Improving and optimizing the target properties of ceramics via the high entropy strategy has attracted significant attention.Rare earth niobate is a potential thermal barrier coating(TBCs)material,but its poor high-te...Improving and optimizing the target properties of ceramics via the high entropy strategy has attracted significant attention.Rare earth niobate is a potential thermal barrier coating(TBCs)material,but its poor high-temperature phase stability limits its further application.In this work,four sets of TBCs high-entropy ceramics,(Sm_(1/5)Dy_(1/5)Ho_(1/5)Er_(1/5)Yb_(1/5))(Nb_(1/2)Ta_(1/2))O_(4)(5NbTa),(Sm_(1/6)Dy_(1/6)Ho_(1/6)Er_(1/6)Yb_(1/6)Lu_(1/6))(Nb_(1/2)Ta_(1/2))O_(4)(6NbTa),(Sm_(1/7)Gd_(1/7)Dy_(1/7)Ho_(1/7)Er_(1/7)Yb_(1/7)Lu_(1/7))(Nb_(1/2)Ta_(1/2))O_(4)(7NbTa),(Sm_(1/8)Gd_(1/8)Dy_(1/8)Ho_(1/8)Er_(1/8)Tm_(1/8)Yb_(1/8)Lu_(1/8))(Nb_(1/2)Ta_(1/2))O_(4)(8NbTa)are synthesized using a solid-state reaction method at 1650℃for 6 h.Firstly,the X-ray diffractometer(XRD)patterns display that the samples are all single-phase solid solution structures(space group C 2/c).Differential scanning calorimetry(DSC)and the high-temperature XRD of 8NbTa cross-check that the addition of Ta element in 8HERN increases the phase transition temperature above 1400℃,which can be attributed to that the Ta/Nb co-doping at B site introduces the fluctuation of the bond strength of Ta-O and Nb-O.Secondly,compared to high-entropy rare-earth niobates,the introduction of Ta atoms at B site substantially reduce thermal conductivity(re-duced by 44%,800℃)with the seven components high entropy ceramic as an example.The low thermal conductivity means strong phonon scattering,which may originate from the softening acoustic mode and flattened phonon dispersion in 5–8 principal element high entropy rare earth niobium tantalates(5–8NbTa)revealed by the first-principles calculations.Thirdly,the Ta/Nb co-doping in 5–8NbTa systems can further optimize the insulation performance of oxygen ions.The oxygen-ion conductivity of 8NbTa(3.31×10^(−6)S cm^(−1),900℃)is about 5 times lower than that of 8HERN(15.8×10^(−6)S cm^(−1),900℃)because of the sluggish diffusion effect,providing better oxygen barrier capacity in 5–8NbTa systems to inhibit the overgrowth of the thermal growth oxide(TGO)of TBCs.In addition,influenced by lattice dis-tortion and solid solution strengthening,the samples possess higher hardness(7.51–8.15 GPa)and TECs(9.78×10^(−6)K−1^(-1)0.78×10^(−6)K^(−1),1500℃)than the single rare-earth niobates and tantalates.Based on their excellent overall properties,it is considered that 5–8NbTa can be used as auspicious TBCs.展开更多
The intermetallic compounds based on the tetragonal ThMn_(12) prototype crystal structure have exhibited great potential as advanced rare-earth-lean permanent magnets due to their excellent intrinsic magnetic properti...The intermetallic compounds based on the tetragonal ThMn_(12) prototype crystal structure have exhibited great potential as advanced rare-earth-lean permanent magnets due to their excellent intrinsic magnetic properties.However,the trade-off between the phase stability and the magnetic performance is often encountered in the ThMn_(12)-type magnets.This work was focused on the effects of V doping and nanos-tructuring on the phase stability and magnetic properties of ThMn_(12)-type Sm-Co-based magnets.Novel SmCo_(12)-based nanocrystalline alloys with the SmCo_(12) main phase were prepared for the first time.The prepared alloys from the optimal design achieved obviously higher coercivity than the isotropic SmFe_(12)-based alloys,together with comparable performance of other magnetic features.The enhancement in the coercivity was ascribed to the pinning of domain walls by the nanocrystalline grain boundaries and stacking faults.First-principles calculations and magnetic structure analysis disclosed that V substitution can stabilize the SmCo_(12) lattice and elevate its magnetocrystalline anisotropy.This study provides a new approach to developing stabilized metastable structured rare-earth-lean alloys with high magnetic per-formance.展开更多
The microstructural evolution,phase stability,and mechanical properties of Al-Li-Mg-Ti-M(M=Zn,Zr,V)lightweight high-entropy alloys(LW-HEAs)were investigated.The LW-HEAs with three components,Al_(20)Li_(20)Mg_(10)-Ti_(...The microstructural evolution,phase stability,and mechanical properties of Al-Li-Mg-Ti-M(M=Zn,Zr,V)lightweight high-entropy alloys(LW-HEAs)were investigated.The LW-HEAs with three components,Al_(20)Li_(20)Mg_(10)-Ti_(40)Zn_(10)(#Zn),Al_(20)Li_(20)Mg_(10)Ti_(30)Zr_(20)(#Zr),and Al_(20)Li_(20)Mg_(10)Ti_(30)V_(20)(#V),were designed according to the thermo-dynamic design criteria of HEA,and prepared via a combination process of mechanical alloying and cold-press sintering.The effects of alloy composition and sintering temperature on the microstructure and mechanical properties of the LW-HEAs were studied.The results show that the as-milled Al-Li-Mg-Ti-M(M=Zn,Zr,V)LW-HEAs form a simple structure with HCP-type solid solution as the primary phase,a dual-HCP type solid solution phase,and a BCC phase,respectively.After cold-press sintering,the#Zn and#V alloys undergo obvious phase transformation;while the#Zr alloy with dual-HCP phases exhibits the best phase stability during heat treatment.The#V-750°C alloy demonstrates the maximum hardness and specific strength of HV 595.2 and 625 MPa∙cm3/g,respectively,under the combined effect of solid solution strengthening of BCC phase and precipitation strengthening ofβ-AlTi_(3).Moreover,the#Zr-650°C,#Zr-750°C,and#Zn-650°C alloys are expected to have excellent plasticity.展开更多
Ti-Hf-Zr-Nb-Ta refractory high-entropy alloys(RHEAs)exhibiting a dual-phase structure resulting from martensitic transformation offer significant ductility enhancement,but their design requires precise control of the ...Ti-Hf-Zr-Nb-Ta refractory high-entropy alloys(RHEAs)exhibiting a dual-phase structure resulting from martensitic transformation offer significant ductility enhancement,but their design requires precise control of the phase stability between body-centred cubic(BCC)and hexagonal close-packed(HCP)phases.This study establishes a comprehensive thermodynamic database for the Ti-Hf-Zr-Nb-Ta system using the 3rd-generation Calculation of Phase Diagrams(CALPHAD)model.The reliability of the database is validated by the strong agreement between the calculated thermodynamic properties and phase equilibria and the experimental data for pure element,as well as for binary and ternary systems.Utilizing this database,the phase stability of various RHEAs within this system was predicted,showing that all RHEAs exhibit a BCC single phase over a wide temperature range.The HCP phase is stable and coexists with BCC phase in both quaternary and quinary RHEAs at lower temepratures.Calculations of the Gibbs energy difference between the BCC and HCP phases(ΔG^(HCP−BCC))in TiHfZrTa_(x) and TiHfZrNb_(x) alloys reveal that both Nb and Ta stabilize the BCC phase,with Nb exerting a stronger influence.Significantly,a metastable BCC+HCP region in the TiHfZrTa_(x) and TiHfZrNb_(x) alloys with ΔG^(HCP−BCC) ranging from 1786 to 2230 J/mol.Utilizing this finding,the critical Nb composition range(0.0367–0.0712)to achieve the metastable BCC+HCP phase is precisely predicted in TiHfZrTa_(0.2)Nb_(x) alloys,enabling targeted design for martensitic transformation.The predictions show excellent agreement with existing experimental measurements.展开更多
