| 1. |
- Jaradeh, Majed M. R., et al.
(författare)
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Solidification Studies of 3003 Aluminium Alloys with Cu and Zr Additions
- 2011
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Ingår i: Journal of Materials Science & Technology. - 1005-0302. ; 27:7, s. 615-627
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Tidskriftsartikel (refereegranskat)abstract
- The effects of Cu and Zr additions, on the microstructure formation, precipitation and ingot cracking, in commercial 3003 Al alloys have been studied. The investigation was carried out by characterizing the grain structure in DC-cast rolling ingots, and studying the solidification microstructure of Bridgman directionally solidified samples. To better understand the influence of the different Cu and Zr contents on the phase precipitations, differential thermal analysis (DTA) experiments were performed. Results from the ingot microstructure analysis show that in commercial alloys with relatively high contents of Cu and Zr, no significant differences in measured grain sizes compared to conventional 3003 Al alloys could be found. However, only Zr containing alloys exhibited significantly larger grain sizes. Increased grain refiner and/or titanium additions could compensate for the negative effects on nucleation normally following Zr alloying. Different types of precipitates were observed. Based on DTA experiments, increased Cu and Zr contents resulted in the formation of Al2Cu phase, and increased solidification range. It was also found that increased Mn content favors an early precipitation of Al(6)(Mn,Fe) giving relatively coarse precipitates. It was concluded that the Cu alloying has a detrimental effect on hot tearing.
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| 2. |
- Somani, M.C., et al.
(författare)
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Effects of plastic deformation and stresses on dilatation during the martensitic transformation in a B-bearing steel
- 2001
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Ingår i: Journal of Materials Science & Technology. - 1005-0302. ; 17:2, s. 203-206
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Tidskriftsartikel (refereegranskat)abstract
- To provide data for improved modelling of the behaviour of steel components in a simultaneous forming and quenching process, the effects of plastic deformation and stresses on dilatation during the martensitic transformation in a B-bearing steel were investigated. It was found that plastic deformation of austenite at high temperatures enhances ferrite formation significantly, and consequently, the dilatation decreases markedly even at a cooling rate of 280°C/s. The created ferritic-martensitic microstructure possesses clearly lower hardness and strength than the martensitic structure. Elastic stresses cause the preferred orientation in martensite to be formed so that diametric dilatation can increase by nearly 200% under axial compression
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| 3. |
- Batool, S S., et al.
(författare)
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Comparative Analysis of Ti, Ni, and Au Electrodes on Characteristics of TiO2 Nanofibers for Humidity Sensor Application
- 2013
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Ingår i: Journal of Materials Science & Technology. - : Elsevier. - 1005-0302. ; 29:5, s. 411-414
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Tidskriftsartikel (refereegranskat)abstract
- The effect of metal (Ti, Ni, and Au) electrodes on humidity sensing properties of electrospun TiO2 nanofibers was investigated in this work. The devices were fabricated by evaporating metal contacts on SiO2 layer thermally grown on silicon substrate. The separation between the electrodes was 90 mm for all sensors. The sensors were tested from 40% to 90% relative humidity (RH) by AC electrical characterization at room temperature. When sensors are switched between 40% and 90% RH, the corresponding response and recovery time are 3 s and 5 s for Ti-electrode sensor, 4 s and 7 s for Ni-electrode sensor, and 7 s and 13 s for Au-electrode sensor. The hysteresis was 3%, 5% and 15% for Ti-, Ni-, and Au-electrode sensor, respectively. The sensitivity of Ti, Ni, and Au-electrode sensors are 7.53 M Omega/% RH, 5.29 MU/% RH and 4.01 M Omega/% RH respectively at 100 Hz. Therefore Ti-electrode sensor is found to have linear response, fast response and recovery time and higher sensitivity as compared with those of Ni- and Au-electrode sensors. Comparison of humidity sensing properties of sensors with different electrode material may propose a compelling route for designing and optimizing humidity sensors.
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| 4. |
- Cao, Yanhui, et al.
(författare)
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Layered double hydroxide (LDH) for multi-functionalized corrosion protection of metals : A review
- 2022
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Ingår i: Journal of Materials Science & Technology. - : Elsevier BV. - 1005-0302. ; 102, s. 232-263
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Forskningsöversikt (refereegranskat)abstract
- Layered double hydroxide (LDH) has been widely developed in the field of corrosion and protection in recent years based on its unique characteristics including anion capacity, anion exchange ability, structure memory effect, and barrier resistance. This paper comprehensively reviews recent work on the preparations, properties of LDH in the forms of powder and film and their applications in different environments in corrosion and protection. Some novel perspectives are also proposed at the end of the review for future research in corrosion and protection field.
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| 5. |
- Cheng, Qing, et al.
(författare)
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A revisit to the role of Mo in an MP35N superalloy : An experimental and theoretical study
- 2023
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Ingår i: Journal of Materials Science & Technology. - : Elsevier BV. - 1005-0302. ; 157, s. 60-70
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Tidskriftsartikel (refereegranskat)abstract
- Molybdenum (Mo) has been recognized as an essential alloying element of the MP35N (Co35.4Cr22.9Ni35.5Mo6.2, at.%) superalloy for enhancing strength and corrosion resistance. However, a full understanding of the addition of Mo on microstructure and mechanical properties of the Mo-free parent alloy is lacking. In this work, we consider five (Co37.7Cr24.4Ni37.9)100-xMox (x = 0, 0.7, 2.0, 3.2, and 6.2) alloys, and reveal that yield/tensile strength and ductility are continuously increased for these alloys with increasing Mo content while a single-phase face-centered cubic structure remains unchanged. It is found that strong solid solution strengthening (SSS) is a main domain to the improved yield strength, whereas grain boundaries are found to soften by the Mo addition. The first-principles calculations demonstrate that a severe local lattice distortion contributes to the enhanced SSS, and the grain boundary softening effect is mostly associated with the decreased shear modulus. Both first-principles calculations and scanning transmission electron microscopy observations reveal that the stacking fault energy (SFE) reduces by the Mo addition. The calculated SFE value decreases from 0.4 mJ/m2 to-11.8 mJ/m2 at 0 K as Mo content increases from 0 at.% to 6.2 at.%, and experimentally measured values of SFE at room temperature for both samples are about 18 mJ/m2 and 9 mJ/m2, respectively. The reduction of SFE promoted the generation of stacking faults and deformation twins, which sustain a high strain hardening rate, thus postponing necking instability and enhancing tensile strength and elongation.
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| 6. |
- Cheng, Q., et al.
