Mechanically activated W-Cu powders were sintered by a spark plasma sinteringsystem (SPS) in order to develop a new process and improve the properties of the alloy. Propertiessuch as density and hardness were measured...Mechanically activated W-Cu powders were sintered by a spark plasma sinteringsystem (SPS) in order to develop a new process and improve the properties of the alloy. Propertiessuch as density and hardness were measured. The microstructures of the sintered W-Cu alloy sampleswere observed by SEM (scanning electron microscope). The results show that spark plasma sinteringcan obviously lower the sintering temperature and increase the density of the alloy. This processcan also improve the hardness of the alloy. SPS is an effective method to obtain W-Cu powders withhigh density and superior physical properties.展开更多
Al-20Sn-1Cu powders were prepared by gas atomization in an argon atmosphere with atomizing pressures of 1.1 and 1.6 MPa. The characteristics of the powders are determined by means of dry sieving, scanning electron mic...Al-20Sn-1Cu powders were prepared by gas atomization in an argon atmosphere with atomizing pressures of 1.1 and 1.6 MPa. The characteristics of the powders are determined by means of dry sieving, scanning electron microscopy （SEM）, optical microscopy （OM）, and X-ray diffractometry （XRD）. The results show that the powders exhibit a bimodal size distribution and a higher gas pressure results in a broad size distribution. All particles in both cases are spherical or nearly spherical and satellites form on the surface of coarse particles. Dendritic and cellular structures coexist in the particle. With decreasing particle diameter, the secondary dendrite arm spacing （SDAS） decreases and the cooling rate increases. The particles processed under high gas atomization pressure （1.6 MPa） exhibit a lower SDAS value and a higher cooling rate than those of the same size under low gas atomization pressure （1.1 MPa）. The XRD results show that the Sn content increases with decreasing particle size.展开更多
Since Cu-Al powder characteristics have important effects on the preparation of Cu/Al2O3 composite, the apparent activation energy of Al internal oxidation reaction in Cu-Al pre-alloyed powders with different characte...Since Cu-Al powder characteristics have important effects on the preparation of Cu/Al2O3 composite, the apparent activation energy of Al internal oxidation reaction in Cu-Al pre-alloyed powders with different characteristics was calculated in the present investigation. The microstructure and properties of the synthesized Cu/Al2O3 were studied. The results show that high-energy milling can obviously promote internal oxidation of Al in Cu-Al powders in the same solid solubility. At the same milling conditions and internal oxidation parameters, the solid solution of Al in Cu either in low or high amount will result in the poor microstructure and properties of the Cu/Al2O3 composite. Subsequently, when high-energy milling and internal oxidation are synchronously used to prepare the Cu/Al2O3 composite, there should be an appropriate solubility and milling effect for the pre-alloyed powders.展开更多
The ultrafine powders of YBa2Cu3O7-x with the size of 100nm were synthesized by Sol-Gel process using cit-rate as complex and ammonium hydroxide to adjust pH of solu-tion. The process of Sol formation and Gel polymeri...The ultrafine powders of YBa2Cu3O7-x with the size of 100nm were synthesized by Sol-Gel process using cit-rate as complex and ammonium hydroxide to adjust pH of solu-tion. The process of Sol formation and Gel polymerization of YBa2Cu3O7-x in the Sol-Gel synthetic reaction has bee studied. The particle size ,pruity, sintering activity and superconducting properties of YBa2Cu3O7-x prepared by Sol-Gel method are better than by solid state reaction.展开更多
Elemental powders of Cu and Fe were ball milled for various time durations up to 100 h. The various stages of forced alloying by ball milling, leading to instability of elemental crystalline phases and formation of qu...Elemental powders of Cu and Fe were ball milled for various time durations up to 100 h. The various stages of forced alloying by ball milling, leading to instability of elemental crystalline phases and formation of quasicrystalline phases were monitored using X-ray diffraction. Diffusion of Fe into the Cu matrix is proposed as the cause which triggers the instability of crystalline phases and leads to the formation of quasicrystalline phases after 10 h of milling. Milling for 100 h resulted in two different quasicrystalline phases with different lattice constants. Role of the nanocrystalline microstructure as an important criterion for the destabilisation of crystalline phases is explained. It is suggested that the formation of nanocrystalline microstructure and their subsequent transformation into quasicrystalline phases may be associated with a continuous increase in the disclination content of the system, which had formed as a result of continued milling and mechanical deformation.展开更多
A direct electroless copper （Cu） coating on tungsten powders method requiring no surface treatment or stabilizing agent and using glyoxylic acid （C2H203） as a reducing agent was reported. The effects of copper sul...A direct electroless copper （Cu） coating on tungsten powders method requiring no surface treatment or stabilizing agent and using glyoxylic acid （C2H203） as a reducing agent was reported. The effects of copper sulfate concentration and the pH of the plating solution on the properties of the prepared W@Cu composite powders were assessed. The content of Cu in the composite powders was controlled by adjusting the concentration of copper sulfate in the electroless plating solution. A uniform, dense, and consistent Cu coating was obtained under the established optimum conditions （flow rate of C2H203 = 5.01 mL/min, solution pH = 12.25 and reaction temperature 45.35℃） by using central composite design method. In addition, the crystalline Cu coating was evenly dispersed within the W@Cu composite powders and Cu element in the coating existed as Cu~. The formation mechanism for the W@Cu composite powders by electroless plating in the absence of surface treatment and stabilizing agent was also proposed.展开更多