First-principles calculations were carried out to investigate the structural stabilities and electronic properties of RhZr.The plane wave based pseudopotential method was used,in which both the local density approxima...First-principles calculations were carried out to investigate the structural stabilities and electronic properties of RhZr.The plane wave based pseudopotential method was used,in which both the local density approximation（LDA） and the generalized gradient approximation（GGA） implanted in the CASTEP code were employed.The internal positions of atoms in the unit cell were optimized and the ground state properties such as lattice parameter,density of state,cohesive energies and enthalpies of formation of ortho-RhZr and cubic-RhZr were calculated.The calculation results indicate that ortho-RhZr can form more easily than cubic-RhZr and the ortho-RhZr is more stable than cubic-RhZr.The density of states（DOS） reveals that the strong bonding in the Rh-Zr and Rh-Rh or Zr-Zr interaction chains accounts for the structural stability of ortho-RhZr and the hybridization between Rh-4d states and Zr-4d states is strong.展开更多
Research and development of green oxidizers and green fuels as a possible replacement for ammonium perchlorate(NH4ClO4,AP) and hydrazine(N2H4) respectively has been increased considerably in the recent years.AP and hy...Research and development of green oxidizers and green fuels as a possible replacement for ammonium perchlorate(NH4ClO4,AP) and hydrazine(N2H4) respectively has been increased considerably in the recent years.AP and hydrazine are the oxidizer and fuel entities,and used in solid and liquid rocket motors respectively.AP is highly toxic and led to adverse health effects,while hydrazine is carcinogenic in nature.AP is in use from the last several decades for rocket and space shuttle propulsion,while hydrazine is used in upper stage liquid propelled rocket motors.It’s a tough task to replace AP with the currently available green oxidizers;since their ballistic properties are weaker when compared to AP and also they can’t be successfully deployed in a solid rocket motor at present Some important available solid green oxidizers are ammonium nitrate(AN),ammonium dinitramide(ADN),hydroxyl ammonium nitrate(HAN),and hydrazinium nitroformate(HNF).However,AN is one of the cheap and readily available oxidizer,and has great potential to use in solid/liquid rocket motors.Tremendous progress has been envisaged till now,and more progress will be there in the coming future over the development of AN based green energetic materials(GEM’s).A concise overview has been presented over the development of phase stabilized ammonium nitrate(PSAN) and AN/KDN based green oxidizers in the present review paper.展开更多
Formamidinium lead iodide(FAPbI_(3))perovskite exhibits an impressive X-ray absorption coefficient and a large carrier mobility-lifetime product(μτ),making it as a highly promising candidate for X-ray detection appl...Formamidinium lead iodide(FAPbI_(3))perovskite exhibits an impressive X-ray absorption coefficient and a large carrier mobility-lifetime product(μτ),making it as a highly promising candidate for X-ray detection application.However,the presence of larger FA^(+)cation induces to an expansion of the Pb-I octahedral framework,which unfortunately affects both the stability and charge carrier mobility of the corresponding devices.To address this challenge,we develop a novel low-dimensional(HtrzT)PbI_(3) perovskite featuring a conjugated organic cation(1H-1,2,4-Triazole-3-thiol,HtrzT^(+))which matches well with theα-FAPbI_(3) lattices in two-dimensional plane.Benefiting from the matched lattice between(HtrzT)PbI_(3) andα-FAPbI_(3),the anchored lattice enhances the Pb-I bond strength and effectively mitigates the inherent tensile strain of theα-FAPbI_(3) crystal lattice.The X-ray detector based on(HtrzT)PbI_(3)(1.0)/FAPbI_(3) device achieves a remarkable sensitivity up to 1.83×10^(5)μC Gy_(air)^(−1) cm^(−2),along with a low detection limit of 27.6 nGy_(air) s^(−1),attributed to the release of residual stress,and the enhancement in carrier mobility-lifetime product.Furthermore,the detector exhibits outstanding stability under X-ray irradiation with tolerating doses equivalent to nearly 1.17×10^(6) chest imaging doses.展开更多
The microstructure evolution and phase composition of an α+β titanium alloy, Ti-3Al-5Mo-4.5V(wt.%),have been investigated. Electron probe micro analysis(EPMA) quantitative results manifest that the stability of β p...The microstructure evolution and phase composition of an α+β titanium alloy, Ti-3Al-5Mo-4.5V(wt.%),have been investigated. Electron probe micro analysis(EPMA) quantitative results manifest that the stability of β phase decreases with increasing quenching temperature, which is influenced by the significant variation of β-stabilizing elements concentration. Detailed microstructure analysis shows that the β→ωphase transformation does occur when quenching at 750℃ and 800 ℃. The ω-reflections change from incommensurate ω-spots(750 ℃) to ideal ω-spots(800 ℃) as the β stability of the alloy decreases. Further the decrease of β phase stability encourages the formation of athermal α " martensite, which has the following orientation relationships: [111]β//[110]α",[100]p//[100]α " and [-110]p//[00-1]α" with respect to the β matrix.展开更多
Formation, solution and phase change of hydration products in MgO-MgCl2-H2O system was studied with thermodynamics method, and resistance to water immersion and phase change of magnesium oxychloride cement with differ...Formation, solution and phase change of hydration products in MgO-MgCl2-H2O system was studied with thermodynamics method, and resistance to water immersion and phase change of magnesium oxychloride cement with different MgO/MgCl2 molar ratio was experimented. The results show that pH value of immersion solution of cement paste has a remarkable influence on phase stability of hydration products. A higher pH value leads to a lower solubility and a better phase stability of hydration products. When the solution pH value is higher than 10.37, the precipitation of much Mg（OH）2 crystal induces a worse phase stability of hydration products. With the increasing MgO/MgCl2 molar ratio （lower than 6）, the more amount of MgO in the hydration products enhances the alkalinity of solution and the phase stability is improved. However, when the MgO/MgCl2 molar ratio is higher than 6 and the excessive MgO exsits in the hydration products, the cement paste may be damaged by the excessive crystallization stress of a great deal of Mg（OH）2 formation.展开更多
In this study, high-entropy films with the compo- sition of NbTiA1SiNx were prepared by a reactive direct current （DC） magnetron sputtering technique, with different nitrogen flow rates （0, 4 and 8 ml.min^-1）. The...In this study, high-entropy films with the compo- sition of NbTiA1SiNx were prepared by a reactive direct current （DC） magnetron sputtering technique, with different nitrogen flow rates （0, 4 and 8 ml.min^-1）. The microstructures and properties were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, high-resolution transmission electron microscopy （HRTEM）, nano-indenter and spectrophotometer. All of the as-deposited NbTiA1SiNx films are shown to have an amorphous structure, and the films exhibit high thermal stability up to 700℃. The maximum hardness and modulus values of the films reach 20.5 GPa （4 ml.min-1） and 206.8 GPa （0 ml.min^-l）, respectively. The films exhibit high absorption of the solar energy in the wavelength of 0.3-2.5 pm, which indicates that NbTiA1SiNx nitride film is a potential candidate solar selective absorbing coating for high-temperature photo-thermal conversion in the concentrated solar power project.展开更多
