Volume 40,Issue 12,2011 Table of Contents
2011, 40(12):2069-2071.
Abstract:
Dispersed silver nanoplates were prepared using silver nitrate and vitamin C in absence of agitation and surfactants in aqueous solution. In contrast, aggregated silver nanoparticles were obtained under mechanical agitation. The morphology and phases of products were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray diffractometer (XRD). The results show that the dispersed silver nanoplates can be obtained under the conditions of no mechanical agitation and no surfactants. The shear will induce the formation of aggregation.
Dispersed silver nanoplates were prepared using silver nitrate and vitamin C in absence of agitation and surfactants in aqueous solution. In contrast, aggregated silver nanoparticles were obtained under mechanical agitation. The morphology and phases of products were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray diffractometer (XRD). The results show that the dispersed silver nanoplates can be obtained under the conditions of no mechanical agitation and no surfactants. The shear will induce the formation of aggregation.
2011, 40(12):2072-2075.
Abstract:
The titanium alloy powder preheating process in electron beam melting (EBM) was investigated, and the connection mode among powder particles after preheating was analyzed. The results show that when the Ti6Al4V powder is preheated to above 600 °C during EBM process, a powder aggregation is formed. The sintering mechanism is that small particles partially or completely melt and play the role of binder to bond the majority of big particles together; this will be not only to help the particles to hold their places, withstanding the impact force of electron beam, but also to prevent the spheroidization effect in the prototyped surface. Using Ti6Al4V powder as starting material and adopting complete preheating of the powder layer, the column samples with full interlayer bonding and excellent mechanical properties are produced.
The titanium alloy powder preheating process in electron beam melting (EBM) was investigated, and the connection mode among powder particles after preheating was analyzed. The results show that when the Ti6Al4V powder is preheated to above 600 °C during EBM process, a powder aggregation is formed. The sintering mechanism is that small particles partially or completely melt and play the role of binder to bond the majority of big particles together; this will be not only to help the particles to hold their places, withstanding the impact force of electron beam, but also to prevent the spheroidization effect in the prototyped surface. Using Ti6Al4V powder as starting material and adopting complete preheating of the powder layer, the column samples with full interlayer bonding and excellent mechanical properties are produced.
2011, 40(12):2076-2079.
Abstract:
A novel type of ceramic composite armor, metal-encased SiC ceramic armor with interpenetrating structure, was fabricated using a composite process, including preparation of reaction bonded SiC ceramic plate with ordered holes and metal casting of the macro-porous ceramic plate. The interface microstructures and elemental distributions or compositions of three different metals (a steel and two Ti alloys)/SiC composite armors were analyzed by scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). Relatively good interfacial bonding between ceramic and metal components was obtained, which is closely related to interfacial interactions and compressive residual stress on the ceramic during the cooling stage of casting. The interface microstructures depend significantly on the metal component composition (including the main element and the state of its existence after casting) and the casting process.
A novel type of ceramic composite armor, metal-encased SiC ceramic armor with interpenetrating structure, was fabricated using a composite process, including preparation of reaction bonded SiC ceramic plate with ordered holes and metal casting of the macro-porous ceramic plate. The interface microstructures and elemental distributions or compositions of three different metals (a steel and two Ti alloys)/SiC composite armors were analyzed by scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). Relatively good interfacial bonding between ceramic and metal components was obtained, which is closely related to interfacial interactions and compressive residual stress on the ceramic during the cooling stage of casting. The interface microstructures depend significantly on the metal component composition (including the main element and the state of its existence after casting) and the casting process.
2011, 40(12):2080-2082.
Abstract:
Effects of Fe, Mn and Si on the hydrogen-induced amorphization in LaNi3 were investigated by XRD and electrochemical method. All the LaNi2.5M0.5 (M = Ni, Fe, Mn and Si) alloys were prepared by melt-spun plus annealing method and their main phase is LaNi3. It is found that the hydrogen-induced amorphization appears in all the alloys for the first charging cycle. During the discharge process, no plateau is observed in LaNi3 and LaNi2.5Fe0.5 but a plateau in LaNi2.5Mn0.5 and LaNi2.5Si0.5, indicating that a small amount of Mn and Si suppresses the tendency of hydrogen-induced amorphization.
Effects of Fe, Mn and Si on the hydrogen-induced amorphization in LaNi3 were investigated by XRD and electrochemical method. All the LaNi2.5M0.5 (M = Ni, Fe, Mn and Si) alloys were prepared by melt-spun plus annealing method and their main phase is LaNi3. It is found that the hydrogen-induced amorphization appears in all the alloys for the first charging cycle. During the discharge process, no plateau is observed in LaNi3 and LaNi2.5Fe0.5 but a plateau in LaNi2.5Mn0.5 and LaNi2.5Si0.5, indicating that a small amount of Mn and Si suppresses the tendency of hydrogen-induced amorphization.
2011, 40(12):2083-2087.
Abstract:
The effects of CeCl3 and Ce(SO4)2 doping on the hydrogen-release capacity of NaAlH4 have been studied by pressure-composition-temperature equipment. The results show that the total amount and the rate of hydrogen release first increase and then decrease with increasing of CeCl3 and Ce(SO4)2 contents. The rate and the amount of decomposition for the sample doped with 4 mol% CeCl3 in the first-stage dehydrogenation processes are both better than those for the sample doped with 3 mol% Ce(SO4)2. The rate and the amount of decomposition at 110, 130, 150 and 180 °C present an obvious increase with increasing of temperature.
The effects of CeCl3 and Ce(SO4)2 doping on the hydrogen-release capacity of NaAlH4 have been studied by pressure-composition-temperature equipment. The results show that the total amount and the rate of hydrogen release first increase and then decrease with increasing of CeCl3 and Ce(SO4)2 contents. The rate and the amount of decomposition for the sample doped with 4 mol% CeCl3 in the first-stage dehydrogenation processes are both better than those for the sample doped with 3 mol% Ce(SO4)2. The rate and the amount of decomposition at 110, 130, 150 and 180 °C present an obvious increase with increasing of temperature.
2011, 40(12):2088-2091.
Abstract:
A modified SiC coating was prepared on the surface of C/C composites by a pack cementation process. Ni-Ti mixed powder was used as an interlayer to join SiC coating modified C/C composites and GH3128 Ni-based high-temperature alloy (GH3128) by a vacuum hot-pressing diffusion process. The chemical element distribution, microstructure and mechanical properties of the joint between C/C composites and GH3128 were investigated by X-ray diffractometry, scanning electron microscopy, energy-dispersive spectrometry and material universal testing machine. Results show that the SiC modified coating on the surface of C/C composites not only improves fully the wettability of C/C composites to the Ni-Ti intermediate layer, but also alleviates effectively the thermal stress in the joint due to mismatch thermal expansion. Under the same joining condition, the shear strength of the joint with SiC modified coating at room temperature is up to 22.50 MPa, whereas that of the joint without SiC coating modification is almost 0.
A modified SiC coating was prepared on the surface of C/C composites by a pack cementation process. Ni-Ti mixed powder was used as an interlayer to join SiC coating modified C/C composites and GH3128 Ni-based high-temperature alloy (GH3128) by a vacuum hot-pressing diffusion process. The chemical element distribution, microstructure and mechanical properties of the joint between C/C composites and GH3128 were investigated by X-ray diffractometry, scanning electron microscopy, energy-dispersive spectrometry and material universal testing machine. Results show that the SiC modified coating on the surface of C/C composites not only improves fully the wettability of C/C composites to the Ni-Ti intermediate layer, but also alleviates effectively the thermal stress in the joint due to mismatch thermal expansion. Under the same joining condition, the shear strength of the joint with SiC modified coating at room temperature is up to 22.50 MPa, whereas that of the joint without SiC coating modification is almost 0.
