Variable-composition evolutionary structure searches are used to explore stable stoichiometries for the Zn-O system below 300 GPa. Our results confirm the previous structural phase transition sequence of pressurised Z...Variable-composition evolutionary structure searches are used to explore stable stoichiometries for the Zn-O system below 300 GPa. Our results confirm the previous structural phase transition sequence of pressurised ZnO. ZnO is thermodynamically stable up to 300GPa and zinc peroxide (Zn02, space group Pa3) is metastable under lower pressure. Insulating I4/mcm-Zn02 is thermodynamically stable between 128.3-300 GPa. Insulated metastable P3121-Zn02, controlling the pressure range of 51.5-128.3 GPa, has a wide band gap compared to the Pa3-Zn02 and I4/mem-Zn02. Phonon and elastic constant calculations conclude the dynamical and mechanical stability for the explored thermodynamically stable or metastable structures.展开更多
The radiation of material surface by high intensity laser beams is used to produce the uhrafine powder of pure Fe and ZrO_2.The morphology,size and phases of the powder were examined by X-ray diffraetometer,scanning e...The radiation of material surface by high intensity laser beams is used to produce the uhrafine powder of pure Fe and ZrO_2.The morphology,size and phases of the powder were examined by X-ray diffraetometer,scanning electron microscopy as well as transmission electron microscopy.In pure Fe a considerable quantity of γ-phase was found in the powder.In ZrO_2 powder,instead of stable phase,two metastable phases appeared.展开更多
The splat foils of Al-Sm alloys with 0.04-0.06mm in thickness were made by hammeranvil technique. The estimated cooling rute was 106K/ order of magnitude. The extended solid solubility of Sm in α-Al reached 0.5at. % ...The splat foils of Al-Sm alloys with 0.04-0.06mm in thickness were made by hammeranvil technique. The estimated cooling rute was 106K/ order of magnitude. The extended solid solubility of Sm in α-Al reached 0.5at. % Sm. The intermediate phase in the rapidlysolidified Al-Sm alloys is Al11Sm3 phase, which is stable only at temperatures above 1339K in equilibrium state and retained to ambient temperature as a metastable phase, whereas the equlibrium intermediate phase, Al3Sm, was restricted to occur.展开更多
Metastable nanostructured electrocatalyst with a completely different surface environment compared to conventional phase-based electrocatalyst often shows distinctive catalytic property.Although Ru-based electrocataly...Metastable nanostructured electrocatalyst with a completely different surface environment compared to conventional phase-based electrocatalyst often shows distinctive catalytic property.Although Ru-based electrocatalysts have been widely investigated toward hydrogen oxidation reaction(HOR)under alkaline electrolytes,these studies are mostly limited to conventional hexagonal-close-packed(hcp)phase,mainly arising from the lack of sufficient synthesis strategies.In this study,we report the precise synthesis of metastable binary RuW alloy with face-centered-cubic(fcc)phase.We find that the introduction of W can serve as fcc phase seeds and reduce the formation energy of metastable fcc-RuW alloy.Impressively,fcc-RuW exhibits remarkable alkaline HOR performance and stability with the activity of 0.67 mA cm_(Ru)^(-2)which is almost five and three times higher than that of hcp-Ru and commercial Pt/C,respectively,which is attributed to the optimized binding strength of adsorbed hydroxide intermediate derived from tailored electronic structure through W doping and phase engineering.Moreover,this strategy can also be applied to synthesize other metastable fcc-RuCr and fcc-RuMo alloys with enhanced HOR performances.展开更多
Pattern recognition and neural network methods have been used to investigate the formability of metastable alloy phases, It has been found that some chemi cal bond parameters Such as valence electron number, electrone...Pattern recognition and neural network methods have been used to investigate the formability of metastable alloy phases, It has been found that some chemi cal bond parameters Such as valence electron number, electronegativity and metallic radii of cor-nponent elements are the dominating fac tors affecting metastable alloy phase formation. Some semi-empirical rules found in this way may be useful for the construction of expert system for materials design.展开更多
A time-resolved x-ray diffraction technique is employed to monitor the structural transformation of laser-shocked bismuth.Results reveal a retarded transformation from the shock-induced Bi-Ⅴphase to a metastable Bi-...A time-resolved x-ray diffraction technique is employed to monitor the structural transformation of laser-shocked bismuth.Results reveal a retarded transformation from the shock-induced Bi-Ⅴphase to a metastable Bi-Ⅳphase during the shock release,instead of the thermodynamically stable Bi-Ⅲphase.The emergence of the metastable Bi-Ⅳphase is understood by the competitive interplay between two transformation pathways towards the Bi-Ⅳand Bi-Ⅲ,respectively.The former is more rapid than the latter because the Bi-Ⅴto B-Ⅳtransformation is driven by interaction between the closest atoms while the Bi-Ⅴto B-Ⅲtransformation requires interaction between the second-closest atoms.The nucleation time for the Bi-Ⅴto Bi-Ⅳtransformation is determined to be 5.1±0.9 ns according to a classical nucleation model.This observation demonstrates the importance of the formation of the transient metastable phases,which can change the phase transformation pathway in a dynamic process.展开更多
