| 1. |
- Dong, Y. B., et al.
(författare)
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The growth of graphene on Ni–Cu alloy thin films at a low temperature and its carbon diffusion mechanism
- 2019
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Ingår i: Nanomaterials. - : MDPI AG. - 2079-4991. ; 9:11
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Tidskriftsartikel (refereegranskat)abstract
- Carbon solid solubility in metals is an important factor affecting uniform graphene growth by chemical vapor deposition (CVD) at high temperatures. At low temperatures, however, it was found that the carbon diffusion rate (CDR) on the metal catalyst surface has a greater impact on the number and uniformity of graphene layers compared with that of the carbon solid solubility. The CDR decreases rapidly with decreasing temperatures, resulting in inhomogeneous and multilayer graphene. In the present work, a Ni–Cu alloy sacrificial layer was used as the catalyst based on the following properties. Cu was selected to increase the CDR, while Ni was used to provide high catalytic activity. By plasma-enhanced CVD, graphene was grown on the surface of Ni–Cu alloy under low pressure using methane as the carbon source. The optimal composition of the Ni–Cu alloy, 1:2, was selected through experiments. In addition, the plasma power was optimized to improve the graphene quality. On the basis of the parameter optimization, together with our previously-reported, in-situ, sacrificial metal-layer etching technique, relatively homogeneous wafer-size patterned graphene was obtained directly on a 2-inch SiO2 /Si substrate at a low temperature (~600◦ C).
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| 2. |
- 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
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Ingår i: Journal of Materials Science & Technology. - : Elsevier BV. - 1005-0302. ; 139, s. 59-68
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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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| 3. |
- Xia, S., et al.
(författare)
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Nonlinear oxidation behavior in pure Ni and Ni-containing entropic alloys
- 2018
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Ingår i: Frontiers in Materials. - : Frontiers Media S.A.. - 2296-8016. ; 5
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Tidskriftsartikel (refereegranskat)abstract
- We performed a combined experimental and theoretical investigation of the oxidation behavior of pure Ni and of the following multi-component Ni-containing alloys with nearly equiatomic compositions: FeNi, CoFeNi, CoCrFeNi, and CoCrFeMnNi. The materials were exposed to air at ambient pressure and at a temperature of 800°C for 150 min, their weight-gain due to oxidation was continuously monitored and the products of oxidation were subsequently characterized by XRD. The most common oxides formed have spinel or halite structure and the materials resistance to oxidation increases as: FeNi < CoFeNi < Ni < CoCrFeMnNi < CoCrFeNi. We found further that the oxidation-resistance of the materials does not correlate linearly with the number of elements present, instead the type of elements impacts significantly the materials susceptibility to oxidative damage. Cr is the element that imparted higher resistance to oxidation while Mn and Fe worsened the materials performance. In order to better understand the mechanisms of oxidation we employed thermodynamic equilibrium calculations and predicted the phase stability of oxides of the elements that are present in the materials, in different ranges of temperature, composition and oxygen activity. Additionally, we determined the phase compositions for the thermodynamically stable oxides at 800°C. The results from the thermodynamic modeling are in good agreement with the experimental finds. The alloys with low resistance to oxidation such as CoFeNi and FeNi, form the Fe 3 O 4 spinel phase which tends to dominate the phase diagram for these materials. The presence of Cr increases the resistance to atomic rearrangement due to slow diffusion in the complex structure of Cr containing spinel phases. This causes the extremely high resistance to oxidation of the CoCrFeNi alloy. The presence of Mn in CoCrFeNi stabilizes the Mn 3 O 4 spinel, which reduces the oxidation-resistance of the alloys due to the high mobility of Mn.
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| 4. |
- He, J. Y., et al.
(författare)
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Precipitation behavior and its effects on tensile properties of FeCoNiCr high-entropy alloys
- 2016
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Ingår i: Intermetallics (Barking). - : Elsevier. - 0966-9795 .- 1879-0216. ; 79, s. 41-52
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Tidskriftsartikel (refereegranskat)abstract
- In this work, we present a systematic study on the precipitation behavior and mechanical properties of a FeCoNiCr-based high-entropy alloy alloyed with dilute amounts of Ti and Al, (FeCoNiCr)(100-x-y)TixAly (where x = 1-3, y = 4-9 at.%). It was found that, upon aging, nano-sized L1(2)-Ni-3(Ti, Al) particles are formed within grains, whilst L2(1)-(Ni, Co)(2)TiAl Heusler particles are formed mainly along grain boundaries. The relative thermal stability of the two phases were studied at different aging temperatures (700-900 degrees C) with various durations of time (up to 48 h) and the results were directly compared with Thermo-talc calculations. Tensile tests were also conducted on alloys aged under different conditions. The measured properties, including strength and ductility, were correlated with the microstructure of aged (FeCoNiCr)(100-x-y)TixAly alloys, with particular attention on the distribution and morphology of the two kinds of precipitate. Whereas both phases could contribute to the strengthening of the alloys via either Orowan bowing or particle shearing mechanism, the brittle (Ni, Co)(2)TiAl Heusler phase was found to mainly affect the tensile plasticity. A simple composite model was proposed to describe the plastic strain of alloys. Based on observed microstructure and its corresponding mechanical performance, the alloy with the composition of (FeCoNiCr)(94)Ti2Al4, when aged between 700 and 800 degrees C, gives the best balanced strength/ductility properties.
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| 5. |
- Li, Xiaolong, 1991, et al.
