The combination of electrospinning and hot pressing,namely the electrospinning-hot pressing technique(EHPT),is an efficient and convenient method for preparing nanofibrous composite materials with good energy storage ...The combination of electrospinning and hot pressing,namely the electrospinning-hot pressing technique(EHPT),is an efficient and convenient method for preparing nanofibrous composite materials with good energy storage performance.The emerging composite membrane prepared by EHPT,which exhibits the advantages of large surface area,controllable morphology,and compact structure,has attracted immense attention.In this paper,the conduction mechanism of composite membranes in thermal and electrical energy storage and the performance enhancement method based on the fabrication process of EHPT are systematically discussed.Moreover,the state-of-the-art applications of composite membranes in these two fields are introduced.In particular,in the field of thermal energy storage,EHPT-prepared membranes have longitudinal and transverse nanofibers,which generate unique thermal conductivity pathways;also,these nanofibers offer enough space for the filling of functional materials.Moreover,EHPT-prepared membranes are beneficial in thermal management systems,building energy conservation,and electrical energy storage,e.g.,improving the electrochemical properties of the separators as well as their mechanical and thermal stability.The application of electrospinning-hot pressing membranes on capacitors,lithium-ion batteries(LIBs),fuel cells,sodium-ion batteries(SIBs),and hydrogen bromine flow batteries(HBFBs)still requires examination.In the future,EHPT is expected to make the field more exciting through its own technological breakthroughs or be combined with other technologies to produce intelligent materials.展开更多
The microstructure characteristics and strengthening mechanism of Inconel738LC(IN-738LC) alloy prepared by using induction-assisted directed energy deposition(IDED) were elucidated through the investigation of samples...The microstructure characteristics and strengthening mechanism of Inconel738LC(IN-738LC) alloy prepared by using induction-assisted directed energy deposition(IDED) were elucidated through the investigation of samples subjected to IDED under 1050℃ preheating with and without hot isostatic pressing(HIP,1190℃,105 MPa,and 3 h).Results show that the as-deposited sample mainly consisted of epitaxial columnar crystals and inhomogeneously distributed γ’ phases in interdendritic and dendritic core regions.After HIP,grain morphology changed negligibly,whereas the size of the γ’ phase became increasingly even.After further heat treatment(HT,1070℃,2 h + 845℃,24 h),the γ’ phase in the as-deposited and HIPed samples presented a bimodal size distribution,whereas that in the as-deposited sample showed a size that remained uneven.The comparison of tensile properties revealed that the tensile strength and uniform elongation of the HIP + HTed sample increased by 5% and 46%,respectively,due to the synergistic deformation of bimodal γ’phases,especially large cubic γ’ phases.Finally,the relationship between phase transformations and plastic deformations in the IDEDed sample was discussed on the basis of generalized stability theory in terms of the trade-off between thermodynamics and kinetics.展开更多
This work investigated the effect of Cr and Si on the mechanical properties and oxidation resistance of press hardened steel.Results indicated that the microstructure of the Cr-Si micro-alloyed press hardened steel co...This work investigated the effect of Cr and Si on the mechanical properties and oxidation resistance of press hardened steel.Results indicated that the microstructure of the Cr-Si micro-alloyed press hardened steel consisted of lath martensite,M_(23)C_(6)carbides,and retained austenite.The retained austenite and carbides are responsible for the increase in elongation of the micro-alloyed steel.In addition,after oxidation at 930℃for 5 min,the thickness of the oxide scales on the Cr-Si micro-alloyed press hardened steel is less than 5μm,much thinner than 45.50μm-thick oxide scales on 22MnB5.The oxide scales of the Cr-Si micro-alloyed steel are composed of Fe_(2)O_(3),Fe_(3)O_(4),mixed spinel oxide(FeCr_(2)O_(4)and Fe_(2)SiO_(4)),and amorphous SiO_(2).Adding Cr and Si significantly reduces the thickness of the oxide scales and prevents the generation of the FeO phase.Due to the increase of spinel FeCr_(2)O_(4)and Fe_(2)SiO_(4)phase in the inner oxide scale and the amorphous SiO_(2)close to the substrate,the oxidation resistance of the Cr-Si micro-alloyed press hardened steel is improved.展开更多
