Co-reporter:F. Teng;G. Q. Lan;Y. Jiang;M. Song;S. J. Liu;C. P. Wu;D. Q. Yi
RSC Advances (2011-Present) 2017 vol. 7(Issue 76) pp:48230-48237
Publication Date(Web):2017/10/11
DOI:10.1039/C7RA08613J
The mechanical properties of oxide dispersion-strengthened copper are largely dictated by its internal interfaces, i.e. the oxide interfaces and the grain boundaries (GBs). Here we present a systematic first-principles study for evaluating the potential impact of Ag alloying on adhesion of Cu/α-Al2O3 interfaces and Cu grain boundaries as well. The results suggest that, in contrast to the strong segregation of S that is always detrimental, Ag only slightly segregates to the Al2O3 interfaces, strengthens the weak stoichiometric interface, and slightly weakens the strong Al-rich interface. Ag cannot pin S inside the matrix. The co-segregation of Ag with S modestly negates the detrimental influence of S on adhesion, but can hardly occur. Ag segregation to most of the GBs is found also to be weak, and reduces the adhesion slightly. The only one exception is on the Σ9 GB. Based on the gained insights, we suggest that Ag alloying has only limited benefits but can still be encouraged.
Co-reporter:S.P. Sun, X.P. Li, Y. Zhang, H.J. Wang, Y. Yu, Y. Jiang, D.Q. Yi
Journal of Alloys and Compounds 2017 Volume 714(Volume 714) pp:
Publication Date(Web):15 August 2017
DOI:10.1016/j.jallcom.2017.04.271
•The mechanical properties of MoSi2 with Cr, Nb and W were studied systematically.•Cr can decrease obviously the mechanical modulus, and the effect of W is contrary.•Nb can improve the ductility, and increase the elastic anisotropy of MoSi2.•The electronic structures of MoSi2 with Cr, Nb and W were also given.The influence of Cr-, Nb- and W-doping on the mechanical properties of C11b MoSi2 has been investigated using first-principles calculations. Firstly, the formation enthalpies of both C11b- and C40-structured MoSi2 with various doping concentrations are calculated and compared, revealing that the C11b structure can retain good structural stability at low doping concentrations of Cr, Nb or W up to ∼9.2 at.%. Based on the calculated elastic constants, the elastic moduli, hardness and several thermodynamic properties of doped MoSi2 have been further predicted. Cr-doping decreases the elastic moduli drastically and W-doping decreases the Debye temperature, while doping with Nb increases the B/G ratio and Poisson ratio significantly, leading to good ductility and strong metallic bonding. As revealed in the three-dimensional contours of the elastic moduli, Cr- and W-doping does not obviously affect the anisotropy of the Young's and shear moduli, but Nb-doping shows a remarkable influence. Finally, in order to clarify the doping effects, the electronic properties of doped MoSi2 are further discussed, based on the analysis of the charge density and density of states.Download high-res image (370KB)Download full-size image
Co-reporter:Litong Yang, Yong Jiang, Yuan Wu, G. Robert Odette, Zhangjian Zhou, Zheng Lu
Acta Materialia 2016 Volume 103() pp:474-482
Publication Date(Web):15 January 2016
DOI:10.1016/j.actamat.2015.10.031
Abstract
Nano-size Y-Ti-oxides are largely responsible for the extraordinary mechanical properties and irradiation tolerance of nano-structured ferritic alloys (NFAs). Here we report a theoretical study to assess the characters and possible roles of the ferrite/oxide interface in managing neutron transmutation product helium in NFAs. Using one observed cube-on-cube orientation relationship, various candidate structures of the ferrite/Y2Ti2O7 interfaces were constructed and the associated energies were carefully evaluated. The interface phase diagram is obtained by expressing the energy as a function of temperature and internal oxygen activity (expressed in terms of oxygen partial pressure). The oxide interfaces are predicted to be Y/Ti-rich at thermodynamic equilibrium for the wide temperature range of interest. Vacancy formation energies are lower and helium segregates to the interfaces, in preference to the iron matrix and grain boundaries. Combined with our previous results on bulk-phase Y2Ti2O7, the profound implications of nano-oxides to helium management in NFAs are discussed.
