Three types of NdFeB magnets with the same composition and different grain sizes were prepared,and then the grain boundary diffusion was conducted using metal Tb under the same technical parameters.The effect of grain...Three types of NdFeB magnets with the same composition and different grain sizes were prepared,and then the grain boundary diffusion was conducted using metal Tb under the same technical parameters.The effect of grain size on the grain boundary diffusion process and properties of sintered NdFeB magnets was investigated.The diffusion process was assessed using X-ray diffractometer,field emission scanning electron microscope,and electron probe microanalyzer.The magnetic properties of the magnet before and after diffusion were investigated.The results show that the grain refinement of the magnet leads to higher Tb utilization efficiency and results in higher coercivity at different temperatures.It can be attributed to the formation of a deeper and more complete core-shell structure,resulting in better magnetic isolation and higher anisotropy of the Nd_(2)Fe_(14)B grains.This work may shed light on developing high coercivity with low heavy rare earth elements through grain refinement.展开更多
In this work,the properties and microstructure of sintered Nd-Pr-Fe-Co-Zr-Ga-Cu-B magnet prepared by the single-step annealing,double-step annealing,and triple-step annealing processes were studied.The triple-step ann...In this work,the properties and microstructure of sintered Nd-Pr-Fe-Co-Zr-Ga-Cu-B magnet prepared by the single-step annealing,double-step annealing,and triple-step annealing processes were studied.The triple-step annealed magnet exhibits the highest intrinsic coercivity of 19.72 kOe,which is a 58.5%enhancement relative to the as-sintered magnet,and has the best temperature stability of coercivity.The best continuity of grain boundary(GB)phase and the highest content of RE6Fe13Ga phase can be observed in the triple-step annealed magnet,along with relatively small grain size.After triple-step annealing process,the phase separation occurs at the triple-junction(TJ)region of the magnet,which is the Fe-rich phase identified as RE6Fe13Ga and the Fe-poor phase identified as Ia-RE_(2)O_(3).The Ia-RE_(2)O_(3)phase located at the corner of the TJ region can extend between the grains of(Nd,Pr)_(2)Fe_(14)B main phase to form the GB phase with a Fe content of less than 15 at%,thereby enhancing the magnetic isolation effect.The lattice misfit between the Ia-RE_(2)O_(3)phase and the adjacent main phase is less than 5%,which is helpful to reduce defects at the edges of the main phase grains,thus reducing the nucleation of reverse domains.展开更多
The low coercivity is the major factor inhibiting the large-scale commercial utilization of Nd-Ce-Fe-B sintered magnets.In this work,we achieved a record-high coercivity of 15.04 kOe in Ga-doped Nd-Ce-Fe-B sintered ma...The low coercivity is the major factor inhibiting the large-scale commercial utilization of Nd-Ce-Fe-B sintered magnets.In this work,we achieved a record-high coercivity of 15.04 kOe in Ga-doped Nd-Ce-Fe-B sintered magnets with 30 wt%Ce replacing Nd,demonstrating enormous potential.The Ga-doped Nd-Ce-Fe-B magnets with higher boron(HB)and lower boron(LB)content are designed.The coercivity of the HB magnet increases slightly from 10.80 to 12.26 kOe after annealing,attributed to the optimized distribution of grain boundary(GB)phases.In contrast,the coercivity of the LB magnet remarkably increases from 8.13 to 15.04 kOe after annealing.Microstructural observations indicate that the narrow GB phase in the as-sintered magnet is rich in Fe,and the strong exchange coupling of adjacent grains resulted in low coercivity.The evolution of Ga-rich phases reveals a potential formation mechanism of the RE_(6)Fe_(13)Ga phase,that is the RE-Fe amorphous phase and REGa phase in the as-sintered magnet combine to form the RE_(6)Fe_(13)Ga phase and RE-Ga amorphous phase during post-sinter annealing(RE:rare earth).Moreover,the GB phase of the annealed magnet transforms into a Fe-lean phase with a thickness of 16.4 nm.Magnetization and demagnetization behavior characterizations reveal that the exchange decoupling of adjacent grains induced by the optimized GB phases is the main reason for the remarkable coercivity enhancement,which is also validated by micromagnetic simulations.展开更多
In this work,the effect of the Al addition amount in the TbAl coatings on the grain boundary diffusion proces s(GBDP)of Tb were systematically explored.Direct current magnetron sputtering(DCMS)method was utilized in c...In this work,the effect of the Al addition amount in the TbAl coatings on the grain boundary diffusion proces s(GBDP)of Tb were systematically explored.Direct current magnetron sputtering(DCMS)method was utilized in co-sputtering manner to synthesize the TbAl coatings with certain Tb consumption and various Al addition amount.Results show that the moderate Al addition amount significantly improves the wettability of grain boundary(GB)phases,thereby acquiring more continuous and uniform Tb-rich shells and GB phases between matrix phases,as well as deeper diffusion depth and denser microstructure.The largest increase amplitude of intrinsic coercivity(Hcj)is improved by 78.4%in TbAIdiffused magnet compared to the pure Tb-diffused magnet,while the remanence(Br)is expected to show an overall decreasing tendency accompanied with a slight increase in the decreasing process.However,when the Al addition amount is excessive,magnetic dilution effect is enhanced,and the Tbrich shells and GB phases between matrix phases become fuzzy and even invisible,which in turn deteriorates the magnetic properties of diffused magnets.展开更多
The particles of different shapes,multi-walled carbon nanotubes(CNTs)and graphene nanosheets(GNs),were used to modulate the mechanical properties and anisotropy of the magnets.It is found that the rodshaped CNTs can i...The particles of different shapes,multi-walled carbon nanotubes(CNTs)and graphene nanosheets(GNs),were used to modulate the mechanical properties and anisotropy of the magnets.It is found that the rodshaped CNTs can increase the bending strength ratio of the c and a axes of the magnet from 1.114 to1.254,while flake-like GNs decrease it from 1.114 to 0.989.In-depth analysis indicates that the mechanical anisotropy of the magnet is greatly influenced by the distribution and thickness of the rare earth phase(RE phase),with the thicker RE phase demonstrating greater capability of blunting at the crack tip.Using the finite element method,it is found that the strength of brittle material can be enhanced by the additive particles owing to the inhibition of crack initiation and stress conduction,as well as the deflection of the crack.The flake-like GNs weaken the mechanical anisotropy of magnets by varying the distribution of RE phase and form a shell encompassing the main phase.Nonetheless,the alignment of CNTs occurring in the process of magnetic orientation process can significantly increase the mechanical anisotropy of the magnet.In particular,when loaded in the parallel c axis(c_(‖))direction,the cracks need to penetrate the main phase due to the strong frictional interlocking between CNTs and the main phase grains,in which case the bending strength will be significantly increased.By contrast,when loaded in the vertical c axis(c_(⊥))direction,the cracks can bypass the rod-like particles and change directions of propagation.As such,the increase in bending strength is smaller than that in loading along with the cll direction.展开更多