(författare)
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Unveiling anneal hardening in dilute Al-doped AlxCoCrFeMnNi (x=0, 0.1) high-entropy alloys
- 2021
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Ingår i: Journal of Materials Science & Technology. - : Elsevier BV. - 1005-0302. ; 91, s. 270-277
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Tidskriftsartikel (refereegranskat)abstract
- Anneal hardening has been one of the approaches to improve mechanical properties of solid solution alloys with the face-centered cubic (FCC) structure, whereby a considerable strengthening can be attained by annealing of cold-worked alloys below the recrystallization temperature (T-rx). Microscopically, this hardening effect has been ascribed to several mechanisms, i.e. solute segregation to defects (dislocation and stacking fault) and short-range chemical ordering, etc. However, none of these mechanisms can well explain the anneal hardening recently observed in phase-pure and coarse-grained FCC-structured high-entropy alloys (HEAs). Here we report the observations, using high-resolution electron channeling contrast imaging and transmission electron microscopy, of profuse and stable dislocation substructures in a cold-rolled CoCrFeMnNi HEA subject to an annealing below T-rx. The dislocation substructures are observed to be thermally stable up to T-rx, which could arise from the chemical complexity of the high-entropy system where certain elemental diffusion retardation occurs. The microstructure feature is markedly different from that of conventional dilute solid solution alloys, in which dislocation substructures gradually vanish by recovery during annealing, leading to a strength drop. Furthermore, dilute addition of 2 at.% Al leads to a reduction in both microhardness and yield strength of the cold-rolled and subsequently annealed (<= 500 degrees C) HEA. This Al induced softening effect, could be associated with the anisotropic formation of dislocation substructure, resulting from enhanced dislocation planar slip due to glide plane softening effect. These findings suggest that the strength of HEAs can be tailored through the anneal hardening effect from dislocation substructure strengthening.
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| 7. |
- Cui, Luqing, et al.
(författare)
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A new approach for determining GND and SSD densities based on indentation size effect : An application to additive-manufactured Hastelloy X
- 2022
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Ingår i: Journal of Materials Science & Technology. - : Elsevier. - 1005-0302. ; 96, s. 295-307
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Tidskriftsartikel (refereegranskat)abstract
- Dislocation plays a crucial role in controlling the strength and plasticity of bulk materials. However, determining the densities of geometrically necessary dislocations (GNDs) and statistically stored dislocations (SSDs) is one of the classical problems in material research for several decades. Here, we proposed a new approach based on indentation size effect (ISE) and strengthening theories. This approach was performed on a laser powder bed fused (L-PBF) Hastelloy X (HX), and the results were verified by the Hough-based EBSD and modified Williamson–Hall (m-WH) methods. Furthermore, to better understand the new approach and essential mechanisms, an in-depth investigation of the microstructure was conducted. The distribution of dislocations shows a clear grain orientation-dependent: low density in large <101> preferentially orientated grains while high density in fine <001> orientated grains. The increment of strengthening in L-PBF HX is attributed to a huge amount of edge-GNDs. Planar slip is the main operative deformation mechanism during indentation tests, and the slip step patterns depend mostly on grain orientations and stacking fault energy. This study provides quantitative results of GND and SSD density for L-PBF HX, which constructs a firm basis for future quantitative work on other metals with different crystal structures.
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| 8. |
- Cui, Luqing, et al.
(författare)
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Superior low cycle fatigue property from cell structures in additively manufactured 316L stainless steel
- 2022
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Ingår i: Journal of Materials Science & Technology. - Amsterdam, Netherlands : Elsevier. - 1005-0302. ; 111, s. 268-278
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the low cycle fatigue (LCF) properties and the extent of strengthening in a dense additively manufactured stainless steel containing different volume fractions of cell structures but having all other microstructure characteristics the same. The samples were produced by laser powder bed fusion (L-PBF), and the concentration of cell structures was varied systematically by varying the annealing treatments. Load-controlled fatigue experiments performed on samples with a high fraction of cell structures reveal an up to 23 times increase in fatigue life compared to an essentially cell-free sample of the same grain configuration. Multiscale electron microscopy characterizations reveal that the cell structures serve as the soft barriers to the dislocation propagation and the partials are the main carrier for cyclic loading. The cell structures, stabilized by the segregated atoms and misorientation between the adjacent cells, are retained during the entire plastic deformation, hence, can continuously interact with dislocations, promote the formation of nanotwins, and provide massive 3D network obstacles to the dislocation motion. The compositional micro-segregation caused by the cellular solidification features serves as another non-negligible strengthening mechanism to dislocation motion. Specifically, the cell structures with a high density of dislocation debris also appear to act as dislocation nucleation sites, very much like coherent twin boundaries. This work indicates the potential of additive manufacturing to design energy absorbent alloys with high performance by tailoring the microstructure through the printing process.
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| 9. |
- Deng, Jiangning, et al.
(författare)
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Texture Evolution in Heavily Cold-Rolled FeCo-2V Alloy during Annealing
- 2009
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Ingår i: JOURNAL OF MATERIALS SCIENCE and TECHNOLOGY. - 1005-0302. ; 25:2, s. 219-224
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Tidskriftsartikel (refereegranskat)abstract
- The recrystallization texture evolution in heavily cold-rolled (93%) FeCo-2V alloy with annealing temperature and time was investigated by X-ray diffraction and electron backscatter diffraction. It was found that the orientation density of a-fiber texture component fluctuates with increasing annealing temperature and time. The transmission electron microscopy images show that abundant precipitates appear inside the recrystallized grains and around the grain boundaries. The amount and size of the precipitates also vary with annealing temperature and time. The enhancement of the a-fiber coincides well with the increase of number density of fine precipitates, indicating that the fine precipitates facilitate the development of a-fiber. The annealing texture evolution observed in the FeCo alloy could be attributed to the facilitating effect of the precipitates on the development of a-fiber and the ordering process.
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| 10. |
- Ding, Yu, et al.
(författare)
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Hydrogen trapping and diffusion in polycrystalline nickel : The spectrum of grain boundary segregation
- 2024
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Ingår i: Journal of Materials Science & Technology. - : Elsevier. - 1005-0302. ; 173, s. 225-236
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogen as an interstitial solute at grain boundaries (GBs) can have a catastrophic impact on the mechanical properties of many metals. Despite the global research effort, the underlying hydrogen-GB interactions in polycrystals remain inadequately understood. In this study, using Voronoi tessellations and atomistic simulations, we elucidate the hydrogen segregation energy spectrum at the GBs of polycrystalline nickel by exploring all the topologically favorable segregation sites. Three distinct peaks in the energy spectrum are identified, corresponding to different structural fingerprints. The first peak ( -0.205 eV) represents the most favorable segregation sites at GB core, while the second and third peaks account for the sites at GB surface. By incorporating a thermodynamic model, the spectrum enables the determination of the equilibrium hydrogen concentrations at GBs, unveiling a remarkable two to three orders of magnitude increase compared to the bulk hydrogen concentration reported in experimental studies. The identified structures from the GB spectrum exhibit vastly different behaviors in hydrogen segregation and diffusion, with the low-barrier channels inside GB core contributing to short-circuit diffusion, while the high energy gaps between GB and neighboring lattice serving as on-plane diffusion barriers. Mean square displacement analysis further confirms the findings, and shows that the calculated GB diffusion coefficient is three orders of magnitude greater than that of lattice. The present study has a significant implication for practical applications since it offers a tool to bridge the gap between atomic-scale interactions and macroscopic behaviors in engineering materials.& COPY; 2023 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology. This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ )
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| 11. |
- Dong, Zhihua, et al.