To increase the adhesion strength between the coating and the substrate, sintered Ti(C,N)-based cermets were selected and deposited with monolayer TiN using a multiarc ion-plating technique; subsequently, hot isosta...To increase the adhesion strength between the coating and the substrate, sintered Ti(C,N)-based cermets were selected and deposited with monolayer TiN using a multiarc ion-plating technique; subsequently, hot isostatic pressing (HIPhag) treatment was performed at 1000℃ using nitrogen pressure up to 110 MPa. The mechanical properties of cermets after a coating process and subsequent HIPing treatment have been evaluated with respect to the hardness, the residual stress, and the coating adhesion. The results show that atter the HIPing process, there was a higher increase ha critical load ha the TiN-coated cermets with lower surface roughness compared with those with higher surface roughness. In all cases, the residual stress was found to be compressive. The effects of substrate surface roughness and posttreatment on the adhesion strength of the coatings were thus investigated. It was also fotmd that the HIPing posttreatment process is well suited for hacreasing the adhesion strength between the coating and the substrate.展开更多
12 vol%WCp/2024Al composite was fabricated from mixed powders by hot-pressing at various tempera-tures. Investigation of the interfacial reaction between the WC phase and the Al alloy matrix was performed by X-ray dif...12 vol%WCp/2024Al composite was fabricated from mixed powders by hot-pressing at various tempera-tures. Investigation of the interfacial reaction between the WC phase and the Al alloy matrix was performed by X-ray diffraction (XRD), transmission electron microscope (TEM) and energy dispersive spectroscopy (EDS). A multiple layer interface structure, which is composed of Al/ WAl12/AlnC3/WC, is found to form by the interfacial reaction during hot-pressing. Further study shows that the AlaC3 layer forms along with a given crystal orientation of WC phase and might retard the interfacial reaction process.展开更多
The Shima yield criterion used in finite element analysis for nickel-based superalloy powder compact during hot isostatic pressing(HIP) was modified through uniaxial compression experiments. The influence of cylindric...The Shima yield criterion used in finite element analysis for nickel-based superalloy powder compact during hot isostatic pressing(HIP) was modified through uniaxial compression experiments. The influence of cylindrical capsule characteristics on FGH4096M superalloy powder compact deformation and densification behavior during HIP was investigated through simulations and experiments. Results revealed the simulation shrinkage prediction fitted well with the experimental shrinkage including a maximum shrinkage error of 1.5%. It was shown that the axial shrinkage was 1.7% higher than radial shrinkage for a cylindrical capsule with the size of ∮50 mm × 100 mm due to the force arm difference along the axial and radial direction of the capsule. The stress deviated from the isostatic state in the capsule led to the uneven shrinkage and non-uniform densification of the powder compact. The ratio of the maximum radial displacement to axial displacement increased from0.47 to 0.75 with the capsule thickness increasing from 2 to 4 mm. The pressure transmission is related to the capsule thickness, the capsule material performance, and physical parameters in the HIP process.展开更多
Characteristics of magnetic hardening in cast-hot pressed magnet Pr_(19)Fe_(74.5)B_5Cu_(1.5)were stu- died.The microstructure features and virgin magnetization curve reveal a nucleation control- led coercivity mechani...Characteristics of magnetic hardening in cast-hot pressed magnet Pr_(19)Fe_(74.5)B_5Cu_(1.5)were stu- died.The microstructure features and virgin magnetization curve reveal a nucleation control- led coercivity mechanism.Regression analysis shows that the intrinsic coercivity varies inversely as the logarithm of the average grain size: _iH_c(MA/m)=1.7312-0.48161nd(μm) which confirms the randomness of nucleation of reversed domains and the statistical nature of coercivity,indicating that the decrease of grain size would reduce the average number of de- fects on its surface and lower the probability of magnetization reversal of a grain and the cu- mulative fraction of the grains that have reversed their magnetization.Coercivity is thus en- hanced.展开更多
Powder hot isostatic pressing(HIP) is an effective method to achieve near-net-shape manufacturing of high-quality complex thinwalled titanium alloy parts, and it has received extensive attention in recent years. Howev...Powder hot isostatic pressing(HIP) is an effective method to achieve near-net-shape manufacturing of high-quality complex thinwalled titanium alloy parts, and it has received extensive attention in recent years. However, there are few reports about the microstructure characteristics on the strengthening and toughening mechanisms of powder hot isostatic pressed(HIPed) titanium alloys. Therefore, TA15powder was prepared into alloy by HIP approach, which was used to explore the microstructure characteristics at different HIP temperatures and the corresponding tensile properties and fracture toughness. Results show that the fabricated alloy has a “basket-like structure” when the HIP temperature is below 950℃, consisting of lath clusters and surrounding small equiaxed grains belts. When the HIP temperature is higher than 950℃, the microstructure gradually transforms into the Widmanstatten structure, accompanied by a significant increase in grain size. The tensile strength and elongation are reduced from 948 MPa and 17.3% for the 910℃ specimen to 861 MPa and 10% for the 970℃ specimen.The corresponding tensile fracture mode changes from transcrystalline plastic fracture to mixed fracture including intercrystalline cleavage.The fracture toughness of the specimens increases from 82.64 MPa·m^(1/2)for the 910℃ specimen to 140.18 MPa·m^(1/2)for the 970℃ specimen.Specimens below 950℃ tend to form holes due to the prior particle boundaries(PPBs), which is not conducive to toughening. Specimens above 950℃ have high fracture toughness due to the crack deflection, crack branching, and shear plastic deformation of the Widmanstatten structure. This study provides a valid reference for the development of powder HIPed titanium alloy.展开更多
