| 1. |
- Chen, K. X., et al.
(författare)
-
3D morphology of the petal-like precipitates in Cu-Fe alloys: Experimental study and phase field modelling
- 2024
-
Ingår i: Acta Materialia. - : Elsevier BV. - 1359-6454 .- 1873-2453. ; 270
-
Tidskriftsartikel (refereegranskat)abstract
- Precipitation hardening is a well-known phenomenon which is widely harnessed in alloy design strategy. In particular, the microstructural features such as shape, size, precipitate number density and volume fraction determine the mechanical behaviour of materials. During service, the morphology of precipitates sometimes achieves a complex 3D shape upon displaying branching and/or splitting patterns. Unfortunately, the detailed information about this intricate morphology cannot be retrieved through traditional experimental techniques based on 2D visualization. Here, we report the implementation of a 3D analysis technique combining Focused Ion Beam (FIB) and Scanning Electron Microscopy (SEM) tomography to visualize the atypical petal-like morphology of Fe-rich precipitates in a Cu-Fe alloy. Using Phase-Field modelling (PFM), we identify the mechanism responsible for the unusual morphologies of Fe-rich particles. Our work highlights the significance of 3D characterization of precipitates and provides a fascinating pathway for refining understanding of precipitation mechanisms in metals and alloys.
|
|
| 2. |
- Zhou, D. Q., et al.
(författare)
-
Precipitate characteristics and their effects on the high-temperature creep resistance of alumina-forming austenitic stainless steels
- 2015
-
Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 622, s. 91-100
-
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.
|
|
| 3. |
- Shuang, S., et al.
(författare)
-
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.
|
|
| 4. |
- Zhao, G-H, et al.
(författare)
-
Alloy design by tailoring phase stability in commercial Ti alloys
- 2021
-
Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 815
-
Tidskriftsartikel (refereegranskat)abstract
- The mechanical characteristics and the operative deformation mechanisms of a metallic alloy can be optimised by explicitly controlling phase stability. Here an integrated thermoelastic and pseudoelastic model is presented to evaluate the beta stability in Ti alloys. The energy landscape of beta ->alpha ' /alpha '' martensitic transformation was expressed in terms of the dilatational and transformational strain energy, the Gibbs free energy change, the external mechanical work as well as the internal frictional resistance. To test the model, new alloys were developed by tailoring two base alloys, Ti-6Al-4V and Ti-6Al-7Nb, with the addition of beta-stabilising element Mo. The alloys exhibited versatile mechanical behaviours with enhanced plasticity. Martensitic nucleation and growth was fundamentally dominated by the competition between elastic strain energy and chemical driving force, where the latter term tends to lower the transformational energy barrier. The model incorporates thermodynamics and micromechanics to quantitatively investigate the threshold energy for operating transformation-induced plasticity and further guides alloy design.
|
|
| 5. |
- Zhou, D. Q., et al.
(författare)
-
Plastic flow behaviour in an alumina-forming austenitic stainless steel at elevated temperatures
- 2014
-
Ingår i: Materials Science & Engineering. - : Elsevier BV. - 0921-5093 .- 1873-4936. ; 594, s. 246-252
-
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.
|
|
| 6. |
- Kapilashrami, Mukes, et al.
(författare)
-
Soft X-ray characterization of Zn1-xSnxOy electronic structure for thin film photovoltaics
- 2012
-
Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry (RSC). - 1463-9076 .- 1463-9084. ; 14:29, s. 10154-10159
-
Tidskriftsartikel (refereegranskat)abstract
- Zinc tin oxide (Zn1-xSnxOy) has been proposed as an alternative buffer layer material to the toxic, and light narrow-bandgap CdS layer in CuIn1-x,GaxSe2 thin film solar cell modules. In this present study, synchrotron-based soft X-ray absorption and emission spectroscopies have been employed to probe the densities of states of intrinsic ZnO, Zn1-xSnxOy and SnOx thin films grown by atomic layer deposition. A distinct variation in the bandgap is observed with increasing Sn concentration, which has been confirmed independently by combined ellipsometry-reflectometry measurements. These data correlate directly to the open circuit potentials of corresponding solar cells, indicating that the buffer layer composition is associated with a modification of the band discontinuity at the CIGS interface. Resonantly excited emission spectra, which express the admixture of unoccupied O 2p with Zn 3d, 4s, and 4p states, reveal a strong suppression in the hybridization between the O 2p conduction band and the Zn 3d valence band with increasing Sn concentration.
|
|
| 7. |
- Liu, X.R., et al.
(författare)
-
Sulphate-ceria composite ceramics for energy environmental co-generation technology
- 2005
-
Ingår i: HIGH-PERFORMANCE CERAMICS III, PTS 1 AND 2. - 0878499598 ; , s. 425-430
-
Konferensbidrag (refereegranskat)abstract
- In this work ion conductivity and FC application were studied for the new type composite material based on SDC (samariurn doped ceria) and Li2SO4. Significant conductivity enhancement was achieved, e.g. 10(-2) - 0.4 Scm(-1) for the SDC-Li2SO4 compared to 10(-4) -10(-2) Scm(-1) for the SDC between 400 and 650degreesC. Some ion conductivity mechanisms were proposed correspondingly. Using the SDC-Li2SO4 composite materials as the electrolytes, we achieved high performances, 200-540 mWcm(-2). for intennediate temperature (450-650degreesC) solid oxide FC (ITSOFC) applications. Sulfates, typically Li2SO4, have an excellent chemical stability in sulfur containing atmosphere. The sulfate-ceria (SDC-Li2SO4) Composite materials can thus meet the demands to develop the sulfur tolerant and H2S FC technologies, which was also demonstrated successfully with significant importance for both fundamental and applied research.
|
|
| 8. |
- He, J. Y., et al.
(författare)
-
Precipitation behavior and its effects on tensile properties of FeCoNiCr high-entropy alloys
- 2016
-
Ingår i: Intermetallics (Barking). - : Elsevier. - 0966-9795 .- 1879-0216. ; 79, s. 41-52
-
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.
|
|
| 9. |
- Yang, Y. -G, et al.
(författare)
-
Effects of strain rate on austenite stability and mechanical properties in a 5Mn steel
- 2021
-
Ingår i: Journal of Iron and Steel Research International. - : Springer Nature. - 1006-706X .- 2210-3988.
-
Tidskriftsartikel (refereegranskat)abstract
- The austenite stability and the mechanical properties in a typical medium Mn grade steel, i.e., 5Mn steel, were investigated under a wide range of strain rates through the combination of experimental and theoretical methodologies. The obtained results indicate that austenite is more stable at a high strain rate, which is due to the suppression of the austenite to martensite transformation. This suppression is attributed to the increased stacking fault energy and the high deformation energy barrier. Moreover, the suppression of martensitic transformation also leads to the decrease in the ultimate tensile strength and the uniform elongation. Owing to the increase in an adiabatic heating temperature, an increase in the uniform elongation is acquired at a high strain rate. The obtained fundamental study results shed light on a wide application of the medium Mn steel under different strain rate conditions.
|
|