2011, 40(12):2092-2095.
Abstract:
Temperature characteristics of metal rubber material were studied. Linear expansion coefficients of metal rubber and metal material were deduced via theories and the relative experiments were also performed. Experimental data approximately agree with the theoretical calculation in linear law in a certain temperature range. The experimental study on the average linear expansion coefficient shows its change rate, revealing the temperature properties of metal rubber material.
Temperature characteristics of metal rubber material were studied. Linear expansion coefficients of metal rubber and metal material were deduced via theories and the relative experiments were also performed. Experimental data approximately agree with the theoretical calculation in linear law in a certain temperature range. The experimental study on the average linear expansion coefficient shows its change rate, revealing the temperature properties of metal rubber material.
2011, 40(12):2096-2100.
Abstract:
The effect of RE addition on the high temperature oxidation behavior of HP40 alloy was studied by SEM, EDS and XRD. The smallest mass gain of the sample with RE addition (Y addition) after 120 h oxidation at 1100 oC is 16.24 g/m2, much lower than that of the sample without RE addition (36.45 g/m2) oxidized under the same condition. The results indicate that RE can improve the high temperature oxidation resistance of HP40 alloy effectively. By analyzing the structure of the oxide scale, it can be inferred that RE addition helps to keep a continuous spinel outer layer while such layer on the sample without RE addition is discontinuous. Moreover, RE addition facilitates the formation of internal oxide, which penetrates into the matrix and increases the contact area with the matrix. As a result, it improves the scale adherence and inhibits the spallation.
The effect of RE addition on the high temperature oxidation behavior of HP40 alloy was studied by SEM, EDS and XRD. The smallest mass gain of the sample with RE addition (Y addition) after 120 h oxidation at 1100 oC is 16.24 g/m2, much lower than that of the sample without RE addition (36.45 g/m2) oxidized under the same condition. The results indicate that RE can improve the high temperature oxidation resistance of HP40 alloy effectively. By analyzing the structure of the oxide scale, it can be inferred that RE addition helps to keep a continuous spinel outer layer while such layer on the sample without RE addition is discontinuous. Moreover, RE addition facilitates the formation of internal oxide, which penetrates into the matrix and increases the contact area with the matrix. As a result, it improves the scale adherence and inhibits the spallation.
2011, 40(12):2101-2105.
Abstract:
The effect of Nd on high temperature creep properties of Al2O3f/AZ91D and the effect of compressive stress on creep stress exponent were analyzed. The results show that the creep resistance of Al2O3f/AZ91D composite is significantly improved by Nd addition, and Al2O3f/AZ91D with 0.8% Nd has the best creep resistance. When the stress is in the range of 60-90 MPa and 156-180 MPa, the creep mechanism is the load transfer between the matrix and the reinforcement, and the composite failure mechanism is the cracking and breaking of fibers. When the stress is in the range of 90-156 MPa, the creep mechanism is viscous glide of dislocation and climb of dislocation.
The effect of Nd on high temperature creep properties of Al2O3f/AZ91D and the effect of compressive stress on creep stress exponent were analyzed. The results show that the creep resistance of Al2O3f/AZ91D composite is significantly improved by Nd addition, and Al2O3f/AZ91D with 0.8% Nd has the best creep resistance. When the stress is in the range of 60-90 MPa and 156-180 MPa, the creep mechanism is the load transfer between the matrix and the reinforcement, and the composite failure mechanism is the cracking and breaking of fibers. When the stress is in the range of 90-156 MPa, the creep mechanism is viscous glide of dislocation and climb of dislocation.
10 Study on Reaction Kinetics in Diffusion Bonding of Ti2AlNb and GH4169 with Nb+Ni Foils as Interlayer
2011, 40(12):2106-2110.
Abstract:
The process of reaction kinetics was investigated for vacuum diffusion bonding of Ti2AlNb and GH4169 by inserting metal foils of Ni+Nb as interlayer. The results show that there is an optimum thickness (about 3.36 μm) for the reaction layer Ni6Nb7, which is the main factor that influences the joint’s shear strength. The modified effective heat of formation (MEHF) theory and the effective Gibbs free energy theory were applied to predict that Ni6Nb7 is the primary phase formed during Ni-Nb interface reaction, i.e., Ni6Nb7 phase inevitably forms during the bonding process. The growth rate of Ni6Nb7 layer is lower than that of Ni3Nb layer. Thus it is possible to control the thickness of Ni6Nb7 layer by optimizing the processing parameters so as to improve the mechanical properties of the joints. The optimized duration time for the samples bonded at 1050 oC under 20 MPa is 49.5 min. This condition issues experimental shear strength of the joint as 468.2 MPa.
The process of reaction kinetics was investigated for vacuum diffusion bonding of Ti2AlNb and GH4169 by inserting metal foils of Ni+Nb as interlayer. The results show that there is an optimum thickness (about 3.36 μm) for the reaction layer Ni6Nb7, which is the main factor that influences the joint’s shear strength. The modified effective heat of formation (MEHF) theory and the effective Gibbs free energy theory were applied to predict that Ni6Nb7 is the primary phase formed during Ni-Nb interface reaction, i.e., Ni6Nb7 phase inevitably forms during the bonding process. The growth rate of Ni6Nb7 layer is lower than that of Ni3Nb layer. Thus it is possible to control the thickness of Ni6Nb7 layer by optimizing the processing parameters so as to improve the mechanical properties of the joints. The optimized duration time for the samples bonded at 1050 oC under 20 MPa is 49.5 min. This condition issues experimental shear strength of the joint as 468.2 MPa.
2011, 40(12):2111-2116.
Abstract:
The effects of Ru on the microstructural stability and stress-rupture property have been investigated for two experimental Ni-based single crystal superalloys with and without Ru (2.5 wt%) addition. The results of standard heat treatment and long-term thermal exposure at 1100 oC indicate that the intermediate γ′ precipitates in the dendrite cores of the Ru-free alloy do not change in morphology and only become coarsening after 2000 h thermal exposure. The Re partitioning ratio of γ/γ′ phases increases with the addition of Ru, thus resulting in more negative lattice misfit and more cuboidal γ′ precipitates. The Ru-containing alloy rafts after 2000 h thermal exposure. Meanwhile, TCP phases enriched in Re, W and Cr precipitate after 700 h thermal exposure in the dendrite cores of the Ru-free alloy while TCP phases are not observed even after 2000 h thermal exposure in the Ru-containing alloy. These results suggest that Ru addition suppresses the precipitation of TCP phases significantly. The investigation of stress-rupture properties at 1100 oC /140 MPa indicates that Ru addition increases the stress-rupture life of the baseline alloy (Ru-free) since Ru addition increases the γ′ volume fraction and decreases the width of γ channels after standard heat treatment, as well as increasing the γ/γ′ lattice misfit with a well rafting microstructure.
The effects of Ru on the microstructural stability and stress-rupture property have been investigated for two experimental Ni-based single crystal superalloys with and without Ru (2.5 wt%) addition. The results of standard heat treatment and long-term thermal exposure at 1100 oC indicate that the intermediate γ′ precipitates in the dendrite cores of the Ru-free alloy do not change in morphology and only become coarsening after 2000 h thermal exposure. The Re partitioning ratio of γ/γ′ phases increases with the addition of Ru, thus resulting in more negative lattice misfit and more cuboidal γ′ precipitates. The Ru-containing alloy rafts after 2000 h thermal exposure. Meanwhile, TCP phases enriched in Re, W and Cr precipitate after 700 h thermal exposure in the dendrite cores of the Ru-free alloy while TCP phases are not observed even after 2000 h thermal exposure in the Ru-containing alloy. These results suggest that Ru addition suppresses the precipitation of TCP phases significantly. The investigation of stress-rupture properties at 1100 oC /140 MPa indicates that Ru addition increases the stress-rupture life of the baseline alloy (Ru-free) since Ru addition increases the γ′ volume fraction and decreases the width of γ channels after standard heat treatment, as well as increasing the γ/γ′ lattice misfit with a well rafting microstructure.