Powder compacts of the system Bi2–xPbxSr2Ca2Cu3Oy with 0 ≤ x ≤ 0.5 molar ratio using both techniques;isothermal hot pressing and the solid state reaction (sintering). The XRD of the hot pressed powder compacts of t...Powder compacts of the system Bi2–xPbxSr2Ca2Cu3Oy with 0 ≤ x ≤ 0.5 molar ratio using both techniques;isothermal hot pressing and the solid state reaction (sintering). The XRD of the hot pressed powder compacts of the nominal compositions Bi2–xPbxSr2Ca2Cu3Oy showed 2212 and 2223 phases. The resistivity temperature variations belonging to the composition Bi1.8Pb0.2Sr2Ca2Cu3Oy showed metal-superconducting transition at Tons = 143 K for the annealed sample for 24 h. The annealed nominal composition Bi1.5Pb0.5Sr2Ca2Cu3Oy for 18 h showed metal to superconducting transition at 80 K.展开更多
Two severe plastic deformation(SPD)techniques of simple shear extrusion(SSE)and equal channel angular pressing(ECAP)were employed to process an extruded Mg-6Gd-3Y-1.5Ag(wt%)alloy at 553 K for 1,2,4 and 6 passes.The mi...Two severe plastic deformation(SPD)techniques of simple shear extrusion(SSE)and equal channel angular pressing(ECAP)were employed to process an extruded Mg-6Gd-3Y-1.5Ag(wt%)alloy at 553 K for 1,2,4 and 6 passes.The microstructural evolutions were studied by electron back scattered diffraction(EBSD)analysis and transmission electron microscopy(TEM).The initial grain size of 7.5μm in the extruded alloy was reduced to about 1.3μm after 6 SPD passes.Discontinuous dynamic recrystallization was suggested to be operative in both SSE and ECAP,with also a potential contribution of continuous dynamic recrystallization at the early stages of deformation.The difference in the shear strain paths of the two SPD techniques caused different progression rate of dynamic recrystallization(DRX),so that the alloys processed by ECAP exhibited higher fractions of recrystallization and high angle grain boundaries(HAGBs).It was revealed that crystallographic texture was also significantly influenced by the difference in the strain paths of the two SPD methods,where dissimilar basal plane texture components were obtained.The compression tests,performed along extrusion direction(ED),indicated that the compressive yield stress(CYS)and ultimate compressive strength(UCS)of the alloys after both SEE and ECAP augmented continuously by increasing the number of passes.ECAP-processed alloys had lower values of CYS and UCS compared to their counterparts processed by SSE.This difference in the mechanical responses was attributed to the different configurations of basal planes with respect to the loading direction(ED)of each SPD technique.展开更多
Densification, phase transformation and fracture toughness were studied in hot-pressed Si_3N_4 seeded by in-houseproduced large, elongated β-Si_3N_4 seeds. A mixture of Y_2O_3-Al_2O_3 was used as the sintering aid. C...Densification, phase transformation and fracture toughness were studied in hot-pressed Si_3N_4 seeded by in-houseproduced large, elongated β-Si_3N_4 seeds. A mixture of Y_2O_3-Al_2O_3 was used as the sintering aid. Concentration ofseeds were varied from 0 to 6 wt pct and the sintering time at 1700℃ was varied from 1 to 4 h. Maximum fracturetoughness of 9.0 MPam^(1/2) was measured in samples containing 5 wt pct seeds, hot pressed at 1700℃ for 4 h.展开更多
A homogenous microstructure of ultrafine-grained (UFG) commercially pure (CP) Ti characterized by equiaxed grains/subgrains with an average grain size of about 150 nm and strong prismatic fiber texture were obtained a...A homogenous microstructure of ultrafine-grained (UFG) commercially pure (CP) Ti characterized by equiaxed grains/subgrains with an average grain size of about 150 nm and strong prismatic fiber texture were obtained after 4 passes of equal channel angular pressing (ECAP).Tension–compression asymmetry in yield and work hardening behavior of UFG CP Ti were investigated by uniaxial tension and compression tests.The experimental results reveal that UFG CP Ti exhibits a relatively obvious tensioncompression asymmetry in yielding and work hardening behavior.The basal and prismaticslip are suppressed either for tension or compression,which is the easiest to activate.The tension twin system{1012}<1011> easily activated in compression deformation due to the prismatic fiber texture based on the Schmidt factor,consequently resulting in a lower yield strength under compression than tension.ECAP can improve the tension-compression asymmetry of CP Ti due to grain refinement.The interaction among the dislocations,grain boundaries and deformation twins are the main work hardening mechanisms for compression deformation,while the interaction between the dislocations and grain boundaries for tension deformation.Deformation twins lead to the higher work hardening under compression than tension.展开更多
