Aqueous zinc-ion batteries are regarded as promising electrochemical energy-storage systems for various applications because of their high safety,low costs,and high capacities.However,dendrite formation and side react...Aqueous zinc-ion batteries are regarded as promising electrochemical energy-storage systems for various applications because of their high safety,low costs,and high capacities.However,dendrite formation and side reactions during zinc plating or stripping greatly reduce the capacity and cycle life of a battery and subsequently limit its practical application.To address these issues,we modified the surface of a zinc anode with a functional bilayer composed of zincophilic Cu and flexible polymer layers.The zincophilic Cu interfacial layer was prepared through CuSO_(4)solution pretreatment to serve as a nucleation site to facilitate uniform Zn deposition.Meanwhile,the polymer layer was coated onto the Cu interface layer to serve as a protective layer that would prevent side reactions between zinc and electrolytes.Benefiting from the synergistic effect of the zincophilic Cu and protective polymer layers,the symmetric battery exhibits an impressive cycle life,lasting over 2900 h at a current density of 1 m A·cm^(-2)with a capacity of 1 m A·h·cm^(-2).Moreover,a full battery paired with a vanadium oxide cathode achieves a remarkable capacity retention of 72%even after 500 cycles.展开更多
Up-and-coming high-temperature materials,refractory high entropy alloys,are suffering from lower oxidation resistance,restricting their applications in the aerospace field.In this study,two novel treatments of Al-depo...Up-and-coming high-temperature materials,refractory high entropy alloys,are suffering from lower oxidation resistance,restricting their applications in the aerospace field.In this study,two novel treatments of Al-deposited and remelted were developed to refine the microstructure and enhance the oxidation resistance of refractory high entropy alloy using electron beam freeform fabrication(EBF3).Finer and short-range ordering structures were observed in the remelted sample,whereas the Al-deposited sample showcased the formation of silicide and intermetallic phases.High-temperature cyclic and isothermal oxidation tests at 1000℃ were carried out.The total weight gain after 60 h of cyclic oxidation decreased by 17.49%and 30.46%for the remelted and deposited samples,respectively,compared to the as-cast state.Oxidation kinetics reveal an evident lower mass gain and oxidation rate in the treated samples.A multilayer oxide consisting of TiO_(2)+Al_(2)O_(3)+SiO_(2)+AlNbO_(4) was studied for its excellent oxidation resistance.The oxidation behavior of rutile,corundum and other oxides was analyzed using first principles calculations and chemical defect analysis.Overall,this research,which introduces novel treatments,offers promising insights for enhancing the inherent oxidation resistance of refractory high entropy alloys.展开更多
In order to strengthen the face-centered-cubic(FCC) type CoCrFeMnNi high entropy alloys(HEAs), different contents of Mo(0–16 at.%, similarly hereinafter) were alloyed. Phase evolution, microstructure,mechanical prope...In order to strengthen the face-centered-cubic(FCC) type CoCrFeMnNi high entropy alloys(HEAs), different contents of Mo(0–16 at.%, similarly hereinafter) were alloyed. Phase evolution, microstructure,mechanical properties and related mechanism of these HEAs were systematically studied. The results show that sigma phase is appeared with addition of Mo, and the volume fraction of it increases gradually from 0 to 66% with increasing Mo content. It is found that Mo is enriched in sigma phase, which indicates that Mo element is beneficial to form sigma phase. Compressive testing shows that the yield strength of the alloys increases gradually from 216 to 765 MPa, while the fracture strain decreases from 50%(no fracture) to 19% with increasing of Mo. The alloy exhibits the best compressive performance when Mo content reaches 11%, the yield strength, fracture strength and fracture strain are 547 MPa, 2672 MPa and44% respectively. The increased volume fraction of sigma phase plays an important role in improving the compressive strength of(CoCrFeMnNi)_(100-x)Mo_xHEAs.展开更多
CoCrFeNiCu(equiatomic ratio)samples(?8 mm)were directionally solidified at different velocities(10,30,60 and 100μm/s)to investigate the relationship between solidification velocity and microstructure formation,Cu mic...CoCrFeNiCu(equiatomic ratio)samples(?8 mm)were directionally solidified at different velocities(10,30,60 and 100μm/s)to investigate the relationship between solidification velocity and microstructure formation,Cu micro-segregation as well as tensile properties.The results indicate that the morphology of the solid-liquid(S-L)interface evolves from convex to planar and then to concave with the increase of solidification velocity.Meanwhile,the primary and the secondary dendritic arm spacings decrease from100μm to 10μm and from 20μm to 5μm,respectively.They are mainly influenced by the axial heat transfer and grain competition growth.During directional solidification,element Cu is repelled from the FCC phase and accumulates in the liquid owe to its positive mixing enthalpy with other elements.Tensile testing results show that the ultimate tensile strength(UTS)gradually increases from 400 MPa to 450 MPa,and the strain of the specimen prepared at the velocity of 60μm/s is higher than those of others.The fracture mode of all specimens is the mixed fracture containing both ductile fracture and brittle fracture,in which ductile fracture plays a fundamental role.In addition,the brittle fracture is induced by Cu segregation.The improvement of UTS is resulted from columnar grain boundary strengthening.展开更多
Corrosion resistance of titanium(Ti)alloys is closely connected with their microstructure which can be adjusted and controlled via different annealing schemes.Herein,we systematically investigate the specific effects ...Corrosion resistance of titanium(Ti)alloys is closely connected with their microstructure which can be adjusted and controlled via different annealing schemes.Herein,we systematically investigate the specific effects of annealing on the corrosion performance of Ti-6 Al-3 Nb-2 Zr-1 Mo(Ti80)alloy in 3.5 wt.%NaCl and 5 M HCl solutions,respectively,based on open circuit potential(OCP),potentiodynamic polarization,electrochemical impedance spectroscopy(EIS),static immersion tests and surface analysis.Results indicate that increasing annealing tempe rature endows Ti80 alloy with a higher volume fraction ofβphase and finerαphase,which in turn improves its corrosion resistance.Surface characterization demonstrates thatβphase is more resistant to corrosion thanαphase owing to a higher content of Nb,Mo,and Zr in the former;additionally,the decreased thickness of a phase alleviates segregation of elements to further restrain the micro-galvanic couple effects betweenαandβphases.Meanwhile,the influential mechanisms of environmental conditions on corrosion of Ti80 alloy are discussed in detail.As the formation of a highly compact and stable oxide film on surface,annealed Ti80 alloys exhibit a low corrosion current density(10^(-6)A/cm^(2))and high polarization impedance(10^(6)Ω·cm^(2))in 3.5 wt.%NaCl solution.However,they suffer severe corrosion in 5 M HCl solution,resulting from the breakdown of native oxide films(the conversion of TiO_(2)to aqueous Ti^(3+)),active dissolution of substrate Ti to aqueous Ti^(3+)and existence of micro-galvanic couple effects.Those findings could provide new insights to designing Ti alloys with high-corrosion resistance through microstructural optimization.展开更多
