Magnesium alloys have emerged as promising light weight materials due to their low density,high specific strength,excellent machinability,and superior damping capacity,making them ideal for aerospace,automotive,and el...Magnesium alloys have emerged as promising light weight materials due to their low density,high specific strength,excellent machinability,and superior damping capacity,making them ideal for aerospace,automotive,and electronics applications.However,broader use of magnesium alloys is limited by poor thermo-mechanical performance,corrosion susceptibility,and low formability at room temperature.The addition of rare-earth elements such as gadolinium,yttrium,and neodymium has meaningfully improved these limitations,enhancing the overall performance of magnesium alloys.This review highlights recent advancements in rare-earth magnesium alloys,focusing on their improved thermo-mechanical properties,microstructural evolution,crystallization behavior,and texture development.Herein,strengthening mechanisms associated with rare-earth additions are discussed in detail.Furthermore,the article explores growing relevance of these alloys in advanced applications,including biomedical implants,Io T devices,aerospace structures,defense systems,and general engineering.With their enhanced mechanical and functional properties,rare-earth magnesium alloys represent a new generation of high-performance,functional materials poised to drive innovation across multiple technology sectors.展开更多
A process of purification of coal-based coke powder as anode the treatment of coke powder with dilute hydrofluoric acid solution, for Li-ion batteries was attempted. The process started with followed by united-acid-le...A process of purification of coal-based coke powder as anode the treatment of coke powder with dilute hydrofluoric acid solution, for Li-ion batteries was attempted. The process started with followed by united-acid-leaching using sulfuric acid and hydrochloric acid. The effects of altering the hydrofluoric acid addition, hydrofluoric acid concentration, contact time, temperature and acid type were investigated. A minimum ash content of 0.35% was obtained when proper conditions were applied. The electrochemical performance of purified coke powder shows greatly improved electrochemical performance. The as-purified coke powder presented an initial reversible capacity of 257.4 mAh/g and a retention rate of 95% after 50 cycles. The proposed purification process paves a way to prepare a promising anode material with good performance with low cost of coke powder for Li-ion batteries.展开更多
In this study,the selective laser melting(SLM)technology has been employed to manufacture a nickelbased superalloy which was conventionally prepared through powder metallurgy(PM)route.The microstructural features and ...In this study,the selective laser melting(SLM)technology has been employed to manufacture a nickelbased superalloy which was conventionally prepared through powder metallurgy(PM)route.The microstructural features and defects were systematically investigated both prior to and after heat treatment and compared with the PM counterpart.Both solidification cracking and liquation cracking were observed in the SLM specimen in which the grain misorientation and low melting point(γ+γ')eutectic played a vital role in their formation mechanism.Columnar grains oriented along building direction were ubiquitous,corresponding to strong<001>fiber texture.Solidification cell structures and melt pools are pervasive and noγ'precipitates were detected at about 10 nm scale before heat treatment.After supersolvus solution and two-step aging treatments,high volume fractionγ'precipitates emerged and their sizes and morphologies were comparable to those in PM alloy.<001>texture is relieved and columnar grains tend to become more equiaxed due to static recrystallization process and grain boundary migration events.Significant annealing twins formed in SLM alloy and are clarified as a consequence of recrystallization.Our results provide fundamental understandings for the SLM PM nickel-based superalloy both before and after heat treatment and demonstrate the potential to fabricate this group of alloys using SLM technology.展开更多
Effects of metal (Ni, Cu, Al) and composite metal (NiB, NiCu, NiCuB) nanopowders on the thermal decomposition of ammonium perchlorate (AP) and composite solid propellant ammonium perchlorate/hydroxyterminated polybuta...Effects of metal (Ni, Cu, Al) and composite metal (NiB, NiCu, NiCuB) nanopowders on the thermal decomposition of ammonium perchlorate (AP) and composite solid propellant ammonium perchlorate/hydroxyterminated polybutadiene (AP/HTPB) were studied by thermal analysis (DTA). The results show that metal and composite metal nanopowders all have good catalytic effects on the thermal decomposition of AP and AP/HTPB composite solid propellant. The effects of metal nanopowders on the thermal decomposition of AP are less than those of the composite metal nanopowders. The effects of metal and composite metal nanopowders on the thermal decomposition of AP are different from those on the thermal decomposition of the AP/HTPB composite solid propellant.展开更多
Perovskite LaMnO3 powders with an average crystallite size of 12.5 nm were rapidly synthesized via a microwave-induced autocombustion reaction using glycine as a fuel and nitrate as an oxidant. After self-propagating ...Perovskite LaMnO3 powders with an average crystallite size of 12.5 nm were rapidly synthesized via a microwave-induced autocombustion reaction using glycine as a fuel and nitrate as an oxidant. After self-propagating combustion, the desired nanocrystalline perovskite LaMnO3 was obtained and no further calcination was carried out. The possible processes of combustion reaction were discussed according to the principle of propellant chemistry. The autocombustion and thermal decomposition of the precursor were investigated using the TG-DTA and FT-IR techniques. The influences of glycine-nitrate molar ratio and heat-treatment temperature on the perovskite phase formation and crystallite size of as-burnt powder were studied by XRD. The morphology and size of the as-burnt powder before and after milling were characterized and compared by TEM.展开更多
