Volume 41,Issue 4,2012 Table of Contents
2012, 41(4):565-569.
Abstract:
The Mg2Ni-type Mg2Ni1-xCox (x=0, 0.1, 0.2, 0.3, 0.4) alloys were prepared by melt-spinning technique. The structures of the as-cast and spun alloys were characterized by XRD, SEM and TEM. The electrochemical hydrogen storage kinetics of the as-spun alloy ribbons was tested by an automatic galvanostatic system. The hydrogen diffusion coefficients in the alloys were calculated by virtue of potential-step method. The electrochemical impedance spectrums (EIS) and the Tafel polarization curves were plotted by an electrochemical workstation. The results show that the as-spun Co-free alloy exhibits a typical nanocrystalline structure, while the as-spun (x=0.4) alloy displays a nanocrystalline and amorphous structure, confirming that the substitution of Co for Ni facilitates the glass formation in the Mg2Ni-type alloy. The amorphization degree of the as-spun alloys substituted by Co visibly increases with the increase in the amount of Co replacement. The Co replacement for Ni notably improves the electrochemical hydrogen storage kinetics of the alloys. With a growth in the amount of Co replacement from 0 to 0.4, the high rate discharge ability of the as-spun (25 m/s) alloy increases from 65.3% to 75.3%, the hydrogen diffusion coefficient (D) from 2.22 to 3.34 cm2/s and the limiting current density IL from 247.8 to 712.4 mA/g, respectively
The Mg2Ni-type Mg2Ni1-xCox (x=0, 0.1, 0.2, 0.3, 0.4) alloys were prepared by melt-spinning technique. The structures of the as-cast and spun alloys were characterized by XRD, SEM and TEM. The electrochemical hydrogen storage kinetics of the as-spun alloy ribbons was tested by an automatic galvanostatic system. The hydrogen diffusion coefficients in the alloys were calculated by virtue of potential-step method. The electrochemical impedance spectrums (EIS) and the Tafel polarization curves were plotted by an electrochemical workstation. The results show that the as-spun Co-free alloy exhibits a typical nanocrystalline structure, while the as-spun (x=0.4) alloy displays a nanocrystalline and amorphous structure, confirming that the substitution of Co for Ni facilitates the glass formation in the Mg2Ni-type alloy. The amorphization degree of the as-spun alloys substituted by Co visibly increases with the increase in the amount of Co replacement. The Co replacement for Ni notably improves the electrochemical hydrogen storage kinetics of the alloys. With a growth in the amount of Co replacement from 0 to 0.4, the high rate discharge ability of the as-spun (25 m/s) alloy increases from 65.3% to 75.3%, the hydrogen diffusion coefficient (D) from 2.22 to 3.34 cm2/s and the limiting current density IL from 247.8 to 712.4 mA/g, respectively
2012, 41(4):570-574.
Abstract:
The microstructures of Ti-46Al, Ti-46Al-0.3B, Ti-46Al-0.5B, Ti-46Al-2Fe, Ti-46Al-2Fe-0.3B, and Ti-46Al-2Fe-0.5B alloys solidified on water-cooled copper crucible were investigated. It is found that the as-cast alloys possess a typical columnar structure, and the mean diameters of the columnar grains decrease significantly as the addition of Fe or B. The mean columnar diameter in Ti-46Al-2Fe-0.5B is found to be the smallest among these alloys. B addition can increase the constitutional supercooling in front of the solid-liquid interface, which refines the columnar structure and the dendritic structure. Moreover, Fe addition can enhance the refining effect of boron on the columnar structure of TiAl-based alloys
The microstructures of Ti-46Al, Ti-46Al-0.3B, Ti-46Al-0.5B, Ti-46Al-2Fe, Ti-46Al-2Fe-0.3B, and Ti-46Al-2Fe-0.5B alloys solidified on water-cooled copper crucible were investigated. It is found that the as-cast alloys possess a typical columnar structure, and the mean diameters of the columnar grains decrease significantly as the addition of Fe or B. The mean columnar diameter in Ti-46Al-2Fe-0.5B is found to be the smallest among these alloys. B addition can increase the constitutional supercooling in front of the solid-liquid interface, which refines the columnar structure and the dendritic structure. Moreover, Fe addition can enhance the refining effect of boron on the columnar structure of TiAl-based alloys
2012, 41(4):575-580.
Abstract:
A high-Mn-N low-Ni superduplex stainless steel 25Cr-2Ni-3Mo-10Mn-0.5N with multi-scale microstructures has been prepared through severe cold rolling and annealing, and the effects of multi-scale grains on the pitting corrosion and mechanical properties have been investigated. The results show that the multi-scale microstructures have a strong relation with the annealing time, that is, the average grain sizes of austenite and ferrite increase with prolonging of the annealing time at 1050 oC, they have the minimum values of 1.5 and 7.18 μm, respectively, when the alloy is annealed for 1 min. The tensile strength, yield strength and reduction in area of the sample decrease with the growth of multi-scale grains, whereas the pitting corrosion resistance of the specimen is enhanced. The multi-scale microstructures play an important role on the pitting corrosion and the mechanical properties of superduplex stainless steel 25Cr-2Ni-3Mo-10Mn-0.5N.
A high-Mn-N low-Ni superduplex stainless steel 25Cr-2Ni-3Mo-10Mn-0.5N with multi-scale microstructures has been prepared through severe cold rolling and annealing, and the effects of multi-scale grains on the pitting corrosion and mechanical properties have been investigated. The results show that the multi-scale microstructures have a strong relation with the annealing time, that is, the average grain sizes of austenite and ferrite increase with prolonging of the annealing time at 1050 oC, they have the minimum values of 1.5 and 7.18 μm, respectively, when the alloy is annealed for 1 min. The tensile strength, yield strength and reduction in area of the sample decrease with the growth of multi-scale grains, whereas the pitting corrosion resistance of the specimen is enhanced. The multi-scale microstructures play an important role on the pitting corrosion and the mechanical properties of superduplex stainless steel 25Cr-2Ni-3Mo-10Mn-0.5N.
2012, 41(4):581-584.
Abstract:
The microstructural evolution and the element distribution of Ti14 (α+Ti2Cu) alloy during semi-solid compression were investigated. Moreover, the Ti2Cu precipitate behaviors were discussed in detail. The results show that the microstructure, the number and distribution of Ti2Cu precipitates have significant dependence on the process parameters. More Ti2Cu will precipitate on grain boundaries at a higher deformation temperature, and/or a lower strain rate as well as deformation ratio, and finally a network structure is formed after deformation at 1100 °C. The precipitation on grain boundaries is found to be mainly controlled by peritectic reactions. The elevated temperatures resulted in more liquid along the prior grain boundaries, and a Cu-rich region is formed, finally. the “coarse” grain boundaries appear during re-solidification
The microstructural evolution and the element distribution of Ti14 (α+Ti2Cu) alloy during semi-solid compression were investigated. Moreover, the Ti2Cu precipitate behaviors were discussed in detail. The results show that the microstructure, the number and distribution of Ti2Cu precipitates have significant dependence on the process parameters. More Ti2Cu will precipitate on grain boundaries at a higher deformation temperature, and/or a lower strain rate as well as deformation ratio, and finally a network structure is formed after deformation at 1100 °C. The precipitation on grain boundaries is found to be mainly controlled by peritectic reactions. The elevated temperatures resulted in more liquid along the prior grain boundaries, and a Cu-rich region is formed, finally. the “coarse” grain boundaries appear during re-solidification
2012, 41(4):585-588.
Abstract:
CMP (chemical mechanical polish) experiments were carried out by using high purity nickel and home-made slurry. The effects of polishing down force, pH value, H2O2 concentration, chelating agent?species and their concentration as well as particle concentration on the material removal rate (MRR) were investigated. The results reveal that MRR can reach 312.3 nm/min under the following conditions: the down force is 13.79 kPa, H2O2 concentration is 0.5% (mass fraction), pH = 3.0, SiO2 concentration is 0.5% and EDTA concentration is 1%, The better surface quality can be obtained under the following conditions: the down force is 13.79 kPa, H2O2 concentration is 1%, pH = 4.0, SiO2 concentration is 1%, EDTA concentration is 1%, and the surface roughness Ra can reach 5 nm.