2011, 40(12):2117-2120.
Abstract:
The as-cast, heat-treated and long-term aged microstructures of DD6 single crystal superalloy blades with low angle boundaries (LABs) were investigated with scanning electron microscope (SEM) and transition electron microscope (TEM). The coarse γ′ phase and bulk γ/γ′ eutectic precipitate along LABs in the as-cast microstructure. There is a thin layer of γ phase in the grain boundaries and imperfect cubic γ′ particle along grain boundaries in the microstructures after heat treatment. The granular carbide exists, but no TCP phase precipitates along grain boundaries after aging at 1070 oC for 500 h, and LABs of DD6 alloy exhibit good microstructure stability.
The as-cast, heat-treated and long-term aged microstructures of DD6 single crystal superalloy blades with low angle boundaries (LABs) were investigated with scanning electron microscope (SEM) and transition electron microscope (TEM). The coarse γ′ phase and bulk γ/γ′ eutectic precipitate along LABs in the as-cast microstructure. There is a thin layer of γ phase in the grain boundaries and imperfect cubic γ′ particle along grain boundaries in the microstructures after heat treatment. The granular carbide exists, but no TCP phase precipitates along grain boundaries after aging at 1070 oC for 500 h, and LABs of DD6 alloy exhibit good microstructure stability.
2011, 40(12):2121-2124.
Abstract:
The mechanical properties and fracture characteristics of 95W-3.5Ni-1.5Fe alloys were investigated by tension in the temperature range of 400-1100 oC and the fracture mechanism was analyzed. The results show that the ultimate tensile strength (UTS) and the yield strength of the alloy decrease with the increasing temperature, while the elongation and the reduction of fracture surface area firstly increase up to the maximum value at 600 oC and then decrease with the increasing temperature. The improved ductility of the alloys in the temperature range of 400-600 oC is due to the enhanced comparable deformation capacity between tungsten and the matrix phases by ductile-brittle transformation of tungsten phase. Above 700 oC, dynamic recrystallization occurs in the matrix, which deteriorates the strength of tungsten/matrix interfaces. Hence, the applied stress can not be transited from the matrix to tungsten particles and the comparable deformation capacity of tungsten and matrix is reduced, resulting in a sharp decrease in strength and toughness of alloys.
The mechanical properties and fracture characteristics of 95W-3.5Ni-1.5Fe alloys were investigated by tension in the temperature range of 400-1100 oC and the fracture mechanism was analyzed. The results show that the ultimate tensile strength (UTS) and the yield strength of the alloy decrease with the increasing temperature, while the elongation and the reduction of fracture surface area firstly increase up to the maximum value at 600 oC and then decrease with the increasing temperature. The improved ductility of the alloys in the temperature range of 400-600 oC is due to the enhanced comparable deformation capacity between tungsten and the matrix phases by ductile-brittle transformation of tungsten phase. Above 700 oC, dynamic recrystallization occurs in the matrix, which deteriorates the strength of tungsten/matrix interfaces. Hence, the applied stress can not be transited from the matrix to tungsten particles and the comparable deformation capacity of tungsten and matrix is reduced, resulting in a sharp decrease in strength and toughness of alloys.
2011, 40(12):2125-2130.
Abstract:
The adsorption isotherms of CO, CO2 and O2 on UO2 powder at 288 K were measured using static volumetric method, and their effects on the induction time for uranium-hydrogen reaction were investigated by measuring pressure drop combined with in-situ micrographic observation. The Langmuir and Freundlich equations were found to describe well the adsorption behavior of CO and CO2 on UO2, respectively, with the adsorption strength following the ordering of O2>CO2>CO. The effects of oxygen-containing gases on the induction time are closely related to their adsorption properties, and their inhibition efficiency follows the ordering of CO2>CO>O2. The induction time is almost direct proportion to CO or O2 concentration, whereas it varies differently as CO2 concentration depends on its concentration region. The inhibition mechanism of CO or CO2 is mainly attributed to their preferred occupation of active adsorption sites on the uranium surface, whereas that of O2 is relatively complex, which may be related to two surface chemical processes: the formation of water precursor state and the diffusion of adsorbed O particles. The derived model based on the inhibition mechanism and gas adsorption property describes well the influence behavior of CO and CO2 on the induction time.
The adsorption isotherms of CO, CO2 and O2 on UO2 powder at 288 K were measured using static volumetric method, and their effects on the induction time for uranium-hydrogen reaction were investigated by measuring pressure drop combined with in-situ micrographic observation. The Langmuir and Freundlich equations were found to describe well the adsorption behavior of CO and CO2 on UO2, respectively, with the adsorption strength following the ordering of O2>CO2>CO. The effects of oxygen-containing gases on the induction time are closely related to their adsorption properties, and their inhibition efficiency follows the ordering of CO2>CO>O2. The induction time is almost direct proportion to CO or O2 concentration, whereas it varies differently as CO2 concentration depends on its concentration region. The inhibition mechanism of CO or CO2 is mainly attributed to their preferred occupation of active adsorption sites on the uranium surface, whereas that of O2 is relatively complex, which may be related to two surface chemical processes: the formation of water precursor state and the diffusion of adsorbed O particles. The derived model based on the inhibition mechanism and gas adsorption property describes well the influence behavior of CO and CO2 on the induction time.
2011, 40(12):2131-2135.
Abstract:
Cu50.3Zr49.7-xNbx(x=0, 2) bulk amorphous alloys were prepared by copper mould suction casting. The effect of 2at% Nb addition on isothermal crystallization behavior of the Cu-Zr alloy in supercooled liquid region has been investigated by differential scanning calorimetry (DSC). Results show that the kinetics of isothermal crystallization of Cu based alloys can be well described by the Johnson-Mehl-Avrami (JMA) model. The minor-Nb-containing alloy exhibits longer incubation time for isothermal crystallization and broader reaction exothermic peak as well as lower crystallization rate constant k and Avrami parameter n. Meanwhile, the variation of local Avrami parameter n with crystallized fraction in the Nb-containing alloy is different from that of Nb-free one. This indicates that the Nb addition enhances the thermal stability against crystallization and changes the isothermal crystallization process of the Cu-based alloy.
Cu50.3Zr49.7-xNbx(x=0, 2) bulk amorphous alloys were prepared by copper mould suction casting. The effect of 2at% Nb addition on isothermal crystallization behavior of the Cu-Zr alloy in supercooled liquid region has been investigated by differential scanning calorimetry (DSC). Results show that the kinetics of isothermal crystallization of Cu based alloys can be well described by the Johnson-Mehl-Avrami (JMA) model. The minor-Nb-containing alloy exhibits longer incubation time for isothermal crystallization and broader reaction exothermic peak as well as lower crystallization rate constant k and Avrami parameter n. Meanwhile, the variation of local Avrami parameter n with crystallized fraction in the Nb-containing alloy is different from that of Nb-free one. This indicates that the Nb addition enhances the thermal stability against crystallization and changes the isothermal crystallization process of the Cu-based alloy.
16 Point Defects Structure and Alloying Effects of V Atoms into Ni3Al Alloy: a First-Principles Study
2011, 40(12):2136-2141.