Investigation about the corrosion behavior of Ti alloys in different ambient environment is of great significance for their practical application.Herein,we systematically investigate the corrosion behavior of a newfou...Investigation about the corrosion behavior of Ti alloys in different ambient environment is of great significance for their practical application.Herein,we systematically investigate the corrosion behavior of a newfound Ti-6 Al-3 Nb-2 Zr-1 Mo(Ti80)alloy in hydrochloric acid(HCl)ranging from 1.37 to 7 M,and temperature ranging from 25 to 55℃,by means of electrochemical measurements,static immersion tests and surface analysis.Results manifest that increasing either HCl concentration or temperature can accelerate the corrosion of Ti80 alloy via promoting the breakdown of native protective oxide film and then further facilitating the active dissolution of Ti80 matrix.According to potentiodynamic polarization curves,Ti80 alloy displays a spontaneous passive behavior in 1.37 M HCl at 25℃,compared to a typical active-passive behavior under the other conditions.As indicated by cathodic Tafel slope,the rate determining step for cathodic hydrogen evolution reaction is likely the discharge reaction step.The apparent activation energies obtained from corrosion current density and maximum anodic current density for Ti80 alloy in 5 M HCl solution are 62.4 and 55.6 kJ mol-1,respectively,which signifies that the rate determining step in the corrosion process of Ti80 alloy is mainly determined by surface-chemical reaction rather than diffusion.Besides,the electrochemical impedance spectroscopy tests demonstrate that a stable and compact oxide film exists in 1.37 M HCl at 25℃,whereas a porous corrosion product film forms under the other conditions.Overall,the critical HCl concentration at which Ti80 alloy can maintain passivation at 25℃can be determined as a value between 1.37 and 3 M.Furthermore,the corroded surface morphology characterization reveals that equiaxedαphase is more susceptible to corrosion compared to intergranularβphase due to a lower content of Nb,Mo,and Zr in the former.展开更多
Ultrasonic treatment has great contributions on modifying the morphology,dimension and distribution of constituent phases during solidification,which serve as dominate factors influencing the hydrogen storage performa...Ultrasonic treatment has great contributions on modifying the morphology,dimension and distribution of constituent phases during solidification,which serve as dominate factors influencing the hydrogen storage performance of Mg-based alloys.In this research,ultrasonic treatment is utilized as a novel method to enhance the de-/hydriding properties of Mg-2Ni(at.%)alloy.Due to ultrasonic treatment,the microstructure of as-cast alloy is significantly refined and homogenized.Ascribing to the increased eutectic boundaries and shortened distance insideα-Mg for hydrogen atoms diffusion,the hydrogen uptake capacities and isothermal de-/hydriding rates improve effectively,especially at lower temperature.The peak desorption temperature reduces from 392.99°C to 345.56°C,and the dehydriding activation energy decreases from 101.93 k J mol^(-1)to 88.65 k J mol^(-1).Weakened hysteresis of plateau pressures and slightly optimized thermodynamics are determined from the pressure-composition isotherms.Owing to the refined primary Mg,a larger amount of hydrogen with the higher hydriding proportion is absorbed in the first stage when hydrides nucleate in eutectic region and grow on primary Mg periphery subsequently before MgH2colonies impinging,resulting in the enhancement of hydrogenation rates and capacities.展开更多
ZL205A alloys tend to form disordered and defective microstructure due to the large solidification intervals and multi-phase.Accordingly,finding ways to effectively optimize the microstructure and mechanical performan...ZL205A alloys tend to form disordered and defective microstructure due to the large solidification intervals and multi-phase.Accordingly,finding ways to effectively optimize the microstructure and mechanical performance is of great significance.In this regard,the coupling of travelling magnetic fields(TMF)with unidirectional solidification was used to continuously regulate the mushy zones of ZL205A alloys.Additionally,experiments are combined with simulations to systematically reveal the mechanisms on the optimizations at each stage of solidification process.Current findings demonstrate that different directional strong melt flows generated by TMF are responsible for these optimizations.Additionally,the effects of TMF on microstructure are different at each stage of solidification process.Specifically,downward TMF coupled with unidirectional solidification can refine and uniform the microstructure,decrease the formation of precipitation,promote the growth consistency of matrix phaseα-Al growing along the<001>crystal orientation,reduce the secondary dendrites and overlaps between dendrites,eliminate the shrinkage defects,and increase the ultimate tensile strength,yield strength,elongation and hardness from 198.3 MPa,102.2 MPa,7.5%and 82.3 kg mm^(-2)without TMF to 225.5 MPa,116.1 MPa,13.6%and 105.2 kg mm^(-2).Contrastively,although upward TMF can reduce Al3Ti and refineα-Al,it increases the formation of Al6Mn,Al2Cu,secondary dendrites,overlaps between dendrites,and shrinkage defects;then it deflects and disorders the growth ofα-Al,further to decrease the overall performance of alloys.展开更多
To improve the strength and ductility of Ti Al alloys by second phase, Ti46 Al4 Nb1 Mo alloys doped with different B content(0.4%, 0.8%, 1.2%, 1.6% and 2.0%, atomic percent, hereafter in at.%, referred to as TNMx B) w...To improve the strength and ductility of Ti Al alloys by second phase, Ti46 Al4 Nb1 Mo alloys doped with different B content(0.4%, 0.8%, 1.2%, 1.6% and 2.0%, atomic percent, hereafter in at.%, referred to as TNMx B) were prepared. Macro/microstructure evolution, mechanical properties and deformation mechanisms of the alloys were studied systematically. Results showed that the microstructure of TNM-0.4 B and TNM-0.8 B alloy remained columnar dendrites, and the secondary dendritic arms of columnar grains were more obvious. When the content of B is 1.2%, the columnar dendrites transformed to equiaxed grains, and theα2/γ lamellae colony size was further refined in TNM-1.6 B and TNM-2.0 B alloy. The morphologies and kinds of the borides were changed with increasing B content, XRD results showed that Ti B phase appeared with 1.6%B content, and both Ti B and Ti B2 phase formed in TNM-2.0 B alloy. There were straight and curved Ti B phases located around grain boundaries in TNM-0.4 B and TNM-0.8 B alloy, and when the content of B increased to 1.2%, the curved Ti B phases were reduced, while the tiny and straight Ti B phases increased. With further increasing B content to 1.6% and 2.0%, the tiny and straight Ti B phases were coarser. Compressive testing results showed that the mechanical properties of the TNM alloy were enhanced with increasing B content. The maximum strength and strain of TNM alloy were 2339 MPa and33.7% with 1.6% B addition. The compressive strength and strain were mainly enhanced via refinement of lamellar colony and formation of Ti B, and it is found that pile-up of dislocations and deformed twins promoted by Ti B are predominant in improving the mechanical properties of TNM alloys with higher strength and strain.展开更多
Alloys with large solidification intervals are prone to issues from the disordered growth and defect formation;accordingly, finding ways to effectively optimize the microstructure, further to improve the mechanical pr...Alloys with large solidification intervals are prone to issues from the disordered growth and defect formation;accordingly, finding ways to effectively optimize the microstructure, further to improve the mechanical properties is of great importance. To this end, we couple travelling magnetic fields with sequential solidification to continuously regulate the mushy zones of Al-Cu-based alloys with large solidification intervals. Moreover, we combine experiments with simulations to comprehensively analyze the mechanisms on the optimization of microstructure and properties. Our results indicate that only downward travelling magnetic fields coupled with sequential solidification can obtain the refined and uniform microstructure, and promote the growth of matrix phase -Al along the direction of temperature gradient.Additionally, the secondary dendrites and precipitates are reduced, while the solute partition coefficient and solute solid-solubility are raised. Ultimately, downward travelling magnetic fields can increase the ultimate tensile strength, yield strength, elongation and hardness from 196.2 MPa, 101.2 MPa, 14.5 % and85.1 kg mm-2 without travelling magnetic fields to 224.1 MPa, 114.5 MPa, 17.1 % and 102.1 kg mm-2,and improve the ductility of alloys. However, upward travelling magnetic fields have the adverse effects on microstructural evolution, and lead to a reduction in the performance and ductility. Our findings demonstrate that long-range directional circular flows generated by travelling magnetic fields directionally alter the transformation and redistribution of solutes and temperature, which finally influences the solidification behavior and performance. Overall, our research present not only an innovative method to optimize the microstructures and mechanical properties for alloys with large solidification intervals,but also a detailed mechanism of travelling magnetic fields on this optimization during the sequential solidification.展开更多
