| 1. |
- Ashrafi, Hamid, et al.
(författare)
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Void formation and plastic deformation mechanism of a cold-rolled dual-phase steel during tension
- 2020
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Ingår i: Acta Metallurgica Sinica (English Letters). - : Springer. - 1006-7191 .- 2194-1289. ; 33, s. 299-306
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Tidskriftsartikel (refereegranskat)abstract
- The void formation and plastic deformation micromechanisms of a cold-rolled DP600 steel during tensile loading were studied by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The SEM observations revealed that the main void nucleation mechanism in the DP600 steel is decohesion at the ferrite–martensite interfaces. The voids were mostly observed between the closely spaced martensite islands situated at the boundaries of relatively finer ferrite grains. The EBSD results indicated a strain gradient developed from the ferrite–martensite and ferrite–ferrite interfaces into the interior of ferrite grains during the tensile deformation, which led to a stress concentration at these interfaces. Moreover, it was demonstrated that local misorientation inside the finer ferrite grains surrounded by martensite islands was higher than that for the coarser ferrite grains, which made the former more prone to void initiation.
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| 2. |
- Hou, R. -Q, et al.
(författare)
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Localized corrosion of binary Mg-Ca alloy in 0.9 wt% sodium chloride solution
- 2016
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Ingår i: Acta Metallurgica Sinica (English Letters). - : Chinese Society for Metals. - 1006-7191 .- 2194-1289. ; 29:1, s. 46-57
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Tidskriftsartikel (refereegranskat)abstract
- To further understand the localized corrosion of magnesium alloy, various in situ electrochemical techniques and ex situ electron microprobe analysis and SEM were used to monitor the corrosion process of Mg-1.0Ca alloy in 0.9 wt% sodium chloride solution. The results indicated that the localized corrosion was accompanied by the formation and thickening of a corrosion product film on the Mg-1.0Ca alloy. A localized corrosion of the alloy initiated selectively on the eutectic micro-constituent zones, then enhanced with the exposure, developed in depth with ring-shaped corrosion products accumulated around and finally formed a volcanic-like pitting. Based on the measurements, an electrochemical corrosion model was proposed accordingly to describe the formation mechanism of the volcanic-like pitting on the alloy in 0.9 wt% sodium chloride solution.
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| 3. |
- Jiao, Xinyang, et al.
(författare)
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Microstructure Evolution and Pore Formation Mechanism of Porous TiAl3 Intermetallics via Reactive Sintering
- 2018
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Ingår i: Acta Metallurgica Sinica (English Letters). - : Springer. - 1006-7191 .- 2194-1289. ; 31:4, s. 440-448
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Tidskriftsartikel (refereegranskat)abstract
- Porous TiAl3 intermetallics were fabricated through vacuum reactive sintering from Ti–75Al at.% elemental powder mixture. The phase compositions, expansion behaviors, pore characteristics and microstructure evolution of TiAl3 intermetallics were investigated, and the pore formation mechanism was also proposed. It was found that the actual temperature of compacts showed an acute climb from 668 to 1244 °C in 166s, while the furnace temperature maintained the linear growth of 5 °C/min, which indicated that an obvious thermal explosion (TE) reaction occurred during sintering, and only single-phase TiAl3 intermetallic was synthesized in TE products. The open porosity increased from 22.2 (green compact) to 32.8% after reactive diffusion sintering at 600 °C and rised to 58.7% after TE, then decreased to 51.2% after high-temperature homogenization at 1100 °C. Therefore, TE reaction is the dominated pore formation mechanism of porous TiAl3 intermetallics. The pore evolution in porous TiAl3 intermetallics occurred by the following mechanisms: certain intergranular pores remained among powder particles of green compact, then low-temperature sintering resulted in a further increase in porosity due to the Kirkendall effect. Moreover, TE reaction gave rise to a dramatic volume expansion because of the rapid increase in temperature, and high-temperature sintering caused densification and a slight shrinkage.
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| 4. |
- Leiro, Alejandro, et al.