The Cu-Sn binary intermetallic powders were obtained via a patented reaction ball milling technique. The Sn melt reacted with the solid-state Cu during the milling process at different temperatures for different inter...The Cu-Sn binary intermetallic powders were obtained via a patented reaction ball milling technique. The Sn melt reacted with the solid-state Cu during the milling process at different temperatures for different intervals. Two kinds of binary intermetallics were obtained. For 12 h,Cu6Sn5 was prepared by milling Sn melt at 573 K while Cu3Sn by milling Sn melt at 773 K. And a mixture of Cu6Sn5 and Cu3Sn was fabricated at 673 K. All these intermetallic powders had mean grain sizes of less than 100 nm. A finer microstructure was obtained by milling Sn melt blended with 20%(mass fraction) Ni powders at 573 K for 12 h. The reaction mechanism and advantages were discussed in comparison with that of high-energy ball milling. The results show the solutionizing of Ni powders in the Cu6Sn5 intermetallic.展开更多
Cu(NO3)(2) and (NH4)(6)H(2)W(12)O(40)center dot 4H(2)O were used to prepare W/Cu nanosized composite powder by sol-gel technique. The influences of heat treatment process, pH value of the solution and the amount of an...Cu(NO3)(2) and (NH4)(6)H(2)W(12)O(40)center dot 4H(2)O were used to prepare W/Cu nanosized composite powder by sol-gel technique. The influences of heat treatment process, pH value of the solution and the amount of an addition agent on particle size were investigated by DSC, XRD and TEM. The results show that, at a certain heat treatment temperature, the W/Cu nanoparticle size increases with the pH value or the amount of the addition agent increasing.展开更多
Mechanical activation and liquid phase sintering were used to manufacture high performance Mo-Cu alloy and develop new processes. The microstructures and properties of the alloy were investigated. The experimental res...Mechanical activation and liquid phase sintering were used to manufacture high performance Mo-Cu alloy and develop new processes. The microstructures and properties of the alloy were investigated. The experimental results showed that: (1) the ball milled Mo/Cu powder has lamellar structure, (2) the microstructures of the sintered Mo-Cu alloy were homogenous compound structures of adhesive phase Cu linking Mo grains, (3) Mo grains frequently strung or gathered in Cu phase, and (4) the full densities of Mo-Cu alloy was achieved through sintering and special densification process. As a result, the properties of the alloy are good enough to satisfy various requirements.展开更多
Highly supersaturated nanocrystalline fcc Fe60Cu40 alloy has been prepared by mechanical alloying of elemental powders. The phase transformation is monitored by X-ray diffraction (XRD),Mossbauer spectroscopy and exten...Highly supersaturated nanocrystalline fcc Fe60Cu40 alloy has been prepared by mechanical alloying of elemental powders. The phase transformation is monitored by X-ray diffraction (XRD),Mossbauer spectroscopy and extended X-ray absorption fine structure (EXAFS). The powder obtained after milling is of single fcc structure with grain size of nanometer order. The Mossbauer spectra of the milled powder can be fitted by two subspectra whose hyperfine magnetic fields are 16 MA/m and 20 MA/m while that of pure Fe disappeared. EXAFS results show that the radial structure function (RSF) of Fe K-edge changed drastically and finally became similar to that of reference Cu K-edge, while that of Cu K-edge nearly keeps unchanged in the process of milling. These imply that bcc Fe really transforms to fcc structure and alloying between Fe and Cu occurs truly on an atomic scale. EXAFS results indicate that iron atoms tend to segregate at the boundaries and Cu atoms are rich in the fcc lattice. Annealing experiments show that the Fe atoms at the interfaces are easy to cluster to α-Fe at a lower temperature, whereas the iron atoms in the lattice will form γ-Fe first at temperature above 350℃, and then transform to bcc Fe展开更多
W-15% Cu (mass fraction) alloys were sintered with mechanically activated powder in order to develop new preparing processes and improve properties of alloys. The microstructures of the activated powder and the sinter...W-15% Cu (mass fraction) alloys were sintered with mechanically activated powder in order to develop new preparing processes and improve properties of alloys. The microstructures of the activated powder and the sintered alloy were observed. Properties such as density were measured. The results show that through mechanical activation, the particle size of the powder becomes finer to sub-micron or nanometer level, some copper was soluble in tungsten, and high density W-Cu alloys can be obtained by mechanically activated powder for its action to the activation sintering.展开更多
基金Natural Science Foundation of China(No.51871244)Hunan Provincial Innovation Foundation for Postgraduate,China(No.CX20200172)Fundamental Research Funds for the Central Universities of Central South University,China(No.1053320190103)。
基金This work was financially supported by the National Natural Science Foundation of China (No. 50174007)
文摘Mechanically activated W-Cu powders were sintered by a spark plasma sinteringsystem (SPS) in order to develop a new process and improve the properties of the alloy. Propertiessuch as density and hardness were measured. The microstructures of the sintered W-Cu alloy sampleswere observed by SEM (scanning electron microscope). The results show that spark plasma sinteringcan obviously lower the sintering temperature and increase the density of the alloy. This processcan also improve the hardness of the alloy. SPS is an effective method to obtain W-Cu powders withhigh density and superior physical properties.