Porosity is a major casting defect in alloys with large solidification intervals due to the disordered microstructure and broad mushy zones,which decreases badly the mechanical performance.Hence,finding ways to effect...Porosity is a major casting defect in alloys with large solidification intervals due to the disordered microstructure and broad mushy zones,which decreases badly the mechanical performance.Hence,finding ways to effectively reduce the porosity,further to optimize microstructure and mechanical performance is of great significance.In this regard,the Al-Cu-based alloys with large solidification intervals are continuously processed by coupling the travelling magnetic fields(TMF)with sequential solidification.Additionally,experiments combined with simulations are utilized to comprehensively analyze the mechanism of TMF on the reduction in porosity,including shrinkage porosity and gas porosity,from different perspectives.Current findings determine that downward TMF can effectually optimize together the porosity,microstructure and performance,by inducing the strong long-range directional melt flows,stabilizing the mushy zones,and optimizing the feeding channels and exhaust paths,as well as increasing the driving force of degassing process.Eventually,downward TMF can increase the ultimate tensile strength,yield strength,elongation and hardness from 175.2 MPa,87.5 MPa,13.3%and 80.2 kg mm^(-2) without TMF to 218.6 MPa,109.3 MPa,15.6%and 95.5 kg mm^(-2),while reduce the total porosity from0.95%to 0.18%.However,Up-TMF exerts negative effects on the optimization of porosity,microstructure and performance due to the opposite strong directional magnetic force and melt flows.Overall,our study provides an effective way to optimize together the porosity,microstructure and mechanical performance,and reveals their relationship,as well as details the relevant mechanisms of TMF on the porosity reduction from different perspectives.展开更多
Nb has a positive effect on improving the mechanical properties of metal materials, and it is expected to strengthen CoCrCuFeNi high-entropy alloys （HEAs） with outstanding ductility and relatively weak strength. In ...Nb has a positive effect on improving the mechanical properties of metal materials, and it is expected to strengthen CoCrCuFeNi high-entropy alloys （HEAs） with outstanding ductility and relatively weak strength. In this paper, the alloying effects of Nb on the microstructural evolution and the mechanical properties of the （CoCrCuFeNi）100-xNbx HEA were investigated systematically. The result shows that Nb promotes the phase transition from FCC （face-centered cubic） to Laves phase, and the volume fractions of Laves phase increase from 0% to 58.2% as the Nb content increases, Compressive testing shows that the addition of Nb has a positive effect on improving the strength of CoCrCuFeNi HEA. The compressive yield strength of （CoCrCuFeNi）100-xNbx HEAs increases from 338 MPa to 1322 MPa and the fracture strain gradually reduces from 60.0% （no fracture） to 8.1% as the Nb content increases from 0 to 16 at.%. The volume fraction increase of hard Laves phase is the key factor for the strength increase, and the reduction of the VEC （valence electron concentration） value induced by the addition of Nb is beneficial for the increase of the Laves phase content in these alloys.展开更多
In order to improve the intrinsic brittleness of TiAl alloys,Ti_(2)AlNb alloys with outstanding ductility and toughness at room temperature,and good high-temperature performance are competitive candidates in construct...In order to improve the intrinsic brittleness of TiAl alloys,Ti_(2)AlNb alloys with outstanding ductility and toughness at room temperature,and good high-temperature performance are competitive candidates in constructing the TiAl-based laminated composites.In this work,TiAl/Ti_(2)AlNb laminated composites are successfully synthesized by vacuum hot pressing combined with the foil-foil(sheet)metallurgy.Under the pressure of 65 MPa,different holding time and temperature of hot pressing are tried and the optimized fabrication parameter is acquired as 1050℃/120 min/65 MPa.Along with the changes of processing parameters,the defect,microstructure,interface,phase transformation and the corresponding mechanical properties are detailly discussed.The results show that the TiAl/Ti_(2)AlNb laminated composite fabricated at 1050℃ for 2 h achieves a good metallurgical interface bonding.The corresponding interface microstructure is composed of region I and region II.The region I consists of O,α_(2)and B2/βphase,and region II is made up ofα2.Subsequently,the tensile tests indicate that the composite synthesized at 1050℃ for 2 h possesses a maximum strength of 812 MPa and a total elongation of 1.31%at room temperature,and a strength of 539.71 MPa and the highest total elongation of 10.34%at 750℃.The well synergistic deformation ability between the interface and the two base alloys endows the composite an excellent tensile performance.Moreover,the composite processed at 1050℃ for 2 h behaves the best fracture toughness in both arrester orientation and divider orientation with the value of 32.6 MPa.m^(1/2)and 30.1 MPa.m^(1/2),respectively.The Ti_(2)AlNb alloy in the laminated structure effectively release the stress around the crack tip and plays a role in toughening.Further,crack deflection,crack bridging,crack blunting and fragmentation also make contributions to enhance the fracture toughness of the laminated composites.展开更多
This work intends to manipulate the internal flow units in Zr_(55)Cu_(30)Ni_(5)Al_(10)bulk-metallic glasses(BMGs)through plasma-assisted hydrogenation to generate a positive microalloying effect on plasticity.Based on...This work intends to manipulate the internal flow units in Zr_(55)Cu_(30)Ni_(5)Al_(10)bulk-metallic glasses(BMGs)through plasma-assisted hydrogenation to generate a positive microalloying effect on plasticity.Based on the cooperative shear model theory,serration-flow statistics during nanoindentation loading and creep tests during the holding stage were used to analyze the influence of hydrogen on the behavior of flow units in BMGs.Experimental observations showed that the hydrogen in the Zr_(55)Cu_(30)Ni_(5)Al_(10)BMGs caused mechanical softening,plasticity improvement,and structural relaxation.Analysis also showed that the average volume,size,and activation energy of internal flow units in the BMGs all increased as a result of the increase in the hydrogen content.The hydrogenation in the BMGs was found to lead to a prolifera-tion of shear bands,which promoted plasticity.The aggregation of these internal flow units reduced the stress required for plastic deformation through shear bands,ultimately causing softening and structural relaxation.展开更多