The effects of size distribution,morphology and volume fraction ofγ′phase and grain size on tensile properties of powder processed Ni-based superalloy were investigated by using two different quenching methods.Oil q...The effects of size distribution,morphology and volume fraction ofγ′phase and grain size on tensile properties of powder processed Ni-based superalloy were investigated by using two different quenching methods.Oil quenching and air cooling were adopted with cooling rate of 183°C/s and 4?15°C/s,respectively.The experimental results show that the average size of the secondaryγ′after oil quenching is 24.5 nm compared with 49.8 nm under air cooling,and corresponding volume fractions ofγ′are 29%and 34%,respectively.Meanwhile,the average grain size remains nearly equivalent from both oil-quenching and air-cooling specimens.The tensile strength at room temperature is higher for the oil-quenched specimen than the equivalent from the air-cooled specimen,but the difference approaches each other as the temperature increases to 650°C.The fractography clearly demonstrates that transgranular fracture governs the failure process at ambient temperature,in contrast to the intergranular fracture at 650°C or even higher temperature.These two mechanical responses indicate the strengthening effects ofγ′precipitates and grain boundary for polycrystalline Ni-based superalloys at different temperatures.展开更多
With the rapid development of indium tin oxide(ITO)in the electronic display industry,choosing which raw powders to prepare high-quality ITO targets has always been a controversial topic.In the work,in order to clearl...With the rapid development of indium tin oxide(ITO)in the electronic display industry,choosing which raw powders to prepare high-quality ITO targets has always been a controversial topic.In the work,in order to clearly understand the effect of the raw powders on the microstructure and properties of ITO targets and thin films,tin-doped indium oxide(dITO)and In_(2)O_3-SnO_(2)mixed(mITO)powders were chosen to prepare ITO targets for depositing the films and a comparative study on their microstructure and properties was conducted.It is found that,(1)dITO targets possess a higher solid solubility of tin in indium oxide and more uniform elemental distribution,while there are a higher density,a finer grain size and a higher mass ratio of In_(2)O_3 to SnO_(2)for the mITO targets;(2)dITO films with more coarser columnar grains and a rougher surface prefer to grow along the[100]direction in an Ar atmosphere;(3)the conductive property of ITO films only depends on the doping amount of tin and is independent of the raw powders and the preparation process of the target source;(4)dITO films possess the superior optical property and narrower optical band gap;(5)the etching property of mITO films is superior to that of dITO films due to the lower solid solubility of tin in indium oxide.展开更多
In this study,molten salt was used as a solvent for calcium(Ca)to let a reduction-diffusion(R-D)reaction occur below the melting point of Ca(1115 K),which is the lower limit temperature of the co nventional RD process...In this study,molten salt was used as a solvent for calcium(Ca)to let a reduction-diffusion(R-D)reaction occur below the melting point of Ca(1115 K),which is the lower limit temperature of the co nventional RD process.When the R-D reaction is conducted below 923 K with LiCl molten salt,submicron-sized TbCu_(7)-type Sm-Fe powder is formed.The c/a ratio of the powder estimated by a synchrotron X-ray diffraction pattern is 0.8456,which is consistent with the Sm_(0.67)Fe_(5.667)(SmFe_(8.5))phase.An electron backscatter diffraction analysis reveals that single-crystalline TbCu_(7)-type SmFe_(8.5) powder was synthesized for the first time.展开更多
A novel salt-assisted combustion process with ethylene glycol as a fuel and nitrate as an oxidant to synthesize high surface area celia nanopowders was reported. The effects of various tunable conditions, such as fuel...A novel salt-assisted combustion process with ethylene glycol as a fuel and nitrate as an oxidant to synthesize high surface area celia nanopowders was reported. The effects of various tunable conditions, such as fuel-to-oxidant ratio, type of salts, and amount of added salts, on the characteristics of the as-prepared powders were investigated by X-ray diffraction, transmission electron microscopy and BET surface area measurement. A mechanism scheme was proposed to illustrate the possible formation processes of well-dispersed ceria nanoparticles in the salt-assisted combustion synthesis. It was verified that the simple introduction of leachable inert inorganic salts as an excellent agglomeration inhibitor into the redox mixture precursor leads to the formation of well-dispersed ceria particles with particle size in the range of 4 ～6 nm and a drastic increase in the surface area. The presence of KCl results in an over ten-fold increment in specific surface area from 14.10 m^2·g^-1 for the produced ceria powders via the conventional combustion synthesis process to 156.74 m^2·g^-1 for the product by the salt-assisted combustion synthesis process at the same molar ratio of ethylene glycol-nitrate.展开更多
In this work,the flow behaviors and microstructure evolution of a powder metallurgy nickel-based superalloy during superplastic compression is investigated.Based on the strain rate sensitivity m determined by flow dat...In this work,the flow behaviors and microstructure evolution of a powder metallurgy nickel-based superalloy during superplastic compression is investigated.Based on the strain rate sensitivity m determined by flow data,superplastic region is estimated at relatively low temperature and strain rate domains,specifically around 1000℃/10^-3s^-1.Thereafter,the cylinder specimens are isothermally compressed at 1000℃/10^-3s^-1 and 1025℃/10^-3s^-1 with different strains,to exam the superplasticity and related mechanisms.The experimental results indicate that the accumulated dislocations are mainly annihilated by dynamic recovery and dynamic recrystallization(DRX),and the grain boundary sliding(GBS)contributes to the total strain during superplastic compression as well.In addition,the cavities and cracks at triple junctions or interfaces between matrix and second phase particle have not been detected,which is different from superplastic tensile deformation.展开更多
In order to obtain ultrafine Nd-Fe-B powder, a spray-dried precursor was treated by reduction-diffusion (R/D) process. And, unlike the conventional R/D process, calcium reduction that is a crucial step for the formati...In order to obtain ultrafine Nd-Fe-B powder, a spray-dried precursor was treated by reduction-diffusion (R/D) process. And, unlike the conventional R/D process, calcium reduction that is a crucial step for the formation of Nd2Fe14B was performed without conglomerating the precursor with Ca powder. By adopting this modified process, it is possible to synthesize the hard magnetic Nd2Fe14B at the reaction temperature as low as 850 ℃. The average size of Nd2Fe14B particles that are uniformly distributed in the optimally treated powder was <<1 μm. Most Nd2Fe14B particles were enclosed with thin layers of Nd-rich phase. Typical magnetic properties of such powder without eliminating impurity CaO were iHc=～5.9 kOe, Br=～5.5 kG, and (BH)max=～6 MGOe.展开更多