In this paper,a comprehensive understanding of stable and metastable phase equilibria in binary Mg-Gd system was conducted with an aid of the CALculation of PHAse Diagram(CALPHAD)modeling.Firstly,thermodynamic descrip...In this paper,a comprehensive understanding of stable and metastable phase equilibria in binary Mg-Gd system was conducted with an aid of the CALculation of PHAse Diagram(CALPHAD)modeling.Firstly,thermodynamic descriptions of all the stable phases in the Mg-Gd system were re-assessed by considering all the experimental data in the literature.The discrepancy between the phase equilibria and thermochemical properties existing in the previous assessments was eliminated,and the better agreement with the experimental data was achieved in the present assessment.Secondly,the Gibbs energies for metastable β"-Mg3Gd and β"-Mg7Gd were constructed based on the first-principles and CALPHAD computed results as well as their correlation,and then incorporated into the CALPHAD descriptions.The model-predicted solvuses of(Mg)in equilibrium with the metastable β"-Mg7Gd and β'-Mg7Gd compounds showed very good agreement with the limited experimental data.Finally,the presently obtained thermodynamic descriptions of both stable and metastable phases in the binary Mg-Gd system were further validated by realizing the quantitative Scheil-Gulliver solidification simulations of 5 as-cast Mg-Gd alloys,and the successful prediction of the precipitation sequences in Mg-15Gd and Mg-12Gd alloys during the aging process.展开更多
The non-equilibrium microstructure and a new metastable phase of Al-9.6wt%Mg alloy solidified at 6 GPa were studied by optical microscope,differential scanning calorimetry,X-ray diffraction and transmission electron m...The non-equilibrium microstructure and a new metastable phase of Al-9.6wt%Mg alloy solidified at 6 GPa were studied by optical microscope,differential scanning calorimetry,X-ray diffraction and transmission electron microscope.The results showed that dendrite microstructure was refined,and the solid solubility of Mg in α-Al phase increased greatly.Correspondingly,the lattice parameter of α-Al phase increased.Al3Mg2 phases disappeared under high pressure solidification.In particular,a metastable phase with small size(20 nm or so) was produced in the alloy,its melting temperature range was 464~518.2 ℃,which was higher than that of Al3Mg2 phase(453~465 ℃) under normal pressure.These metastable phases located in the interdendritic position.It was the first time that the metastable phase was found in Al-Mg alloy at a high pressure of 6 GPa.The formation mechanism of the metastable phases was discussed.展开更多
The metastable liquid phase separation and rapid solidification behaviors of Co_(40) Fe_(40) Cu_(20) alloy were investigated by using differential thermal analysis(DTA) in combination with glass fluxing and el...The metastable liquid phase separation and rapid solidification behaviors of Co_(40) Fe_(40) Cu_(20) alloy were investigated by using differential thermal analysis(DTA) in combination with glass fluxing and electromagnetic levitation(EML) techniques. The critical liquid phase separation undercooling for this alloy was determined by DTA to be 174 K. Macrosegregation morphologies are formed in the bulk samples processed by both DTA and EML. It is revealed that undercooling level, cooling rate, convection, and surface tension difference between the two separated phases play a dominant role in the coalescence and segregation of the separated phases. The growth velocity of the(Fe,Co) dendrite has been measured as a function of undercooling up to 275 K. The temperature rise resulting from recalescence increases linearly with the increase of undercooling because of the enhancement of recalescence. The slope change of the recalescence temperature rise versus undercooling at the critical undercooling also implies the occurrence of liquid demixing.展开更多
The powder mixture of Al, Ti and graphite has been mechanically alloyed in a planetary ball mill.The structural evolution of as-milled powder sample has been characterized by XRD, DTA. The results show that the amorph...The powder mixture of Al, Ti and graphite has been mechanically alloyed in a planetary ball mill.The structural evolution of as-milled powder sample has been characterized by XRD, DTA. The results show that the amorphous phase is formed first at an early milling stage, then crystallization occurs during further milling, leading to formation of a nanocrystalline fcc metastable phase. In contrast, during annealing the amorphous phase is crystallized to the equilibrium phase instead of the fcc phase. This indicates that crystallization during ball milling is different from that induced by annealing展开更多
