The distribution of boron and the microstructure of grain boundary（GB） precipitates（M23（C,B） 6 and M 2B）have been analyzed with their effects on the susceptibility of ductility-dip-cracking（DDC） and tensile pr...The distribution of boron and the microstructure of grain boundary（GB） precipitates（M23（C,B） 6 and M 2B）have been analyzed with their effects on the susceptibility of ductility-dip-cracking（DDC） and tensile properties for NiCrFe-7 weld metal,using optical microscopy（OM）,secondary ion mass spectroscopy（SIMS）,scanning electron microscopy（SEM）,and transmission electron microscopy（TEM）.The results show that boron segregates at GBs in NiCrFe-7 weld metal during the welding process.The segregation of boron at GBs promotes the formation of continuous M23（C,B） 6 carbide chains and M 2B borides along GBs.The addition of boron aggravates GB embrittlement and causes more DDC in the weld metal,by its segregation at GBs presenting as an impurity,and promoting the formation of larger and continuous M 23（C,B） 6 carbides,and M 2B borides along GBs.DDC in the weld metal deteriorates the ductility and tensile strength of the weld metal simultaneously.展开更多
Investment and suction casting （ISC） represents an economic and promising process route to fabricate auto-motive exhaust valves of γ-TiAI based alloys, but information available on the metal flow and the temperatur...Investment and suction casting （ISC） represents an economic and promising process route to fabricate auto-motive exhaust valves of γ-TiAI based alloys, but information available on the metal flow and the temperature changeseduring mould filling and solidification process for the ISC process is meager. A sequentially coupled mathematical flow-thermal model, based on the commercial finite-volume/finite-difference code FLOW-3D and the finite-element code PROCAST, has been developed to investigate the ISC process. In term of calcu-lating the flow and temperature fields during the filling and solidification stages, potential defects including the gas bubbles and the surface air entrainment occurred in the mould filling process and the shrinkage porosities formed in the solidification process are predicted and the reasons for the formation of these defects are also analyzed. The effects of filling pressure difference control methods and moulds on gas bubble and surface air entrainment behavior are presented. It is found that by changing the filling pressure difference control methods from general suction casting to ＂air leakage＂ suction casting and reducing air leakage flow rates, the gas bubbles are eliminated effectively, and the surface air entrainment attenuate dramatically. With resort to a mould with a tetragonal runner, the surface air entrainment decrease to the lowest level. Finally, the water analogue and suction casting experiments of exhaust valves are implemented for further validation of the simulation results.展开更多
The influence of surface roughness on the interfacial dynamic recrystallization kinetics and mechanical properties of Ti-6 Al-3 Nb-2 Zr-1 Mo hot-compression bonding joints was systematically investigated.It is found t...The influence of surface roughness on the interfacial dynamic recrystallization kinetics and mechanical properties of Ti-6 Al-3 Nb-2 Zr-1 Mo hot-compression bonding joints was systematically investigated.It is found that for the bonding interface of rough surfaces,elongated fine grains are formed at the bonding interface due to shear deformation of the interfacial area.As the surface roughness increases,the proportion of elongated grains drastically decreases as they further reorient to form equiaxed grains along the bonding interface of rougher surfaces resulting from severe incompatible deformation of the interface area.Meanwhile,high-density geometrically necessary dislocations accumulate around the interfacial recrystallization area to accommodate the incompatible strain and lattice rotation.A rotational dynamic recrystallization mechanism is thereby proposed to rationalize the formation of fine interfacial recrystallization grains during bonding of rough surfaces.In contrast to that of rough surfaces,bonding interface of polished surfaces exists in the form of straight interface grain boundaries without fine grains under the same deformation conditions.While with the increase of deformation strain,small grain nuclei form along the bonding interface,which is associated with discontinuous dynamic recrystallization assisted by strain-induced boundary migration of interface grain boundaries.Moreover,the bonding joints of rough surfaces show lower elongation compared with that of polished surfaces.This is because the formation of heterogeneous fine grains with low Schmid factor along the bonding interface of rough surfaces,leading to worse compatible deformation capability and thereby poor ductility of bonding joints.展开更多
A simple powder forging process was presented herein to fabricate an Fe-14 Cr-4.5 Al-2 W-0.4 Ti-0.5 Y_(2)O_(3)ODS Fe Cr Al alloy.The forged alloy exhibits a high density that exceeds 97%of the theoretical density.The ...A simple powder forging process was presented herein to fabricate an Fe-14 Cr-4.5 Al-2 W-0.4 Ti-0.5 Y_(2)O_(3)ODS Fe Cr Al alloy.The forged alloy exhibits a high density that exceeds 97%of the theoretical density.The ODS alloy was investigated in terms of the residual porosity,morphology and phase structure of oxide nanoparticles,impact toughness and tensile properties.It was found that refined grains were obtained during powder forging.A residual porosity less than 1.1%has no impact on the precipitation of oxide nanoparticles.The average diameter of the oxide particles is 7.99 nm,with a number density of 2.75×10^(22)m^(-3).Almost all of the oxides are identified as orthorhombic YAl O3 particles.The refined grains and uniformly distributed oxide nanoparticles enable the alloy to show excellent mechanical strength and ductility below 700℃,and enable the ductile-to-brittle transition temperature to be close to room temperature.However,a slight decrease in strength at 1000℃and the Charpy upper shelf energy has been suggested to be due to the residual porosity.These results indicate that powder forging can be used as a promising technique for the fabrication of ODS alloys.展开更多
Single dendrite and multi-dendrite growth for Al-2 mol pct Si alloy during isothermal solidification are simulated by phase field method. In the case of single equiaxed dendrite growth, the secondary and the necking p...Single dendrite and multi-dendrite growth for Al-2 mol pct Si alloy during isothermal solidification are simulated by phase field method. In the case of single equiaxed dendrite growth, the secondary and the necking phenomenon can be observed. For multi-dendrite growth, there exists the competitive growth among the dendrites during solidification. As solidification proceeds, growing and coarsening of the primary arms occurs, together with the branching and coarsening of the secondary arms. When the diffusion fields of dendrite tips come into contact with those of the branches growing from the neighboring dendrites, the dendrites stop growing and being to ripen and thicken.展开更多
