Alloys with composition of Mg_(96-x)Gd_3Zn_1Li_x(at.%)(x=0, 2, 4, and 6) were prepared by conventional casting. The microstructures of these alloys under as-cast and solid-solution conditions have been observed, and t...Alloys with composition of Mg_(96-x)Gd_3Zn_1Li_x(at.%)(x=0, 2, 4, and 6) were prepared by conventional casting. The microstructures of these alloys under as-cast and solid-solution conditions have been observed, and the mechanical properties were investigated. The results showed that Li is an effective element to refine the grains and break the eutectic networks in as-cast MgGd_3Zn_1 alloy. During solid solution treatment, these broken eutectic networks are spheroidized and highly dispersed. In addition, plentiful lamellar long period stacking ordered(LPSO) phases are precipitated in an α-Mg matrix when the Li addition is not more than 4%. Solid-solution treated Mg_(92)Gd_3Zn_1Li_4 alloy exhibits an optimal ultimate tensile strength(UTS) of 226 MPa and elongation of 5.8%. The strength of MgGd_3Zn_1 alloy is improved significantly, meanwhile, the toughness is apparently increased.展开更多
Understanding the interface between strengthening precipitates and matrix in alloys, especially at the atomic level, is a critical issue for tailoring the precipitate strengthening to achieve desired mechanical proper...Understanding the interface between strengthening precipitates and matrix in alloys, especially at the atomic level, is a critical issue for tailoring the precipitate strengthening to achieve desired mechanical properties. Using high-resolution scanning transmission electron microscopy, we here clarify the semicoherent interfaces between the matrix and long-period stacking ordered(LPSO) phases, including 18 R and 14 H, in Mg–Zn–Y alloys. The LPSO/Mg interface features the unique configuration of the Shockley partial dislocations, which produces a near zero macroscopic strain because the net Burgers vectors equal zero. The 18 R/Mg interface characterizes a dissociated structure that can be described as a narrow slab of 54 R. There are two dislocation arrays accompanied to the 18 R/54 R and 54 R/Mg interface, resulting a slight deviation(about 2.3°). The 14 R/Mg interface exhibits the dislocation pairs associated with solute atoms. We further evaluate the stability and morphology of the corresponding interfaces based on elastic interaction, via calculating the mutual strong interactions between dislocation arrays, as well as that between the dislocations and solute atoms. The synchronized migration of interfacial dislocations and solute atoms, like move-drag behavior, dominates the lateral growth of LPSO phases in Mg alloys.展开更多
Herein,the evolution of long-period stacking ordered(LPSO)phases in the as-cast Mg-6Gd-1Zn-0.6Zr(wt.%)alloy are investigated via transmission electron microscopy(TEM)and atom probe tomography(APT).The TEM results reve...Herein,the evolution of long-period stacking ordered(LPSO)phases in the as-cast Mg-6Gd-1Zn-0.6Zr(wt.%)alloy are investigated via transmission electron microscopy(TEM)and atom probe tomography(APT).The TEM results reveal that two types of LPSO phase(a bulky interdendritic phase and a plate-like matrix LPSO phase)are formed in the as-cast sample.Most of the LPSO phases are confirmed to be of the 14H type,with a smaller proportion being of the 18R LPSO.Further,the APT results reveal that the composition of the interdendritic LPSO phase is closer to that of the ideal 14H phase compared to the matrix LPSO phase,and both the interdendritic and matrix LPSO phases exhibit a Gd/Zn ratio of 2.5,thereby indicating a deficient Zn content compared to the ideal 14H phase(i.e.,1.3).In addition,the influence of the LPSO phases on the deformation behavior is investigated at different compressive plastic strains using electron backscatter diffraction(EBSD)analysis to reveal twinning and slip behavior during deformation.The results indicate that the LPSO phase induces additional work hardening in the late stage of deformation via the suppression of{1011}compressive twinning and the activation of non-basal slip systems.展开更多
The precipitation characteristics of the α2 ordered phase in Ti-AI-Sn-Zr-Mo-Si-Nd alloys with various content of Al, under different aging conditions, were investigated. The distribution and size of the α2 ordered p...The precipitation characteristics of the α2 ordered phase in Ti-AI-Sn-Zr-Mo-Si-Nd alloys with various content of Al, under different aging conditions, were investigated. The distribution and size of the α2 ordered phase changed with temperature and Al content. The dislocations were the only places where the α2 ordered phase could precipitate at higher temperature near the critical transformation temperature for each alloy experimented. With the addition of Al content, the critical transformation temperature of α2 ordered phase increased. When the aging temperature was relatively low (650℃), the precedent precipitation of α2 ordered phase took place in primary a phase at the early stage of aging, in the duplex microstructure (the primary a with the transformed (3) of the alloys with lower Al content. But after certain aging time (50 h), the size of α2 particles was almost equal in both the primary a and the transformed β. And no obvious growth of α2 particles could be observed after 50 h.展开更多
Some experimental α+α2 alloys were prepared by the addition of tin or aluminum elements into Ti-55 alloy. These alloys were designed with varied electron concentration values and named as Sn-rich alloys...Some experimental α+α2 alloys were prepared by the addition of tin or aluminum elements into Ti-55 alloy. These alloys were designed with varied electron concentration values and named as Sn-rich alloys and Al-rich alloys, respectively. The precipita- tion and growth of α2 ordered phase in the tested alloys under various heat treatment conditions were investigated. Some compari- sons among the experimental results were performed and discussed in detail. Stronger precipitation and growth of α2 ordered phase were caused in Al-rich alloys but relatively weak change in Sn-rich alloys with increasing the electron concentration. The precipita- tion of α2 ordered phase in Al-rich alloys is stronger than that in Sn-rich alloys when the electron concentration value is the same for the two alloys.展开更多