Comparative studies on Zr35Cu65and Zr65Cu35amorphous systems were performed using molecular dynamic simulations to explore whether their hydrogenated mechanical behavior depends on the content of hydride-forming eleme...Comparative studies on Zr35Cu65and Zr65Cu35amorphous systems were performed using molecular dynamic simulations to explore whether their hydrogenated mechanical behavior depends on the content of hydride-forming elements.Although both of them present an increased strength and ductility after hydrogen microalloying,we observe the improved mechanical behavior for Zr35Cu65is more pronounced than that for Zr65Cu35.In these two samples,the distribution of configurational potential energy and flexibility volume respectively follows a similar H-induced variation tendency;all of the hydrogenated alloys not just have more stable atoms with smaller flexibility volume,but possess a larger fraction of readily activated atoms.However,the atomic-scale details,based on the local"gradient atomic packing structure"model,indicate minor additions of hydrogen can promote more"soft spots"along with more strengthened"backbones"in the low-Zr alloy than that in the high-Zr sample,which endows the former with much higher strength and deformability after hydrogen microalloying.We regard this finding as a further step forward to distilling the tell-tale metrics of the H-dependent mechanical behavior observed in Zr-based metallic glasses.展开更多
How to control melt composition is the key for getting high quality alloy melt. The paper made the following efforts: (1) The activity coefficients in Ti-15-3 melt have been calculated. (2) Taking advantage of the act...How to control melt composition is the key for getting high quality alloy melt. The paper made the following efforts: (1) The activity coefficients in Ti-15-3 melt have been calculated. (2) Taking advantage of the activity coefficients, the evaporation losses of components in Ti-15-3 melt during ISM process have been studied. The calculated results show that there is a critical vacuum degree (about 1.33 Pa) during melting process.展开更多
“Hydrogen in metallic glasses”has become a popular topic for material scientists,yet few studies focus on the atomic⁃scale details.Herein,by utilizing molecular dynamic simulations,the changes on the atomic structur...“Hydrogen in metallic glasses”has become a popular topic for material scientists,yet few studies focus on the atomic⁃scale details.Herein,by utilizing molecular dynamic simulations,the changes on the atomic structure of Cu50Zr50 metallic glasses after melt hydrogenation were systematically analyzed,with the aim of understanding the differences of mechanical behavior between these amorphous alloys.The simulated analyses indicate that the hydrogenated samples become more compact than the H⁃free one,but the fraction of the dominant coordination polyhedra with higher degree of local fivefold symmetry significantly decreases accompanied by the addition of H atoms.Accordingly,melt hydrogenation can induce much more local“soft spots”in metallic glasses to alleviate the degree of strain localization during deformation,i.e.,it has a positive influence on the deformability of glassy alloys in agreement with experimental results.展开更多
In order to refine microstructure grains and improve mechanical properties of TiAl alloys,Ti44Al(at.%)alloy was rapidly solidified by melt spinning under different cooling rates.Microstructure and microhardness of the...In order to refine microstructure grains and improve mechanical properties of TiAl alloys,Ti44Al(at.%)alloy was rapidly solidified by melt spinning under different cooling rates.Microstructure and microhardness of the alloy before and after rapid solidification were investigated.XRD results show that the ratio ofα2 phase in binary alloy increased with the cooling rates,which is caused by moreαphases directly transforming toα2 phases.Grain morphology changed from long dendrite to the mixture of equiaxed and dendrite to equiaxed with the increase of cooling rates.The grain size was refined from 200-600μm of as⁃cast to 18μm of the alloy cooled at 4.9×10^5 K/s,which is caused by the undercooling induced from rapid solidification.Lamellar spacing was decreased from 4.5μm of as⁃cast to 1.1μm by rapid solidification.With the increase of cooling rate,the content ofα2 phase increased andγphase decreased gradually.Rapid solidification can reduce the segregation of elements.The microhardness was improved from 247 HV to 556 HV,which results from grain refinement strengthening,reduction of lamellar spacing,and more content ofα2 phase.展开更多
Using direct finite difference method, a numerical model for simulating the temperature field in the charge during induction skull melting (ISM) has been developed. On the basis of the model, the temperature field in ...Using direct finite difference method, a numerical model for simulating the temperature field in the charge during induction skull melting (ISM) has been developed. On the basis of the model, the temperature field in Ti- 47Ni-9Nb ingot has been calculated under various melting conditions. Finally, the processing parameters (melting power, melting-down time and the final melt temperature) have been optimized.展开更多
The hidden order of atomic packing in amorphous structures and how this may provide the origin of plastic events have long been a goal in the understanding of plastic deformation in metallic glasses.To pursue this iss...The hidden order of atomic packing in amorphous structures and how this may provide the origin of plastic events have long been a goal in the understanding of plastic deformation in metallic glasses.To pursue this issue,we employ here molecular dynamic simulations to create three-dimensional models for a few metallic glasses where,based on the geometrical frustration of the coordination polyhedra,we classify the atoms in the amorphous structure into six distinct species,where“gradient atomic packing structure”exists.The local structure in the amorphous state can display a gradual transition from loose stacking to dense stacking of atoms,followed by a gradient evolution of atomic performance.As such,the amorphous alloy specifically comprises three discernible regions:solid-like,transition,and liquid-like regions,each one possessing different types of atoms.We also demonstrate that the liquid-like atoms correlate most strongly with fertile sites for shear transformation,the transition atoms take second place,whereas the solid-like atoms contribute the least because of their lowest correlation level with the liquid-like atoms.Unlike the“geometrically unfavored motifs”model which fails to consider the role of medium-range order,our model gives a definite structure for the so-called“soft spots”,that is,a combination of liquid-like atoms and their neighbors,in favor of quantifying and comparing their number between different metallic glasses,which can provide a rational explanation for the unique mechanical behavior of metallic glasses.展开更多
基金financially supported by the Science and Technology Development Project of Henan Province,China(No.242102241042)the Joint Fund of Henan Province Science and Technology R&D Program(No.225200810093)+1 种基金the Startup Research of Henan Academy of Sciences(No.231817001)the Key Innovation Projects for Postgraduates of Henan Academy of Sciences(No.24331712)。
文摘Aqueous zinc-ion batteries are regarded as promising electrochemical energy-storage systems for various applications because of their high safety,low costs,and high capacities.However,dendrite formation and side reactions during zinc plating or stripping greatly reduce the capacity and cycle life of a battery and subsequently limit its practical application.To address these issues,we modified the surface of a zinc anode with a functional bilayer composed of zincophilic Cu and flexible polymer layers.The zincophilic Cu interfacial layer was prepared through CuSO_(4)solution pretreatment to serve as a nucleation site to facilitate uniform Zn deposition.Meanwhile,the polymer layer was coated onto the Cu interface layer to serve as a protective layer that would prevent side reactions between zinc and electrolytes.Benefiting from the synergistic effect of the zincophilic Cu and protective polymer layers,the symmetric battery exhibits an impressive cycle life,lasting over 2900 h at a current density of 1 m A·cm^(-2)with a capacity of 1 m A·h·cm^(-2).Moreover,a full battery paired with a vanadium oxide cathode achieves a remarkable capacity retention of 72%even after 500 cycles.