Co-reporter:S.P. Sun, X.P. Li, H.J. Wang, Y. Jiang, D.Q. Yi
Applied Surface Science 2016 Volume 382() pp:239-248
Publication Date(Web):30 September 2016
DOI:10.1016/j.apsusc.2016.04.133
Highlights
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The adsorption of oxygen atom on MoSi2 (110) surface was studied systematically.
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The stability of MoSi2 low-index surfaces was also investigated.
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The preference adsorption site of MoSi2 (110) surface for oxygen atom was H site.
Co-reporter:Jian Xu, Yong Jiang, Litong Yang, Jiangxu Li
Computational Materials Science 2016 Volume 122() pp:22-29
Publication Date(Web):September 2016
DOI:10.1016/j.commatsci.2016.05.009
We present a systematic first principles investigation on a group of representative low-Σ (Σ ⩽ 11) symmetric tilt grain boundaries in bcc-Fe. The grain boundary (GB) structures were constructed using both the coincident site lattice (CSL) and structural unit (SU) models. Calculations are performed to address the relation and applicability of the two models. Results suggest that on some of the GBs, the CSL and SU models may yield different atomistic structures. In these cases, their structures differ only by one vacancy, and the SU model always predicts a much lower GB formation energy than the CSL does. Further calculations on GB vacancy formation suggest that the SU model is more appropriate for describing the low-Σ bcc GBs.For some BCC STGBs, such as the Σ3{1 1 2}〈1 1 0〉, Σ3{1 1 1}〈1 1 0〉, and Σ5{3 1 0}〈1 0 0〉 GB, the CSL and SU models yield the exactly same GB structure, while for other BCC STGBs, such as the Σ5{2 1 0}〈1 0 0〉, Σ9{1 1 4}〈1 1 0〉, and Σ11{3 3 2}〈1 1 0〉 GB, the two models yield different structures, which however differ only by one vacancy. The above figure shows that a vacancy-containing CSL-model Σ5{2 1 0}〈1 0 0〉 GB (Fig. (f)) fully relaxes to the SU-model counterpart (Fig. (e)). In this case, the SU model always predicts a much lower GB formation energy than the CSL model does.
Co-reporter:Fanghua Shen, Danqing Yi, Yong Jiang, Bin Wang, Huiqun Liu, Cong Tang, Wenbin Shou
Materials Science and Engineering: A 2016 Volume 657() pp:15-25
Publication Date(Web):7 March 2016
DOI:10.1016/j.msea.2016.01.026
Effect of main texture components (Cube, Goss and Brass) on the fatigue property of 2524 T3 (Al–Cu–Mg) aluminum alloy sheet was investigated by means of X-Ray diffraction, electron back scattering diffraction, scanning electron microscopy, transmission electron microscopy and fatigue tests. A new kind of factors, which was based on the intensity ratio of texture components, were firstly defined to evaluate and discuss the relationship between texture components and the fatigue crack growth (FCG) rate semi-quantitatively. The results showed that the rate of FCG in the stable stage (II) decreased with an increase of the factor FCGB (the intensity ratio of Cube to Brass texture) obviously. When the new factor FCGB, FCG (the intensity ratio of Cube to Goss texture), and FGB (the intensity ratio of Goss to Brass texture) all exceeded than 1, as well as FCG was close to FGB, the 2524 T3 sheet exhibited the lowest fatigue crack growth rate (ΔK=33 MPa m1/2, da/dN<2.0×10−3). The Schmid factor and misorientation of grains boundaries would be responsible for such influence on the fatigue property.