The microstructure and damping capacities of MgZnxYi.33x(x=l-4at.%)alloys were discussed and researched.The main phase composition of the alloys consists of a_Mg and long-period stacking ordered(LPSO)phase.Due to incr...The microstructure and damping capacities of MgZnxYi.33x(x=l-4at.%)alloys were discussed and researched.The main phase composition of the alloys consists of a_Mg and long-period stacking ordered(LPSO)phase.Due to increasedLPSO phase,grain size was refined.LPSO phase was advantageous to the damping properties of the Mg-Zn-Y alloys.Mg-7%Zn-12.8%Y has the highest damping capacity up to0.04.Due to stacking fault probability,the LPSO phase in the Mg-Zn-Yalloys could be new damping source to dissipate energy so as to contribute to the improvement of damping capacities.展开更多
The study of temperature-driven phase transitions is significant in phosphate chemistry,as these transitions often lead to unique physical properties for specific applications,such as catalysis,energy storage,ion cond...The study of temperature-driven phase transitions is significant in phosphate chemistry,as these transitions often lead to unique physical properties for specific applications,such as catalysis,energy storage,ion conduction,and nonlinear optics[1–3].The phase transition from room temperature(RT)to high temperature(HT)in phosphates is always from periodic structures to disordered or amorphous states[4–8].At RT,phosphates often maintain a highly ordered crystalline structure,which is stabilized by the lower thermal energy.As the temperature increases,the thermal energy disrupts the periodic arrangement of atoms and leads to a phase transition,where the once ordered structure becomes increasingly disordered or even amorphous.展开更多
The precipitation of ordered alpha_2 phase in a near - alphaTi-6.3Al-4.8Sn-2.0Zr-1.0Mo-0.34Si-0.9Nd (mass fraction) alloy with duplex microstructure, duringaging at various temperatures, was investigated. It is conclu...The precipitation of ordered alpha_2 phase in a near - alphaTi-6.3Al-4.8Sn-2.0Zr-1.0Mo-0.34Si-0.9Nd (mass fraction) alloy with duplex microstructure, duringaging at various temperatures, was investigated. It is concluded that the precipitation and growthof the alpha_2 phase can be controlled by suitable selection of the aging temperature. Aging athigher temperatures can result in the uniform precipitation and growth of alpha_2 ordered phase inalpha_p whereas the alpha_2 ordered phase precipitated only at the lamella boundaries anddislocations in beta_t. Aging at a moderate temperature can promote the tendency of uniformprecipitation of alpha_2 phase in both alpha_p and beta_t. Aging at a relatively low temperature issuitable for the uniform precipitation and growth of fine alpha_2 particles throughout both thealpha_p and beta_t matrix.展开更多
Different structure models of a long-period ordered phase in Fe-C martenstie formed during aging have been checked by computer simulation of electron diffraction(ED) patterns based on these models.The results showed t...Different structure models of a long-period ordered phase in Fe-C martenstie formed during aging have been checked by computer simulation of electron diffraction(ED) patterns based on these models.The results showed that the simulated ED pattern of γ'-FexC(Ⅱ) model proposed by the present authors is in good agreement with experimentally observed ED pattern.It was also confirmed that the incommensurate superperiod stems from the coexistence of several γ'-Fe_xC(H) phases with different superperiods.The Fe(144)C(24)(Fe6C) model proposed by Uwakweh et al.generated ED patterns remarkably different from the experimental ones.展开更多
AGE-hardened Cu-Ti has been an important alloy of investigation in the field of continuousphase transformation due to its complicated transformation processes which involve short rangeordering (SRO), spinodal decompos...AGE-hardened Cu-Ti has been an important alloy of investigation in the field of continuousphase transformation due to its complicated transformation processes which involve short rangeordering (SRO), spinodal decomposition (SD), long range ordering (LRO), etc. So far, ithas been a controversial topic whether each process exists, and in what sequence they pro-ceed.展开更多
First-principles computation on the basis of density functional theory(DFT) is executed with the CASTEP code to explore the structural, elastic, and electronic properties along with Debye temperature and theoretical V...First-principles computation on the basis of density functional theory(DFT) is executed with the CASTEP code to explore the structural, elastic, and electronic properties along with Debye temperature and theoretical Vickers’ hardness of newly discovered ordered MAX phase carbide Mo2TiAlC2. The computed structural parameters are very reasonable compared with the experimental results. The mechanical stability is verified by using the computed elastic constants. The brittleness of the compound is indicated by both the Poisson’s and Pugh’s ratios. The new MAX phase is capable of resisting the pressure and tension and also has the clear directional bonding between atoms. The compound shows significant elastic anisotropy. The Debye temperature estimated from elastic moduli(B, G) is found to be 413.6 K. The electronic structure indicates that the bonding nature of Mo2TiAlC2is a mixture of covalent and metallic with few ionic characters. The electron charge density map shows a strong directional Mo–C–Mo covalent bonding associated with a relatively weak Ti–C bond.The calculated Fermi surface is due to the low-dispersive Mo 4d-like bands, which makes the compound a conductive one.The hardness of the compound is also evaluated and a high value of 9.01 GPa is an indication of its strong covalent bonding.展开更多
