Volume 38,Issue 4,2009 Table of Contents
2009, 38(4):565-569.
Abstract:
Single-crystalline GaN nanowires have been synthesized on Si(111) substrates by magnetron sputtering through ammoniating the Ga2O3/Nb films at 900 °C in a quartz tube. The as-prepared nanowires are confirmed as single crystalline GaN with wurtzite structure by X-ray diffraction (XRD), selected-area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM). Transmission electron microscopy (TEM) shows that the GaN nanowires are straight and smooth, and possess the diameters of about 50 nm and lengths up to several microns. When excited by 325 nm helium-cadmium (He-Cd) laser light at room temperature, the GaN nanowires only have a strong ultraviolet luminescence peak located at 367 nm, owing to GaN band-edge emission. Finally, the growth mechanism of GaN nanowires is discussed briefly.
Single-crystalline GaN nanowires have been synthesized on Si(111) substrates by magnetron sputtering through ammoniating the Ga2O3/Nb films at 900 °C in a quartz tube. The as-prepared nanowires are confirmed as single crystalline GaN with wurtzite structure by X-ray diffraction (XRD), selected-area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM). Transmission electron microscopy (TEM) shows that the GaN nanowires are straight and smooth, and possess the diameters of about 50 nm and lengths up to several microns. When excited by 325 nm helium-cadmium (He-Cd) laser light at room temperature, the GaN nanowires only have a strong ultraviolet luminescence peak located at 367 nm, owing to GaN band-edge emission. Finally, the growth mechanism of GaN nanowires is discussed briefly.
2009, 38(4):570-573.
Abstract:
The damage and cold work hardening of 4043 and 2024 T4 aluminum alloy were introduced by tensile test under the applied stress between the yield strength and ultimate tensile strength. Fatigue damage of 2024 T4 aluminum alloy was introduced by cycling to half of fatigue life (85 000 cycles) at 225 MPa. Then the damaged specimens were healed by D. C. electropulsing. The electric resistances of as-received, damaged and healed specimens were measured by electric bridge, respectively. The results show that the elongation increases, and yield strength and ultimate strength decrease with the increase of healing time for the 4043 aluminum alloy tensile damaged specimen. The mechanical properties of the 4043 aluminum alloy damaged specimens treated by a 0.5 s electropulsing are close to the values of undamaged specimens. Fatigue life is considerably prolonged by a 0.8 s electropulsing treatment for the fatigue damaged specimen of 2024 T4 aluminum alloy. The electric resistance of aluminum alloys increases obviously after fatigue or tension damage, and decreases after electropulsing treatment, but it is still larger than that of the as-received specimen. The treatment time has little influence on the final resistances, but the mechanical properties are quite different for the samples treated by various electropulsing time. Although the resistance can describe the damage of aluminum alloys, it is not very sensitive to the mechanical properties, so it can not be considered as a good criterion for healing evaluation. The observation of microstructure reveals that the damages can be partly healed after D. C. electropulsing, and recrystallizaton phenomenon appears.
The damage and cold work hardening of 4043 and 2024 T4 aluminum alloy were introduced by tensile test under the applied stress between the yield strength and ultimate tensile strength. Fatigue damage of 2024 T4 aluminum alloy was introduced by cycling to half of fatigue life (85 000 cycles) at 225 MPa. Then the damaged specimens were healed by D. C. electropulsing. The electric resistances of as-received, damaged and healed specimens were measured by electric bridge, respectively. The results show that the elongation increases, and yield strength and ultimate strength decrease with the increase of healing time for the 4043 aluminum alloy tensile damaged specimen. The mechanical properties of the 4043 aluminum alloy damaged specimens treated by a 0.5 s electropulsing are close to the values of undamaged specimens. Fatigue life is considerably prolonged by a 0.8 s electropulsing treatment for the fatigue damaged specimen of 2024 T4 aluminum alloy. The electric resistance of aluminum alloys increases obviously after fatigue or tension damage, and decreases after electropulsing treatment, but it is still larger than that of the as-received specimen. The treatment time has little influence on the final resistances, but the mechanical properties are quite different for the samples treated by various electropulsing time. Although the resistance can describe the damage of aluminum alloys, it is not very sensitive to the mechanical properties, so it can not be considered as a good criterion for healing evaluation. The observation of microstructure reveals that the damages can be partly healed after D. C. electropulsing, and recrystallizaton phenomenon appears.
2009, 38(4):574-578.
Abstract:
The microstructure and mechanical properties of laser solid formed Ti-6Al-4V from the blend of Ti, Al, and V powders were investigated. It is found that the macrostructure changes from equiaxed to columnar grains with the increase of the laser power, which is very different from that of the samples using pre-alloyed powders as cladding materials. The disturbance effect of the mixing enthalpy during laser deposition is considered responsible for the formation of equiaxed grains at low laser powers. The microstructure within prior-β grains mainly consists of Widmanst?tten α laths separated by β-Ti, which is basically identical to those from pre-alloyed powders. Oxygen content of as-deposited samples was measured and the tensile testing was carried out. The results show that the oxygen content of as-deposited Ti-6Al-4V from blended elemental powders is only about 0.1wt.% and the mechanical properties are comparable to or even better than that of conventionally wrought material.
The microstructure and mechanical properties of laser solid formed Ti-6Al-4V from the blend of Ti, Al, and V powders were investigated. It is found that the macrostructure changes from equiaxed to columnar grains with the increase of the laser power, which is very different from that of the samples using pre-alloyed powders as cladding materials. The disturbance effect of the mixing enthalpy during laser deposition is considered responsible for the formation of equiaxed grains at low laser powers. The microstructure within prior-β grains mainly consists of Widmanst?tten α laths separated by β-Ti, which is basically identical to those from pre-alloyed powders. Oxygen content of as-deposited samples was measured and the tensile testing was carried out. The results show that the oxygen content of as-deposited Ti-6Al-4V from blended elemental powders is only about 0.1wt.% and the mechanical properties are comparable to or even better than that of conventionally wrought material.
2009, 38(4):579-582.