Carbon fiber reinforced silicon carbide ceramic composite(C/SiC)has become a key structural material due to its excellent high temperature resistance,corrosion resistance and oxidation resistance.However,C/SiC composi...Carbon fiber reinforced silicon carbide ceramic composite(C/SiC)has become a key structural material due to its excellent high temperature resistance,corrosion resistance and oxidation resistance.However,C/SiC composites are prone to oxidation under long-term high temperature loading conditions.In this work,the research progress of SiC coating and its modified coating on the surface of C/SiC composite is reviewed.The optimization of these coatings mainly involves two aspects:structure and composition.The focus of structural optimization is to improve the interphase structure by such as SiC nanowires,thereby improving the interfacial bonding strength between the coatings and between the coatings and the substrate.The focus of composition optimization is to improve the performance of the coatings under high temperature loads by rare earth silicates,etc.The modification strategies of various modified coatings are emphatically introduced,which is helpful to guide the preparation of high-performance C/SiC coating materials in the future.展开更多
Porous intermetallics show potential in the field of filtration and separation as well as in the field of catalysis.Herein,porous Ti Fe2intermetallics were fabricated by the reactive synthesis of elemental powders.The...Porous intermetallics show potential in the field of filtration and separation as well as in the field of catalysis.Herein,porous Ti Fe2intermetallics were fabricated by the reactive synthesis of elemental powders.The phase transformation and pore formation of porous TiFe2intermetallics were investigated,and its corrosion behavior and hydrogen evolution reaction(HER)performance in alkali solution were studied.Porous TiFe2intermetallics with porosity in the range of 34.4%-56.4%were synthesized by the diffusion reaction of Ti and Fe elements,and the pore formation of porous TiFe2intermetallic compound is the result of a combination of the bridging effect and the Kirkendall effect.The porous TiFe2samples exhibit better corrosion resistance compared with porous 316L stainless steel,which is related to the formation of uniform nanosheets on the surface that hinder further corrosion,and porous TiFe2electrode shows the overpotential of 220.6 and 295.6 mV at 10 and 100 mA·cm-2,suggesting a good catalytic performance.The synthesized porous Fe-based intermetallic has a controllable pore structure as well as excellent corrosion resistance,showing its potential in the field of filtration and separation.展开更多
Direct explosive compaction and sintering of a mixture of Ti-30Al-2Mn(wt%)and Ti-38Al-2Mn(wt%) intermetallic compound powders were carried out.Microstructure and phase characteristics of the alloys were analysed by TE...Direct explosive compaction and sintering of a mixture of Ti-30Al-2Mn(wt%)and Ti-38Al-2Mn(wt%) intermetallic compound powders were carried out.Microstructure and phase characteristics of the alloys were analysed by TEM,SEM,X-ray diffractometry and optical microscopy.The results showed that the rel- ative density of the samples which were explosive-compacted and sintered reached 99.90%,and fine grain structure was obtained.Through the explosive-compacting and then sintering at 1373 K in argon atmos- phere,mutual diffusion between Ti-30Al-2Mn particles and Ti-38Al-2Mn particles took place and TiAl phase was formed in the alloy.TiAl based alloys prepared by high-energy ball-milling powders had much fi- ner grain size than those prepared by general ball-milling powdeis.展开更多
The present study introduces a screw-pressing charging method to tackle deficiencies in automation and charge uniformity during the melt-casting of polymer-based energetic materials.To ensure the safety of the experim...The present study introduces a screw-pressing charging method to tackle deficiencies in automation and charge uniformity during the melt-casting of polymer-based energetic materials.To ensure the safety of the experiments,this study used inert materials with similar physical properties to partially substitute for the actual energetic components in the preparation of simulant materials.By thoroughly analyzing slurry physical properties,a simulation framework and an extensive performance evaluation method were developed.Such tools guide the design of the structure and configuration of process parameters.Results demonstrate that employing the Pin element significantly enhances radial mixing within the screw,minimizes temperature variations in the slurry,and improves both efficiency and safety in the mixing process.Further,adjustments such as widening the cone angle of the barrel,modifying the solid content of the slurry,and varying the speed of the screw can optimize the mechanical and thermal coupling in the flow field.These adjustments promote higher-quality slurry and create a safer production environment for the extrusion process.展开更多
The hot compression curves and deformed microstructures were investigated under various hot deformation conditions in three states:hot isostatic pressing(HIP,A1),HIP+hot extrusion at 1100℃(A2),and HIP+hot extrusion a...The hot compression curves and deformed microstructures were investigated under various hot deformation conditions in three states:hot isostatic pressing(HIP,A1),HIP+hot extrusion at 1100℃(A2),and HIP+hot extrusion at 1150℃(A3).The results show that A2 sample,extruded at 1100℃ with uniform γ+γ′duplex microstructures,demonstrates excellent hot deformation behavior at both 1050 and 1100℃.The true stress-true strain curves of A2 sample maintain a hardening-softening equilibrium over a larger strain range,with post-deformation average grain size of 5μm.The as-HIPed A1 sample and 1150℃ extruded A3 sample exhibit a softening region in deformation curves at 1050℃,and the grain microstructures reflect an incomplete recrystallized state,i.e.combination of fine recrystallized grains and initial larger grains,characterized by a necklace-like microstructure.The predominant recrystallization mechanism for these samples is strain-induced boundary migration.At 1150℃ with a strain rate of 0.001 s^(-1),the influence of the initial microstructure on hot deformation behavior and resultant microstructure is relatively less pronounced,and postdeformation microstructures are fully recrystallized grains.Fine-grained microstructures are conducive to maximizing the hot deformation potential of alloy.By judiciously adjusting deformation regimes,a fine and uniform deformed microstructure can be obtained.展开更多