(författare)
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MnxCr0.3Fe0.5Co0.2Ni0.5Al0.3 high entropy alloys for magnetocaloric refrigeration near room temperature
- 2021
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Ingår i: Journal of Materials Science & Technology. - : Chinese Society of Metals. - 1005-0302. ; 79, s. 15-20
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Tidskriftsartikel (refereegranskat)abstract
- High entropy alloys (HEAs) based on transition metals display rich magnetic characteristics, however attempts on their application in energy efficient technologies remain scarce. Here, we explore the magnetocaloric application for a series of MnxCr0.3Fe0.5Co0.2Ni0.5Al0.3 (0.8 < x < 1.1) HEAs by integrated theoretical and experimental methods. Both theory and experiment indicate the designed HEAs have the Curie temperature close to room temperature and is tunable with Mn concentration. A non-monotonic evolution is observed for both the entropy change and the relative cooling power with changing Mn concentration. The underlying atomic mechanism is found to primarily emerge from the complex impact of Mn on magnetism. Advanced magnetocaloric properties can be achieved by tuning Mn concentration in combination with controlling structural phase stability for the designed HEAs.
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| 12. |
- Gui, Lintao, et al.
(författare)
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Quantitative effects of phase transition on solute partition coefficient, inclusion precipitation, and microsegregation for high-sulfur steel solidification
- 2019
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Ingår i: Journal of Materials Science & Technology. - : JOURNAL MATER SCI TECHNOL. - 1005-0302. ; 35:10, s. 2383-2395
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Tidskriftsartikel (refereegranskat)abstract
- Segregation and inclusion precipitation are the common behaviours of steel solidification, which are resulted from the redistribution and diffusion of the solute elements at the solid-liquid interface. The effect of the phase transition of high-sulfur free-cutting steel is quantified in the present work for the solute partition coefficient (k(i)), inclusion precipitation, and microsegregation by establishing a coupling model of microsegregation and inclusion precipitation, wherein the quantified dependencies of k(i) in terms of temperature, phase and carbon temperature range and phase transition of high-sulfur steel that under different solidification paths and C contents were quite different, leading to differences in k(i) and eventually in microsegregation. k k(p), and k(s) were mainly affected by phase composition and k(si) was primarily by temperature, while k(mn) depended on both phase composition and temperature during solidification. Increasing the C content within the interval 0.07-0.48 wt%, the 'proportion of the delta phase maintained temperature region during solidification' (P-delta), k(p)(ave) and k(s)(ave) (k(i)(ave) the average value of the k(i) across the whole stages of solidification) decreased monotonically, whereas k phase composition and k(i), leading to the change in microsegregation. Such effect of the peritectic reaction was more significant at the last stage of solidification. When the P-delta was between 75% and 100% (corresponding to 0.07-0.16 wt% C), the solidification path resulted in a greater effect on the microsegregation of solutes C, P, and S because of the peritectic reaction. The microsegregation of solutes Mn and S were comprehensively influenced by k(Mn), k(s) and MnS precipitation as well. The studies would help reveal the solute redistribution at the solid-liquid interface, and improve the segregation of high-sulfur steel by controlling the solidification and precipitation in practice.
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| 13. |
- Guo, Lulu, et al.
(författare)
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Additive manufacturing of 18% nickel maraging steels : Defect, structure and mechanical properties: A review
- 2022
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Ingår i: Journal of Materials Science & Technology. - : Chinese Society of Metals. - 1005-0302. ; 120, s. 227-252
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Tidskriftsartikel (refereegranskat)abstract
- This paper reviews the latest research progress in the additive manufacturing (AM) process of 18% nickel maraging steels, which involves laser-based powder bed fusion (L-PBF), laser-based directed energy deposition (L-DED), and wire arc additive manufacturing (WAAM). The emphasis is on the defects, structure, and mechanical properties of the additive manufactured 18% nickel maraging steels. At first, this article outlines the influences of the processing parameters of AM techniques on the defects formed in the fabricated parts, in terms of the L-PBF and WAAM. The macrostructure and microstructure characteristics of as-built and heat-treated 18% nickel maraging steel are then described in detail. Later, the mechanical properties of as-built and heat-treated 18% nickel maraging steel are assessed, such as their tensile, hardness, impact toughness, and fatigue performances. Finally, future directions for work on the AM of 18% nickel maraging steel are provided.
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| 14. |
- Jiang, Shuang, et al.
(författare)
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Microstructural and textural evolutions in multilayered Ti/Cu composites processed by accumulative roll bonding
- 2019
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Ingår i: Journal of Materials Science & Technology. - : JOURNAL MATER SCI TECHNOL. - 1005-0302. ; 35:6, s. 1165-1174
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Tidskriftsartikel (refereegranskat)abstract
- Ti/Cu multilayered composites were fabricated via accumulative roll bonding (ARB). During co-deformation of the constituent metals, the hard Ti layers necked preferentially and then fragmented with the development of shear bands. Transmission electron microscopy showed that with increasing ARB cycles, grains in Ti were significantly refined even though dynamic recrystallization has occurred. For Cu the significant grain refinement was only found within the shear banded region when the composite was processed after five ARB cycles. Due to the diffusion of Cu atoms into Ti at the heterophase inter faces, amorphization with a width less than 10 nm was identified even in the composite processed by one cycle. At higher ARB cycles, the width of amorphous region increased and intermetallic compounds CuTi appeared from the region. The lattice defects introduced at the heterophase interfaces under roll bonding was responsible for the formation of the nano-scaled compounds. X-ray diffraction showed that an abnormal {11 (2) over bar0} fiber texture was developed in Ti layers, while significant brass-type textures were developed in Cu layers. Some orientations along the {11 (2) over bar0} fiber favored the prismatic amp;lt;aamp;gt; slip for Ti. Tensile tests revealed the elevated strength without a substantial sacrifice of ductility in the composites during ARB. The unique mechanical properties were attributed to the significantly refined grains in individual metals, the good bonding between the constituent metals, as well as the development of an abnormal {11 (2) over bar0} fiber texture in Ti layers. (C) 2019 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science amp; Technology.
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| 15. |
- Jiang, Shuang, et al.
(författare)
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Shear banding-induced ⟨c + a⟩ slip enables unprecedented strength-ductility combination of laminated metallic composites
- 2022
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Ingår i: Journal of Materials Science & Technology. - Shenyang, China : Elsevier. - 1005-0302. ; 110, s. 260-268
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Tidskriftsartikel (refereegranskat)abstract
- Shear bands in metallic materials have been reported to be catastrophic because they normally lead to non-uniform plastic deformation. Ductility of laminated metallic composites deteriorates with increasing processing strain, particularly for those having hexagonal-close-packed (hcp) constituents due to inadequate slip systems and consequently prominent shear banding. Here, we propose a design strategy that counterintuitively tolerates the bands with localized strains, i.e. the shear banded laminar (SBL) structure, which promotes ⟨c + a⟩ dislocation activation in hcp metals and renders unprecedented strengthductility combination in hcp-metal-based composites fabricated by accumulative roll bonding (ARB). The SBL structure is characterized with one soft hcp metal constrained by adjacent hard metal in which dislocations have been accumulated near the bimetal interfaces. High-energy X-ray diffraction astonishingly reveals that more than 90% of dislocations are non-basal in Ti layers of the SBL Ti/Nb composite processed by eight ARB cycles. Moreover, ⟨c + a⟩ dislocations occupy a high fraction of ∼30%, promoting further ⟨c + a⟩ cross slip. The unique stress field tailored by both shear banding and heterophase interface-mediated deformation accommodation triggers important ⟨c + a⟩ slip. This SBL design is of significance for developing hcp-based laminates and other heterostructured materials with high performances.
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| 16. |
- Kunwar, Anil, et al.