An ideal method has been established for calculating the precipitation of α2 ordered phase in near-α titanium alloys based on the theory on the critical electron concentration for the precipitation of α2 ordered ph...An ideal method has been established for calculating the precipitation of α2 ordered phase in near-α titanium alloys based on the theory on the critical electron concentration for the precipitation of α2 ordered phase in near-α titanium alloys. With complete precipitation of α2 phase in near-α titanium alloys, the alloys can be considered to be composed of two parts： （1） the α2 ordered phase with the stoichiometric atomic ratio of Ti3X; （2） the disorder solid solution with the critical composition in which the α2 ordered phase is just unable to precipitate. By using this method, the volume fractions of α2 ordered phase precipitated in Ti-Al, Ti-Sn, Ti-Al-Sn-Zr alloys with various AI, Sn and/or Zr contents have been calculated. The influences of AI and Sn on the precipitation of α2 ordered phase are discussed. The calculating results show substantial agreement with the experimental ones.展开更多
Phase transitions,as one of the most intriguing phenomena in nature,are divided into first-order phase transitions(FOPTs)and continuous ones in current classification.While the latter shows striking phenomena of scali...Phase transitions,as one of the most intriguing phenomena in nature,are divided into first-order phase transitions(FOPTs)and continuous ones in current classification.While the latter shows striking phenomena of scaling and universality,the former has recently also been demonstrated to exhibit scaling and universal behavior within a mesoscopic,coarse-grained Landau-Ginzburg theory.Here we apply this theory to a microscopic model-the paradigmatic Ising model,which undergoes FOPTs between two ordered phases below its critical temperature-and unambiguously demonstrate universal scaling behavior in such FOPTs.These results open the door for extending the theory to other microscopic FOPT systems and experimentally testing them to systematically uncover their scaling and universal behavior.展开更多
Mg-Y-Zn alloys with long period stacking ordered(LPSO)structure have received much attention recently and exhibit great potential in applications such as automotive,aerospace and in bio-medical fields.This paper aimed...Mg-Y-Zn alloys with long period stacking ordered(LPSO)structure have received much attention recently and exhibit great potential in applications such as automotive,aerospace and in bio-medical fields.This paper aimed to investigate the effect of different phase constitution of LPSO structures on corrosion rate of bio-medical Mg-Y-Zn alloys.The results showed that as-cast Mg98.5Y1Zn0.5 alloys containing only 18R structure exhibited the highest corrosion resistance with the corrosion rate of 2.78 mm/year.The precipitation of 14H lamellas within a-Mg grains during solid solution treatment introduced the crystallographic orientation corrosion by accelerating micro-galvanic corrosion.The increase of 18R/14H interfaces deteriorated the corrosion resistance,and the grain boundaries also suffered from severe electrochemical dissolution.This work suggested that Mg-Y-Zn alloys with single LPSO structure(either 18R or 14H)exhibited better corrosion resistance than alloys with co-existence 18R and I4H LPSO structures.展开更多
Mg-RE(rear earth) alloys with long period stacking(LPSO) structures have great potential in biomedical applications. The present work focused on the microstructure and corrosion behaviors of Mg 98.5 Y1 Zn0.5 alloys wi...Mg-RE(rear earth) alloys with long period stacking(LPSO) structures have great potential in biomedical applications. The present work focused on the microstructure and corrosion behaviors of Mg 98.5 Y1 Zn0.5 alloys with 18 R LPSO structure after equal channel angular pressing(ECAP). The results showed that the ECAP process changed the grain size and the distribution of LPSO particles thus controlled the total corrosion rates of Mg 98.5 Y1 Zn0.5 alloys. During the ECAP process from 0 p to 12 p, the grain size reduced from 160–180 μm(as-cast) to 6–8 μm(12 p). The LPSO structures became kinked(4 p), then started to be broken into smaller pieces(8 p), and at last comminuted to fine particles and redistributed uniformly inside the matrix(12 p). The improvement in the corrosion resistance for ECAP samples was obtained from 0 p to 8 p, with the corrosion rate reduced from 3.24 mm/year(0 p) to 2.35 mm/year(8 p) in simulated body fluid, and the 12 p ECAP alloy exhibited the highest corrosion rate of 4.54 mm/year.展开更多
The fatigue behavior of four extruded Mg-Y-Zn alloys containing different volume fractions of long-period stacking ordered(LPSO)grains was investigated through a comparative study combining experiments and crystal pla...The fatigue behavior of four extruded Mg-Y-Zn alloys containing different volume fractions of long-period stacking ordered(LPSO)grains was investigated through a comparative study combining experiments and crystal plasticity finite element simulations.Strain controlled low-cycle fatigue experiments were conducted at different strain amplitudes and revealed a limited cyclic hardening in Mg_(89)Zn_(4)Y_(7)alloy or softening in Mg_(99.2)Zn_(0.2)Y_(0.6)and Mg_(97)Zn_(1)Y_(2)alloys.A decrease in the fatigue life against the plastic strain with the increase in LPSO phase volume fraction was observed and was related the limited ductility of extruded LPSO grains.Stress-strain hysteresis curves were used to calibrate and validate a crystal plasticity model taking into account twinning and detwinning.The interaction of the different phases on the distribution of local micro-mechanical fields at the grain scale was then analyzed on synthetic microstructures under strain-controlled conditions.Deformation twinning activity was predicted in coarse unrecrystallized grains and tended to disappear with the increase in the LPSO phase volume fraction.Cleavage-like facets observed in LPSO grains were related to high tensile stress,especially at the Mg/LPSO interface,due to the limited number of deformation mechanisms in LPSO crystal to accommodate out-of-basal plane strain.The increase of the fatigue limit with the increase in LPSO phase volume fraction was finally associated with the decreasing presence of coarse unrecrystallizedα-Mg grains due to a higher dynamic recrystallization activity during the extrusion process.展开更多