The nature of the oxygen contained in β-W was investigated with DSC,X-ray analysis on quenched samples and Auger spectroscope.It was shown that the oxygen contained in nonpyrophoric β-W consists of the reversibly ch...The nature of the oxygen contained in β-W was investigated with DSC,X-ray analysis on quenched samples and Auger spectroscope.It was shown that the oxygen contained in nonpyrophoric β-W consists of the reversibly chemisorbed oxygen and the interstitial oxygen which could form an interstitial solid solution with β-W.It seems better to consider β-W to be a metastable phase of tungsten with the interstitial oxygen as stabilizer.展开更多
A general approach is reported for ultra-fast phosphating synthesis of a series of ultra-small(<5 nm)noble metal phosphides(MPX/CNT,M=Pd,Pt,Ru)which are successfully produced in just 75 s for the first time.The cat...A general approach is reported for ultra-fast phosphating synthesis of a series of ultra-small(<5 nm)noble metal phosphides(MPX/CNT,M=Pd,Pt,Ru)which are successfully produced in just 75 s for the first time.The catalytic performance of the catalysts can be optimized by controlling the nanomaterials as the metastable crystalline phases.By altering the phosphorus source under the same conditions,the hexagonal structured Pd_(7)P_(3)(NaH_(2)PO_(2).H_(2)O as P source)and monoclinic structured Pd_(6)P(Na_(4)P_(2)O_(7) as P source)can be prepared successfully.Both of them exhibit excellent polyol oxidation performance in alkaline media.Monoclinic Pd_(6)P/CNT and hexagonal Pd_(7)P_(3)/CNT have large ECSA which are confirmed as 82.1 m2 g^(-1)and 86.2 m2 g^(-1),respectively.Hexagonal Pd_(7)P_(3)/CNT has the highest mass activity of 6.14 A mgPd^(-1)(3.21 A mgPd^(-1)for Pd_(6)P/CNT)for GOR,which far exceeded Pt/C(2.81 A mgPt^(-1)).Meanwhile,the mass activity of monoclinic Pt_(5)P_(2)/CNT for EGOR achieved 12.4 A mg_(Pt)^(-1),which far exceeded Pt/C(6.8 A mg_(Pt)^(-1)).The stability test proved that the activity decay of these catalysts was negligible after the 12-hour durability test.Meanwhile,they have excellent CO anti-poisoning abilities.展开更多
The metastable phase equilibria of the quaternary system NaCl+Na2CO3+Na2SO4+H2O were studied at 273.15 K. The salts' solubilities, densities and pH values of the equilibrated solution in this system were determine...The metastable phase equilibria of the quaternary system NaCl+Na2CO3+Na2SO4+H2O were studied at 273.15 K. The salts' solubilities, densities and pH values of the equilibrated solution in this system were determined. According to the experimental data, the metastable equilibrium phase diagram, the diagram of density vs. composition and pH vs. composition diagram were plotted. The phase diagram consists of five univariant curves, four crystallization fields and two invariant points. The four crystallization fields correspond to sodium carbonate decahydrate (Na2CO3·10H2O), sodium sulfate decahydrate(Na2SOn-10H2O), sodium chloride(NaCl) and burkeite(2Na2SO4. Na2CO3), respectively. The crystallization field of sodium sulfate decahydrate(Na2SO4.10H2O) is the largest, which indicates that sodium sulfate is easy to saturate and crystallize from solution at 273.15 K.展开更多
1 Introduction The Pingluoba brine,which characterized as high concentration with sodium,potassium,boron,lithium,and rubidium,possess great development value.The main composition of the brine can be summarized to the
The precipitation process of aged Cu-Ni-Be alloy was investigated by X-ray diffraction (XRD), trans- mission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). The tensile s...The precipitation process of aged Cu-Ni-Be alloy was investigated by X-ray diffraction (XRD), trans- mission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). The tensile strength, yield strength, and electronic conductivity of this alloy after aging were also studied. The precipitation sequence of the C17510 alloy aged at 525 ℃ is supersat-urated solid solution→G.P zones→ γ″-γ′→ γ. This transformation can be achieved by the accumulation of Be-atom layers. The G.P zones are composed of disk-shaped monolayers of Be atoms, which are formed on (001) matrix planes. The intermediate γ″ precipitate is nucleated in the G.P zones. The γ″ and γ′ precipitates have the same orientation relationship with matrix, e.g., (110)p||(100)M,[001]p||[001]M. The tensile strength of specimen shows a maximum during the aging process and then continuously decreases if the specimen is over aged. The strengthening effect of γ′ phase precipitated in aging at 525 ℃ for 4 h is calculated to be 436 MPa according to the Orowan strengthening, which is quite consistent with the experimental data.展开更多