基金supported by the National Key Research and Development Program of China(Grant No.2022YFF0609000)National Natural Science Foundation of China(Grant Nos.52171034 and 52101037)Postdoctoral Fellowship Program of CPSFara(No.GZB20230944).
文摘Up-and-coming high-temperature materials,refractory high entropy alloys,are suffering from lower oxidation resistance,restricting their applications in the aerospace field.In this study,two novel treatments of Al-deposited and remelted were developed to refine the microstructure and enhance the oxidation resistance of refractory high entropy alloy using electron beam freeform fabrication(EBF3).Finer and short-range ordering structures were observed in the remelted sample,whereas the Al-deposited sample showcased the formation of silicide and intermetallic phases.High-temperature cyclic and isothermal oxidation tests at 1000℃ were carried out.The total weight gain after 60 h of cyclic oxidation decreased by 17.49%and 30.46%for the remelted and deposited samples,respectively,compared to the as-cast state.Oxidation kinetics reveal an evident lower mass gain and oxidation rate in the treated samples.A multilayer oxide consisting of TiO_(2)+Al_(2)O_(3)+SiO_(2)+AlNbO_(4) was studied for its excellent oxidation resistance.The oxidation behavior of rutile,corundum and other oxides was analyzed using first principles calculations and chemical defect analysis.Overall,this research,which introduces novel treatments,offers promising insights for enhancing the inherent oxidation resistance of refractory high entropy alloys.
基金supported by the Fund of State Key Laboratory of Advanced Welding and Joining,and the National Natural Science Foundation of China (No.51741404)
文摘In order to strengthen the face-centered-cubic(FCC) type CoCrFeMnNi high entropy alloys(HEAs), different contents of Mo(0–16 at.%, similarly hereinafter) were alloyed. Phase evolution, microstructure,mechanical properties and related mechanism of these HEAs were systematically studied. The results show that sigma phase is appeared with addition of Mo, and the volume fraction of it increases gradually from 0 to 66% with increasing Mo content. It is found that Mo is enriched in sigma phase, which indicates that Mo element is beneficial to form sigma phase. Compressive testing shows that the yield strength of the alloys increases gradually from 216 to 765 MPa, while the fracture strain decreases from 50%(no fracture) to 19% with increasing of Mo. The alloy exhibits the best compressive performance when Mo content reaches 11%, the yield strength, fracture strength and fracture strain are 547 MPa, 2672 MPa and44% respectively. The increased volume fraction of sigma phase plays an important role in improving the compressive strength of(CoCrFeMnNi)_(100-x)Mo_xHEAs.
基金supported financially by the National Natural Science Foundation of China(Nos.51825401and51741404)the State Key Laboratory of Advanced Welding and Joining.
文摘CoCrFeNiCu(equiatomic ratio)samples(?8 mm)were directionally solidified at different velocities(10,30,60 and 100μm/s)to investigate the relationship between solidification velocity and microstructure formation,Cu micro-segregation as well as tensile properties.The results indicate that the morphology of the solid-liquid(S-L)interface evolves from convex to planar and then to concave with the increase of solidification velocity.Meanwhile,the primary and the secondary dendritic arm spacings decrease from100μm to 10μm and from 20μm to 5μm,respectively.They are mainly influenced by the axial heat transfer and grain competition growth.During directional solidification,element Cu is repelled from the FCC phase and accumulates in the liquid owe to its positive mixing enthalpy with other elements.Tensile testing results show that the ultimate tensile strength(UTS)gradually increases from 400 MPa to 450 MPa,and the strain of the specimen prepared at the velocity of 60μm/s is higher than those of others.The fracture mode of all specimens is the mixed fracture containing both ductile fracture and brittle fracture,in which ductile fracture plays a fundamental role.In addition,the brittle fracture is induced by Cu segregation.The improvement of UTS is resulted from columnar grain boundary strengthening.
基金supported by the National Key Research and Development Program of China(2016YFB0301201)the Yunnan Rare Metal Materials Genetic Engineering Project(2018ZE013)the National Natural Science Foundation of China(51425402 and 51671073)。
文摘Corrosion resistance of titanium(Ti)alloys is closely connected with their microstructure which can be adjusted and controlled via different annealing schemes.Herein,we systematically investigate the specific effects of annealing on the corrosion performance of Ti-6 Al-3 Nb-2 Zr-1 Mo(Ti80)alloy in 3.5 wt.%NaCl and 5 M HCl solutions,respectively,based on open circuit potential(OCP),potentiodynamic polarization,electrochemical impedance spectroscopy(EIS),static immersion tests and surface analysis.Results indicate that increasing annealing tempe rature endows Ti80 alloy with a higher volume fraction ofβphase and finerαphase,which in turn improves its corrosion resistance.Surface characterization demonstrates thatβphase is more resistant to corrosion thanαphase owing to a higher content of Nb,Mo,and Zr in the former;additionally,the decreased thickness of a phase alleviates segregation of elements to further restrain the micro-galvanic couple effects betweenαandβphases.Meanwhile,the influential mechanisms of environmental conditions on corrosion of Ti80 alloy are discussed in detail.As the formation of a highly compact and stable oxide film on surface,annealed Ti80 alloys exhibit a low corrosion current density(10^(-6)A/cm^(2))and high polarization impedance(10^(6)Ω·cm^(2))in 3.5 wt.%NaCl solution.However,they suffer severe corrosion in 5 M HCl solution,resulting from the breakdown of native oxide films(the conversion of TiO_(2)to aqueous Ti^(3+)),active dissolution of substrate Ti to aqueous Ti^(3+)and existence of micro-galvanic couple effects.Those findings could provide new insights to designing Ti alloys with high-corrosion resistance through microstructural optimization.