The characteristic of the precipitation and growth of α2 ordered phase during aging treatment in near α Ti alloys have been investigated in terms of the influences of aging temperature, aging time and aging manner. ...The characteristic of the precipitation and growth of α2 ordered phase during aging treatment in near α Ti alloys have been investigated in terms of the influences of aging temperature, aging time and aging manner. The results exhibit that aging temperatures influence the distribution of α2 phase precipitated and cause the changes in growth speed of α2 phase. For various aging temperatures, the time to finish precipitation of α2 phase is different. The facts that various distribution characteristics and growth speed of α2 ordered phase are caused by changed aging condition imply optimal selection and control for precipitation of α2 ordered phase reachable. Some discussions on adoptable aging steps are presented.展开更多
Phase compositions and microstructure evolutions of three Mg-Y-Zn cast alloys during isothermal annealing at 773 K have been systematically investigated to clarify the formation behavior of 14 H long period stacking o...Phase compositions and microstructure evolutions of three Mg-Y-Zn cast alloys during isothermal annealing at 773 K have been systematically investigated to clarify the formation behavior of 14 H long period stacking ordered（LPSO） structure from α-Mg grains.The annealed microstructure characteristics indicate that the 18 R phase is thermal stable in Mg86Y8Zn6 alloy where 18 R serves as matrix,and 14 H lamellar phase only forms within tiny α-Mg slices（less than 1% for volume fraction）.The α-Mg grains in Mg88Y8Zn4 and Mg89Y8Zn3 alloys exhibit cellular shape,and 14 H phase forms and develops into lamellar shape in these cellular grains after annealing.The results suggest that the presence of α-Mg grains is a requirement for the generation of 14 H phase.The nucleation and growth rates of 14 H lamellas are accelerated in α-Mg grains with higher concentrations of stacking faults and solute atoms.Moreover,the 14 H lamellas are parallel to adjacent 18 R plates in Mg86Y8Zn6 alloy,but the 14 H phase precipitated in cellularα-Mg grains of Mg88Y8Zn4 and Mg89Y8Zn3 alloys exhibits random orientation relationship with surrounding 18 R phase,indicating that the orientation relationship between 14 H and 18 R phases depends on the relationship between α-Mg grains and 18 R phase.展开更多
The microstructure and phase composition of as-cast Mg-9Er-6Y-xZn-0.6Zr （x=1, 2, 3, 4; normal mass fraction in %） alloys were investigated. In low Zn content, aside from the major second phase of Mg24（Er, Y, Zn）5,...The microstructure and phase composition of as-cast Mg-9Er-6Y-xZn-0.6Zr （x=1, 2, 3, 4; normal mass fraction in %） alloys were investigated. In low Zn content, aside from the major second phase of Mg24（Er, Y, Zn）5, there are a few lamellar phases that grow parallel with each other from the grain boundaries to the grain interior. With Zn content increasing, the Mg24（Er, Y, Zn）5 phase decreases, but the Mg12Zn（Y, Er） phase and lamellar phases continuously increase. When Zn content reaches 4% （normal mass fraction）, the Mg12Zn（Y, Er） phase mainly exists as large bulks, and some a-Mg grains are thoroughly penetrated by the lamellar phases. Moreover, the crystallography structures of the Mgl2Zn（Y, Er） and Mg24（Er, Y, Zn）5 phases are confirmed as 18R-type long-period stacking ordered structure and body-centred cubic structure, respectively.展开更多
Density order is usually a consequence of the competition between long-range and short-range interactions.Here we report a density ordered superfluid emergent from a homogeneous Mott insulator due to the competition b...Density order is usually a consequence of the competition between long-range and short-range interactions.Here we report a density ordered superfluid emergent from a homogeneous Mott insulator due to the competition between frustrations and local interactions.This transition is found in a Bose–Hubbard model on a frustrated triangle lattice with an extra pairing term.Furthermore,we find a quantum phase transition between two different density ordered superfluids,which is beyond the Landau–Ginzburg(LG)paradigm.A U(1)symmetry is emergent at the critical point,while the symmetry in each density ordered superfluid is Z_(2)×Z_(3).We call the transition a‘shamrock transition’,due to its degenerate ground state in the parameter space being a shamrock-like curve rather than a circle in an LG-type transition.Effective low energy theories are established for the two transitions mentioned above and we find their resemblance and differences with clock models.展开更多
基金supported by the National Natural Science Foundation of China(Nos.50571073,51574175 and 51474153)the Ph. D. Programs Foundation of Ministry of Education of China(20111402110004)the Natural Science Foundation of Shanxi Province(Nos.2009011028-3 and 2012011022-1)
文摘Alloys with composition of Mg_(96-x)Gd_3Zn_1Li_x(at.%)(x=0, 2, 4, and 6) were prepared by conventional casting. The microstructures of these alloys under as-cast and solid-solution conditions have been observed, and the mechanical properties were investigated. The results showed that Li is an effective element to refine the grains and break the eutectic networks in as-cast MgGd_3Zn_1 alloy. During solid solution treatment, these broken eutectic networks are spheroidized and highly dispersed. In addition, plentiful lamellar long period stacking ordered(LPSO) phases are precipitated in an α-Mg matrix when the Li addition is not more than 4%. Solid-solution treated Mg_(92)Gd_3Zn_1Li_4 alloy exhibits an optimal ultimate tensile strength(UTS) of 226 MPa and elongation of 5.8%. The strength of MgGd_3Zn_1 alloy is improved significantly, meanwhile, the toughness is apparently increased.
