| 1. |
- Chen, Kaixuan, et al.
(författare)
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Mapping formation mechanisms and transformation regimes of multiple Fe precipitates in Cu-Fe-Co alloy during casting process
- 2024
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Ingår i: Scripta Materialia. - : Elsevier BV. - 1359-6462 .- 1872-8456. ; 246
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Tidskriftsartikel (refereegranskat)abstract
- Precipitate features including size, morphology, crystal structure, etc., are important parameters determining the performance of precipitate-strengthened alloys. Multiple Fe precipitates were identified in as-cast Cu alloys exhibiting the distinct features, which dramatically influence mechanical properties. However, a complete understanding of precipitation behaviors of Fe particles during casting, in terms of both microscopic kinetics and thermodynamics, remains experimentally challenging. Here, we report the combined implementation of transmission electron microscopy, Thermo-Calc calculations and First-principles calculations to map mechanisms and growth regimes of Fe precipitation in a Cu-Fe-Co system. Our analyses support the idea that to understand the microstructural evolution in the system, both thermodynamic and kinetic arguments must be taken into account. Then, using our multi-approach strategy, the complete picture of the formation and transformation of Fe precipitates is proposed. This work is vital to promote microstructural design for Cu-Fe(-Co) systems, and sheds new insights into understanding of intricate precipitation in alloys.
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| 2. |
- Chen, Kaixuan, et al.
(författare)
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Slow strain rate tensile tests on notched specimens of as-cast pure Cu and Cu–Fe–Co alloys
- 2020
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Ingår i: Journal of Alloys and Compounds. - : Elsevier. - 0925-8388 .- 1873-4669. ; 822
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Tidskriftsartikel (refereegranskat)abstract
- Microstructure evolution in the as-cast pure Cu, Cu-(1.0, 2.0, 3.0)Fe-0.5Co (wt. %) alloys were characterized in the former work. The aim of the present study is to investigate the slow strain rate tensile (SSRT) performance and fracture behavior of the Cu–Fe–Co alloys reinforced with fined grains (FG) and iron-rich nanoparticles (NP), referred as NPFG structure. The plastic deformation and fracture characteristics were examined by multiaxial SSRT tests at 75 and 125 °C on notched specimens. The addition of Fe and Co enhanced the ultimate tensile strength and yield strength almost by double to triple times the properties compare to pure Cu, along with an acceptable reduction in ductility, both at 75 and 125 °C. The SSRT properties of the copper samples varied as a function of temperature and alloying content. The analysis of fracture surface indicates the effect of iron-rich nanoparticles and grain boundaries on the deformation and fracture processes. The Kocks-Mecking model was applied to describe the SSRT experimental results with fitting parameters. The model predicted the dynamic recovery ability of the copper samples with different Fe, Co content and temperature. The evolution mechanism of SSRT properties upon alloying content and temperature was discussed in terms of the microstructure characterization, fractographic observation, deformation modeling, strengthening models as well as the analysis of strain-hardening curves. The results indicate through further microstructural engineering the NPFG Cu–Fe–Co alloy is promising in utilization as the canister for the storage of the nuclear waste.
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| 3. |
- Chen, Kaixuan, et al.
(författare)
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Effects of solute content on microstructure of nano precipitate-fine grain synergistically reinforced copper alloys
- 2020
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Ingår i: Materials Science and Technology. - : Taylor and Francis Ltd.. - 0267-0836 .- 1743-2847.
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Tidskriftsartikel (refereegranskat)abstract
- Alloying of Fe, Co was reported to tailor microstructure of copper alloys into a nanoprecipitate-fine grain (NPFG) structure, i.e. nano-sized iron-rich precipitates dispersed inside refined grains. Here, we investigate the solute effect of Sn, Zn on NPFG structure in as-cast copper samples. Mechanisms are proposed to account for the solute effect on precipitate and grain features. Solutes restrict coarsening but facilitate undesirable morphology transition from spherical to angular of iron-rich precipitates. Meantime, solutes allow more precipitates to be active in the nucleation of copper and consequently induce finer grains. Minor Sn is added to optimise NPFG structure and leads to an excellent strength–ductility combination in Cu–1.5Fe–0.1Sn (wt-%) alloy. This work provides a solute-alloying strategy to achieve desired mechanical properties in metals.
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| 4. |
- Chen, Kaixuan, et al.