Commercial N52 sintered NdFeB magnets were processed by grain boundary diffusion(GBD)with Dy-Co-M(M=Cu,AI)alloys.The coercivity of magnets greatly increase to 17.62 and 18.83 kOe respectively when diffusing Dy_(58)Co_...Commercial N52 sintered NdFeB magnets were processed by grain boundary diffusion(GBD)with Dy-Co-M(M=Cu,AI)alloys.The coercivity of magnets greatly increase to 17.62 and 18.83 kOe respectively when diffusing Dy_(58)Co_(25)Cu_(17)and Dy_(58)Co_(25)Al_(17)alloys,which are obviously higher than that of Dy58Co42GBD-treated magnet with 16.64 kOe,Further thermal stability studies indicate that the thermal stability of Dy_(58)Co_(25)Cu_(17)and Dy_(58)Co_(25)Al_(17)GBD-treated magnets is further improved compared to the Dy58Co42GBD-treated magnet The results show that th e temperature coefficients of remanence(20-120℃)are reduced from-0.148%/℃to-0.134%/℃and-0.132%/℃by Dy_(58)Co_(25)Cu_(17)and Dy_(58)Co_(25)Al_(17)GBD-treatment,respectively.Besides,the irreversible magnetic flux losses(120℃)for Dy_(58)Co_(25)Cu_(17)and Dy_(58)Co_(25)Al_(17)diffusion magnets are 4.76%and 2.79%,respectively.Microstructural analyses demonstrate that the presence of Cu and Al elements reduces the excessive accumulation of Dy and Co on the surface in the diffusion magnets an d improves the diffusion depth and utilization of Dy and Co.Furthermore,the flow of Co from the triple junction phase to the thin grain boundary phase is promoted,which contributes to the uniform distribution of Co.In addition,the dynamic evolution of the magnetic domain structure during the temperature rise process was studied.This work provides insight into the preparation of high-performance and high-thermal stability magnets.展开更多
A procedure of low temperature solid-phase sintering（LTSS） was carried out to fabricate sintered metal fibrous media（SMFM） with high specific surface area.Stainless steel fibers which were produced by cutting proc...A procedure of low temperature solid-phase sintering（LTSS） was carried out to fabricate sintered metal fibrous media（SMFM） with high specific surface area.Stainless steel fibers which were produced by cutting process were first plated with a coarse copper coating layer by electroless plating process.A low-temperature sintering process was then completed at about 800 °C for 1 h under the protection of hydrogen atmosphere.The results show that a novel SMFM with complex surface morphology and high specific surface area（0.2 m2/g） can be obtained in this way.The effect of sintering temperature on the surface morphology and specific surface area of SMFM was studied by means of scanning electron microscopy and Brunauer-Emmett-Teller.The damage of micro-structure during the sintering process mainly contributed to the loss of specific surface area of SMFM and the optimal sintering temperature was 800 °C.展开更多
Fabrication, characterization and performance of a porous metal-fiber sintered felt （PMFSF） based on multi-tooth cutting and solid-phase sintering were studied. The PMFSF was used as the anodic methanol barrier in a...Fabrication, characterization and performance of a porous metal-fiber sintered felt （PMFSF） based on multi-tooth cutting and solid-phase sintering were studied. The PMFSF was used as the anodic methanol barrier in a passive air-breathing direct methanol fuel cell to mitigate the effects of methanol crossover. Compared with the commercial SUS316L felt made of bundle-drawn fibers, this self-made PMFSF has larger pore diameter, polarized pore distribution, irregular fiber shape, rougher surface, lower mass flow resistance and evident hydrophobicity. The results reveal that the use of a PMFSF significantly enhances the cell performance since it helps to maintain a balance between the reactant and product management while depressing methanol crossover. The PMFSF with a porosity of 70% yields the highest cell performance at a methanol concentration of 4 mol/L.展开更多
MnS growth in sintered steels with admixed Fe, Cu, C and MnS has been investigated by SEM and X-ray diffraction, MnS in Fe-Cu-C-MnS sintered steels in which MnS has been admixed is not stable and MnS growth may be asc...MnS growth in sintered steels with admixed Fe, Cu, C and MnS has been investigated by SEM and X-ray diffraction, MnS in Fe-Cu-C-MnS sintered steels in which MnS has been admixed is not stable and MnS growth may be ascribed to sintering between MnS particles or reaction between MnS and Fe, Cu, C elements.展开更多
In this work,we present an innovative method for fabricating high-performance proton-conductive fuel cells(PCFCs)by combining magnetron sputtering and flashlight sintering(FLS)techniques.BaZr_(0.8)Y_(0.2)O_(3–δ)(BZY...In this work,we present an innovative method for fabricating high-performance proton-conductive fuel cells(PCFCs)by combining magnetron sputtering and flashlight sintering(FLS)techniques.BaZr_(0.8)Y_(0.2)O_(3–δ)(BZY20)electrolyte thin-films are successfully prepared by improving the crystallinity while maintaining the stoichiometry.All components of PCFC,Ni-YSZ anode,BZY20 electrolyte and Pt-GDC cathode are fabricated by sequentially sputtering them onto an AAO substrate.Electrolytic sintering is performed at 550 and 650 V conditions using FLS,effectively solving the Ba evaporation problem encountered in conventional thermal sintering methods.XRD analysis confirms that the perovskite structure is retained,and crystallinity is improved in the FLS samples.Furthermore,FE-SEM and EDS analyses confirm the uniform elemental distribution and consistent thickness of the FLS-treated electrolyte.An optimized PCFC unit cell with FLS-treated electrolyte exhibits a peak power density of 200.0 mW cm^(-2) at 500℃ and an ohmic resistance of 376.0 mΩ cm^(-2).These results suggest that the combination of magnetron sputtering and FLS techniques is a promising approach for fabricating highperformance thin-film PCFCs.展开更多