Co-reporter:S.P. Sun, X.P. Li, H.J. Wang, Y. Jiang, D.Q. Yi
Journal of Alloys and Compounds 2015 Volume 652() pp:106-115
Publication Date(Web):15 December 2015
DOI:10.1016/j.jallcom.2015.08.207
•The anisotropic elastic of C11b MoSi2 under pressure were studied systematically.•The anisotropy is weak under zero pressure but increase consistently with pressure.•The heat capacity has weak pressure dependence, and Grüneisen constant is contrary.•Some rules of the thermodynamic properties under pressure were revealed.The anisotropic elastic and thermodynamic properties of C11b MoSi2 under pressure have been investigated using the plane-wave pseudopotential method of density functional theory and the quasi-harmonic Debye model. The anisotropy in sound velocities under pressure was evaluated using Christoffel's equation. As shown in three dimensional surface projections, the anisotropy in elasticity is weak under zero pressure but increase consistently with increasing the pressure. The equilibrium volume decreases but the bulk modulus and the entropy increases with pressure. The heat capacities have weak pressure dependence, while the Grüneisen constant shows strong pressure dependence. The thermal expansion coefficient depends on co-effects of temperature and pressure, especially obviously on low pressure and on high temperature. Our calculated results are in excellent agreement with the available experiments and other theoretical data.
Co-reporter:Jiangang Yao, Chaomin Zhang, Yong Jiang, Huijin Tao, Dengfeng Yin
Computational Materials Science 2015 Volume 107() pp:184-189
Publication Date(Web):September 2015
DOI:10.1016/j.commatsci.2015.05.027
The impact of point defects on the elastic properties of off-stoichiometric L12-Al3Li intermetallic was investigated through the first principle pseudopotential calculations. The results show that at the temperature of 600 K, the AlLi and LiAl anti-sites dominate in the equilibrium defect concentrations in Li-rich and Al-rich L12-Al3Li, respectively. In the whole composition range of interest, the concentrations of anti-site defects (both AlLi and LiAl) far outnumber those of vacancies (VLi and VAl). The defective stoichiometric L12-Al3Li is predicted to be intrinsically brittle. The Al-rich L12-Al3Li has the increasing LiAl and VLi densities that tend to reduce the hardness and brittleness, while the Li-rich L12-Al3Li does the reverse.Predicted point defect concentrations in L12-Al3Li versus composition for T = 600 K.
Co-reporter:Canhui Xu;Danqing Yi;Haibin Zhang
Journal of Materials Science 2015 Volume 50( Issue 4) pp:1646-1654
Publication Date(Web):2015 February
DOI:10.1007/s10853-014-8725-y
We present a combined experimental and theoretical study on interfacial structure and thermodynamics in internally oxidized Ag(SnO2)p composites. The orientation relation between in situ formed SnO2 particles and the silver matrix was characterized using high-resolution transmission electron microscopy techniques. First-principles energetic calculations were then performed to predict the equilibrium interface structures and corresponding adhesion properties as functions of temperature and oxygen partial pressure. All results were combined to construct the interface-level thermodynamic stability diagram, for guiding the optimal design of internal oxidation parameters.
Co-reporter:S.P. Sun, X.P. Li, H.J. Wang, H.F. Jiang, W.N. Lei, Y. Jiang, D.Q. Yi
Applied Surface Science 2014 Volume 288() pp:609-618
Publication Date(Web):1 January 2014
DOI:10.1016/j.apsusc.2013.10.083
Highlights
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The low-index surfaces of L12–Al3Sc intermetallic were studied systematically.
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The present obtained results agree with experiments well.
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The calculated results suggest that our method is accurate.
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Some rules of the stabilities of low-index surfaces were revealed.
Co-reporter:X.P. Li, S.P. Sun, H.J. Wang, W.N. Lei, Y. Jiang, D.Q. Yi
Journal of Alloys and Compounds 2014 Volume 605() pp:45-50
Publication Date(Web):25 August 2014
DOI:10.1016/j.jallcom.2014.03.159
•The point defects of C11b MoSi2 were studied systematically.•MoSi2 is semimetallic with strong directional covalent bonds.•Some rules of the point defect concentrations were revealed.•Vacancy is a main type of point defect in MoSi2.The electronic structure and point defect concentrations of C11b MoSi2 were studied systematically by the first-principles calculations based on density functional theory. Mo vacancy-induced charge density shows strong directional covalent bonds caused by hybridization of Mo-4d and Si-3p orbitals, which indicates that MoSi2 has low fracture toughness at room temperature. Combining with Wagner–Schottky model, these point defect concentrations of C11b MoSi2 at 2173, 1673, 1223, 773 K as function of composition were also investigated. It is found that the point defect concentrations change drastically for off-stoichiometric compounds. The main structural defects are preferably Mo vacancies or Si anti-structure atoms on the Mo sublattices in Si-rich alloy, and Mo anti-site in Mo-rich alloy, respectively. According to the calculated effective formation enthalpies of point defects, the effective formation enthalpies from big to small in sequence are Mo anti-site, Si anti-site and vacancy (Mo and Si). This result suggests that the vacancy, especially for Si vacancy, is a main type of point defect in C11b MoSi2 system.
