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Transition from Metastablity to Instability in Dynamics for the Precipitation of δ'(Al_3Li)

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Rare Metals 2001年第4期20卷 240-247页

作者： xiaoling Li, zheng chen, Bing Liu, Yongxin Wang Department of materials science and engineering, northwestern polytechnical university. xi’an, 710072, china northwestern Polytech Univ Dept Mat Sci & Engn Xian 710072 Peoples R China

A computer simulation study on dynamics for the precipitation of δ'(Al_3Li) ordered particles from a disor- dered matrix (α) in binary Al-Li alloys is performed using the microscopic Langevin equation. A unique precipitation mechanism is found near the ordering spinodal line. Different from the classical nucleation mechanism in the me- tastable region and the congruent ordering followed by spinodal decomposition in the instable region, a nonstoichi- ometric single ordered phase with composition fluctuations is formed by non-classical nucleation, and this ordered phase decomposes spinodally. It can be concluded that the precipitation dynamics of δ' phase from metastability to instability is gradual, and no sharp transition occurs near the mean-field spinodal line as the mean-field theory pre- dicts.

关键词： δ'(Al_3Li) precipitation dynamics non-classical nucleation gradual transition

Influence Mechanism of Cerium on the Threshold of Short Fatigue Crack for Aluminum-lithium Alloy 2090

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Rare Metals 2001年第1期20卷 32-37页

作者： zheng chen, Yongxin Wang, Bing Liu, xiaoling Li, Qilong Wei (School of materials science and engineering, northwestern polytechnical university, xi’an 710072, china) northwestern Polytech Univ Sch Mat Sci & Engn Xian 710072 Peoples R China

The thresholds of short fatigue cracks for aluminum-lithium alloys 2090 and 2090+Ce are quantitatively evaluated. The essential reason resulting in stronger short crack effect has been ascertained. Influence of cerium on the threshold of short fatigue cracks for aluminum-lithium alloy 2090 was investigated. The results show that, by adding Ce into this alloy, DeltaK(i) and DeltaK(***) are increased. The influence mechanism of Ce on the threshold of short fatigue crack for alloy 2090 was explored fi om the bound energy, T, phase, the energy of anti-phase boundary, the energy of super-lattice intrinsic stacking fault and the electron bonds. By adding Ce into alloy 2090, the bound energy of Cu atom in this alloy is increased; the effect of thinning and dispersing T, phase is obtained; the effect of increasing the energy of anti-phase boundary and decreasing the energy of super-lattice intrinsic stacking fault for delta ' phase can be achieved.

关键词： aluminum-lithium alloy Ce short fatigue crack bound energy fault energy

Subgrain-assisted spontaneous grain refinement in rapid solidification of undercooled melts

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Journal of materials science & Technology 2024年第7期174卷 234-248页

作者： Jianbao Zhang Dongpeng Hua Dexu Cui xin Li Ke Hua Yixuan He Haifeng Wang yuhong zhao State Key Laboratory of Solidification Processing Center of Advanced Lubrication and Seal MaterialsNorthwestern Polytechnical UniversityXi’an 710072China School of materials science and engineering North University of ChinaTaiyuan 030051China

The grain refinement mechanism for rapid solidification of undercooled melts is still an open problem even after 60 years of on-going *** this work,rapid solidification of undercooled Ni and equi-atomic FeCoNiPd melts was studied and spontaneous grain refinement was found at both low and high *** a detailed electron backscattered diffraction analysis,subgrain-induced grain orien-tation scattering and splitting were found to occur along with the transition from coarse dendrites to fine equiaxed grains at low and high undercooling,respectively,indicating that subgrains play an im-portant role during the formation of fine equiaxed *** this basis,a compromise mechanism of subgrain-assisted spontaneous grain refinement was *** the dendrite re-melting induced thermo-mechanical process and fluid flow induced dendrite deformation occur simultaneously during the post-recalescence stage,stress accumulation would be maximum at both low and high undercooling,thus inducing dynamic recrystallization,during which the formation and rotation of subgrains make the grain orientations scattering and even ***,the grain/subgrain size of undercooled FeCoNiPd ascribing to its unique co-segregation behavior keeps almost invariable from low to high undercooling,indicating that the co-segregation strategy would be effective to inhibit grain growth after rapid solidifi-cation and would be useful in practice.