CMP (chemical mechanical polish) experiments were carried out by using high purity nickel and home-made slurry. The effects of polishing down force, pH value, H2O2 concentration, chelating agent?species and their concentration as well as particle concentration on the material removal rate (MRR) were investigated. The results reveal that MRR can reach 312.3 nm/min under the following conditions: the down force is 13.79 kPa, H2O2 concentration is 0.5% (mass fraction), pH = 3.0, SiO2 concentration is 0.5% and EDTA concentration is 1%, The better surface quality can be obtained under the following conditions: the down force is 13.79 kPa, H2O2 concentration is 1%, pH = 4.0, SiO2 concentration is 1%, EDTA concentration is 1%, and the surface roughness Ra can reach 5 nm.
2012, 41(4):589-593.
Abstract:
silver mesocrystals have been synthesized via oriented attachment of primary building nanoparticles in simple and fast replacement reactions between AgNO3 solution and Sn. The formation process of silver mesocrystals is discussed in detail and the growth mechanism is suggested to describe the formation of silver mesocrystals. In a 200 mmol/L solution, the primary nanoparticles orientationally aggregate along <211> directions to form a dendrite, the proposed attachment planes and directions for Ag nanoparticles are 3×{422} planes and <211> directions, respectively. When the concentration increases to 1 mol/L, the primary building nanoparticles orientotionally aggregate along <211> directions to form dendrites. The dendrites that can be proposed as the second building units orientationally attach along <110> directions to construct a porous monocrystalline plate, and finally transit to a mesocrystal with a thickness about 50 nm. When the AgNO3 concentration is 2 mol/L, the building units are Ag triangle platelets. These platelets also orientationally attach along <110> directions to form a monocrystalline dense plate and finally the plate transforms to monocrystalline mesocrystal with a thickness over 100 nm
silver mesocrystals have been synthesized via oriented attachment of primary building nanoparticles in simple and fast replacement reactions between AgNO3 solution and Sn. The formation process of silver mesocrystals is discussed in detail and the growth mechanism is suggested to describe the formation of silver mesocrystals. In a 200 mmol/L solution, the primary nanoparticles orientationally aggregate along <211> directions to form a dendrite, the proposed attachment planes and directions for Ag nanoparticles are 3×{422} planes and <211> directions, respectively. When the concentration increases to 1 mol/L, the primary building nanoparticles orientotionally aggregate along <211> directions to form dendrites. The dendrites that can be proposed as the second building units orientationally attach along <110> directions to construct a porous monocrystalline plate, and finally transit to a mesocrystal with a thickness about 50 nm. When the AgNO3 concentration is 2 mol/L, the building units are Ag triangle platelets. These platelets also orientationally attach along <110> directions to form a monocrystalline dense plate and finally the plate transforms to monocrystalline mesocrystal with a thickness over 100 nm
2012, 41(4):594-598.
Abstract:
Based on a large amount of experimental data, the relationship model of chemical elements and mechanical property for TC11 titanium alloy has been developed using artificial neural network. The input parameters of this model were 9 kinds of elements, including Al, Mo, Zr, Si, Fe, C, O, N and H. The mechanical properties were used as output parameters, including ultimate tensile strength, yield strength, elongation and reduction of area. The prediction capability of the established model was tested by the unseen data sample. Additionally, the effect of chemical elements (Al、Mo、Zr and C) on the mechanical property was studied using the present model. It is found that the relative errors between predicted and experimental values all within 10%, indicating that the neural network model possesses excellent prediction capability. With the help of the trained ANN model, the nonlinear relationship of chemical elements and mechanical property can also be clearly presented.
Based on a large amount of experimental data, the relationship model of chemical elements and mechanical property for TC11 titanium alloy has been developed using artificial neural network. The input parameters of this model were 9 kinds of elements, including Al, Mo, Zr, Si, Fe, C, O, N and H. The mechanical properties were used as output parameters, including ultimate tensile strength, yield strength, elongation and reduction of area. The prediction capability of the established model was tested by the unseen data sample. Additionally, the effect of chemical elements (Al、Mo、Zr and C) on the mechanical property was studied using the present model. It is found that the relative errors between predicted and experimental values all within 10%, indicating that the neural network model possesses excellent prediction capability. With the help of the trained ANN model, the nonlinear relationship of chemical elements and mechanical property can also be clearly presented.
2012, 41(4):599-602.
Abstract:
The electrodeposition of lanthanum on a Pt electrode was investigated in 0.01 mol/L LaCl3-0.1 mol/L LiCl-EMIMBF4 ionic liquid. The cyclic voltammetry, chronoamperometry and constant voltage electrolysis techniques were employed. The results of the cyclic voltammogram and the XRD pattern of deposits after electrolysis under constant voltage have supported a one step electrodeposition mechanism of lanthanum, La3+ + 3e-→La. The results also indicate that the reduction of La3+ ion is irreversible. The transfer coefficient and the diffusion coefficient of La3+ ion in 0.01 mol/L LaCl3-0.1 mol/L LiCl-EMIMBF4 ionic liquid are 0.0492 and (1.07-1.19)×10-6 cm2/s, respectively
The electrodeposition of lanthanum on a Pt electrode was investigated in 0.01 mol/L LaCl3-0.1 mol/L LiCl-EMIMBF4 ionic liquid. The cyclic voltammetry, chronoamperometry and constant voltage electrolysis techniques were employed. The results of the cyclic voltammogram and the XRD pattern of deposits after electrolysis under constant voltage have supported a one step electrodeposition mechanism of lanthanum, La3+ + 3e-→La. The results also indicate that the reduction of La3+ ion is irreversible. The transfer coefficient and the diffusion coefficient of La3+ ion in 0.01 mol/L LaCl3-0.1 mol/L LiCl-EMIMBF4 ionic liquid are 0.0492 and (1.07-1.19)×10-6 cm2/s, respectively
2012, 41(4):603-606.
Abstract:
Rene88DT superalloy was prepared by laser solid forming (LSF). The morphology, size and coarsening kinetics of γ′ precipitates of LSF Rene88DT during aging treatment at high temperature (760-840 ℃) for short time (4-16 h) were studied by microscopic measurements and analysis. The results show that γ′ precipitates are evolved gradually to be spherical in morphology and uniformly distributed in the γ matrix during high temperature and short time aging treatment. It can be found that the aging temperature has more significant effect on the γ′ precipitates than the aging time. Meanwhile, the coarsening behavior of the main strengthening precipitates γ′ obeys the Lifshitz-Slyozov-Wagner (LSW) theory. The diffusion activation energy Q in coarsening of LSF Rene88DT γ′ precipitates is 211.65 kJ/mol. The coarsening behavior of γ′ precipitates is controlled by the diffusion of Al and Ti in the g matrix.
Rene88DT superalloy was prepared by laser solid forming (LSF). The morphology, size and coarsening kinetics of γ′ precipitates of LSF Rene88DT during aging treatment at high temperature (760-840 ℃) for short time (4-16 h) were studied by microscopic measurements and analysis. The results show that γ′ precipitates are evolved gradually to be spherical in morphology and uniformly distributed in the γ matrix during high temperature and short time aging treatment. It can be found that the aging temperature has more significant effect on the γ′ precipitates than the aging time. Meanwhile, the coarsening behavior of the main strengthening precipitates γ′ obeys the Lifshitz-Slyozov-Wagner (LSW) theory. The diffusion activation energy Q in coarsening of LSF Rene88DT γ′ precipitates is 211.65 kJ/mol. The coarsening behavior of γ′ precipitates is controlled by the diffusion of Al and Ti in the g matrix.
2012, 41(4):607-611.
Abstract:
In order to understand the effects of nonlinear microstructures on the damage evolution in laser welded joint of titanium alloy, a multi-specimen method with volume fraction of microvoids was applied to estimate the damage evolution for TC4 titanium alloy. The results show that there are great nonlinear gradient distributions of the microstructure morphology in TC4 laser deep penetration welded joints from weld metal, HAZ to base metal, the damage performance and mechanism change according to these gradient characters, the damage mechanism presents the pattern of microvoids-polymerization, and the volume fraction of microvoids has a great gradient distribution which increases faster in the base metal near welding HAZ than in the weld metal as the load increasing.