High-temperature structural metals remain in high demand for aerospace aircraft,gas turbine engines,and nuclear power plants.Refractory high-entropy alloys(RHEAs)with superior mechanical properties at elevated tempera...High-temperature structural metals remain in high demand for aerospace aircraft,gas turbine engines,and nuclear power plants.Refractory high-entropy alloys(RHEAs)with superior mechanical properties at elevated temperatures are promising candidates for high-temperature structural materials.In this work,a WTaMoNbTi RHEA with adequate room temperature plasticity and considerable strength at 1600℃was fabricated by vacuum arc-melting.The room temperature fracture strain of the as-cast WTaMoNbTi RHEA was 7.8%,which was about 5.2 times that of the NbMoTaW alloy.The alloy exhibited a strong resistance to high-temperature softening,with a high yield strength of 173 MPa and compressive strength of 218 MPa at 1600℃.The WTaMoNbTi RHEA possessed excellent phase stability in the range of room temperature to 2000℃.The dendritic grains grew into equiaxed grains after compression test at 1600℃due to the dynamic recrystallization process at high temperature.This work presents a promising high-temperature structural material that can be applied at 1600℃.展开更多
An investigation of electronic property and high pressure phase stability of SmN has been conducted using first principles calculations based on density functional theory. The elec- tronic properties of Stun show a st...An investigation of electronic property and high pressure phase stability of SmN has been conducted using first principles calculations based on density functional theory. The elec- tronic properties of Stun show a striking feature of a half metal, the majority-spin electrons are metallic and the minority-spin electrons are semiconducting. It was found that Stun undergoes a pressure-induced phase transition from NaCl-type （B1） to CsCl-type structure （B2） at 117 GPa. The elastic constants of Stun satisfy Born conditions at ambient pressure, indicating that B1 phase of SmN is mechanically stable at 0 GPa. The result of phonon spectra shows that B1 structure is dynamically stable at ambient pressure, which agrees with the conclusion derived from the elastic constants.展开更多
The phase stability,elastic properties and electronic structures of three typical Mg-Y intermetallics including Mg_(24)Y_(5),Mg_(2)Y and MgY are systematically investigated using first-principles calculations based on...The phase stability,elastic properties and electronic structures of three typical Mg-Y intermetallics including Mg_(24)Y_(5),Mg_(2)Y and MgY are systematically investigated using first-principles calculations based on density functional theory.The optimized structural parameters including lattice constants and atomic coordinates are in good agreement with experimental values.The calculated cohesive energies and formation enthalpies show that either phase stability or alloying ability of the three intermetallics is gradually enhanced with increasing Y content.The single-crystal elastic constants C_(ij) of Mg-Y intermetallics are also calculated,and the bulk modulus B,shear modulus G,Young's modulus E,Poisson ratio v and anisotropy factor A of polycrystalline materials are derived.It is suggested that the resistances to volume and shear deformation as well as the stiffness of the three intermetallics are raised with increasing Y content.Besides,these intermetallics all exhibit ductile characteristics,and they are isotropic in compression but anisotropic to a certain degree in shear and stiffness.Comparatively,Mg_(24)Y_(5) presents a relatively higher ductility,while MgY has a relatively stronger anisotropy in shear and stiffness.Further analysis of electronic structures indicates that the phase stability of Mg-Y intermetallics is closely related with their bonding electrons numbers below Fermi level.Namely,the more bonding electrons number below Fermi level corresponds to the higher structural stability of Mg-Y intermetallics.展开更多
Two experimental single crystal superalloys, the Ru-free alloy and the Ru-containing alloy with [001 ] orientation, were cast in a directionally solidified furnace, while other alloying element contents were kept unch...Two experimental single crystal superalloys, the Ru-free alloy and the Ru-containing alloy with [001 ] orientation, were cast in a directionally solidified furnace, while other alloying element contents were kept unchanged. The effects of Ru on the microstructure and phase stability of the single crystal superalloy were investigated, y＇ directional coarsening and rafting were observed in the Ru-free alloy and Ru-containing alloy after long-term aging at 1070~C for 800 h. Needle-shaped o topologically close packed （TCP） phases precipitated and grew along the fixed direction in both the alloys. The precipitating rate and volume fraction of TCP phases decreased significantly by adding Ru. The compositions ofy and y＇ phases measured using an energy-dispersive X-ray spectroscope （EDS） in transmission electron microscopy （TEM） analysis showed that the addition of Ru lessened the partition ratio of TCP forming elements, Re, W and Mo, and decreased the satu- ration degrees of these elements in y phase, which can enable the Ru-containing alloy to be more resistant to the formation of TCP phases. It is indicated that the addition of Ru to the Ni-based single crystal superalloy with high content of the refractory alloying element can enhance phase stability.展开更多
Evolution of deformation mechanisms and mechanical properties of Ti-3Al-5Mo-4.5V alloy with different β phase stability have been systematically investigated. β phase stability alteration is achieved through quenchi...Evolution of deformation mechanisms and mechanical properties of Ti-3Al-5Mo-4.5V alloy with different β phase stability have been systematically investigated. β phase stability alteration is achieved through quenching temperature variation from dual α+β field(700℃) to single β field(880℃). Tensile tests at ambient temperature show that apparent yield strength of the alloy experiences an abrupt decrease followed by a significant increase from 700℃ to 880℃. Work hardening behavior is characterized by transition from the initial two-regime feature to the three-stage outlook. Concurrently, the maximum working hardening rate drops from 14000 MPa to 3000 MPa, which is concurrent with the shrinking volume fraction of primary a phase. Detailed discussion about the relationship between deformation mechanisms and β phase stability has been outlined.展开更多
Electronic structure and elastic properties of Al_(2)Y,Al_(3)Y,Al_(2)Gd and Al_(3)Gd phases were investigated by means of first-principles calculations from CASTEP program based on density functional theory(DFT).The g...Electronic structure and elastic properties of Al_(2)Y,Al_(3)Y,Al_(2)Gd and Al_(3)Gd phases were investigated by means of first-principles calculations from CASTEP program based on density functional theory(DFT).The ground state energy and elastic constants of each phase were calculated,the formation enthalpy(ΔH),bulk modulus(B),shear modulus(G),Young's modulus(E),Poisson's ratio(ν)and anisotropic coefficient(A)were derived.The formation enthalpy shows that Al_(2)RE is more stable than Al_(3)RE,and Al-Y intermetallics have stronger phase stability than Al-Gd intermetallics.The calculated mechanical properties indicate that all these four intermetallics are strong and hard brittle phases,it may lead to the similar performance when deforming due to their similar elastic constants.The total and partial electron density of states(DOS),Mulliken population and metallicity were calculated to analyze the electron structure and bonding characteristics of the phases.Finally,phonon calculation was conducted,and the thermodynamic properties were obtained and further discussed.展开更多