(författare)
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Fatigue of 0.55C-1.72Si Steel with Tempered Martensitic and Carbide-Free Bainitic Microstructures
- 2014
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Ingår i: Acta Metallurgica Sinica (English Letters). - : Springer Science and Business Media LLC. - 1006-7191 .- 2194-1289. ; 27:1, s. 55-62
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Tidskriftsartikel (refereegranskat)abstract
- High-Si spring steel was heat treated in three different ways: Quenching and tempering at 460 °C to obtain a tempered martensite microstructure, and austempering at 300 and 350 °C, respectively, to obtain two different carbide-free bainitic microstructures. In the steel austempered at 350 °C, both the bainite lath thickness and retained austenite content were higher than those of the steel austempered at 300 °C. Rotating-bending fatigue tests were done in order to evaluate the effect of each heat treatment on the high-cycle fatigue behavior of the steel. When the austempering temperature was 300 °C, the endurance limit was increased by 25% despite a 5% reduction in tensile strength when compared with that of the quenched and tempered steel. The relationship between endurance limit [Rfat (50%)] and ultimate tensile strength (Rm) was higher for the austempered samples in comparison with that of the quenched and tempered material. Therefore, it is believed that the presence of retained austenite affects the relationship between endurance limit and tensile strength.
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| 5. |
- Liu, Hui, et al.
(författare)
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Helium Bubble Growth in He + Ions Implanted 304L Stainless Steel Processed by Laser Powder Bed Fusion During Post-Irradiation Annealing at 600 °C
- 2022
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Ingår i: Acta Metallurgica Sinica (English Letters). - : Springer Science and Business Media LLC. - 1006-7191 .- 2194-1289. ; 35:9, s. 1509-1518
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Tidskriftsartikel (refereegranskat)abstract
- The abundancy of defect sinks in the microstructure of laser powder bed fusion (LPBF) processed austenitic stainless steels was found to be beneficial for helium resistance. In the current study, the influence of the novel microstructure in LPBF processed 304L on the helium bubble growth behaviour was investigated using transmission electron microscopy in samples implanted with He+ ion and post-irradiation annealing treated at 600 °C for 1 h. Two variants of LPBF processed 304L samples were used, one in as-built condition and the other solution-annealed. The comparison between the two samples indicated that the helium bubble growth was inhibited and remained stable in the as-built sample but coarsened significantly in the solution-annealed sample. The sub-grain boundaries and oxide nano-inclusions acted as defect sinks to trap helium atoms and inhibited the growth of helium bubble in the as-built sample under the post-irradiation annealing conditions used.
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| 6. |
- Qiu, Siyi, et al.
(författare)
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A Brief Review on He Ion Irradiation Research of Steel and Iron-Based Alloys in Nuclear Power Plants
- 2023
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Ingår i: Acta Metallurgica Sinica (English Letters). - : Springer Science and Business Media LLC. - 1006-7191 .- 2194-1289. ; 36:4, s. 529-551
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Forskningsöversikt (refereegranskat)abstract
- Nuclear power plays a key role as renewable energy in alleviating the worldwide energy shortage. The material degradation caused by high-temperature and high-flux neutron irradiation is the most concerning issue for nuclear reactor safety. A large number of He atoms produced through the (n, alpha) transmutation reaction diffuse and migrate in metals and accumulate to form He bubbles because of the extremely low solubility of He atoms in metal materials. The helium bubbles gather at the grain boundary or grain to cause swelling, hardening, embrittlement, and other damages to the in-core structural components. This paper mainly summarizes the research progress on He irradiation in steel and iron-based alloys, including the diffusion and accumulation of He atoms, the nucleation and growth of He bubbles, and the microstructure and macroscopic degradation of material performance caused by He irradiation. The mechanism of helium irradiation-induced corrosion in steel and iron-based alloys in recent years is reviewed as well. Moreover, the investigations on irradiation performance in additive manufactured stainless steels are summarized, and the mechanism of irradiation resistance is prospected.
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| 7. |
- Wang, Dian-Zheng, et al.