基金the Major State Ba-sic Research Development Program of China (Nos. 2006CB605203 and 2006CB605204)
文摘Al-20Sn-1Cu powders were prepared by gas atomization in an argon atmosphere with atomizing pressures of 1.1 and 1.6 MPa. The characteristics of the powders are determined by means of dry sieving, scanning electron microscopy （SEM）, optical microscopy （OM）, and X-ray diffractometry （XRD）. The results show that the powders exhibit a bimodal size distribution and a higher gas pressure results in a broad size distribution. All particles in both cases are spherical or nearly spherical and satellites form on the surface of coarse particles. Dendritic and cellular structures coexist in the particle. With decreasing particle diameter, the secondary dendrite arm spacing （SDAS） decreases and the cooling rate increases. The particles processed under high gas atomization pressure （1.6 MPa） exhibit a lower SDAS value and a higher cooling rate than those of the same size under low gas atomization pressure （1.1 MPa）. The XRD results show that the Sn content increases with decreasing particle size.
基金supported by the National Natural Science Foundation of China (No.50574075)Program for New Century Excellent Talents in University(No.NCET-05-0873)Specialized Research Fund for the Doctoral Program of Higher Education (SRFDP 20060700011)
文摘Since Cu-Al powder characteristics have important effects on the preparation of Cu/Al2O3 composite, the apparent activation energy of Al internal oxidation reaction in Cu-Al pre-alloyed powders with different characteristics was calculated in the present investigation. The microstructure and properties of the synthesized Cu/Al2O3 were studied. The results show that high-energy milling can obviously promote internal oxidation of Al in Cu-Al powders in the same solid solubility. At the same milling conditions and internal oxidation parameters, the solid solution of Al in Cu either in low or high amount will result in the poor microstructure and properties of the Cu/Al2O3 composite. Subsequently, when high-energy milling and internal oxidation are synchronously used to prepare the Cu/Al2O3 composite, there should be an appropriate solubility and milling effect for the pre-alloyed powders.
文摘The ultrafine powders of YBa2Cu3O7-x with the size of 100nm were synthesized by Sol-Gel process using cit-rate as complex and ammonium hydroxide to adjust pH of solu-tion. The process of Sol formation and Gel polymerization of YBa2Cu3O7-x in the Sol-Gel synthetic reaction has bee studied. The particle size ,pruity, sintering activity and superconducting properties of YBa2Cu3O7-x prepared by Sol-Gel method are better than by solid state reaction.
文摘Elemental powders of Cu and Fe were ball milled for various time durations up to 100 h. The various stages of forced alloying by ball milling, leading to instability of elemental crystalline phases and formation of quasicrystalline phases were monitored using X-ray diffraction. Diffusion of Fe into the Cu matrix is proposed as the cause which triggers the instability of crystalline phases and leads to the formation of quasicrystalline phases after 10 h of milling. Milling for 100 h resulted in two different quasicrystalline phases with different lattice constants. Role of the nanocrystalline microstructure as an important criterion for the destabilisation of crystalline phases is explained. It is suggested that the formation of nanocrystalline microstructure and their subsequent transformation into quasicrystalline phases may be associated with a continuous increase in the disclination content of the system, which had formed as a result of continued milling and mechanical deformation.
