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Microscopic phase-field simulation of the coarsening behavior of coherent precipitates in Ni-Al alloys

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Journal of University of Science and Technology Beijing 2008年第2期15卷 161-166页

作者： Yanli Lu Zheng Chen yongxin wang Yongsheng Li School of Materials Science and Engineering Northwestern Polytechnical University Xi＇an 710072 China State Key Laboratory of Solidification Processing Northwestern Polytechnical University Xi＇an 710072 China

On the basis of the microscopic phase-field dynamic model and the microelasticity theory, the characteristics of the coarsening behavior of γ＇ phase in Ni-Al alloys have been systematically studied in a certain volume fraction of the precipitates. It was found that the initial irregular shape, randomly distributed γ＇ phase, gradually transformed into cuboidal shape, regularly aligned along the [100] and [010] directions, and a highly preferential selected microstructure was formed during the later stage of precipitation. The volume fraction of the precipitates produced some effects on the precipitate morphology but did not produce an obvious effect on the regularities of precipitate distribution. The coarsening rate constant from the cubic growth law decreased as a function of volume fraction for small volume fractions, remained constant for intermediate volume fractions, and increased as a function of volume fraction for large volume fractions. During the coherent coarsening process, four ＂splitting＂ patterns between γ＇ phases, which belonged to different antiphase domains, were produced via particle aggregation, such as an L-shaped pattern, a doublet, a triplet, and a quartet.

关键词： Ni-Al alloy precipitates elastic strain coarsening microscopic phase-field simulation

Simulation of Microstructure Evolution of Ni_(75)Al_(2.9)V_(22.1) Alloy with Progressive Aging Mechanisms

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Journal of Materials Science & Technology 2008年第2期24卷 251-255页

作者： Yongsheng LI Zheng CHEN Qingbo LAI yongxin wang StateKey Laboratory of Solidification Processing Northwestern Polytechnical University Xi＇an 710072 China

The interrupted aging mechanisms were applied to Ni75Al2.9V22.1 alloy by using the microscopic phase-field simulation method. For the single phase region existing at high temperature, the low content alloy was used as the study object. With the progressive aging mechanisms, the metastable phase γ′ of high temperature can be obtained from the low temperature two phase regions, and the quantity of γ′ phase reduces with increasing temperature. The θ single phase morphology at high temperature regions will turn to be the γ′＋θ two phase morphology at low temperature with the interrupted aging method. Despite of the different precipitation paths of γ′ phase, the precipitation mechanisms are the same for the low temperature aging and high temperature interrupted aging.

关键词： Microstructure Progressive aging Ni75AlxV25-x Simulation

Calculation of electric field effects on the Gibbs free energy of the Al-Li-Mg alloy

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Rare Metals 2007年第5期26卷 508-514页

作者： ZHANG Jianjun CHEN Zheng wang yongxin LIU Bing LI Yongsheng School of Materials Science and Engineering Northwestern Polytechnical University Xi＇an 710072 China

Based on the Thomas-Fermi model,the calculation methods of the monatomic Gibbs free energy were found. The interior potential boundary condition under electric field was defined. The calculation methods of Gibbs free energy for the monatomic,compound,and solid solution with electric field were set up. Under the influence of electric field,the Gibbs free energy of Al is the most sensitive,followed by those of Li and Mg. At the solution temperature the Gibbs free energies of Al3Li and its elements under electric field are not symmetrical about the zero point of electric field,whereas at the aging temperature their values are symmetrical about the zero point of electric field. At the solution temperature near the zero point of electric field,the Gibbs free energy of Al3Li is higher than that of Al-2.14%Li. And at 460 K the Gibbs free energy of Al3Li is lower than that of Al-2.14wt.%Li under electric field. The Gibbs free energy of 1420 alloy decreases from both sides of electric field to the zero point at the aging temperature.

关键词： Al-Li-Mg alloy thermodynamics parameters Thomas-Fermi model electric field

Simulation of the precipitation process of Ni_(75)Al_xV_(25-x) alloys incorporated in the microelasticity field

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Journal of University of Science and Technology Beijing 2007年第1期14卷 61-66页

作者： Yongsheng Li Zheng Chen Yungang Li Yanli Lu yongxin wang Materials Science and Engineering School Northwestern Polytechnical University Xi＇an 710072 China State Key Laboratory of Solidification Processing Northwestern Polytechnical University Xi＇an 710072 China

The microelasticity field was incorporated into the microscopic phase-field equation for the ternary alloy systems, the morphology evolution and coarsening behavior of the Ni75AixV25-x alloy were simulated. The γ phase precipitates initially for Ni75Al7aV17.9 and Ni75Al5.5V19.5 alloys and the two phases transform from the equiaxed or strip-like to the quadrate as the growth and coarsening processes. For the anisotropic elasticity interaction of the system, the orientation of γ is along the 〈001〉 directions and the θ phase is along the short axis direction of [10]. Analysis of the structure and the pair-correlation functions indicate that the average precipitate length scale of the particles increases at the late-stage coarsening, and the dynamical scaling behavior is obeyed.

关键词： Ni75AixV25-x microelasticity field precipitation coarsening structure function

Microscopic phase-field simulation of L1_2 and D0_(22) phases during the early precipitation process of Ni-Cr-Al alloys

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Journal of University of Science and Technology Beijing 2006年第5期13卷 429-434页

作者： Zhong Chu Zheng Chen yongxin wang Yanli Lu Yongsheng Li State Key Laboratory for Solidification Processing Northwestern Polytechnical University Xi＇an 710072 China

The influence of temperature on the precipitation mechanism and sequence of L 12 and D022 phases during the early precipitation process of a ***%Cr-14at%Al alloy was simulated based on the microscopic phase-field model. In the range from 873 to 1373 K, the precipitation mechanism transformed from spinodal decomposition to non-classic nucleation and growth; the incubation period prolonged gradually with increasing temperature. The volume fraction of L12 phases increased and that of D022 phases decreased. D022 phases disappeared at 1373 K, and finally single-phase L12 phases were formed.