关键词： Rapid solidification Undercooling Spontaneous grain refinement Grain growth High entropy alloy

Atomic-scale computer simulation for early precipitation process of Ni75 Al10 V15 alloy

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Progress in Natural science:materials International 2004年第3期 49-54页

作者： zhao yuhong*, chen zheng, WANG Yongxin and LU Yanli (Department of materials science and engineering, northwestern polytechnical university, xi’an 710072, china)

The kinetic model for a ternary system is introduced based on the microscopic diffusion form of the phase field equations for a binary alloy. The equation is solved in the reciprocal space. This model is used to investigate the early precipitation process of Ni 75 Al 10 V 15 by simulating the atomic pictures of the two ordered phases and calculating the order parameters of γ ′(Ni 3Al) phase. Simulation results show that the γ ′ ordered phases precipitate from the disordered matrix by a non classical nucleation mechanism, and the nonstoichiometric γ ′ ordered phase appears first and then transforms into the stoichiometric one. Clusters of V atoms appear at the γ ′ phase boundaries followed by the formation of the nonstoichiometric θ ordered phase. The farther the location from γ ′ phase boundary is, the lower the order degree of θ phase is. There exist two kinds of DO 22 ordered domains: a horizontal one and a vertical one, related to their adjacent γ ′ phase boundaries. The model could describe the atomic ordering and composition clustering simultaneously, and any a priori assumption about the new phase structure and precipitation mechanism etc. is unnecessary.

关键词： early precipitation process computer simulation Ni 75 Al 10 V 15 alloy.

Core-rim structured MXene@SiO_(2)composites as oil-based additives for enhanced tribological properties

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Friction 2024年第8期12卷 1728-1740页

作者： yuhong CUI Shenghua XUE Tiantian WANG Shujuan LIU Qian YE Feng ZHOU Weimin LIU State Key Laboratory of Solidification Processing Center of Advanced Lubrication and Seal MaterialsSchool of Materials Science and EngineeringNorthwestern Polytechnical UniversityXi'an 710072China State Key Laboratory of Solid Lubrication Lanzhou Institute of Chemical PhysicsChinese Academy of SciencesLanzhou 730000China

Herein,we have prepared SiO_(2)particles uploaded MXene nanosheets via in-situ hydrolysis of *** to the large number of groups at the edges of MXene,SiO_(2)grows at the edges first,forming MXene@SiO_(2)composites with a unique core-rim *** tribological properties of MXene@SiO_(2)as lubricating additive in 500 SN are evaluated by *** results show that MXene@SiO_(2)can reduce the friction coefficient of 500 SN from 0.572 to 0.108,the wear volume is reduced by 73.7%,and the load capacity is increased to 800 *** superior lubricity of MXene@SiO_(2)is attributed to the synergistic effect of MXene and SiO_(2).The rolling friction caused by SiO_(2)not only improves the bearing capacity but also increases the interlayer distance of MXene,avoiding accumulation and making it more prone to interlayer ***@SiO_(2)is adsorbed on the friction interface to form a physical adsorption film and isolate the friction *** addition,the high temperature and high load induce the tribochemical reaction and form a chemical protection film during in the friction ***,the presence of these protective films results in MXene@SiO_(2)having good lubricating properties.

关键词： Ti3C2Tx MXene SiO_(2)nanoparticles lubricating additives protective film

Atomic-scale computer simulation for early precipitation process of Ni75 Alx V25-x alloy with intermediate Al composition

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Progress in Natural science:materials International 2005年第4期 64-70页

作者： zhao yuhong 1*, JU Dongying 2, chen zheng 3* and HOU Hua 1(1. College of Material science & engineering, china North university, Taiyuan 030051, china 2. Department of Mechanical engineering, Saitama Institute of Technology, Okabe, Saitama 369 0239, Japan 3. Colledge of materials science & engineering, northwestern polytechnical university, xi'an 710072, china) College of Material science & engineering China North University Taiyuan 030051 China Department of Mechanical engineering Saitama Institute of Technology Okabe Saitama 369-0239 Japan Colledge of materials science & engineering Northwestern Polytechnical University Xi' an 710072 China

The microscopic phase field approach is applied to model the early precipitation process of Ni 75 Al x V 25- x alloy. Without any prior assumptions, this model can be used to simulate the temporal evolution of arbitrary morphologies and microstructures on atomic scale. By simulating the atomic pictures, and calculating the order parameters and volume fraction of the θ (Ni 3V) and γ′ (Ni 3Al) ordered phases, we study Ni 75 Al x V 25- x alloys with Al composition of 0.05, 0.053 and 0.055 (atom fraction). Our calculated results show that, for these alloys, θ and γ′ phases precipitate at the same time; with the increase of Al content, the amount of γ′ phase increases and that of θ phase decreases; the precipitation characteristic of γ′ phase transforms from Non Classical Nucleation and Growth (NCNG) to Congruent Ordering + Spinodal Decomposition (CO+SD) gradually; otherwise, the precipitation characteristic of θ phase transforms from Congruent Ordering + Spinodal Decomposition (CO+SD) to Non Classical Nucleation and Growth (NCNG) mechanism gradually. Both θ and γ′ phases have undergone the transition process of mixture precipitation mechanism characterized by both NCNG and CO+SD mechanisms. No incontinuous transition of precipitation mechanism has been found.

关键词： computer simulation early precipitation mechanism phase field model Ni75Alx V25-x alloy.