Biomedicalβ-phase Ti-Nb-Ta-Zr alloys usually exhibit low elastic modulus with inadequate strength.In the present work,a series of newly developed dual-phase Ti-xNb-yTa-2Zr(wt.%)alloys with high performance were inves...Biomedicalβ-phase Ti-Nb-Ta-Zr alloys usually exhibit low elastic modulus with inadequate strength.In the present work,a series of newly developed dual-phase Ti-xNb-yTa-2Zr(wt.%)alloys with high performance were investigated in which the stability ofβ-phase was reduced under the guidelines of ab initio calculations and d-electronic theory.The effects of Nb and Ta contents on the microstructure,compressive and tensile properties were investigated.Results demonstrate that the designed Ti-xNb-yTa-2Zr alloys exhibit typical characteristics ofα+βdual-phase microstructure.The microstructure of the alloys is more sensitive to Nb rather than Ta.The as-cast alloys exhibit needle-likeα′martensite at a lower Nb content of 3 wt.%and lamellarα′martensite at an Nb content of 5 wt.%.Among the alloys,the Ti-3Nb-13Ta-2Zr alloy shows the highest compressive strength(2270±10 MPa)and compressive strain(74.3%±0.4%).This superior performance is due to the combination ofα+βdual-phase microstructure and stressinducedα"martensite.Besides,lattice distortion caused by Ta element also contributes to the compressive properties.Nb and Ta contents of the alloys strongly affect Young's modulus and tensile properties after rolling.The as-rolled Ti-3Nb-13Ta-2Zr alloy exhibits much lower modulus due to lower Nb content as well as moreα"martensite andβphase with a good combination of low modulus and high strength among all the designed alloys.Atom probe tomography analysis reveals the element partitioning between theαandβphases in which Ta concentration is higher than Nb in theαphase.Also,the concentration of Ta is lower than that of Nb in theβphase,indicating that theβ-stability of Nb is higher than that of Ta.This work proposes modernα+βdual-phase Ti-xNb-yTa-2Zr alloys as a new concept to design novel biomedical Ti alloys with high performance.展开更多
High-entropy alloys(HEAs)generally possess complex component combinations and abnormal properties.The traditional methods of investigating these alloys are becoming increasingly inefficient because of the unpredictabl...High-entropy alloys(HEAs)generally possess complex component combinations and abnormal properties.The traditional methods of investigating these alloys are becoming increasingly inefficient because of the unpredictable phase transformation and the combination of many constituents.The development of compositionally complex materials such as HEAs requires high-throughput experimental methods,which involves preparing many samples in a short time.Here we apply the high-throughput method to investigate the phase evolution and mechanical properties of novel HEA film with the compositional gradient of(Cr,Fe,V)-(Ta,W).First,we deposited the compositional gradient film by co-sputtering.Second,the mechanical properties and thermal stability of the(Cr0.33Fe0.33V0.33)x(Ta0.5W0.5)100−x(x=13-82)multiplebased-elemental(MBE)alloys were investigated.After the deposited wafer was annealed at 600℃for 0.5 h,the initial amorphous phase was transformed into a body-centered cubic(bcc)structure phase when x=33.Oxides were observed on the film surface when x was 72 and 82.Finally,the highest hardness of as-deposited films was found when x=18,and the maximum hardness of annealed films was found when x=33.展开更多
Brittleness is a bottleneck hindering the applications of fruitful functional properties of Ni–Mn-based multiferroic alloys.Recently,experimental studies on B alloying shed new light on this issue.However,the knowled...Brittleness is a bottleneck hindering the applications of fruitful functional properties of Ni–Mn-based multiferroic alloys.Recently,experimental studies on B alloying shed new light on this issue.However,the knowledge related to B alloying is limited until now.More importantly,the mechanism of the improved ductility,which is intrinsically related to the chemical bond that is difficult to reveal by routine experiments,is still unclear.In this context,by first-principles calculations,the impact and the correlated mechanism of B alloying were systemically studied by investigating four alloying systems,i.e.,(Ni_(2-x)B_(x))MnGa,Ni_(2)(Mn_(1-x)B_(x))Ga,Ni_(2)Mn(Ga_(1-x)B_(x))and(Ni_(2)MnGa)_(1-x)B_(x).Results show that B prefers the direct occupation manner when it replaces Ni,Mn and Ga.For interstitial doping,B tends to locate at octahedral rather than tetrahedral interstice.Calculations show that the replacement of B for Ga can effectively improve(reduce)the inherent ductility(inherent strength)due to the weaker covalent strength of Ni(Mn)–B compared with Ni(Mn)–Ga.In contrast,B staying at octahedral interstice will lead to the formation of new chemical bonds between Ni(Mn)and B,bringing about a significantly improved strength and a greatly reduced ductility.Upon the substitutions for Ni and Mn,they affect both the inherent ductility and strength insignificantly.For phase transition,the replacement of B for Ga tends to destabilize the austenite,which can be understood in the picture of the band Jahn–Teller effect.Besides,the substitution for Ga would not lead to an obvious reduction of magnetization.展开更多
Dual-phase membranes of 60 wt% Ce0.8Gd0.2O2-δ-40 wt% Pr Ba Co2exFexO3 d（0 x 2） were prepared by a combined citrate and ethylene diamine tetraacetic acid（EDTA） complexing method. X-ray diffraction（XRD）results re...Dual-phase membranes of 60 wt% Ce0.8Gd0.2O2-δ-40 wt% Pr Ba Co2exFexO3 d（0 x 2） were prepared by a combined citrate and ethylene diamine tetraacetic acid（EDTA） complexing method. X-ray diffraction（XRD）results revealed the good chemical compatibility between ion-conducting phase CGO and electron-conducting phases PBC2 xFxO after sintering in air. The Fe ionic dopant had a significant effect on the phase structure stability and oxygen permeability under CO2 atmosphere, which was confirmed by XRD, thermogravimetrye differential scanning calorimetry（TGeD SC）, scanning electron microscopy（SEM） and oxygen permeation experiments. CGOeP BC0.5F1.5O dual-phase membrane demonstrated a stable oxygen permeation flux of2.71x10-7mol cm 2s 1with 50 mol% He/CO2 as the sweep gas at 925 C, and this value was much higher than that of perovskite-type membranes. The rate-limiting step in the oxygen permeation process changed from the bulk diffusion to the surface oxygen exchange when the CGOeP BC0.5F1.5O membrane thickness decreased to 0.8 mm or less. Due to the high oxygen permeation fluxes and the excellent structural stability under CO2 atmosphere, the CGOeP BC0.5F1.5O membrane is a great potential candidate material for separating oxygen from air in the oxy-fuel combustion techniques.展开更多
基金support from Yunnan Major Scientific and Technological Projects(No.202302AG050010)Yunnan Fundamental Research Projects(Nos.202101AW070011 and202101BE070001–015)+1 种基金National Natural Science Foundation of China(No.52303295)Project Funds of“Xingdian Talent Support Program”.