Because atoms in high-entropy alloys （HEAs） coordinate in very different and distorted local environ- ments in the lattice sites, even for the same type of constituent, their point defects could highly vary. Therefo...Because atoms in high-entropy alloys （HEAs） coordinate in very different and distorted local environ- ments in the lattice sites, even for the same type of constituent, their point defects could highly vary. Therefore, theoretical determination of the thermodynamic quantities （i.e., defect formation enthalpies） of various point defects is rather challenging because each corresponding thermodynamic quantity of all involve constituents is not unique. The knowledge of these thermodynamic quantities is prerequisite for designing novel HEAs and understanding the mechanical and physical behaviors of HEAs. However, to date there has not been a good method to theoretically derive the defect formation enthalpies of HEAs. Here, using first-principles calculations within the density functional theory （DFT） in combina- tion of special quasi-random structure models （SQSs）, we have developed a general method to derive corresponding formation enthalpies of point defects in HEAs, using vacancy formation enthalpies of a four-component equiatomic fcc-type FeCoCrNi HEA as prototypical and benchmark examples. In difference from traditional ordered alloys, the vacancy formation enthalpies of FeCoCrNi HEA vary in a highly wide range from 0.72 to 2.89 eV for Fe, 0.88-2.90 eV for Co, 0.78-3.09 eV for Cr, and 0.91-2.95 eV for Ni due to high-level site-to-site lattice distortions and compositional complexities. On average, the vacancy formation enthalpies of 1.58 eV for Fe, 1.61 eV for Cr, 1.70 eV for Co and 1.89 eV for Ni are all larger than that （1.41 eV） of pure fcc nickel. This fact implies that the vacancies are much more difficult to be created than in nickel, indicating a reasonable agreement with the recent experimental observation that FeCoCrNi exhibits two orders of amplitudes enhancement of radiation tolerance with the suppression of void formation at elevated temperatures than in pure nickel.展开更多
Two 15Cr–9Ni–Nb austenitic stainless steel weld metals with 2.5%Si and 3.5%Si(namely 2.5Si and 3.5Si samples,respectively)were designed and prepared through tungsten inert gas(TIG)welding and then hold at 800℃ or ...Two 15Cr–9Ni–Nb austenitic stainless steel weld metals with 2.5%Si and 3.5%Si(namely 2.5Si and 3.5Si samples,respectively)were designed and prepared through tungsten inert gas(TIG)welding and then hold at 800℃ or 900℃ for 3 h for stabilization.The microstructure and mechanical properties were investigated both for the as-welded and after-stabilization heat treatment(SHT)weld metals.There are 3.0–4.0%martensite and 2.5–3.5%δferrite in the 2.5Si as-welded weld metal and 6.0–7.0%δferrite in the 3.5Si as-welded weld metal.After SHT,a large amount of martensite formed in the 2.5Si weld metal,andδ→γtransition occurred during the SHT process both for the 2.5Si and 3.5Si weld metals.There were a large amount of coarse NbC and few nanoscale NbC in the as-welded weld metal.During the SHT,a large amount of nanoscale NbC formed in the matrix,while a large number of G phases formed at the austenite grain boundaries and theδ/γinterfaces.The decrease in solid solution C andδferrite content led to the decline of the yield strength of the weld metal after SHT.The martensite formed in 2.5Si weld metal after SHT had less effect on strength because of its low carbon content.The G phases formed during the SHT reduced the impact energy of the weld metal because it promoted the intergranular fracture,while theδ→γtransition reduced the amount of theδ/γinterfaces and avoided the intergranular fracture,which was beneficial for the impact toughness of the weld metals.展开更多
This report investigated the ordering of the alky chain of sphingomyelin （SMs） monolayers induced by cholesterol at the air/water interface using high-resolution broadband sum frequency generation vibrational spectr...This report investigated the ordering of the alky chain of sphingomyelin （SMs） monolayers induced by cholesterol at the air/water interface using high-resolution broadband sum frequency generation vibrational spectroscopy （HR-BB-SFG-VS）. The SFG spectra of the three nature sphingomyelin/cholesterol mixture monolayers with two concentrations of the cholesterol at the air/water interface are performed under different polarization combination. A new resolved CH2 symmetric stretching （d＋, ~2834 cm-1） and the CH3 symmetric stretching （r＋, ~2874 cm-1） mode are applied to characterize the conformational order in the sphingomyelin/cholesterol mixture monolayers. It was found that the cholesterol make the sphingosine backbones more conformational order. During this process, the conformational order of the N-linked acyl chain remains unaltered. Moreover, the sphingosine backbones of SMs have much larger contributions to gauche defects of SMs than one in the N-linked acyl chain. These results presented here not only shed lights on understanding of the interactions of sphingomyelin molecules with cholesterol molecules at interface but also demonstrates the ability of HR-BB-SFG to probe such complicated molecular systems.展开更多
This paper has attempted to simulate the microstructure formation based on fully coupling of temperature field, concentration field and velocity field with micro-kinetics. The authors presented a new way, which is the...This paper has attempted to simulate the microstructure formation based on fully coupling of temperature field, concentration field and velocity field with micro-kinetics. The authors presented a new way, which is the combination of FDM and cellular automata (CAFD) to visualize the microstructure formation of the thin complex superalloy turbine blades cast by the vacuum investment process. The distribution, orientation and mechanism of the heterogeneous nucleation, the growth kinetics of dendrites and the columnar to equiaxed transition (CET) are considered. Capitalizing on these simulating schemes, the comprehensive influence of key process variables on the scale and uniformity of grains has been investigated quantitatively. The simulated grain size and morphology agree well with the experimental results.展开更多