基金the National Key Research and Development Program of China(No.2016YFB0301201)the Yunnan Rare Metal Materials Genetic Engineering Project(No.2018ZE013)the National Natural Science Foundation of China(Nos.51425402 and 51671073)。
文摘Investigation about the corrosion behavior of Ti alloys in different ambient environment is of great significance for their practical application.Herein,we systematically investigate the corrosion behavior of a newfound Ti-6 Al-3 Nb-2 Zr-1 Mo(Ti80)alloy in hydrochloric acid(HCl)ranging from 1.37 to 7 M,and temperature ranging from 25 to 55℃,by means of electrochemical measurements,static immersion tests and surface analysis.Results manifest that increasing either HCl concentration or temperature can accelerate the corrosion of Ti80 alloy via promoting the breakdown of native protective oxide film and then further facilitating the active dissolution of Ti80 matrix.According to potentiodynamic polarization curves,Ti80 alloy displays a spontaneous passive behavior in 1.37 M HCl at 25℃,compared to a typical active-passive behavior under the other conditions.As indicated by cathodic Tafel slope,the rate determining step for cathodic hydrogen evolution reaction is likely the discharge reaction step.The apparent activation energies obtained from corrosion current density and maximum anodic current density for Ti80 alloy in 5 M HCl solution are 62.4 and 55.6 kJ mol-1,respectively,which signifies that the rate determining step in the corrosion process of Ti80 alloy is mainly determined by surface-chemical reaction rather than diffusion.Besides,the electrochemical impedance spectroscopy tests demonstrate that a stable and compact oxide film exists in 1.37 M HCl at 25℃,whereas a porous corrosion product film forms under the other conditions.Overall,the critical HCl concentration at which Ti80 alloy can maintain passivation at 25℃can be determined as a value between 1.37 and 3 M.Furthermore,the corroded surface morphology characterization reveals that equiaxedαphase is more susceptible to corrosion compared to intergranularβphase due to a lower content of Nb,Mo,and Zr in the former.
基金supported by National Key Research and Development Program of China(2017YFA0403804)National Natural Science Foundation of China(51825401)
文摘Ultrasonic treatment has great contributions on modifying the morphology,dimension and distribution of constituent phases during solidification,which serve as dominate factors influencing the hydrogen storage performance of Mg-based alloys.In this research,ultrasonic treatment is utilized as a novel method to enhance the de-/hydriding properties of Mg-2Ni(at.%)alloy.Due to ultrasonic treatment,the microstructure of as-cast alloy is significantly refined and homogenized.Ascribing to the increased eutectic boundaries and shortened distance insideα-Mg for hydrogen atoms diffusion,the hydrogen uptake capacities and isothermal de-/hydriding rates improve effectively,especially at lower temperature.The peak desorption temperature reduces from 392.99°C to 345.56°C,and the dehydriding activation energy decreases from 101.93 k J mol^(-1)to 88.65 k J mol^(-1).Weakened hysteresis of plateau pressures and slightly optimized thermodynamics are determined from the pressure-composition isotherms.Owing to the refined primary Mg,a larger amount of hydrogen with the higher hydriding proportion is absorbed in the first stage when hydrides nucleate in eutectic region and grow on primary Mg periphery subsequently before MgH2colonies impinging,resulting in the enhancement of hydrogenation rates and capacities.
基金the National Key Research and Development Program of China(No.2017YFA0403804)the National Natural Science Foundation of China(Nos.51425402,51671073)。
文摘ZL205A alloys tend to form disordered and defective microstructure due to the large solidification intervals and multi-phase.Accordingly,finding ways to effectively optimize the microstructure and mechanical performance is of great significance.In this regard,the coupling of travelling magnetic fields(TMF)with unidirectional solidification was used to continuously regulate the mushy zones of ZL205A alloys.Additionally,experiments are combined with simulations to systematically reveal the mechanisms on the optimizations at each stage of solidification process.Current findings demonstrate that different directional strong melt flows generated by TMF are responsible for these optimizations.Additionally,the effects of TMF on microstructure are different at each stage of solidification process.Specifically,downward TMF coupled with unidirectional solidification can refine and uniform the microstructure,decrease the formation of precipitation,promote the growth consistency of matrix phaseα-Al growing along the<001>crystal orientation,reduce the secondary dendrites and overlaps between dendrites,eliminate the shrinkage defects,and increase the ultimate tensile strength,yield strength,elongation and hardness from 198.3 MPa,102.2 MPa,7.5%and 82.3 kg mm^(-2)without TMF to 225.5 MPa,116.1 MPa,13.6%and 105.2 kg mm^(-2).Contrastively,although upward TMF can reduce Al3Ti and refineα-Al,it increases the formation of Al6Mn,Al2Cu,secondary dendrites,overlaps between dendrites,and shrinkage defects;then it deflects and disorders the growth ofα-Al,further to decrease the overall performance of alloys.
基金supported by the National Natural Science Foundation of China (No. 51825401, 51971121)the China Postdoctoral Science Foundation (2019TQ0077, 2019M660071)。
文摘To improve the strength and ductility of Ti Al alloys by second phase, Ti46 Al4 Nb1 Mo alloys doped with different B content(0.4%, 0.8%, 1.2%, 1.6% and 2.0%, atomic percent, hereafter in at.%, referred to as TNMx B) were prepared. Macro/microstructure evolution, mechanical properties and deformation mechanisms of the alloys were studied systematically. Results showed that the microstructure of TNM-0.4 B and TNM-0.8 B alloy remained columnar dendrites, and the secondary dendritic arms of columnar grains were more obvious. When the content of B is 1.2%, the columnar dendrites transformed to equiaxed grains, and theα2/γ lamellae colony size was further refined in TNM-1.6 B and TNM-2.0 B alloy. The morphologies and kinds of the borides were changed with increasing B content, XRD results showed that Ti B phase appeared with 1.6%B content, and both Ti B and Ti B2 phase formed in TNM-2.0 B alloy. There were straight and curved Ti B phases located around grain boundaries in TNM-0.4 B and TNM-0.8 B alloy, and when the content of B increased to 1.2%, the curved Ti B phases were reduced, while the tiny and straight Ti B phases increased. With further increasing B content to 1.6% and 2.0%, the tiny and straight Ti B phases were coarser. Compressive testing results showed that the mechanical properties of the TNM alloy were enhanced with increasing B content. The maximum strength and strain of TNM alloy were 2339 MPa and33.7% with 1.6% B addition. The compressive strength and strain were mainly enhanced via refinement of lamellar colony and formation of Ti B, and it is found that pile-up of dislocations and deformed twins promoted by Ti B are predominant in improving the mechanical properties of TNM alloys with higher strength and strain.
