2024 Aluminum alloy powder( 60wt%) and Fe-based amorphous powder( 40 wt%) were adopted. They were mechanical machined for 48hours after being mixed. Bulk material was gained after Spark Plasma Sintering. The sintering...2024 Aluminum alloy powder( 60wt%) and Fe-based amorphous powder( 40 wt%) were adopted. They were mechanical machined for 48hours after being mixed. Bulk material was gained after Spark Plasma Sintering. The sintering parameters included sintering temperature,heating or cooling rates,pressure and holding time. 300 ℃- 800 ℃ were adopted while the heating or cooling rate was 100 ℃ / min and with the pressure of 50 MPa in the experiments. The holding time was 10 min or 20 min at different temperatures, respectively. Bulk materials after sintering were examined by Scanning Electron Microscopy and X-Ray Diffraction. The micro-hardness and relative density also were tested. The sintering temperature had the most significant influence on the microstructure and property of the bulk material. The influence of holding time came second while the heating or cooling rates and pressure were fixed. The density became larger with the increase of the temperature. The compactness was best at 500℃. The pressure and generation of high-temperature phases were the factors which affected the density and the compactness.展开更多
With the large-scale service of lithium-ion batteries(LIBs),their failures have attracted significant attentions.While the decay of active materials is the primary cause for LIB failures,the degradation of auxiliary m...With the large-scale service of lithium-ion batteries(LIBs),their failures have attracted significant attentions.While the decay of active materials is the primary cause for LIB failures,the degradation of auxiliary materials,such as current collector corrosion,should not be disregarded.Therefore,it is necessary to conduct a comprehensive review in this field.In this review,from the perspectives of electrochemistry and materials,we systematically summarize the corrosion behavior of aluminum cathode current collector and propose corresponding countermeasures.Firstly,the corrosion type is clarified based on the properties of passivation layers in different organic electrolyte components.Furthermore,a thoroughgoing analysis is presented to examine the impact of various factors on aluminum corrosion,including lithium salts,organic solvents,water impurities,and operating conditions.Subsequently,strategies for electrolyte and protection layer employed to suppress corrosion are discussed in detail.Lastly and most importantly,we provide insights and recommendations to prevent corrosion of current collectors,facilitate the development of advanced current collectors and the implementation of next-generation high-voltage stable LIBs.展开更多
The effect of oxygen addition and annealing time on microstructure and mechanical properties of Ti-34Nb and Ti-34Nb-0.2O alloys was investigated.The addition of O suppresses the martensitic transformation.The phase co...The effect of oxygen addition and annealing time on microstructure and mechanical properties of Ti-34Nb and Ti-34Nb-0.2O alloys was investigated.The addition of O suppresses the martensitic transformation.The phase composition changes from singleα''phase toα''+βphases with oxygen addition.The addition of oxygen increases strength significantly at as-received,cold-rolled,and annealed alloys through solid solution strengthening.The accumulation of abundance of defects and grain refinement introduced by cold rolling have a significant strengthening effect but also damage plasticity.The addition of oxygen increasesα/βtransformation temperature and promotes the precipitation ofαphase during annealing in Ti-34Nb-0.2O alloy.αprecipitates can inhibit grain growth during annealing.The strength decreases with annealing time increased due to the increase in grain size in Ti-34Nb alloy,while the strength increases in Ti-34Nb-0.2O alloy mainly due to the precipitation ofαphase.The cold rolling followed by annealing and addition of oxygen can improve the properties of alloys.展开更多
The Al-5Ti-0.5B-0.5C grain refiner was pre-pared by powder metallurgy(PM).Microstructures of the grain refiner and its grain refinement performance in commercially pure aluminum(Al)were investigated by X-ray diffracti...The Al-5Ti-0.5B-0.5C grain refiner was pre-pared by powder metallurgy(PM).Microstructures of the grain refiner and its grain refinement performance in commercially pure aluminum(Al)were investigated by X-ray diffraction(XRD),scanning electron microscopy(SEM),and differential scanning calorimetry(DSC).It is found that the average grain size of commercially pure Al can be reduced from~15,000 to~180μm by the addition of Al-5Ti-0.5B-0.5C grain refiner prepared by PM,based on 0.01 wt%Ti addition.The grain refinement efficiency begins to decrease slightly when the grain refiner is kept in the melt for 60 min.The grain refinement is attributed to high stability,proper size,and high density of Al3Ti,TiB2,and TiC particles.展开更多