Abstract:
Using the first-principles plane-wave pseudopotential method based on the density functional theory, the electronic structure and the point defects structure of V into Ni3Al alloy were studied. The approximate algorithm of Ni3Al alloy was selected by comparing experimental results with the calculation. The lattice constant, the formation enthalpies, cohesive energies, formation energies and equilibrium concentration of point defects, density of states of the supercell and charge density were calculated. The calculation results show that anti-site defects are more easily formed than vacancy defects, NiAl is the most important anti-site defect, and the Al-sites are the defects more easily formed than Ni-sites in the Ni3Al alloy. The equilibrium concentration of vacancy defects in Ni3Al alloy at 1400 K is far below that of the anti-site defects. V atoms into Ni3Al alloy system can increase the stability of the alloy.
Using the first-principles plane-wave pseudopotential method based on the density functional theory, the electronic structure and the point defects structure of V into Ni3Al alloy were studied. The approximate algorithm of Ni3Al alloy was selected by comparing experimental results with the calculation. The lattice constant, the formation enthalpies, cohesive energies, formation energies and equilibrium concentration of point defects, density of states of the supercell and charge density were calculated. The calculation results show that anti-site defects are more easily formed than vacancy defects, NiAl is the most important anti-site defect, and the Al-sites are the defects more easily formed than Ni-sites in the Ni3Al alloy. The equilibrium concentration of vacancy defects in Ni3Al alloy at 1400 K is far below that of the anti-site defects. V atoms into Ni3Al alloy system can increase the stability of the alloy.
2011, 40(12):2142-2146.
Abstract:
Ru/C catalysts were prepared by supercritical CO2 deposition using RuCl3 as active precursor and activated carbon as support. The activity of Ru/C catalysts for hydrogenation of glucose were tested under 4.0 MPa and at 120 oC. The effects of the co-solvent category, co-solvent amount and supercritical CO2 pressure on catalytic activity were tested. The surface morphology, crystal form and Ru distribution of Ru/C catalysts were investigated by SEM, XRD and XPS. The results show that supercritical CO2 deposition technology can increase the activity of the Ru/C catalysts. In the experimental range, optimal activity of the catalysts can be obtained under the appropriate conditions of 2 ml methanol co-solvent and supercritical CO2 pressure 12.0 MPa. The highest reaction rate for hydrogenation of glucose exhibits 1.48 times higher than that of the catalyst prepared by the traditional method. Ru exists in the amorphous form in the catalysts with good dispersion on the activated carbon. Supercritical fluid deposition can enhance interaction between Ru and activated carbon.
Ru/C catalysts were prepared by supercritical CO2 deposition using RuCl3 as active precursor and activated carbon as support. The activity of Ru/C catalysts for hydrogenation of glucose were tested under 4.0 MPa and at 120 oC. The effects of the co-solvent category, co-solvent amount and supercritical CO2 pressure on catalytic activity were tested. The surface morphology, crystal form and Ru distribution of Ru/C catalysts were investigated by SEM, XRD and XPS. The results show that supercritical CO2 deposition technology can increase the activity of the Ru/C catalysts. In the experimental range, optimal activity of the catalysts can be obtained under the appropriate conditions of 2 ml methanol co-solvent and supercritical CO2 pressure 12.0 MPa. The highest reaction rate for hydrogenation of glucose exhibits 1.48 times higher than that of the catalyst prepared by the traditional method. Ru exists in the amorphous form in the catalysts with good dispersion on the activated carbon. Supercritical fluid deposition can enhance interaction between Ru and activated carbon.
2011, 40(12):2147-2151.
Abstract:
Transformation behavior of TiNiCr shape memory alloys with different aging treatment was investigated by DSC, scanning electron microscopy (SEM) and the D/max2500PC automatic X-ray diffraction equipment (XRD). The results indicate that with increasing of the aging temperature, the transformation temperature As and Af increase but they decrease after 700 oC and TiNiCr alloy exhibits B2→R→B19′ two-stage martensitic transformation during cooling. Lots of Ti3Ni4 precipitants from aging treatment induce R phase transformation.
Transformation behavior of TiNiCr shape memory alloys with different aging treatment was investigated by DSC, scanning electron microscopy (SEM) and the D/max2500PC automatic X-ray diffraction equipment (XRD). The results indicate that with increasing of the aging temperature, the transformation temperature As and Af increase but they decrease after 700 oC and TiNiCr alloy exhibits B2→R→B19′ two-stage martensitic transformation during cooling. Lots of Ti3Ni4 precipitants from aging treatment induce R phase transformation.
2011, 40(12):2152-2155.
Abstract:
Cu/Ag多层膜；Hall-Petch关系；位错塞积模型；位错稳定性
Cu/Ag多层膜；Hall-Petch关系；位错塞积模型；位错稳定性
2011, 40(12):2156-2161.
Abstract:
The solidification process of Mg15Al binary magnesium alloy was controlled by the rotating magnetic field (RMF) to obtain even and small equiaxed grains, which make the followed equal channel-angular pressing proceed. The effect of various-strength rotating magnetic field on microstructure and the solute distribution of the Mg15Al binary magnesium alloy was investigated by OM, SEM and EDS. The results show that the distribution of the temperature field and solute field can be obviously improved by the severe fluid flow from the interaction between the RMF and the liquid metal, so the primary phase α-Mg in the as-cast Mg15Al binary alloy can be refined and the solid solution of aluminium in the primary phase α-Mg can be increased by RMF. But the eutectic microstructure has no change by RMF since no effective flow is formed in the end of solidification. The grain refinement increases gradually with the increase of magnetizing voltage. When the magnetizing voltage reaches 60 V, the finest grain and the highest solid solution of aluminium in the primary phase α-Mg can be obtained. But for the magnetizing voltage higher than 60 V, the grain size will decrease partially as the magnetic field-induced heat weakens the secondary cooling.
The solidification process of Mg15Al binary magnesium alloy was controlled by the rotating magnetic field (RMF) to obtain even and small equiaxed grains, which make the followed equal channel-angular pressing proceed. The effect of various-strength rotating magnetic field on microstructure and the solute distribution of the Mg15Al binary magnesium alloy was investigated by OM, SEM and EDS. The results show that the distribution of the temperature field and solute field can be obviously improved by the severe fluid flow from the interaction between the RMF and the liquid metal, so the primary phase α-Mg in the as-cast Mg15Al binary alloy can be refined and the solid solution of aluminium in the primary phase α-Mg can be increased by RMF. But the eutectic microstructure has no change by RMF since no effective flow is formed in the end of solidification. The grain refinement increases gradually with the increase of magnetizing voltage. When the magnetizing voltage reaches 60 V, the finest grain and the highest solid solution of aluminium in the primary phase α-Mg can be obtained. But for the magnetizing voltage higher than 60 V, the grain size will decrease partially as the magnetic field-induced heat weakens the secondary cooling.
2011, 40(12):2162-2166.
Abstract:
The microformability in the supercooled liquid region of 4 bulk metallic glasses (Pd40Cu30Ni10P20, Zr65Cu15Al10Ni10, Cu46Zr42Al7Y5, Zr58.5Cu15.6Al10.3Ni12.8Nb2.8) with different fragility values was investigated with microimprinting experiment on a micro-V shaped silicon mould. Results show that the bulk metallic glasses (BMGs) show different apparent viscosity. But under the condition of the same deformation, the 4 BMGs exhibit almost the same area of flowed into the groove, namely they show similar microformability. This is attributed to the adopted experimental conditions (T＝1.07Tg,＝2×10-3 s-1) under which the BMGs show a Newtonian flow behavior. The FEM study also verifies this conclusion.