This study demonstrates the successful fabrication of solid-state bilayers using LiFePO_(4)(LFP)cathodes and Li_(1.3)Al_(0.3)Ti_(1.7)(PO_(4))_(3)(LATP)-based Composite Solid Electrolytes(CSEs)via Cold Sintering Proces...This study demonstrates the successful fabrication of solid-state bilayers using LiFePO_(4)(LFP)cathodes and Li_(1.3)Al_(0.3)Ti_(1.7)(PO_(4))_(3)(LATP)-based Composite Solid Electrolytes(CSEs)via Cold Sintering Process(CSP).By optimizing the sintering pressure,it is achieved an intimate contact between the cathode and the solid electrolyte,leading to an enhanced electrochemical performance.Bilayers cold sintered at 300 MPa and a low-sintering temperature of 150℃exhibit high ionic conductivities(0.5 mS cm^(-1))and stable specific capacities at room temperature(160.1 mAh g^(-1)LFP at C/10 and 75.8 mAh g^(-1)_(LFP)at 1 C).Moreover,an operando electrochemical impedance spectroscopy(EIS)technique is employed to identify limiting factors of the bilayer kinetics and to anticipate the overall electrochemical behavior.Results suggest that capacity fading can occur in samples prepared with high sintering pressures due to a volume reduction in the LFP crystalline cell.This work demonstrates the potential of CSP to produce straightforward high-performance bilayers and introduces a valuable non-destructive instrument for understanding and avoiding degradation in solid-state lithium-based batteries.展开更多
Silver paste is widely used in power electronics as a die-attach material owing to its low-temperature sinterability,high melting point,and excellent electrical and thermal conductivities in sintered joints.However,ow...Silver paste is widely used in power electronics as a die-attach material owing to its low-temperature sinterability,high melting point,and excellent electrical and thermal conductivities in sintered joints.However,owing to the mismatch in the coefficient of thermal expansion(CTE)between the joints and chip,the high Young's modulus of sintered silver hinders the mitigation of the high thermal stress generated during the operation of power modules,which increases the susceptibility of sintered joints to cracking,thereby leading to potential failure.This study developed a facile approach to synthesizing bayberry-like Ag microparticles(AgMPs)through the in situ assembly of silver nanorods,resulting in a uniform distribution of nanoscale structures and mesopores on the particle surface.These particles exhibited a high specific surface area of 2.5389 m^(2)·g^(-1),which enhanced theirsintering activity,enabling sintering to occur at 149.7℃.Furthermore,the porous structure of the AgMPs effectively reduced the density of joints formed by sintering AgMP paste,thereby lowering the Young's modulus of the joints.The small grain size and intricate internal substructure of the joints yielded high shear strength,which reached112.50 MPa at 250℃.The Young's modulus could be adjusted,and the pores provided by the AgMPs maintained the Young's modulus within a low range(15.11-29.61GPa),effectively mitigating thermal stress.These new bayberry-like porous AgMPs offer a promising option for die-attach materials in electronic packaging.展开更多
Low cobalt(Co)WC hard materials were prepared using vacuum sintering.The influences of Co content on the sintering densification behavior,grain growth characteristics,microstructure and mechanical properties of WC har...Low cobalt(Co)WC hard materials were prepared using vacuum sintering.The influences of Co content on the sintering densification behavior,grain growth characteristics,microstructure and mechanical properties of WC hard material were studied.The experimental results show that the addition of a small amount of Co significantly promotes the densification and reduces the sintering temperature.Meantime,the abnormal growth of WC grains was observed.When the sintering temperature is 1300℃and the content of Co is less than 1.0wt%,densed WC/Co hard material with fine grains is obtained.When the content of Co is 1wt%,the relative density,Vickers hardness,and flexural strength of WC material are 98.76±0.17%,24.23±0.41 GPa,and 1376±67 MPa,respectively.When the Co content is 0.25wt%and 0.5wt%,the optimal sintering temperature of the sample is 1350℃.Among them,the relative density,hardness,and flexural strength of WC-0.5wt%Co are 98.79±0.15%,23.44±0.38 GPa,and 1233±85 MPa,respectively.展开更多
The authors regret the following changes to the paper:1.The following author is added to this article:Agnieszka Chmielewska-Wysockaa 2.Section 2.1:●“An aqueous binder”should be changed to“A solvent binder”.●Repl...The authors regret the following changes to the paper:1.The following author is added to this article:Agnieszka Chmielewska-Wysockaa 2.Section 2.1:●“An aqueous binder”should be changed to“A solvent binder”.●Replace“a composition of ethylene glycol monobutyl ether and ethylene glycol”by“50% binder saturation”.展开更多
Three different kinds of corundum aggregates-tabular sintered alumina, dense sintered alumina, and fused dense corundum-were introduced into the silica fume .free or silica fume containing Al2O3 -SiC - C iron runner c...Three different kinds of corundum aggregates-tabular sintered alumina, dense sintered alumina, and fused dense corundum-were introduced into the silica fume .free or silica fume containing Al2O3 -SiC - C iron runner castables to investigate their influences on the flow ability, linear change on heating, bulk density, apparent porosity, cold strength, hot modulus of rupture, therm, al shock resistance, slag resistance, oxidation resistance as well as wear resistance of Al2O3 - SiC - C iron runner castables. The results show that （ 1 ） compared with the specimens with fused dense corundum, the specimens with dense sintered alumina have equivalent installation property, slag resistance and oxidation resistance, equivalent or even higher cold modulus of rupture, cold crushing strength and hot modulus of rupture, exhibiting better thermal shock resistance and cold wear resistance ; （2） adopting bimodal alumina micropowder LISAL22RABL as well as water reducers ZX2 and ZD2 can well reduce the water requirement of silica fume free castables, solving the problem of deteriorated flow ability resulted from the lack of silica fume; since the lack of silica fume avoids the formation of low melting point liquid, the hot modulus of rupture and the thermal shock resistance of the silica fume free castables are both better than those of the silica fume containing castables ; （3） the density of the castable specimens with dense sintered alumina is 4% -6% lower than that of the castable specimens with Jhsed dense corundum so the refractories consumption of one iron runner reduces by 5% by using the tastable with dense sintered alumina, which obviously reduces the cost of refractories.展开更多
A novel porous metal fiber sintered sheet （PMFSS） with a three-dimensional reticulated structure was fabricated by multi-tooth cutting and high-temperature solid-phase sintering process with copper fibers. A uniaxia...A novel porous metal fiber sintered sheet （PMFSS） with a three-dimensional reticulated structure was fabricated by multi-tooth cutting and high-temperature solid-phase sintering process with copper fibers. A uniaxial tensile test was conducted to investigate the effect of fiber length and natural aging factor on the tensile properties of the PMFSS. Results indicated that, under given stress, the increase of fiber length helped reinforce the tensile strength. The elongation of the PMFSS with medium length fiber of 15 mm exhibited the optimal performance, reaching about 13.5%. After natural aging treatment for a month, the tensile strength of PMFSS significantly decreased, but the change of elongation was negligible except for the one with the shortest fiber length of 5 mm, whose elongation was effectively improved. The morphological fracture features of PMFSSs were also characterized.展开更多