Ion beam assisted deposition technique (IBAD) was utilized to systematically study amorphization in binary metal systems of Nb-magnetic element, i.e., Nb-M (M=Fe, Co or Ni). The glass forming range termed as Nb fracti...Ion beam assisted deposition technique (IBAD) was utilized to systematically study amorphization in binary metal systems of Nb-magnetic element, i.e., Nb-M (M=Fe, Co or Ni). The glass forming range termed as Nb fraction of Nb-Fe system was about 34at.% to 56at.%, that of Nb-Co system was about 32at.% to 72at.% and that of Nb-Ni about 20at. % to 80at. %. Similar percolation patterns were found in amorphous alloy films. The fractal dimensions of the percolation patterns approach to 2, which indicates 2-D layer growth for amorphous phases. It is regarded that the assisted Ar+ ion beam during the deposition process plays important role for the 2-D layer growth. Some metastable crystalline phases were obtained in these three systems by IBAD, e.g., bcc supersaturated solid solutions in Nb-Fe and Nb-Co systems, fcc and hcp phases in Nb-Co and Nb-Ni systems. The formation and competing between the amorphous and the metastable crystalline phases were determined by both the phases' thermodynamic states in binary metal systems and kinetics during IBAD process.展开更多
Nb/Nb5Si3 in-situ composites are very attractive structural materials because these materials perform a good balance in mechanical properties, including high strength at high temperature (> 1000 degrees C) and reas...Nb/Nb5Si3 in-situ composites are very attractive structural materials because these materials perform a good balance in mechanical properties, including high strength at high temperature (> 1000 degrees C) and reasonably high fracture toughness at room temperature. Metastable phase Nb3Si plays an important role in the properties of Nb/Nb5Si3 composites by affecting the volume fraction of ductile phase. The addition of Mo affects on the microstructure of ductile phase and the stability of metastable phase Nb3Si. In this paper, Nb-10Si-xMo and Nb-18Si-xMo (x = 0, 5, and 15) alloys were prepared by arc melting and annealed at 1473 K for 100 h. Single edge-notched bending (SENB) test was used to study the fracture toughness of Nb-Si-Mo alloys. The room temperature fracture toughness of Nb-10Si is 10.48 MPa center dot m(1/2) and higher than that of binary Nb-18Si alloys at near-eutectic composites. The addition of 5 at.% Mo improved the fracture toughness of as-cast Nb-Si alloys from 4.1 MPa center dot m(1/2) to 9.99 MPa center dot m(1/2) at near-eutectic compositions and reduced it from 10.48 MPa center dot m(1/2) to 8.86 MPa center dot m(1/2) at hypoeutectic compositions.展开更多
The influence of Cr substitution on the crystallization behavior and magnetic properties of melt-spun Nd_ 11Fe_ 72-xCo_8V_ 1.5Cr_xB_ 7.5 (x=0, 1) nanocomposite alloys was studied. The annealed samples consist of a mix...The influence of Cr substitution on the crystallization behavior and magnetic properties of melt-spun Nd_ 11Fe_ 72-xCo_8V_ 1.5Cr_xB_ 7.5 (x=0, 1) nanocomposite alloys was studied. The annealed samples consist of a mixture of Nd_2Fe_ 14B and α-Fe phases. Presence of grains of the metastable Nd_2Fe_ 23B_3 phase was revealed in the Cr-containing Nd_ 11Fe_ 71Co_8V_ 1.5Cr_1B_ 7.5 sample. The magnetic properties of the bonded magnets are obviously improved by the Cr substitution. The intrinsic coercivity (_JH_c) and maximum magnetic energy product ((BH)_ max) are increased from 780 kA·m -1 and 68 kJ·m -3 for x=0 to 903.5 kA·m -1 and 71 kJ·m -3 for x=1, respectively. The addition of Cr element shows significant advantage in reducing grain size and increasing intrinsic coercivity.展开更多
1 Introduction Salt lakes are widely distributed in the world,and salt lakes in China are mainly located in the area of the Qinghai-Xizang(Tibet),and the Autonomous Regions of Xinjiang and Inner Mongolia.There are mor...1 Introduction Salt lakes are widely distributed in the world,and salt lakes in China are mainly located in the area of the Qinghai-Xizang(Tibet),and the Autonomous Regions of Xinjiang and Inner Mongolia.There are more than 700salt lakes,each with an area larger than 1 km2,in the展开更多
The microstructures of laser cladding of (Ni-24.5%(atom fraction)Al)+5O%(mass haction)WC coatingsbefore and after aging was comparetively studied by using SEM and TEM. It is shown that dissolving of WC and reprecipita...The microstructures of laser cladding of (Ni-24.5%(atom fraction)Al)+5O%(mass haction)WC coatingsbefore and after aging was comparetively studied by using SEM and TEM. It is shown that dissolving of WC and reprecipitating in the forms of WC and W,Coccurred during laser cladding, and intermetallic γ' (Ni3Al) orderly precipitatefrom metastable supersaturant Ni-matrix solid solution after heat treatment. The structures are favorable for coating'sproperties.展开更多
基金Supported by the National Natural Science Foundation of China under Grant No 11347007the Qing Lan Project+1 种基金the Colleges and Universities in Jiangsu Province Natural Science Research Project under Grant No 14KJB460013the Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘Variable-composition evolutionary structure searches are used to explore stable stoichiometries for the Zn-O system below 300 GPa. Our results confirm the previous structural phase transition sequence of pressurised ZnO. ZnO is thermodynamically stable up to 300GPa and zinc peroxide (Zn02, space group Pa3) is metastable under lower pressure. Insulating I4/mcm-Zn02 is thermodynamically stable between 128.3-300 GPa. Insulated metastable P3121-Zn02, controlling the pressure range of 51.5-128.3 GPa, has a wide band gap compared to the Pa3-Zn02 and I4/mem-Zn02. Phonon and elastic constant calculations conclude the dynamical and mechanical stability for the explored thermodynamically stable or metastable structures.