基金Funded by the National Natural Science Foundation of China(Nos.51202175 and 11072228)the National 111 Project(No.B13035)
文摘A direct electroless copper （Cu） coating on tungsten powders method requiring no surface treatment or stabilizing agent and using glyoxylic acid （C2H203） as a reducing agent was reported. The effects of copper sulfate concentration and the pH of the plating solution on the properties of the prepared W@Cu composite powders were assessed. The content of Cu in the composite powders was controlled by adjusting the concentration of copper sulfate in the electroless plating solution. A uniform, dense, and consistent Cu coating was obtained under the established optimum conditions （flow rate of C2H203 = 5.01 mL/min, solution pH = 12.25 and reaction temperature 45.35℃） by using central composite design method. In addition, the crystalline Cu coating was evenly dispersed within the W@Cu composite powders and Cu element in the coating existed as Cu~. The formation mechanism for the W@Cu composite powders by electroless plating in the absence of surface treatment and stabilizing agent was also proposed.
基金Project(50574039) supported by the National Natural Science Foundation of China
文摘The Cu-Sn binary intermetallic powders were obtained via a patented reaction ball milling technique. The Sn melt reacted with the solid-state Cu during the milling process at different temperatures for different intervals. Two kinds of binary intermetallics were obtained. For 12 h,Cu6Sn5 was prepared by milling Sn melt at 573 K while Cu3Sn by milling Sn melt at 773 K. And a mixture of Cu6Sn5 and Cu3Sn was fabricated at 673 K. All these intermetallic powders had mean grain sizes of less than 100 nm. A finer microstructure was obtained by milling Sn melt blended with 20%(mass fraction) Ni powders at 573 K for 12 h. The reaction mechanism and advantages were discussed in comparison with that of high-energy ball milling. The results show the solutionizing of Ni powders in the Cu6Sn5 intermetallic.
基金supported by the Key Laboratory of Micro-systems and Micro-structures Manufacturing of Ministry of Education,Harbin Institute of Technology,China(No.2020KM005)the Natural Science Foundation of Heilongjiang Province,China(No.YQ2020E030)。
基金This Project was financially supported by the National Natural Science Foundation of China (No. 50471033).
文摘Cu(NO3)(2) and (NH4)(6)H(2)W(12)O(40)center dot 4H(2)O were used to prepare W/Cu nanosized composite powder by sol-gel technique. The influences of heat treatment process, pH value of the solution and the amount of an addition agent on particle size were investigated by DSC, XRD and TEM. The results show that, at a certain heat treatment temperature, the W/Cu nanoparticle size increases with the pH value or the amount of the addition agent increasing.
文摘Mechanical activation and liquid phase sintering were used to manufacture high performance Mo-Cu alloy and develop new processes. The microstructures and properties of the alloy were investigated. The experimental results showed that: (1) the ball milled Mo/Cu powder has lamellar structure, (2) the microstructures of the sintered Mo-Cu alloy were homogenous compound structures of adhesive phase Cu linking Mo grains, (3) Mo grains frequently strung or gathered in Cu phase, and (4) the full densities of Mo-Cu alloy was achieved through sintering and special densification process. As a result, the properties of the alloy are good enough to satisfy various requirements.
文摘Highly supersaturated nanocrystalline fcc Fe60Cu40 alloy has been prepared by mechanical alloying of elemental powders. The phase transformation is monitored by X-ray diffraction (XRD),Mossbauer spectroscopy and extended X-ray absorption fine structure (EXAFS). The powder obtained after milling is of single fcc structure with grain size of nanometer order. The Mossbauer spectra of the milled powder can be fitted by two subspectra whose hyperfine magnetic fields are 16 MA/m and 20 MA/m while that of pure Fe disappeared. EXAFS results show that the radial structure function (RSF) of Fe K-edge changed drastically and finally became similar to that of reference Cu K-edge, while that of Cu K-edge nearly keeps unchanged in the process of milling. These imply that bcc Fe really transforms to fcc structure and alloying between Fe and Cu occurs truly on an atomic scale. EXAFS results indicate that iron atoms tend to segregate at the boundaries and Cu atoms are rich in the fcc lattice. Annealing experiments show that the Fe atoms at the interfaces are easy to cluster to α-Fe at a lower temperature, whereas the iron atoms in the lattice will form γ-Fe first at temperature above 350℃, and then transform to bcc Fe
文摘W-15% Cu (mass fraction) alloys were sintered with mechanically activated powder in order to develop new preparing processes and improve properties of alloys. The microstructures of the activated powder and the sintered alloy were observed. Properties such as density were measured. The results show that through mechanical activation, the particle size of the powder becomes finer to sub-micron or nanometer level, some copper was soluble in tungsten, and high density W-Cu alloys can be obtained by mechanically activated powder for its action to the activation sintering.