文摘Improving and optimizing the target properties of ceramics via the high entropy strategy has attracted significant attention.Rare earth niobate is a potential thermal barrier coating(TBCs)material,but its poor high-temperature phase stability limits its further application.In this work,four sets of TBCs high-entropy ceramics,(Sm_(1/5)Dy_(1/5)Ho_(1/5)Er_(1/5)Yb_(1/5))(Nb_(1/2)Ta_(1/2))O_(4)(5NbTa),(Sm_(1/6)Dy_(1/6)Ho_(1/6)Er_(1/6)Yb_(1/6)Lu_(1/6))(Nb_(1/2)Ta_(1/2))O_(4)(6NbTa),(Sm_(1/7)Gd_(1/7)Dy_(1/7)Ho_(1/7)Er_(1/7)Yb_(1/7)Lu_(1/7))(Nb_(1/2)Ta_(1/2))O_(4)(7NbTa),(Sm_(1/8)Gd_(1/8)Dy_(1/8)Ho_(1/8)Er_(1/8)Tm_(1/8)Yb_(1/8)Lu_(1/8))(Nb_(1/2)Ta_(1/2))O_(4)(8NbTa)are synthesized using a solid-state reaction method at 1650℃for 6 h.Firstly,the X-ray diffractometer(XRD)patterns display that the samples are all single-phase solid solution structures(space group C 2/c).Differential scanning calorimetry(DSC)and the high-temperature XRD of 8NbTa cross-check that the addition of Ta element in 8HERN increases the phase transition temperature above 1400℃,which can be attributed to that the Ta/Nb co-doping at B site introduces the fluctuation of the bond strength of Ta-O and Nb-O.Secondly,compared to high-entropy rare-earth niobates,the introduction of Ta atoms at B site substantially reduce thermal conductivity(re-duced by 44%,800℃)with the seven components high entropy ceramic as an example.The low thermal conductivity means strong phonon scattering,which may originate from the softening acoustic mode and flattened phonon dispersion in 5–8 principal element high entropy rare earth niobium tantalates(5–8NbTa)revealed by the first-principles calculations.Thirdly,the Ta/Nb co-doping in 5–8NbTa systems can further optimize the insulation performance of oxygen ions.The oxygen-ion conductivity of 8NbTa(3.31×10^(−6)S cm^(−1),900℃)is about 5 times lower than that of 8HERN(15.8×10^(−6)S cm^(−1),900℃)because of the sluggish diffusion effect,providing better oxygen barrier capacity in 5–8NbTa systems to inhibit the overgrowth of the thermal growth oxide(TGO)of TBCs.In addition,influenced by lattice dis-tortion and solid solution strengthening,the samples possess higher hardness(7.51–8.15 GPa)and TECs(9.78×10^(−6)K−1^(-1)0.78×10^(−6)K^(−1),1500℃)than the single rare-earth niobates and tantalates.Based on their excellent overall properties,it is considered that 5–8NbTa can be used as auspicious TBCs.
基金supported by the National Key R&D Program of China(Nos.2021YFB3501502 and 2021YFB3501504).
文摘The intermetallic compounds based on the tetragonal ThMn_(12) prototype crystal structure have exhibited great potential as advanced rare-earth-lean permanent magnets due to their excellent intrinsic magnetic properties.However,the trade-off between the phase stability and the magnetic performance is often encountered in the ThMn_(12)-type magnets.This work was focused on the effects of V doping and nanos-tructuring on the phase stability and magnetic properties of ThMn_(12)-type Sm-Co-based magnets.Novel SmCo_(12)-based nanocrystalline alloys with the SmCo_(12) main phase were prepared for the first time.The prepared alloys from the optimal design achieved obviously higher coercivity than the isotropic SmFe_(12)-based alloys,together with comparable performance of other magnetic features.The enhancement in the coercivity was ascribed to the pinning of domain walls by the nanocrystalline grain boundaries and stacking faults.First-principles calculations and magnetic structure analysis disclosed that V substitution can stabilize the SmCo_(12) lattice and elevate its magnetocrystalline anisotropy.This study provides a new approach to developing stabilized metastable structured rare-earth-lean alloys with high magnetic per-formance.
基金financially supported by China Aeronautical Science Foundation (No.2023Z0530Q9002)the Program for Chongqing Talents,China (No.cstc2024ycjh-bgzxm0066)。
文摘The microstructural evolution,phase stability,and mechanical properties of Al-Li-Mg-Ti-M(M=Zn,Zr,V)lightweight high-entropy alloys(LW-HEAs)were investigated.The LW-HEAs with three components,Al_(20)Li_(20)Mg_(10)-Ti_(40)Zn_(10)(#Zn),Al_(20)Li_(20)Mg_(10)Ti_(30)Zr_(20)(#Zr),and Al_(20)Li_(20)Mg_(10)Ti_(30)V_(20)(#V),were designed according to the thermo-dynamic design criteria of HEA,and prepared via a combination process of mechanical alloying and cold-press sintering.The effects of alloy composition and sintering temperature on the microstructure and mechanical properties of the LW-HEAs were studied.The results show that the as-milled Al-Li-Mg-Ti-M(M=Zn,Zr,V)LW-HEAs form a simple structure with HCP-type solid solution as the primary phase,a dual-HCP type solid solution phase,and a BCC phase,respectively.After cold-press sintering,the#Zn and#V alloys undergo obvious phase transformation;while the#Zr alloy with dual-HCP phases exhibits the best phase stability during heat treatment.The#V-750°C alloy demonstrates the maximum hardness and specific strength of HV 595.2 and 625 MPa∙cm3/g,respectively,under the combined effect of solid solution strengthening of BCC phase and precipitation strengthening ofβ-AlTi_(3).Moreover,the#Zr-650°C,#Zr-750°C,and#Zn-650°C alloys are expected to have excellent plasticity.
基金financially supported by the Natural Science Foundation of Hebei Province,China(No.E202302154).