文摘The radiation of material surface by high intensity laser beams is used to produce the uhrafine powder of pure Fe and ZrO_2.The morphology,size and phases of the powder were examined by X-ray diffraetometer,scanning electron microscopy as well as transmission electron microscopy.In pure Fe a considerable quantity of γ-phase was found in the powder.In ZrO_2 powder,instead of stable phase,two metastable phases appeared.
文摘The splat foils of Al-Sm alloys with 0.04-0.06mm in thickness were made by hammeranvil technique. The estimated cooling rute was 106K/ order of magnitude. The extended solid solubility of Sm in α-Al reached 0.5at. % Sm. The intermediate phase in the rapidlysolidified Al-Sm alloys is Al11Sm3 phase, which is stable only at temperatures above 1339K in equilibrium state and retained to ambient temperature as a metastable phase, whereas the equlibrium intermediate phase, Al3Sm, was restricted to occur.
基金the support from the National Natural Science Foundation of China(22272121,21972107)the National Key Research and Development program of China(2021YFB4001200)。
文摘Metastable nanostructured electrocatalyst with a completely different surface environment compared to conventional phase-based electrocatalyst often shows distinctive catalytic property.Although Ru-based electrocatalysts have been widely investigated toward hydrogen oxidation reaction(HOR)under alkaline electrolytes,these studies are mostly limited to conventional hexagonal-close-packed(hcp)phase,mainly arising from the lack of sufficient synthesis strategies.In this study,we report the precise synthesis of metastable binary RuW alloy with face-centered-cubic(fcc)phase.We find that the introduction of W can serve as fcc phase seeds and reduce the formation energy of metastable fcc-RuW alloy.Impressively,fcc-RuW exhibits remarkable alkaline HOR performance and stability with the activity of 0.67 mA cm_(Ru)^(-2)which is almost five and three times higher than that of hcp-Ru and commercial Pt/C,respectively,which is attributed to the optimized binding strength of adsorbed hydroxide intermediate derived from tailored electronic structure through W doping and phase engineering.Moreover,this strategy can also be applied to synthesize other metastable fcc-RuCr and fcc-RuMo alloys with enhanced HOR performances.
文摘Pattern recognition and neural network methods have been used to investigate the formability of metastable alloy phases, It has been found that some chemi cal bond parameters Such as valence electron number, electronegativity and metallic radii of cor-nponent elements are the dominating fac tors affecting metastable alloy phase formation. Some semi-empirical rules found in this way may be useful for the construction of expert system for materials design.
基金supported by the National Natural Science Foundation of China (Grant No.12072331)the Science Challenge Project (Grant No.TZ2018001)+2 种基金the Japan Society for the Promotion of Science (Grant Nos.17H04820 and 21H01677)the Foundation of the United Laboratory of High-Pressure Physics and Earthquake Scienceperformed under the approval of the Photon Factory Program Advisory Committee (Proposal Nos.2016S2-006 and 2020G680)。
文摘A time-resolved x-ray diffraction technique is employed to monitor the structural transformation of laser-shocked bismuth.Results reveal a retarded transformation from the shock-induced Bi-Ⅴphase to a metastable Bi-Ⅳphase during the shock release,instead of the thermodynamically stable Bi-Ⅲphase.The emergence of the metastable Bi-Ⅳphase is understood by the competitive interplay between two transformation pathways towards the Bi-Ⅳand Bi-Ⅲ,respectively.The former is more rapid than the latter because the Bi-Ⅴto B-Ⅳtransformation is driven by interaction between the closest atoms while the Bi-Ⅴto B-Ⅲtransformation requires interaction between the second-closest atoms.The nucleation time for the Bi-Ⅴto Bi-Ⅳtransformation is determined to be 5.1±0.9 ns according to a classical nucleation model.This observation demonstrates the importance of the formation of the transient metastable phases,which can change the phase transformation pathway in a dynamic process.