The microformability in the supercooled liquid region of 4 bulk metallic glasses (Pd40Cu30Ni10P20, Zr65Cu15Al10Ni10, Cu46Zr42Al7Y5, Zr58.5Cu15.6Al10.3Ni12.8Nb2.8) with different fragility values was investigated with microimprinting experiment on a micro-V shaped silicon mould. Results show that the bulk metallic glasses (BMGs) show different apparent viscosity. But under the condition of the same deformation, the 4 BMGs exhibit almost the same area of flowed into the groove, namely they show similar microformability. This is attributed to the adopted experimental conditions (T＝1.07Tg,＝2×10-3 s-1) under which the BMGs show a Newtonian flow behavior. The FEM study also verifies this conclusion.
2011, 40(12):2167-2170.
Abstract:
Plasma spray (PS) is the dominant technology for preparing tungsten (W) coatings used as plasma facing materials (PFM). Two types of tungsten powders, i.e. crystal tungsten powder and carbonyl tungsten powder, produced by different methods, were adopted during plasma spray. Three thick tungsten coatings with thickness of 3-4 mm on copper-chromium-zirconium (Cu, Cr, Zr) alloy substrate with 110 mm × 130 mm were fabricated by means of atmospheric plasma spray (APS). The CuMo/MoW was used as the interlayer of tungsten coatings. Characterization of coatings was performed in order to assess microstructure, mechanical and thermal properties. The results indicate that the coating from carbonyl tungsten powder has better over-all properties than that from crystal tungsten powder, and for the coatings from the same powder, the thin coating possesses higher bond strength than the thick. The porosity of the coating is less than 2% by digital image analysis. The maximal tensile strength value of coatings is about 10 MPa. The content of oxygen is about 6 wt% by EDS. The maximal thermal conductivity of the pure tungsten coatings is 12.52 W/(m·K). The high oxygen results in the low thermal conductivity of the tungsten coating. The work performed has demonstrated the feasibility of 3-4 mm thick W coatings on flat geometries by APS, which is the foundation of preparing the low cost and high property thick tungsten coatings.
Plasma spray (PS) is the dominant technology for preparing tungsten (W) coatings used as plasma facing materials (PFM). Two types of tungsten powders, i.e. crystal tungsten powder and carbonyl tungsten powder, produced by different methods, were adopted during plasma spray. Three thick tungsten coatings with thickness of 3-4 mm on copper-chromium-zirconium (Cu, Cr, Zr) alloy substrate with 110 mm × 130 mm were fabricated by means of atmospheric plasma spray (APS). The CuMo/MoW was used as the interlayer of tungsten coatings. Characterization of coatings was performed in order to assess microstructure, mechanical and thermal properties. The results indicate that the coating from carbonyl tungsten powder has better over-all properties than that from crystal tungsten powder, and for the coatings from the same powder, the thin coating possesses higher bond strength than the thick. The porosity of the coating is less than 2% by digital image analysis. The maximal tensile strength value of coatings is about 10 MPa. The content of oxygen is about 6 wt% by EDS. The maximal thermal conductivity of the pure tungsten coatings is 12.52 W/(m·K). The high oxygen results in the low thermal conductivity of the tungsten coating. The work performed has demonstrated the feasibility of 3-4 mm thick W coatings on flat geometries by APS, which is the foundation of preparing the low cost and high property thick tungsten coatings.
2011, 40(12):2171-2174.
Abstract:
DSC and XRD detection methods were used to investigate glass transition temperature (Tg), onset crystallization temperature (Tx), crystallization peak temperature (Tp), and specific heat difference (ΔCp.g) during glass transition period of Fe68Ni1Al5Ga2P9.65B4.6Si3C6.75 amorphous alloys, which were pre-annealed at 673 K ((Tg-100 K)
DSC and XRD detection methods were used to investigate glass transition temperature (Tg), onset crystallization temperature (Tx), crystallization peak temperature (Tp), and specific heat difference (ΔCp.g) during glass transition period of Fe68Ni1Al5Ga2P9.65B4.6Si3C6.75 amorphous alloys, which were pre-annealed at 673 K ((Tg-100 K)
2011, 40(12):2175-2178.
Abstract:
Al2O3 particle reinforced Mo composites were prepared by a sol-gel technique. The micro-hardness of the molybdenum matrix of the composites was determined, and the microscopic analysis of the mixed powder and the sintered billet were carried out by XRD, SEM and TEM. The sliding wear performance of the composite materials was measured by a pin-disc friction and wear testing machine. Results show that in the composite materials Al2O3 as disperse phase can refine the grains. The micro-hardness of the molybdenum matrix increases with the increasing of volume fraction of Al2O3 and the friction coefficient of composites decreases slowly. Meanwhile, the wear mass-loss first increases and then decreases. Therefore, the Al2O3 particles help to improve the abrasion performance of molybdenum matrix material.
Al2O3 particle reinforced Mo composites were prepared by a sol-gel technique. The micro-hardness of the molybdenum matrix of the composites was determined, and the microscopic analysis of the mixed powder and the sintered billet were carried out by XRD, SEM and TEM. The sliding wear performance of the composite materials was measured by a pin-disc friction and wear testing machine. Results show that in the composite materials Al2O3 as disperse phase can refine the grains. The micro-hardness of the molybdenum matrix increases with the increasing of volume fraction of Al2O3 and the friction coefficient of composites decreases slowly. Meanwhile, the wear mass-loss first increases and then decreases. Therefore, the Al2O3 particles help to improve the abrasion performance of molybdenum matrix material.
2011, 40(12):2179-2183.
Abstract:
Two kinds of nanosized indium-tin-oxide (ITO) powders were prepared by heating the ITO precursors at 600 and 1000 oC respectively. The compacts were obtained by press molding of the powders. Then ITO targets were prepared by sintering the compacts at 400-1550 oC in oxygen atmosphere. The powders and the targets were characterized. The grain growth during sintering, the relationship between the targets’ microstructure and the sintering temperature, and the oxygen content of the targets were investigated. The results show that powders prepared by heating the ITO precursors at 600 oC (600 oC ITO powder) are single phase, and their grain size is 15 nm. Powders prepared by heating the ITO precursors at 1000 oC (1000 oC ITO powder) contain a little SnO2, and the grain size is 28 nm. 1000 oC ITO powders exhibit better dispersivity and keep higher crystallization degree. The sintering process of these two kinds of ITO powders corresponds with Coble Solid Phase Sintering process. When the sintering temperature is 1550 oC, crystal growth steps similar to the steps appearing in the two-dimensional nucleation growth can be observed. ITO targets’ density increases as the temperature rises and holding time extends. The density of ITO targets made from 1000 oC ITO powders is higher than that of the targets made from 600 oC ITO powders. This phenomenon indicates that targets’ densification is determined by the degree of agglomeration and the size of agglomerates. Both types of targets contain less oxygen than the theoretical value. And the oxygen content of targets made from 1000 oC ITO powders are higher than that of targets made from 600 oC ITO powders.
Two kinds of nanosized indium-tin-oxide (ITO) powders were prepared by heating the ITO precursors at 600 and 1000 oC respectively. The compacts were obtained by press molding of the powders. Then ITO targets were prepared by sintering the compacts at 400-1550 oC in oxygen atmosphere. The powders and the targets were characterized. The grain growth during sintering, the relationship between the targets’ microstructure and the sintering temperature, and the oxygen content of the targets were investigated. The results show that powders prepared by heating the ITO precursors at 600 oC (600 oC ITO powder) are single phase, and their grain size is 15 nm. Powders prepared by heating the ITO precursors at 1000 oC (1000 oC ITO powder) contain a little SnO2, and the grain size is 28 nm. 1000 oC ITO powders exhibit better dispersivity and keep higher crystallization degree. The sintering process of these two kinds of ITO powders corresponds with Coble Solid Phase Sintering process. When the sintering temperature is 1550 oC, crystal growth steps similar to the steps appearing in the two-dimensional nucleation growth can be observed. ITO targets’ density increases as the temperature rises and holding time extends. The density of ITO targets made from 1000 oC ITO powders is higher than that of the targets made from 600 oC ITO powders. This phenomenon indicates that targets’ densification is determined by the degree of agglomeration and the size of agglomerates. Both types of targets contain less oxygen than the theoretical value. And the oxygen content of targets made from 1000 oC ITO powders are higher than that of targets made from 600 oC ITO powders.