基金supported financially by the National Natural Science Foundation of China(Nos.51801214 and 51871222)the Liaoning Provincial Natural Science Foundation(No.2019-MS-335)。
文摘Understanding the interface between strengthening precipitates and matrix in alloys, especially at the atomic level, is a critical issue for tailoring the precipitate strengthening to achieve desired mechanical properties. Using high-resolution scanning transmission electron microscopy, we here clarify the semicoherent interfaces between the matrix and long-period stacking ordered(LPSO) phases, including 18 R and 14 H, in Mg–Zn–Y alloys. The LPSO/Mg interface features the unique configuration of the Shockley partial dislocations, which produces a near zero macroscopic strain because the net Burgers vectors equal zero. The 18 R/Mg interface characterizes a dissociated structure that can be described as a narrow slab of 54 R. There are two dislocation arrays accompanied to the 18 R/54 R and 54 R/Mg interface, resulting a slight deviation(about 2.3°). The 14 R/Mg interface exhibits the dislocation pairs associated with solute atoms. We further evaluate the stability and morphology of the corresponding interfaces based on elastic interaction, via calculating the mutual strong interactions between dislocation arrays, as well as that between the dislocations and solute atoms. The synchronized migration of interfacial dislocations and solute atoms, like move-drag behavior, dominates the lateral growth of LPSO phases in Mg alloys.
基金This work was supported by the National Research Foundation of Korea(Grant number:NRF-2019K1A3A1A18116059 and NRF-2023R1A2C200529811)Austrian Science Fund(FWF)(P 32378-N37)Federal Ministry of Austria Education,Science and Research(BMBWF)(KR 06/2020).
文摘Herein,the evolution of long-period stacking ordered(LPSO)phases in the as-cast Mg-6Gd-1Zn-0.6Zr(wt.%)alloy are investigated via transmission electron microscopy(TEM)and atom probe tomography(APT).The TEM results reveal that two types of LPSO phase(a bulky interdendritic phase and a plate-like matrix LPSO phase)are formed in the as-cast sample.Most of the LPSO phases are confirmed to be of the 14H type,with a smaller proportion being of the 18R LPSO.Further,the APT results reveal that the composition of the interdendritic LPSO phase is closer to that of the ideal 14H phase compared to the matrix LPSO phase,and both the interdendritic and matrix LPSO phases exhibit a Gd/Zn ratio of 2.5,thereby indicating a deficient Zn content compared to the ideal 14H phase(i.e.,1.3).In addition,the influence of the LPSO phases on the deformation behavior is investigated at different compressive plastic strains using electron backscatter diffraction(EBSD)analysis to reveal twinning and slip behavior during deformation.The results indicate that the LPSO phase induces additional work hardening in the late stage of deformation via the suppression of{1011}compressive twinning and the activation of non-basal slip systems.
文摘The precipitation characteristics of the α2 ordered phase in Ti-AI-Sn-Zr-Mo-Si-Nd alloys with various content of Al, under different aging conditions, were investigated. The distribution and size of the α2 ordered phase changed with temperature and Al content. The dislocations were the only places where the α2 ordered phase could precipitate at higher temperature near the critical transformation temperature for each alloy experimented. With the addition of Al content, the critical transformation temperature of α2 ordered phase increased. When the aging temperature was relatively low (650℃), the precedent precipitation of α2 ordered phase took place in primary a phase at the early stage of aging, in the duplex microstructure (the primary a with the transformed (3) of the alloys with lower Al content. But after certain aging time (50 h), the size of α2 particles was almost equal in both the primary a and the transformed β. And no obvious growth of α2 particles could be observed after 50 h.
基金This work was financially supported by the National Natural Science Foundation of China (No.50471085).