基金The financial support from the National Key Research and Development Program of China(Grant no.2016YFB0301101)the Hunan Provincial Science and Technology Program of China(Grant no.2017RS3002)-Huxiang Youth Talent Plan+2 种基金the Youth Talent Project of Innovation-driven Plan at Central South University(Grant no.2019XZ027)the Hebei Provincial Science and Technology Program of China(Grant no.BJ2018026)-Outstanding Young Talents Plan is acknowledgedYing Tang acknowledges the financial support from the Yuanguang fellowship released by Hebei University of Technology.
文摘In this paper,a comprehensive understanding of stable and metastable phase equilibria in binary Mg-Gd system was conducted with an aid of the CALculation of PHAse Diagram(CALPHAD)modeling.Firstly,thermodynamic descriptions of all the stable phases in the Mg-Gd system were re-assessed by considering all the experimental data in the literature.The discrepancy between the phase equilibria and thermochemical properties existing in the previous assessments was eliminated,and the better agreement with the experimental data was achieved in the present assessment.Secondly,the Gibbs energies for metastable β"-Mg3Gd and β"-Mg7Gd were constructed based on the first-principles and CALPHAD computed results as well as their correlation,and then incorporated into the CALPHAD descriptions.The model-predicted solvuses of(Mg)in equilibrium with the metastable β"-Mg7Gd and β'-Mg7Gd compounds showed very good agreement with the limited experimental data.Finally,the presently obtained thermodynamic descriptions of both stable and metastable phases in the binary Mg-Gd system were further validated by realizing the quantitative Scheil-Gulliver solidification simulations of 5 as-cast Mg-Gd alloys,and the successful prediction of the precipitation sequences in Mg-15Gd and Mg-12Gd alloys during the aging process.
基金This work is financially supported by the Science Foundation of Harbin Institute of Technology ( No HIT2002 29)
文摘The non-equilibrium microstructure and a new metastable phase of Al-9.6wt%Mg alloy solidified at 6 GPa were studied by optical microscope,differential scanning calorimetry,X-ray diffraction and transmission electron microscope.The results showed that dendrite microstructure was refined,and the solid solubility of Mg in α-Al phase increased greatly.Correspondingly,the lattice parameter of α-Al phase increased.Al3Mg2 phases disappeared under high pressure solidification.In particular,a metastable phase with small size(20 nm or so) was produced in the alloy,its melting temperature range was 464~518.2 ℃,which was higher than that of Al3Mg2 phase(453~465 ℃) under normal pressure.These metastable phases located in the interdendritic position.It was the first time that the metastable phase was found in Al-Mg alloy at a high pressure of 6 GPa.The formation mechanism of the metastable phases was discussed.
基金Project supported by the National Key Research and Development Program of China(Grant No.2016YFB1100101)the National Natural Science Foundation of China(Grant No.51471135)+2 种基金Shenzhen Science and Technology Program,China(Grant No.JCYJ20170815162201821)Shaanxi Provincial Key R&D Program,China(Grant No.2017KW-ZD-07)the Fundamental Research Funds for the Central Universities,China(Grant No.31020170QD102)
文摘The metastable liquid phase separation and rapid solidification behaviors of Co_(40) Fe_(40) Cu_(20) alloy were investigated by using differential thermal analysis(DTA) in combination with glass fluxing and electromagnetic levitation(EML) techniques. The critical liquid phase separation undercooling for this alloy was determined by DTA to be 174 K. Macrosegregation morphologies are formed in the bulk samples processed by both DTA and EML. It is revealed that undercooling level, cooling rate, convection, and surface tension difference between the two separated phases play a dominant role in the coalescence and segregation of the separated phases. The growth velocity of the(Fe,Co) dendrite has been measured as a function of undercooling up to 275 K. The temperature rise resulting from recalescence increases linearly with the increase of undercooling because of the enhancement of recalescence. The slope change of the recalescence temperature rise versus undercooling at the critical undercooling also implies the occurrence of liquid demixing.
文摘The powder mixture of Al, Ti and graphite has been mechanically alloyed in a planetary ball mill.The structural evolution of as-milled powder sample has been characterized by XRD, DTA. The results show that the amorphous phase is formed first at an early milling stage, then crystallization occurs during further milling, leading to formation of a nanocrystalline fcc metastable phase. In contrast, during annealing the amorphous phase is crystallized to the equilibrium phase instead of the fcc phase. This indicates that crystallization during ball milling is different from that induced by annealing
文摘The nature of the oxygen contained in β-W was investigated with DSC,X-ray analysis on quenched samples and Auger spectroscope.It was shown that the oxygen contained in nonpyrophoric β-W consists of the reversibly chemisorbed oxygen and the interstitial oxygen which could form an interstitial solid solution with β-W.It seems better to consider β-W to be a metastable phase of tungsten with the interstitial oxygen as stabilizer.