The microstructure of single crystal superalloy is relatively simple,consisting primarily ofγdendrites andγ/γ′eutectics.During the directional solidification process of Ni-based single crystal superalloys,withdraw...The microstructure of single crystal superalloy is relatively simple,consisting primarily ofγdendrites andγ/γ′eutectics.During the directional solidification process of Ni-based single crystal superalloys,withdrawal rate is a critical parameter affecting the spatial distribution ofγ/γ′eutectic along gravity direction.The results show that theγ/γ′eutectic fraction of the upper platform surface is always higher than that of the lower one,regardless of withdrawal rate.As the withdrawal rate decreases,there is a significant increase inγ/γ′eutectic fraction on the upper surface,while it decreases on the lower surface.The upward accumulation ofγ/γ′eutectic becomes more severe as the withdrawal rate decreases.It is also found that the percentage of Al+Ta is positively correlated with theγ/γ′eutectic fraction.Thermo-solute convection of Al and Ta solutes in the solidification front is the prime reason for the non-uniform distribution of eutectic.The non-uniform distribution ofγ/γ′eutectic cannot be eliminated even after subsequent solution heat treatment,resulting in excess eutectic on the upper surface and thus leading to the scrapping of the blade.展开更多
The present investigation introduces a composite frequency selective Rasorber(CFSR)that demonstrates a wide−1 dB transmission band,two high absorption bands with absorptivity higher than 90%,and large oblique incidenc...The present investigation introduces a composite frequency selective Rasorber(CFSR)that demonstrates a wide−1 dB transmission band,two high absorption bands with absorptivity higher than 90%,and large oblique incidence angles up to 60°.The CFSR consists of four functional layers separated by three dielectric slabs,which includes lossless metasurface-Ⅰ(MS-Ⅰ),loss metasurface-Ⅱ(MS-Ⅱ),loss metasurface-Ⅲ(MS-Ⅲ),and a three-dimensional metastructure(3D-MS).MS-Ⅰfunctions as a reflector for two absorption bands with a minimal insertion loss transmission window.MS-Ⅱis designed for high-frequency absorption.MS-Ⅲserves as a low-frequency absorption layer for CFSR and an impedance matching layer for MS-Ⅱ.The design methodologies for the transmission window in MS-III and the introduction of 3D-MS are key to achieving high-performance CFSR.The physical mechanisms of CFSR are explained through equivalent circuit model(ECM)analysis and impedance characterization.Finally,measurement results confirm that the proposed CFSR exhibits a−1 dB transmission band ranging from 8.79 to 10.41 GHz with a minimum insertion loss of 0.44 dB at 9.59 GHz;furthermore,the frequency range where reflection coefficient remains below−10 dB is measured to be between 3.33 and 18.00 GHz,aligning well with simulation outcomes.展开更多
The durability performance in molten aluminum with high chemical activity is considered to be a crucial factor for the application of traditional ceramicmatrix composites in the aluminum industry.Herein,novel Ti(C,N)c...The durability performance in molten aluminum with high chemical activity is considered to be a crucial factor for the application of traditional ceramicmatrix composites in the aluminum industry.Herein,novel Ti(C,N)cermet composites with excellent corrosion resistance,featuring distinct ratios of high-entropy alloy binders,were meticulously synthesized by spark plasma sintering(SPS).The synergetic effect of porosity and binder on the corrosion resistance was detailed analyzed.The results show that 8 wt%binder provides an optimum balance of porosity,hardness,fracture toughness and corrosion resistance of the cermets.The appealing corrosion resistance is intimately associated with the formation of a continuous layer consisting of Ti N/Al N,which is introduced through the decarburization of the Ti(C,N)cermets.Additionally,a corrosion mechanism is proposed to elucidate the formation of alternating morphologies within the reaction layers of the cermets.This work is beneficial for selecting structural materials for use in the aluminum industry.展开更多
The selective reduction of carbon dioxide(CO_(2))into high-value-added chemicals is one of the most effective means to solve the current energy and environmental problems,which could realize the utilization of CO_(2) ...The selective reduction of carbon dioxide(CO_(2))into high-value-added chemicals is one of the most effective means to solve the current energy and environmental problems,which could realize the utilization of CO_(2) and promote the balance of the carbon cycle.Formate is one of the most economical and practical products of all the electrochemical CO_(2) reduction products.Among the many metal-based electrocatalysts that can convert CO_(2) into formate,Sn-based catalysts have received a lot of attention because of their low-cost,non-toxic characteristics and high selectivity for formate.In this article,the most recent development of Sn-based electrocatalysts is comprehensively summarized by giving examples,which are mainly divided into monometallic Sn,alloyed Sn,Sn-based compounds and Sn composite catalysts.Finally,the current performance enhancement strategies and future directions of the field are summarized.展开更多
基金the support of the SPARC project(P3808)UKIERI-4 Strand 1 Institutional Research&Mobility Partnerships Grant(45580615 UKIERISPARC/01/18)under the Indo-UK schemeSKT extends heartfelt gratitude to Nitte University for providing the research grant(grant no.NUFR-23-070)。
文摘Magnesium alloys have emerged as promising light weight materials due to their low density,high specific strength,excellent machinability,and superior damping capacity,making them ideal for aerospace,automotive,and electronics applications.However,broader use of magnesium alloys is limited by poor thermo-mechanical performance,corrosion susceptibility,and low formability at room temperature.The addition of rare-earth elements such as gadolinium,yttrium,and neodymium has meaningfully improved these limitations,enhancing the overall performance of magnesium alloys.This review highlights recent advancements in rare-earth magnesium alloys,focusing on their improved thermo-mechanical properties,microstructural evolution,crystallization behavior,and texture development.Herein,strengthening mechanisms associated with rare-earth additions are discussed in detail.Furthermore,the article explores growing relevance of these alloys in advanced applications,including biomedical implants,Io T devices,aerospace structures,defense systems,and general engineering.With their enhanced mechanical and functional properties,rare-earth magnesium alloys represent a new generation of high-performance,functional materials poised to drive innovation across multiple technology sectors.