Miniature cylindrical metal powder sintered wick heat pipe （sintered heat pipe） is an ideal component with super-high thermal efficiency for high heat flux electronics cooling. The sintering process for sintered wic...Miniature cylindrical metal powder sintered wick heat pipe （sintered heat pipe） is an ideal component with super-high thermal efficiency for high heat flux electronics cooling. The sintering process for sintered wick is important for its quality. The sintering process was optimally designed based on the equation of the heat transfer limit of sintered heat pipe. Four-step sintering process was proposed to fabricate sintered wick. The sintering parameters including sintering temperature, sintering time, sintering atmosphere and sintering position were discussed. The experimental results showed that the proper sintering temperature was 950 ℃ for Cu powder of 159μm and 900 ℃ for Cu powders of 81 and 38 μm, respectively, while the wick thickness was 0.45 mm and sintering time was 3 h. The optimized sintering time was 3 h for 0.45 and 0.6 mm wick thickness and 1 h for 0.75 mm wick thickness, respectively, when copper powder diameter was 159μm and sintering temperature was 950 ℃. Redox reduction reaction between H2 and CuO during sintering could produce segmentation cracks in Cu powders as a second structure. Sintering at vertical position can effectively avoid the generation of gap between wick and the inner wall of pipe.展开更多
Cemented tungsten carbide with ultra fine grains was prepared via microwave sintering.η phase（W3Co3C） was formed on the surface of the samples during the preparation process.Extra carbon black was premixed and the ...Cemented tungsten carbide with ultra fine grains was prepared via microwave sintering.η phase（W3Co3C） was formed on the surface of the samples during the preparation process.Extra carbon black was premixed and the influence of carbon content on mechanical properties was studied.The results show that the maximum value of hardness and transverse rupture strength are HRA 93.2 and 3396 MPa respectively when the carbon black content is 0.45%.The microstructure investigated by SEM show that the WC grains growth mainly occurs during the early stage of microwave sintering by the coalescence of grains.展开更多
TiAl alloy bulk samples with the composition of Ti-45Al-5.5(Cr,Nb,B,Ta) (mole fraction, %) were prepared by high energy mechanical milling and spark plasma sintering (SPS) and then heat treatment. The microstructure a...TiAl alloy bulk samples with the composition of Ti-45Al-5.5(Cr,Nb,B,Ta) (mole fraction, %) were prepared by high energy mechanical milling and spark plasma sintering (SPS) and then heat treatment. The microstructure and mechanical properties after heat treatment of TiAl alloy prepared by SPS at different temperatures were studied. The results showed that the morphology of high energy mechanically milled powder was irregular and the average grain size was about decades micrometers. X-ray diffraction analysis showed that the mechanically milled powder was composed of two phases of TiAl and Ti3Al. The main phase of TiAl and few phases of Ti3Al and TiB2 were observed in the SPS bulk samples of Ti-45Al-5.5(Cr,Nb,B,Ta) alloy. For samples sintered at 900 °C and 1000 °C, the microstructure was duplex structure with some fine equiaxed gamma grains and thin needly TiB2 phases. With the SPS temperature increasing from 900 °C to 1000 °C, the micro-hardness was changed little, the compression strength increased from 1812 MPa to 2275 MPa and the compression ratio increased from 22.66% to 25.59%. The fractography results showed that the compression fracture transform of the SPS Ti-45Al-5.5(Cr,Nb,B,Ta) alloy was rgranular rupture.展开更多
Different from the grain boundary diffusion process(GBDP),which is suitable for modifying thin magnet,a green-pressing agents permeation process(GAPP)that uses low melting point alloys was applied to the Nd-Fe-B green...Different from the grain boundary diffusion process(GBDP),which is suitable for modifying thin magnet,a green-pressing agents permeation process(GAPP)that uses low melting point alloys was applied to the Nd-Fe-B green compact with a thickness over 15 mm to reconstruct the boundary microstructure of a sintered Nd-Fe-B magnet.The coercivity increases from 12.3 kOe for the sample free of Pr80Al20 to16.8 kOe for the sample with 2 wt%Pr80Al20.By further increasing the Pr80Al20 content to 3 wt%,the coercivity increases slightly,but the remanence and Hk/Hcj deteriorate obviously.The optimal comprehensive properties of Hcj=16.8 kOe,Br=13.4 kG and Hk/Hcj=0.975 are obtained at 2 wt%Pr80Al20,since matrix phase grains are separated by relatively continuous thin grain boundary layers,which weaken the magnetic coupling between adjacent grains.The coercivities of the samples from the GAPP that use2 wt%Pr80Al20,Pr70Al30 and Pr60Tb20Al20 alloys,respectively,can be enhanced to a large extent.However,the coercivity of the magnet reconstructed with Pr80Al20 is lower than that of the sample with Pr60Tb20Al20 but is higher than that of the sample reconstructed with Pr70Cu30 alloy.Moreover,the coercivity of the sample from the GAPP using 2 wt%Pr80Al20 is much higher than that of the sample from the GBDP,which is due to a nearly uniform boundary microstructure from the surface to the interior of the thick magnet from the GAPP,thus providing new insights into the fabrication of thick and bulky permanent magnets with high coercivity.展开更多
基金Key Research and Development Program of Shandong Province(2021CXGC010310)Shandong Province Science and Technology Small and Medium Sized Enterprise Innovation Ability Enhancement Project(2023TSGC0287,2024TSGC0519)+1 种基金Shandong Provincial Natural Science Foundation(ZR2022ME222)National Natural Science Foundation of China(51702187)。
文摘Three types of NdFeB magnets with the same composition and different grain sizes were prepared,and then the grain boundary diffusion was conducted using metal Tb under the same technical parameters.The effect of grain size on the grain boundary diffusion process and properties of sintered NdFeB magnets was investigated.The diffusion process was assessed using X-ray diffractometer,field emission scanning electron microscope,and electron probe microanalyzer.The magnetic properties of the magnet before and after diffusion were investigated.The results show that the grain refinement of the magnet leads to higher Tb utilization efficiency and results in higher coercivity at different temperatures.It can be attributed to the formation of a deeper and more complete core-shell structure,resulting in better magnetic isolation and higher anisotropy of the Nd_(2)Fe_(14)B grains.This work may shed light on developing high coercivity with low heavy rare earth elements through grain refinement.