文摘Ti-Hf-Zr-Nb-Ta refractory high-entropy alloys(RHEAs)exhibiting a dual-phase structure resulting from martensitic transformation offer significant ductility enhancement,but their design requires precise control of the phase stability between body-centred cubic(BCC)and hexagonal close-packed(HCP)phases.This study establishes a comprehensive thermodynamic database for the Ti-Hf-Zr-Nb-Ta system using the 3rd-generation Calculation of Phase Diagrams(CALPHAD)model.The reliability of the database is validated by the strong agreement between the calculated thermodynamic properties and phase equilibria and the experimental data for pure element,as well as for binary and ternary systems.Utilizing this database,the phase stability of various RHEAs within this system was predicted,showing that all RHEAs exhibit a BCC single phase over a wide temperature range.The HCP phase is stable and coexists with BCC phase in both quaternary and quinary RHEAs at lower temepratures.Calculations of the Gibbs energy difference between the BCC and HCP phases(ΔG^(HCP−BCC))in TiHfZrTa_(x) and TiHfZrNb_(x) alloys reveal that both Nb and Ta stabilize the BCC phase,with Nb exerting a stronger influence.Significantly,a metastable BCC+HCP region in the TiHfZrTa_(x) and TiHfZrNb_(x) alloys with ΔG^(HCP−BCC) ranging from 1786 to 2230 J/mol.Utilizing this finding,the critical Nb composition range(0.0367–0.0712)to achieve the metastable BCC+HCP phase is precisely predicted in TiHfZrTa_(0.2)Nb_(x) alloys,enabling targeted design for martensitic transformation.The predictions show excellent agreement with existing experimental measurements.
基金Project(u0837601)supported by the National Natural Science Foundation of China
文摘First-principles calculations were carried out to investigate the structural stabilities and electronic properties of RhZr.The plane wave based pseudopotential method was used,in which both the local density approximation（LDA） and the generalized gradient approximation（GGA） implanted in the CASTEP code were employed.The internal positions of atoms in the unit cell were optimized and the ground state properties such as lattice parameter,density of state,cohesive energies and enthalpies of formation of ortho-RhZr and cubic-RhZr were calculated.The calculation results indicate that ortho-RhZr can form more easily than cubic-RhZr and the ortho-RhZr is more stable than cubic-RhZr.The density of states（DOS） reveals that the strong bonding in the Rh-Zr and Rh-Rh or Zr-Zr interaction chains accounts for the structural stability of ortho-RhZr and the hybridization between Rh-4d states and Zr-4d states is strong.
文摘Research and development of green oxidizers and green fuels as a possible replacement for ammonium perchlorate(NH4ClO4,AP) and hydrazine(N2H4) respectively has been increased considerably in the recent years.AP and hydrazine are the oxidizer and fuel entities,and used in solid and liquid rocket motors respectively.AP is highly toxic and led to adverse health effects,while hydrazine is carcinogenic in nature.AP is in use from the last several decades for rocket and space shuttle propulsion,while hydrazine is used in upper stage liquid propelled rocket motors.It’s a tough task to replace AP with the currently available green oxidizers;since their ballistic properties are weaker when compared to AP and also they can’t be successfully deployed in a solid rocket motor at present Some important available solid green oxidizers are ammonium nitrate(AN),ammonium dinitramide(ADN),hydroxyl ammonium nitrate(HAN),and hydrazinium nitroformate(HNF).However,AN is one of the cheap and readily available oxidizer,and has great potential to use in solid/liquid rocket motors.Tremendous progress has been envisaged till now,and more progress will be there in the coming future over the development of AN based green energetic materials(GEM’s).A concise overview has been presented over the development of phase stabilized ammonium nitrate(PSAN) and AN/KDN based green oxidizers in the present review paper.
基金supports from the National Natural Science Foundation of China(22375220,U2001214,22471302)the Guangdong Basic and Applied Basic Research Foundation(2024B1515020101)Open Project Fund from State Key Laboratory of Optoelectronic Materials and Technologies(OEMT-2024-KF-08).
文摘Formamidinium lead iodide(FAPbI_(3))perovskite exhibits an impressive X-ray absorption coefficient and a large carrier mobility-lifetime product(μτ),making it as a highly promising candidate for X-ray detection application.However,the presence of larger FA^(+)cation induces to an expansion of the Pb-I octahedral framework,which unfortunately affects both the stability and charge carrier mobility of the corresponding devices.To address this challenge,we develop a novel low-dimensional(HtrzT)PbI_(3) perovskite featuring a conjugated organic cation(1H-1,2,4-Triazole-3-thiol,HtrzT^(+))which matches well with theα-FAPbI_(3) lattices in two-dimensional plane.Benefiting from the matched lattice between(HtrzT)PbI_(3) andα-FAPbI_(3),the anchored lattice enhances the Pb-I bond strength and effectively mitigates the inherent tensile strain of theα-FAPbI_(3) crystal lattice.The X-ray detector based on(HtrzT)PbI_(3)(1.0)/FAPbI_(3) device achieves a remarkable sensitivity up to 1.83×10^(5)μC Gy_(air)^(−1) cm^(−2),along with a low detection limit of 27.6 nGy_(air) s^(−1),attributed to the release of residual stress,and the enhancement in carrier mobility-lifetime product.Furthermore,the detector exhibits outstanding stability under X-ray irradiation with tolerating doses equivalent to nearly 1.17×10^(6) chest imaging doses.
基金supported from the National Natural Science Foundation of China(No.51401221,51622401 and 51628402)support from the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB06050100)
文摘The microstructure evolution and phase composition of an α+β titanium alloy, Ti-3Al-5Mo-4.5V(wt.%),have been investigated. Electron probe micro analysis(EPMA) quantitative results manifest that the stability of β phase decreases with increasing quenching temperature, which is influenced by the significant variation of β-stabilizing elements concentration. Detailed microstructure analysis shows that the β→ωphase transformation does occur when quenching at 750℃ and 800 ℃. The ω-reflections change from incommensurate ω-spots(750 ℃) to ideal ω-spots(800 ℃) as the β stability of the alloy decreases. Further the decrease of β phase stability encourages the formation of athermal α " martensite, which has the following orientation relationships: [111]β//[110]α",[100]p//[100]α " and [-110]p//[00-1]α" with respect to the β matrix.
基金Funded by the National Natural Science Foundation of China(No50078019)
文摘Formation, solution and phase change of hydration products in MgO-MgCl2-H2O system was studied with thermodynamics method, and resistance to water immersion and phase change of magnesium oxychloride cement with different MgO/MgCl2 molar ratio was experimented. The results show that pH value of immersion solution of cement paste has a remarkable influence on phase stability of hydration products. A higher pH value leads to a lower solubility and a better phase stability of hydration products. When the solution pH value is higher than 10.37, the precipitation of much Mg（OH）2 crystal induces a worse phase stability of hydration products. With the increasing MgO/MgCl2 molar ratio （lower than 6）, the more amount of MgO in the hydration products enhances the alkalinity of solution and the phase stability is improved. However, when the MgO/MgCl2 molar ratio is higher than 6 and the excessive MgO exsits in the hydration products, the cement paste may be damaged by the excessive crystallization stress of a great deal of Mg（OH）2 formation.