(författare)
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Integration of machine learning with phase field method to model the electromigration induced Cu6Sn5 IMC growth at anode side Cu/Sn interface
- 2020
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Ingår i: Journal of Materials Science and Technology. - : Elsevier BV. - 1005-0302. ; 59, s. 203-219
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Tidskriftsartikel (refereegranskat)abstract
- Currently, in the era of big data and 5G communication technology, electromigration has become a serious reliability issue for the miniaturized solder joints used in microelectronic devices. Since the effective charge number (Z*) is considered as the driving force for electromigration, the lack of accurate experimental values for Z* poses severe challenges for the simulation-aided design of electronic materials. In this work, a data-driven framework is developed to predict the Z* values of Cu and Sn species at the anode based LIQUID, Cu6Sn5 intermetallic compound (IMC) and FCC phases for the binary Cu-Sn system undergoing electromigration at 523.15 K. The growth rate constants (kem) of the anode IMC at several magnitudes of applied low current density (j = 1 × 106 to 10 × 106 A/m2) are extracted from simulations based on a 1D multi-phase field model. A neural network employing Z* and j as input features, whereas utilizing these computed kem data as the expected output is trained. The results of the neural network analysis are optimized with experimental growth rate constants to estimate the effective charge numbers. For a negligible increase in temperature at low j values, effective charge numbers of all phases are found to increase with current density and the increase is much more pronounced for the IMC phase. The predicted values of effective charge numbers Z* are then utilized in a 2D simulation to observe the anode IMC grain growth and electrical resistance changes in the multi-phase system. As the work consists of the aspects of experiments, theory, computation, and machine learning, it can be called the four paradigms approach for the study of electromigration in Pb-free solder. Such a combination of multiple paradigms of materials design can be problem-solving for any future research scenario that is marked by uncertainties regarding the determination of material properties.
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| 17. |
- Lan, Meng, et al.
(författare)
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Highly redispersible CNT dough for better processiblity
- 2023
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Ingår i: Journal of Materials Science & Technology. - : Elsevier BV. - 1005-0302. ; 152, s. 65-74
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Tidskriftsartikel (refereegranskat)abstract
- Carbon nanotubes (CNTs) have received considerable attention for their excellent thermal and electrical conductivity as well as scalable production. However, CNT dispersions are prone to settling and have a short shelf time, especially under high concentration, which significantly hinders their further processing and increases transportation costs. Here, we report a highly concentrated CNT dough enabled by ionic liquid crystal (ILC) as auxiliaries. Benefiting from the temperature-controlled physical transformation of the ILC, the CNTs of the powder state are successfully transferred to highly processable dough with excellent electrical conductivity, flame retardancy, and outstanding redispersibility even after 180 days of storage. In particular, the CNT dough exhibits excellent self-healing properties and good reshapable capability. Various bulk form CNT derived from the ILC armored CNT dough are realized by facile processing technique. Hybrid nanocomposite papers with ANF nanofiber exhibited excellent photothermal conversion and Joule heating properties. The redispersible CNT doughs presented here promise to revolutionize traditional CNT powder and dispersions as the primary raw material for building CNT-based architectures and facilitate the large-scale application of CNTs.
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| 18. |
- Le, Thanh-Tung, et al.
(författare)
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Phosphorus-doped Fe7S8@C nanowires for efficient electrochemical hydrogen and oxygen evolutions: Controlled synthesis and electronic modulation on active sites
- 2021
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Ingår i: Journal of Materials Science & Technology. - : JOURNAL MATER SCI TECHNOL. - 1005-0302. ; 74, s. 168-175
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Tidskriftsartikel (refereegranskat)abstract
- Developing low-cost, efficient, and stable non-precious-metal electrocatalysts with controlled crystal structure, morphology and compositions are highly desirable for hydrogen and oxygen evolution reactions. Herein, a series of phosphorus-doped Fe7S8 nanowires integrated within carbon (P-Fe7S8@C) are rationally synthesized via a one-step phosphorization of one-dimensional (1D) Fe-based organic-inorganic nanowires. The as-obtained P-Fe7S8@C catalysts with modified electronic configurations present typical porous structure, providing plentiful active sites for rapid reaction kinetics. Density functional calculations demonstrate that the doping Fe7S8 with P can effectively enhance the electron density of Fe7S8 around the Fermi level and weaken the Fe-H bonding, leading to the decrease of adsorption free energy barrier on active sites. As a result, the optimal catalyst of P-Fe7S8-600@C exhibits a relatively low overpotential of 136 mV for hydrogen evolution reaction (HER) to reach the current density of 10 mA/cm(2), and a significantly low overpotential of 210 mV for oxygen evolution reaction (OER) at 20 mA/cm(2) in alkaline media. The work presented here may pave the way to design and synthesis of other prominent Fe-based catalysts for water splitting via electronic regulation. (C) 2021 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.
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| 19. |
- Li, Shaohan, et al.
(författare)
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Pushing the limit of thermal conductivity of MAX borides and MABs
- 2022
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Ingår i: Journal of Materials Science & Technology. - : Elsevier. - 1005-0302. ; 97, s. 79-88
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Tidskriftsartikel (refereegranskat)abstract
- The emergence of MAX borides as well as MAB phases attracted great attention because of the renewable developments of ternary ceramics and offering great opportunities in potential applications. However, the number of borides remains limited, and further fundamental descriptions and detailed investigations on various properties are still lacking. In this report, we employ an integrated computational scheme that combines density functional theory with the evolutional algorithm to search for the favorable structures of P- and S-glued ternary borides terminated by Nb metal. We discover that the structures of 212-type, as e.g. Nb2PB2 and Nb2SB2, belong to the P‾6m2 space group, while those of 211-type, as e.g. Nb2PB and Nb2SB, prefer to crystallize in the P63/mmc space group, and the corresponding carbides Nb2PC and Nb2SC are also considered for the sake of completeness and comparative analsys. The predicted Nb2PB2, Nb2PB, Nb2SB, Nb2PC and Nb2SC are energetically stable, as revealed by the negative formation energies and by the proposed reaction paths with respect to the most competing phases, as well as dynamically stable, as suggested by the non-imaginary phonon spectra. The thermal conductivities of the six materials show unusual behaviors, particularly for the acoustic and optical contributions, and are accompanied by a strong anisotropy. Most importantly, Nb2PB2 is found to be an excellent thermal conductor with a total thermal conductivity of ~65 W/(m K), while Nb2SC is found to be an ultra-low thermal conductor, with a total thermal conductivity of ~5 W/(m K). These values are clearly outside the currently reported range of thermal conductivities, which makes Nb2PB2 and Nb2SC extremely interesting for fundamental research as well as prospective applications with the aid of artificial tunings on the almost independent MB block and the A layer. The discovery of these novel materials is expected to contribute substantially to the rapid development of ternary ceramics and to accelerate attempts in the applicability of MAX phases for heat conduction.
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| 20. |
- Li, Xue, et al.