基金Project supported by the Major Special Project of Fujian Province(2023HZ021005)the Guiding Project of Fujian Province(2023H0006)+2 种基金the Major Project of Science and Technology of Fuzhou(2022-ZD-010)the Young and Middle-aged Teachers Education Scientific Research Project of Fujian Province(JAT200594,JAT231008)the Natural Science Foundation of Fujian Province(2022J011151)。
文摘In this work,the properties and microstructure of sintered Nd-Pr-Fe-Co-Zr-Ga-Cu-B magnet prepared by the single-step annealing,double-step annealing,and triple-step annealing processes were studied.The triple-step annealed magnet exhibits the highest intrinsic coercivity of 19.72 kOe,which is a 58.5%enhancement relative to the as-sintered magnet,and has the best temperature stability of coercivity.The best continuity of grain boundary(GB)phase and the highest content of RE6Fe13Ga phase can be observed in the triple-step annealed magnet,along with relatively small grain size.After triple-step annealing process,the phase separation occurs at the triple-junction(TJ)region of the magnet,which is the Fe-rich phase identified as RE6Fe13Ga and the Fe-poor phase identified as Ia-RE_(2)O_(3).The Ia-RE_(2)O_(3)phase located at the corner of the TJ region can extend between the grains of(Nd,Pr)_(2)Fe_(14)B main phase to form the GB phase with a Fe content of less than 15 at%,thereby enhancing the magnetic isolation effect.The lattice misfit between the Ia-RE_(2)O_(3)phase and the adjacent main phase is less than 5%,which is helpful to reduce defects at the edges of the main phase grains,thus reducing the nucleation of reverse domains.
基金supported by the National Natural Science Foundation of China(Nos.52261037,52088101)the Key research project of Jiangxi Province(No.20203ABC28W006)the Double-Thousand Plan of Jiangxi Province(No.jxsq2023101057).
文摘The low coercivity is the major factor inhibiting the large-scale commercial utilization of Nd-Ce-Fe-B sintered magnets.In this work,we achieved a record-high coercivity of 15.04 kOe in Ga-doped Nd-Ce-Fe-B sintered magnets with 30 wt%Ce replacing Nd,demonstrating enormous potential.The Ga-doped Nd-Ce-Fe-B magnets with higher boron(HB)and lower boron(LB)content are designed.The coercivity of the HB magnet increases slightly from 10.80 to 12.26 kOe after annealing,attributed to the optimized distribution of grain boundary(GB)phases.In contrast,the coercivity of the LB magnet remarkably increases from 8.13 to 15.04 kOe after annealing.Microstructural observations indicate that the narrow GB phase in the as-sintered magnet is rich in Fe,and the strong exchange coupling of adjacent grains resulted in low coercivity.The evolution of Ga-rich phases reveals a potential formation mechanism of the RE_(6)Fe_(13)Ga phase,that is the RE-Fe amorphous phase and REGa phase in the as-sintered magnet combine to form the RE_(6)Fe_(13)Ga phase and RE-Ga amorphous phase during post-sinter annealing(RE:rare earth).Moreover,the GB phase of the annealed magnet transforms into a Fe-lean phase with a thickness of 16.4 nm.Magnetization and demagnetization behavior characterizations reveal that the exchange decoupling of adjacent grains induced by the optimized GB phases is the main reason for the remarkable coercivity enhancement,which is also validated by micromagnetic simulations.
基金Project supported by National Key Research and Development Program of China(2021YFB3500100)National Natural Science Foundation of China(52301068)。
文摘In this work,the effect of the Al addition amount in the TbAl coatings on the grain boundary diffusion proces s(GBDP)of Tb were systematically explored.Direct current magnetron sputtering(DCMS)method was utilized in co-sputtering manner to synthesize the TbAl coatings with certain Tb consumption and various Al addition amount.Results show that the moderate Al addition amount significantly improves the wettability of grain boundary(GB)phases,thereby acquiring more continuous and uniform Tb-rich shells and GB phases between matrix phases,as well as deeper diffusion depth and denser microstructure.The largest increase amplitude of intrinsic coercivity(Hcj)is improved by 78.4%in TbAIdiffused magnet compared to the pure Tb-diffused magnet,while the remanence(Br)is expected to show an overall decreasing tendency accompanied with a slight increase in the decreasing process.However,when the Al addition amount is excessive,magnetic dilution effect is enhanced,and the Tbrich shells and GB phases between matrix phases become fuzzy and even invisible,which in turn deteriorates the magnetic properties of diffused magnets.
基金Project supported by National Key R&D Project of China(2022YFB3505400)Jiangxi Natural Science Foundation Youth Fund(20232BAB214011)+3 种基金the Young Elite Scientists Sponsorship Program by CAST(2022QNRC001)National Natural Science Foundation of China(52361033)Ministry of Industry and Information Technology Heavy Rare Earth Special Use of Sintered NdFeB Project(TC220H06J)Academic and Technical Leaders in Major Disciplines in Jiangxi Province(20225BCJ23007)。
文摘The particles of different shapes,multi-walled carbon nanotubes(CNTs)and graphene nanosheets(GNs),were used to modulate the mechanical properties and anisotropy of the magnets.It is found that the rodshaped CNTs can increase the bending strength ratio of the c and a axes of the magnet from 1.114 to1.254,while flake-like GNs decrease it from 1.114 to 0.989.In-depth analysis indicates that the mechanical anisotropy of the magnet is greatly influenced by the distribution and thickness of the rare earth phase(RE phase),with the thicker RE phase demonstrating greater capability of blunting at the crack tip.Using the finite element method,it is found that the strength of brittle material can be enhanced by the additive particles owing to the inhibition of crack initiation and stress conduction,as well as the deflection of the crack.The flake-like GNs weaken the mechanical anisotropy of magnets by varying the distribution of RE phase and form a shell encompassing the main phase.Nonetheless,the alignment of CNTs occurring in the process of magnetic orientation process can significantly increase the mechanical anisotropy of the magnet.In particular,when loaded in the parallel c axis(c_(‖))direction,the cracks need to penetrate the main phase due to the strong frictional interlocking between CNTs and the main phase grains,in which case the bending strength will be significantly increased.By contrast,when loaded in the vertical c axis(c_(⊥))direction,the cracks can bypass the rod-like particles and change directions of propagation.As such,the increase in bending strength is smaller than that in loading along with the cll direction.
