The sintering resistance for conductive TiB2 and non-conductive A12O3 as well as empty die during pulse current sintering were investigated in this paper. Equivalent resistances were measured by current and valtage du...The sintering resistance for conductive TiB2 and non-conductive A12O3 as well as empty die during pulse current sintering were investigated in this paper. Equivalent resistances were measured by current and valtage during sintering the conductive and non-conductive materials in the same conditions. It is found that the current paths for conductive are different from those for non-conductive materials. For non-conductive materials, sintering resistances are influenced by powder sizes and heating rates, which indicates that pulse current has some interaction with non-conductive powders. For conductive TiB2 , sintering resistances are influenced by heating rates and ball-milling time, which indicates the effect of powders activated by spark.展开更多
ZrO2-WC composites exhibit comparable mechanical properties as traditional WC-Co materials, which provides an opportunity to partially replace WC-Co for some applications. In this study, 2 mol.% Y2O3 stabilized ZrO2 c...ZrO2-WC composites exhibit comparable mechanical properties as traditional WC-Co materials, which provides an opportunity to partially replace WC-Co for some applications. In this study, 2 mol.% Y2O3 stabilized ZrO2 composites with 40 vol.% WC were consolidated in the 1150℃-1850℃ range under a pressure of 60 MPa by pulsed electric current sintering （PECS）. The densification behavior, microstructure and phase constitution of the composites were investigated to clarify the role of the sintering temperature on the grain growth, mechanical properties and thermal stability of ZrO2 and WC components. Analysis results indicated that the composites sintered at 1350℃ and 1450℃ exhibited the highest tetragonal ZrO2 phase transformability, maximum toughness, and hardness and an optimal flexural strength. Chemical reaction of ZrO2 and C, originating from the graphite die, was detected in the composite PECS for 20 min at 1850℃ in vacuum.展开更多
The microstructure and properties of the 93W-4Ni-2Co-1Fe(mass fraction,%) tungsten heavy alloys prepared by mechanical alloying and electric current activated sintering from mixed elemental powders were investigated.A...The microstructure and properties of the 93W-4Ni-2Co-1Fe(mass fraction,%) tungsten heavy alloys prepared by mechanical alloying and electric current activated sintering from mixed elemental powders were investigated.After 15 h milling,the average W grain size in the powders is decreased to 120 nm.For the powders milled for 15 h,the density,hardness and transverse rupture strength of the alloys sintered only by an intensive pulse electric current are the maximum.When the total sintering time keeps constant,the properties of the sintered alloys can be obviously improved by optimizing the sintering time of pulse-and constant-currents.A bulk ultrafine alloy with an average W grain size of about 340 nm can be obtained by sintering 15 h-milled powders in a total sintering time of 6 min.The corresponding sintered density,hardness and transverse rupture strength reach 16.78 g /cm3,HRA84.3 and 968 MPa,respectively.展开更多
Microstructure of reaction sintering of ZnAl2O4 at 1500℃ by hot-pressing(HP) and pulse electric current was investigated. The results indicated that the existed cracks in sintered body were caused by structure mismat...Microstructure of reaction sintering of ZnAl2O4 at 1500℃ by hot-pressing(HP) and pulse electric current was investigated. The results indicated that the existed cracks in sintered body were caused by structure mismatch. It is the evidence that periodical temperature field existed during pulse electric current sintering of nonconductive materials. The distance between high temperature areas was related to die diameter.展开更多
In this study we fabricated, for the first time, magnesium gallate (MgGa_(2)O_(4), a partially inverted spinel) transparent ceramics, both undoped and doped with 1 at% Ni. The specimens were derived from in-house prep...In this study we fabricated, for the first time, magnesium gallate (MgGa_(2)O_(4), a partially inverted spinel) transparent ceramics, both undoped and doped with 1 at% Ni. The specimens were derived from in-house prepared powder, with a crystallite size of ∼10 nm (by wet chemistry) and densified by pulsed electric current sintering (PECS;peak temperature 950 ℃ for 90 min). Densification levels of 99.84% and 99.52% of theoretical density were attained for doped and undoped materials, respectively. Doping with Ni was seen to marginally improve the densification level. Quite transparent specimens were produced: the best showing transmission of ∼89% of the theoretical level (thickness t = 0.85 mm). The absorption spectra revealed that the dopant was accumulated as Ni^(2+) in the octahedral sites of the lattice, as occurs in single-crystal specimens. After excitation at 980 nm, the doped disks exhibited a wide fluorescence band centered at 1264 nm.展开更多
基金Supported by the Natural Science Foundation of China (59872024) Key Teacher Fund of National Education Ministry and Fund of State Key Lab of Plastic Forming Simulation and Die and Mould Technology(02 -11)
文摘The sintering resistance for conductive TiB2 and non-conductive A12O3 as well as empty die during pulse current sintering were investigated in this paper. Equivalent resistances were measured by current and valtage during sintering the conductive and non-conductive materials in the same conditions. It is found that the current paths for conductive are different from those for non-conductive materials. For non-conductive materials, sintering resistances are influenced by powder sizes and heating rates, which indicates that pulse current has some interaction with non-conductive powders. For conductive TiB2 , sintering resistances are influenced by heating rates and ball-milling time, which indicates the effect of powders activated by spark.