The site preferences, fast and huge anisotropic diffusion mechanisms of Cu （Ag） in β-Sn as well as their reduction on the self-diffusivity of Sn, have been investigated using the first-principles and ab initio mole...The site preferences, fast and huge anisotropic diffusion mechanisms of Cu （Ag） in β-Sn as well as their reduction on the self-diffusivity of Sn, have been investigated using the first-principles and ab initio molecular dynamics methods. We have found that Cu prefers the interstitial site, whereas Ag is preferable in the substitutional site, which is mostly dominated by their different size factors. Electronic structure further evidences that the d-s hybridization between the solute and the host atom also contributes to the site preferences. It is also deduced that the fast diffusion of Cu （Ag） is mostly due to the interstitial diffusion mechanism and their diffusivity can be correlated with the amount of their respective interstitial solution. Their faster diffusion along the c-axis can be attributed to the extremely low migration energy barrier caused by the straight tunnel of considerable size with the screw axis symmetry of 2π/4 along the c-axis. Furthermore, it is found that during the process of diffusion the interstitially dissolved Cu （Ag） atoms would combine with the nearby Sn-vacancy and further annihilate the vacancy, thereby reducin~ the self-diffusion of Sn.展开更多
High-carbon chromium bearing steels with different rare earth (RE) contents were prepared to investigate the effects of RE on inclusions and impact toughness by different techniques. The results showed that RE additio...High-carbon chromium bearing steels with different rare earth (RE) contents were prepared to investigate the effects of RE on inclusions and impact toughness by different techniques. The results showed that RE addition could modify irregular Al2O3 and MnS into regular RE inclusions. With the increase of RE content, the reaction sequence of RE and potential inclusion forming elements should be O, S, As, P and C successively. RE inclusions containing C might precipitate in molten steel and solid state, but the precipitation tem perature was significantly higher than that of carbides in high-carbon chromium bearing steel. For experim ental bearing steels, the volume fraction of inclusions increased steadily with the increase of RE content, but smaller and more dispersed inclusions could be obtained by 0.018% RE content compared with bearing steel without RE, whereas the continuous increase of RE content led to an increasing trend for inclusion size and a gradual deterioration for inclusion distribution. RE addition could improve the transverse impact toughness and isotropy of bearing steel, and for modified highcarbon chrom ium bearing steel by RE alloying, the increase of RE content continuously increased both transverse and longitudinal im pact toughness until excessive RE addition.展开更多
The effects of rare earth(RE) on the microstructure and impact toughness of low alloy Cr-Mo-V bainitic steels have been investigated where the steels have RE content of 0 to 0.048 wt.%. The results indicate that the n...The effects of rare earth(RE) on the microstructure and impact toughness of low alloy Cr-Mo-V bainitic steels have been investigated where the steels have RE content of 0 to 0.048 wt.%. The results indicate that the normalized microstructures of the steels are typical granular bainite(GB) composed primarily of bainitic ferrite and martensite and/or austenite(M-A) constituents. The M-A constituents are transformed into ferrite and carbides and/or agglomerated carbides after tempering at 700℃ for 4 h. The addition of RE decreases the onset temperature of bainitic transformation and results in the formation of finer bainitic ferrite, and reduces the amount of carbon-rich M-A constituents. For the normalized and tempered samples, the ductile-to-brittle transition temperature(DBTT) decreases with increasing RE content to a critical value of 0.012 wt.%. Lower DBTT and higher upper shelf energy are attributed to the decreased effective grain size and lower amount of coarse agglomerated carbides from the decomposition of massive M-A constituents. However, the addition of RE in excess of 0.012 wt.% leads to a substantial increase in the volume fraction of large-sized inclusions, which are extremely detrimental to the impact toughness.展开更多
Fractional anisotropy values in diffusion tensor imaging can quantitatively reflect the consistency of nerve fibers after brain damage, where higher values generally indicate less damage to nerve fibers. Therefore, we...Fractional anisotropy values in diffusion tensor imaging can quantitatively reflect the consistency of nerve fibers after brain damage, where higher values generally indicate less damage to nerve fibers. Therefore, we hypothesized that diffusion tensor imaging could be used to evaluate the effect of mild hypothermia on diffuse axona[ injury. A total of 102 patients with diffuse axonal injury were randomly divided into two groups： normothermic and mild hypothermic treatment groups. Patient＇s modified Rankin scale scores 2 months after mild hypothermia were significant- ly lower than those for the normothermia group. The difference in average fractional anisotropy value for each region of interest before and after mild hypothermia was 1.32-1.36 times higher than the value in the normothermia group. Quantitative assessment of diffusion tensor imaging indicates that mild hypothermia therapy may be beneficial for patients with diffuse axonal injury.展开更多
The effects of filler metal （FM） composition on inclusions and inclusion defects for ER NiCrFe-7 weldments have been investigated and analyzed. Results show that as Al, Ti content in FM increases from 0.14 wt% Al, 0...The effects of filler metal （FM） composition on inclusions and inclusion defects for ER NiCrFe-7 weldments have been investigated and analyzed. Results show that as Al, Ti content in FM increases from 0.14 wt% Al, 0.30 wt% Ti to 0.42 wt% Al, 0.92 wt% Ti, the Al, Ti reduction will increase during welding. Inclusion defects （point-like defects named by welding workers） are prone to form in the high Al, Ti content weldments. Inclusion defects with Mg, Ca, Al, and Ti as major metallic elements have been found on the surface and interior of the weldments, as Al, Ti content in FM is over 0.29 wt% Al, 0.62 wt% Ti. Less -ri content in FM cannot prevent ductility-dip-cracking （DDC） through producing enough intragranular precipitates and lessening intergranular M23C6 precipitates. Nb can be used to replace Ti to reduce the sensitivity of the DDC in the NiCrFe-7 alloy weldments.展开更多
Here,we report the leading manu facture of the large-scale integral weldless stainless steel forging ring(φ=15.6 m)by the multilayer additive hot-compression bonding technology.Moreover,the detailed interface healing...Here,we report the leading manu facture of the large-scale integral weldless stainless steel forging ring(φ=15.6 m)by the multilayer additive hot-compression bonding technology.Moreover,the detailed interface healing mecha nism involving interfacial oxide evolution is elucidated,which validates the feasibility and reliability of the technique we proposed.展开更多