基金Project supported by the National Key R&D Program of China(2022YFB3505003,2021YFB3502802)the Natural Science Foundation of Zhejiang Province(LQ23E010001)+3 种基金"Pioneer"and"Leading Goose"R&D program of Zhejiang(2022C01020)Key Research and Development Program of Ningbo City(2023Z093)Kunpeng Plan of Zhejiang ProvinceNingbo Top Talent Program。
文摘Commercial N52 sintered NdFeB magnets were processed by grain boundary diffusion(GBD)with Dy-Co-M(M=Cu,AI)alloys.The coercivity of magnets greatly increase to 17.62 and 18.83 kOe respectively when diffusing Dy_(58)Co_(25)Cu_(17)and Dy_(58)Co_(25)Al_(17)alloys,which are obviously higher than that of Dy58Co42GBD-treated magnet with 16.64 kOe,Further thermal stability studies indicate that the thermal stability of Dy_(58)Co_(25)Cu_(17)and Dy_(58)Co_(25)Al_(17)GBD-treated magnets is further improved compared to the Dy58Co42GBD-treated magnet The results show that th e temperature coefficients of remanence(20-120℃)are reduced from-0.148%/℃to-0.134%/℃and-0.132%/℃by Dy_(58)Co_(25)Cu_(17)and Dy_(58)Co_(25)Al_(17)GBD-treatment,respectively.Besides,the irreversible magnetic flux losses(120℃)for Dy_(58)Co_(25)Cu_(17)and Dy_(58)Co_(25)Al_(17)diffusion magnets are 4.76%and 2.79%,respectively.Microstructural analyses demonstrate that the presence of Cu and Al elements reduces the excessive accumulation of Dy and Co on the surface in the diffusion magnets an d improves the diffusion depth and utilization of Dy and Co.Furthermore,the flow of Co from the triple junction phase to the thin grain boundary phase is promoted,which contributes to the uniform distribution of Co.In addition,the dynamic evolution of the magnetic domain structure during the temperature rise process was studied.This work provides insight into the preparation of high-performance and high-thermal stability magnets.
基金Project (50930005) supported by the National Natural Science Foundation of ChinaProject (U0834002) supported by the Key Programof NSFC-Guangdong Joint Funds of China+1 种基金Project (LYM09024) supported by Training Program for Excellent Young Teachers withInnovation of Guangdong University, ChinaProject (2009ZM0121) supported by the Fundamental Research Funds for the CentralUniversities of South China University of Technology,China
文摘A procedure of low temperature solid-phase sintering（LTSS） was carried out to fabricate sintered metal fibrous media（SMFM） with high specific surface area.Stainless steel fibers which were produced by cutting process were first plated with a coarse copper coating layer by electroless plating process.A low-temperature sintering process was then completed at about 800 °C for 1 h under the protection of hydrogen atmosphere.The results show that a novel SMFM with complex surface morphology and high specific surface area（0.2 m2/g） can be obtained in this way.The effect of sintering temperature on the surface morphology and specific surface area of SMFM was studied by means of scanning electron microscopy and Brunauer-Emmett-Teller.The damage of micro-structure during the sintering process mainly contributed to the loss of specific surface area of SMFM and the optimal sintering temperature was 800 °C.
基金Projects(50930005,51075155)supported by the National Natural Science Foundation of ChinaProject(20100172110001)supported by PhD Programs Foundation of Ministry of Education of China
文摘Fabrication, characterization and performance of a porous metal-fiber sintered felt （PMFSF） based on multi-tooth cutting and solid-phase sintering were studied. The PMFSF was used as the anodic methanol barrier in a passive air-breathing direct methanol fuel cell to mitigate the effects of methanol crossover. Compared with the commercial SUS316L felt made of bundle-drawn fibers, this self-made PMFSF has larger pore diameter, polarized pore distribution, irregular fiber shape, rougher surface, lower mass flow resistance and evident hydrophobicity. The results reveal that the use of a PMFSF significantly enhances the cell performance since it helps to maintain a balance between the reactant and product management while depressing methanol crossover. The PMFSF with a porosity of 70% yields the highest cell performance at a methanol concentration of 4 mol/L.
文摘MnS growth in sintered steels with admixed Fe, Cu, C and MnS has been investigated by SEM and X-ray diffraction, MnS in Fe-Cu-C-MnS sintered steels in which MnS has been admixed is not stable and MnS growth may be ascribed to sintering between MnS particles or reaction between MnS and Fe, Cu, C elements.
基金supported by the Korea Institute of Energy Technology Evaluation and Planning and the Ministry of Trade,Industry and Energy of the Republic of Korea(No.20213030030150)by the National Research Foundation of Korea funded by the Korea government(MSIT)(No.RS-2021-NR057434).
文摘In this work,we present an innovative method for fabricating high-performance proton-conductive fuel cells(PCFCs)by combining magnetron sputtering and flashlight sintering(FLS)techniques.BaZr_(0.8)Y_(0.2)O_(3–δ)(BZY20)electrolyte thin-films are successfully prepared by improving the crystallinity while maintaining the stoichiometry.All components of PCFC,Ni-YSZ anode,BZY20 electrolyte and Pt-GDC cathode are fabricated by sequentially sputtering them onto an AAO substrate.Electrolytic sintering is performed at 550 and 650 V conditions using FLS,effectively solving the Ba evaporation problem encountered in conventional thermal sintering methods.XRD analysis confirms that the perovskite structure is retained,and crystallinity is improved in the FLS samples.Furthermore,FE-SEM and EDS analyses confirm the uniform elemental distribution and consistent thickness of the FLS-treated electrolyte.An optimized PCFC unit cell with FLS-treated electrolyte exhibits a peak power density of 200.0 mW cm^(-2) at 500℃ and an ohmic resistance of 376.0 mΩ cm^(-2).These results suggest that the combination of magnetron sputtering and FLS techniques is a promising approach for fabricating highperformance thin-film PCFCs.