An extruded Mg-6Gd-3Y-1.5Ag(wt%) alloy was processed by 6 passes of equal channel angular pressing(ECAP) at 553 K using route Bc to refine the microstructure. Electron back-scattered diffraction(EBSD) analysis showed ...An extruded Mg-6Gd-3Y-1.5Ag(wt%) alloy was processed by 6 passes of equal channel angular pressing(ECAP) at 553 K using route Bc to refine the microstructure. Electron back-scattered diffraction(EBSD) analysis showed a fully recrystallized microstructure for the extruded alloy with a mean grain size of 8.6 μm. The microstructure of the ECAP-processed alloy was uniformly refined through dynamic recrystallization(DRX). This microstructure contained fine grains with an average size of 1.3 μm, a high fraction of high angle grain boundaries(HAGBs), and nano-sized Mg_(5)Gd-type particles at the boundaries of the DRXed grains, detected by transmission electron microscopy(TEM). High-temperature shear punch testing(SPT) was used to evaluate the superplastic behavior of both the extruded and ECAP-processed alloys by measuring the strain rate sensitivity(SRS) index(m-value). While the highest m-value for the extruded alloy was measured to be 0.24 at 673 K, the ECAP-processed alloy exhibited much higher m-values of 0.41 and 0.52 at 598 and 623 K, respectively,delineating the occurrence of superplastic flow. Based on the calculated average activation energy of 118 kJ mol^(-1) and m-values close to 0.5, the deformation mechanism for superplastic flow at the temperatures of 598 and 623 K for the ECAP-processed alloys was recognized to be grain boundary sliding(GBS) assisted by grain boundary diffusion.展开更多
Hot isostatic pressing parameters are critical to Ti60 high temperature titanium alloy castings which have wide application perspective in aerospace.In order to obtain optimal processing parameters,the effects of hot ...Hot isostatic pressing parameters are critical to Ti60 high temperature titanium alloy castings which have wide application perspective in aerospace.In order to obtain optimal processing parameters,the effects of hot isostatic pressing parameters on defects,composition uniformity,microstructure and mechanical properties of Ti60 cast high temperature titanium alloy were investigated in detail.Results show that increasing temperature and pressure of hot isostatic pressing can reduce defects,especially,the internal defects are substantially eliminated when the temperature exceeds 920℃or the pressure exceeds 125 MPa.The higher temperature and pressure can improve the microstructure uniformity.Besides,the higher pressure can promote the composition uniformity.With the temperature increases from 880℃to 960℃,α-laths are coarsened.But with increasing pressure,the grain size of prior-βphase,the widths ofα-laths andα-colony are reduced.The tensile strength of Ti60 alloy is 949 MPa,yield strength is 827 MPa,and the elongation is 11%when the hot isostatic pressing parameters are 960℃/125 MPa/2 h,which exhibits the best match between the strength and plasticity.展开更多
The present work discusses the experimental study on wire-cut electric discharge machining of hot-pressed boron carbide.The effects of machining parameters,such as pulse on time(TON),peak current(IP),flushing pressure...The present work discusses the experimental study on wire-cut electric discharge machining of hot-pressed boron carbide.The effects of machining parameters,such as pulse on time(TON),peak current(IP),flushing pressure(FP) and spark voltage on material removal rate(MRR)and surface roughness(R_a) of the material,have been evaluated.These parameters are found to have an effect on the surface integrity of boron carbide machined samples.Wear rate of brass wire increases with rise in input energy in machining of hot-pressed boron carbide.The surfaces of machined samples were examined using scanning electron microscopy(SEM).The influence of machining parameters on mechanism of MRR and R_a was described.It was demonstrated that higher TON and peak current deteriorate the surface finish of boron carbide samples and result in the formation of large craters,debris and micro cracks.The generation of spherical particles was noticed and it was attributed to surface tension of molten material.Macro-ridges were also observed on the surface due to protrusion of molten material at higher discharge energy levels.展开更多
基金supported by the National Natural Science Foundation of China(No.52274252),the Key Science and Technology Project of Changsha City,China(No.kq2102005)the Special Fund for the Construction of Innovative Province in Hunan Province,China(Nos.2020RC3038 and 2022WK4004)the Changsha City Fund for Distinguished and Innovative Young Scholars,China(No.kq1802007).