(författare)
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Self-supported porous copper oxide nanosheet arrays for efficient and selective electrochemical conversion of nitrate ions to nitrogen gas
- 2023
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Ingår i: Journal of Materials Science & Technology. - : Elsevier. - 1005-0302. ; 137, s. 104-111
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Tidskriftsartikel (refereegranskat)abstract
- Electrochemical techniques have shown advantages for the removal of low-concentration nitrate. Here, copper oxide nanosheets were grown on self-supporting nickel foam (NF) to prepare electrodes (CuO/NF), which realized the rapid and highly selective conversion of nitrate pollutants in sewage into nontoxic and harmless N2. The CuO/NF afforded 100% NO3– removal within 100 min and 99.53% selectivity for N2 at –50 mA without producing a lot of by-products (NO2–, NH4+, and N2H4). Furthermore, 81.8% of NO3– was removed under the given conditions after six experimental repetitions. These results suggest that the catalyst has excellent electrochemical stability. The performance of CuO/NF for the electrocatalytic removal of NO3– in simulated wastewater (which contained Cl– and SO42–) was almost unaffected. Because of the high efficiency, high stability, and low cost of CuO/NF, this catalyst is practical for the removal of nitrate for wastewater purification.
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| 21. |
- Li, Yi, et al.
(författare)
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Promoting photocatalytic hydrogen evolution by modulating the electron-transfer in an ultrafast timescale through Mo-S6 configuration
- 2024
-
Ingår i: Journal of Materials Science and Technology. - 1005-0302. ; 193, s. 73-80
-
Tidskriftsartikel (refereegranskat)abstract
- Maximizing ultrafast electron-transfer kinetics in semiconductor is pivotal but challenging for high-efficiency solar-to-energy during the photocatalytic reaction process due to the intrinsic property of photocatalysts with low surface electron density. Herein, a model photocatalyst CdS@Mo is synthesized through a typical hydrothermal method for modulating the ultrafast electron-transfer to enhance the surface electron density. X-ray absorption fine spectra (XAFS) reveal that Mo is coordinated with S atoms to form a Mo-S6 configuration which is different from common MoS2 and Mo foil structures. Based on the femtosecond transient absorption spectra (fs-TAS), it is found that the formation of Mo-S6 configuration contributes to the fast decay of CdS signal and Mo-S6 signal reactivation, illustrating the ultrafast electron-transfer (∼2.2 ps) from CdS to Mo-S6 configuration, which achieves the enhanced electron density of photocatalyst surface. Finally, a holistic photocatalytic performance evaluation discloses that the growing of Mo-S6 configuration obviously improves the photocatalytic hydrogen evolution (PHE) efficiency of CdS from 28.5 to 47.5 mmol g–1 h–1 with a solar-to-hydrogen (STH) efficiency of 0.10 % which is seldomly discussed in the system containing sacrificial agents. This work opens a new path to modulate the surface electron density by tuning the ultrafast electron-transfer for enhancing reaction efficiency in electron-density-dependent systems.
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| 22. |
- Ni, Y., et al.
(författare)
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Corrosion mechanism of CuAl-NiC abradable seal coating system—The influence of porosity, multiphase, and multilayer structure on the corrosion failure
- 2021
-
Ingår i: Journal of Materials Science & Technology. - : Elsevier BV. - 1005-0302. ; 88, s. 258-269
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, the corrosion behavior of the CuAl-NiC abradable seal coating system in chloride solution was investigated to systematically research the effect of porosity, multiphase, and multilayer structure on the corrosion failure. Through the composition and structure analysis, the corrosion process of the system was predicted and then verified with mercury intrusion porosimetry, cross-section SEM/EDS analysis, and electrochemical measurements. The results demonstrated that the interphase selective corrosion caused the porosity of the top layer to decrease first and then increase during the corrosion development. The interlayer galvanic corrosion, determined by the pore connectivity, is crucial for corrosion failure.
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| 23. |
- Ren, Yaojia, et al.
(författare)
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A comparative study on microstructure, nanomechanical and corrosion behaviors of AlCoCuFeNi high entropy alloys fabricated by selective laser melting and laser metal deposition
- 2022
-
Ingår i: Journal of Materials Science and Technology. - : Elsevier BV. - 1005-0302. ; 131, s. 221-230
-
Tidskriftsartikel (refereegranskat)abstract
- The present study investigated the microstructure, nanomechanics, and corrosion behavior of AlCoCuFeNi high entropy alloys fabricated by selective laser melting (SLM) and laser metal deposition (LMD). The microstructure of SLM-processed specimens was mainly composed of columnar-grained BCC matrix (∼90 µm in width) and Cu-rich twinned FCC phase. The columnar grains grew epitaxially along the building direction and exhibited a strong {001} texture. In comparison, a coarse columnar-grained BCC matrix (∼150 µm in width) with a stronger 〈001〉 texture, rod-like B2 precipitates, and large core-shell structured FCC phases were formed in the LMD-processed specimens due to the higher heat accumulation effect. Consequently, the LMD-processed specimens showed a lower hardness, wear resistance, and corrosion resistance, but higher creep resistance and reduced Young's modulus than the SLM-processed specimens. Hot cracks occurred in both types of specimens, which could not be completely suppressed due to Cu segregation.
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| 24. |
- Scholz, S. M., et al.
(författare)
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Raman spectroscopic study of silicon nanopowders
- 1997
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Ingår i: Journal of Materials Science & Technology. - : Chinese Society of Metals. - 1005-0302. ; 13:4, s. 327-332
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Tidskriftsartikel (refereegranskat)abstract
- Vibrational properties of silicon nanopowders are discussed with reference to Raman spectroscopic measurements. The powders were produced in a low pressure rf plasma from the cluster induced agglomeration of positive ions formed during the dissociation of silane. Influence of thermal treatment and the crystallization phenomena of the powder were studied. Raman spectroscopic measurements reveal size quantization effects for the particles as well as the existence of partially ordered regions in the apparently amorphous primary particles. The crystalline and amorphous volume fraction in the material were calculated from the relative spectral intensities. The results obtained in these experiments are consistent with the observations from recent high resolution transmission electron microscopy studies of these powders.
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| 25. |
- Shuang, S., et al.
(författare)
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Unusually high corrosion resistance in MoxCrNiCo medium entropy alloy enhanced by acidity in aqueous solution
- 2023
-
Ingår i: Journal of Materials Science & Technology. - : Elsevier BV. - 1005-0302. ; 139, s. 59-68
-
Tidskriftsartikel (refereegranskat)abstract
- High corrosion resistance of alloys is essential for their structural applications; however, most alloys suffer from degradation of their corrosion resistance with the increasing acidity of their surround-ings. Nonetheless, we developed a series of medium-entropy alloys (MEAs) in this work, which ex-hibit high strength, superior fracture toughness and ultra-high corrosion resistance, outperforming the variety of corrosion resistant alloys hitherto reported. Most interestingly, our MEAs exhibit an unusual anti-corrosion behavior and their corrosion resistance increases with acidity in Cl- containing solutions. Through extensive thermodynamic calculations, density functional theory (DFT) simulations and experi-ments, we reveal that the unusual anti-corrosion behavior of our MEAs can be attributed to their surface chemical complexity, which facilitates the physio-chemical-absorption of H2O and O 2 and thus the rapid formation of metastable medium entropy passive films that contain the lowest amount of defects, as compared to the passive films on conventional alloys reported in the literature.
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| 26. |
- Stormvinter, Albin, et al.