In order to understand the effects of nonlinear microstructures on the damage evolution in laser welded joint of titanium alloy, a multi-specimen method with volume fraction of microvoids was applied to estimate the damage evolution for TC4 titanium alloy. The results show that there are great nonlinear gradient distributions of the microstructure morphology in TC4 laser deep penetration welded joints from weld metal, HAZ to base metal, the damage performance and mechanism change according to these gradient characters, the damage mechanism presents the pattern of microvoids-polymerization, and the volume fraction of microvoids has a great gradient distribution which increases faster in the base metal near welding HAZ than in the weld metal as the load increasing.
11 Effects of Surface Film on Superhydrophobic Characteristics of Ti6Al4V with Dotted Matrix Structure
2012, 41(4):612-616.
Abstract:
The dotted matrix structures on Ti6Al4V specimens with different spacing were manufactured by laser technology. Four kinds of self-assembled monolayers (SAMs) were prepared on the above Ti6Al4V substrates by self-assembled technique. The surface characteristics of Ti6Al4V specimens were characterized with topography and contact angle measurement. The results show that the water contact angles of the Ti6Al4V specimens increase significantly by dotted matrix structure manufacturing and SAMs deposition. The contact angles of the Ti6Al4V specimens deposited with long chain molecules of FDTS, FOTS and OTS are larger than 150° and the superhydrophobic surfaces are formed. The maximum contact angle of 164.5° can be acquired when FDTS SAMs are deposited on the Ti6Al4V specimens. The superhydrophobic surface of the Ti6Al4V specimens can be formed for short chain MPS molecule deposition only when the spacing of laser manufacturing is set to 50 μm. The superhydrophobic surface will change to the hydrophobic surface with spacing increasing. The contact angles of the Ti6Al4V specimens for all four SAMs deposition reduce with increasing of the spacing of dotted matrix
The dotted matrix structures on Ti6Al4V specimens with different spacing were manufactured by laser technology. Four kinds of self-assembled monolayers (SAMs) were prepared on the above Ti6Al4V substrates by self-assembled technique. The surface characteristics of Ti6Al4V specimens were characterized with topography and contact angle measurement. The results show that the water contact angles of the Ti6Al4V specimens increase significantly by dotted matrix structure manufacturing and SAMs deposition. The contact angles of the Ti6Al4V specimens deposited with long chain molecules of FDTS, FOTS and OTS are larger than 150° and the superhydrophobic surfaces are formed. The maximum contact angle of 164.5° can be acquired when FDTS SAMs are deposited on the Ti6Al4V specimens. The superhydrophobic surface of the Ti6Al4V specimens can be formed for short chain MPS molecule deposition only when the spacing of laser manufacturing is set to 50 μm. The superhydrophobic surface will change to the hydrophobic surface with spacing increasing. The contact angles of the Ti6Al4V specimens for all four SAMs deposition reduce with increasing of the spacing of dotted matrix
Zhang Jinshan
,
Ji Guoqiang
,
Wang Xing
,
Zhang Zhaoguang
,
Xu Chunxiang
,
Wang Hongxia
,
Tao Weijian
,
Sun Yong
2012, 41(4):617-622.
Abstract:
Microstructures and mechanical properties of AM60 magnesium alloy with Sm addition were investigated through OM, SEM XRD and DNS100 electronic universal testing machines. The results show that the addition of Sm can refine grains, change the morphology and the size of β-Mg17A112 phase from continuous/discontinuous netlike or strip form to cobble or particulate form. The distribution also becomes homogeneous and dispersed, and obviously improves the microstructure. After Sm addition to the alloy, the dispersed, high-melting-point particles (mainly Al2Sm phase) are formed. With increasing of Sm content, the tensile strength and elongation of AM60 magnesium alloy increase first and then decrease. With addition of 1.0wt% Sm, the tensile strength and elongation of the alloy reach the maximum 210 MPa and 6.9%, respectively. The tensile fracture mechanism of AM60 magnesium alloy is changed from cleavage fracture to quasi-cleavage fracture with toughness characteristic.
Microstructures and mechanical properties of AM60 magnesium alloy with Sm addition were investigated through OM, SEM XRD and DNS100 electronic universal testing machines. The results show that the addition of Sm can refine grains, change the morphology and the size of β-Mg17A112 phase from continuous/discontinuous netlike or strip form to cobble or particulate form. The distribution also becomes homogeneous and dispersed, and obviously improves the microstructure. After Sm addition to the alloy, the dispersed, high-melting-point particles (mainly Al2Sm phase) are formed. With increasing of Sm content, the tensile strength and elongation of AM60 magnesium alloy increase first and then decrease. With addition of 1.0wt% Sm, the tensile strength and elongation of the alloy reach the maximum 210 MPa and 6.9%, respectively. The tensile fracture mechanism of AM60 magnesium alloy is changed from cleavage fracture to quasi-cleavage fracture with toughness characteristic.
2012, 41(4):623-626.
Abstract:
The surface modification treatment on pure magnesium was conducted at 390 ℃ by atmosphere solid zinc-yttrium co-diffusing. The microstructure, the microhardness and the corrosion resistance of the diffusing layer were investigated with optical microscope, SEM, EDS, XRD, microhardness test and the electrochemical corrosion polarization curves test. The results show that the dense diffusing layer with an thickness of 900 μm has formed on the surface of pure magnesium after surface modification treatment. The diffusion layer contains a transition layer and an alloy reaction layer. The transition layer is α-Mg solid solution. The alloy reaction layer contains a plenty of Mg7Zn3, α-Mg solid solution and α-Mg+MgZn lamellar eutectic structure. The microhardness of the surface diffusion alloying layer increases significantly. The average microhardness is about 4 times higher than that of magnesium matrix. The open circuit potential of the alloyed specimen increases by 87 mV. The corrosion current density of alloyed specimen decreases by one order of magnitude. Its corrosion resistance is improved obviously
The surface modification treatment on pure magnesium was conducted at 390 ℃ by atmosphere solid zinc-yttrium co-diffusing. The microstructure, the microhardness and the corrosion resistance of the diffusing layer were investigated with optical microscope, SEM, EDS, XRD, microhardness test and the electrochemical corrosion polarization curves test. The results show that the dense diffusing layer with an thickness of 900 μm has formed on the surface of pure magnesium after surface modification treatment. The diffusion layer contains a transition layer and an alloy reaction layer. The transition layer is α-Mg solid solution. The alloy reaction layer contains a plenty of Mg7Zn3, α-Mg solid solution and α-Mg+MgZn lamellar eutectic structure. The microhardness of the surface diffusion alloying layer increases significantly. The average microhardness is about 4 times higher than that of magnesium matrix. The open circuit potential of the alloyed specimen increases by 87 mV. The corrosion current density of alloyed specimen decreases by one order of magnitude. Its corrosion resistance is improved obviously
2012, 41(4):627-630.
Abstract:
The dehydrogenation properties of NaAlH4 doped with Ag2SO4, SrCO3, TiO2 and ZnO were studied by PCT (pressure-content-temperature) and XRD. The results indicate that NaAlH4 doped with TiO2 presents the largest amount of hydrogen release, comparatively, the sample doped with SrCO3 presents the least amount of hydrogen release. Compared to the rate of hydrogen release of all doped samples in the first stage, NaAlH4 doped with TiO2 shows the maximum rate of hydrogen release. In addition, all of the doped samples display an obvious two-stage dehydrogenation in the whole process of hydrogen release, and it is obvious that the dehydrogenation rate in the first stage is faster than that in the second stage. The results from XRD patterns prove that 30 min ball-milling does not cause any structure change and new phase appearing.
The dehydrogenation properties of NaAlH4 doped with Ag2SO4, SrCO3, TiO2 and ZnO were studied by PCT (pressure-content-temperature) and XRD. The results indicate that NaAlH4 doped with TiO2 presents the largest amount of hydrogen release, comparatively, the sample doped with SrCO3 presents the least amount of hydrogen release. Compared to the rate of hydrogen release of all doped samples in the first stage, NaAlH4 doped with TiO2 shows the maximum rate of hydrogen release. In addition, all of the doped samples display an obvious two-stage dehydrogenation in the whole process of hydrogen release, and it is obvious that the dehydrogenation rate in the first stage is faster than that in the second stage. The results from XRD patterns prove that 30 min ball-milling does not cause any structure change and new phase appearing.