Abstract:
The cold workability of solution-treated TiNbZr biomedical β titanium alloy was investigated. TiNbZr alloy was fabricated by vacuum consumable arc melting furnace. Cold drawing was carried out for further deformation of the studied alloy. During cold drawing, the alloy exhibited excellent workability. Deformation twins appeared when the reduction of cold deformation was around 20%. Dislocations slipping contributed much to plastic deformation in further drawing. The ultimate tensile strength will go up to 1170 MPa and the elongation is larger than 10% when the reduction reaches 80%. Small grains ranging from 20 nm to 50 nm can be obtained when the reduction is 80%.
The cold workability of solution-treated TiNbZr biomedical β titanium alloy was investigated. TiNbZr alloy was fabricated by vacuum consumable arc melting furnace. Cold drawing was carried out for further deformation of the studied alloy. During cold drawing, the alloy exhibited excellent workability. Deformation twins appeared when the reduction of cold deformation was around 20%. Dislocations slipping contributed much to plastic deformation in further drawing. The ultimate tensile strength will go up to 1170 MPa and the elongation is larger than 10% when the reduction reaches 80%. Small grains ranging from 20 nm to 50 nm can be obtained when the reduction is 80%.
2009, 38(4):583-586.
Abstract:
Ba1-xKxBiO3 (BKBO) samples with 0.315 ￡ x ￡ 0.6 were synthesized at a relatively low temperature of 260 °C by molten salt method. The superconductivity was tested in the whole range of x value, the highest superconducting transition temperature Tc = 30.6 K at x = 0.4. X-ray Diffraction patterns reveal that small amount of impurity phase of BaCO3 were detected in BKBO which is attributed to the reactions between Ba(OH)2·8H2O and CO2 in air. The plate-like morphology of BKBO was observed from SEM images. For comparison, sol-gel method was also used in synthesizing Ba0.6K0.4BiO3 sample, but no single phase of BKBO was obtained. For the sample of Ba0.6K0.4BiO3 prepared by molten salt method, the thermostability was investigated by thermo- gravimetric analysis (TGA) and annealing treatment, and the sample was decomposed at 400 °C . The result showed that Ba0.6K0.4BiO3 was thermally unstable above 400 °C.
Ba1-xKxBiO3 (BKBO) samples with 0.315 ￡ x ￡ 0.6 were synthesized at a relatively low temperature of 260 °C by molten salt method. The superconductivity was tested in the whole range of x value, the highest superconducting transition temperature Tc = 30.6 K at x = 0.4. X-ray Diffraction patterns reveal that small amount of impurity phase of BaCO3 were detected in BKBO which is attributed to the reactions between Ba(OH)2·8H2O and CO2 in air. The plate-like morphology of BKBO was observed from SEM images. For comparison, sol-gel method was also used in synthesizing Ba0.6K0.4BiO3 sample, but no single phase of BKBO was obtained. For the sample of Ba0.6K0.4BiO3 prepared by molten salt method, the thermostability was investigated by thermo- gravimetric analysis (TGA) and annealing treatment, and the sample was decomposed at 400 °C . The result showed that Ba0.6K0.4BiO3 was thermally unstable above 400 °C.
2009, 38(4):587-593.
Abstract:
Glass-forming ability of multicomponent Gd (Tb)-Co-Al alloys was predicted by multicomponent Miedema model theory and equivalent bond parameter theory. The pre-designed alloy samples were prepared by casting the melt ingots into a water-cooled copper mould with various diameters such as 1, 3, 5 mm. The structure of the alloy samples were analyzed by X-ray diffraction. The glass transition, crystallization and melting behavior of the alloys were investigated by differential scanning calorimetry (DSC). The result shows that the multicomponent Miedema model theory and the equivalent bond parameter theory are effective on composition design of bulk amorphous alloys, and the experimental outcome approximately accords with the theoretical prediction.
Glass-forming ability of multicomponent Gd (Tb)-Co-Al alloys was predicted by multicomponent Miedema model theory and equivalent bond parameter theory. The pre-designed alloy samples were prepared by casting the melt ingots into a water-cooled copper mould with various diameters such as 1, 3, 5 mm. The structure of the alloy samples were analyzed by X-ray diffraction. The glass transition, crystallization and melting behavior of the alloys were investigated by differential scanning calorimetry (DSC). The result shows that the multicomponent Miedema model theory and the equivalent bond parameter theory are effective on composition design of bulk amorphous alloys, and the experimental outcome approximately accords with the theoretical prediction.
7 Infiltration Flux and Similarity Criterion during Centrifugal Casting Titanium Alloy Melts Feeding
2009, 38(4):594-598.
Abstract:
The quantitative formula of infiltration flux during titanium alloy melt feeding in centrifugal field was deducted. The infiltration flow mechanism in centrifugal field was analyzed. Based on the formula of infiltration flux and the similar physical simulation theory, the similarity criterion was presented. The results show that, the deduction of the formula of infiltration flux during titanium alloy melt feeding in centrifugal field can be divided into four stages in terms of Reynolds number, that is low-speed infiltration, Darcy infiltration, transient zone infiltration and high-speed infiltration. The feeding infiltration fluxes at four stages increase with increasing of rotation speed and centrifugal radius. The viscosity ratio of the model fluid to the titanium alloy melt is 0.365.
The quantitative formula of infiltration flux during titanium alloy melt feeding in centrifugal field was deducted. The infiltration flow mechanism in centrifugal field was analyzed. Based on the formula of infiltration flux and the similar physical simulation theory, the similarity criterion was presented. The results show that, the deduction of the formula of infiltration flux during titanium alloy melt feeding in centrifugal field can be divided into four stages in terms of Reynolds number, that is low-speed infiltration, Darcy infiltration, transient zone infiltration and high-speed infiltration. The feeding infiltration fluxes at four stages increase with increasing of rotation speed and centrifugal radius. The viscosity ratio of the model fluid to the titanium alloy melt is 0.365.
2009, 38(4):599-602.
Abstract:
Dynamic compression tests and projectile impact tests were used to investigate the adiabatic shear behavior of Mg-10Gd-2Y- 0.5Zr alloy. The microstructural characterization of the post-test specimen was studied by means of optical microscopy. Two kinds of adiabatic shear bands were found in the post-test specimens impacted by spherical bullet and Hopkinson pressure Bar. The bands formed in the process of projectile impact are “white” bands of width about 10 μm. The microhardness in the “white” band is obviously higher than that in the matrix. In addition, the “white” bands come into being only in the stable penetrating stage because of enough strain. Obvious deformation bands can form only at T=735 K in the process of Hopkinson compression. The cracks within a propagating shear band are induced by twins paralleling to the shear direction.