(författare)
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A Transmission Electron Microscopy Study of Plate Martensite Formation in High-carbon Low Alloy Steels
- 2013
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Ingår i: Journal of Materials Science & Technology. - : Elsevier BV. - 1005-0302. ; 29:4, s. 373-379
-
Tidskriftsartikel (refereegranskat)abstract
- The martensitic microstructures in two high-carbon low alloy steels have been investigated by classical and automated crystallographic analysis under a transmission electron microscope. It is found that the martensitic substructure changes from consisting mostly of transformation twins for 1.20 mass% carbon (C) steel to both transformation twins and planar defects on {101}(M) for 1.67 mass% C steel. In the 1.67 mass% C steel it is further found that small martensite units have a rather homogeneous substructure, while large martensite units are more inhomogeneous. In addition, the martensite units in both steels are frequently found to be of zigzag patterns and have distinct crystallographic relationships with neighboring martensite units, e.g. kink or wedge couplings. Based on the present findings the development of martensite in high-carbon low alloy steels is discussed and a schematic of the martensite formation is presented. Moreover, whether the schematic view can be applied to plate martensite formation in general, is discussed.
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| 27. |
- Tan, Qiyang, et al.
(författare)
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Unravelling the roles of TiN-nanoparticle inoculant in additively manufactured 316 stainless steel
- 2024
-
Ingår i: Journal of Materials Science & Technology. - : Elsevier BV. - 1005-0302. ; 175, s. 153-169
-
Tidskriftsartikel (refereegranskat)abstract
- As a potent grain refiner for steel casting, TiN is now widely used to refine γ-austenite in steel additive manufacturing (AM). However, the refining mechanism of TiN during AM remains unclear despite intensive research in recent years. This work aims to boost our understanding on the mechanism of TiN in refining the γ-austenite in AM-fabricated 316 stainless steel and its corresponding effect on the mechanical behaviour. Experimental results show that addition of 1 wt.% TiN nanoparticles led to complete columnar-to-equiaxed transition and significant refinement of the austenite grains to ∼2 µm in the 316 steel. Thermodynamic and kinetic simulations confirmed that, despite the rapid AM solidification, δ-ferrite is the primary solid phase during AM of the 316 steel and γ-austenite forms through subsequent peritectic reaction or direct transformation from the δ-ferrite. This implies that the TiN nanoparticles actually refined the δ-ferrite through promoting its heterogenous nucleation, which in turn refined the γ-austenite. This assumption is verified by the high grain refining efficiency of TiN nanoparticles in an AM-fabricated Fe-4 wt.%Si δ-ferrite alloy, in which δ-ferrite forms directly from the melt and is retained at room temperature. The grain refinement is attributed to the good atomic matching between δ-ferrite and TiN. Grain refinement in the 316 steel through 1 wt.% TiN inoculation not only eliminated the property anisotropy but also led to a high strain-hardening rate upon plastic deformation and thereby a superior strength-ductility synergy with yield strength of 561 MPa, tensile strength of 860 MPa and elongation of 48%.
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| 28. |
- Wan, Yi, et al.
(författare)
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Osteogenic and antibacterial ability of micro-nano structures coated with ZnO on Ti-6Al-4V implant fabricated by two-step laser processing
- 2022
-
Ingår i: Journal of Materials Science & Technology. - : Elsevier BV. - 1005-0302. ; 131, s. 240-252
-
Tidskriftsartikel (refereegranskat)abstract
- The biological performance of Ti-6Al-4V implant is primarily determined by their surface properties. However, traditional surface modification methods, such as acid etching, hardly make improvement in their osseointegration ability and antibacterial capacity. In this study, we prepared a multi-scale composite structure coated with zinc oxide (ZnO) on Ti-6Al-4V implant by an innovative technology of two-step laser processing combined with solution-assistant. Compared with the acid etching method, the physicochemical properties of surface significantly improved. The in vitro results showed that the particular dimension of micro-nano structure and the multifaceted nature of ZnO synergistically affected MC3T3-E1 osteogenesis and bacterial activities: (1) The surface morphology showed a 'contact guidance' effect on cell arrangement, which was conducive to the adhesion of filopodia and cell spreading, and the osteogenesis level of MC3T3-E1 was enhanced due to the release of zinc ions (Zn2+); (2) the characterization of bacterial response revealed that periodic nanostructures and Zn2+ released could cause damage to the cell wall of E. coli and reduce the adhesion and aggregation of S. aureus. In conclusion, the modified surface showed a synergistic effect of physical topography and chemical composition, making this a promising method and providing new insight into bone defect repairment.
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| 29. |
- Wang, Chenchong, et al.
(författare)
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A generic and extensible model for the martensite start temperature incorporating thermodynamic data mining and deep learning framework
- 2022
-
Ingår i: Journal of Materials Science & Technology. - : Elsevier BV. - 1005-0302. ; 128, s. 31-43
-
Tidskriftsartikel (refereegranskat)abstract
- The martensite start temperature is a critical parameter for steels with metastable austenite. Although numerous models have been developed to predict the martensite start (M-s) temperature, the complexity of the martensitic transformation greatly limits their performance and extensibility. In this work, we apply deep data mining of thermodynamic calculations and deep learning to develop a generic model for M-s prediction. Deep data mining was used to establish a hierarchical database with three levels of information. Then, a convolutional neural network model, which can accurately treat the hierarchical data structure, was used to obtain the final model. By integrating thermodynamic calculations, traditional machine learning and deep learning modeling, the final predictor model shows excellent generalizability and extensibility, i.e. model performance both within and beyond the composition range of the original database. The effects of 15 alloying elements were considered successfully using the proposed methodology. The work suggests that, with the help of deep data mining considering the physical mechanisms, deep learning methods can partially mitigate the challenge with limited data in materials science and provide a means for solving complex problems with small databases.
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| 30. |
- Yang, Zhibiao, et al.
(författare)
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Assessing the magnetic order dependent gamma-surface of Cr-Co-Ni alloys
- 2021
-
Ingår i: Journal of Materials Science & Technology. - : Elsevier BV. - 1005-0302. ; 80, s. 66-74
-
Tidskriftsartikel (refereegranskat)abstract
- In order to efficiently explore the nearly infinite composition space in multicomponent solid solution alloys for reaching higher mechanical performance, it is important to establish predictive design strategies using computation-aided methods. Here, using ab initio calculations we systematically study the effects of magnetism and chemical composition on the generalized stacking fault energy surface (gamma-surface) of Cr-Co-Ni medium entropy alloys and show that both chemistry and the coupled magnetic state strongly affect the gamma-surface, consequently, the primary deformation modes. The relations among various stable and unstable stacking fault energies are revealed and discussed. The present findings are useful for studying the deformation behaviors of Cr-Co-Ni alloys and facilitate a density functional theory based design of transformation-induced plasticity and twinning-induced plasticity mechanisms in Cr-Co-Ni alloys.
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| 31. |
- Yang, Zhibiao, et al.
(författare)
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Theoretical and experimental study of phase transformation and twinning behavior in metastable high-entropy alloys
- 2022
-
Ingår i: Journal of Materials Science & Technology. - : Elsevier BV. - 1005-0302. ; 99, s. 161-168
-
Tidskriftsartikel (refereegranskat)abstract
- Combined theoretical and experimental efforts are put forward to study the critical factors influencing deformation mode transitions in face-centered cubic materials. We revisit the empirical relationship between the stacking fault energy (SFE) and the prevalent deformation mechanism. With ab initio calculated SFE, we establish the critical boundaries between various deformation modes in the model Cr-CoNi solid solution alloys. Satisfying agreement between theoretical predictions and experimental observations are reached. Our findings shield light on applying quantum mechanical calculations in designing transformation-induced plasticity and twinning-induced plasticity mechanisms for achieving advanced mechanical properties.