2012, 41(4):631-634.
Abstract:
In order to investigate the diffusion and transition mechanism of Ag in Ag-Al supersaturated solid during heat treatment in oxidizing atmosphere, Ag/Al alloy powder was prepared by atomization, then Ag/Al2O3 composite was prepared by high energy ball milling and oxidizing reaction. The diffusion rate and the phase state were calculated by the Molecular Dynamics Simulation model of solid solution alloy. The results show that the precipitation of great quantity of Ag occurs at 600 K, accompanied by the formation of compact alumina film and the transition of alloy phase internal particles. The precipitated phase can be controlled in the range of nano size. The experimental results can be explained and predicted properly by the calculated model.
In order to investigate the diffusion and transition mechanism of Ag in Ag-Al supersaturated solid during heat treatment in oxidizing atmosphere, Ag/Al alloy powder was prepared by atomization, then Ag/Al2O3 composite was prepared by high energy ball milling and oxidizing reaction. The diffusion rate and the phase state were calculated by the Molecular Dynamics Simulation model of solid solution alloy. The results show that the precipitation of great quantity of Ag occurs at 600 K, accompanied by the formation of compact alumina film and the transition of alloy phase internal particles. The precipitated phase can be controlled in the range of nano size. The experimental results can be explained and predicted properly by the calculated model.
2012, 41(4):635-639.
Abstract:
SiC fiber reinforced Ti-6Al-4V composites (TMCs) was prepared by the foil-fiber-foil method. The fatigue crack growth rate of the TMCs was investigated under the condition of f=10 Hz, R=0.1 and σmax =300 MPa, and the fracture surface of TMCs was observed by scanning electron microscopy (SEM). Results show that the crack growth rate at the stage Ⅱ of crack propagation is well consistent with Gaussian function. SEM observation indicates that distinct fatigue striations exist in the stable propagation area of the fatigue crack of the Ti-6Al-4V matrix. The failure modes of TMCs include fiber breakage, matrix cracking, fiber/matrix interfacial debonding, et al under the loading condition
SiC fiber reinforced Ti-6Al-4V composites (TMCs) was prepared by the foil-fiber-foil method. The fatigue crack growth rate of the TMCs was investigated under the condition of f=10 Hz, R=0.1 and σmax =300 MPa, and the fracture surface of TMCs was observed by scanning electron microscopy (SEM). Results show that the crack growth rate at the stage Ⅱ of crack propagation is well consistent with Gaussian function. SEM observation indicates that distinct fatigue striations exist in the stable propagation area of the fatigue crack of the Ti-6Al-4V matrix. The failure modes of TMCs include fiber breakage, matrix cracking, fiber/matrix interfacial debonding, et al under the loading condition
2012, 41(4):640-644.
Abstract:
The key technologies of 3D backward simulation are explored and the 3D backward simulation system for uniform deformation has been developed. Its precision forging process is simulated and analyzed using this system, and the perform of the blade forging have been designed, which can achieve a net-shape product and uniform deformation
The key technologies of 3D backward simulation are explored and the 3D backward simulation system for uniform deformation has been developed. Its precision forging process is simulated and analyzed using this system, and the perform of the blade forging have been designed, which can achieve a net-shape product and uniform deformation
2012, 41(4):645-648.
Abstract:
The NdFe absorbing powder was prepared by high-energy ball-milling and crystallization heat treatment. The influence of Si contents on the absorbing properties of NdFe powder was investigated. The result shows that the microstructures of Nd8Fe92, Nd8Fe89Si3 and Nd8Fe87Si5 powders consist of α-Fe, Nd2O3 and Fe17Nd2 phase after high-energy milling and 700 ℃, 1 h crystallization heat treatment in a micro-oxidation atmosphere. The relative amount of Fe17Nd2 phase increases after adding Si. The minimum reflectance of Nd8Fe92 powder is -4.5 dB, the frequency of the absorption peak is 4.4 GHz. After adding Si the minimum reflectance of powder decreases, while the frequency of the absorption peak increases and the absorption band of NdFe powder is widened. Nd8Fe92 powder takes dielectric loss, as main loss, while Nd8Fe89Si3 and Nd8Fe87Si5 powder take magnetic loss as main loss
The NdFe absorbing powder was prepared by high-energy ball-milling and crystallization heat treatment. The influence of Si contents on the absorbing properties of NdFe powder was investigated. The result shows that the microstructures of Nd8Fe92, Nd8Fe89Si3 and Nd8Fe87Si5 powders consist of α-Fe, Nd2O3 and Fe17Nd2 phase after high-energy milling and 700 ℃, 1 h crystallization heat treatment in a micro-oxidation atmosphere. The relative amount of Fe17Nd2 phase increases after adding Si. The minimum reflectance of Nd8Fe92 powder is -4.5 dB, the frequency of the absorption peak is 4.4 GHz. After adding Si the minimum reflectance of powder decreases, while the frequency of the absorption peak increases and the absorption band of NdFe powder is widened. Nd8Fe92 powder takes dielectric loss, as main loss, while Nd8Fe89Si3 and Nd8Fe87Si5 powder take magnetic loss as main loss
2012, 41(4):649-652.
Abstract:
The sliver nanoparticles (n-Ag) were synthesized in-situ in bisphenol-A epoxy resin(E-51) by acetaldehyde at 80 ℃. The size, size distribution and conglomeration behavior of n-Ag were observed by freeze-etching replication transmission electron microscopy(FRTEM). The centrifuge tests were used for evaluating the dispersion and dispersion stability of n-Ag. The microwave-absorbing properties of n-Ag synthesized in-situ and the microwave curing performance of epoxy resin dispersion system containing n-Ag were studied by pulse microwave. The toughening modification effect of epoxy resin were evaluated by tensile test. The results show that n-Ag is composed of spherical particles with a homogeneity and the average size of 30 nm. The n-Ag can maintain stability, no sedimentation and no agglomeration appear in the dispersion system. n-Ag synthesized in-situ have a good microwave-absorbing property, and it can obviously decrease the microwave curing time of modified epoxy resin. The curing time of 2.5% n-Ag epoxy resin is 38% less compared to that of epoxy resin. The microwave curing rate of n-Ag epoxy resin dispersion system is several times faster than the traditional heating curing. The silver nanoparticles have a significant toughening function to epoxy resin. The toughening effect to epoxy resin is best when the mass ratio of the resin to ultra-dispersion-stability n-Ag is 2% to 2.5%. Under this situation, fracture elongation of the composite material increases by about 110%-130% compared with unmodified resin
The sliver nanoparticles (n-Ag) were synthesized in-situ in bisphenol-A epoxy resin(E-51) by acetaldehyde at 80 ℃. The size, size distribution and conglomeration behavior of n-Ag were observed by freeze-etching replication transmission electron microscopy(FRTEM). The centrifuge tests were used for evaluating the dispersion and dispersion stability of n-Ag. The microwave-absorbing properties of n-Ag synthesized in-situ and the microwave curing performance of epoxy resin dispersion system containing n-Ag were studied by pulse microwave. The toughening modification effect of epoxy resin were evaluated by tensile test. The results show that n-Ag is composed of spherical particles with a homogeneity and the average size of 30 nm. The n-Ag can maintain stability, no sedimentation and no agglomeration appear in the dispersion system. n-Ag synthesized in-situ have a good microwave-absorbing property, and it can obviously decrease the microwave curing time of modified epoxy resin. The curing time of 2.5% n-Ag epoxy resin is 38% less compared to that of epoxy resin. The microwave curing rate of n-Ag epoxy resin dispersion system is several times faster than the traditional heating curing. The silver nanoparticles have a significant toughening function to epoxy resin. The toughening effect to epoxy resin is best when the mass ratio of the resin to ultra-dispersion-stability n-Ag is 2% to 2.5%. Under this situation, fracture elongation of the composite material increases by about 110%-130% compared with unmodified resin
2012, 41(4):653-657.