文摘Some experimental α+α2 alloys were prepared by the addition of tin or aluminum elements into Ti-55 alloy. These alloys were designed with varied electron concentration values and named as Sn-rich alloys and Al-rich alloys, respectively. The precipita- tion and growth of α2 ordered phase in the tested alloys under various heat treatment conditions were investigated. Some compari- sons among the experimental results were performed and discussed in detail. Stronger precipitation and growth of α2 ordered phase were caused in Al-rich alloys but relatively weak change in Sn-rich alloys with increasing the electron concentration. The precipita- tion of α2 ordered phase in Al-rich alloys is stronger than that in Sn-rich alloys when the electron concentration value is the same for the two alloys.
基金National Natural Science Foundation of China(Nos.U1610123,51674226,51574207,51574206,51274175)International Cooperation project of the Ministry of Science and Technology of China(No.2014DFA50320)+4 种基金The Science and Technology Major Project of Shanxi Province(No.MC2016-06)International Science and Technology Cooperation Project of Shanxi Province(No.2015081041)Research Project Supported by Shanxi Scholarship Council of China(No.2016-Key 2)Transformation of Scientific and Technological Achievements Special Guide Project of Shanxi Province(No.201604D131029)Shanxi Province Science Foundation for Youths(No.201601D021062)
文摘The microstructure and damping capacities of MgZnxYi.33x(x=l-4at.%)alloys were discussed and researched.The main phase composition of the alloys consists of a_Mg and long-period stacking ordered(LPSO)phase.Due to increasedLPSO phase,grain size was refined.LPSO phase was advantageous to the damping properties of the Mg-Zn-Y alloys.Mg-7%Zn-12.8%Y has the highest damping capacity up to0.04.Due to stacking fault probability,the LPSO phase in the Mg-Zn-Yalloys could be new damping source to dissipate energy so as to contribute to the improvement of damping capacities.
基金supported by the National Natural Science Foundation of China(22105218)Science and Technology Project of Jiangxi Provincial Education Department(GJJ2201525).
文摘The study of temperature-driven phase transitions is significant in phosphate chemistry,as these transitions often lead to unique physical properties for specific applications,such as catalysis,energy storage,ion conduction,and nonlinear optics[1–3].The phase transition from room temperature(RT)to high temperature(HT)in phosphates is always from periodic structures to disordered or amorphous states[4–8].At RT,phosphates often maintain a highly ordered crystalline structure,which is stabilized by the lower thermal energy.As the temperature increases,the thermal energy disrupts the periodic arrangement of atoms and leads to a phase transition,where the once ordered structure becomes increasingly disordered or even amorphous.
文摘The precipitation of ordered alpha_2 phase in a near - alphaTi-6.3Al-4.8Sn-2.0Zr-1.0Mo-0.34Si-0.9Nd (mass fraction) alloy with duplex microstructure, duringaging at various temperatures, was investigated. It is concluded that the precipitation and growthof the alpha_2 phase can be controlled by suitable selection of the aging temperature. Aging athigher temperatures can result in the uniform precipitation and growth of alpha_2 ordered phase inalpha_p whereas the alpha_2 ordered phase precipitated only at the lamella boundaries anddislocations in beta_t. Aging at a moderate temperature can promote the tendency of uniformprecipitation of alpha_2 phase in both alpha_p and beta_t. Aging at a relatively low temperature issuitable for the uniform precipitation and growth of fine alpha_2 particles throughout both thealpha_p and beta_t matrix.
文摘Different structure models of a long-period ordered phase in Fe-C martenstie formed during aging have been checked by computer simulation of electron diffraction(ED) patterns based on these models.The results showed that the simulated ED pattern of γ'-FexC(Ⅱ) model proposed by the present authors is in good agreement with experimentally observed ED pattern.It was also confirmed that the incommensurate superperiod stems from the coexistence of several γ'-Fe_xC(H) phases with different superperiods.The Fe(144)C(24)(Fe6C) model proposed by Uwakweh et al.generated ED patterns remarkably different from the experimental ones.
文摘AGE-hardened Cu-Ti has been an important alloy of investigation in the field of continuousphase transformation due to its complicated transformation processes which involve short rangeordering (SRO), spinodal decomposition (SD), long range ordering (LRO), etc. So far, ithas been a controversial topic whether each process exists, and in what sequence they pro-ceed.
文摘First-principles computation on the basis of density functional theory(DFT) is executed with the CASTEP code to explore the structural, elastic, and electronic properties along with Debye temperature and theoretical Vickers’ hardness of newly discovered ordered MAX phase carbide Mo2TiAlC2. The computed structural parameters are very reasonable compared with the experimental results. The mechanical stability is verified by using the computed elastic constants. The brittleness of the compound is indicated by both the Poisson’s and Pugh’s ratios. The new MAX phase is capable of resisting the pressure and tension and also has the clear directional bonding between atoms. The compound shows significant elastic anisotropy. The Debye temperature estimated from elastic moduli(B, G) is found to be 413.6 K. The electronic structure indicates that the bonding nature of Mo2TiAlC2is a mixture of covalent and metallic with few ionic characters. The electron charge density map shows a strong directional Mo–C–Mo covalent bonding associated with a relatively weak Ti–C bond.The calculated Fermi surface is due to the low-dispersive Mo 4d-like bands, which makes the compound a conductive one.The hardness of the compound is also evaluated and a high value of 9.01 GPa is an indication of its strong covalent bonding.