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| 32. |
- Yu, Peng, et al.
(författare)
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A modified theta projection model for creep behavior of RPV steel 16MND5
- 2020
-
Ingår i: Journal of Materials Science & Technology. - : Elsevier. - 1005-0302. ; 47, s. 231-242
-
Tidskriftsartikel (refereegranskat)abstract
- During a hypothetical severe accident of light water reactors, the reactor pressure vessel (RPV) could fail due to its creep under the influence of high-temperature corium. Hence, modelling of creep behavior of the RPV is paramount to reactor safety analysis since it predicts the transition point of accident progression from in-vessel to ex-vessel phase. In the present study we proposed a new creep model for the classical French RPV steel 16MND5, which is adapted from the “theta-projection model” and contains all three stages of a creep process. Creep curves are expressed as a function of time with five model parameters θi(i=1−4 and m). A model parameter dataset was constructed by fitting experimental creep curves into this function. To correlate the creep curves for different temperatures and stress loads, we directly interpolate the model’s parameters θi(i=1−4 and m) from this dataset, in contrast to the conventional “theta-projection model” which employs an extra single correlation for each θi(i=1−4 and m), to better accommodate all experimental curves over the wide ranges of temperature and stress loads. We also put a constraint on the trend of the creep strain that it would monotonically increase with temperature and stress load. A good agreement was achieved between each experimental creep curve and corresponding model’s prediction. The widely used time-hardening and strain-hardening models were performing reasonably well in the new method.
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| 33. |
- Yu, Z., et al.
(författare)
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Explanation of unusual photoluminescence behavior from InAs quantum dots with InAlAs capping
- 2005
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Ingår i: Journal of Materials Science and Technology. - 1005-0302. ; 21:4, s. 559-562
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Tidskriftsartikel (refereegranskat)abstract
- The effect of different kinds of cap layers on optical property of InAs quantum dots (QDs) on GaAs (100) substrate was studied. Temperature dependent photoluminescence (PL) indicates that the PL integrated intensity from the ground state of InAs QDs capped with an intermediate InAlAs layer drops very little as compared to QDs capped with a thin InGaAs or GaAs cap layer from 15 K up to room temperature. PL integrated intensity ratio of the first excited to ground states for InAs QDs capped with an intermediate InAlAs layer is unexpectedly decreased with increasing temperature, which are attributed to phonon bottleneck effect. A virtual barrier is proposed to describe this physics process and shows good agreement with experimental results when fitting the curve with the value of the virtual barrier 30 meV.
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| 34. |
- Yue, Xiaoqi, et al.
(författare)
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Passivation characteristics of ultra-thin 316L foil in NaCl solutions
- 2022
-
Ingår i: Journal of Materials Science & Technology. - : Elsevier BV. - 1005-0302. ; 127, s. 192-205
-
Tidskriftsartikel (refereegranskat)abstract
- Electrochemical behaviour and passive film characteristics of an ultra-thin 316L foil with a thickness of 20 ??m in 3.5 wt.% NaCl solution were investigated using multiple techniques, focusing on the effect of microstructure, the applied potential, and the pH of the solution. The microstructure contains mainly fine grains ( ???4 ??m) with high-angle boundaries and preferential orientation of (220), and no MnS inclusion was detected. The electrochemical measurements show a significantly higher breakdown potential and lower passive current density for the 316L foil than traditional wrought 316L. The surface analyses using angle-resolved X-ray photoelectron spectroscopy (ARXPS) and time-of-flight secondary ion mass spectroscopy (TOF-SIMS) reveal that, compared to the wrought material, both the inner and out parts of the passive film on the 316L foil are more enriched in Cr- and Mo-oxides. The microstructure favourable for elemental diffusion and the absence of MnS inclusion facilitate the formation of a continuous compact Cr- and Mo-rich passive film, which effectively retards corrosion in NaCl solution and remains stable in acidic solution (pH 2) or at high polarised potential up to 600 mV vs Ag/AgCl. ?? 2022 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology. This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ )
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| 35. |
- Yue, Xiaoqi, et al.
(författare)
-
Unveiling nano-scale chemical inhomogeneity in surface oxide films formed on V- and N-containing martensite stainless steel by synchrotron X-ray photoelectron emission spectroscopy/microscopy and microscopic X-ray absorption spectroscopy
- 2025
-
Ingår i: Journal of Materials Science & Technology. - : Chinese Society of Metals. - 1005-0302. ; 205, s. 191-203
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Tidskriftsartikel (refereegranskat)abstract
- Nano-scale chemical inhomogeneity in surface oxide films formed on a V- and N-containing martensite stainless steel and tempering heating induced changes are investigated by a combination of synchrotron- based hard X-ray Photoelectron emission spectroscopy (HAXPES) and microscopy (HAXPEEM) as well as microscopic X-ray absorption spectroscopy (μ-XAS) techniques. The results reveal the inhomogeneity in the oxide films on the micron-sized Cr2N- and VN-type particles, while the inhomogeneity on the martensite matrix phase exists due to localised formation of nano-sized tempering nitride particles at 600 °C. The oxide film formed on Cr2N-type particles is rich in Cr2O3 compared with that on the martensite matrix and VN-type particles. With the increase of tempering temperature, Cr2O3 formation is faster for the oxidation of Cr in the martensite matrix than the oxidation of Cr nitride-rich particles.
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| 36. |
- Zhang, B., et al.
(författare)
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Magnetic transformation of Mn from anti-ferromagnetism to ferromagnetism in FeCoNiZMnx (Z = Si, Al, Sn, Ge) high entropy alloys
- 2021
-
Ingår i: Journal of Materials Science & Technology. - : Elsevier BV. - 1005-0302. ; 68, s. 124-131
-
Tidskriftsartikel (refereegranskat)abstract
- We design high entropy alloys (HEAs) with different induction elements (Si/Al/Sn). In order to keep the crystal structure invariant and to investigate how the increment in saturation magnetization (Ms) is caused only by the change of electron spin state, each set of HEAs contains a different amount of Mn. Synergistic effects among induction elements that induce the magnetic transformation of Mn from anti-ferromagnetism to ferromagnetism are found. Ms of added Mn reduces when a particular induction element (Si0.4/Al0.4/Sn0.4) exists, while a larger increment of Ms appears when two induction elements coexist, Si0.4Al0.4 (25.79 emu/g) and Sn0.4Al0.4 (15.43 emu/g). This is reflected in the microcosmic magnetic structure for the emergence of closed domains due to large demagnetization energy, which is confirmed by the Lorentz transmission electron microscope (LTEM) data. The calculated magnetic moments and the exchange integral constants from density functional theory based on the Exact Muffin-Tin Orbits formalism reveal that the magnetic state and the strength of ferromagnetic and anti-ferromagnetic coupling determine the variation of Ms in different chemical environments. The difference in energy levels of coexisting multiple induction elements also leads to a larger increment of Ms, Si0.4Al0.4Sn0.4 (29.78 emu/g), and Si0.4Al0.4Ge0.4Sn0.4 (31.00 emu/g).
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| 37. |
- Zhang, H., et al.