基金Projects(51274240,51204209) supported by the National Natural Science Foundation of ChinaProject(2012M521545) supported by the National Postdoctoral Science Foundation of China
文摘A process of purification of coal-based coke powder as anode the treatment of coke powder with dilute hydrofluoric acid solution, for Li-ion batteries was attempted. The process started with followed by united-acid-leaching using sulfuric acid and hydrochloric acid. The effects of altering the hydrofluoric acid addition, hydrofluoric acid concentration, contact time, temperature and acid type were investigated. A minimum ash content of 0.35% was obtained when proper conditions were applied. The electrochemical performance of purified coke powder shows greatly improved electrochemical performance. The as-purified coke powder presented an initial reversible capacity of 257.4 mAh/g and a retention rate of 95% after 50 cycles. The proposed purification process paves a way to prepare a promising anode material with good performance with low cost of coke powder for Li-ion batteries.
基金supported financially by the National Key Research and Development Program of China(No.2018YFB0704100)the Outstanding Graduate Project of Advanced Non-ferrous Metal Structural Materials and Manufacturing Collaborative Innovation Center+2 种基金the Funding from the Opening Project of State Key Laboratory of Nickel and Cobalt Resources Comprehensive Utilizationthe Project of Innovation and Entrepreneur Team Introduced by Guangdong Province(No.201301G0105337290)the Special Funds for Future Industrial Development of Shenzhen(No.HKHTZD20140702020004)。
文摘In this study,the selective laser melting(SLM)technology has been employed to manufacture a nickelbased superalloy which was conventionally prepared through powder metallurgy(PM)route.The microstructural features and defects were systematically investigated both prior to and after heat treatment and compared with the PM counterpart.Both solidification cracking and liquation cracking were observed in the SLM specimen in which the grain misorientation and low melting point(γ+γ')eutectic played a vital role in their formation mechanism.Columnar grains oriented along building direction were ubiquitous,corresponding to strong<001>fiber texture.Solidification cell structures and melt pools are pervasive and noγ'precipitates were detected at about 10 nm scale before heat treatment.After supersolvus solution and two-step aging treatments,high volume fractionγ'precipitates emerged and their sizes and morphologies were comparable to those in PM alloy.<001>texture is relieved and columnar grains tend to become more equiaxed due to static recrystallization process and grain boundary migration events.Significant annealing twins formed in SLM alloy and are clarified as a consequence of recrystallization.Our results provide fundamental understandings for the SLM PM nickel-based superalloy both before and after heat treatment and demonstrate the potential to fabricate this group of alloys using SLM technology.
文摘Effects of metal (Ni, Cu, Al) and composite metal (NiB, NiCu, NiCuB) nanopowders on the thermal decomposition of ammonium perchlorate (AP) and composite solid propellant ammonium perchlorate/hydroxyterminated polybutadiene (AP/HTPB) were studied by thermal analysis (DTA). The results show that metal and composite metal nanopowders all have good catalytic effects on the thermal decomposition of AP and AP/HTPB composite solid propellant. The effects of metal nanopowders on the thermal decomposition of AP are less than those of the composite metal nanopowders. The effects of metal and composite metal nanopowders on the thermal decomposition of AP are different from those on the thermal decomposition of the AP/HTPB composite solid propellant.
基金Project supported bythe National Natural Science Foundation of China (50306008) and the Fund fromthe Preli minary Research Project of General Equipment Ministry (41328030507)
文摘Perovskite LaMnO3 powders with an average crystallite size of 12.5 nm were rapidly synthesized via a microwave-induced autocombustion reaction using glycine as a fuel and nitrate as an oxidant. After self-propagating combustion, the desired nanocrystalline perovskite LaMnO3 was obtained and no further calcination was carried out. The possible processes of combustion reaction were discussed according to the principle of propellant chemistry. The autocombustion and thermal decomposition of the precursor were investigated using the TG-DTA and FT-IR techniques. The influences of glycine-nitrate molar ratio and heat-treatment temperature on the perovskite phase formation and crystallite size of as-burnt powder were studied by XRD. The morphology and size of the as-burnt powder before and after milling were characterized and compared by TEM.