(författare)
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Cracking Behavior in Additively Manufactured Pure Tungsten
- 2019
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Ingår i: Acta Metallurgica Sinica (English Letters). - : Springer Science and Business Media LLC. - 1006-7191 .- 2194-1289. ; 32:1, s. 127-135
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Tidskriftsartikel (refereegranskat)abstract
- In this study, near fully dense (96.5%) pure tungsten bulks were additively manufactured and the cracking behavior was investigated. A crack network with a spacing of similar to 100m was observed in the fabricated bulks. It was observed that the laser scanning strategy, which could tailor the microstructure, affected the crack distribution pattern in fabricated tungsten. The calculated surface temperature difference (7300K) was much higher than the cracking criterion (800K) of tungsten, indicating that cracking is almost inevitable in laser additive manufacturing of tungsten. It could be concluded that crack network formed because the cracks emerged in every laser molten track and then interconnected in the layer-by-layer building process.
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| 8. |
- Xing, Lei-Lei, et al.
(författare)
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Microstructure of a Ti-50 wt% Ta alloy produced via laser powder bed fusion
- 2020
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Ingår i: Acta Metallurgica Sinica (English Letters). - : Springer Science and Business Media LLC. - 1006-7191 .- 2194-1289. ; 33, s. 981-990
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Tidskriftsartikel (refereegranskat)abstract
- Ti-Ta alloys have been widely studied for biomedical applications due to their high biocompatibility and corrosion resistance. In this work, nearly fully dense and in situ alloyed Ti-50 wt% Ta samples were fabricated by the laser powder bed fusion (LPBF) of mechanically mixed powders. With increased exposure time, and thereby increased laser energy density, insoluble Ta particles were almost dissolved, and a Ti-50 wt% Ta alloy was formed. Cellular and dendritic structures were formed due to constitutional undercooling, which was caused by the high cooling rate of LPBF process. Both retained beta phases and alpha '' phases were observed in the LPBFed Ti-50 wt% Ta alloy. The alpha '' phase was found at the boundary of the cellular structures, where the tantalum content was not high enough to suppress the bcc lattice transition completely but could suppress the beta phase -> alpha ' phase transition.
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| 9. |
- Yu, Chenfan, et al.
(författare)
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Effect of Build Direction on Fatigue Performance of L-PBF 316L Stainless Steel
- 2020
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Ingår i: Acta Metallurgica Sinica (English Letters). - : Springer Science and Business Media LLC. - 1006-7191 .- 2194-1289. ; 33:4, s. 539-550
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Tidskriftsartikel (refereegranskat)abstract
- The microstructure and fatigue and tensile properties of 316L stainless steel fabricated via laser powder bed fusion (L-PBF) were investigated. Two 316L stainless steel specimens with different loading directions which are either perpendicular to or parallel to building direction were prepared by L-PBF process. The results of X-ray diffraction tomography showed that there was no significant difference in morphology and size/distribution of the defects in the HB and VB samples. Since long axis of columnar grains is generally parallel to the build direction, the fatigue crack encounters more grain boundaries in VB samples under cyclic loading, which led to enhanced fatigue resistance of VB samples compared with HB sample. In contrast to HB sample, the VB sample has a higher fatigue strength due to a higher resistance to localized plastic deformation under cyclic loading. The differences in fatigue properties of L-PBF 316L SS with different build directions were predominantly controlled by solidification microstructures.
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| 10. |
- Leygraf, Christofer, et al.
(författare)
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Microscopic corrosion studies of duplex stainless steels
- 2004
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Ingår i: Acta Metallurgica Sinica (English Letters). - 1006-7191. ; 17:5, s. 625-631
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Tidskriftsartikel (refereegranskat)abstract
- Electrochemical scanning tunneling microscopy and scanning electrochemical microscopy have been used for in situ monitoring of localized corrosion processes of different Duplex stainless steels (DSS) in acidic chloride solutions. The techniques allow imaging of local dissolution events with micrometer resolution, as opposed to conventional electrochemical techniques, which only give an overall view of the corrosion behavior. In addition, combined scanning Kelvin probe force microscopy and magnetic force microscopy were used for mapping the Volta potential variation over the surface of DSSs. A significant difference in Volta potential between the austenite and ferrite phases suggests galvanic interaction between the phases. A compositional gradient appears within 2 micrometers across the phase boundary, as seen with scanning Auger microscopy (SAM). In all, the studies suggest that higher alloyed DSS exhibit a more homogeneous dissolution behavior than lower alloyed DSS, due to higher and more similar corrosion resistance of the two phases, and enhanced resistance of the ferrite/austenite phase boundary regions.
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