基金supported by the National Natural Science Foundation of China(51772162,22001143,and 52072197)the Youth Innovation and Technology Foundation of Shandong Higher Education Institutions,China(2019KJC004)+4 种基金the Outstanding Youth Foundation of Shandong Province,China(ZR2019JQ14)the Taishan Scholar Young Talent Program(tsqn201909114,tsqn201909123)the Natural Science Foundation of Shandong Province(ZR2020YQ34)the Major Basic Research Program of Natural Science Foundation of Shandong Province under Grant(ZR2020ZD09)the Major Scientific and Technological Innovation Project(2019JZZY020405)。
文摘A general approach is reported for ultra-fast phosphating synthesis of a series of ultra-small(<5 nm)noble metal phosphides(MPX/CNT,M=Pd,Pt,Ru)which are successfully produced in just 75 s for the first time.The catalytic performance of the catalysts can be optimized by controlling the nanomaterials as the metastable crystalline phases.By altering the phosphorus source under the same conditions,the hexagonal structured Pd_(7)P_(3)(NaH_(2)PO_(2).H_(2)O as P source)and monoclinic structured Pd_(6)P(Na_(4)P_(2)O_(7) as P source)can be prepared successfully.Both of them exhibit excellent polyol oxidation performance in alkaline media.Monoclinic Pd_(6)P/CNT and hexagonal Pd_(7)P_(3)/CNT have large ECSA which are confirmed as 82.1 m2 g^(-1)and 86.2 m2 g^(-1),respectively.Hexagonal Pd_(7)P_(3)/CNT has the highest mass activity of 6.14 A mgPd^(-1)(3.21 A mgPd^(-1)for Pd_(6)P/CNT)for GOR,which far exceeded Pt/C(2.81 A mgPt^(-1)).Meanwhile,the mass activity of monoclinic Pt_(5)P_(2)/CNT for EGOR achieved 12.4 A mg_(Pt)^(-1),which far exceeded Pt/C(6.8 A mg_(Pt)^(-1)).The stability test proved that the activity decay of these catalysts was negligible after the 12-hour durability test.Meanwhile,they have excellent CO anti-poisoning abilities.
基金Supported by the National Natural Science Foundation of China(No.40673050)the Research Fund for the Doctoral Program of Higher Education from the Ministry of Education of China(No.20070616008)the Scholarship Leaders Training Fund from Sichuan Province,China(No.2008-140)
文摘The metastable phase equilibria of the quaternary system NaCl+Na2CO3+Na2SO4+H2O were studied at 273.15 K. The salts' solubilities, densities and pH values of the equilibrated solution in this system were determined. According to the experimental data, the metastable equilibrium phase diagram, the diagram of density vs. composition and pH vs. composition diagram were plotted. The phase diagram consists of five univariant curves, four crystallization fields and two invariant points. The four crystallization fields correspond to sodium carbonate decahydrate (Na2CO3·10H2O), sodium sulfate decahydrate(Na2SOn-10H2O), sodium chloride(NaCl) and burkeite(2Na2SO4. Na2CO3), respectively. The crystallization field of sodium sulfate decahydrate(Na2SO4.10H2O) is the largest, which indicates that sodium sulfate is easy to saturate and crystallize from solution at 273.15 K.
基金Project supported by National High Technology Research and Development Program of China (2012AA061704)China National Nature Science Foundation (No. 41173071)+2 种基金the Research Fund for the Doctoral Program of Higher Education from the Ministry of Education of China (20115122110001)the Sichuan Youth Science and Technology Innovation Research Team Funding Scheme (2013TD0005)Innovation Team of CDUT(KYTD201405)
文摘1 Introduction The Pingluoba brine,which characterized as high concentration with sodium,potassium,boron,lithium,and rubidium,possess great development value.The main composition of the brine can be summarized to the
基金financially supported by the Project of Science and Technology of Beijing(No.10231103)
文摘The precipitation process of aged Cu-Ni-Be alloy was investigated by X-ray diffraction (XRD), trans- mission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). The tensile strength, yield strength, and electronic conductivity of this alloy after aging were also studied. The precipitation sequence of the C17510 alloy aged at 525 ℃ is supersat-urated solid solution→G.P zones→ γ″-γ′→ γ. This transformation can be achieved by the accumulation of Be-atom layers. The G.P zones are composed of disk-shaped monolayers of Be atoms, which are formed on (001) matrix planes. The intermediate γ″ precipitate is nucleated in the G.P zones. The γ″ and γ′ precipitates have the same orientation relationship with matrix, e.g., (110)p||(100)M,[001]p||[001]M. The tensile strength of specimen shows a maximum during the aging process and then continuously decreases if the specimen is over aged. The strengthening effect of γ′ phase precipitated in aging at 525 ℃ for 4 h is calculated to be 436 MPa according to the Orowan strengthening, which is quite consistent with the experimental data.