基金Project(2012AA03A514)supported by the National High-Tech Research and Development Program of ChinaProjects(2016YFB0700300,2016YFB0701404)supported by the National Key Research and Development Program of China
文摘The effects of size distribution,morphology and volume fraction ofγ′phase and grain size on tensile properties of powder processed Ni-based superalloy were investigated by using two different quenching methods.Oil quenching and air cooling were adopted with cooling rate of 183°C/s and 4?15°C/s,respectively.The experimental results show that the average size of the secondaryγ′after oil quenching is 24.5 nm compared with 49.8 nm under air cooling,and corresponding volume fractions ofγ′are 29%and 34%,respectively.Meanwhile,the average grain size remains nearly equivalent from both oil-quenching and air-cooling specimens.The tensile strength at room temperature is higher for the oil-quenched specimen than the equivalent from the air-cooled specimen,but the difference approaches each other as the temperature increases to 650°C.The fractography clearly demonstrates that transgranular fracture governs the failure process at ambient temperature,in contrast to the intergranular fracture at 650°C or even higher temperature.These two mechanical responses indicate the strengthening effects ofγ′precipitates and grain boundary for polycrystalline Ni-based superalloys at different temperatures.
基金financially supported by the National Key R&D Program of China(No.2017YFB0305401)the National Natural Science Foundation of China(Nos.51874369 and 51871249)the Huxiang Young Talents Plan(No.2018RS3007)。
文摘With the rapid development of indium tin oxide(ITO)in the electronic display industry,choosing which raw powders to prepare high-quality ITO targets has always been a controversial topic.In the work,in order to clearly understand the effect of the raw powders on the microstructure and properties of ITO targets and thin films,tin-doped indium oxide(dITO)and In_(2)O_3-SnO_(2)mixed(mITO)powders were chosen to prepare ITO targets for depositing the films and a comparative study on their microstructure and properties was conducted.It is found that,(1)dITO targets possess a higher solid solubility of tin in indium oxide and more uniform elemental distribution,while there are a higher density,a finer grain size and a higher mass ratio of In_(2)O_3 to SnO_(2)for the mITO targets;(2)dITO films with more coarser columnar grains and a rougher surface prefer to grow along the[100]direction in an Ar atmosphere;(3)the conductive property of ITO films only depends on the doping amount of tin and is independent of the raw powders and the preparation process of the target source;(4)dITO films possess the superior optical property and narrower optical band gap;(5)the etching property of mITO films is superior to that of dITO films due to the lower solid solubility of tin in indium oxide.
基金Project supported by JSPS KAKENHI(16K18230,18K13986,20K05072)。
文摘In this study,molten salt was used as a solvent for calcium(Ca)to let a reduction-diffusion(R-D)reaction occur below the melting point of Ca(1115 K),which is the lower limit temperature of the co nventional RD process.When the R-D reaction is conducted below 923 K with LiCl molten salt,submicron-sized TbCu_(7)-type Sm-Fe powder is formed.The c/a ratio of the powder estimated by a synchrotron X-ray diffraction pattern is 0.8456,which is consistent with the Sm_(0.67)Fe_(5.667)(SmFe_(8.5))phase.An electron backscatter diffraction analysis reveals that single-crystalline TbCu_(7)-type SmFe_(8.5) powder was synthesized for the first time.
基金Project supported bythe National Natural Science Foundation of China (50306008) andthefundfromthe Preli minary ResearchProject of General Equipment Ministry (41328030507)
文摘A novel salt-assisted combustion process with ethylene glycol as a fuel and nitrate as an oxidant to synthesize high surface area celia nanopowders was reported. The effects of various tunable conditions, such as fuel-to-oxidant ratio, type of salts, and amount of added salts, on the characteristics of the as-prepared powders were investigated by X-ray diffraction, transmission electron microscopy and BET surface area measurement. A mechanism scheme was proposed to illustrate the possible formation processes of well-dispersed ceria nanoparticles in the salt-assisted combustion synthesis. It was verified that the simple introduction of leachable inert inorganic salts as an excellent agglomeration inhibitor into the redox mixture precursor leads to the formation of well-dispersed ceria particles with particle size in the range of 4 ～6 nm and a drastic increase in the surface area. The presence of KCl results in an over ten-fold increment in specific surface area from 14.10 m^2·g^-1 for the produced ceria powders via the conventional combustion synthesis process to 156.74 m^2·g^-1 for the product by the salt-assisted combustion synthesis process at the same molar ratio of ethylene glycol-nitrate.
基金supported financially by the National Key Research and Development Program of China (No.2016YFB0701404)the National Natural Science Foundation of China (No.91860105)the Fund from Innovation and Entrepreneur Team Introduced by Guangdong Province (No. 201301G0105337290)
文摘In this work,the flow behaviors and microstructure evolution of a powder metallurgy nickel-based superalloy during superplastic compression is investigated.Based on the strain rate sensitivity m determined by flow data,superplastic region is estimated at relatively low temperature and strain rate domains,specifically around 1000℃/10^-3s^-1.Thereafter,the cylinder specimens are isothermally compressed at 1000℃/10^-3s^-1 and 1025℃/10^-3s^-1 with different strains,to exam the superplasticity and related mechanisms.The experimental results indicate that the accumulated dislocations are mainly annihilated by dynamic recovery and dynamic recrystallization(DRX),and the grain boundary sliding(GBS)contributes to the total strain during superplastic compression as well.In addition,the cavities and cracks at triple junctions or interfaces between matrix and second phase particle have not been detected,which is different from superplastic tensile deformation.