Morphology characteristics of α precipitates related to the crystal defects and the strain accommodation of variant selection in a metastableβtitanium alloy

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Journal of materials science & Technology 2021年第36期95卷 1-9页

作者： Ruifeng Dong Hongchao Kou yuhong zhao xiaoyang Zhang Ling Yang Hua Hou School of materials science and engineering North University of ChinaTaiyuan030051China State Key Laboratory of Solidification Processing Northwestern Polytechnical UniversityXi’an710072China

Profound and comprehensive investigations on the morphology characteristics ofαprecipitates are essential for the microstructural control of metastableβtitanium *** the very beginning of aging treatment,intragranularαprecipitates with a dot-like morphology begin to generate nearby the dislocations,then those dot-likeαprecipitates with the same crystallographic orientation tend to connect with each other to develop a lath-like *** the progress of aging treatment,the orientated lath-likeαprecipitates gradually combine with each other to form the V-shaped clusters or the triangular *** dislocations of{110}_(β)βedge type are evidenced within theβgrains,and it is found that variant selection ofαprecipitates induced by the transformation strain and the interplay betweenαvariants and the dislocations are confirmed as the key factors for the formation of the V-shaped or triangular *** results of this work could provide underlying knowledge on the morphology characteristics of intraguranularαprecipitates related to the crystal defects and the strain accommodation ofαvariants in metastableβtitanium alloys.

关键词： Metastableβtitanium alloys αPrecipitates Morphology characteristics Phase transformation Strain accommodation Dislocations

Crystallographic evidences for twin-assisted eutectic growth in undercooled Ni-18.7 at.%Sn eutectic melts

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Journal of materials science & Technology 2023年第4期135卷 65-79页

作者： Fan Zhang Jianbao Zhang xinlei Lü Ke Hua yuhong zhao Haifeng Wang State Key Laboratory of Solidification Processing Center of Advanced Lubrication and Seal MaterialsNorthwestern Polytechnical UniversityXi’an 710072China School of materials science and engineering North University of ChinaTaiyuan 030051China

Rapid solidification in undercooled Ni-18.7 at.%Sn eutectic melts was observed in-situ by a high-speed high-resolution camera and the microstructures were characterized in detail by electron backscattering *** the first time,the exact crystallographic orientation relations(ORs)between HCP-Ni_(3)Sn(α-Ni)subsets were *** HCP-Ni_(3)Sn,the{1121}and/or{1122}twin ORs(i.e.,HCP-Ni_(3)Sn twins)hold independently on undercooling,whereas forα-Ni,the{111}twin OR is the case at low undercooling and would hold initially at intermediate and high *** roles of twinning and allotropy transformation(i.e.,FCC-Ni_(3)Sn→HCP-Ni_(3)Sn)were integrated to reveal the formation mechanism of HCP-Ni_(3)Sn twins,and a reversed OR transition analysis was carried out for rep-resentative samples from low to high ***,novel twin-assisted eutectic growth was found to occur all *** this basis,we showed that the single nucleation mode of Herlach is followed,and speculated that primary and secondary coupled eutectic dendrite growth and un-coupled growth ofα-Ni and FCC-Ni_(3)Sn might all be the origins of anomalous *** work would shed some lights on the long-time controversies about the nucleation mode and the formation mechanism of anomalous eutectics in undercooled eutectic alloys.

关键词： Twin-assisted eutectic growth Allotropy transformation Nucleation mode Anomalous eutectics Undercooling

ω-Assisted refinement of α phase and its effect on the tensile properties of a near β titanium alloy

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Journal of materials science & Technology 2020年第9期44卷 24-30页

作者： Ruifeng Dong Jinshan Li Hongchao Kou Jiangkun Fan yuhong zhao Hua Hou Li Wu College of materials science and engineering North University of ChinaTaiyuan 030051China State Key Laboratory of Solidification Processing Northwestern Polytechnical UniversityXi’an 710072China

In this work, the phase transformation sequence during the continuous heating process(3℃/min) was investigated in a near β titanium alloy. The results show that the staring formation of ω phase is about267℃, and the ending precipitation temperature about 386℃ during the heating process. When the heating temperature is greater than 485℃, there are no ω phase detected within the β matrix. Combined with the microstructural characterization, it is found that ω phase facilitates the nucleation of αphase nearby the ω/β interface and has a great effect on the refinement for α phase. As compared with the specimens directly aged, the specimens with ω-assisted refinement of α phase possess high tensile strength, but there is no yield stage detected on their stress-strain curve. Combined with the analyses of the fracture morphology, the specimens with ω-assisted refinement of α phase present a brittle *** is mainly ascribed to its relatively lager width of grain boundaries and the absence of widmanst?ttenα precipitates.

关键词： Neartitanium alloy Continuous heating Phase transformation -Assisted nucleation Precipitation Tensile properties