文摘ZrO2-WC composites exhibit comparable mechanical properties as traditional WC-Co materials, which provides an opportunity to partially replace WC-Co for some applications. In this study, 2 mol.% Y2O3 stabilized ZrO2 composites with 40 vol.% WC were consolidated in the 1150℃-1850℃ range under a pressure of 60 MPa by pulsed electric current sintering （PECS）. The densification behavior, microstructure and phase constitution of the composites were investigated to clarify the role of the sintering temperature on the grain growth, mechanical properties and thermal stability of ZrO2 and WC components. Analysis results indicated that the composites sintered at 1350℃ and 1450℃ exhibited the highest tetragonal ZrO2 phase transformability, maximum toughness, and hardness and an optimal flexural strength. Chemical reaction of ZrO2 and C, originating from the graphite die, was detected in the composite PECS for 20 min at 1850℃ in vacuum.
基金Project(2007CB616905) supported by the National Basic Research Program of ChinaProject(2007AA03Z112) supported by the National High-tech Research and Development Program of China+1 种基金Project(x2jqB6080210) supported by the Natural Science Foundation of Guangdong Province,ChinaProject(9140A18040709JW1601) supported by the Advanced Research Fund of Department of Defense,China
文摘The microstructure and properties of the 93W-4Ni-2Co-1Fe(mass fraction,%) tungsten heavy alloys prepared by mechanical alloying and electric current activated sintering from mixed elemental powders were investigated.After 15 h milling,the average W grain size in the powders is decreased to 120 nm.For the powders milled for 15 h,the density,hardness and transverse rupture strength of the alloys sintered only by an intensive pulse electric current are the maximum.When the total sintering time keeps constant,the properties of the sintered alloys can be obviously improved by optimizing the sintering time of pulse-and constant-currents.A bulk ultrafine alloy with an average W grain size of about 340 nm can be obtained by sintering 15 h-milled powders in a total sintering time of 6 min.The corresponding sintered density,hardness and transverse rupture strength reach 16.78 g /cm3,HRA84.3 and 968 MPa,respectively.
基金This work was supported by the National Natural Science Foundation of China under grant No.50232020 and 50220160657.
文摘Microstructure of reaction sintering of ZnAl2O4 at 1500℃ by hot-pressing(HP) and pulse electric current was investigated. The results indicated that the existed cracks in sintered body were caused by structure mismatch. It is the evidence that periodical temperature field existed during pulse electric current sintering of nonconductive materials. The distance between high temperature areas was related to die diameter.
基金The authors gratefully acknowledge the National Science Foundation CAREER Grant(No.1554094)Office of Naval Research(No.N00014-17-1-2548)for funding this researchPart of this material(Raman data)is based upon work supported by the National Science Foundation(No.DMR-1626164).
文摘In this study we fabricated, for the first time, magnesium gallate (MgGa_(2)O_(4), a partially inverted spinel) transparent ceramics, both undoped and doped with 1 at% Ni. The specimens were derived from in-house prepared powder, with a crystallite size of ∼10 nm (by wet chemistry) and densified by pulsed electric current sintering (PECS;peak temperature 950 ℃ for 90 min). Densification levels of 99.84% and 99.52% of theoretical density were attained for doped and undoped materials, respectively. Doping with Ni was seen to marginally improve the densification level. Quite transparent specimens were produced: the best showing transmission of ∼89% of the theoretical level (thickness t = 0.85 mm). The absorption spectra revealed that the dopant was accumulated as Ni^(2+) in the octahedral sites of the lattice, as occurs in single-crystal specimens. After excitation at 980 nm, the doped disks exhibited a wide fluorescence band centered at 1264 nm.