文摘In order to obtain ultrafine Nd-Fe-B powder, a spray-dried precursor was treated by reduction-diffusion (R/D) process. And, unlike the conventional R/D process, calcium reduction that is a crucial step for the formation of Nd2Fe14B was performed without conglomerating the precursor with Ca powder. By adopting this modified process, it is possible to synthesize the hard magnetic Nd2Fe14B at the reaction temperature as low as 850 ℃. The average size of Nd2Fe14B particles that are uniformly distributed in the optimally treated powder was <<1 μm. Most Nd2Fe14B particles were enclosed with thin layers of Nd-rich phase. Typical magnetic properties of such powder without eliminating impurity CaO were iHc=～5.9 kOe, Br=～5.5 kG, and (BH)max=～6 MGOe.
基金The authors would like to thank the National Key Research and Development Program of China(No.2021YFB3703800)the National Natural Science Foundation of China(No.52075555)the Hunan Provincial Intelligent Agricultural Machinery Equipment Innovation Project in 2023 by Hunan Provincial Department of Agriculture and Rural,China,for their financial support.
文摘Carbon fiber reinforced silicon carbide ceramic composite(C/SiC)has become a key structural material due to its excellent high temperature resistance,corrosion resistance and oxidation resistance.However,C/SiC composites are prone to oxidation under long-term high temperature loading conditions.In this work,the research progress of SiC coating and its modified coating on the surface of C/SiC composite is reviewed.The optimization of these coatings mainly involves two aspects:structure and composition.The focus of structural optimization is to improve the interphase structure by such as SiC nanowires,thereby improving the interfacial bonding strength between the coatings and between the coatings and the substrate.The focus of composition optimization is to improve the performance of the coatings under high temperature loads by rare earth silicates,etc.The modification strategies of various modified coatings are emphatically introduced,which is helpful to guide the preparation of high-performance C/SiC coating materials in the future.
基金financially supported by the National Natural Science Foundation of China(No.51971251)。
文摘Porous intermetallics show potential in the field of filtration and separation as well as in the field of catalysis.Herein,porous Ti Fe2intermetallics were fabricated by the reactive synthesis of elemental powders.The phase transformation and pore formation of porous TiFe2intermetallics were investigated,and its corrosion behavior and hydrogen evolution reaction(HER)performance in alkali solution were studied.Porous TiFe2intermetallics with porosity in the range of 34.4%-56.4%were synthesized by the diffusion reaction of Ti and Fe elements,and the pore formation of porous TiFe2intermetallic compound is the result of a combination of the bridging effect and the Kirkendall effect.The porous TiFe2samples exhibit better corrosion resistance compared with porous 316L stainless steel,which is related to the formation of uniform nanosheets on the surface that hinder further corrosion,and porous TiFe2electrode shows the overpotential of 220.6 and 295.6 mV at 10 and 100 mA·cm-2,suggesting a good catalytic performance.The synthesized porous Fe-based intermetallic has a controllable pore structure as well as excellent corrosion resistance,showing its potential in the field of filtration and separation.
基金Project was supported by National Advanced Materials Committee of China.
文摘Direct explosive compaction and sintering of a mixture of Ti-30Al-2Mn(wt%)and Ti-38Al-2Mn(wt%) intermetallic compound powders were carried out.Microstructure and phase characteristics of the alloys were analysed by TEM,SEM,X-ray diffractometry and optical microscopy.The results showed that the rel- ative density of the samples which were explosive-compacted and sintered reached 99.90%,and fine grain structure was obtained.Through the explosive-compacting and then sintering at 1373 K in argon atmos- phere,mutual diffusion between Ti-30Al-2Mn particles and Ti-38Al-2Mn particles took place and TiAl phase was formed in the alloy.TiAl based alloys prepared by high-energy ball-milling powders had much fi- ner grain size than those prepared by general ball-milling powdeis.
基金financially supported by the Fundamental Research Funds for the Central Universities(Grant No.30923011018)。
文摘The present study introduces a screw-pressing charging method to tackle deficiencies in automation and charge uniformity during the melt-casting of polymer-based energetic materials.To ensure the safety of the experiments,this study used inert materials with similar physical properties to partially substitute for the actual energetic components in the preparation of simulant materials.By thoroughly analyzing slurry physical properties,a simulation framework and an extensive performance evaluation method were developed.Such tools guide the design of the structure and configuration of process parameters.Results demonstrate that employing the Pin element significantly enhances radial mixing within the screw,minimizes temperature variations in the slurry,and improves both efficiency and safety in the mixing process.Further,adjustments such as widening the cone angle of the barrel,modifying the solid content of the slurry,and varying the speed of the screw can optimize the mechanical and thermal coupling in the flow field.These adjustments promote higher-quality slurry and create a safer production environment for the extrusion process.