(författare)
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In situ observations of crack propagation in as-cast Cu-1.5Fe-0.5Co (wt%) alloy
- 2017
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Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5093 .- 1873-4936. ; 706, s. 211-216
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Tidskriftsartikel (refereegranskat)abstract
- As-cast Cu-1.5Fe-0.5Co (wt%) alloy displays both high tensile strength of 307 MPa and elongation of 33%. In situ transmission electron microscopy was used to investigate crack propagation in the alloy, to analyze the origin of the good properties. At different deformation stages in thin Cu foils, the interactions of a propagating crack with iron-rich nanoparticles and growth twins are investigated. Crack-bridging processes via near-tip twinned bridges were identified. The multiple deformation mechanisms act synergistically to contribute to high strength and high ductility in the alloy.
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| 5. |
- Chen, Kaixuan, et al.
(författare)
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Optimisation of deformation properties in as-cast copper by microstructural engineering. Part II. Mechanical properties
- 2020
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Ingår i: Journal of Alloys and Compounds. - : Elsevier Ltd. - 0925-8388 .- 1873-4669. ; 812
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Tidskriftsartikel (refereegranskat)abstract
- The microstructure evolution in the as-cast pure Cu and Cu-(1.0–3.0)Fe-0.5Co and Cu-1.5Fe-0.1Sn (wt. %) alloys was characterised in the previous work. Herein, the plastic deformation characteristics were examined by uniaxial tensile tests at room temperature. Along with the microstructure evolution, the yield strength increased with increasing Fe content and reached a peak value at 1.5 wt % Fe, but thereafter decreased with the further addition of Fe in the Cu–Fe–Co alloys. Nevertheless, the tensile strength and elongation synchronously improve with increasing Fe content. In particular, the Cu-1.5Fe-0.1Sn alloy achieved the optimal strength–ductility combination. In terms of the strengthening mechanism, the (Fe, Co)- or (Fe, Sn)-doped copper encouraged impediment, trapping, and storage of dislocations by the iron-rich nanoparticles and grain boundaries, which enhanced the strength and sustained the work hardening and elongation. The evolution of mechanical properties under an alloying effect was quantitatively described by the strengthening models. The results indicate that the optimum balance between strength and ductility was achieved by designing a microstructure containing fine grains, intragranular smaller spherical nanoparticles, and a minor solute element with higher misfit and higher growth restriction effect. The necessities for engineering a microstructure to achieve simultaneously strong and ductile bulk metals were discussed.
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| 6. |
- Chen, Kaixuan, et al.
(författare)
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Optimization of deformation properties in as-cast copper by microstructural engineering. Part I. microstructure
- 2018
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Ingår i: Journal of Alloys and Compounds. - : Elsevier. - 0925-8388 .- 1873-4669. ; 763, s. 592-605
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Tidskriftsartikel (refereegranskat)abstract
- The microstructural features required to optimize both the strength and ductility of copper are investigated by examining the as-cast pure Cu and Cu-(1.0e3.0)Fe-0.5Co and Cu-1.5Fe-0.1Sn (wt %) alloys. Uniaxial tensile tests show that (Fe, Co)- or (Fe, Sn)-doping improves both the strength and ductility of pure copper. The microstructure evolution with Fe, Co, or Sn doping is characterized by using optical and scanning and transmission electron microscopies. The effects of Fe, Co, and Sn doping on the microstructure clearly show that (i) iron-rich nanoparticles are dispersed inside the grains. The spherical nanoparticles grow in size with increasing Fe content, and when the Fe content exceeds 2.0 wt %, the particles transition into a petal-like morphology. (ii) The microstructure of the alloys (grain size and morphology) is notably influenced by the Fe and Co contents, and the grain size is reduced from an average of 603 mu m in pure Cu to an average of 26 mm in the Cu-3.0Fe-0.5Co alloy. (iii) The addition of 1.5wt % Fe and 0.1wt % Sn dramatically reduces the grain size to an average of 42 mu m, and this reduction is correlated with the appearance of smaller spherical iron-rich nanoparticles. The evolution mechanisms of the iron-rich nanoparticles and grain structure under the alloying effect are discussed.
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| 7. |
- Chen, Kaixuan, et al.
(författare)
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Precipitates-interaction capture of nano-sized iron-rich precipitates during copper solidification
- 2019
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Ingår i: Materials Science and Technology. - : Taylor & Francis. - 0267-0836 .- 1743-2847. ; 35:9, s. 1028-1037
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Tidskriftsartikel (refereegranskat)abstract
- Nano-sized iron-rich precipitates reinforced copper alloys achieve excellent mechanical properties. Capture mechanism of iron-rich precipitates into copper grains during solidification was described but needs further validation. Here, Cu-1.5Fe-0.5Co (wt-%) alloy is fabricated by gravity casting. Iron-rich precipitates in nano and submicron scale (mostly < 100 nm) are well dispersed in copper grain interior. Traditional pushing/engulfment transition (PET) models are used to interpret the capture process of iron-rich precipitates during copper solidification, but all fail to match the experimental results. The precipitates-interaction capture mechanism is most reasonable for describing the capture process.