基金This work was supported in part by the National Natural Science Foundation of China(Grant No.19875027)the Ministry of Scienc
文摘Ion beam assisted deposition technique (IBAD) was utilized to systematically study amorphization in binary metal systems of Nb-magnetic element, i.e., Nb-M (M=Fe, Co or Ni). The glass forming range termed as Nb fraction of Nb-Fe system was about 34at.% to 56at.%, that of Nb-Co system was about 32at.% to 72at.% and that of Nb-Ni about 20at. % to 80at. %. Similar percolation patterns were found in amorphous alloy films. The fractal dimensions of the percolation patterns approach to 2, which indicates 2-D layer growth for amorphous phases. It is regarded that the assisted Ar+ ion beam during the deposition process plays important role for the 2-D layer growth. Some metastable crystalline phases were obtained in these three systems by IBAD, e.g., bcc supersaturated solid solutions in Nb-Fe and Nb-Co systems, fcc and hcp phases in Nb-Co and Nb-Ni systems. The formation and competing between the amorphous and the metastable crystalline phases were determined by both the phases' thermodynamic states in binary metal systems and kinetics during IBAD process.
文摘Nb/Nb5Si3 in-situ composites are very attractive structural materials because these materials perform a good balance in mechanical properties, including high strength at high temperature (> 1000 degrees C) and reasonably high fracture toughness at room temperature. Metastable phase Nb3Si plays an important role in the properties of Nb/Nb5Si3 composites by affecting the volume fraction of ductile phase. The addition of Mo affects on the microstructure of ductile phase and the stability of metastable phase Nb3Si. In this paper, Nb-10Si-xMo and Nb-18Si-xMo (x = 0, 5, and 15) alloys were prepared by arc melting and annealed at 1473 K for 100 h. Single edge-notched bending (SENB) test was used to study the fracture toughness of Nb-Si-Mo alloys. The room temperature fracture toughness of Nb-10Si is 10.48 MPa center dot m(1/2) and higher than that of binary Nb-18Si alloys at near-eutectic composites. The addition of 5 at.% Mo improved the fracture toughness of as-cast Nb-Si alloys from 4.1 MPa center dot m(1/2) to 9.99 MPa center dot m(1/2) at near-eutectic compositions and reduced it from 10.48 MPa center dot m(1/2) to 8.86 MPa center dot m(1/2) at hypoeutectic compositions.
文摘The influence of Cr substitution on the crystallization behavior and magnetic properties of melt-spun Nd_ 11Fe_ 72-xCo_8V_ 1.5Cr_xB_ 7.5 (x=0, 1) nanocomposite alloys was studied. The annealed samples consist of a mixture of Nd_2Fe_ 14B and α-Fe phases. Presence of grains of the metastable Nd_2Fe_ 23B_3 phase was revealed in the Cr-containing Nd_ 11Fe_ 71Co_8V_ 1.5Cr_1B_ 7.5 sample. The magnetic properties of the bonded magnets are obviously improved by the Cr substitution. The intrinsic coercivity (_JH_c) and maximum magnetic energy product ((BH)_ max) are increased from 780 kA·m -1 and 68 kJ·m -3 for x=0 to 903.5 kA·m -1 and 71 kJ·m -3 for x=1, respectively. The addition of Cr element shows significant advantage in reducing grain size and increasing intrinsic coercivity.
基金Financial support from the State Key Program of NNSFC (20836009)the NNSFCs (Grants 21106136, 21276194 and 21306136)
文摘1 Introduction Salt lakes are widely distributed in the world,and salt lakes in China are mainly located in the area of the Qinghai-Xizang(Tibet),and the Autonomous Regions of Xinjiang and Inner Mongolia.There are more than 700salt lakes,each with an area larger than 1 km2,in the
文摘The microstructures of laser cladding of (Ni-24.5%(atom fraction)Al)+5O%(mass haction)WC coatingsbefore and after aging was comparetively studied by using SEM and TEM. It is shown that dissolving of WC and reprecipitating in the forms of WC and W,Coccurred during laser cladding, and intermetallic γ' (Ni3Al) orderly precipitatefrom metastable supersaturant Ni-matrix solid solution after heat treatment. The structures are favorable for coating'sproperties.