2011, 40(12):2184-2187.
Abstract:
Sulfuric acid-methanol electrolytes were applied for the electropolishing of tantalum. The effects of electrolyte composition and voltage on the finish quality of tantalum were investigated. The optimum parameters for polishing tantalum are determined as follows: V(H2SO4):V(CH3OH) =1:7, voltage=~20 V when the stir speed is 16 m/s, and the electrolysis time is 3 min at 0 oC. The results show that RMS Rq of the polished tantalum is less than 30 nm and the requirement of tantalum surface and EOS thin film can be satisfied.
Sulfuric acid-methanol electrolytes were applied for the electropolishing of tantalum. The effects of electrolyte composition and voltage on the finish quality of tantalum were investigated. The optimum parameters for polishing tantalum are determined as follows: V(H2SO4):V(CH3OH) =1:7, voltage=~20 V when the stir speed is 16 m/s, and the electrolysis time is 3 min at 0 oC. The results show that RMS Rq of the polished tantalum is less than 30 nm and the requirement of tantalum surface and EOS thin film can be satisfied.
2011, 40(12):2188-2192.
Abstract:
The strain fatigue property of the welding fittings of Zr-Sn-Nb alloy plates was investigated both at room temperature and 375 ℃, and also we compared that with the smoothed samples. The results showed that the fatigue life of welding samples was less than half of that of the smoothed samples. The fatigue property of longitudinal samples was obviously better than that of transverse samples both at room temperature and 375 ℃. The cycle plastic strain range and the fatigue life followed the Coffin-Manson relation. The cycle- deformation property of the welding fittings differed at different temperature and strains. The microstructure and the fatigue crack were also investigated.
The strain fatigue property of the welding fittings of Zr-Sn-Nb alloy plates was investigated both at room temperature and 375 ℃, and also we compared that with the smoothed samples. The results showed that the fatigue life of welding samples was less than half of that of the smoothed samples. The fatigue property of longitudinal samples was obviously better than that of transverse samples both at room temperature and 375 ℃. The cycle plastic strain range and the fatigue life followed the Coffin-Manson relation. The cycle- deformation property of the welding fittings differed at different temperature and strains. The microstructure and the fatigue crack were also investigated.
2011, 40(12):2193-2196.
Abstract:
The Gd5Ge4 alloy with the peritectic reaction during solidification was prepared by the arc-melt method under protection of argon atmosphere. The as-cast alloys were cut and directionally solidified with the help of laser rapid solidification technique. Microstructure characteristics and phase selection of Gd5Ge4 during the rapid directional solidification by laser zone re-melting were investigated. The microstructure originating from steady-state growth?was evaluated with the help of optical microscope (OM) and X-ray diffraction (XRD). The alloy after laser zone directional solidification possesses obvious preferred orientation and the amorphization occurs under this condition. The cellular spacing could be expressed as a function of the laser scanning velocity during the rapid solidification. An acceptable combination is found between the experimental results and the classical J-H numerical solidification model for a rapid cellular/dendritic growth.
The Gd5Ge4 alloy with the peritectic reaction during solidification was prepared by the arc-melt method under protection of argon atmosphere. The as-cast alloys were cut and directionally solidified with the help of laser rapid solidification technique. Microstructure characteristics and phase selection of Gd5Ge4 during the rapid directional solidification by laser zone re-melting were investigated. The microstructure originating from steady-state growth?was evaluated with the help of optical microscope (OM) and X-ray diffraction (XRD). The alloy after laser zone directional solidification possesses obvious preferred orientation and the amorphization occurs under this condition. The cellular spacing could be expressed as a function of the laser scanning velocity during the rapid solidification. An acceptable combination is found between the experimental results and the classical J-H numerical solidification model for a rapid cellular/dendritic growth.
2011, 40(12):2197-2202.
Abstract:
The master alloy ingot with the nominal composition of Nb-20Ti-16Si-6Cr-5Hf-4Al-2B-0.06Y (at%) was prepared using vacuum consumable arc-melting. The integrally directional solidification of the alloy was conducted in a self-made high vacuum and ultrahigh temperature directional solidification furnace with the use of ceramic crucibles at the melt temperature of 2050 oC. Room temperature fracture toughness of both arc-melted and integrally directionally solidified specimens have been measured by single-edge notched bending test. The directionally solidified microstructure, fractographs and crack propagation path of single-edge notched bending specimens of the alloy at different solidifying rate V (10, 20 and 50 μm/s) have been investigated by SEM and EDS analyses. The fracture mechanism of the single-edge notched bending test has been discussed. The results show that the integrally directionally solidified microstructure of the alloy is mainly composed of hexagonally cross-sectioned primary (Nb, X)5Si3 columns and coupled lamellar Nbss/(Nb, X)5Si3 eutectic colonies both aligned straightly and uprightly along the growth direction (here X represents Ti, Hf and Cr elements, Nbss denotes Nb solid solution). The directional solidification effects are remarkable. Both the average diameter of eutectic cells and lamellar spacing in them decrease with the increase in solidifying rate. The directional alignment of both Nbss and (Nb, X)5Si3 normal to the notch provides more resistance to the crack initiation and propagation, and therefore the room temperature fracture toughness KQ is improved significantly by the integrally directional solidification. The maximum KQ value occurs for the directionally solidified specimens with V=50 μm/s and is about 16.1 MPa·m1/2.
The master alloy ingot with the nominal composition of Nb-20Ti-16Si-6Cr-5Hf-4Al-2B-0.06Y (at%) was prepared using vacuum consumable arc-melting. The integrally directional solidification of the alloy was conducted in a self-made high vacuum and ultrahigh temperature directional solidification furnace with the use of ceramic crucibles at the melt temperature of 2050 oC. Room temperature fracture toughness of both arc-melted and integrally directionally solidified specimens have been measured by single-edge notched bending test. The directionally solidified microstructure, fractographs and crack propagation path of single-edge notched bending specimens of the alloy at different solidifying rate V (10, 20 and 50 μm/s) have been investigated by SEM and EDS analyses. The fracture mechanism of the single-edge notched bending test has been discussed. The results show that the integrally directionally solidified microstructure of the alloy is mainly composed of hexagonally cross-sectioned primary (Nb, X)5Si3 columns and coupled lamellar Nbss/(Nb, X)5Si3 eutectic colonies both aligned straightly and uprightly along the growth direction (here X represents Ti, Hf and Cr elements, Nbss denotes Nb solid solution). The directional solidification effects are remarkable. Both the average diameter of eutectic cells and lamellar spacing in them decrease with the increase in solidifying rate. The directional alignment of both Nbss and (Nb, X)5Si3 normal to the notch provides more resistance to the crack initiation and propagation, and therefore the room temperature fracture toughness KQ is improved significantly by the integrally directional solidification. The maximum KQ value occurs for the directionally solidified specimens with V=50 μm/s and is about 16.1 MPa·m1/2.
2011, 40(12):2203-2206.