基金support from Generalitat Valenciana under Pla Complementari“Programa de Materials Avanc¸ats”,2022(grant number MFA/2022/030)Ministerio de Ciencia,Innovaci´on y Universidades(Spain)(grant number MCIN/AEI/10.13039/501100011033)+1 种基金support from UJI(UJI-2023-16 and GACUJIMC/2023/08)Generalitat Valenciana through FPI Fellowship Program(grant numbers ACIF/2020/294 and CIACIF/2021/050).
文摘This study demonstrates the successful fabrication of solid-state bilayers using LiFePO_(4)(LFP)cathodes and Li_(1.3)Al_(0.3)Ti_(1.7)(PO_(4))_(3)(LATP)-based Composite Solid Electrolytes(CSEs)via Cold Sintering Process(CSP).By optimizing the sintering pressure,it is achieved an intimate contact between the cathode and the solid electrolyte,leading to an enhanced electrochemical performance.Bilayers cold sintered at 300 MPa and a low-sintering temperature of 150℃exhibit high ionic conductivities(0.5 mS cm^(-1))and stable specific capacities at room temperature(160.1 mAh g^(-1)LFP at C/10 and 75.8 mAh g^(-1)_(LFP)at 1 C).Moreover,an operando electrochemical impedance spectroscopy(EIS)technique is employed to identify limiting factors of the bilayer kinetics and to anticipate the overall electrochemical behavior.Results suggest that capacity fading can occur in samples prepared with high sintering pressures due to a volume reduction in the LFP crystalline cell.This work demonstrates the potential of CSP to produce straightforward high-performance bilayers and introduces a valuable non-destructive instrument for understanding and avoiding degradation in solid-state lithium-based batteries.
基金financially supported by the National Natural Science Foundation of China(Nos.52075125 and 52105331)Guangdong Basic and Applied Basic Research Foundation(No.2023A1515010591)Shenzhen Science and Technology Innovation Committee(Nos.JCYJ20210324124203009,JSGG20201102154600003,GXWD20231130103814001,GXWD20220721182229001)
文摘Silver paste is widely used in power electronics as a die-attach material owing to its low-temperature sinterability,high melting point,and excellent electrical and thermal conductivities in sintered joints.However,owing to the mismatch in the coefficient of thermal expansion(CTE)between the joints and chip,the high Young's modulus of sintered silver hinders the mitigation of the high thermal stress generated during the operation of power modules,which increases the susceptibility of sintered joints to cracking,thereby leading to potential failure.This study developed a facile approach to synthesizing bayberry-like Ag microparticles(AgMPs)through the in situ assembly of silver nanorods,resulting in a uniform distribution of nanoscale structures and mesopores on the particle surface.These particles exhibited a high specific surface area of 2.5389 m^(2)·g^(-1),which enhanced theirsintering activity,enabling sintering to occur at 149.7℃.Furthermore,the porous structure of the AgMPs effectively reduced the density of joints formed by sintering AgMP paste,thereby lowering the Young's modulus of the joints.The small grain size and intricate internal substructure of the joints yielded high shear strength,which reached112.50 MPa at 250℃.The Young's modulus could be adjusted,and the pores provided by the AgMPs maintained the Young's modulus within a low range(15.11-29.61GPa),effectively mitigating thermal stress.These new bayberry-like porous AgMPs offer a promising option for die-attach materials in electronic packaging.
基金Funded by the National Natural Science Foundation of China(No.52022072)the Key Research and Development Plan of Jiangxi Province(No.2020ZDYFB0017)。
文摘Low cobalt(Co)WC hard materials were prepared using vacuum sintering.The influences of Co content on the sintering densification behavior,grain growth characteristics,microstructure and mechanical properties of WC hard material were studied.The experimental results show that the addition of a small amount of Co significantly promotes the densification and reduces the sintering temperature.Meantime,the abnormal growth of WC grains was observed.When the sintering temperature is 1300℃and the content of Co is less than 1.0wt%,densed WC/Co hard material with fine grains is obtained.When the content of Co is 1wt%,the relative density,Vickers hardness,and flexural strength of WC material are 98.76±0.17%,24.23±0.41 GPa,and 1376±67 MPa,respectively.When the Co content is 0.25wt%and 0.5wt%,the optimal sintering temperature of the sample is 1350℃.Among them,the relative density,hardness,and flexural strength of WC-0.5wt%Co are 98.79±0.15%,23.44±0.38 GPa,and 1233±85 MPa,respectively.
文摘The authors regret the following changes to the paper:1.The following author is added to this article:Agnieszka Chmielewska-Wysockaa 2.Section 2.1:●“An aqueous binder”should be changed to“A solvent binder”.●Replace“a composition of ethylene glycol monobutyl ether and ethylene glycol”by“50% binder saturation”.
文摘Three different kinds of corundum aggregates-tabular sintered alumina, dense sintered alumina, and fused dense corundum-were introduced into the silica fume .free or silica fume containing Al2O3 -SiC - C iron runner castables to investigate their influences on the flow ability, linear change on heating, bulk density, apparent porosity, cold strength, hot modulus of rupture, therm, al shock resistance, slag resistance, oxidation resistance as well as wear resistance of Al2O3 - SiC - C iron runner castables. The results show that （ 1 ） compared with the specimens with fused dense corundum, the specimens with dense sintered alumina have equivalent installation property, slag resistance and oxidation resistance, equivalent or even higher cold modulus of rupture, cold crushing strength and hot modulus of rupture, exhibiting better thermal shock resistance and cold wear resistance ; （2） adopting bimodal alumina micropowder LISAL22RABL as well as water reducers ZX2 and ZD2 can well reduce the water requirement of silica fume free castables, solving the problem of deteriorated flow ability resulted from the lack of silica fume; since the lack of silica fume avoids the formation of low melting point liquid, the hot modulus of rupture and the thermal shock resistance of the silica fume free castables are both better than those of the silica fume containing castables ; （3） the density of the castable specimens with dense sintered alumina is 4% -6% lower than that of the castable specimens with Jhsed dense corundum so the refractories consumption of one iron runner reduces by 5% by using the tastable with dense sintered alumina, which obviously reduces the cost of refractories.