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| 8. |
- Ma, Zili, et al.
(författare)
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Structural Properties of NdTiO2+xN1-x and Its Application as Photoanode
- 2021
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 60:2, s. 919-929
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Tidskriftsartikel (refereegranskat)abstract
- Mixed-anion inorganic compounds offer diverse functionalities as a function of the different physicochemical characteristics of the secondary anion. The quaternary metal oxynitrides, which originate from substituting oxygen anions (O2-) in a parent oxide by nitrogen (N3-), are encouraging candidates for photoelectrochemical (PEC) water splitting because of their suitable and adjustable narrow band gap and relative negative conduction band (CB) edge. Given the known photochemical activity of LaTiO2N, we investigated the paramagnetic counterpart NdTiO2+xN1-x. The electronic structure was explored both experimentally and theoretically at the density functional theory (DFT) level. A band gap (E-g) of 2.17 eV was determined by means of ultraviolet-visible (UV-vis) spectroscopy, and a relative negative flat band potential of -0.33 V vs reversible hydrogen electrode (RHE) was proposed via Mott-Schottky measurements. N-14 solid state nuclear magnetic resonance (NMR) signals from NdTiO2+xN1-x could not be detected, which indicates that NdTiO2+xN1-x is berthollide, in contrast to other structurally related metal oxynitrides. Although the bare particle-based photoanode did not exhibit a noticeable photocurrent, Nb2O5 and CoOx overlayers were deposited to extract holes and activate NdTiO2+xN1-x. Multiple electrochemical methods were employed to understand the key features required for this metal oxynitride to fabricate photoanodes.
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| 9. |
- Pan, Shiwei, et al.
(författare)
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In-Situ Nanoparticles : A New Strengthening Method for Metallic Structural Material
- 2018
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Ingår i: Applied Sciences. - : MDPI. - 2076-3417. ; 8:12
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Forskningsöversikt (refereegranskat)abstract
- Over the past several years, coherent interface strengthening was proposed and has since drawn much attention. Unfortunately, many fabrication techniques are restricted to very small size. Recently, a brand new method of in-situ nanoparticle strengthening was systematically investigated, which was proved to be an efficacious way to optimize microstructure and improve mechanical property by utilizing uniformly dispersed nanoparticles. In this review, we summarized recent related advances in investigated steels and Cu alloys, including details of preparation technique and characterization of in-situ nanoparticles. In-situ nanoparticles formed in the melt possess a coherent/semi-coherent relationship with the matrix, which has a similar effect of coherent interface strengthening. In this case, bulk metallic structural materials with dispersed nanoparticles in the matrix can be fabricated through conventional casting process. The effects of in-situ nanoparticles on grain refinement, inhibiting segregation, optimizing inclusions and strengthening are also deeply discussed, which is beneficial for obtaining comprehensive mechanical response. Consequently, it is expected that in-situ nanoparticle strengthening method will become a potential future direction in industrial mass production.
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| 10. |
- Chen, Kaixuan, et al.
(författare)
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Morphological instability of iron-rich precipitates in Cu-Fe-Co alloys
- 2019
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Ingår i: Acta Materialia. - : PERGAMON-ELSEVIER SCIENCE LTD. - 1359-6454 .- 1873-2453. ; 163, s. 55-67
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Tidskriftsartikel (refereegranskat)abstract
- The mechanical properties of metallic materials are determined by their microstructure, and in particular, the different morphologies of precipitates lead to distinct strengthening effects. Usually, the shape of precipitates changes during growth and coarsening regimes, leading to modification of the macroscopic properties of the materials. Thus, understanding of this phenomenon is key to tailoring the precipitate strengthening of industrial alloys. In this article, a general approach to explain the shape instability of iron-rich nanoparticles in Cu-Fe-Co alloys during casting and ageing processes is proposed. The evolution of particle shape from sphere to cuboid to petal and finally splitting into eight subnanoparticles is observed using transmission electron microscopy. Phase-field modelling and thermodynamic calculations are combined into a general model that describes and elucidates the morphological evolution of precipitates in alloys in terms of particle size, interfacial and elastic strain energy, and chemical driving force. These findings have the potential to promote new microstructural design approaches for a wide range of materials.
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