The microstructure evolutions and the mechanical properties of the 25Cr-20Ni austenitic stainless steel weld metals with different Nb contents were investigated during the long term aging treatment at 700~?C.M_(23)C_6...The microstructure evolutions and the mechanical properties of the 25Cr-20Ni austenitic stainless steel weld metals with different Nb contents were investigated during the long term aging treatment at 700~?C.M_(23)C_6,Nb(C,N),α-Cr phase and Nb-nitride phase(Z phase)were observed in the microstructures of the aged weld metals.The results showed that theα-Cr phase precipitated in the interdendritic regions of the weld metals after being exposed to~ 700?C for 500 h and the element Nb accelerated the precipitation of theα-Cr phase significantly.The density of theα-Cr phase decreased with the increase of the distance away from the primary Nb(C,N).Additionally,theα-Cr phase showed a crystallographic relationship with the austenitic matrix,■.It was observed that the Z phase precipitated in the periphery of the Nb(C,N)and may replace the Nb(C,N)after long term exposure to high temperature.The transformation of the Nb(C,N)into Z phase suggested that the Z phase had a higher stability than the Nb(C,N)par^ticles at 700?C for long term aging.The tensile strength of the Nb-bearing weld metal showed a continuous decrease at the initial stage of the aging treatment and then went up slightly with the prolonged aging time.However,the elongations and the impact energies of the weld metals decreased monotonously with the increase of the aging time.展开更多
The heterogeneous deformation behavior of austenite and ferrite in the 2205 duplex stainless steel was subjected to multiscale analysis based on the in situ synchrotron-based high energy X-ray diffraction,microscopic ...The heterogeneous deformation behavior of austenite and ferrite in the 2205 duplex stainless steel was subjected to multiscale analysis based on the in situ synchrotron-based high energy X-ray diffraction,microscopic digital image correlation,electron backscatter diffraction,and transmission electron microscopy.It is found that the heterogeneous deformation triggers from the yielding of austenite.During this deformation stage,austenite experiences greater strain in the area near the phase boundaries because of the impeded function of the phase boundaries to dislocations.Owing to the relatively small difference in hardness between the constituent phases,the strain in austenite grains extends into the adjacent ferrite grains when entering into the ferrite yielding stage.In addition,the strain distribution of the austenite grains is more homogeneous than that of the ferrite grains because of the lower stacking fault energy of austenite,which results in a planar slip,and higher stacking fault energy in case of ferrite,causing cross slip.The interaction between austenite and ferrite becomes considerably obvious when the strain further increases after both constituent phases yielding because of the back stress and forward stress in austenite and ferrite,respectively,which are generated by the pile-up of the geometrically necessary dislocations.展开更多
The effects of double shielded TIG （tungsten inert gas） torch＇s structural parameters, including the flow rate ratio between the inner and outer layers of gas and the extended length of the electrode （abbreviated ...The effects of double shielded TIG （tungsten inert gas） torch＇s structural parameters, including the flow rate ratio between the inner and outer layers of gas and the extended length of the electrode （abbreviated as ELE in this work）, on the fusion zone profile have been investigated for OCrl3NiSMo martensitic stainless steel. Results show that the double shielded TIG process yields relatively high penetration of the weld pool in a broad range of the structural parameters. ELE over 3 mm is too large and causes adverse reactions on the protection of electrode. The outer gas with relatively high flow rate or the outer layer with high oxygen content is conducive to the oxygen dissolved into the arc, which results in the oxidation of the weld pool surface and the electrode tip. The double shielded TIG welded metal was tested and presented good impact property.展开更多
We synthesized a mesoporous film based on TiO2-reduced graphene oxide(RGO)hybrids using a one-step vapor-thermal method without the need for an additional annealing process.The vapor-thermally prepared TiO2-graphene h...We synthesized a mesoporous film based on TiO2-reduced graphene oxide(RGO)hybrids using a one-step vapor-thermal method without the need for an additional annealing process.The vapor-thermally prepared TiO2-graphene hybrid(VTH)features unique structures with an ultra-large specific surface area of^260 m^2 g^-1 and low aggregation,giving rise to enhanced light harvesting and increased charge generation and separation efficiency.It was observed that a mesoporous film with uniform pore distribution is simultaneously obtained during the VTH growth process.When a 5.0 wt%RGO VTH film was used as the active layer in photocatalysis,the highest photocatalytic activity for degradation of methyl orange was achieved.For another,when a 0.75 wt%RGO VTH film was used as the photoanode in a dye-sensitized solar cell,the power conversion efficiency reached 7.58%,which represents an increase of 73.1%compared to a solar cell using an a photoanode of pure TiO2 synthesized by a traditional solvothermal method.It is expected that this facile method for the synthesis of TiO2/graphene hybrid mesoporous films will be useful in practical applications for preparing other metal oxide/graphene hybrids with ultra-high photocatalytic activity and photovoltaic performance.展开更多
基金financial support by the National Natural Science Foundation of China (No.51474203)Key Research Program of the Chinese Academy of Sciences (No.KGZD-EW-XXX-2)
文摘The distribution of boron and the microstructure of grain boundary（GB） precipitates（M23（C,B） 6 and M 2B）have been analyzed with their effects on the susceptibility of ductility-dip-cracking（DDC） and tensile properties for NiCrFe-7 weld metal,using optical microscopy（OM）,secondary ion mass spectroscopy（SIMS）,scanning electron microscopy（SEM）,and transmission electron microscopy（TEM）.The results show that boron segregates at GBs in NiCrFe-7 weld metal during the welding process.The segregation of boron at GBs promotes the formation of continuous M23（C,B） 6 carbide chains and M 2B borides along GBs.The addition of boron aggravates GB embrittlement and causes more DDC in the weld metal,by its segregation at GBs presenting as an impurity,and promoting the formation of larger and continuous M 23（C,B） 6 carbides,and M 2B borides along GBs.DDC in the weld metal deteriorates the ductility and tensile strength of the weld metal simultaneously.