A thermally induced hexagonal close-packed(HCP)to face-centered cubic(FCC)phase transition was investigated in anα-type Ti35 alloy with twinned structure by in situ heating transmission electron microscopy(TEM)and ab...A thermally induced hexagonal close-packed(HCP)to face-centered cubic(FCC)phase transition was investigated in anα-type Ti35 alloy with twinned structure by in situ heating transmission electron microscopy(TEM)and ab initio calculations.TEM observations indicated that the HCP to FCC phase transition occurred both within matrix/twin and at the twin boundaries in the thinner region of the TEM film,and the FCC-Ti precipitated as plates within the matrix/twin,while as equiaxed cells at twin boundaries.The crystallographic orientation relationship between HCP-Ti and FCC-Ti can be described as:{111}FCC//{0002}HCP and<110>FCC//<1210>HCP.The HCP to FCC phase transition was accomplished by forming an intermediate state with a BB stacking sequence through the slip of partial dislocations.The formation of such FCC-Ti may be related to the thermal stress and temperature.Ab initio calculations showed that the formation of FCC-Ti may also be related to the contamination of interstitial atoms such as oxygen.展开更多
The Al-5Ti-0.2C-based grain refiners with different contents of rare earth(RE) were successfully prepared via powder metallurgy and vacuum casting. The microstructural evolution has been studied by X-ray diffraction(X...The Al-5Ti-0.2C-based grain refiners with different contents of rare earth(RE) were successfully prepared via powder metallurgy and vacuum casting. The microstructural evolution has been studied by X-ray diffraction(XRD), differential scanning calorimetry(DSC), scanning electron microscopy(SEM) and transmission electron microscopy(TEM). The results showed that the RE addition resulted in the formation of Ti Al3/Ti2Al20 RE core-shell structured primary particles, and the size of Ti Al3 core decreased, while the thickness of Ti2Al20 RE increased with increase of RE contents. As compared to Al-5Ti-0.2C grain refiner, the grain refining efficiency was gradually improved with increase of RE contents, which was mainly attributed to the Ti Al3/Ti2Al20 RE core-shell structured primary particles and insoluble Ti C nuclei formed in α-Al matrix. The formation mechanism of core-shell structure was further investigated based on Ginstling-Brounstein model.展开更多
Mechanical properties and microstructural stability under the service temperature are important to the high temperature titanium alloy.In order to evaluate the potential in increase the service temperature of Ti alloy...Mechanical properties and microstructural stability under the service temperature are important to the high temperature titanium alloy.In order to evaluate the potential in increase the service temperature of Ti alloy,two near-αTi alloys with high content of Al asα-stabilizer and Ta,Nb and/or Re asβ-stabilizers were designed and prepared by ingot metallurgy and thermomechanical processing,and the microstructure and mechanical properties before and after thermal exposure at 650℃ for 100 h were characterized.The results indicated that due to the weakβ-stabilizing ability of Ta and Nb elements,only a small amount ofβphase was formed in Ti-10Al-4Ta-2Nb alloy.With a trace Re addition,theβphase was obviously increased in Ti-10Al-4Ta-2Nb-0.25Re,indicating that the Re was a strongβ-stabilizer.Under the same thermomechanical conditions,the Re addition decreased the volume fraction of primaryα(α_(p))phase and refined the secondaryα(α_(s))phase evidently.The primaryαphase presented an obvious core-shell structure in the Ti-10Al-4Ta-2Nb alloy,with higher Al concentration in the shell.While the core-shell structure was not obvious in the Re-containing alloy due to the Re decreases the diffusion of Al,Ta and Nb elements.A large number of orderedα_(2)precipitates can be observed in theα_(p)andα_(s) phases of two alloys.Theα_(2)precipitates continuously grew up during thermal exposure,however,their growth rate in theα_(s)phase of Re-containing alloy were lower than that of Ti-10Al-4Ta-2Nb alloy.Although plenty of orderedα_(2)precipitates formed in the Ti-10Al-4Ta-2Nb alloy,the alloy had a certain plasticity at room temperature.The trace Re addition evidently increased the tensile strength but caused the decrease of the plasticity.After thermal exposure,the strength was further increased,while the plasticity was decreased for both of alloys.展开更多
With the rapid development of 3C industries,the demand for high-thermal-conductivity magnesium alloys with high mechanical performance is increasing quickly.However,the thermal conductivities of most common Mg foundry...With the rapid development of 3C industries,the demand for high-thermal-conductivity magnesium alloys with high mechanical performance is increasing quickly.However,the thermal conductivities of most common Mg foundry alloys(such as Mg-9wt%-1wt%Zn)are still relatively low.In this study,we developed a high-thermal-conductivity Mg-4Al-4Zn-4RE-1Ca(wt%,AZEX4441)alloy with good mechanical properties for ultrathin-walled cellphone components via high-pressure die casting(HPDC).The HPDC AZEX4441 alloy exhibited a fine homogeneous microstructure(average grain size of 2.8μm)with granular Al_(11)RE_(3),fibrous Al_(2)REZn_(2),and networked Ca_(6)Mg_(2)Zn_(3) phases distributed at the grain