文摘The combination of electrospinning and hot pressing,namely the electrospinning-hot pressing technique(EHPT),is an efficient and convenient method for preparing nanofibrous composite materials with good energy storage performance.The emerging composite membrane prepared by EHPT,which exhibits the advantages of large surface area,controllable morphology,and compact structure,has attracted immense attention.In this paper,the conduction mechanism of composite membranes in thermal and electrical energy storage and the performance enhancement method based on the fabrication process of EHPT are systematically discussed.Moreover,the state-of-the-art applications of composite membranes in these two fields are introduced.In particular,in the field of thermal energy storage,EHPT-prepared membranes have longitudinal and transverse nanofibers,which generate unique thermal conductivity pathways;also,these nanofibers offer enough space for the filling of functional materials.Moreover,EHPT-prepared membranes are beneficial in thermal management systems,building energy conservation,and electrical energy storage,e.g.,improving the electrochemical properties of the separators as well as their mechanical and thermal stability.The application of electrospinning-hot pressing membranes on capacitors,lithium-ion batteries(LIBs),fuel cells,sodium-ion batteries(SIBs),and hydrogen bromine flow batteries(HBFBs)still requires examination.In the future,EHPT is expected to make the field more exciting through its own technological breakthroughs or be combined with other technologies to produce intelligent materials.
基金financial support of the National Natural Science Foundation of China(Nos.52130110 and U22A20189)the Research Fund of the State Key Laboratory of Solidification Processing(No.2023-TS-10)。
文摘The microstructure characteristics and strengthening mechanism of Inconel738LC(IN-738LC) alloy prepared by using induction-assisted directed energy deposition(IDED) were elucidated through the investigation of samples subjected to IDED under 1050℃ preheating with and without hot isostatic pressing(HIP,1190℃,105 MPa,and 3 h).Results show that the as-deposited sample mainly consisted of epitaxial columnar crystals and inhomogeneously distributed γ’ phases in interdendritic and dendritic core regions.After HIP,grain morphology changed negligibly,whereas the size of the γ’ phase became increasingly even.After further heat treatment(HT,1070℃,2 h + 845℃,24 h),the γ’ phase in the as-deposited and HIPed samples presented a bimodal size distribution,whereas that in the as-deposited sample showed a size that remained uneven.The comparison of tensile properties revealed that the tensile strength and uniform elongation of the HIP + HTed sample increased by 5% and 46%,respectively,due to the synergistic deformation of bimodal γ’phases,especially large cubic γ’ phases.Finally,the relationship between phase transformations and plastic deformations in the IDEDed sample was discussed on the basis of generalized stability theory in terms of the trade-off between thermodynamics and kinetics.
基金The authors gratefully acknowledge the financial support from the National Natural Science Foundation of China(Nos.52274372 and 52201101)the National Key R&D Program of China(No.2021YFB3702404)the Fundamental Research Funds for the Central Universities(No.FRF-TP-22-013A1).
文摘This work investigated the effect of Cr and Si on the mechanical properties and oxidation resistance of press hardened steel.Results indicated that the microstructure of the Cr-Si micro-alloyed press hardened steel consisted of lath martensite,M_(23)C_(6)carbides,and retained austenite.The retained austenite and carbides are responsible for the increase in elongation of the micro-alloyed steel.In addition,after oxidation at 930℃for 5 min,the thickness of the oxide scales on the Cr-Si micro-alloyed press hardened steel is less than 5μm,much thinner than 45.50μm-thick oxide scales on 22MnB5.The oxide scales of the Cr-Si micro-alloyed steel are composed of Fe_(2)O_(3),Fe_(3)O_(4),mixed spinel oxide(FeCr_(2)O_(4)and Fe_(2)SiO_(4)),and amorphous SiO_(2).Adding Cr and Si significantly reduces the thickness of the oxide scales and prevents the generation of the FeO phase.Due to the increase of spinel FeCr_(2)O_(4)and Fe_(2)SiO_(4)phase in the inner oxide scale and the amorphous SiO_(2)close to the substrate,the oxidation resistance of the Cr-Si micro-alloyed press hardened steel is improved.