文摘Investment and suction casting （ISC） represents an economic and promising process route to fabricate auto-motive exhaust valves of γ-TiAI based alloys, but information available on the metal flow and the temperature changeseduring mould filling and solidification process for the ISC process is meager. A sequentially coupled mathematical flow-thermal model, based on the commercial finite-volume/finite-difference code FLOW-3D and the finite-element code PROCAST, has been developed to investigate the ISC process. In term of calcu-lating the flow and temperature fields during the filling and solidification stages, potential defects including the gas bubbles and the surface air entrainment occurred in the mould filling process and the shrinkage porosities formed in the solidification process are predicted and the reasons for the formation of these defects are also analyzed. The effects of filling pressure difference control methods and moulds on gas bubble and surface air entrainment behavior are presented. It is found that by changing the filling pressure difference control methods from general suction casting to ＂air leakage＂ suction casting and reducing air leakage flow rates, the gas bubbles are eliminated effectively, and the surface air entrainment attenuate dramatically. With resort to a mould with a tetragonal runner, the surface air entrainment decrease to the lowest level. Finally, the water analogue and suction casting experiments of exhaust valves are implemented for further validation of the simulation results.
基金financially supported by the National Key Research and Development Program(No.2018YFA0702900)the Postdoctoral Science Foundation of China(No.2020M681004)+2 种基金the National Natural Science Foundation of China(No.51774265)the National Science and Technology Major Project of China(No.2019ZX06004010)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDC04000000)。
文摘The influence of surface roughness on the interfacial dynamic recrystallization kinetics and mechanical properties of Ti-6 Al-3 Nb-2 Zr-1 Mo hot-compression bonding joints was systematically investigated.It is found that for the bonding interface of rough surfaces,elongated fine grains are formed at the bonding interface due to shear deformation of the interfacial area.As the surface roughness increases,the proportion of elongated grains drastically decreases as they further reorient to form equiaxed grains along the bonding interface of rougher surfaces resulting from severe incompatible deformation of the interface area.Meanwhile,high-density geometrically necessary dislocations accumulate around the interfacial recrystallization area to accommodate the incompatible strain and lattice rotation.A rotational dynamic recrystallization mechanism is thereby proposed to rationalize the formation of fine interfacial recrystallization grains during bonding of rough surfaces.In contrast to that of rough surfaces,bonding interface of polished surfaces exists in the form of straight interface grain boundaries without fine grains under the same deformation conditions.While with the increase of deformation strain,small grain nuclei form along the bonding interface,which is associated with discontinuous dynamic recrystallization assisted by strain-induced boundary migration of interface grain boundaries.Moreover,the bonding joints of rough surfaces show lower elongation compared with that of polished surfaces.This is because the formation of heterogeneous fine grains with low Schmid factor along the bonding interface of rough surfaces,leading to worse compatible deformation capability and thereby poor ductility of bonding joints.
基金financially supported by National Defense Science and Technology Industry Nuclear Material Technology Innovation Center Project(No.ICNM-2020-ZH-17)。
文摘A simple powder forging process was presented herein to fabricate an Fe-14 Cr-4.5 Al-2 W-0.4 Ti-0.5 Y_(2)O_(3)ODS Fe Cr Al alloy.The forged alloy exhibits a high density that exceeds 97%of the theoretical density.The ODS alloy was investigated in terms of the residual porosity,morphology and phase structure of oxide nanoparticles,impact toughness and tensile properties.It was found that refined grains were obtained during powder forging.A residual porosity less than 1.1%has no impact on the precipitation of oxide nanoparticles.The average diameter of the oxide particles is 7.99 nm,with a number density of 2.75×10^(22)m^(-3).Almost all of the oxides are identified as orthorhombic YAl O3 particles.The refined grains and uniformly distributed oxide nanoparticles enable the alloy to show excellent mechanical strength and ductility below 700℃,and enable the ductile-to-brittle transition temperature to be close to room temperature.However,a slight decrease in strength at 1000℃and the Charpy upper shelf energy has been suggested to be due to the residual porosity.These results indicate that powder forging can be used as a promising technique for the fabrication of ODS alloys.
基金financially supported by the Educational Department of Liaoning Province (No.20060744)the Shenyang Nurturing Young Scientific Technological Talents Items (No.1081230-1-00)
文摘Single dendrite and multi-dendrite growth for Al-2 mol pct Si alloy during isothermal solidification are simulated by phase field method. In the case of single equiaxed dendrite growth, the secondary and the necking phenomenon can be observed. For multi-dendrite growth, there exists the competitive growth among the dendrites during solidification. As solidification proceeds, growing and coarsening of the primary arms occurs, together with the branching and coarsening of the secondary arms. When the diffusion fields of dendrite tips come into contact with those of the branches growing from the neighboring dendrites, the dendrites stop growing and being to ripen and thicken.