Dynamic compression tests and projectile impact tests were used to investigate the adiabatic shear behavior of Mg-10Gd-2Y- 0.5Zr alloy. The microstructural characterization of the post-test specimen was studied by means of optical microscopy. Two kinds of adiabatic shear bands were found in the post-test specimens impacted by spherical bullet and Hopkinson pressure Bar. The bands formed in the process of projectile impact are “white” bands of width about 10 μm. The microhardness in the “white” band is obviously higher than that in the matrix. In addition, the “white” bands come into being only in the stable penetrating stage because of enough strain. Obvious deformation bands can form only at T=735 K in the process of Hopkinson compression. The cracks within a propagating shear band are induced by twins paralleling to the shear direction.
2009, 38(4):603-606.
Abstract:
The purpose of the present study is to know the influences of thermo-mechanical processing and heat-treatment on the prior b-grain size of TC4 titanium alloy, and the influence of grain size on damage-tolerance properties is also discussed. The average b-grain sizes under different thermo-mechanical processing and solution treatment conditions were measured. Noticeable difference of b-grain growth behavior was found between α+b forged and b forged TC4 alloy under the same heat-treatment conditions. The exponential relationship between b-grain size and solution time was presented. The results show that b-grain size does not always increase with increasing of solution-treatment temperature; a limit value of the grain size will appear in certain temperature region. For different forging process, the fluctuation of the prior b -grain size is different. This phenomenon is discussed in terms of grain growth thermodynamics and kinetics laws. Damage-tolerance properties results show that grain size has noticeable influence on fatigue crack growth rate and fracture toughness property.
The purpose of the present study is to know the influences of thermo-mechanical processing and heat-treatment on the prior b-grain size of TC4 titanium alloy, and the influence of grain size on damage-tolerance properties is also discussed. The average b-grain sizes under different thermo-mechanical processing and solution treatment conditions were measured. Noticeable difference of b-grain growth behavior was found between α+b forged and b forged TC4 alloy under the same heat-treatment conditions. The exponential relationship between b-grain size and solution time was presented. The results show that b-grain size does not always increase with increasing of solution-treatment temperature; a limit value of the grain size will appear in certain temperature region. For different forging process, the fluctuation of the prior b -grain size is different. This phenomenon is discussed in terms of grain growth thermodynamics and kinetics laws. Damage-tolerance properties results show that grain size has noticeable influence on fatigue crack growth rate and fracture toughness property.
2009, 38(4):607-611.
Abstract:
Al-Zn-Mg-Cu-Zr alloys containing Yb were prepared by cast metallurgy. Effects of 0.30 wt% Yb additions on the recrystallization behavior and the performances of Al-Zn-Mg-Cu-Zr alloys were investigated by hardness and electric resistance measurement, tensile test, stress corrosion cracking test measurement, optical microscopy and transmission electron microscopy. The results show that the ytterbium additions to Al-Zn-Mg-Cu-Zr aluminum alloys will increase the recrystallization temperature, obviously enhance the resistance to stress corrosion cracking and the fracture toughness property, and slightly increase the strengths and ductility at T6 treatment. It is attributed to the dispersoids with Yb containing. Those dispersoids homogeneously distributed in the Al matrix strongly pin dislocation and subgrain boundaries, which can significantly retard the recrystallization by inhibiting the nucleation of recrystallization.
Al-Zn-Mg-Cu-Zr alloys containing Yb were prepared by cast metallurgy. Effects of 0.30 wt% Yb additions on the recrystallization behavior and the performances of Al-Zn-Mg-Cu-Zr alloys were investigated by hardness and electric resistance measurement, tensile test, stress corrosion cracking test measurement, optical microscopy and transmission electron microscopy. The results show that the ytterbium additions to Al-Zn-Mg-Cu-Zr aluminum alloys will increase the recrystallization temperature, obviously enhance the resistance to stress corrosion cracking and the fracture toughness property, and slightly increase the strengths and ductility at T6 treatment. It is attributed to the dispersoids with Yb containing. Those dispersoids homogeneously distributed in the Al matrix strongly pin dislocation and subgrain boundaries, which can significantly retard the recrystallization by inhibiting the nucleation of recrystallization.
2009, 38(4):612-616.
Abstract:
The microstructure and stress rupture properties of three experimental single crystal nickel superalloys with different Ti/Al ratios were investigated. The microstructure as-cast state and after heat treatment was analyzed by OPM and SEM. Partition ratio of alloy element in two phase and misfit degree were measured and analyzed by TEM with EDS. The results show that with increasing of Ti/Al ratio, the amount of g-g ￠ eutectic in interdendrtic region as-cast state increases slightly, the size of g ￠ phase in heat treated state decreases a little and the morphology turns regular and the misfit decreases. The change of Ti/Al ratio has no obvious effect on the transformation temperatures. The stress rupture life is improved gradually with increasing of Ti/Al ratio.
The microstructure and stress rupture properties of three experimental single crystal nickel superalloys with different Ti/Al ratios were investigated. The microstructure as-cast state and after heat treatment was analyzed by OPM and SEM. Partition ratio of alloy element in two phase and misfit degree were measured and analyzed by TEM with EDS. The results show that with increasing of Ti/Al ratio, the amount of g-g ￠ eutectic in interdendrtic region as-cast state increases slightly, the size of g ￠ phase in heat treated state decreases a little and the morphology turns regular and the misfit decreases. The change of Ti/Al ratio has no obvious effect on the transformation temperatures. The stress rupture life is improved gradually with increasing of Ti/Al ratio.
2009, 38(4):617-621.