基金This work was financially supported by the National Natural Science Foundation of China (No. 50074017).
文摘To increase the adhesion strength between the coating and the substrate, sintered Ti(C,N)-based cermets were selected and deposited with monolayer TiN using a multiarc ion-plating technique; subsequently, hot isostatic pressing (HIPhag) treatment was performed at 1000℃ using nitrogen pressure up to 110 MPa. The mechanical properties of cermets after a coating process and subsequent HIPing treatment have been evaluated with respect to the hardness, the residual stress, and the coating adhesion. The results show that atter the HIPing process, there was a higher increase ha critical load ha the TiN-coated cermets with lower surface roughness compared with those with higher surface roughness. In all cases, the residual stress was found to be compressive. The effects of substrate surface roughness and posttreatment on the adhesion strength of the coatings were thus investigated. It was also fotmd that the HIPing posttreatment process is well suited for hacreasing the adhesion strength between the coating and the substrate.
基金financially supported by the Program for Changjiang Scholars and Innovative Research Teams in University(PCSIRT)(No.IRT0713)
文摘12 vol%WCp/2024Al composite was fabricated from mixed powders by hot-pressing at various tempera-tures. Investigation of the interfacial reaction between the WC phase and the Al alloy matrix was performed by X-ray diffraction (XRD), transmission electron microscope (TEM) and energy dispersive spectroscopy (EDS). A multiple layer interface structure, which is composed of Al/ WAl12/AlnC3/WC, is found to form by the interfacial reaction during hot-pressing. Further study shows that the AlaC3 layer forms along with a given crystal orientation of WC phase and might retard the interfacial reaction process.
基金financially supported by Guangdong Province Key Field R&D Program, China (No. 2019B01 0935001)the National Nature Science Foundation of China (No. 51905192)the Fundamental Research Funds for the Central Universities (No. FRT-TP-20-006A2)
文摘The Shima yield criterion used in finite element analysis for nickel-based superalloy powder compact during hot isostatic pressing(HIP) was modified through uniaxial compression experiments. The influence of cylindrical capsule characteristics on FGH4096M superalloy powder compact deformation and densification behavior during HIP was investigated through simulations and experiments. Results revealed the simulation shrinkage prediction fitted well with the experimental shrinkage including a maximum shrinkage error of 1.5%. It was shown that the axial shrinkage was 1.7% higher than radial shrinkage for a cylindrical capsule with the size of ∮50 mm × 100 mm due to the force arm difference along the axial and radial direction of the capsule. The stress deviated from the isostatic state in the capsule led to the uneven shrinkage and non-uniform densification of the powder compact. The ratio of the maximum radial displacement to axial displacement increased from0.47 to 0.75 with the capsule thickness increasing from 2 to 4 mm. The pressure transmission is related to the capsule thickness, the capsule material performance, and physical parameters in the HIP process.
文摘Characteristics of magnetic hardening in cast-hot pressed magnet Pr_(19)Fe_(74.5)B_5Cu_(1.5)were stu- died.The microstructure features and virgin magnetization curve reveal a nucleation control- led coercivity mechanism.Regression analysis shows that the intrinsic coercivity varies inversely as the logarithm of the average grain size: _iH_c(MA/m)=1.7312-0.48161nd(μm) which confirms the randomness of nucleation of reversed domains and the statistical nature of coercivity,indicating that the decrease of grain size would reduce the average number of de- fects on its surface and lower the probability of magnetization reversal of a grain and the cu- mulative fraction of the grains that have reversed their magnetization.Coercivity is thus en- hanced.
