct on the solidification and precipitation behavior of aluminum alloys of AA 3003 type was investigated with differential thermal analysis (DTA), differential scanning calorimetry (DSC), optical microscopy, and scanning electron microscopy/energy-dispersive X-ray (SEM/EDX). The results show that the additions of varying Zn and Cu have significant effects on the crystallization process, phase precipitation, and microstructure formation of the alloys. Phases formed have been identified and morphological differences have been discussed
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