基金supported by the National Science Fund for Distinguished Young Scholars (No. 51725103)by the National Natural Science Foundation of China (Grant Nos. 51671193 and 51474202)+7 种基金by the Science Challenging (Project No. TZ2016004)by the “Hundred Talented Project” of the Chinese Academy of Sciencesfinancially supported by the National Natural Science Foundation of China (Nos. 51671018 and 51671021)111 Project (No. B07003)International S&T Cooperation Program of China (No. 2015DFG52600)the Program for Changjiang Scholars and Innovative Research Team in University of China (No. IRT 14R05)the Projects of SKL-AMM-USTB (Nos. 2016Z-04, 2016-09 and 2016Z-16)supported by the Hong Kong URC grant under the contract with City University of Hong Kong
文摘Because atoms in high-entropy alloys （HEAs） coordinate in very different and distorted local environ- ments in the lattice sites, even for the same type of constituent, their point defects could highly vary. Therefore, theoretical determination of the thermodynamic quantities （i.e., defect formation enthalpies） of various point defects is rather challenging because each corresponding thermodynamic quantity of all involve constituents is not unique. The knowledge of these thermodynamic quantities is prerequisite for designing novel HEAs and understanding the mechanical and physical behaviors of HEAs. However, to date there has not been a good method to theoretically derive the defect formation enthalpies of HEAs. Here, using first-principles calculations within the density functional theory （DFT） in combina- tion of special quasi-random structure models （SQSs）, we have developed a general method to derive corresponding formation enthalpies of point defects in HEAs, using vacancy formation enthalpies of a four-component equiatomic fcc-type FeCoCrNi HEA as prototypical and benchmark examples. In difference from traditional ordered alloys, the vacancy formation enthalpies of FeCoCrNi HEA vary in a highly wide range from 0.72 to 2.89 eV for Fe, 0.88-2.90 eV for Co, 0.78-3.09 eV for Cr, and 0.91-2.95 eV for Ni due to high-level site-to-site lattice distortions and compositional complexities. On average, the vacancy formation enthalpies of 1.58 eV for Fe, 1.61 eV for Cr, 1.70 eV for Co and 1.89 eV for Ni are all larger than that （1.41 eV） of pure fcc nickel. This fact implies that the vacancies are much more difficult to be created than in nickel, indicating a reasonable agreement with the recent experimental observation that FeCoCrNi exhibits two orders of amplitudes enhancement of radiation tolerance with the suppression of void formation at elevated temperatures than in pure nickel.
基金financially supported by the China Institute of Atomic Energy(E141L803J1)the innovation project of Shenyang National Laboratory for Materials Science(SYNL-2022).
文摘Two 15Cr–9Ni–Nb austenitic stainless steel weld metals with 2.5%Si and 3.5%Si(namely 2.5Si and 3.5Si samples,respectively)were designed and prepared through tungsten inert gas(TIG)welding and then hold at 800℃ or 900℃ for 3 h for stabilization.The microstructure and mechanical properties were investigated both for the as-welded and after-stabilization heat treatment(SHT)weld metals.There are 3.0–4.0%martensite and 2.5–3.5%δferrite in the 2.5Si as-welded weld metal and 6.0–7.0%δferrite in the 3.5Si as-welded weld metal.After SHT,a large amount of martensite formed in the 2.5Si weld metal,andδ→γtransition occurred during the SHT process both for the 2.5Si and 3.5Si weld metals.There were a large amount of coarse NbC and few nanoscale NbC in the as-welded weld metal.During the SHT,a large amount of nanoscale NbC formed in the matrix,while a large number of G phases formed at the austenite grain boundaries and theδ/γinterfaces.The decrease in solid solution C andδferrite content led to the decline of the yield strength of the weld metal after SHT.The martensite formed in 2.5Si weld metal after SHT had less effect on strength because of its low carbon content.The G phases formed during the SHT reduced the impact energy of the weld metal because it promoted the intergranular fracture,while theδ→γtransition reduced the amount of theδ/γinterfaces and avoided the intergranular fracture,which was beneficial for the impact toughness of the weld metals.
基金the National Natural Science Foundation of China(No.21227802)the National Natural Science Foundation of China(Nos. 21503235, 21673251)the ICCAS for Start-up Funding
文摘This report investigated the ordering of the alky chain of sphingomyelin （SMs） monolayers induced by cholesterol at the air/water interface using high-resolution broadband sum frequency generation vibrational spectroscopy （HR-BB-SFG-VS）. The SFG spectra of the three nature sphingomyelin/cholesterol mixture monolayers with two concentrations of the cholesterol at the air/water interface are performed under different polarization combination. A new resolved CH2 symmetric stretching （d＋, ~2834 cm-1） and the CH3 symmetric stretching （r＋, ~2874 cm-1） mode are applied to characterize the conformational order in the sphingomyelin/cholesterol mixture monolayers. It was found that the cholesterol make the sphingosine backbones more conformational order. During this process, the conformational order of the N-linked acyl chain remains unaltered. Moreover, the sphingosine backbones of SMs have much larger contributions to gauche defects of SMs than one in the N-linked acyl chain. These results presented here not only shed lights on understanding of the interactions of sphingomyelin molecules with cholesterol molecules at interface but also demonstrates the ability of HR-BB-SFG to probe such complicated molecular systems.
基金financially supported by the National Super-steel Project,with the grant number G1998061512.