(författare)
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Solid solution softening at room temperature and hardening at elevated temperatures: a case by minor Mn addition in a (HfNbTi) 85 Mo 15 refractory high entropy alloy
- 2023
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Ingår i: Materials Research Express. - 2053-1591. ; 10:11
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Tidskriftsartikel (refereegranskat)abstract
- To address the conflict between room-temperature (RT) ductility and high-temperature (HT) strength in single phase bcc-structured refractory high entropy alloys, here we propose to use minor alloying to achieve solid solution softening at RT and simultaneously, solid solution hardening at HT. Our strategy was manifested by minor Mn additions in a RT brittle (HfNbTi)85Mo15 refractory high entropy alloy, where nominal Mn additions ranging from 2 at. % down to 0.03 at. % were seen to soften the base (HfNbTi)85Mo15 alloy at RT, while to harden the base alloy at the temperature range from 400 to 800 °C. The yield stress in all studied alloys showed a three-stage pattern, characterized by a temperature dependent stage at temperatures below 400 °C, followed by a temperature independent stage at intermediate temperatures ranging from 400 to 800 °C, and finally another temperature dependent stage at temperatures higher than 800 °C. The mechanisms for solid solution softening and solid solution hardening in single phase bcc-structured refractory high entropy alloys were discussed, together with their temperature dependence.
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| 6. |
- Zhang, B., et al.
(författare)
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Recent advances in nature inspired triboelectric nanogenerators for self-powered systems
- 2024
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Ingår i: International Journal of Extreme Manufacturing. - : IOP Publishing. - 2631-8644. ; 6:6
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Forskningsöversikt (refereegranskat)abstract
- Highlights Comprehensive and systematic summary of nature inspired TENGs, including materials and structures. Summary of bionic approaches to nature inspired TENGs. Analysis and evaluation of the latest applications of nature inspired TENGs in energy harvesting and self-powered systems. Explanation of current challenges and future development directions of nature inspired TENGs.
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| 7. |
- Zhou, D. Q., et al.
(författare)
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Precipitate characteristics and their effects on the high-temperature creep resistance of alumina-forming austenitic stainless steels
- 2015
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Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 622, s. 91-100
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the dynamic evolution of precipitates and its influence on the high-temperature mechanical properties of newly developed AFA steels were systematically investigated. At 1023 K or above, three main types of precipitates, i.e., the B2-NiAl, Laves-Fe2Nb, and delta/sigma phases, were formed in the base steel, and the major strengthening medium is Laves-Fe2Nb, which coarsened quickly, leading to undesirable creep properties. Phase competition between the most effective strengthening NbC nanosized precipitates and the Laves-Fe2Nb phase was analyzed, and it was found that adjusting the Nb/C ratio in the steels could enable the precipitation of highly stable, fine NbC particles. In addition, the formation of detrimental sigma phases could be suppressed by lowering the Mo and Si content in the alloy. Eventually, a new type of AFA steel consisting of a high density of nanosized NbC particles homogeneously dispersed in the austenitic matrix was successfully developed, and significant enhancement in the creep resistance was achieved due to the effective strengthening resulting from the tiny secondary NbC particles.
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| 8. |
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| 9. |
- Zhou, D. Q., et al.
(författare)
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Plastic flow behaviour in an alumina-forming austenitic stainless steel at elevated temperatures
- 2014
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Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 594, s. 246-252
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Tidskriftsartikel (refereegranskat)abstract
- The deformation behaviour of a newly developed alumina-forming austenitic (AFA) stainless steel at elevated temperatures was investigated. It was found that the steady-state data could be well described by a stress power law that considered the threshold stress and temperature dependence of the shear modulus and self-diffusion coefficient, suggesting that the deformation of the austenite matrix was controlled by the lattice self-diffusion. The threshold stress was temperature-dependent and appeared to be caused by Orowan bowing stress. At temperatures below 1023 K, the secondary NbC phase was the major hardening precipitate, but at temperatures above 1023 K, the Laves Fe2Nb phase became dominant. The apparent interaction energy required for mobile dislocations to overcome the particle obstacles decreased from 163 to 34 kJ/mol with increasing temperature, which was most likely associated with the formation of the two different precipitates.
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| 10. |
- Cui, K., et al.
(författare)
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An all-digital phase-locked-loop with a robustness enhanced dual-mode DCO
- 2017
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Ingår i: Microwave and optical technology letters (Print). - : John Wiley & Sons. - 0895-2477 .- 1098-2760. ; 59:2, s. 312-315
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Tidskriftsartikel (refereegranskat)abstract
- An all-digital-phase-locked-loop (ADPLL) with a dual-mode Class-A/Class-C Digital-controlled-oscillator (DCO) is presented in this letter. During the start-up phase, the DCO operates in the Class-A mode with increasing tail current. A low-power amplitude-to-pulse-converter (APC) is proposed to detect the oscillating amplitude of the DCO. After the start-up, the DCO switches to the Class-C mode with reduced tail current, resulting in better phase noise and lower power consumption. The ADPLL with the proposed DCO is implemented in a 65-nm CMOS technology. The Class-C mode DCO exhibits a phase noise of −123.3 dBc/Hz at 1-MHz offset with a 2.7-GHz carrier frequency. Measured results show about a 2.9-dB phase noise improvement at 1-MHz offset among the tuning range of 2.5–2.9 GHz, compared to the Class-A DCO under the same power consumption. The figure-of-merit (FOM) and FOM including the tuning range (FOMT) of the DCO is 188.7 and 192.1, respectively.
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