Abstract:
Foil-Fiber-Foil (FFF) method was used to prepare Ti6Al4V-matrix composites reinforced by SiC fibers without coating, with C coating and Cu/Mo duplex coatings, respectively. The mechanical properties as well as interfacial microstructure of the as-prepared composites were compared. Moreover, the interfacial reaction characteristics of the SiCf/Cu/Mo/Ti6Al4V composites were also investigated by different vacuum heat treatments. The results show that for as-prepared samples, Cu/Mo coating is better than C-coating to improve the interfacial microstructure and properties of titanium matrix composites; the growth kinetic expression of the SiCf/Cu/Mo/Ti6Al4V interfacial reaction at 900 ℃ is H=1.380t1/2+5.397
Foil-Fiber-Foil (FFF) method was used to prepare Ti6Al4V-matrix composites reinforced by SiC fibers without coating, with C coating and Cu/Mo duplex coatings, respectively. The mechanical properties as well as interfacial microstructure of the as-prepared composites were compared. Moreover, the interfacial reaction characteristics of the SiCf/Cu/Mo/Ti6Al4V composites were also investigated by different vacuum heat treatments. The results show that for as-prepared samples, Cu/Mo coating is better than C-coating to improve the interfacial microstructure and properties of titanium matrix composites; the growth kinetic expression of the SiCf/Cu/Mo/Ti6Al4V interfacial reaction at 900 ℃ is H=1.380t1/2+5.397
2012, 41(4):658-662.
Abstract:
The rod of the (Cu50Zr50)92Al8 (at%) bulk metallic glass(BMG) with a diameter of 2 mm was prepared by water-cooled copper mould sucking method, and its amorphous feature of the as-cast alloy was characterized by X-ray diffraction (XRD). The thermodynamic parameters of the bulk metallic glass were determined by differential scanning calorimeter (DSC). The alloy was compressed to different strains(20%, 60% and 80%) in the super-cooled liquid region, and the effects of the plastic strains on the microstructure and the thermal stability of the alloy were investigated. It is found that the deformation reduces the thermal stability of the alloy, and a partial crystallization occurs during the deformation in the alloy. The extent of the crystallization is strongly dependent on the deformation strain, and as the strain increases to 80%, the peaks of the crystallites can be clearly observed on the XRD pattern of the alloy. The present of the crystallites increase the mico-hardness of the alloy
The rod of the (Cu50Zr50)92Al8 (at%) bulk metallic glass(BMG) with a diameter of 2 mm was prepared by water-cooled copper mould sucking method, and its amorphous feature of the as-cast alloy was characterized by X-ray diffraction (XRD). The thermodynamic parameters of the bulk metallic glass were determined by differential scanning calorimeter (DSC). The alloy was compressed to different strains(20%, 60% and 80%) in the super-cooled liquid region, and the effects of the plastic strains on the microstructure and the thermal stability of the alloy were investigated. It is found that the deformation reduces the thermal stability of the alloy, and a partial crystallization occurs during the deformation in the alloy. The extent of the crystallization is strongly dependent on the deformation strain, and as the strain increases to 80%, the peaks of the crystallites can be clearly observed on the XRD pattern of the alloy. The present of the crystallites increase the mico-hardness of the alloy
2012, 41(4):663-666.
Abstract:
The microstructure of TC18 titanium alloy was investigated by XRD，SEM and TEM. The impact toughness of the TC18 titanium with different notch depths was tested by instrumented pendulum impact tester, and the curve showing the impact process was gained. The fracture was analyzed by SEM. The results show that the impact toughness decreases as the notch depth increases, and the toughness of the specimen with 0.02 cm notch was much smaller than that with no notch. The specimen with no notch just curves without breaking.
The microstructure of TC18 titanium alloy was investigated by XRD，SEM and TEM. The impact toughness of the TC18 titanium with different notch depths was tested by instrumented pendulum impact tester, and the curve showing the impact process was gained. The fracture was analyzed by SEM. The results show that the impact toughness decreases as the notch depth increases, and the toughness of the specimen with 0.02 cm notch was much smaller than that with no notch. The specimen with no notch just curves without breaking.
2012, 41(4):667-671.
Abstract:
Hot compression deformation behavior of Ultrafine-grained (UFG) commercially pure (CP) Ti with the average grain size of 200 nm was studied by thermal simulation test at the deformation temperature of 298-673 K and the strain rate of 10-3-100 s-1 on the Gleeble-1500 thermal-mechanical simulator. UFG CP-Ti was produced by ECAP up to 8 passes with a die of Φ=120° using route Bc at room temperature. The microstructural evolution of UFG CP-Ti was investigated by transmission electron microscopy. The results show that the flow stress increases with increasing of strain and tends to be constant after a peak value. The peak stress increases with increasing of strain rate and decreases with increasing of deformation temperature. Strain rate sensitivity value m of the UFG CP-Ti is found to increase with increasing of temperature and decreasing of strain rate. And the grains in the deformed samples are coarsened and the size of subgrains increases; the number of fine grains in grain boundaries also increases, indicating that the main softening mechanism of the alloy during hot compression deformation is attributed to the transformation from dynamic recovery to dynamic recrystallization
Hot compression deformation behavior of Ultrafine-grained (UFG) commercially pure (CP) Ti with the average grain size of 200 nm was studied by thermal simulation test at the deformation temperature of 298-673 K and the strain rate of 10-3-100 s-1 on the Gleeble-1500 thermal-mechanical simulator. UFG CP-Ti was produced by ECAP up to 8 passes with a die of Φ=120° using route Bc at room temperature. The microstructural evolution of UFG CP-Ti was investigated by transmission electron microscopy. The results show that the flow stress increases with increasing of strain and tends to be constant after a peak value. The peak stress increases with increasing of strain rate and decreases with increasing of deformation temperature. Strain rate sensitivity value m of the UFG CP-Ti is found to increase with increasing of temperature and decreasing of strain rate. And the grains in the deformed samples are coarsened and the size of subgrains increases; the number of fine grains in grain boundaries also increases, indicating that the main softening mechanism of the alloy during hot compression deformation is attributed to the transformation from dynamic recovery to dynamic recrystallization
24 Influence of Laser Shock Processing on Mechanical Properties of TC4 Titanium Alloy TIG Welding Bead
2012, 41(4):672-676.
Abstract:
Laser shock processing (LSP) was employed to treat TC4 titanium alloy Tungsten Inert Gas (TIG) welding joints. HV hardness, tensile property and fatigue life of the TC4 titanium alloy TIG welding joints and the untreated joints were studied. Compared with those joints keeping primal TIG weld bead, microhardness of LSP treatment welding bead zone surface is reduced; however, that of welding heat affected zone surface is are increased. Tensile strength, yield strength, specific elongation, and fatigue life of LSP treatment joints are improved to different extent.
Laser shock processing (LSP) was employed to treat TC4 titanium alloy Tungsten Inert Gas (TIG) welding joints. HV hardness, tensile property and fatigue life of the TC4 titanium alloy TIG welding joints and the untreated joints were studied. Compared with those joints keeping primal TIG weld bead, microhardness of LSP treatment welding bead zone surface is reduced; however, that of welding heat affected zone surface is are increased. Tensile strength, yield strength, specific elongation, and fatigue life of LSP treatment joints are improved to different extent.
2012, 41(4):677-680.
Abstract:
The Mm0.3Ml0.7Ni3.55Co0.75Mn0.4Al0.3 metal hydride electrodes were prepared at pressure-holding time of t (t=10, 15, 20 and 25 min). The effects of the pressure-holding time on the activation performance, maximum discharge capacity, discharge potential characteristic and cycle stability of the electrode were investigated. The mechanism of the effect of the pressure-holding time on the electrochemical properties of metal hydride electrodes was also discussed in detail. The results show that the pressure-holding time has no effect on the activation performance of the electrode basically, and the other electrochemical properties of the electrodes are improved firstly and then degenerated with increasing of pressure-holding time. The electrode at pressure-holding time of 15 min exhibits the best electrochemical properties. The improvements of the electrochemical properties are attributed to the increase of the charge-transfer reaction rate on the alloy and the decrease of the internal resistance of the electrodes
The Mm0.3Ml0.7Ni3.55Co0.75Mn0.4Al0.3 metal hydride electrodes were prepared at pressure-holding time of t (t=10, 15, 20 and 25 min). The effects of the pressure-holding time on the activation performance, maximum discharge capacity, discharge potential characteristic and cycle stability of the electrode were investigated. The mechanism of the effect of the pressure-holding time on the electrochemical properties of metal hydride electrodes was also discussed in detail. The results show that the pressure-holding time has no effect on the activation performance of the electrode basically, and the other electrochemical properties of the electrodes are improved firstly and then degenerated with increasing of pressure-holding time. The electrode at pressure-holding time of 15 min exhibits the best electrochemical properties. The improvements of the electrochemical properties are attributed to the increase of the charge-transfer reaction rate on the alloy and the decrease of the internal resistance of the electrodes
2012, 41(4):681-684.