boundaries.The room-temperature thermal conductivity of the HPDC AZEX4441 alloy was 94.4 W·m^(-1)·K^(-1),which was much higher than 53.7 W·m^(-1)·K^(-1) of the HPDC AZ91D alloy.Al and Zn in the AZEX4441 alloy were largely consumed by the formation of Al_(11)RE_(3),Al_(2)REZn_(2),and Ca_(2)Mg_(6)Zn_(3) phases because of the addition of RE and Ca.Therefore,the lattice distortion induced by solute atoms of the AZEX4441 alloy(0.171%)was much lower than that of the AZ91D alloy(0.441%),which was responsible for the high thermal conductivity of the AZEX4441 alloy.The AZEX4441 alloy exhibited a high yield strength of~185 MPa,an ultimate tensile strength of~233 MPa,and an elongation of~4.2%.This result indicated that the tensile properties were comparable with those of the AZ91D alloy.Therefore,this study contributed to the development of high-performance Mg alloys with a combination of high thermal conductivity,high strength,and good castability.展开更多
A significant refinement of the microstructure of structural NiTi alloy was achieved through a combination of Al addition and fabrication by suction casting.This is attributed to the change from a layer-by-layer to vo...A significant refinement of the microstructure of structural NiTi alloy was achieved through a combination of Al addition and fabrication by suction casting.This is attributed to the change from a layer-by-layer to volume solidification mode with Al content increasing,which causes a change in grain shape from columnar to equiaxed.Furthermore,when compared with conventional casting,suction casting optimizes the microstructure of the alloy by refining the grain size and ensuring a homogeneous distribution of Ti2 Ni and Ni_(2)TiAl phases.The high cooling rate of suction casting also delays the formation ofβ'-Ni_(2)TiAl phase.Finally,this fine microstructure and uniform distribution of intermetallic phases result in the ultimate compressive strength of up to 2463.7 MPa,representing an improvement of 370 MPa over conventionally cast NiTi-Al alloy.展开更多
2D nanosheets such as graphene, silicene, phosphorene, metal dichalcogenides and MXenes are emerging and promising for lithium storage due to their ultrathin nature and corresponding chemical/physical properties. Howe...2D nanosheets such as graphene, silicene, phosphorene, metal dichalcogenides and MXenes are emerging and promising for lithium storage due to their ultrathin nature and corresponding chemical/physical properties. However, the serious restacking and aggregation of the 2D nanosheets are still hampering their applications. To circumvent the issues of 2D nanosheets, one efficient strategy is to construct 3D structures with hierarchical porous structures, good chemical/mechanical stabilities and tunable electrical conductivities. In this review, we firstly focus on the available synthetic approaches of 3D structures from 2D nanosheets, and then summarize the relationships between the microstructures of 3D structures built from 2D nanosheets and their electrochemical behaviors for lithium storage. On the basis of above results, some challenges are briefly discussed in the perspective of the development of various functional 3D structures.展开更多
In this study,a novel strategy for developingα+βdual-phase titanium alloys with low Young's modulus and high yield strength was proposed,and a Ti-15Nb-5Zr-4Sn-1 Fe alloy was developed through theoretical composi...In this study,a novel strategy for developingα+βdual-phase titanium alloys with low Young's modulus and high yield strength was proposed,and a Ti-15Nb-5Zr-4Sn-1 Fe alloy was developed through theoretical composition design and microstructure manipulation.After hot-rolling and subsequent annealing,a high volume fraction of ultrafine grainedαphase embedded in metastableβ-matrix was formed in the microstructure as intended.Consequently,this alloy exhibits both low Young's modulus(61 GPa)and high yield strength(912 MPa).The experimental results prove that the proposed strategy is appropriate for developing titanium alloys with superior yield strength-to-modulus ratio than those of conventional metallic biomedical materials.Present study might shed light on the research and development of advanced biomedical titanium alloys with low Young's modulus and high yield strength.展开更多
Primary solidification phase and lamellar orientation are investigated in Ti-45Al-7Nb alloy at very high ratio of temperature gradient to growth rate (G/v) by a liquid-metal-cooled directionally solidified method. It ...Primary solidification phase and lamellar orientation are investigated in Ti-45Al-7Nb alloy at very high ratio of temperature gradient to growth rate (G/v) by a liquid-metal-cooled directionally solidified method. It shows that Ti-45Al-7Nb alloy solidifies with primary α phase. Longitudinal (parallel to growth direction) microstructure shows that α dendrites in solid-liquid mushy zone are discontinuous and transverse microstructure of α dendrites is worm-like feature. Growth direction of α phase is about 80° away from〈0001〉α direction, and close to〈1120〉α direction. The corresponding lamellar orientation is aligned at the angle of about 10° to growth direction, which is consistent with α-dendrite growth direction according to Blackburn orientation relationship. Therefore, due to the altered growth direction of α phase, the lamellar orientation in Ti-45Al-7Nb alloy is controlled at the G/v ratio of 5×109 K·sm-2.展开更多