文摘This paper has attempted to simulate the microstructure formation based on fully coupling of temperature field, concentration field and velocity field with micro-kinetics. The authors presented a new way, which is the combination of FDM and cellular automata (CAFD) to visualize the microstructure formation of the thin complex superalloy turbine blades cast by the vacuum investment process. The distribution, orientation and mechanism of the heterogeneous nucleation, the growth kinetics of dendrites and the columnar to equiaxed transition (CET) are considered. Capitalizing on these simulating schemes, the comprehensive influence of key process variables on the scale and uniformity of grains has been investigated quantitatively. The simulated grain size and morphology agree well with the experimental results.
基金supported by the ‘Hundred Talents Project’ of the Chinese Academy of Sciences and from the Major Research Plan (Grant No. 91226204)the Key Research Program of Chinese Academy of Sciences (Grant No. KGZD-EW-T06)+2 种基金the National Natural Science Foundation of China (Grant Nos. 51474202 and 51174188)the Beijing Supercomputing Center of CAS (including its Shenyang branch)the high-performance computational cluster in the Shenyang National University Science and Technology Park
文摘The site preferences, fast and huge anisotropic diffusion mechanisms of Cu （Ag） in β-Sn as well as their reduction on the self-diffusivity of Sn, have been investigated using the first-principles and ab initio molecular dynamics methods. We have found that Cu prefers the interstitial site, whereas Ag is preferable in the substitutional site, which is mostly dominated by their different size factors. Electronic structure further evidences that the d-s hybridization between the solute and the host atom also contributes to the site preferences. It is also deduced that the fast diffusion of Cu （Ag） is mostly due to the interstitial diffusion mechanism and their diffusivity can be correlated with the amount of their respective interstitial solution. Their faster diffusion along the c-axis can be attributed to the extremely low migration energy barrier caused by the straight tunnel of considerable size with the screw axis symmetry of 2π/4 along the c-axis. Furthermore, it is found that during the process of diffusion the interstitially dissolved Cu （Ag） atoms would combine with the nearby Sn-vacancy and further annihilate the vacancy, thereby reducin~ the self-diffusion of Sn.
基金financially supported by the National Natural Science Foundation of China (Nos. U1508215 and U1708252)the National Key Research and Development Program (No. 2016YFB0300401)
文摘High-carbon chromium bearing steels with different rare earth (RE) contents were prepared to investigate the effects of RE on inclusions and impact toughness by different techniques. The results showed that RE addition could modify irregular Al2O3 and MnS into regular RE inclusions. With the increase of RE content, the reaction sequence of RE and potential inclusion forming elements should be O, S, As, P and C successively. RE inclusions containing C might precipitate in molten steel and solid state, but the precipitation tem perature was significantly higher than that of carbides in high-carbon chromium bearing steel. For experim ental bearing steels, the volume fraction of inclusions increased steadily with the increase of RE content, but smaller and more dispersed inclusions could be obtained by 0.018% RE content compared with bearing steel without RE, whereas the continuous increase of RE content led to an increasing trend for inclusion size and a gradual deterioration for inclusion distribution. RE addition could improve the transverse impact toughness and isotropy of bearing steel, and for modified highcarbon chrom ium bearing steel by RE alloying, the increase of RE content continuously increased both transverse and longitudinal im pact toughness until excessive RE addition.
基金the National Natural Science Foundation of China[Grant No.U1708252]the Youth Innovation Promotion Association,Chinese Academy of Sciences[Grant No.2013126]+1 种基金Innovation Foundation of Graduate School of Institute of Metals Research,Chinese Academy of Sciences,ChinaLiaoNing Revitalization Talents Program[Grant No.XLYC 1807022]。
文摘The effects of rare earth(RE) on the microstructure and impact toughness of low alloy Cr-Mo-V bainitic steels have been investigated where the steels have RE content of 0 to 0.048 wt.%. The results indicate that the normalized microstructures of the steels are typical granular bainite(GB) composed primarily of bainitic ferrite and martensite and/or austenite(M-A) constituents. The M-A constituents are transformed into ferrite and carbides and/or agglomerated carbides after tempering at 700℃ for 4 h. The addition of RE decreases the onset temperature of bainitic transformation and results in the formation of finer bainitic ferrite, and reduces the amount of carbon-rich M-A constituents. For the normalized and tempered samples, the ductile-to-brittle transition temperature(DBTT) decreases with increasing RE content to a critical value of 0.012 wt.%. Lower DBTT and higher upper shelf energy are attributed to the decreased effective grain size and lower amount of coarse agglomerated carbides from the decomposition of massive M-A constituents. However, the addition of RE in excess of 0.012 wt.% leads to a substantial increase in the volume fraction of large-sized inclusions, which are extremely detrimental to the impact toughness.
基金supported by the Natural Science Foundation of Guangdong Province in China,No.10151600101000002
文摘Fractional anisotropy values in diffusion tensor imaging can quantitatively reflect the consistency of nerve fibers after brain damage, where higher values generally indicate less damage to nerve fibers. Therefore, we hypothesized that diffusion tensor imaging could be used to evaluate the effect of mild hypothermia on diffuse axona[ injury. A total of 102 patients with diffuse axonal injury were randomly divided into two groups： normothermic and mild hypothermic treatment groups. Patient＇s modified Rankin scale scores 2 months after mild hypothermia were significant- ly lower than those for the normothermia group. The difference in average fractional anisotropy value for each region of interest before and after mild hypothermia was 1.32-1.36 times higher than the value in the normothermia group. Quantitative assessment of diffusion tensor imaging indicates that mild hypothermia therapy may be beneficial for patients with diffuse axonal injury.