Abstract:
The microstructure and fracture behavior of electron beam and laser beam welded stainless steel samples after charging hydrogen and tritium were studied by electron microscopy and the fracture strength was measured by tensile test. The results show that the fracture strength of the welding charged with tritium decreases a little, and the morphology of fracture surface has the typical hydrogen embrittlement mechanisms such as cleavage fracture, the second cracks and intergranular fracture. TEM observation indicates that there is a tendency to form cracks caused by the interaction between gas tritium and precipitates in grain boundary, and the microcracks initiate along deformation bands and grain boundary.
The microstructure and fracture behavior of electron beam and laser beam welded stainless steel samples after charging hydrogen and tritium were studied by electron microscopy and the fracture strength was measured by tensile test. The results show that the fracture strength of the welding charged with tritium decreases a little, and the morphology of fracture surface has the typical hydrogen embrittlement mechanisms such as cleavage fracture, the second cracks and intergranular fracture. TEM observation indicates that there is a tendency to form cracks caused by the interaction between gas tritium and precipitates in grain boundary, and the microcracks initiate along deformation bands and grain boundary.
2011, 40(12):2207-2211.
Abstract:
The large-scale regular silver triangular nanoplates were synthesized by the reduction of silver nitrate with sodium borohydride in the presence of sodium citrate and dioctyl sulfosuccinate sodium salt (AOT) and in the water bath. The morphologies of silver triangular nanoplates were studied by transmission electron microscopy, high resolution transmission electron microscopy and atomic force microscopy and X-ray diffraction. The optical properties were studied by UV-visible—infrared photospectrometery. The results confirm that the silver nanoplates are the single crystallinity with regular arrangement of atoms. The optical in-plane dipole plasmon band of the silver nanoplate has been extended to about 1230 nm, which is in the near-infrared (NIR) regime. Studies from different AOT concentrations, pH values and reaction time demonstrate that triangular nanoframe-mediated growth mechanism is supported only in the proper experimental conditions.
The large-scale regular silver triangular nanoplates were synthesized by the reduction of silver nitrate with sodium borohydride in the presence of sodium citrate and dioctyl sulfosuccinate sodium salt (AOT) and in the water bath. The morphologies of silver triangular nanoplates were studied by transmission electron microscopy, high resolution transmission electron microscopy and atomic force microscopy and X-ray diffraction. The optical properties were studied by UV-visible—infrared photospectrometery. The results confirm that the silver nanoplates are the single crystallinity with regular arrangement of atoms. The optical in-plane dipole plasmon band of the silver nanoplate has been extended to about 1230 nm, which is in the near-infrared (NIR) regime. Studies from different AOT concentrations, pH values and reaction time demonstrate that triangular nanoframe-mediated growth mechanism is supported only in the proper experimental conditions.
2011, 40(12):2212-2215.
Abstract:
The effect of withdrawal rates on the solidification microstructure of a single crystal Ni-based superalloy containing ruthenium was investigated. The results show that with the increase of the withdrawal rate, the as-cast microstructure of the single crystal alloy transforms from coarse dendrite to fine dendrite. Meanwhile, the size of the g ￠ particles decreases, segregation of alloying elements for the dendrite and interdendritic regions tends to be reduced, the volume fraction of g-g ￠ eutectic and NiAl-based b phase decreases gradually. In addition, the withdrawal rate has little influence on the phase transformation temperature of the superalloy.
The effect of withdrawal rates on the solidification microstructure of a single crystal Ni-based superalloy containing ruthenium was investigated. The results show that with the increase of the withdrawal rate, the as-cast microstructure of the single crystal alloy transforms from coarse dendrite to fine dendrite. Meanwhile, the size of the g ￠ particles decreases, segregation of alloying elements for the dendrite and interdendritic regions tends to be reduced, the volume fraction of g-g ￠ eutectic and NiAl-based b phase decreases gradually. In addition, the withdrawal rate has little influence on the phase transformation temperature of the superalloy.
2011, 40(12):2216-2220.
Abstract:
Nano-tungsten powder was prepared on the basis of an industrialized production technique, using WO2.72 as the raw materials. The phase, composition, morphology, thermal stability, special surface area and pore structure of the samples were characterized by XRD, EDS, SEM, FESEM, DTA-TG, BET and Pore Size Analyzer. The results show that high-quality nano-tungsten powder can be produced by reducing the hydrogen reduction temperature, slowing down the pushing boat speed, reducing the boat charging capacity and increasing hydrogen flow rate.
Nano-tungsten powder was prepared on the basis of an industrialized production technique, using WO2.72 as the raw materials. The phase, composition, morphology, thermal stability, special surface area and pore structure of the samples were characterized by XRD, EDS, SEM, FESEM, DTA-TG, BET and Pore Size Analyzer. The results show that high-quality nano-tungsten powder can be produced by reducing the hydrogen reduction temperature, slowing down the pushing boat speed, reducing the boat charging capacity and increasing hydrogen flow rate.
Gao Mangmang
,
Suo Hongli
,
Zhao Yue
,
Gao Peikuo
,
Cheng Yanling
,
Tian Hui
,
Ma Lin
,
Liu Min
,
Zhou Meiling
2011, 40(12):2221-2226.
Abstract:
Composite substrate which has high mechanical property and low magnetic property and is easy to form the sharp cube texture in the outer layer can satisfy the requirements of the advanced metallic substrate used for coated conductors. The Ni5W/Ni12W/Ni5W composite substrate has been fabricated by Sparking Plasma Sintering (SPS) followed by traditional cold rolling and recrystallization annealing. The investigation on the interface between the inner layer and the outer layer of the composite substrate shows that the diffusion layer is beneficial for formation of the cube texture in outer layer of the substrate. The fractions of cube texture on the surface of the outer Ni5W layer in the composite substrate all exceed 98%, when the substrate is annealed at 1250 oC for 60, 120 and 180 min respectively. This is possibly caused by element mutual diffusion during the heat-treatment process in the diffusion layer. The grain abnormal growth has been restrained duo to W atom pinning in grain-boundary diffused from inner layer, subsequently stabilizing the cube texture of the outer layer during the severely annealing process.
Composite substrate which has high mechanical property and low magnetic property and is easy to form the sharp cube texture in the outer layer can satisfy the requirements of the advanced metallic substrate used for coated conductors. The Ni5W/Ni12W/Ni5W composite substrate has been fabricated by Sparking Plasma Sintering (SPS) followed by traditional cold rolling and recrystallization annealing. The investigation on the interface between the inner layer and the outer layer of the composite substrate shows that the diffusion layer is beneficial for formation of the cube texture in outer layer of the substrate. The fractions of cube texture on the surface of the outer Ni5W layer in the composite substrate all exceed 98%, when the substrate is annealed at 1250 oC for 60, 120 and 180 min respectively. This is possibly caused by element mutual diffusion during the heat-treatment process in the diffusion layer. The grain abnormal growth has been restrained duo to W atom pinning in grain-boundary diffused from inner layer, subsequently stabilizing the cube texture of the outer layer during the severely annealing process.
2011, 40(12):2227-2231.
Abstract:
The influence of element addition ways on the microstructure and the performance of P/M Ti-6Al-3Nb-2Zr-1Mo alloy (Ti80) was investigated in order to improve the processing properties. The results indicate that Al must be added by NbAl, ZrAl, MoAl or MoAlTi pre-alloy to obtain the relative density above 97%; Nb and Zr can be added by elementary substance or pre-alloy; Mo should be added by MoAl or MoTiAl pre-alloy. Ti can not completely added by TiH2 powder. The tensile fracture of P/M Ti80 alloy exhibits outstretch rupture and has no crack when Ti is added by Ti powder while the tensile fracture shows brittle rupture and has distinct cracks when Ti is added by TiH2 powder. Hydrogen is the main reason causing cracks of the alloy. Adopting appropriate element addition ways, good performance of the P/M Ti80 alloy can be obtained, such as σb=890-1020 MPa, σ0.1=755-875 MPa, σ0.2=785-895 MPa, δ5=5.5%-9.0%, and ψ=11%-20%. Compared with the forged alloy, the sintered alloy has much higher intensity and lower plasticity.
