| 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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