Although Cu was studied extensively,the Hall-Petch relationship was mainly reported in the coarsegrained regime.In this work,fully recrystallized Cu specimens with a wide grain size regime of 0.51–14.93μm manifest a...Although Cu was studied extensively,the Hall-Petch relationship was mainly reported in the coarsegrained regime.In this work,fully recrystallized Cu specimens with a wide grain size regime of 0.51–14.93μm manifest a two-stage Hall-Petch relationship.There is a critical grain size of 3μm that divides stagesⅠandⅡwhere the Hall-Petch slope k value are quite different.The stageⅡis supposed to be validified down to 100 nm at least by comparing with a Cu-Ag alloy.The critical grain size varies in different materials systems,and the underline mechanisms are discussed based on the dislocation glide modes.展开更多
The microstructural evolution of Ni–42Ti–7Al and Ni–41Ti–7Al alloys as a function of solution and aging heat treatment was investigated using transmission electron microscopy(TEM), electron probe, and X-ray diffra...The microstructural evolution of Ni–42Ti–7Al and Ni–41Ti–7Al alloys as a function of solution and aging heat treatment was investigated using transmission electron microscopy(TEM), electron probe, and X-ray diffraction(XRD). The results reveal that the volume fraction of Ti2 Ni phase as well as its composition does not change significantly after as-solution treated at 1200 °C and aged at850 °C. At the early stage of the aging treatment at 850 °C for 1 h, the cuboidal b0 precipitate keeps coherency with the matrix; further aging, b0 precipitate coarsens, and the semicoherency between the b/b0 two phases are observed.The shape of coarsened b0 precipitates changes to the globule, and the interface dislocations are introduced accompanied by the occurrence of semicoherent precipitates. Under the same heat treatment, compared to the Ni–42Ti–7Al alloy, the lattice misfits of the Ni–41Ti–7Al alloy between the b and b0 two phases are larger, so the b0 precipitates in Ni–41Ti–7Al alloy are coarsened severely and easily lose coherency with the matrix. The thermal stability of Ni–41Ti–7Al alloy is much worse when aging at 850 °C.展开更多
Although platinum nanocrystals have been considered as potential electrocatalysts for methanol oxidation reaction(MOR)in fuel cells,the large-scale practical implementation has been stagnated by their limited abundanc...Although platinum nanocrystals have been considered as potential electrocatalysts for methanol oxidation reaction(MOR)in fuel cells,the large-scale practical implementation has been stagnated by their limited abundance,easy poisoning,and low durability.Here,grain boundary-enriched platinum(GB-Pt)scaffolds are produced in large scale via facilely reducing fast cryomediated dynamic equilibrium hydrolysates of platinum salts.Such plentiful platinum grain boundaries are originated from the fast fusion of short platinum nanowires during reduction of the individually and homogeneously dispersed platinum intermediates.These grain boundaries can provide abundant active sites to efficiently catalyze MOR and meanwhile enable to oxidize the adsorbed poisonous CO during the electrocatalytic process.As a consequence,the as-synthesized GB-Pt scaffolds exhibit an impressively high mass activity of 1027.1 mA mgPt^(−1) for MOR,much higher than that of commercial Pt/C(345.2 mA mgPt^(−1)),as well as good stability up to 5000 cycles.We are confident that this synthetic protocol can be further extended to synthesize various grain boundary-enriched metal scaffolds with broad applications in catalysis.展开更多
基金Sponsored by the National Basic Research Development Program of China(973 Program)(Grant No.2012CB619503)National High Technology Research and Development Program of China(863 Program)(Grant No.2013AA031001)International S&T Cooperation Program of China(Grant No.2012DFA50630)
文摘2024 Aluminum alloy powder( 60wt%) and Fe-based amorphous powder( 40 wt%) were adopted. They were mechanical machined for 48hours after being mixed. Bulk material was gained after Spark Plasma Sintering. The sintering parameters included sintering temperature,heating or cooling rates,pressure and holding time. 300 ℃- 800 ℃ were adopted while the heating or cooling rate was 100 ℃ / min and with the pressure of 50 MPa in the experiments. The holding time was 10 min or 20 min at different temperatures, respectively. Bulk materials after sintering were examined by Scanning Electron Microscopy and X-Ray Diffraction. The micro-hardness and relative density also were tested. The sintering temperature had the most significant influence on the microstructure and property of the bulk material. The influence of holding time came second while the heating or cooling rates and pressure were fixed. The density became larger with the increase of the temperature. The compactness was best at 500℃. The pressure and generation of high-temperature phases were the factors which affected the density and the compactness.