基金supported by the National Key Research and Development Program of China[2017YFA0403804]National Natural Science Foundation of China[51425402,51671073]。
文摘Alloys with large solidification intervals are prone to issues from the disordered growth and defect formation;accordingly, finding ways to effectively optimize the microstructure, further to improve the mechanical properties is of great importance. To this end, we couple travelling magnetic fields with sequential solidification to continuously regulate the mushy zones of Al-Cu-based alloys with large solidification intervals. Moreover, we combine experiments with simulations to comprehensively analyze the mechanisms on the optimization of microstructure and properties. Our results indicate that only downward travelling magnetic fields coupled with sequential solidification can obtain the refined and uniform microstructure, and promote the growth of matrix phase -Al along the direction of temperature gradient.Additionally, the secondary dendrites and precipitates are reduced, while the solute partition coefficient and solute solid-solubility are raised. Ultimately, downward travelling magnetic fields can increase the ultimate tensile strength, yield strength, elongation and hardness from 196.2 MPa, 101.2 MPa, 14.5 % and85.1 kg mm-2 without travelling magnetic fields to 224.1 MPa, 114.5 MPa, 17.1 % and 102.1 kg mm-2,and improve the ductility of alloys. However, upward travelling magnetic fields have the adverse effects on microstructural evolution, and lead to a reduction in the performance and ductility. Our findings demonstrate that long-range directional circular flows generated by travelling magnetic fields directionally alter the transformation and redistribution of solutes and temperature, which finally influences the solidification behavior and performance. Overall, our research present not only an innovative method to optimize the microstructures and mechanical properties for alloys with large solidification intervals,but also a detailed mechanism of travelling magnetic fields on this optimization during the sequential solidification.
基金supported by the National Key Research and Development Program of China [2017YFA0403804]National Natural Science Foundation of China [51425402,51671073]
文摘Porosity is a major casting defect in alloys with large solidification intervals due to the disordered microstructure and broad mushy zones,which decreases badly the mechanical performance.Hence,finding ways to effectively reduce the porosity,further to optimize microstructure and mechanical performance is of great significance.In this regard,the Al-Cu-based alloys with large solidification intervals are continuously processed by coupling the travelling magnetic fields(TMF)with sequential solidification.Additionally,experiments combined with simulations are utilized to comprehensively analyze the mechanism of TMF on the reduction in porosity,including shrinkage porosity and gas porosity,from different perspectives.Current findings determine that downward TMF can effectually optimize together the porosity,microstructure and performance,by inducing the strong long-range directional melt flows,stabilizing the mushy zones,and optimizing the feeding channels and exhaust paths,as well as increasing the driving force of degassing process.Eventually,downward TMF can increase the ultimate tensile strength,yield strength,elongation and hardness from 175.2 MPa,87.5 MPa,13.3%and 80.2 kg mm^(-2) without TMF to 218.6 MPa,109.3 MPa,15.6%and 95.5 kg mm^(-2),while reduce the total porosity from0.95%to 0.18%.However,Up-TMF exerts negative effects on the optimization of porosity,microstructure and performance due to the opposite strong directional magnetic force and melt flows.Overall,our study provides an effective way to optimize together the porosity,microstructure and mechanical performance,and reveals their relationship,as well as details the relevant mechanisms of TMF on the porosity reduction from different perspectives.
基金supported by the National Natural Science Foundation of China (No. 51331005)the National Science Fund for Distinguished Young Scholars (No. 51425402)
文摘Nb has a positive effect on improving the mechanical properties of metal materials, and it is expected to strengthen CoCrCuFeNi high-entropy alloys （HEAs） with outstanding ductility and relatively weak strength. In this paper, the alloying effects of Nb on the microstructural evolution and the mechanical properties of the （CoCrCuFeNi）100-xNbx HEA were investigated systematically. The result shows that Nb promotes the phase transition from FCC （face-centered cubic） to Laves phase, and the volume fractions of Laves phase increase from 0% to 58.2% as the Nb content increases, Compressive testing shows that the addition of Nb has a positive effect on improving the strength of CoCrCuFeNi HEA. The compressive yield strength of （CoCrCuFeNi）100-xNbx HEAs increases from 338 MPa to 1322 MPa and the fracture strain gradually reduces from 60.0% （no fracture） to 8.1% as the Nb content increases from 0 to 16 at.%. The volume fraction increase of hard Laves phase is the key factor for the strength increase, and the reduction of the VEC （valence electron concentration） value induced by the addition of Nb is beneficial for the increase of the Laves phase content in these alloys.
基金supported by Major Special Science and Technology Project of Yunnan Province 202002AB080001-3the National Natural Science Foundation of China(no.51704088)Fundamental Research and Development Program of China(Grant no.JCKY2017205B032)。
文摘In order to improve the intrinsic brittleness of TiAl alloys,Ti_(2)AlNb alloys with outstanding ductility and toughness at room temperature,and good high-temperature performance are competitive candidates in constructing the TiAl-based laminated composites.In this work,TiAl/Ti_(2)AlNb laminated composites are successfully synthesized by vacuum hot pressing combined with the foil-foil(sheet)metallurgy.Under the pressure of 65 MPa,different holding time and temperature of hot pressing are tried and the optimized fabrication parameter is acquired as 1050℃/120 min/65 MPa.Along with the changes of processing parameters,the defect,microstructure,interface,phase transformation and the corresponding mechanical properties are detailly discussed.The results show that the TiAl/Ti_(2)AlNb laminated composite fabricated at 1050℃ for 2 h achieves a good metallurgical interface bonding.The corresponding interface microstructure is composed of region I and region II.The region I consists of O,α_(2)and B2/βphase,and region II is made up ofα2.Subsequently,the tensile tests indicate that the composite synthesized at 1050℃ for 2 h possesses a maximum strength of 812 MPa and a total elongation of 1.31%at room temperature,and a strength of 539.71 MPa and the highest total elongation of 10.34%at 750℃.The well synergistic deformation ability between the interface and the two base alloys endows the composite an excellent tensile performance.Moreover,the composite processed at 1050℃ for 2 h behaves the best fracture toughness in both arrester orientation and divider orientation with the value of 32.6 MPa.m^(1/2)and 30.1 MPa.m^(1/2),respectively.The Ti_(2)AlNb alloy in the laminated structure effectively release the stress around the crack tip and plays a role in toughening.Further,crack deflection,crack bridging,crack blunting and fragmentation also make contributions to enhance the fracture toughness of the laminated composites.