基金Shenzhen Science and Technology Program(KJZD20230923113900001)Project of Industry and Information Technology Bureau of Shenzhen Municipality(201806071403422960)。
文摘The hot compression curves and deformed microstructures were investigated under various hot deformation conditions in three states:hot isostatic pressing(HIP,A1),HIP+hot extrusion at 1100℃(A2),and HIP+hot extrusion at 1150℃(A3).The results show that A2 sample,extruded at 1100℃ with uniform γ+γ′duplex microstructures,demonstrates excellent hot deformation behavior at both 1050 and 1100℃.The true stress-true strain curves of A2 sample maintain a hardening-softening equilibrium over a larger strain range,with post-deformation average grain size of 5μm.The as-HIPed A1 sample and 1150℃ extruded A3 sample exhibit a softening region in deformation curves at 1050℃,and the grain microstructures reflect an incomplete recrystallized state,i.e.combination of fine recrystallized grains and initial larger grains,characterized by a necklace-like microstructure.The predominant recrystallization mechanism for these samples is strain-induced boundary migration.At 1150℃ with a strain rate of 0.001 s^(-1),the influence of the initial microstructure on hot deformation behavior and resultant microstructure is relatively less pronounced,and postdeformation microstructures are fully recrystallized grains.Fine-grained microstructures are conducive to maximizing the hot deformation potential of alloy.By judiciously adjusting deformation regimes,a fine and uniform deformed microstructure can be obtained.
基金Shenzhen Science and Technology Program(JSGG20220831092800001)。
文摘The microstructure of single crystal superalloy is relatively simple,consisting primarily ofγdendrites andγ/γ′eutectics.During the directional solidification process of Ni-based single crystal superalloys,withdrawal rate is a critical parameter affecting the spatial distribution ofγ/γ′eutectic along gravity direction.The results show that theγ/γ′eutectic fraction of the upper platform surface is always higher than that of the lower one,regardless of withdrawal rate.As the withdrawal rate decreases,there is a significant increase inγ/γ′eutectic fraction on the upper surface,while it decreases on the lower surface.The upward accumulation ofγ/γ′eutectic becomes more severe as the withdrawal rate decreases.It is also found that the percentage of Al+Ta is positively correlated with theγ/γ′eutectic fraction.Thermo-solute convection of Al and Ta solutes in the solidification front is the prime reason for the non-uniform distribution of eutectic.The non-uniform distribution ofγ/γ′eutectic cannot be eliminated even after subsequent solution heat treatment,resulting in excess eutectic on the upper surface and thus leading to the scrapping of the blade.
基金Project(2021RC3003) supported by the Hunan Science and Technology Innovation Talents Program,China。
文摘The present investigation introduces a composite frequency selective Rasorber(CFSR)that demonstrates a wide−1 dB transmission band,two high absorption bands with absorptivity higher than 90%,and large oblique incidence angles up to 60°.The CFSR consists of four functional layers separated by three dielectric slabs,which includes lossless metasurface-Ⅰ(MS-Ⅰ),loss metasurface-Ⅱ(MS-Ⅱ),loss metasurface-Ⅲ(MS-Ⅲ),and a three-dimensional metastructure(3D-MS).MS-Ⅰfunctions as a reflector for two absorption bands with a minimal insertion loss transmission window.MS-Ⅱis designed for high-frequency absorption.MS-Ⅲserves as a low-frequency absorption layer for CFSR and an impedance matching layer for MS-Ⅱ.The design methodologies for the transmission window in MS-III and the introduction of 3D-MS are key to achieving high-performance CFSR.The physical mechanisms of CFSR are explained through equivalent circuit model(ECM)analysis and impedance characterization.Finally,measurement results confirm that the proposed CFSR exhibits a−1 dB transmission band ranging from 8.79 to 10.41 GHz with a minimum insertion loss of 0.44 dB at 9.59 GHz;furthermore,the frequency range where reflection coefficient remains below−10 dB is measured to be between 3.33 and 18.00 GHz,aligning well with simulation outcomes.
基金financially supported by the National Natural Science Foundation of China(No.52271014)the Foundation of Education Bureau of Hunan Province(No.22B0163)Jiangxi Provincial Department of Education(No.GJJ2200819)。
文摘The durability performance in molten aluminum with high chemical activity is considered to be a crucial factor for the application of traditional ceramicmatrix composites in the aluminum industry.Herein,novel Ti(C,N)cermet composites with excellent corrosion resistance,featuring distinct ratios of high-entropy alloy binders,were meticulously synthesized by spark plasma sintering(SPS).The synergetic effect of porosity and binder on the corrosion resistance was detailed analyzed.The results show that 8 wt%binder provides an optimum balance of porosity,hardness,fracture toughness and corrosion resistance of the cermets.The appealing corrosion resistance is intimately associated with the formation of a continuous layer consisting of Ti N/Al N,which is introduced through the decarburization of the Ti(C,N)cermets.Additionally,a corrosion mechanism is proposed to elucidate the formation of alternating morphologies within the reaction layers of the cermets.This work is beneficial for selecting structural materials for use in the aluminum industry.
基金Project(52204378)supported by the National Natural Science Foundation of China。
文摘The selective reduction of carbon dioxide(CO_(2))into high-value-added chemicals is one of the most effective means to solve the current energy and environmental problems,which could realize the utilization of CO_(2) and promote the balance of the carbon cycle.Formate is one of the most economical and practical products of all the electrochemical CO_(2) reduction products.Among the many metal-based electrocatalysts that can convert CO_(2) into formate,Sn-based catalysts have received a lot of attention because of their low-cost,non-toxic characteristics and high selectivity for formate.In this article,the most recent development of Sn-based electrocatalysts is comprehensively summarized by giving examples,which are mainly divided into monometallic Sn,alloyed Sn,Sn-based compounds and Sn composite catalysts.Finally,the current performance enhancement strategies and future directions of the field are summarized.