Abstract:
Several strontium-incorporated nonstoichiometric hydroxyapatites with different contents of strontium were synthesized with a hydration process. Their phase structures, chemical compositions and grain sizes and morphologies were investigated by using XRD, FTIR and TEM to study their thermal ability at various firing temperatures. Results show that the incorporation of strontium into hydroxyapatite crystal by replacing equivalent calcium decreases its thermal stability under a given hydration condition and a same moral ratio of (Ca+Sr)/P. The decomposed product is the mixed calcium strontium phosphate ((Ca, Sr)3(PO4)2), whose decomposing temperature is lower than that of pure tricalcium phosphate. The more the content of strontium in place of calcium in hydroxyapatite is, the larger the amount of strontium incorporated into the crystal lattice of tricalcium strontium phosphate is. At elevated firing temperatures, the grains of strontium-incorporated hydroxyapatites and pure hydroxyapatite grow up gradually. However, below 1200 ℃, the grains of the former hydroxyapatite basically keep an equi-axed SrHA while those of the latter become irregular. At 1300 ℃, both hydroxyapatites are mainly composed of larger grains and few of small ones. The former is a grown apatite with irregular morphology and the latter is a decomposed mixed calcium phosphate or tricalcium strontium phosphate with spheric morphology.
Several strontium-incorporated nonstoichiometric hydroxyapatites with different contents of strontium were synthesized with a hydration process. Their phase structures, chemical compositions and grain sizes and morphologies were investigated by using XRD, FTIR and TEM to study their thermal ability at various firing temperatures. Results show that the incorporation of strontium into hydroxyapatite crystal by replacing equivalent calcium decreases its thermal stability under a given hydration condition and a same moral ratio of (Ca+Sr)/P. The decomposed product is the mixed calcium strontium phosphate ((Ca, Sr)3(PO4)2), whose decomposing temperature is lower than that of pure tricalcium phosphate. The more the content of strontium in place of calcium in hydroxyapatite is, the larger the amount of strontium incorporated into the crystal lattice of tricalcium strontium phosphate is. At elevated firing temperatures, the grains of strontium-incorporated hydroxyapatites and pure hydroxyapatite grow up gradually. However, below 1200 ℃, the grains of the former hydroxyapatite basically keep an equi-axed SrHA while those of the latter become irregular. At 1300 ℃, both hydroxyapatites are mainly composed of larger grains and few of small ones. The former is a grown apatite with irregular morphology and the latter is a decomposed mixed calcium phosphate or tricalcium strontium phosphate with spheric morphology.
2009, 38(4):622-626.
Abstract:
The effect of small addition of Ag, Mg on the microstructure and the aging characteristics of Al-3.5Cu-1.0Li alloy has been studied by mechanical testing and transmission electron microscopy. The results indicate that only sliver addition has almost no effect on the age-hardening and strengthening of the baseline alloy upon aging at 175 ℃. At peak aging state the main precipitates are both coarse T1 and θ′ phases for the Ag-bearing alloy and the baseline alloy. The Mg-containing alloy has a faster aging response and higher aging-strengthening effect than the baseline alloy. GP zone, θ′ and T1 are formed at different aging stages. The combined addition of Ag and Mg to the alloy greatly accelerates T1 precipitation, resulting in increasing density of T1 precipitates. The high volume fraction of T1 phase causes 2050 alloy having the highest strength. The independent and combined roles of small addition of Ag and Mg can be interpreted in terms of the solute-vacancy interaction and solute-solute atom interaction.
The effect of small addition of Ag, Mg on the microstructure and the aging characteristics of Al-3.5Cu-1.0Li alloy has been studied by mechanical testing and transmission electron microscopy. The results indicate that only sliver addition has almost no effect on the age-hardening and strengthening of the baseline alloy upon aging at 175 ℃. At peak aging state the main precipitates are both coarse T1 and θ′ phases for the Ag-bearing alloy and the baseline alloy. The Mg-containing alloy has a faster aging response and higher aging-strengthening effect than the baseline alloy. GP zone, θ′ and T1 are formed at different aging stages. The combined addition of Ag and Mg to the alloy greatly accelerates T1 precipitation, resulting in increasing density of T1 precipitates. The high volume fraction of T1 phase causes 2050 alloy having the highest strength. The independent and combined roles of small addition of Ag and Mg can be interpreted in terms of the solute-vacancy interaction and solute-solute atom interaction.
2009, 38(4):627-631.
Abstract:
The variations of the microscopic morphology and oxides of metal uranium were in-situ investigated in the range of 20~400 ℃ by optical metalloscopy (OM), Raman spectroscopy(RS) and atomic force microscopy(AFM). Experiments were performed in ambient air, dry air and saturated vapor, respectively. The corrosion products and some inclusions were identified. In ambient air, uranium adsorbed oxygen, water and carbon dioxide, and subsequently reacted with them resulting in forming uranium dioxide, uranyl compounds, uranium carbonate etc. Contrastively in dry air, reactive corroded spots appeared at the beginning of heating and cumulated gradually, and generated pitting, with a simultaneous constituent transformation from uranium dioxde to triuranium octoxide. Meanwhile, uranium dioxde was heated at a low rate in saturated vapor, resulting in a conversion to triuranium octoxide at the temperature of 260~280 ℃.
The variations of the microscopic morphology and oxides of metal uranium were in-situ investigated in the range of 20~400 ℃ by optical metalloscopy (OM), Raman spectroscopy(RS) and atomic force microscopy(AFM). Experiments were performed in ambient air, dry air and saturated vapor, respectively. The corrosion products and some inclusions were identified. In ambient air, uranium adsorbed oxygen, water and carbon dioxide, and subsequently reacted with them resulting in forming uranium dioxide, uranyl compounds, uranium carbonate etc. Contrastively in dry air, reactive corroded spots appeared at the beginning of heating and cumulated gradually, and generated pitting, with a simultaneous constituent transformation from uranium dioxde to triuranium octoxide. Meanwhile, uranium dioxde was heated at a low rate in saturated vapor, resulting in a conversion to triuranium octoxide at the temperature of 260~280 ℃.
2009, 38(4):632-636.