基金financially supported by the National Natural Science Foundation of China (Nos. 51874037 and 51922004)the Beijing Natural Science Foundation (No. 2212035)+1 种基金the Fundamental Research Funds for the Central Universities (No. FRF-TP-19005C1Z)the National Defense Basic Research Project (No. JCKY2017213004)。
文摘Powder hot isostatic pressing(HIP) is an effective method to achieve near-net-shape manufacturing of high-quality complex thinwalled titanium alloy parts, and it has received extensive attention in recent years. However, there are few reports about the microstructure characteristics on the strengthening and toughening mechanisms of powder hot isostatic pressed(HIPed) titanium alloys. Therefore, TA15powder was prepared into alloy by HIP approach, which was used to explore the microstructure characteristics at different HIP temperatures and the corresponding tensile properties and fracture toughness. Results show that the fabricated alloy has a “basket-like structure” when the HIP temperature is below 950℃, consisting of lath clusters and surrounding small equiaxed grains belts. When the HIP temperature is higher than 950℃, the microstructure gradually transforms into the Widmanstatten structure, accompanied by a significant increase in grain size. The tensile strength and elongation are reduced from 948 MPa and 17.3% for the 910℃ specimen to 861 MPa and 10% for the 970℃ specimen.The corresponding tensile fracture mode changes from transcrystalline plastic fracture to mixed fracture including intercrystalline cleavage.The fracture toughness of the specimens increases from 82.64 MPa·m^(1/2)for the 910℃ specimen to 140.18 MPa·m^(1/2)for the 970℃ specimen.Specimens below 950℃ tend to form holes due to the prior particle boundaries(PPBs), which is not conducive to toughening. Specimens above 950℃ have high fracture toughness due to the crack deflection, crack branching, and shear plastic deformation of the Widmanstatten structure. This study provides a valid reference for the development of powder HIPed titanium alloy.
文摘Powder compacts of the system Bi2–xPbxSr2Ca2Cu3Oy with 0 ≤ x ≤ 0.5 molar ratio using both techniques;isothermal hot pressing and the solid state reaction (sintering). The XRD of the hot pressed powder compacts of the nominal compositions Bi2–xPbxSr2Ca2Cu3Oy showed 2212 and 2223 phases. The resistivity temperature variations belonging to the composition Bi1.8Pb0.2Sr2Ca2Cu3Oy showed metal-superconducting transition at Tons = 143 K for the annealed sample for 24 h. The annealed nominal composition Bi1.5Pb0.5Sr2Ca2Cu3Oy for 18 h showed metal to superconducting transition at 80 K.
基金This research did not receive any specific grant from funding agencies in the public,commercial,or not-for-profit sectors.
文摘Two severe plastic deformation(SPD)techniques of simple shear extrusion(SSE)and equal channel angular pressing(ECAP)were employed to process an extruded Mg-6Gd-3Y-1.5Ag(wt%)alloy at 553 K for 1,2,4 and 6 passes.The microstructural evolutions were studied by electron back scattered diffraction(EBSD)analysis and transmission electron microscopy(TEM).The initial grain size of 7.5μm in the extruded alloy was reduced to about 1.3μm after 6 SPD passes.Discontinuous dynamic recrystallization was suggested to be operative in both SSE and ECAP,with also a potential contribution of continuous dynamic recrystallization at the early stages of deformation.The difference in the shear strain paths of the two SPD techniques caused different progression rate of dynamic recrystallization(DRX),so that the alloys processed by ECAP exhibited higher fractions of recrystallization and high angle grain boundaries(HAGBs).It was revealed that crystallographic texture was also significantly influenced by the difference in the strain paths of the two SPD methods,where dissimilar basal plane texture components were obtained.The compression tests,performed along extrusion direction(ED),indicated that the compressive yield stress(CYS)and ultimate compressive strength(UCS)of the alloys after both SEE and ECAP augmented continuously by increasing the number of passes.ECAP-processed alloys had lower values of CYS and UCS compared to their counterparts processed by SSE.This difference in the mechanical responses was attributed to the different configurations of basal planes with respect to the loading direction(ED)of each SPD technique.
文摘Densification, phase transformation and fracture toughness were studied in hot-pressed Si_3N_4 seeded by in-houseproduced large, elongated β-Si_3N_4 seeds. A mixture of Y_2O_3-Al_2O_3 was used as the sintering aid. Concentration ofseeds were varied from 0 to 6 wt pct and the sintering time at 1700℃ was varied from 1 to 4 h. Maximum fracturetoughness of 9.0 MPam^(1/2) was measured in samples containing 5 wt pct seeds, hot pressed at 1700℃ for 4 h.