The influence of element addition ways on the microstructure and the performance of P/M Ti-6Al-3Nb-2Zr-1Mo alloy (Ti80) was investigated in order to improve the processing properties. The results indicate that Al must be added by NbAl, ZrAl, MoAl or MoAlTi pre-alloy to obtain the relative density above 97%; Nb and Zr can be added by elementary substance or pre-alloy; Mo should be added by MoAl or MoTiAl pre-alloy. Ti can not completely added by TiH2 powder. The tensile fracture of P/M Ti80 alloy exhibits outstretch rupture and has no crack when Ti is added by Ti powder while the tensile fracture shows brittle rupture and has distinct cracks when Ti is added by TiH2 powder. Hydrogen is the main reason causing cracks of the alloy. Adopting appropriate element addition ways, good performance of the P/M Ti80 alloy can be obtained, such as σb=890-1020 MPa, σ0.1=755-875 MPa, σ0.2=785-895 MPa, δ5=5.5%-9.0%, and ψ=11%-20%. Compared with the forged alloy, the sintered alloy has much higher intensity and lower plasticity.
2011, 40(12):2232-2235.
Abstract:
Micro-arc oxidation (MAO) layers which were prepared on magnesium alloy WE42 and AM20 by MAO were sealed with PLLA by immersion technique to get composite coatings. The microstructure of the MAO coatings and the composite coatings were analyzed by scanning electron microscopy. The composition of MAO coating is MgSiO3 and SiO2 by X-ray diffractometer (XRD) and the rate of mass loss were tested by immersion test. Electrochemical impedance spectroscopy (EIS) shows that PLLA coating seals the pores in the MAO coating and improves the corrosion resistance by preventing the corrosive ions from diffusing to the magnesium alloy substrate. This composite coating is of high biocompatibility so it is of significance to improve the property of bioabsorbable magnesium stent.
Micro-arc oxidation (MAO) layers which were prepared on magnesium alloy WE42 and AM20 by MAO were sealed with PLLA by immersion technique to get composite coatings. The microstructure of the MAO coatings and the composite coatings were analyzed by scanning electron microscopy. The composition of MAO coating is MgSiO3 and SiO2 by X-ray diffractometer (XRD) and the rate of mass loss were tested by immersion test. Electrochemical impedance spectroscopy (EIS) shows that PLLA coating seals the pores in the MAO coating and improves the corrosion resistance by preventing the corrosive ions from diffusing to the magnesium alloy substrate. This composite coating is of high biocompatibility so it is of significance to improve the property of bioabsorbable magnesium stent.
2011, 40(12):2236-2240.
Abstract:
The composite coatings on AZ31 magnesium alloy substrate were prepared by micro-arc oxidation (MAO) technique in sodium phosphate electrolyte. The effects of positive voltage on phase composition of different-thickness MAO films were investigated. Grain size, d-spacing and residual stresses were calculated based on systematical XRD class study. Results reveal that the diffraction peak intensity, phases and crystallinity of different-depth are different and the grain size of Mg3(PO4)2 (200) peak becomes bigger with increasing the positive voltage. Even preparing the film under the same voltage, the grain sizes of the same crystal orientation at different depths are still different, decreasing with reducing the depth from the surface of thin films, while the d-spacing has the same tendency. Residual stresses attributed to the MgO constituent of the coatings were calculated to be tensile. With the increase of the applied voltages, stress values are decreased sharply.
The composite coatings on AZ31 magnesium alloy substrate were prepared by micro-arc oxidation (MAO) technique in sodium phosphate electrolyte. The effects of positive voltage on phase composition of different-thickness MAO films were investigated. Grain size, d-spacing and residual stresses were calculated based on systematical XRD class study. Results reveal that the diffraction peak intensity, phases and crystallinity of different-depth are different and the grain size of Mg3(PO4)2 (200) peak becomes bigger with increasing the positive voltage. Even preparing the film under the same voltage, the grain sizes of the same crystal orientation at different depths are still different, decreasing with reducing the depth from the surface of thin films, while the d-spacing has the same tendency. Residual stresses attributed to the MgO constituent of the coatings were calculated to be tensile. With the increase of the applied voltages, stress values are decreased sharply.
2011, 40(12):2241-2244.
Abstract:
In order to understand the adhesion failure between Ni-coating and sintered NdFeB substrate, the effect of pickling process on the adhesion strength of Ni-coating on NdFeB substrate was studied. The results reveal that the pickling leads to the formation of loose structure on NdFeB surface and the reduction of micro-hardness of NdFeB surface. The adhesion strength of Ni-coating on NdFeB substrate declines gradually with the increasing time of pickling. It can be found from the cross section morphology of stripped layer that the adhesion failure occurs in inner NdFeB substrate close to the surface, rather than in the interface between Ni-coating and NdFeB substrate.
In order to understand the adhesion failure between Ni-coating and sintered NdFeB substrate, the effect of pickling process on the adhesion strength of Ni-coating on NdFeB substrate was studied. The results reveal that the pickling leads to the formation of loose structure on NdFeB surface and the reduction of micro-hardness of NdFeB surface. The adhesion strength of Ni-coating on NdFeB substrate declines gradually with the increasing time of pickling. It can be found from the cross section morphology of stripped layer that the adhesion failure occurs in inner NdFeB substrate close to the surface, rather than in the interface between Ni-coating and NdFeB substrate.
2011, 40(12):2245-2251.
Abstract:
The ability to control the uniformity of electrodeposition is the key to successful application of electrodeposition technology such as electroplating and electroforming. The principle of micro-electroforming is briefly introduced. The latest research progresses of the thickness uniformity of micro-device electrodeposition at home and abroad are summarized, including optimization of parameters in electrodeposition, modification of current density and application of modulated current, metal ion transportation, auxiliary cathode, shields and baffles, careful control of anode properties, numerical simulation. A new electroplating method in supercritical carbon dioxide and its advantages are presented in detail. Finally, the research focus and future aspects about the uniformity are proposed.
The ability to control the uniformity of electrodeposition is the key to successful application of electrodeposition technology such as electroplating and electroforming. The principle of micro-electroforming is briefly introduced. The latest research progresses of the thickness uniformity of micro-device electrodeposition at home and abroad are summarized, including optimization of parameters in electrodeposition, modification of current density and application of modulated current, metal ion transportation, auxiliary cathode, shields and baffles, careful control of anode properties, numerical simulation. A new electroplating method in supercritical carbon dioxide and its advantages are presented in detail. Finally, the research focus and future aspects about the uniformity are proposed.
2011, 40(12):2252-2256.
Abstract:
Intermetallic TiAl based alloys are a novel light-weight high-temperature structural material, with wide applications in aerospace and automotive industries. Electron beam melting (EBM) is the most novel technology for manufacturing TiAl alloys now. The principle and merits of EBM for TiAl based alloy components, as well as the latest research progress are reported. The present status of prealloyed powder is also reported. The obstacle of EBM of TiAl based alloys is analyzed and its prospect is forecast.
Intermetallic TiAl based alloys are a novel light-weight high-temperature structural material, with wide applications in aerospace and automotive industries. Electron beam melting (EBM) is the most novel technology for manufacturing TiAl alloys now. The principle and merits of EBM for TiAl based alloy components, as well as the latest research progress are reported. The present status of prealloyed powder is also reported. The obstacle of EBM of TiAl based alloys is analyzed and its prospect is forecast.