关键词： Ni-Cr-AI alloys microscope phase-field model precipitation ordering parameter simulation

Simulation of the coarsening behavior of intermetallic precipitates in Ni_(75)Al_xV_(25-x) alloys

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Rare Metals 2007年第5期26卷 498-503页

作者： LI Yongsheng CHEN Zheng wang yongxin LU Yanli ZHANG Jianjun State Key Laboratory of Solidification Processing Northwestem Polytechnical University Xi＇an 710072 China

The coarsening behavior of L12 and D022 in Ni75AlxV25-x （x,at.%） alloys including coherent strain was investigated using the microscopic phase-field model. The simulation results indicate that the shape transition and spatial correlation of L12 and D022 are caused by the morphological-dependent anisotropic elastic interactions in the system. The coarsening process of the particles is by means of neighbor particles impingement and aggregation into larger ones. For the strain-induced interactions between the precipitates,the LSW theory is altered for the coarsening behavior of L12 and D022. In addition,the simulation reveals that the growth and coarsening of D022 present two obvious stages at lower Al concentration regions and proceed simultaneously at high Al concentration regions. The growth and coarsening processes of L12 at the same regions is reverse to those of D022.

关键词： ternary system phase transformation coarsening dynamics microscopic phase-field Ni75AlxV25-x

Microscopic Phase-field Simulation of Competition Mechanism Between Ll_2 and D0_(22) Structure in Ni-Cr-Al Alloy

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Journal of Materials Science & Technology 2006年第3期22卷 315-320页

作者： Zhong CHU Zheng CHEN yongxin wang Yanli LU Yongsheng LI State Key Lab of Solidification Processing Northwestern Polytechnical University Xi＇an 710072 China

Simulations are performed on temporal evolution of atom morphology and ordering parameters of Ni-14.5 Cr-16.5 Al alloy during early precipitation process at different temperatures based on microscopic phase-field theory; the relationship between precipitation sequence and mechanism of L12 and D022 structure and precipitation temperature are illuminated. The nonstoichiometric ordered L12 phases appear first with congruent ordering＋spinodal decomposition mechanism which is then followed by precipitation of D022 phases at ordering domain boundaries of L12 phases by spinodal decomposition mechanism at 1073 K and 1223 K. The nonstoichiometric L12 phases transform to stoichiometric ordering phases gradually. The incubation period of L12 and D022 phases is shorter at 1073 K than that 1223 K, and growth speed is higher at 1073 K. At 1373 K, L12 and D022 phases appear simultaneously by non-classical nucleation and growth mechanism. After that the particles of D022 phases diminish and disappear gradually; L12 phases grow and single L12 phases are remained at last.

关键词： Ni-Cr-Al Microscopic phase-field model Precipitation Ordering parameter Simulation

Energy studies of precipitation sequence in Ni_(75)Al_(10)Cr_(15) alloy based on the phase field theory

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Science China(Physics,Mechanics & Astronomy) 2011年第5期54卷 821-826页

作者： DONG WeiPing CHEN Zheng wang yongxin State Key Laboratory of Solidification Processing Northwestern Polytechnical University Xi'an 710072 China

Based on the phase field theory, the phase precipitation sequence of Ni75A110Cr15 alloy and the free energy of each phase were studied. Moreover, the interatomic potentials of Llo phase, L12 phase and DO22 phase changing with temperature and concen- trations were computed through utilizing the interatomic potentials equations induced by Khachaturyan＇s relational equations between the interatomic potentials and the long-range order （LRO） parameters. Results match preceding work and demonstrate that the phase precipitation sequence of Ni75AlloCr15 alloy is the disordered phase -L10 pre-precipitation phase -L12 equilibrium phase -L12＋DO22 equilibrium phase. Free energies of Llo pre-precipitation phase are higher and interatomic potentials are smaller than those of L12 equilibrium phase; therefore, it is concluded that Llo phase is unstable, and phase transformation would occur to L12 which is more stable; L12 phase precipitates earlier than DO22 phase because L12＇s interaction potentials are larger than DO22＇s.

关键词： precipitation sequence pre-precipitation phase equilibrium phase interatomic potentials free energy phase field theory

Microscopic phase-field study for oriented diffusion channel effect of nickel-based alloy and phases' effect mechanism

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Science China(Technological Sciences) 2011年第4期54卷 835-840页

作者： YANG Kun CHEN Zheng DONG WeiPing wang yongxin ZHANG MingYi State Key Laboratory of Solidification Processing Northwestern Polytechnical UniversityXi'an 710072China

In this paper,a microscopic phase-field model was used to investigate the effect of the oriented diffusion channel and the phases' effect mechanism for the Ni75Al6.0V19.0 alloy during a phase transformation process.A diffusion channel of V was formed in the [100] *** oriented growth of DO22 in this direction,when an elastic misfit stress field existed,forced Al to form a diffusion channel next to DO22,resulting in L12-oriented *** an increase in stress,the oriented growth increased initially and then *** a higher stress,the average values of the occupation probability for V atoms became constant later while Al atoms earlier.

关键词： diffusion channel effect stresses-induced diffusion diffusion-induced stresses microscopic phase-field