基金financially supported by the National Natural Science Foundation of China (No.51471025)
文摘In this study, high-entropy films with the compo- sition of NbTiA1SiNx were prepared by a reactive direct current （DC） magnetron sputtering technique, with different nitrogen flow rates （0, 4 and 8 ml.min^-1）. The microstructures and properties were characterized by X-ray diffraction （XRD）, scanning electron microscopy （SEM）, high-resolution transmission electron microscopy （HRTEM）, nano-indenter and spectrophotometer. All of the as-deposited NbTiA1SiNx films are shown to have an amorphous structure, and the films exhibit high thermal stability up to 700℃. The maximum hardness and modulus values of the films reach 20.5 GPa （4 ml.min-1） and 206.8 GPa （0 ml.min^-l）, respectively. The films exhibit high absorption of the solar energy in the wavelength of 0.3-2.5 pm, which indicates that NbTiA1SiNx nitride film is a potential candidate solar selective absorbing coating for high-temperature photo-thermal conversion in the concentrated solar power project.
基金financially supported by the National Key Research and Development Program of China(Grant No.2018YFC1902400)the National Natural Science Foundation of China(Grant No.51975582)。
文摘High-temperature structural metals remain in high demand for aerospace aircraft,gas turbine engines,and nuclear power plants.Refractory high-entropy alloys(RHEAs)with superior mechanical properties at elevated temperatures are promising candidates for high-temperature structural materials.In this work,a WTaMoNbTi RHEA with adequate room temperature plasticity and considerable strength at 1600℃was fabricated by vacuum arc-melting.The room temperature fracture strain of the as-cast WTaMoNbTi RHEA was 7.8%,which was about 5.2 times that of the NbMoTaW alloy.The alloy exhibited a strong resistance to high-temperature softening,with a high yield strength of 173 MPa and compressive strength of 218 MPa at 1600℃.The WTaMoNbTi RHEA possessed excellent phase stability in the range of room temperature to 2000℃.The dendritic grains grew into equiaxed grains after compression test at 1600℃due to the dynamic recrystallization process at high temperature.This work presents a promising high-temperature structural material that can be applied at 1600℃.
文摘An investigation of electronic property and high pressure phase stability of SmN has been conducted using first principles calculations based on density functional theory. The elec- tronic properties of Stun show a striking feature of a half metal, the majority-spin electrons are metallic and the minority-spin electrons are semiconducting. It was found that Stun undergoes a pressure-induced phase transition from NaCl-type （B1） to CsCl-type structure （B2） at 117 GPa. The elastic constants of Stun satisfy Born conditions at ambient pressure, indicating that B1 phase of SmN is mechanically stable at 0 GPa. The result of phonon spectra shows that B1 structure is dynamically stable at ambient pressure, which agrees with the conclusion derived from the elastic constants.
基金This work was financially supported by the National Natural Science Foundation of China(No.51401036)the Hunan Provincial Natural Science Foundation of China(No.14JJ3086),the Research Foundation of Education Bureau of Hunan Province(No.12B001)the Key Laboratory of Efficient and Clean Energy Utilization,College of Hunan Province(No.2015NGQ005).
文摘The phase stability,elastic properties and electronic structures of three typical Mg-Y intermetallics including Mg_(24)Y_(5),Mg_(2)Y and MgY are systematically investigated using first-principles calculations based on density functional theory.The optimized structural parameters including lattice constants and atomic coordinates are in good agreement with experimental values.The calculated cohesive energies and formation enthalpies show that either phase stability or alloying ability of the three intermetallics is gradually enhanced with increasing Y content.The single-crystal elastic constants C_(ij) of Mg-Y intermetallics are also calculated,and the bulk modulus B,shear modulus G,Young's modulus E,Poisson ratio v and anisotropy factor A of polycrystalline materials are derived.It is suggested that the resistances to volume and shear deformation as well as the stiffness of the three intermetallics are raised with increasing Y content.Besides,these intermetallics all exhibit ductile characteristics,and they are isotropic in compression but anisotropic to a certain degree in shear and stiffness.Comparatively,Mg_(24)Y_(5) presents a relatively higher ductility,while MgY has a relatively stronger anisotropy in shear and stiffness.Further analysis of electronic structures indicates that the phase stability of Mg-Y intermetallics is closely related with their bonding electrons numbers below Fermi level.Namely,the more bonding electrons number below Fermi level corresponds to the higher structural stability of Mg-Y intermetallics.
文摘Two experimental single crystal superalloys, the Ru-free alloy and the Ru-containing alloy with [001 ] orientation, were cast in a directionally solidified furnace, while other alloying element contents were kept unchanged. The effects of Ru on the microstructure and phase stability of the single crystal superalloy were investigated, y＇ directional coarsening and rafting were observed in the Ru-free alloy and Ru-containing alloy after long-term aging at 1070~C for 800 h. Needle-shaped o topologically close packed （TCP） phases precipitated and grew along the fixed direction in both the alloys. The precipitating rate and volume fraction of TCP phases decreased significantly by adding Ru. The compositions ofy and y＇ phases measured using an energy-dispersive X-ray spectroscope （EDS） in transmission electron microscopy （TEM） analysis showed that the addition of Ru lessened the partition ratio of TCP forming elements, Re, W and Mo, and decreased the satu- ration degrees of these elements in y phase, which can enable the Ru-containing alloy to be more resistant to the formation of TCP phases. It is indicated that the addition of Ru to the Ni-based single crystal superalloy with high content of the refractory alloying element can enhance phase stability.
基金supported by the National Natural Science Foundation of China(No.51401221,51622401 and 51628402)the support from the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB06050100)
文摘Evolution of deformation mechanisms and mechanical properties of Ti-3Al-5Mo-4.5V alloy with different β phase stability have been systematically investigated. β phase stability alteration is achieved through quenching temperature variation from dual α+β field(700℃) to single β field(880℃). Tensile tests at ambient temperature show that apparent yield strength of the alloy experiences an abrupt decrease followed by a significant increase from 700℃ to 880℃. Work hardening behavior is characterized by transition from the initial two-regime feature to the three-stage outlook. Concurrently, the maximum working hardening rate drops from 14000 MPa to 3000 MPa, which is concurrent with the shrinking volume fraction of primary a phase. Detailed discussion about the relationship between deformation mechanisms and β phase stability has been outlined.
基金This work is supported by the Key Technologies Research and Development Program of Liaoning Province(2013201018).
文摘Electronic structure and elastic properties of Al_(2)Y,Al_(3)Y,Al_(2)Gd and Al_(3)Gd phases were investigated by means of first-principles calculations from CASTEP program based on density functional theory(DFT).The ground state energy and elastic constants of each phase were calculated,the formation enthalpy(ΔH),bulk modulus(B),shear modulus(G),Young's modulus(E),Poisson's ratio(ν)and anisotropic coefficient(A)were derived.The formation enthalpy shows that Al_(2)RE is more stable than Al_(3)RE,and Al-Y intermetallics have stronger phase stability than Al-Gd intermetallics.The calculated mechanical properties indicate that all these four intermetallics are strong and hard brittle phases,it may lead to the similar performance when deforming due to their similar elastic constants.The total and partial electron density of states(DOS),Mulliken population and metallicity were calculated to analyze the electron structure and bonding characteristics of the phases.Finally,phonon calculation was conducted,and the thermodynamic properties were obtained and further discussed.