Co-reporter:Litong Yang, Yong Jiang, G. Robert Odette, Wenchong Zhou, Zuming Liu, Yong Liu
Acta Materialia 2013 Volume 61(Issue 19) pp:7260-7270
Publication Date(Web):November 2013
DOI:10.1016/j.actamat.2013.08.031
Abstract
Density functional theory calculations were carried out to predict the surface structures and relative stabilities of (1 0 0) and (1 1 0) polar surfaces of a complex metal oxide, Y2Ti2O7. Based on a thermodynamic defect model, surface stabilities were evaluated as a direct function of stoichiometry and environmental factors, i.e. oxygen partial pressure and temperature. Calculations show that, as the oxygen partial pressure increases, the most stable termination of the (1 1 0) changes from Y/Ti-rich to O-rich. For the (1 0 0) surfaces, the most stable termination changes from Y/Ti-rich to stoichiometric, and then to O-rich, with increasing oxygen partial pressure. All variants of the (1 1 0) surfaces were found to be more stable than (1 0 0) surfaces. In particular, non-stoichiometric (1 1 0) surfaces are always more stable than their stoichiometric counterparts.
Co-reporter:Guoqiang Lan, Yong Jiang, Danqing Yi and Shaojun Liu
RSC Advances 2013 vol. 3(Issue 36) pp:16136-16143
Publication Date(Web):05 Aug 2013
DOI:10.1039/C3RA41620H
We report a systematic strategy for theoretically characterizing the interface-level microstructure evolution during in situ internal oxidation of the metal-oxide composite Cu–Al2O3. First, the interface phase stability diagram and phase diagram are constructed from first principles based on thermodynamics calculations, to predict the equilibrium structures and corresponding energetics of the internal interfaces as a function of thermodynamic oxidation parameters (i.e. the ambient oxygen partial pressure and temperature). Further, the equilibrium solubility of oxygen in Cu is coupled with diffusion kinetics derivations, to find a way to connect between the ambient oxygen partial pressure and the local internal oxygen activity in the matrix. Eventually, by combining both thermodynamic and kinetic calculations, the microstructure evolution with time during the internal oxidation fabrication can be predicted at interface level for any practical internal oxidation conditions, such as using the oxidizer Cu2O.
Co-reporter:Kang Luo;Danqing Yi;Shang Fu;Bing Zang
Journal of Materials Science 2013 Volume 48( Issue 22) pp:7927-7934
Publication Date(Web):2013 November
DOI:10.1007/s10853-013-7603-3
θ″-phase, with a formal stoichiometry of Al3Cu, is a coherent, metastable precipitate (GP-II) phase commonly found in Al-based aerospace alloys. In this paper, we employed a first-principles based method to study the energetics of the Al/θ″ interface as response to external strains. The potential effects of temperature, Cu activity, and different strain modes on interface energy (γAl/θ″) were systematically investigated. Calculations show that (i) an unstrained γAl/θ″ always increases with temperature: as temperature increases from T = 298 to 498 K, γAl/θ″ increases by ~9.0 %; (ii) γAl/θ″ is more sensitive to compressive strains than to tensile strains of the same magnitude. In particular, for a parallel compressive strain increasing from 0 to 2 % at a typical aging temperature, γAl/θ″ decreases by ~6.6 %, while a vertical compressive strain of 2 % has a slightly stronger impact by decreasing γAl/θ″ by ~9.6 %. Different influences of applied strain/stress on the formation energies of different orientated interfaces can be further exaggerated by the Poisson effect, and eventually affect the preferential precipitation orientation of θ″ in the matrix.