文摘An ideal method has been established for calculating the precipitation of α2 ordered phase in near-α titanium alloys based on the theory on the critical electron concentration for the precipitation of α2 ordered phase in near-α titanium alloys. With complete precipitation of α2 phase in near-α titanium alloys, the alloys can be considered to be composed of two parts： （1） the α2 ordered phase with the stoichiometric atomic ratio of Ti3X; （2） the disorder solid solution with the critical composition in which the α2 ordered phase is just unable to precipitate. By using this method, the volume fractions of α2 ordered phase precipitated in Ti-Al, Ti-Sn, Ti-Al-Sn-Zr alloys with various AI, Sn and/or Zr contents have been calculated. The influences of AI and Sn on the precipitation of α2 ordered phase are discussed. The calculating results show substantial agreement with the experimental ones.
基金supported by the National Natural Science Foundation of China(Grant No.12175316).
文摘Phase transitions,as one of the most intriguing phenomena in nature,are divided into first-order phase transitions(FOPTs)and continuous ones in current classification.While the latter shows striking phenomena of scaling and universality,the former has recently also been demonstrated to exhibit scaling and universal behavior within a mesoscopic,coarse-grained Landau-Ginzburg theory.Here we apply this theory to a microscopic model-the paradigmatic Ising model,which undergoes FOPTs between two ordered phases below its critical temperature-and unambiguously demonstrate universal scaling behavior in such FOPTs.These results open the door for extending the theory to other microscopic FOPT systems and experimentally testing them to systematically uncover their scaling and universal behavior.
基金the National Natural Science Foundation of China(Grant Nos.51774109 and 51979099)the Fundamental Research Funds for the Central Universities(Grant No.2018B48414 and 2018B690X14)+3 种基金Postgraduate Research&Practice Innovation Program of Jiangsu Province(Grant No.KYCX18_0570)The Key Research and Development Project of Jiangsu Province of China(Grant No.BE2017148)Postgraduate Education Reform Project of Jiangsu Province(JGLX19_027)Natural Science Foundation of China(Grant No.51979099).
文摘Mg-Y-Zn alloys with long period stacking ordered(LPSO)structure have received much attention recently and exhibit great potential in applications such as automotive,aerospace and in bio-medical fields.This paper aimed to investigate the effect of different phase constitution of LPSO structures on corrosion rate of bio-medical Mg-Y-Zn alloys.The results showed that as-cast Mg98.5Y1Zn0.5 alloys containing only 18R structure exhibited the highest corrosion resistance with the corrosion rate of 2.78 mm/year.The precipitation of 14H lamellas within a-Mg grains during solid solution treatment introduced the crystallographic orientation corrosion by accelerating micro-galvanic corrosion.The increase of 18R/14H interfaces deteriorated the corrosion resistance,and the grain boundaries also suffered from severe electrochemical dissolution.This work suggested that Mg-Y-Zn alloys with single LPSO structure(either 18R or 14H)exhibited better corrosion resistance than alloys with co-existence 18R and I4H LPSO structures.
基金the National Natural Science Foundation of China(Nos.51774109,51979099 and 51901068)the Fundamental Research Funds for the Central Universities(No.2018B690X14)+3 种基金the Natural Science Foundation of Jiangsu Province of China(No.BK20191303)the Postgraduate Research&Practice Innovation Program of Jiangsu Province(No.KYCX18_0570)the Key Research and Development Project of Jiangsu Province of China(No.BE2017148)the Public Service Platform Program of Suqian City of China(No.M201614)。
文摘Mg-RE(rear earth) alloys with long period stacking(LPSO) structures have great potential in biomedical applications. The present work focused on the microstructure and corrosion behaviors of Mg 98.5 Y1 Zn0.5 alloys with 18 R LPSO structure after equal channel angular pressing(ECAP). The results showed that the ECAP process changed the grain size and the distribution of LPSO particles thus controlled the total corrosion rates of Mg 98.5 Y1 Zn0.5 alloys. During the ECAP process from 0 p to 12 p, the grain size reduced from 160–180 μm(as-cast) to 6–8 μm(12 p). The LPSO structures became kinked(4 p), then started to be broken into smaller pieces(8 p), and at last comminuted to fine particles and redistributed uniformly inside the matrix(12 p). The improvement in the corrosion resistance for ECAP samples was obtained from 0 p to 8 p, with the corrosion rate reduced from 3.24 mm/year(0 p) to 2.35 mm/year(8 p) in simulated body fluid, and the 12 p ECAP alloy exhibited the highest corrosion rate of 4.54 mm/year.
基金This work was partially supported by the JSPS KAKENHI for Scientific Research on Innovative Areas”MFS Materials Science”(Grant no.JP18H05478)the JSPS KAKENHI for Early-Career Scientists(Grant no.20K14604).