文摘With the large-scale service of lithium-ion batteries(LIBs),their failures have attracted significant attentions.While the decay of active materials is the primary cause for LIB failures,the degradation of auxiliary materials,such as current collector corrosion,should not be disregarded.Therefore,it is necessary to conduct a comprehensive review in this field.In this review,from the perspectives of electrochemistry and materials,we systematically summarize the corrosion behavior of aluminum cathode current collector and propose corresponding countermeasures.Firstly,the corrosion type is clarified based on the properties of passivation layers in different organic electrolyte components.Furthermore,a thoroughgoing analysis is presented to examine the impact of various factors on aluminum corrosion,including lithium salts,organic solvents,water impurities,and operating conditions.Subsequently,strategies for electrolyte and protection layer employed to suppress corrosion are discussed in detail.Lastly and most importantly,we provide insights and recommendations to prevent corrosion of current collectors,facilitate the development of advanced current collectors and the implementation of next-generation high-voltage stable LIBs.
基金supported by the National Natural Science Foundation of China (No.51671012)the China Postdoctoral Science Foundation (2019TQ0015).
文摘The effect of oxygen addition and annealing time on microstructure and mechanical properties of Ti-34Nb and Ti-34Nb-0.2O alloys was investigated.The addition of O suppresses the martensitic transformation.The phase composition changes from singleα''phase toα''+βphases with oxygen addition.The addition of oxygen increases strength significantly at as-received,cold-rolled,and annealed alloys through solid solution strengthening.The accumulation of abundance of defects and grain refinement introduced by cold rolling have a significant strengthening effect but also damage plasticity.The addition of oxygen increasesα/βtransformation temperature and promotes the precipitation ofαphase during annealing in Ti-34Nb-0.2O alloy.αprecipitates can inhibit grain growth during annealing.The strength decreases with annealing time increased due to the increase in grain size in Ti-34Nb alloy,while the strength increases in Ti-34Nb-0.2O alloy mainly due to the precipitation ofαphase.The cold rolling followed by annealing and addition of oxygen can improve the properties of alloys.
基金financially supported by the National Basic Research Program of China (No. 2012CB619503)the National High Technology Research and Development Program of China (No. 2013AA031001)the International Science & Technology Cooperation Program of China (No. 2012DFA50630)
文摘The Al-5Ti-0.5B-0.5C grain refiner was pre-pared by powder metallurgy(PM).Microstructures of the grain refiner and its grain refinement performance in commercially pure aluminum(Al)were investigated by X-ray diffraction(XRD),scanning electron microscopy(SEM),and differential scanning calorimetry(DSC).It is found that the average grain size of commercially pure Al can be reduced from~15,000 to~180μm by the addition of Al-5Ti-0.5B-0.5C grain refiner prepared by PM,based on 0.01 wt%Ti addition.The grain refinement efficiency begins to decrease slightly when the grain refiner is kept in the melt for 60 min.The grain refinement is attributed to high stability,proper size,and high density of Al3Ti,TiB2,and TiC particles.