Abstract:
The hot deformation behaviors of TC11 alloy were investigated at temperature range of 800~1050 ℃ and strain rate range of 0.005~5 s-1. Based on dynamic materials modeling (DMM) the processing map was established. Combined with the microstructure observation the hot deformation mechanism of TC11 alloy was worked out. The results show that the globularization of lamella α is the main deformation mechanism at low strain rate (0.005~0.05 s-1) in the (α+β) phase field. The globularization intensities increasing obviously with decreasing of temperature and increasing of strain rate. The unstable flowing will occur at high strain rate (0.05~5 s-1), and shear crack and shear bands will take place. In the β phase field, the dynamic recrystallization occurs at low strain rate (0.005~0.05 s-1) and the dynamic recovery occurs at high strain rate (0.05~5 s-1). Furthermore, the flow instability maybe occur when the strain rate is higher than 0.1 s-1. The peak efficiency of power dissipation of about 57% is obtained at about 900 ℃ and 0.005 s-1.
The hot deformation behaviors of TC11 alloy were investigated at temperature range of 800~1050 ℃ and strain rate range of 0.005~5 s-1. Based on dynamic materials modeling (DMM) the processing map was established. Combined with the microstructure observation the hot deformation mechanism of TC11 alloy was worked out. The results show that the globularization of lamella α is the main deformation mechanism at low strain rate (0.005~0.05 s-1) in the (α+β) phase field. The globularization intensities increasing obviously with decreasing of temperature and increasing of strain rate. The unstable flowing will occur at high strain rate (0.05~5 s-1), and shear crack and shear bands will take place. In the β phase field, the dynamic recrystallization occurs at low strain rate (0.005~0.05 s-1) and the dynamic recovery occurs at high strain rate (0.05~5 s-1). Furthermore, the flow instability maybe occur when the strain rate is higher than 0.1 s-1. The peak efficiency of power dissipation of about 57% is obtained at about 900 ℃ and 0.005 s-1.
2009, 38(4):637-641.
Abstract:
Based on the results of notch 3PB fatigue tests and the observation of metallographic surfaces and fracture surfaces, it is found that for fatigue bending tests, the fatigue crack initiated and extended directly from the notch root, then extended step by step by the fatigue bending loads. When a crack extended to the length, which acts as a Griffiths crack and matches the loading stress, the crack propagated catastrophically through entire specimen. In the fatigue bending tests at the certain stress amplitude values, the crack length increased with increasing of fatigue unloading cycles, and the damage produced by fatigue process increased, the fatigue regions became wider, the fracture mechanism is that the fatigue regions propagate along a single orientation, the cleavage regions propagate dispersedly to different orientations. However, for shorter fatigue cycles the fracture mechanism is that initiation origins are produced at the notch root, then propagate dispersedly to final fracture. No any differences appear between the fatigue and the cleavage regions on the propagation path.
Based on the results of notch 3PB fatigue tests and the observation of metallographic surfaces and fracture surfaces, it is found that for fatigue bending tests, the fatigue crack initiated and extended directly from the notch root, then extended step by step by the fatigue bending loads. When a crack extended to the length, which acts as a Griffiths crack and matches the loading stress, the crack propagated catastrophically through entire specimen. In the fatigue bending tests at the certain stress amplitude values, the crack length increased with increasing of fatigue unloading cycles, and the damage produced by fatigue process increased, the fatigue regions became wider, the fracture mechanism is that the fatigue regions propagate along a single orientation, the cleavage regions propagate dispersedly to different orientations. However, for shorter fatigue cycles the fracture mechanism is that initiation origins are produced at the notch root, then propagate dispersedly to final fracture. No any differences appear between the fatigue and the cleavage regions on the propagation path.
2009, 38(4):642-646.
Abstract:
A firm joint between steel base and diamond was realized by using Ag-Cu-Ti brazing diamond in vacuum. The interface between diamond and filler and carbide formed on the diamond surface was analyzed by using SEM, EDS, XRD and Raman Spectroscope. Results showed that carbide layer was formed as a result of the reaction between Ti and diamond, and discontinuous-lump-like TiC carbide with less than 1 μm on the surface of diamond appeared. There was almost no heat damage in the brazed diamond. The maximal tensile stress in the diamond located at the top reached 60 MPa, while the maximal compressive stress located at the bottom was 120 MPa. As a result, the metallurgical bonding was obtained between filler metal and diamond through the forming the serial of diamond-TiC-filler layer.
A firm joint between steel base and diamond was realized by using Ag-Cu-Ti brazing diamond in vacuum. The interface between diamond and filler and carbide formed on the diamond surface was analyzed by using SEM, EDS, XRD and Raman Spectroscope. Results showed that carbide layer was formed as a result of the reaction between Ti and diamond, and discontinuous-lump-like TiC carbide with less than 1 μm on the surface of diamond appeared. There was almost no heat damage in the brazed diamond. The maximal tensile stress in the diamond located at the top reached 60 MPa, while the maximal compressive stress located at the bottom was 120 MPa. As a result, the metallurgical bonding was obtained between filler metal and diamond through the forming the serial of diamond-TiC-filler layer.
2009, 38(4):647-650.
Abstract:
Using X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) the mechanism of pore formation of superconducting MgB2 synthesized at low temperature by in-situ process was studied. It is showed that B powder was embedded into Mg powder after the ball-milling process. MgB2 phase formed firstly in these embedded areas. The closed pores in MgB2 bulks are caused by kirkendall effect due to the different diffusion speeds of Mg and B atoms. The open pores are caused by Mg gas.
Using X-ray diffraction (XRD), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) the mechanism of pore formation of superconducting MgB2 synthesized at low temperature by in-situ process was studied. It is showed that B powder was embedded into Mg powder after the ball-milling process. MgB2 phase formed firstly in these embedded areas. The closed pores in MgB2 bulks are caused by kirkendall effect due to the different diffusion speeds of Mg and B atoms. The open pores are caused by Mg gas.
2009, 38(4):651-654.