Abstract:
The influences of the process parameters and the concentration of the compound complexant consisting of ethylenediamine, ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) and acrylic acid on the quality of electroless palladium (Pd) were studied using L9(34) orthogonal table. The brightness of Pd coating, the bath stability and the plating speed were taken as assessment standard. The results show that the optimized bath of the electroless Pd is possessed of good stability and high depositing rate. The binding force between Pd film and Ni coating is strong, and Pd film surface is bright. The optimized concentration of ethylenediamine is 0.2 mol/L, EDTA-2Na was 0.01 mol/L, acrylic acid was 0.3 mol/L and pH was 8
The influences of the process parameters and the concentration of the compound complexant consisting of ethylenediamine, ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) and acrylic acid on the quality of electroless palladium (Pd) were studied using L9(34) orthogonal table. The brightness of Pd coating, the bath stability and the plating speed were taken as assessment standard. The results show that the optimized bath of the electroless Pd is possessed of good stability and high depositing rate. The binding force between Pd film and Ni coating is strong, and Pd film surface is bright. The optimized concentration of ethylenediamine is 0.2 mol/L, EDTA-2Na was 0.01 mol/L, acrylic acid was 0.3 mol/L and pH was 8
2012, 41(4):685-691.
Abstract:
The effect of solution cooling rate on the microstructure and microhardness of a novel type nickel-based P/M superalloy FGH98Ⅰin subslovus plus superslovus and superslovus heat treatment condition was studied by means of optical microscope (OM), field emission scanning electron microscope (FESEM) and microhardness tester. The results show that subslovus pre-heat treatment makes the large grain boundary γ ' phase of as-forged alloy partial dissolution, and the grains grow a little, while the influence on the cooling γ ' precipitates of superslovus heat treatment is not obvious. The average sizes of secondary and tertiary γ ' precipitates decrease with the cooling rate increasing. Meanwhile, the shape of secondary γ ' precipitates changes from the butterfly-like to the spherical, the γ ' phase particle density increases and the area fraction decreases. It is also found that γ ' phases nucleate and precipitate in two stages if the cooling rate is not faster than 1.4 °C/s. The higher the cooling rate, the higher the microhardness, and the microhardness increases more after aging. In addition, the average sizes of γ′ precipitates and the microhardness as a function of cooling rate are established. The above results can be used as a theoretical reference for the selection of actual superslovus processing of FGH98Ⅰdual-property disk
The effect of solution cooling rate on the microstructure and microhardness of a novel type nickel-based P/M superalloy FGH98Ⅰin subslovus plus superslovus and superslovus heat treatment condition was studied by means of optical microscope (OM), field emission scanning electron microscope (FESEM) and microhardness tester. The results show that subslovus pre-heat treatment makes the large grain boundary γ ' phase of as-forged alloy partial dissolution, and the grains grow a little, while the influence on the cooling γ ' precipitates of superslovus heat treatment is not obvious. The average sizes of secondary and tertiary γ ' precipitates decrease with the cooling rate increasing. Meanwhile, the shape of secondary γ ' precipitates changes from the butterfly-like to the spherical, the γ ' phase particle density increases and the area fraction decreases. It is also found that γ ' phases nucleate and precipitate in two stages if the cooling rate is not faster than 1.4 °C/s. The higher the cooling rate, the higher the microhardness, and the microhardness increases more after aging. In addition, the average sizes of γ′ precipitates and the microhardness as a function of cooling rate are established. The above results can be used as a theoretical reference for the selection of actual superslovus processing of FGH98Ⅰdual-property disk
2012, 41(4):692-696.
Abstract:
Metallurgical defects and the changes of O，N and S contents in superalloy IN792 were studied in the different refining processes. S content was measured using CS analysis apparatus, O and N contents were measured by TC-436 measurement apparatus, the mechanical properties of alloy were measured, also. The results show that shrinkage is easier to produce with increasing of O and N contents, and the contents of impurities are increased with increment of the contents of O，N and S. When the refining temperature is higher and refining time is longer, the contents of O，N and S are decreased, the UTS and YS are improved at room temperature.
Metallurgical defects and the changes of O，N and S contents in superalloy IN792 were studied in the different refining processes. S content was measured using CS analysis apparatus, O and N contents were measured by TC-436 measurement apparatus, the mechanical properties of alloy were measured, also. The results show that shrinkage is easier to produce with increasing of O and N contents, and the contents of impurities are increased with increment of the contents of O，N and S. When the refining temperature is higher and refining time is longer, the contents of O，N and S are decreased, the UTS and YS are improved at room temperature.
2012, 41(4):697-700.
Abstract:
The high-temperature tensile experiments were conducted to study the stress relaxation behavior of Hastelloy C-276 Alloy at various temperatures and initial stresses. As a result, a set of stress relaxation curves of Hastelloy C-276 Alloy were obtained and these curves can be fitted by twice delay function well. The relationships between creep strain rate and stress were derived from the experimental stress relaxation curves. In addition, the effects of temperature on the stress relaxation behavior of Hastelloy C-276 Alloy were also discussed. This work lays a theoretical foundation for numerical simulation of vacuum hot bulge forming process of rotor-can
The high-temperature tensile experiments were conducted to study the stress relaxation behavior of Hastelloy C-276 Alloy at various temperatures and initial stresses. As a result, a set of stress relaxation curves of Hastelloy C-276 Alloy were obtained and these curves can be fitted by twice delay function well. The relationships between creep strain rate and stress were derived from the experimental stress relaxation curves. In addition, the effects of temperature on the stress relaxation behavior of Hastelloy C-276 Alloy were also discussed. This work lays a theoretical foundation for numerical simulation of vacuum hot bulge forming process of rotor-can
2012, 41(4):701-706.
Abstract:
The solidification experiment of Cu-25%Ag alloy used in high field magnet was carried out under HMF (high magnetic field), then the ingots were cold drawn into wires. The solidified structure, drawn structure and electrical conductivity were investigated systematically. In the case of no HMF, it is found that the columnar Cu dendrites is longer, moreover, on top of the sample the dendrites grow along the radial direction of the arc; on the middle part, the angle between the dendrites growing direction and axis of the ingot is about 45°; on the bottom part, the angle is about 90°. In other sides, the thickness of eutectic is thinner, the two phases present a non-uniformity distribution and the lamellar spacing is larger. In the case of HMF, the cellular Cu dendrites is shorter, moreover, on top of the sample the dendrites grow along the radial direction of the arc; on the middle and bottom parts the angle between the dendrites growing direction and axis of the ingot is about 90°, the thickness of eutectic is thicker, the two phases present a uniformity distribution, and the lamellar spacing is smaller. After cold drawn treatment, the eutectic “net” structure changes into filamentary structure. The thickness and spacing of the eutectic filamentary are thinner in the case of no HMF, but the thickness and spacing of the eutectic filamentary are thicker with in the case of HMF. By the influence of the filamentary structure, the electrical conductivity of the wires is different with and without HMF
The solidification experiment of Cu-25%Ag alloy used in high field magnet was carried out under HMF (high magnetic field), then the ingots were cold drawn into wires. The solidified structure, drawn structure and electrical conductivity were investigated systematically. In the case of no HMF, it is found that the columnar Cu dendrites is longer, moreover, on top of the sample the dendrites grow along the radial direction of the arc; on the middle part, the angle between the dendrites growing direction and axis of the ingot is about 45°; on the bottom part, the angle is about 90°. In other sides, the thickness of eutectic is thinner, the two phases present a non-uniformity distribution and the lamellar spacing is larger. In the case of HMF, the cellular Cu dendrites is shorter, moreover, on top of the sample the dendrites grow along the radial direction of the arc; on the middle and bottom parts the angle between the dendrites growing direction and axis of the ingot is about 90°, the thickness of eutectic is thicker, the two phases present a uniformity distribution, and the lamellar spacing is smaller. After cold drawn treatment, the eutectic “net” structure changes into filamentary structure. The thickness and spacing of the eutectic filamentary are thinner in the case of no HMF, but the thickness and spacing of the eutectic filamentary are thicker with in the case of HMF. By the influence of the filamentary structure, the electrical conductivity of the wires is different with and without HMF
2012, 41(4):707-710.