基金supported by the Natural Science Foundation of Shanghai(Grant No.21ZR1445100)the National Natural Science Foundation of China(Grant No.52271108)+2 种基金the Foundation of Xi'an Key Laboratory of High-Performance Titanium Alloy(Grant No.NIN-HTL-2022-02)financial support from the Frontier and Key Projects of the Chinese Academy of Sciences(Grant No.QYZDJ-SSW-JSC031-01)financial support from Xi’an Science and Technology Plan Project(Grant No.2020YZ0028).
文摘A thermally induced hexagonal close-packed(HCP)to face-centered cubic(FCC)phase transition was investigated in anα-type Ti35 alloy with twinned structure by in situ heating transmission electron microscopy(TEM)and ab initio calculations.TEM observations indicated that the HCP to FCC phase transition occurred both within matrix/twin and at the twin boundaries in the thinner region of the TEM film,and the FCC-Ti precipitated as plates within the matrix/twin,while as equiaxed cells at twin boundaries.The crystallographic orientation relationship between HCP-Ti and FCC-Ti can be described as:{111}FCC//{0002}HCP and<110>FCC//<1210>HCP.The HCP to FCC phase transition was accomplished by forming an intermediate state with a BB stacking sequence through the slip of partial dislocations.The formation of such FCC-Ti may be related to the thermal stress and temperature.Ab initio calculations showed that the formation of FCC-Ti may also be related to the contamination of interstitial atoms such as oxygen.
基金Project supported by National High Technology Research and Development Program of China(2013AA031001)the National Basic Research Program of China(2012CB619503)International Science&Technology Cooperation Program of China(2012DFA50630)
文摘The Al-5Ti-0.2C-based grain refiners with different contents of rare earth(RE) were successfully prepared via powder metallurgy and vacuum casting. The microstructural evolution has been studied by X-ray diffraction(XRD), differential scanning calorimetry(DSC), scanning electron microscopy(SEM) and transmission electron microscopy(TEM). The results showed that the RE addition resulted in the formation of Ti Al3/Ti2Al20 RE core-shell structured primary particles, and the size of Ti Al3 core decreased, while the thickness of Ti2Al20 RE increased with increase of RE contents. As compared to Al-5Ti-0.2C grain refiner, the grain refining efficiency was gradually improved with increase of RE contents, which was mainly attributed to the Ti Al3/Ti2Al20 RE core-shell structured primary particles and insoluble Ti C nuclei formed in α-Al matrix. The formation mechanism of core-shell structure was further investigated based on Ginstling-Brounstein model.
基金financially support by National Key Research and Development Program of China(No.2017YFB0306205)National Natural Science Foundation of China(NSFC,No.51671012)+1 种基金the Fundamental Research Funds for the Central UniversitiesInternational Science and Technology Cooperation Program of China(2015DFA51430)。
文摘Mechanical properties and microstructural stability under the service temperature are important to the high temperature titanium alloy.In order to evaluate the potential in increase the service temperature of Ti alloy,two near-αTi alloys with high content of Al asα-stabilizer and Ta,Nb and/or Re asβ-stabilizers were designed and prepared by ingot metallurgy and thermomechanical processing,and the microstructure and mechanical properties before and after thermal exposure at 650℃ for 100 h were characterized.The results indicated that due to the weakβ-stabilizing ability of Ta and Nb elements,only a small amount ofβphase was formed in Ti-10Al-4Ta-2Nb alloy.With a trace Re addition,theβphase was obviously increased in Ti-10Al-4Ta-2Nb-0.25Re,indicating that the Re was a strongβ-stabilizer.Under the same thermomechanical conditions,the Re addition decreased the volume fraction of primaryα(α_(p))phase and refined the secondaryα(α_(s))phase evidently.The primaryαphase presented an obvious core-shell structure in the Ti-10Al-4Ta-2Nb alloy,with higher Al concentration in the shell.While the core-shell structure was not obvious in the Re-containing alloy due to the Re decreases the diffusion of Al,Ta and Nb elements.A large number of orderedα_(2)precipitates can be observed in theα_(p)andα_(s) phases of two alloys.Theα_(2)precipitates continuously grew up during thermal exposure,however,their growth rate in theα_(s)phase of Re-containing alloy were lower than that of Ti-10Al-4Ta-2Nb alloy.Although plenty of orderedα_(2)precipitates formed in the Ti-10Al-4Ta-2Nb alloy,the alloy had a certain plasticity at room temperature.The trace Re addition evidently increased the tensile strength but caused the decrease of the plasticity.After thermal exposure,the strength was further increased,while the plasticity was decreased for both of alloys.