文摘The fatigue behavior of four extruded Mg-Y-Zn alloys containing different volume fractions of long-period stacking ordered(LPSO)grains was investigated through a comparative study combining experiments and crystal plasticity finite element simulations.Strain controlled low-cycle fatigue experiments were conducted at different strain amplitudes and revealed a limited cyclic hardening in Mg_(89)Zn_(4)Y_(7)alloy or softening in Mg_(99.2)Zn_(0.2)Y_(0.6)and Mg_(97)Zn_(1)Y_(2)alloys.A decrease in the fatigue life against the plastic strain with the increase in LPSO phase volume fraction was observed and was related the limited ductility of extruded LPSO grains.Stress-strain hysteresis curves were used to calibrate and validate a crystal plasticity model taking into account twinning and detwinning.The interaction of the different phases on the distribution of local micro-mechanical fields at the grain scale was then analyzed on synthetic microstructures under strain-controlled conditions.Deformation twinning activity was predicted in coarse unrecrystallized grains and tended to disappear with the increase in the LPSO phase volume fraction.Cleavage-like facets observed in LPSO grains were related to high tensile stress,especially at the Mg/LPSO interface,due to the limited number of deformation mechanisms in LPSO crystal to accommodate out-of-basal plane strain.The increase of the fatigue limit with the increase in LPSO phase volume fraction was finally associated with the decreasing presence of coarse unrecrystallizedα-Mg grains due to a higher dynamic recrystallization activity during the extrusion process.
文摘The characteristic of the precipitation and growth of α2 ordered phase during aging treatment in near α Ti alloys have been investigated in terms of the influences of aging temperature, aging time and aging manner. The results exhibit that aging temperatures influence the distribution of α2 phase precipitated and cause the changes in growth speed of α2 phase. For various aging temperatures, the time to finish precipitation of α2 phase is different. The facts that various distribution characteristics and growth speed of α2 ordered phase are caused by changed aging condition imply optimal selection and control for precipitation of α2 ordered phase reachable. Some discussions on adoptable aging steps are presented.
基金supported by the Natural Science Foundation of Jiangsu Province of China(No.BK2010392)the Fundamental Research Funds for the Central Universities(No.2015B01314)
文摘Phase compositions and microstructure evolutions of three Mg-Y-Zn cast alloys during isothermal annealing at 773 K have been systematically investigated to clarify the formation behavior of 14 H long period stacking ordered（LPSO） structure from α-Mg grains.The annealed microstructure characteristics indicate that the 18 R phase is thermal stable in Mg86Y8Zn6 alloy where 18 R serves as matrix,and 14 H lamellar phase only forms within tiny α-Mg slices（less than 1% for volume fraction）.The α-Mg grains in Mg88Y8Zn4 and Mg89Y8Zn3 alloys exhibit cellular shape,and 14 H phase forms and develops into lamellar shape in these cellular grains after annealing.The results suggest that the presence of α-Mg grains is a requirement for the generation of 14 H phase.The nucleation and growth rates of 14 H lamellas are accelerated in α-Mg grains with higher concentrations of stacking faults and solute atoms.Moreover,the 14 H lamellas are parallel to adjacent 18 R plates in Mg86Y8Zn6 alloy,but the 14 H phase precipitated in cellularα-Mg grains of Mg88Y8Zn4 and Mg89Y8Zn3 alloys exhibits random orientation relationship with surrounding 18 R phase,indicating that the orientation relationship between 14 H and 18 R phases depends on the relationship between α-Mg grains and 18 R phase.
基金Project(NCET-11-0554) supported by the Program for New Century Excellent Talents in University,ChinaProject(2011BAE22B04) supported by the National Key Technology R&D Program,ChinaProject(51271206) supported by the National Natural Science Foundation of China
文摘The microstructure and phase composition of as-cast Mg-9Er-6Y-xZn-0.6Zr （x=1, 2, 3, 4; normal mass fraction in %） alloys were investigated. In low Zn content, aside from the major second phase of Mg24（Er, Y, Zn）5, there are a few lamellar phases that grow parallel with each other from the grain boundaries to the grain interior. With Zn content increasing, the Mg24（Er, Y, Zn）5 phase decreases, but the Mg12Zn（Y, Er） phase and lamellar phases continuously increase. When Zn content reaches 4% （normal mass fraction）, the Mg12Zn（Y, Er） phase mainly exists as large bulks, and some a-Mg grains are thoroughly penetrated by the lamellar phases. Moreover, the crystallography structures of the Mgl2Zn（Y, Er） and Mg24（Er, Y, Zn）5 phases are confirmed as 18R-type long-period stacking ordered structure and body-centred cubic structure, respectively.
基金supported by the Beijing Natural Science Foundation(Z180013)(YC)National Natural Science Foundation of China(NSFC)under Grant No.12174358(YC)and No.11734010(YC and CW)MOST Grant No.2016YFA0301600(CW)。
文摘Density order is usually a consequence of the competition between long-range and short-range interactions.Here we report a density ordered superfluid emergent from a homogeneous Mott insulator due to the competition between frustrations and local interactions.This transition is found in a Bose–Hubbard model on a frustrated triangle lattice with an extra pairing term.Furthermore,we find a quantum phase transition between two different density ordered superfluids,which is beyond the Landau–Ginzburg(LG)paradigm.A U(1)symmetry is emergent at the critical point,while the symmetry in each density ordered superfluid is Z_(2)×Z_(3).We call the transition a‘shamrock transition’,due to its degenerate ground state in the parameter space being a shamrock-like curve rather than a circle in an LG-type transition.Effective low energy theories are established for the two transitions mentioned above and we find their resemblance and differences with clock models.