基金National Natural Science Foundation of China (No.51474170)Natural Science Foundation of Shaanxi Province (No.2023-JC-YB-312)Key Laboratory Project of Shaanxi Province Educational Committee (No.20JS075)。
文摘A homogenous microstructure of ultrafine-grained (UFG) commercially pure (CP) Ti characterized by equiaxed grains/subgrains with an average grain size of about 150 nm and strong prismatic fiber texture were obtained after 4 passes of equal channel angular pressing (ECAP).Tension–compression asymmetry in yield and work hardening behavior of UFG CP Ti were investigated by uniaxial tension and compression tests.The experimental results reveal that UFG CP Ti exhibits a relatively obvious tensioncompression asymmetry in yielding and work hardening behavior.The basal and prismaticslip are suppressed either for tension or compression,which is the easiest to activate.The tension twin system{1012}<1011> easily activated in compression deformation due to the prismatic fiber texture based on the Schmidt factor,consequently resulting in a lower yield strength under compression than tension.ECAP can improve the tension-compression asymmetry of CP Ti due to grain refinement.The interaction among the dislocations,grain boundaries and deformation twins are the main work hardening mechanisms for compression deformation,while the interaction between the dislocations and grain boundaries for tension deformation.Deformation twins lead to the higher work hardening under compression than tension.
文摘An extruded Mg-6Gd-3Y-1.5Ag(wt%) alloy was processed by 6 passes of equal channel angular pressing(ECAP) at 553 K using route Bc to refine the microstructure. Electron back-scattered diffraction(EBSD) analysis showed a fully recrystallized microstructure for the extruded alloy with a mean grain size of 8.6 μm. The microstructure of the ECAP-processed alloy was uniformly refined through dynamic recrystallization(DRX). This microstructure contained fine grains with an average size of 1.3 μm, a high fraction of high angle grain boundaries(HAGBs), and nano-sized Mg_(5)Gd-type particles at the boundaries of the DRXed grains, detected by transmission electron microscopy(TEM). High-temperature shear punch testing(SPT) was used to evaluate the superplastic behavior of both the extruded and ECAP-processed alloys by measuring the strain rate sensitivity(SRS) index(m-value). While the highest m-value for the extruded alloy was measured to be 0.24 at 673 K, the ECAP-processed alloy exhibited much higher m-values of 0.41 and 0.52 at 598 and 623 K, respectively,delineating the occurrence of superplastic flow. Based on the calculated average activation energy of 118 kJ mol^(-1) and m-values close to 0.5, the deformation mechanism for superplastic flow at the temperatures of 598 and 623 K for the ECAP-processed alloys was recognized to be grain boundary sliding(GBS) assisted by grain boundary diffusion.
基金financially supported by the National Key Research and Development Program of China(Grant No.2020YFB2008300)。
文摘Hot isostatic pressing parameters are critical to Ti60 high temperature titanium alloy castings which have wide application perspective in aerospace.In order to obtain optimal processing parameters,the effects of hot isostatic pressing parameters on defects,composition uniformity,microstructure and mechanical properties of Ti60 cast high temperature titanium alloy were investigated in detail.Results show that increasing temperature and pressure of hot isostatic pressing can reduce defects,especially,the internal defects are substantially eliminated when the temperature exceeds 920℃or the pressure exceeds 125 MPa.The higher temperature and pressure can improve the microstructure uniformity.Besides,the higher pressure can promote the composition uniformity.With the temperature increases from 880℃to 960℃,α-laths are coarsened.But with increasing pressure,the grain size of prior-βphase,the widths ofα-laths andα-colony are reduced.The tensile strength of Ti60 alloy is 949 MPa,yield strength is 827 MPa,and the elongation is 11%when the hot isostatic pressing parameters are 960℃/125 MPa/2 h,which exhibits the best match between the strength and plasticity.
文摘The present work discusses the experimental study on wire-cut electric discharge machining of hot-pressed boron carbide.The effects of machining parameters,such as pulse on time(TON),peak current(IP),flushing pressure(FP) and spark voltage on material removal rate(MRR)and surface roughness(R_a) of the material,have been evaluated.These parameters are found to have an effect on the surface integrity of boron carbide machined samples.Wear rate of brass wire increases with rise in input energy in machining of hot-pressed boron carbide.The surfaces of machined samples were examined using scanning electron microscopy(SEM).The influence of machining parameters on mechanism of MRR and R_a was described.It was demonstrated that higher TON and peak current deteriorate the surface finish of boron carbide samples and result in the formation of large craters,debris and micro cracks.The generation of spherical particles was noticed and it was attributed to surface tension of molten material.Macro-ridges were also observed on the surface due to protrusion of molten material at higher discharge energy levels.