基金The authors are grateful for the financial support by the National Key Research and Development Program of China(No.2016YFB0301103)the National Natural Science Foundation of China(NSFC,No.51401010).
文摘With the rapid development of 3C industries,the demand for high-thermal-conductivity magnesium alloys with high mechanical performance is increasing quickly.However,the thermal conductivities of most common Mg foundry alloys(such as Mg-9wt%-1wt%Zn)are still relatively low.In this study,we developed a high-thermal-conductivity Mg-4Al-4Zn-4RE-1Ca(wt%,AZEX4441)alloy with good mechanical properties for ultrathin-walled cellphone components via high-pressure die casting(HPDC).The HPDC AZEX4441 alloy exhibited a fine homogeneous microstructure(average grain size of 2.8μm)with granular Al_(11)RE_(3),fibrous Al_(2)REZn_(2),and networked Ca_(6)Mg_(2)Zn_(3) phases distributed at the grain boundaries.The room-temperature thermal conductivity of the HPDC AZEX4441 alloy was 94.4 W·m^(-1)·K^(-1),which was much higher than 53.7 W·m^(-1)·K^(-1) of the HPDC AZ91D alloy.Al and Zn in the AZEX4441 alloy were largely consumed by the formation of Al_(11)RE_(3),Al_(2)REZn_(2),and Ca_(2)Mg_(6)Zn_(3) phases because of the addition of RE and Ca.Therefore,the lattice distortion induced by solute atoms of the AZEX4441 alloy(0.171%)was much lower than that of the AZ91D alloy(0.441%),which was responsible for the high thermal conductivity of the AZEX4441 alloy.The AZEX4441 alloy exhibited a high yield strength of~185 MPa,an ultimate tensile strength of~233 MPa,and an elongation of~4.2%.This result indicated that the tensile properties were comparable with those of the AZ91D alloy.Therefore,this study contributed to the development of high-performance Mg alloys with a combination of high thermal conductivity,high strength,and good castability.
基金financially supported by the National Natural Science Foundation of China (Nos.51101003 and 51471012)
文摘A significant refinement of the microstructure of structural NiTi alloy was achieved through a combination of Al addition and fabrication by suction casting.This is attributed to the change from a layer-by-layer to volume solidification mode with Al content increasing,which causes a change in grain shape from columnar to equiaxed.Furthermore,when compared with conventional casting,suction casting optimizes the microstructure of the alloy by refining the grain size and ensuring a homogeneous distribution of Ti2 Ni and Ni_(2)TiAl phases.The high cooling rate of suction casting also delays the formation ofβ'-Ni_(2)TiAl phase.Finally,this fine microstructure and uniform distribution of intermetallic phases result in the ultimate compressive strength of up to 2463.7 MPa,representing an improvement of 370 MPa over conventionally cast NiTi-Al alloy.
基金financially supported by the National Science Foundation of China(Nos.51572007 and 51622203),"Recruitment Program of Global Experts"
文摘2D nanosheets such as graphene, silicene, phosphorene, metal dichalcogenides and MXenes are emerging and promising for lithium storage due to their ultrathin nature and corresponding chemical/physical properties. However, the serious restacking and aggregation of the 2D nanosheets are still hampering their applications. To circumvent the issues of 2D nanosheets, one efficient strategy is to construct 3D structures with hierarchical porous structures, good chemical/mechanical stabilities and tunable electrical conductivities. In this review, we firstly focus on the available synthetic approaches of 3D structures from 2D nanosheets, and then summarize the relationships between the microstructures of 3D structures built from 2D nanosheets and their electrochemical behaviors for lithium storage. On the basis of above results, some challenges are briefly discussed in the perspective of the development of various functional 3D structures.
基金the National Natural Science Foundation of China(Nos.51671012,51831006 and 51971009)the International Science and Technology Cooperation Program of China(No.2015DFA51430)the Fundamental Research Funds for the Central Universities。
文摘In this study,a novel strategy for developingα+βdual-phase titanium alloys with low Young's modulus and high yield strength was proposed,and a Ti-15Nb-5Zr-4Sn-1 Fe alloy was developed through theoretical composition design and microstructure manipulation.After hot-rolling and subsequent annealing,a high volume fraction of ultrafine grainedαphase embedded in metastableβ-matrix was formed in the microstructure as intended.Consequently,this alloy exhibits both low Young's modulus(61 GPa)and high yield strength(912 MPa).The experimental results prove that the proposed strategy is appropriate for developing titanium alloys with superior yield strength-to-modulus ratio than those of conventional metallic biomedical materials.Present study might shed light on the research and development of advanced biomedical titanium alloys with low Young's modulus and high yield strength.