基金support from the key research program of the Chinese Academy of Sciences(Grant No.KGZD-EW-XXX-2)
文摘The effects of filler metal （FM） composition on inclusions and inclusion defects for ER NiCrFe-7 weldments have been investigated and analyzed. Results show that as Al, Ti content in FM increases from 0.14 wt% Al, 0.30 wt% Ti to 0.42 wt% Al, 0.92 wt% Ti, the Al, Ti reduction will increase during welding. Inclusion defects （point-like defects named by welding workers） are prone to form in the high Al, Ti content weldments. Inclusion defects with Mg, Ca, Al, and Ti as major metallic elements have been found on the surface and interior of the weldments, as Al, Ti content in FM is over 0.29 wt% Al, 0.62 wt% Ti. Less -ri content in FM cannot prevent ductility-dip-cracking （DDC） through producing enough intragranular precipitates and lessening intergranular M23C6 precipitates. Nb can be used to replace Ti to reduce the sensitivity of the DDC in the NiCrFe-7 alloy weldments.
基金supported by the National Key Research and Development Program[Grant No.2018YFA0702900]the National Natural Science Foundation of China[Grant No.51774265]+2 种基金the National Science and Technology Major Project of China[Grant No.2019ZX06004010]Program of CAS Interdisciplinary Innovation TeamYouth Innovation Promotion Association,CAS。
文摘Here,we report the leading manu facture of the large-scale integral weldless stainless steel forging ring(φ=15.6 m)by the multilayer additive hot-compression bonding technology.Moreover,the detailed interface healing mecha nism involving interfacial oxide evolution is elucidated,which validates the feasibility and reliability of the technique we proposed.
基金supported by the research and development of nuclear materials and service safety assurance technology (Grant No.ZDRW-CN-2017-1)the National Natural Science Foundation of China (NSFC) (Grant No.51474203)
文摘The microstructure evolutions and the mechanical properties of the 25Cr-20Ni austenitic stainless steel weld metals with different Nb contents were investigated during the long term aging treatment at 700~?C.M_(23)C_6,Nb(C,N),α-Cr phase and Nb-nitride phase(Z phase)were observed in the microstructures of the aged weld metals.The results showed that theα-Cr phase precipitated in the interdendritic regions of the weld metals after being exposed to~ 700?C for 500 h and the element Nb accelerated the precipitation of theα-Cr phase significantly.The density of theα-Cr phase decreased with the increase of the distance away from the primary Nb(C,N).Additionally,theα-Cr phase showed a crystallographic relationship with the austenitic matrix,■.It was observed that the Z phase precipitated in the periphery of the Nb(C,N)and may replace the Nb(C,N)after long term exposure to high temperature.The transformation of the Nb(C,N)into Z phase suggested that the Z phase had a higher stability than the Nb(C,N)par^ticles at 700?C for long term aging.The tensile strength of the Nb-bearing weld metal showed a continuous decrease at the initial stage of the aging treatment and then went up slightly with the prolonged aging time.However,the elongations and the impact energies of the weld metals decreased monotonously with the increase of the aging time.
基金financial support provided by Youth Innovation Promotion Association,CAS(No.Y201732)LiaoNing Revitalization Talents Program(No.XLYC1807022)the Project to Strengthen Industrial Development at the Grass-roots level。
文摘The heterogeneous deformation behavior of austenite and ferrite in the 2205 duplex stainless steel was subjected to multiscale analysis based on the in situ synchrotron-based high energy X-ray diffraction,microscopic digital image correlation,electron backscatter diffraction,and transmission electron microscopy.It is found that the heterogeneous deformation triggers from the yielding of austenite.During this deformation stage,austenite experiences greater strain in the area near the phase boundaries because of the impeded function of the phase boundaries to dislocations.Owing to the relatively small difference in hardness between the constituent phases,the strain in austenite grains extends into the adjacent ferrite grains when entering into the ferrite yielding stage.In addition,the strain distribution of the austenite grains is more homogeneous than that of the ferrite grains because of the lower stacking fault energy of austenite,which results in a planar slip,and higher stacking fault energy in case of ferrite,causing cross slip.The interaction between austenite and ferrite becomes considerably obvious when the strain further increases after both constituent phases yielding because of the back stress and forward stress in austenite and ferrite,respectively,which are generated by the pile-up of the geometrically necessary dislocations.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.50874101 and 51104142)
文摘The effects of double shielded TIG （tungsten inert gas） torch＇s structural parameters, including the flow rate ratio between the inner and outer layers of gas and the extended length of the electrode （abbreviated as ELE in this work）, on the fusion zone profile have been investigated for OCrl3NiSMo martensitic stainless steel. Results show that the double shielded TIG process yields relatively high penetration of the weld pool in a broad range of the structural parameters. ELE over 3 mm is too large and causes adverse reactions on the protection of electrode. The outer gas with relatively high flow rate or the outer layer with high oxygen content is conducive to the oxygen dissolved into the arc, which results in the oxidation of the weld pool surface and the electrode tip. The double shielded TIG welded metal was tested and presented good impact property.
文摘We synthesized a mesoporous film based on TiO2-reduced graphene oxide(RGO)hybrids using a one-step vapor-thermal method without the need for an additional annealing process.The vapor-thermally prepared TiO2-graphene hybrid(VTH)features unique structures with an ultra-large specific surface area of^260 m^2 g^-1 and low aggregation,giving rise to enhanced light harvesting and increased charge generation and separation efficiency.It was observed that a mesoporous film with uniform pore distribution is simultaneously obtained during the VTH growth process.When a 5.0 wt%RGO VTH film was used as the active layer in photocatalysis,the highest photocatalytic activity for degradation of methyl orange was achieved.For another,when a 0.75 wt%RGO VTH film was used as the photoanode in a dye-sensitized solar cell,the power conversion efficiency reached 7.58%,which represents an increase of 73.1%compared to a solar cell using an a photoanode of pure TiO2 synthesized by a traditional solvothermal method.It is expected that this facile method for the synthesis of TiO2/graphene hybrid mesoporous films will be useful in practical applications for preparing other metal oxide/graphene hybrids with ultra-high photocatalytic activity and photovoltaic performance.