(författare)
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Investigation of La9.33Si6O26 oxygen ionic conductor
- 2007
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Ingår i: Journal of Materials Science & Technology. - 1005-0302. ; 23:5, s. 629-632
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Tidskriftsartikel (refereegranskat)abstract
- La9.33Si6O26 oxygen ionic conductor was synthesized by solid state reaction method. Its structure was determined by single-crystal X-ray diffraction analysis at room temperature. The results showed that La9.33Si6O26 oxide has the apatite structure with space group P6(3)/m. AC impedance measurements indicated that the oxides sintered in nitrogen have much higher conductivity than those sintered in air. The effects of grain boundaries on the conductivity were discussed.
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| 38. |
- Zhang, H. L., et al.
(författare)
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Solid solution strengthening of high-entropy alloys from first-principles study
- 2022
-
Ingår i: Journal of Materials Science & Technology. - : Elsevier BV. - 1005-0302. ; 121, s. 105-116
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Tidskriftsartikel (refereegranskat)abstract
- Solid solution strengthening (SSS) is one kind of strengthening mechanisms and plays an important role in alloy design, in particular for single-phase alloys including high-entropy alloys (HEAs). The classical Labusch-Nabarro model and its expansions are most widely applicable to treating SSS of solid solution alloys including both conventional alloys (CAs) and HEAs. In this study, the SSS effects in a series of Fe based CAs and HEAs are investigated by using the classical Labusch-Nabarro model and its expansions. The size misfit and shear modulus misfit parameters are derived from first-principles calculations. Based on available experimental data in combination with empirical SSS model, we propose fitting constants (i.e., the ratio between experimental hardness and predicted SSS effect) for these two families of alloys. The predicted host/alloy family-dependent fitting constants can be used to estimate the hardness of these SSS alloys. General agreement between predicted and measured hardness values is satisfactory for both CAs and HEAs, implying that the proposed approach is reliable and successful.
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| 39. |
- Zhang, Ting, et al.
(författare)
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Microstructure evolution and deformation mechanism of alpha plus beta dual-phase Ti-xNb-yTa-2Zr alloys with high performance
- 2022
-
Ingår i: Journal of Materials Science & Technology. - : Elsevier BV. - 1005-0302. ; 131, s. 68-81
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Tidskriftsartikel (refereegranskat)abstract
- Biomedical beta-phase Ti-Nb-Ta-Zr alloys usually exhibit low elastic modulus with inadequate strength. In the present work, a series of newly developed dual-phase Ti-xNb-yTa-2Zr (wt.%) alloys with high performance were investigated in which the stability of beta-phase was reduced under the guidelines of ab initio calculations and d-electronic theory. The effects of Nb and Ta contents on the microstructure, compressive and tensile properties were investigated. Results demonstrate that the designed Ti-xNb-yTa-2Zr alloys exhibit typical characteristics of alpha+beta dual-phase microstructure. The microstructure of the alloys is more sensitive to Nb rather than Ta. The as-cast alloys exhibit needle-like alpha' martensite at a lower Nb content of 3 wt.% and lamellar alpha' martensite at an Nb content of 5 wt.%. Among the alloys, the Ti-3Nb-13Ta-2Zr alloy shows the highest compressive strength (2270 +/- 10 MPa) and compressive strain (74.3% +/- 0.4%). This superior performance is due to the combination of alpha+beta dual-phase microstructure and stress-induced alpha '' martensite. Besides, lattice distortion caused by Ta element also contributes to the compressive properties. Nb and Ta contents of the alloys strongly affect Young's modulus and tensile properties after rolling. The as-rolled Ti-3Nb-13Ta-2Zr alloy exhibits much lower modulus due to lower Nb content as well as more alpha '' martensite and beta phase with a good combination of low modulus and high strength among all the designed alloys. Atom probe tomography analysis reveals the element partitioning between the a and beta phases in which Ta concentration is higher than Nb in the alpha phase. Also, the concentration of Ta is lower than that of Nb in the beta phase, indicating that the beta-stability of Nb is higher than that of Ta. This work proposes modern alpha+beta dual-phase Ti-xNb-yTa-2Zr alloys as a new concept to design novel biomedical Ti alloys with high performance.
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| 40. |
- Zhang, Yangfan, et al.
(författare)
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Interfacial defective Ti3+ on Ti/TiO2 as visible-light responsive sites with promoted charge transfer and photocatalytic performance
- 2022
-
Ingår i: Journal of Materials Science and Technology. - : Elsevier BV. - 1005-0302. ; 106, s. 139-146
-
Tidskriftsartikel (refereegranskat)abstract
- Defect sites on oxide semiconductors play a crucial role in promoting photocatalytiperformance and modulating the bandgap structure of photocatalysts. However, the role of interfacial coordinatively unsaturated defect sites between metal and oxide in photocatalysis is still under debate. So, we designed an experiment to probe the role of interfacial coordinatively unsaturated defect sites. In this work, a series of Ti/TiO2 photocatalysts with varying concentrations of interfacial Ti3+ sites were prepared through an epitaxial growth method under hydrothermal conditions. Through experimental and computational investigations, the roles of interfacial defect sites were discussed in detail. On the one hand, the interfacial coordinatively unsaturated Ti3+ sites could act as visible-light-responsive sites in photocatalytic reactions due to the overlap and hybridization of multiple electronic orbitals. On the other hand, the Ti/TiO2 interface exhibited a certain degree of metallic character near the Fermi level because of the partial delocalization and redistribution of electrons, facilitating the charge migration and separation across the metal-oxide interface. Consequently, the obtained Ti/TiO2 catalysts showed notably enhanced charge transfer efficiency and visible light photocatalytic activity compared to their pristine counterparts. This work may provide a new perspective to interfacial defect engineering in classic metal/oxide heterojunction photocatalysts and figure a more precise direction to synthesize higher effective photocatalysts for environmental governance.
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| 41. |
- Zhong, Yuan, et al.
(författare)
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Oxide dispersion strengthened stainless steel 316L with superior strength and ductility by selective laser melting
- 2020
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Ingår i: Journal of Materials Science & Technology. - : Elsevier BV. - 1005-0302. ; 42, s. 97-105
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Tidskriftsartikel (refereegranskat)abstract
- Dense oxide dispersion strengthened (ODS) 316 L steels with different amount of Y2O3 additions were successfully fabricated by selective laser melting (SLM) even though part of the added Y2O3 got lost during the process. The microstructure was characterized in details and the mechanical properties were tested at room temperature, 250 degrees C and 400 degrees C, respectively. The effect of the scanning speed on agglomeration of nanoparticles during SLM process was discussed. Superior properties, e.g., yield strength of 574 MPa and elongation of 91%, were achieved at room temperature in SLM ODS 316 L with additional 1% of Y2O3. At elevated temperatures, the strength kept high but the elongations dropped dramatically. It was observed that nano-voids nucleated throughout the whole gauge section at the sites where nanoinclusions located. The growth and coalescence of these voids were suppressed by the formation of an element segregation network before necking, which relieved local stress concentration and thus delayed necking. This unusual necking behavior was studied and compared to the previous theory. It appeared that the strong convection presented in the melt pool can evenly redistribute the short-time milled coarse Y2O3 precursor powder during SLM process. These findings can not only solve the problems encountered during the fabrication of ODS components but also replenish the strengthening mechanism of SLM 316 L thus pave a way for further improving of mechanical properties.
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