Abstract:
FePt nanoparticles with flower-like assembly were synthesized at room temperature by a simple wet chemical reduction process using NaBH4 as the reducing reagent and PEG as the surfactant. XRD and TEM characterizations show that the as-synthesized FePt particles are possessed of chemically disordered face-centered cubic (fcc) structure. The shapes present the fusiform and the spherical with the mean sizes of 19.2 and 4.9 nm, respectively. These fusiform “petals” and spherical “stamens” are found to be assembled into flower-like structures. We suggest that the formation of flower-like assemble of FePt nanoparticles is result from the surfactant assemblage. VSM indicates that the as-synthesized samples show paramagnetic property at room temperature with the saturation magnetization Ms 10.9 (A·m2)/kg. when PVP is used as surfactant, Ms is about 0.6 (A·m2)/kg. comparing the nanoparticles synthesized and the same condition, Ms increases by 18 times when PEG is used as surfactant.
FePt nanoparticles with flower-like assembly were synthesized at room temperature by a simple wet chemical reduction process using NaBH4 as the reducing reagent and PEG as the surfactant. XRD and TEM characterizations show that the as-synthesized FePt particles are possessed of chemically disordered face-centered cubic (fcc) structure. The shapes present the fusiform and the spherical with the mean sizes of 19.2 and 4.9 nm, respectively. These fusiform “petals” and spherical “stamens” are found to be assembled into flower-like structures. We suggest that the formation of flower-like assemble of FePt nanoparticles is result from the surfactant assemblage. VSM indicates that the as-synthesized samples show paramagnetic property at room temperature with the saturation magnetization Ms 10.9 (A·m2)/kg. when PVP is used as surfactant, Ms is about 0.6 (A·m2)/kg. comparing the nanoparticles synthesized and the same condition, Ms increases by 18 times when PEG is used as surfactant.
2012, 41(4):711-716.
Abstract:
Multi-Walled Carbon Nonotubes (MWCNTs)/AZ31 composites were fabricated by joining preform of MWCNTs during melting. The corrosion behaviors of the composites with equal channel angular pressing (ECAP) for different passes were studied by immersion and electrochemical corrosion experiments in 3.5%NaCl (mass fraction) corrosion medium. The effects of ECAP on corrosion resistance of MWCNTs/AZ31 composite were investigated. The surface morphologies of the composites before and after the corrosion testing were observed and analyzed by digital camera and scanning electron microscope (SEM). The results show that ECAP effectively improves the corrosion resistance of MWCNTs/AZ31 composites. After 4 passes-ECAP, the average corrosion rate of MWCNTs/AZ31 composites immersed in 3.5%NaCl corrosion medium for 24 h changes from 0.6035 mg/(m2·s) to 0.2963 mg/(m2·s) and the corrosion current density (Icorr) is decreases from 3.363 μA/cm2 to 2.269 μA/cm2
Multi-Walled Carbon Nonotubes (MWCNTs)/AZ31 composites were fabricated by joining preform of MWCNTs during melting. The corrosion behaviors of the composites with equal channel angular pressing (ECAP) for different passes were studied by immersion and electrochemical corrosion experiments in 3.5%NaCl (mass fraction) corrosion medium. The effects of ECAP on corrosion resistance of MWCNTs/AZ31 composite were investigated. The surface morphologies of the composites before and after the corrosion testing were observed and analyzed by digital camera and scanning electron microscope (SEM). The results show that ECAP effectively improves the corrosion resistance of MWCNTs/AZ31 composites. After 4 passes-ECAP, the average corrosion rate of MWCNTs/AZ31 composites immersed in 3.5%NaCl corrosion medium for 24 h changes from 0.6035 mg/(m2·s) to 0.2963 mg/(m2·s) and the corrosion current density (Icorr) is decreases from 3.363 μA/cm2 to 2.269 μA/cm2
2012, 41(4):717-721.
Abstract:
The characteristics of FA/O chelating agent with extremely strong chelating ability were used for the chemical-mechanical planarization of copper interconnection on the conditions of abrasive-free slurry and low down pressure to obtain a high polishing rate and a fine within-wafer non-uniformity (WIWNU). The planarization principle of the abrasive-free alkaline slurry technology of the copper surface at low down pressure was put forward. Based on the analyzing of the planarization principle and the chemical reaction mechanism in abrasive-free alkaline slurry at low down pressure the main ingredient and prescription of slurry(containing FA/O chelating agent and oxidizer ) and polishing technological parameter (pressure and speed) were investigated. The results indicate that the polishing rate can reach 1825 nm/min and WIWNU is 0.25 when the down pressure is 6.3 kPa, the polishing machine speed 60 r/min, the slurry contains 5vol% chelating agent and 1 vol% oxidizer.
The characteristics of FA/O chelating agent with extremely strong chelating ability were used for the chemical-mechanical planarization of copper interconnection on the conditions of abrasive-free slurry and low down pressure to obtain a high polishing rate and a fine within-wafer non-uniformity (WIWNU). The planarization principle of the abrasive-free alkaline slurry technology of the copper surface at low down pressure was put forward. Based on the analyzing of the planarization principle and the chemical reaction mechanism in abrasive-free alkaline slurry at low down pressure the main ingredient and prescription of slurry(containing FA/O chelating agent and oxidizer ) and polishing technological parameter (pressure and speed) were investigated. The results indicate that the polishing rate can reach 1825 nm/min and WIWNU is 0.25 when the down pressure is 6.3 kPa, the polishing machine speed 60 r/min, the slurry contains 5vol% chelating agent and 1 vol% oxidizer.
2012, 41(4):722-726.
Abstract:
Low temperature synthesis of Mo-Cu composite powders was conducted by mechanochemical treatment (ball-milling) of CuMoO4 and MoO3 mixtures followed by subsequent coreduction process. The preparation temperature of the precursors (CuMoO4-MoO3 mixtures), phases and microstructures of the Mo-Cu composites were investigated by differential scanning calorimeter (DSC), X-ray diffractometer (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM), respectively. The thermodynamical conditions at different stages of hydrogen reduction of Mo-Cu nanocomposite powders were analyzed. Results show that the mechanochemical treatment (ball-milling) can significantly enhance the reduction activity by reducing the particle sizes of powders and hence increasing the reaction surface area, therefore giving rise to the synthesis of Mo-Cu composite powders at relatively low temperature (680 ℃). By optimizing the experimental parameters, Mo-25 wt% Cu nanocomposite powders with superfine particles ranging from 50 to 100 nm can be obtained by ball-milling for 15 h followed by reduction in hydrogen at 680 ℃
Low temperature synthesis of Mo-Cu composite powders was conducted by mechanochemical treatment (ball-milling) of CuMoO4 and MoO3 mixtures followed by subsequent coreduction process. The preparation temperature of the precursors (CuMoO4-MoO3 mixtures), phases and microstructures of the Mo-Cu composites were investigated by differential scanning calorimeter (DSC), X-ray diffractometer (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM), respectively. The thermodynamical conditions at different stages of hydrogen reduction of Mo-Cu nanocomposite powders were analyzed. Results show that the mechanochemical treatment (ball-milling) can significantly enhance the reduction activity by reducing the particle sizes of powders and hence increasing the reaction surface area, therefore giving rise to the synthesis of Mo-Cu composite powders at relatively low temperature (680 ℃). By optimizing the experimental parameters, Mo-25 wt% Cu nanocomposite powders with superfine particles ranging from 50 to 100 nm can be obtained by ball-milling for 15 h followed by reduction in hydrogen at 680 ℃
2012, 41(4):727-732.