Abstract:
In this study, V-7.4Zr-7.4Ti-7.4Ni alloy was prepared from high-pure Zr, V, Ti and Ni metal powders. The microstructure of alloy was investigated by using optical metallograph, scanning electron microscope (SEM) and XRD. The hydrogen desorbing PCT curves have been obtained at different temperatures. The thermodynamic parameters were calculated according to the chemical reaction equilibrium equations. It is found that the microstructure of alloy is consisted of two phases, a main phase of V based solid solution phase, and the second phase of Laves phase. The alloy has remarkable hydrogen storage properties at room temperature and 353 K, the maximum hydrogen desorbing capacities are 3.11 wt% and 2.31 wt%, respectively. From the thermodynamics study it is found that the V based solid solution phase is the primitive phase for desorbing the hydrogen and has great influence on the formation of wide flat pressure plateaus on the PCT curve; the equilibrium temperature of the hydrogen desorbing reaction was calculated to be 358.4 K
In this study, V-7.4Zr-7.4Ti-7.4Ni alloy was prepared from high-pure Zr, V, Ti and Ni metal powders. The microstructure of alloy was investigated by using optical metallograph, scanning electron microscope (SEM) and XRD. The hydrogen desorbing PCT curves have been obtained at different temperatures. The thermodynamic parameters were calculated according to the chemical reaction equilibrium equations. It is found that the microstructure of alloy is consisted of two phases, a main phase of V based solid solution phase, and the second phase of Laves phase. The alloy has remarkable hydrogen storage properties at room temperature and 353 K, the maximum hydrogen desorbing capacities are 3.11 wt% and 2.31 wt%, respectively. From the thermodynamics study it is found that the V based solid solution phase is the primitive phase for desorbing the hydrogen and has great influence on the formation of wide flat pressure plateaus on the PCT curve; the equilibrium temperature of the hydrogen desorbing reaction was calculated to be 358.4 K
2009, 38(4):655-658.
Abstract:
The uniaxial isothermal hot compression test of AZ61 magnesium alloy was carried out on Gleeble-1500D thermal-mechanical simulator, the flow stress-strain curves and other information of dynamic recrystallization were investigated by numerical analysis. The relations between Z and other characteristic values of dynamic recrystallization, including peak stress, peak strain and grain size, were developed by regression analysis. The numerical simulation model of flow stress was introduced, its predicted values were proved to be close to the measured values with errors not more than 10%. The errors between predicted values and measured values for grain size were not more than 5%.
The uniaxial isothermal hot compression test of AZ61 magnesium alloy was carried out on Gleeble-1500D thermal-mechanical simulator, the flow stress-strain curves and other information of dynamic recrystallization were investigated by numerical analysis. The relations between Z and other characteristic values of dynamic recrystallization, including peak stress, peak strain and grain size, were developed by regression analysis. The numerical simulation model of flow stress was introduced, its predicted values were proved to be close to the measured values with errors not more than 10%. The errors between predicted values and measured values for grain size were not more than 5%.
2009, 38(4):659-662.
Abstract:
In order to study on the influence of parameters on process of warm compaction of molybdenum powder, a finite element method (FEM) model for molybdenum powder has been established using the elasto-plasticity FEM software. Warm compaction process of three-dimensional (3-D) cylinder was simulated on by FEM. The distributions of the density and the stress inside the compacts, the longitudinal and horizontal flowing of molybdenum particles were investigated by means of the simulation results. The reliability of FEM model was proved by the experiment, and the effects of the technology and material parameters on the molybdenum powder compaction were analyzed. The results show that the distributions of the relative density and the stress are very close at the top, the longitudinal section and the lateral wall of the compacts during the warm compaction.
In order to study on the influence of parameters on process of warm compaction of molybdenum powder, a finite element method (FEM) model for molybdenum powder has been established using the elasto-plasticity FEM software. Warm compaction process of three-dimensional (3-D) cylinder was simulated on by FEM. The distributions of the density and the stress inside the compacts, the longitudinal and horizontal flowing of molybdenum particles were investigated by means of the simulation results. The reliability of FEM model was proved by the experiment, and the effects of the technology and material parameters on the molybdenum powder compaction were analyzed. The results show that the distributions of the relative density and the stress are very close at the top, the longitudinal section and the lateral wall of the compacts during the warm compaction.
2009, 38(4):663-666.
Abstract:
The pseudopotential method and the generalized gradient approximation have been employed to calculate the elastic constant, cohesive energy and electronic structure of β, α″ and ω metastable phases in the Ti-25at%Nb alloy. The phase stability of β, α″ and ω phases is discussed adopting these calculated results. The results show that all of the β, α″ and ω phases satisfy the criteria of elastic stability. The phase stability of α″ phase is the highest and that of β phase the lowest among β, α″ and ω phases. The results further show that the Young’s modulus of ω phase is the highest and that of β phase the lowest in the Ti-25at%Nb alloy.
The pseudopotential method and the generalized gradient approximation have been employed to calculate the elastic constant, cohesive energy and electronic structure of β, α″ and ω metastable phases in the Ti-25at%Nb alloy. The phase stability of β, α″ and ω phases is discussed adopting these calculated results. The results show that all of the β, α″ and ω phases satisfy the criteria of elastic stability. The phase stability of α″ phase is the highest and that of β phase the lowest among β, α″ and ω phases. The results further show that the Young’s modulus of ω phase is the highest and that of β phase the lowest in the Ti-25at%Nb alloy.
2009, 38(4):667-670.
Abstract:
The effect of aging treatment on the mechanical properties, the electrical conductivity and the microstructure of Pd-Ag-Sn-In-Zn alloy were studied. The result show that the aging process of the alloy after solution treatment and cold deformation was controlled by both precipitation of the supersaturated solid solution and recrystallization of the matrix. The high strength comes from strain hardening and precipitation strengthening. The change of electrical resistivity was effected by the precipitation and the recrystallization.
The effect of aging treatment on the mechanical properties, the electrical conductivity and the microstructure of Pd-Ag-Sn-In-Zn alloy were studied. The result show that the aging process of the alloy after solution treatment and cold deformation was controlled by both precipitation of the supersaturated solid solution and recrystallization of the matrix. The high strength comes from strain hardening and precipitation strengthening. The change of electrical resistivity was effected by the precipitation and the recrystallization.
2009, 38(4):671-676.
Abstract:
The fatigue and neutral salt spray corrosion resistance for bare and coated high strength steel were investigated in this paper. The results indicated that WC-17Co and WC-10Co4Cr coatings led to significant increase of fatigue resistance compared with the substrate. There were also comparably similar cycles to failure for the bare and the coated substrates even though the stress which was WC-based coatings shouldered was taken into account. The lower cycles to the failure for WC-10Co4Cr coated substrate than those for WC-17Co coated substrate were attributed to embeding of blasted alumina grit on the substrate surface, which resulted in the great decrease of the cycles to failure. Both WC coatings produced no negative effect on the fatigue performance of 300M steel. The neutral salt spray corrosion resistance for 300M steel substrate was significantly improved after coating process, especially for WC-10Co4Cr coating. As a conclusion, HVAF WC-10Co4Cr coated high strength steel exhibited better performances in both fatigue and neutral salt spray corrosion resistance than that of the substrate, and WC-10Co4Cr coating was a better candidate to chrome plating.