基金supported the National Natural Science Foundation of China(51401129)Natural Science Foundation of Liaoning Province(2019-ZD-0216,20180510056)+2 种基金Foundation of Liaoning Province Education Administration(LQGD2019001)support from the National Science Foundation(DMR1611180 and 1809640)with the program directorssupported by the U.S.Department of Energy,Office of Science,Office of Basic Energy Sciences,Materials Sciences and Engineering Division under Contract No.DEAC02–05-CH11231。
文摘This work intends to manipulate the internal flow units in Zr_(55)Cu_(30)Ni_(5)Al_(10)bulk-metallic glasses(BMGs)through plasma-assisted hydrogenation to generate a positive microalloying effect on plasticity.Based on the cooperative shear model theory,serration-flow statistics during nanoindentation loading and creep tests during the holding stage were used to analyze the influence of hydrogen on the behavior of flow units in BMGs.Experimental observations showed that the hydrogen in the Zr_(55)Cu_(30)Ni_(5)Al_(10)BMGs caused mechanical softening,plasticity improvement,and structural relaxation.Analysis also showed that the average volume,size,and activation energy of internal flow units in the BMGs all increased as a result of the increase in the hydrogen content.The hydrogenation in the BMGs was found to lead to a prolifera-tion of shear bands,which promoted plasticity.The aggregation of these internal flow units reduced the stress required for plastic deformation through shear bands,ultimately causing softening and structural relaxation.
基金National Key Research and Development Program of China2016YFB0301201National Natural Science Foundation of China51425402,51371066,51671073。
文摘Comparative studies on Zr35Cu65and Zr65Cu35amorphous systems were performed using molecular dynamic simulations to explore whether their hydrogenated mechanical behavior depends on the content of hydride-forming elements.Although both of them present an increased strength and ductility after hydrogen microalloying,we observe the improved mechanical behavior for Zr35Cu65is more pronounced than that for Zr65Cu35.In these two samples,the distribution of configurational potential energy and flexibility volume respectively follows a similar H-induced variation tendency;all of the hydrogenated alloys not just have more stable atoms with smaller flexibility volume,but possess a larger fraction of readily activated atoms.However,the atomic-scale details,based on the local"gradient atomic packing structure"model,indicate minor additions of hydrogen can promote more"soft spots"along with more strengthened"backbones"in the low-Zr alloy than that in the high-Zr sample,which endows the former with much higher strength and deformability after hydrogen microalloying.We regard this finding as a further step forward to distilling the tell-tale metrics of the H-dependent mechanical behavior observed in Zr-based metallic glasses.
文摘How to control melt composition is the key for getting high quality alloy melt. The paper made the following efforts: (1) The activity coefficients in Ti-15-3 melt have been calculated. (2) Taking advantage of the activity coefficients, the evaporation losses of components in Ti-15-3 melt during ISM process have been studied. The calculated results show that there is a critical vacuum degree (about 1.33 Pa) during melting process.
基金National Key Research and Development Program of China(Grant No.2016YFB0301201)the National Natural Science Foundation of China(Grant No.51425402,51371066,and 51671073).
文摘“Hydrogen in metallic glasses”has become a popular topic for material scientists,yet few studies focus on the atomic⁃scale details.Herein,by utilizing molecular dynamic simulations,the changes on the atomic structure of Cu50Zr50 metallic glasses after melt hydrogenation were systematically analyzed,with the aim of understanding the differences of mechanical behavior between these amorphous alloys.The simulated analyses indicate that the hydrogenated samples become more compact than the H⁃free one,but the fraction of the dominant coordination polyhedra with higher degree of local fivefold symmetry significantly decreases accompanied by the addition of H atoms.Accordingly,melt hydrogenation can induce much more local“soft spots”in metallic glasses to alleviate the degree of strain localization during deformation,i.e.,it has a positive influence on the deformability of glassy alloys in agreement with experimental results.
基金National Natural Science Foundation of China(Grant No.51825401)the China Postdoctoral Science Foundation(Grant No.2019TQ0077).
文摘In order to refine microstructure grains and improve mechanical properties of TiAl alloys,Ti44Al(at.%)alloy was rapidly solidified by melt spinning under different cooling rates.Microstructure and microhardness of the alloy before and after rapid solidification were investigated.XRD results show that the ratio ofα2 phase in binary alloy increased with the cooling rates,which is caused by moreαphases directly transforming toα2 phases.Grain morphology changed from long dendrite to the mixture of equiaxed and dendrite to equiaxed with the increase of cooling rates.The grain size was refined from 200-600μm of as⁃cast to 18μm of the alloy cooled at 4.9×10^5 K/s,which is caused by the undercooling induced from rapid solidification.Lamellar spacing was decreased from 4.5μm of as⁃cast to 1.1μm by rapid solidification.With the increase of cooling rate,the content ofα2 phase increased andγphase decreased gradually.Rapid solidification can reduce the segregation of elements.The microhardness was improved from 247 HV to 556 HV,which results from grain refinement strengthening,reduction of lamellar spacing,and more content ofα2 phase.
基金supported by the National Defense foundation of China under grant No.97J18.0.0HT0126.
文摘Using direct finite difference method, a numerical model for simulating the temperature field in the charge during induction skull melting (ISM) has been developed. On the basis of the model, the temperature field in Ti- 47Ni-9Nb ingot has been calculated under various melting conditions. Finally, the processing parameters (melting power, melting-down time and the final melt temperature) have been optimized.
基金This work was supported by National Natural Science Foundation of China 51425402,51371066,51671073National Key Research and Development Program of China 2016YFB0301201R.O.R.was supported by U.S.Department of Energy,Office of Science,Office of Basic Energy Sciences,Materials Sciences and Engineering Division,under Contract No.DE-AC02-05CH11231.
文摘The hidden order of atomic packing in amorphous structures and how this may provide the origin of plastic events have long been a goal in the understanding of plastic deformation in metallic glasses.To pursue this issue,we employ here molecular dynamic simulations to create three-dimensional models for a few metallic glasses where,based on the geometrical frustration of the coordination polyhedra,we classify the atoms in the amorphous structure into six distinct species,where“gradient atomic packing structure”exists.The local structure in the amorphous state can display a gradual transition from loose stacking to dense stacking of atoms,followed by a gradient evolution of atomic performance.As such,the amorphous alloy specifically comprises three discernible regions:solid-like,transition,and liquid-like regions,each one possessing different types of atoms.We also demonstrate that the liquid-like atoms correlate most strongly with fertile sites for shear transformation,the transition atoms take second place,whereas the solid-like atoms contribute the least because of their lowest correlation level with the liquid-like atoms.Unlike the“geometrically unfavored motifs”model which fails to consider the role of medium-range order,our model gives a definite structure for the so-called“soft spots”,that is,a combination of liquid-like atoms and their neighbors,in favor of quantifying and comparing their number between different metallic glasses,which can provide a rational explanation for the unique mechanical behavior of metallic glasses.