Abstract:
The flow stress behaviors and microstructure characteristics of 690 alloy were investigated by isothermal compression tests in the temperature range of 1050-1200 °C and strain rate range of 0.1-10 s-1 on Gleeble 1500 thermo-simulation machine. The flow stress constitutive equation and dynamic recrystallization model of 690 alloy during hot compression was established. The results show that the flow stress can be represented by a Zenner-Hollomon parameter in the hyperbolic sine type equation. The flow stress of 690 alloy predicted by the proposed models well agrees with experimental results. Therefore, the proposed model can provide the references for the microstructure control during hot extrusion process
The flow stress behaviors and microstructure characteristics of 690 alloy were investigated by isothermal compression tests in the temperature range of 1050-1200 °C and strain rate range of 0.1-10 s-1 on Gleeble 1500 thermo-simulation machine. The flow stress constitutive equation and dynamic recrystallization model of 690 alloy during hot compression was established. The results show that the flow stress can be represented by a Zenner-Hollomon parameter in the hyperbolic sine type equation. The flow stress of 690 alloy predicted by the proposed models well agrees with experimental results. Therefore, the proposed model can provide the references for the microstructure control during hot extrusion process
2012, 41(4):733-737.
Abstract:
The ruthenium oxide-carbon composite electrodes with different carbon contents were prepared by a colloid method and then they were annealed at 240 ℃. The morphologies and the microstructures of the AC/RuO2 composites were characterized by thermo-gravimetric analysis, SEM and XRD, and their electrochemical properties were also tested. Results show that the compositing of active carbon and ruthenium oxide is beneficial to obtaining of fine particles and does not affect the structure of ruthenium oxide. When the carbon content increases from 13.4% to 36.18wt% in the AC/Ruthenium oxide electrode, the capacitance decreases from 664 F/g to 526 F/g, the energy density drops from 103.27 Wh/kg to 75.18 Wh/kg, and the power density increases from 0.48 kW/kg to 0.64 kW/kg as well as the impedance decreases. In addition, the colloid method is practical and convenient
The ruthenium oxide-carbon composite electrodes with different carbon contents were prepared by a colloid method and then they were annealed at 240 ℃. The morphologies and the microstructures of the AC/RuO2 composites were characterized by thermo-gravimetric analysis, SEM and XRD, and their electrochemical properties were also tested. Results show that the compositing of active carbon and ruthenium oxide is beneficial to obtaining of fine particles and does not affect the structure of ruthenium oxide. When the carbon content increases from 13.4% to 36.18wt% in the AC/Ruthenium oxide electrode, the capacitance decreases from 664 F/g to 526 F/g, the energy density drops from 103.27 Wh/kg to 75.18 Wh/kg, and the power density increases from 0.48 kW/kg to 0.64 kW/kg as well as the impedance decreases. In addition, the colloid method is practical and convenient
37 Directional Solidification of a Ni-Based Single Crystal Superalloy under High Temperature Gradient
2012, 41(4):738-742.
Abstract:
The effects of solidification rate on the microstructure of a Ni-based superalloy were investigated by zoom melting liquid metal cooling (ZMLMC) unidirectional solidification. The temperature gradient was approximately constant. It is revealed that with the increase of solidification rate, the dendrite structure is refined, and both the primary dendrite spacing λ1 and the secondary dendrite spacing λ2 are reduced, they show a linear relationship with v-1/4 and v-1/2, respectively. The sizes of γ' precipitates decrease with increasing of solidification rate, and the shapes turn to be regular. At the same rate, the γ' phase in interdendrite area is larger and more irregular than that in dendrite area. The γ/γ' eutectic also becomes smaller and more dispersed with the increase of solidification rate, but the total volume proportion remains stable
The effects of solidification rate on the microstructure of a Ni-based superalloy were investigated by zoom melting liquid metal cooling (ZMLMC) unidirectional solidification. The temperature gradient was approximately constant. It is revealed that with the increase of solidification rate, the dendrite structure is refined, and both the primary dendrite spacing λ1 and the secondary dendrite spacing λ2 are reduced, they show a linear relationship with v-1/4 and v-1/2, respectively. The sizes of γ' precipitates decrease with increasing of solidification rate, and the shapes turn to be regular. At the same rate, the γ' phase in interdendrite area is larger and more irregular than that in dendrite area. The γ/γ' eutectic also becomes smaller and more dispersed with the increase of solidification rate, but the total volume proportion remains stable
2012, 41(4):743-747.
Abstract:
Chopped carbon fibers reinforced magnesium was made using the powder metallurgy technique followed by hot extrusion. In order to enhance the carbon fiber wettability to the matrix, the carbon fibers were nickel-coated by palladium-free activated electroless coating method and then characterized by field emission-scanning electron microscope (FE-SEM) equipped with energy dispersive spectroscopy (EDS). The fiber distribution in composite materials were evaluated by super depth digital microscope and the composite extrusion process was analyzed. The results show that nickel-plated carbon fibers can meet the requirement for the preparation and the dispersion in the composite. The composite containing 4.0wt% carbon fibers can obtain the optimum mechanical properties, and its preparation process is as fellows: its green is produced by applying 420 MPa pressure at room temperature, then consolidated by hot extrusion at 480 °C and 280 MPa pressure, and sintered at 550?°C for 0.5 h.
Chopped carbon fibers reinforced magnesium was made using the powder metallurgy technique followed by hot extrusion. In order to enhance the carbon fiber wettability to the matrix, the carbon fibers were nickel-coated by palladium-free activated electroless coating method and then characterized by field emission-scanning electron microscope (FE-SEM) equipped with energy dispersive spectroscopy (EDS). The fiber distribution in composite materials were evaluated by super depth digital microscope and the composite extrusion process was analyzed. The results show that nickel-plated carbon fibers can meet the requirement for the preparation and the dispersion in the composite. The composite containing 4.0wt% carbon fibers can obtain the optimum mechanical properties, and its preparation process is as fellows: its green is produced by applying 420 MPa pressure at room temperature, then consolidated by hot extrusion at 480 °C and 280 MPa pressure, and sintered at 550?°C for 0.5 h.
2012, 41(4):748-752.
Abstract:
电极材料是推进电池技术发展及应用的关键。作为锂离子电池正极材料的LiFePO4表现出优异的电池性能 (大容量、优异循环特性)，但也有本征低电导率的缺点。具有橄榄石结构的LiFePO4在电池充放电过程发生FePO4 与LiFePO4 之间的相变， 已有实验证明充放电过程中出现固溶体LixFePO4。掺杂是提高材料电导率的常用手段，但LiFePO4的掺杂却一直饱受争议；缺陷化学的研究初步认定通过适当点缺陷的电荷补偿，晶体内引入掺杂元素是可以实现的，并且提出几种缺陷补偿机制。导电相复合可降低电极颗粒间的接触电阻，特别是LiFePO4的碳包覆有效地改善其电化学性能，促进其工业化推广；碳包覆的有效性取决于碳的sp2杂化键的比例及碳含量。由于电极材料形貌影响电池的充放电动力学过程，LiFePO4的颗粒尺寸、形状、表面粗糙度等的控制都成为提高电池性能的重要手段；LiFePO4的薄膜制备及三维构架技术则进一步推动微型电池的应用发展
电极材料是推进电池技术发展及应用的关键。作为锂离子电池正极材料的LiFePO4表现出优异的电池性能 (大容量、优异循环特性)，但也有本征低电导率的缺点。具有橄榄石结构的LiFePO4在电池充放电过程发生FePO4 与LiFePO4 之间的相变， 已有实验证明充放电过程中出现固溶体LixFePO4。掺杂是提高材料电导率的常用手段，但LiFePO4的掺杂却一直饱受争议；缺陷化学的研究初步认定通过适当点缺陷的电荷补偿，晶体内引入掺杂元素是可以实现的，并且提出几种缺陷补偿机制。导电相复合可降低电极颗粒间的接触电阻，特别是LiFePO4的碳包覆有效地改善其电化学性能，促进其工业化推广；碳包覆的有效性取决于碳的sp2杂化键的比例及碳含量。由于电极材料形貌影响电池的充放电动力学过程，LiFePO4的颗粒尺寸、形状、表面粗糙度等的控制都成为提高电池性能的重要手段；LiFePO4的薄膜制备及三维构架技术则进一步推动微型电池的应用发展