The fatigue and neutral salt spray corrosion resistance for bare and coated high strength steel were investigated in this paper. The results indicated that WC-17Co and WC-10Co4Cr coatings led to significant increase of fatigue resistance compared with the substrate. There were also comparably similar cycles to failure for the bare and the coated substrates even though the stress which was WC-based coatings shouldered was taken into account. The lower cycles to the failure for WC-10Co4Cr coated substrate than those for WC-17Co coated substrate were attributed to embeding of blasted alumina grit on the substrate surface, which resulted in the great decrease of the cycles to failure. Both WC coatings produced no negative effect on the fatigue performance of 300M steel. The neutral salt spray corrosion resistance for 300M steel substrate was significantly improved after coating process, especially for WC-10Co4Cr coating. As a conclusion, HVAF WC-10Co4Cr coated high strength steel exhibited better performances in both fatigue and neutral salt spray corrosion resistance than that of the substrate, and WC-10Co4Cr coating was a better candidate to chrome plating.
2009, 38(4):677-680.
Abstract:
Two Mg-Nd-Pr alloys were prepared adopting different cooling methods, and the microstructural characteristics and phase structure of both alloys were examined by transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The results show that the crystalline grain size is decreased greatly under the condition of melt-spin, the supersaturated α-Mg solid solution is developed, and the mechanical properties of Mg-Nd-Pr alloy are increased remarkably. The alloying elements will precipitate along the grain boundaries in a state of slow cooling owing to lower solubility for Nd, Pr in α-Mg phase at room temperature. The phase composition of such alloy includes α-Mg, Mg41Nd5 and Mg12Pr. Mg41Nd5 and Mg12Pr are distributed in the grain boundaries. At the same time, many twins within the grains are observed.
Two Mg-Nd-Pr alloys were prepared adopting different cooling methods, and the microstructural characteristics and phase structure of both alloys were examined by transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The results show that the crystalline grain size is decreased greatly under the condition of melt-spin, the supersaturated α-Mg solid solution is developed, and the mechanical properties of Mg-Nd-Pr alloy are increased remarkably. The alloying elements will precipitate along the grain boundaries in a state of slow cooling owing to lower solubility for Nd, Pr in α-Mg phase at room temperature. The phase composition of such alloy includes α-Mg, Mg41Nd5 and Mg12Pr. Mg41Nd5 and Mg12Pr are distributed in the grain boundaries. At the same time, many twins within the grains are observed.
2009, 38(4):681-685.
Abstract:
Based on the principle that the aligned precipitation of second phase can improve shape memory effect (SME), the following effects were investigated, including the effects of different deformation temperatures on the amount and the structure of g /e interface, on the amount and orientation of the second precipitation phase after subsequent aging, and the effects of whick on the martensite transformation and SME. The SEM analysis shows that no g /e interfaces were produced after deformation at the temperature far higher than Ms , and few carbides precipitated after ageing. Much more g /e interfaces were produced after deformation at temperature near Ms , and much more directional carbides precipitated after ageing. With further decreasing the deformation temperature to Ms, some g /e interfaces intersected and carbides precipitated along different directions after ageing. TEM analysis shows that the thick stress-induced martensite plates had the uniform orientation in the 5% preformed alloys with orientationaly precipitated carbides. The reason is that Cr23C6 and strain fields produced by Cr23C6 will restrain martensite transformation and avoid the intersection among martensite plates thus remarkably improve the reversibility of stress-induced martensite.
Based on the principle that the aligned precipitation of second phase can improve shape memory effect (SME), the following effects were investigated, including the effects of different deformation temperatures on the amount and the structure of g /e interface, on the amount and orientation of the second precipitation phase after subsequent aging, and the effects of whick on the martensite transformation and SME. The SEM analysis shows that no g /e interfaces were produced after deformation at the temperature far higher than Ms , and few carbides precipitated after ageing. Much more g /e interfaces were produced after deformation at temperature near Ms , and much more directional carbides precipitated after ageing. With further decreasing the deformation temperature to Ms, some g /e interfaces intersected and carbides precipitated along different directions after ageing. TEM analysis shows that the thick stress-induced martensite plates had the uniform orientation in the 5% preformed alloys with orientationaly precipitated carbides. The reason is that Cr23C6 and strain fields produced by Cr23C6 will restrain martensite transformation and avoid the intersection among martensite plates thus remarkably improve the reversibility of stress-induced martensite.
2009, 38(4):686-690.
Abstract:
Nanocrystalline Ti-Al composite powders with composition of Ti-47Al (at%) and Ti-45Al-2Cr-2Nb-1B-0.5Ta (at%) were prepared by double-steps balll milling (ball milling+heat treatment+ball milling) using elemental powders. The as prepared and heat treated powders were analyzed and characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), differential thermal analysis (DTA) and particle-size distribution analyzer. The results demonstrated that high-quality composite powders with low contaminant, uniform size distribution and homogeneous elements dispersion could be obtained by the double-steps ball milling. The composite Ti/Al powders prepared by primary ball milling (6 h) were uniform. Ti3Al、Ti、Al3Ti and TiAl phases were found after heat treatment (700 ℃, 2 h) while Al phase disappeared. The fined grain size and particle size were further reduced by subsequent ball milling.
Nanocrystalline Ti-Al composite powders with composition of Ti-47Al (at%) and Ti-45Al-2Cr-2Nb-1B-0.5Ta (at%) were prepared by double-steps balll milling (ball milling+heat treatment+ball milling) using elemental powders. The as prepared and heat treated powders were analyzed and characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), differential thermal analysis (DTA) and particle-size distribution analyzer. The results demonstrated that high-quality composite powders with low contaminant, uniform size distribution and homogeneous elements dispersion could be obtained by the double-steps ball milling. The composite Ti/Al powders prepared by primary ball milling (6 h) were uniform. Ti3Al、Ti、Al3Ti and TiAl phases were found after heat treatment (700 ℃, 2 h) while Al phase disappeared. The fined grain size and particle size were further reduced by subsequent ball milling.