Co-reporter:Y. Q. Chen;D. Q. Yi;Y. Jiang;B. Wang;D. Z. Xu;S. C. Li
Journal of Materials Science 2013 Volume 48( Issue 8) pp:3225-3231
Publication Date(Web):2013 April
DOI:10.1007/s10853-012-7102-y
The recent increasing interest of T-phase in Al alloy has been switched to its twins. In this study, we employed high resolution transmission electron microscopy to study and compare the morphology and orientation relationships (OR) of T-phase and its twins in an Al–Cu–Mg–Mn alloy. It is found that T-phase tends to form on the {403}Al habit planes and exhibit a rod-like shape, with it longitudinal axis, [010]T, being parallel to the matrix [010]Al direction. Three different OR types are determined between T-phase and Al matrix, namely, {200}T〈010〉T//{200}Al〈010〉Al (OR-I), {200}T〈010〉T//\( \{ 40\bar{3}\}_{\text{Al}} \)〈010〉Al (OR-II), and {200}T〈010〉T//{301}Al〈010〉Al (OR-III). OR-II is the most widely observed OR, while OR-I and III can form from the OR-II by twinning. During the twinning, the cross-section of T-phase transforms from a parallelogram-like shape into a shell-like shape. Further analyses on the shell-like T-twins strongly suggest that tenfold twins could form directly from the successive twinning of an individual T crystal.
Co-reporter:Guoqiang Lan, Yong Jiang, Danqing Yi and Shaojun Liu
Physical Chemistry Chemical Physics 2012 vol. 14(Issue 31) pp:11178-11184
Publication Date(Web):19 Jun 2012
DOI:10.1039/C2CP41079F
A detrimental sulfur effect on adhesion is known for iron– and nickel–oxide interfaces, but has never been reported on copper–oxide interfaces. Here we present a first-principles based study on the effects of temperature, interfacial stoichiometry, Al activity, and S segregation on the internally oxidized Cu/α-Al2O3 interface. The calculated “interfacial phase diagram” for temperatures of interest suggests that the equilibrium interface structure is near the transition between Al-rich and stoichiometric phases. The Al-rich type interface is significantly stronger than the stoichiometric counterpart. The S effect on the Cu/α-Al2O3 interface is obvious: S strongly segregates to both types of interface, degrades the adhesion (by ∼65%) and also reduces the size stability of alumina particles in Cu.
Co-reporter:S.P. Sun, D.Q. Yi, Y. Jiang, B. Zang, C.H. Xu, Y. Li
Chemical Physics Letters 2011 Volume 513(1–3) pp:149-153
Publication Date(Web):6 September 2011
DOI:10.1016/j.cplett.2011.07.076
Abstract
We improved the atomic size factor term that can be used in extended Miedema’s models for calculating formation enthalpies of binary transition-metal compounds. With this new prefactor, the effects of the atomic size difference between two dissimilar transition metals can be taken into account in a more insightful way. Calculations using the present model were compared with experiments as well as with the original Miedema’s model, showing that it can effectively improve the prediction precision of formation enthalpies.
Co-reporter:Guoqiang Lan, Yong Jiang, Danqing Yi and Shaojun Liu
Physical Chemistry Chemical Physics 2012 - vol. 14(Issue 31) pp:NaN11184-11184
Publication Date(Web):2012/06/19
DOI:10.1039/C2CP41079F
A detrimental sulfur effect on adhesion is known for iron– and nickel–oxide interfaces, but has never been reported on copper–oxide interfaces. Here we present a first-principles based study on the effects of temperature, interfacial stoichiometry, Al activity, and S segregation on the internally oxidized Cu/α-Al2O3 interface. The calculated “interfacial phase diagram” for temperatures of interest suggests that the equilibrium interface structure is near the transition between Al-rich and stoichiometric phases. The Al-rich type interface is significantly stronger than the stoichiometric counterpart. The S effect on the Cu/α-Al2O3 interface is obvious: S strongly segregates to both types of interface, degrades the adhesion (by ∼65%) and also reduces the size stability of alumina particles in Cu.