基金financially supported by the National Natural Science Foundation of China(Nos.52011530181 and 51831011)the Shanghai Science and Technology Commission(No.20S31900100)。
文摘Biomedicalβ-phase Ti-Nb-Ta-Zr alloys usually exhibit low elastic modulus with inadequate strength.In the present work,a series of newly developed dual-phase Ti-xNb-yTa-2Zr(wt.%)alloys with high performance were investigated in which the stability ofβ-phase was reduced under the guidelines of ab initio calculations and d-electronic theory.The effects of Nb and Ta contents on the microstructure,compressive and tensile properties were investigated.Results demonstrate that the designed Ti-xNb-yTa-2Zr alloys exhibit typical characteristics ofα+βdual-phase microstructure.The microstructure of the alloys is more sensitive to Nb rather than Ta.The as-cast alloys exhibit needle-likeα′martensite at a lower Nb content of 3 wt.%and lamellarα′martensite at an Nb content of 5 wt.%.Among the alloys,the Ti-3Nb-13Ta-2Zr alloy shows the highest compressive strength(2270±10 MPa)and compressive strain(74.3%±0.4%).This superior performance is due to the combination ofα+βdual-phase microstructure and stressinducedα"martensite.Besides,lattice distortion caused by Ta element also contributes to the compressive properties.Nb and Ta contents of the alloys strongly affect Young's modulus and tensile properties after rolling.The as-rolled Ti-3Nb-13Ta-2Zr alloy exhibits much lower modulus due to lower Nb content as well as moreα"martensite andβphase with a good combination of low modulus and high strength among all the designed alloys.Atom probe tomography analysis reveals the element partitioning between theαandβphases in which Ta concentration is higher than Nb in theαphase.Also,the concentration of Ta is lower than that of Nb in theβphase,indicating that theβ-stability of Nb is higher than that of Ta.This work proposes modernα+βdual-phase Ti-xNb-yTa-2Zr alloys as a new concept to design novel biomedical Ti alloys with high performance.
基金the National Natural Science Foundation of China(No.51671020)the Fundamental Research Funds for the Central Universities(No.FRF-MP-19-013).
文摘High-entropy alloys(HEAs)generally possess complex component combinations and abnormal properties.The traditional methods of investigating these alloys are becoming increasingly inefficient because of the unpredictable phase transformation and the combination of many constituents.The development of compositionally complex materials such as HEAs requires high-throughput experimental methods,which involves preparing many samples in a short time.Here we apply the high-throughput method to investigate the phase evolution and mechanical properties of novel HEA film with the compositional gradient of(Cr,Fe,V)-(Ta,W).First,we deposited the compositional gradient film by co-sputtering.Second,the mechanical properties and thermal stability of the(Cr0.33Fe0.33V0.33)x(Ta0.5W0.5)100−x(x=13-82)multiplebased-elemental(MBE)alloys were investigated.After the deposited wafer was annealed at 600℃for 0.5 h,the initial amorphous phase was transformed into a body-centered cubic(bcc)structure phase when x=33.Oxides were observed on the film surface when x was 72 and 82.Finally,the highest hardness of as-deposited films was found when x=18,and the maximum hardness of annealed films was found when x=33.
基金the National Natural Science Foundation of China(Grant No.51801020,51922026,51771044)the Fundamental Research Funds for the Central Universities(Grant No.N2002005,N2002021)+2 种基金the Liao Ning Revitalization Talents Program(Grant No.XLYC1802023)the Ph.D.Starting Foundation of Liaoning Province(Grant No.20180540115)Programme of Introducing Talents of Discipline Innovation to Universities(the 111 Project of China,No.BP0719037,B20029)。
文摘Brittleness is a bottleneck hindering the applications of fruitful functional properties of Ni–Mn-based multiferroic alloys.Recently,experimental studies on B alloying shed new light on this issue.However,the knowledge related to B alloying is limited until now.More importantly,the mechanism of the improved ductility,which is intrinsically related to the chemical bond that is difficult to reveal by routine experiments,is still unclear.In this context,by first-principles calculations,the impact and the correlated mechanism of B alloying were systemically studied by investigating four alloying systems,i.e.,(Ni_(2-x)B_(x))MnGa,Ni_(2)(Mn_(1-x)B_(x))Ga,Ni_(2)Mn(Ga_(1-x)B_(x))and(Ni_(2)MnGa)_(1-x)B_(x).Results show that B prefers the direct occupation manner when it replaces Ni,Mn and Ga.For interstitial doping,B tends to locate at octahedral rather than tetrahedral interstice.Calculations show that the replacement of B for Ga can effectively improve(reduce)the inherent ductility(inherent strength)due to the weaker covalent strength of Ni(Mn)–B compared with Ni(Mn)–Ga.In contrast,B staying at octahedral interstice will lead to the formation of new chemical bonds between Ni(Mn)and B,bringing about a significantly improved strength and a greatly reduced ductility.Upon the substitutions for Ni and Mn,they affect both the inherent ductility and strength insignificantly.For phase transition,the replacement of B for Ga tends to destabilize the austenite,which can be understood in the picture of the band Jahn–Teller effect.Besides,the substitution for Ga would not lead to an obvious reduction of magnetization.
基金supported by the National Natural Science Foundation of China (Nos. 51004069 and 51474145)the National Science Fund for Distinguished Young Scholars (No. 51225401)the Innovation Program of Shanghai Municipal Education Commission and Shanghai University (Nos. 14YZ013 and SDCX2012002)
文摘Dual-phase membranes of 60 wt% Ce0.8Gd0.2O2-δ-40 wt% Pr Ba Co2exFexO3 d（0 x 2） were prepared by a combined citrate and ethylene diamine tetraacetic acid（EDTA） complexing method. X-ray diffraction（XRD）results revealed the good chemical compatibility between ion-conducting phase CGO and electron-conducting phases PBC2 xFxO after sintering in air. The Fe ionic dopant had a significant effect on the phase structure stability and oxygen permeability under CO2 atmosphere, which was confirmed by XRD, thermogravimetrye differential scanning calorimetry（TGeD SC）, scanning electron microscopy（SEM） and oxygen permeation experiments. CGOeP BC0.5F1.5O dual-phase membrane demonstrated a stable oxygen permeation flux of2.71x10-7mol cm 2s 1with 50 mol% He/CO2 as the sweep gas at 925 C, and this value was much higher than that of perovskite-type membranes. The rate-limiting step in the oxygen permeation process changed from the bulk diffusion to the surface oxygen exchange when the CGOeP BC0.5F1.5O membrane thickness decreased to 0.8 mm or less. Due to the high oxygen permeation fluxes and the excellent structural stability under CO2 atmosphere, the CGOeP BC0.5F1.5O membrane is a great potential candidate material for separating oxygen from air in the oxy-fuel combustion techniques.