文摘Primary solidification phase and lamellar orientation are investigated in Ti-45Al-7Nb alloy at very high ratio of temperature gradient to growth rate (G/v) by a liquid-metal-cooled directionally solidified method. It shows that Ti-45Al-7Nb alloy solidifies with primary α phase. Longitudinal (parallel to growth direction) microstructure shows that α dendrites in solid-liquid mushy zone are discontinuous and transverse microstructure of α dendrites is worm-like feature. Growth direction of α phase is about 80° away from〈0001〉α direction, and close to〈1120〉α direction. The corresponding lamellar orientation is aligned at the angle of about 10° to growth direction, which is consistent with α-dendrite growth direction according to Blackburn orientation relationship. Therefore, due to the altered growth direction of α phase, the lamellar orientation in Ti-45Al-7Nb alloy is controlled at the G/v ratio of 5×109 K·sm-2.
基金supported financially by the Fundamental Research Funds for the Central Universities(No.N180204015)supported by Chinese Academy of Sciences(CAS)and Japan Society for the Promotion of Science(JSPS)through the Bilateral Program(No.GJHZ1774)supported by Ministry of Education,Culture,Sports,Science and Technology(MEXT),Japan,through the Elements Strategy Initiative for Structural Materials(ESISM)Project and the Grant-in-Aid for Scientific Research(S)(No.15H05767)。
文摘Although Cu was studied extensively,the Hall-Petch relationship was mainly reported in the coarsegrained regime.In this work,fully recrystallized Cu specimens with a wide grain size regime of 0.51–14.93μm manifest a two-stage Hall-Petch relationship.There is a critical grain size of 3μm that divides stagesⅠandⅡwhere the Hall-Petch slope k value are quite different.The stageⅡis supposed to be validified down to 100 nm at least by comparing with a Cu-Ag alloy.The critical grain size varies in different materials systems,and the underline mechanisms are discussed based on the dislocation glide modes.
基金financially supported by the National Natural Science Foundation of China (NSFC) (No. 5110100)
文摘The microstructural evolution of Ni–42Ti–7Al and Ni–41Ti–7Al alloys as a function of solution and aging heat treatment was investigated using transmission electron microscopy(TEM), electron probe, and X-ray diffraction(XRD). The results reveal that the volume fraction of Ti2 Ni phase as well as its composition does not change significantly after as-solution treated at 1200 °C and aged at850 °C. At the early stage of the aging treatment at 850 °C for 1 h, the cuboidal b0 precipitate keeps coherency with the matrix; further aging, b0 precipitate coarsens, and the semicoherency between the b/b0 two phases are observed.The shape of coarsened b0 precipitates changes to the globule, and the interface dislocations are introduced accompanied by the occurrence of semicoherent precipitates. Under the same heat treatment, compared to the Ni–42Ti–7Al alloy, the lattice misfits of the Ni–41Ti–7Al alloy between the b and b0 two phases are larger, so the b0 precipitates in Ni–41Ti–7Al alloy are coarsened severely and easily lose coherency with the matrix. The thermal stability of Ni–41Ti–7Al alloy is much worse when aging at 850 °C.
基金This work was financially supported by the National Science Foundation of China(Nos.51622203 and 51572007),“Recruitment Program of Global Experts.”。
文摘Although platinum nanocrystals have been considered as potential electrocatalysts for methanol oxidation reaction(MOR)in fuel cells,the large-scale practical implementation has been stagnated by their limited abundance,easy poisoning,and low durability.Here,grain boundary-enriched platinum(GB-Pt)scaffolds are produced in large scale via facilely reducing fast cryomediated dynamic equilibrium hydrolysates of platinum salts.Such plentiful platinum grain boundaries are originated from the fast fusion of short platinum nanowires during reduction of the individually and homogeneously dispersed platinum intermediates.These grain boundaries can provide abundant active sites to efficiently catalyze MOR and meanwhile enable to oxidize the adsorbed poisonous CO during the electrocatalytic process.As a consequence,the as-synthesized GB-Pt scaffolds exhibit an impressively high mass activity of 1027.1 mA mgPt^(−1) for MOR,much higher than that of commercial Pt/C(345.2 mA mgPt^(−1)),as well as good stability up to 5000 cycles.We are confident that this synthetic protocol can be further extended to synthesize various grain boundary-enriched metal scaffolds with broad applications in catalysis.