基金Projects(51475172,51275180,51375177) supported by the National Natural Science Foundation of ChinaProject(S2013040016899) supported by the Natural Science Foundation of Guangdong Province,ChinaProjects(2013ZM0003,2013ZZ017) supported by the Fundamental Research Funds for the Central Universities,South China University of Technology,China
文摘A novel porous metal fiber sintered sheet （PMFSS） with a three-dimensional reticulated structure was fabricated by multi-tooth cutting and high-temperature solid-phase sintering process with copper fibers. A uniaxial tensile test was conducted to investigate the effect of fiber length and natural aging factor on the tensile properties of the PMFSS. Results indicated that, under given stress, the increase of fiber length helped reinforce the tensile strength. The elongation of the PMFSS with medium length fiber of 15 mm exhibited the optimal performance, reaching about 13.5%. After natural aging treatment for a month, the tensile strength of PMFSS significantly decreased, but the change of elongation was negligible except for the one with the shortest fiber length of 5 mm, whose elongation was effectively improved. The morphological fracture features of PMFSSs were also characterized.
基金Project(50905119)supported by the National Natural Science Foundation of ChinaProject(20120171120036)supported by New Teachers'Fund for Doctor Stations,Ministry of Education,ChinaProject(S2012040007715)supported by Natural Science Foundation of Guangdong Province,China
文摘Miniature cylindrical metal powder sintered wick heat pipe （sintered heat pipe） is an ideal component with super-high thermal efficiency for high heat flux electronics cooling. The sintering process for sintered wick is important for its quality. The sintering process was optimally designed based on the equation of the heat transfer limit of sintered heat pipe. Four-step sintering process was proposed to fabricate sintered wick. The sintering parameters including sintering temperature, sintering time, sintering atmosphere and sintering position were discussed. The experimental results showed that the proper sintering temperature was 950 ℃ for Cu powder of 159μm and 900 ℃ for Cu powders of 81 and 38 μm, respectively, while the wick thickness was 0.45 mm and sintering time was 3 h. The optimized sintering time was 3 h for 0.45 and 0.6 mm wick thickness and 1 h for 0.75 mm wick thickness, respectively, when copper powder diameter was 159μm and sintering temperature was 950 ℃. Redox reduction reaction between H2 and CuO during sintering could produce segmentation cracks in Cu powders as a second structure. Sintering at vertical position can effectively avoid the generation of gap between wick and the inner wall of pipe.
基金Project (2008890) supported by the Scientific Research Foundation for the Returned Overseas Chinese Scholars,China
文摘Cemented tungsten carbide with ultra fine grains was prepared via microwave sintering.η phase（W3Co3C） was formed on the surface of the samples during the preparation process.Extra carbon black was premixed and the influence of carbon content on mechanical properties was studied.The results show that the maximum value of hardness and transverse rupture strength are HRA 93.2 and 3396 MPa respectively when the carbon black content is 0.45%.The microstructure investigated by SEM show that the WC grains growth mainly occurs during the early stage of microwave sintering by the coalescence of grains.
基金Project (51001040) supported by the National Natural Science Foundation of ChinaProject (HITQNJS.2009.022) supported by Development Program for Outstanding Young Teachers in Harbin Institute of TechnologyProject (2012RFQXG109) supported by the Youth Science and Technology Innovation Talents
文摘TiAl alloy bulk samples with the composition of Ti-45Al-5.5(Cr,Nb,B,Ta) (mole fraction, %) were prepared by high energy mechanical milling and spark plasma sintering (SPS) and then heat treatment. The microstructure and mechanical properties after heat treatment of TiAl alloy prepared by SPS at different temperatures were studied. The results showed that the morphology of high energy mechanically milled powder was irregular and the average grain size was about decades micrometers. X-ray diffraction analysis showed that the mechanically milled powder was composed of two phases of TiAl and Ti3Al. The main phase of TiAl and few phases of Ti3Al and TiB2 were observed in the SPS bulk samples of Ti-45Al-5.5(Cr,Nb,B,Ta) alloy. For samples sintered at 900 °C and 1000 °C, the microstructure was duplex structure with some fine equiaxed gamma grains and thin needly TiB2 phases. With the SPS temperature increasing from 900 °C to 1000 °C, the micro-hardness was changed little, the compression strength increased from 1812 MPa to 2275 MPa and the compression ratio increased from 22.66% to 25.59%. The fractography results showed that the compression fracture transform of the SPS Ti-45Al-5.5(Cr,Nb,B,Ta) alloy was rgranular rupture.
基金Project supported by the National Natural Science Foundation of China(51401021)the State Key Laboratory Advanced Metals and Materials(20162-14).
文摘Different from the grain boundary diffusion process(GBDP),which is suitable for modifying thin magnet,a green-pressing agents permeation process(GAPP)that uses low melting point alloys was applied to the Nd-Fe-B green compact with a thickness over 15 mm to reconstruct the boundary microstructure of a sintered Nd-Fe-B magnet.The coercivity increases from 12.3 kOe for the sample free of Pr80Al20 to16.8 kOe for the sample with 2 wt%Pr80Al20.By further increasing the Pr80Al20 content to 3 wt%,the coercivity increases slightly,but the remanence and Hk/Hcj deteriorate obviously.The optimal comprehensive properties of Hcj=16.8 kOe,Br=13.4 kG and Hk/Hcj=0.975 are obtained at 2 wt%Pr80Al20,since matrix phase grains are separated by relatively continuous thin grain boundary layers,which weaken the magnetic coupling between adjacent grains.The coercivities of the samples from the GAPP that use2 wt%Pr80Al20,Pr70Al30 and Pr60Tb20Al20 alloys,respectively,can be enhanced to a large extent.However,the coercivity of the magnet reconstructed with Pr80Al20 is lower than that of the sample with Pr60Tb20Al20 but is higher than that of the sample reconstructed with Pr70Cu30 alloy.Moreover,the coercivity of the sample from the GAPP using 2 wt%Pr80Al20 is much higher than that of the sample from the GBDP,which is due to a nearly uniform boundary microstructure from the surface to the interior of the thick magnet from the GAPP,thus providing new insights into the fabrication of thick and bulky permanent magnets with high coercivity.