2009, 38(4):691-695.
Abstract:
The V2O5 thin film was prepared on the substrates of Si glass and commercial glass by the sol-gel technique. The samples prepared were annealed in air atmosphere at different temperatures. The microstructure, the morphology and optical properties of V2O5 thin films were studied by XRD, SEM and spectrophotometer. The results of XRD and SEM indicate that the better crystalline states and orientation with V2O5 (001) and (200) after annealing can be obtained, and the grain homogeneity on nano-V2O5 film surface can be improved through proper increasing of annealing temperatures; The results of transmission and absorption spectra show that a red shift will occur at the absorption edges of V2O5 films, and optical band gaps are shortened gradually with the increase of annealing temperature.
The V2O5 thin film was prepared on the substrates of Si glass and commercial glass by the sol-gel technique. The samples prepared were annealed in air atmosphere at different temperatures. The microstructure, the morphology and optical properties of V2O5 thin films were studied by XRD, SEM and spectrophotometer. The results of XRD and SEM indicate that the better crystalline states and orientation with V2O5 (001) and (200) after annealing can be obtained, and the grain homogeneity on nano-V2O5 film surface can be improved through proper increasing of annealing temperatures; The results of transmission and absorption spectra show that a red shift will occur at the absorption edges of V2O5 films, and optical band gaps are shortened gradually with the increase of annealing temperature.
2009, 38(4):696-699.
Abstract:
The method of solid-gas reaction milling was used to prepare nanocrystalline MgH2 powder. The hydrogen absorption kinetics of pure Mg during reaction milling was measured, and the powder morphology and phase structure evolution were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), respectively. It was found, upon milling in hydrogen, the process of Mg absorbing hydrogen presented a three-stages, i.e., slow-fast-saturation, whose phase compositions corresponded to Mg(H), Mg(H)+MgH2 and MgH2, respectively. By milling for 21 h under H2 atmosphere at 0.5 MPa, Mg could be fully hydrided into nanocrystalline MgH2 powder with an average particle size of 1~3 μm and crystallite grain size of about 10 nm, respectively. Such nanocrystalline MgH2 presented the hydrogen capacity as high as 7.03 wt%.
The method of solid-gas reaction milling was used to prepare nanocrystalline MgH2 powder. The hydrogen absorption kinetics of pure Mg during reaction milling was measured, and the powder morphology and phase structure evolution were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), respectively. It was found, upon milling in hydrogen, the process of Mg absorbing hydrogen presented a three-stages, i.e., slow-fast-saturation, whose phase compositions corresponded to Mg(H), Mg(H)+MgH2 and MgH2, respectively. By milling for 21 h under H2 atmosphere at 0.5 MPa, Mg could be fully hydrided into nanocrystalline MgH2 powder with an average particle size of 1~3 μm and crystallite grain size of about 10 nm, respectively. Such nanocrystalline MgH2 presented the hydrogen capacity as high as 7.03 wt%.
2009, 38(4):700-704.
Abstract:
Aluminum oxide films doped with Ce were prepared by the medium frequency reactive magnetron sputtering technique. Ce3+ content, the composition and the crystalline structure of the films were characterized by EDS, XRD and AES. The results show that the photoluminescence emission of these films shows peaks at the range of 374~405 nm which are associated with 5d to 4f transitions of Ce. The relative intensities of these peaks are strongly dependent on the amount of Ce incorporated in the films, and the substrate temperature during deposition. It is proposed that the light emission observed is generated by the luminescent center associated with cerium chloride molecular rather than the doped cerium ions (Ce3+). With the increase of Ce concentration, the photoluminescence peaks shift to lower energy, it would be associated with the existence of element chrorine in the films.
Aluminum oxide films doped with Ce were prepared by the medium frequency reactive magnetron sputtering technique. Ce3+ content, the composition and the crystalline structure of the films were characterized by EDS, XRD and AES. The results show that the photoluminescence emission of these films shows peaks at the range of 374~405 nm which are associated with 5d to 4f transitions of Ce. The relative intensities of these peaks are strongly dependent on the amount of Ce incorporated in the films, and the substrate temperature during deposition. It is proposed that the light emission observed is generated by the luminescent center associated with cerium chloride molecular rather than the doped cerium ions (Ce3+). With the increase of Ce concentration, the photoluminescence peaks shift to lower energy, it would be associated with the existence of element chrorine in the films.
Zhang Yongjun
,
Zhang Pingxiang
,
Li Chengshan
,
Zheng Huiling
,
Yu Zeming
,
Lu Yafeng
,
Chen Shaokai
2009, 38(4):705-708.
Abstract:
A Ni-5at%W ingot was prepared by a combination process of PM and remelting. Afterwards the ingot was swaged and drawn into wires which were finally cold-rolled into trips with 70 μm thickness. A recrystallization annealing for the substrate trip was carried out at different temperatures (800~1300 ℃) for different time (0~3 h). Cube texture in the substrate was evaluated by means of X-ray diffraction and electron back-scatter diffraction, meanwhile, the hardness of the substrate was characterized. It was found that the recrystallization process was almost completed below 800 ℃ and the fraction of cube texture did not obviously change upon annealing time prolonging for 1~3 h at 980 ℃. Strong cube texture was obtained after annealing at 1100 ℃ and 1300 ℃, and the surface area fraction of the grains orientated within 8° around ideal {001}<100> texture were about 93% and 99.8% of the total grains, respectively. After the substrate trip was annealed at and below 1300 ℃, its microstructure was uniform, no abnormal grain growth was found, and the cube texture exhibited good stability at high temperature. However, abnormal grain growth and other texture components appeared in the substrate trip after annealed at 1400 ℃.
A Ni-5at%W ingot was prepared by a combination process of PM and remelting. Afterwards the ingot was swaged and drawn into wires which were finally cold-rolled into trips with 70 μm thickness. A recrystallization annealing for the substrate trip was carried out at different temperatures (800~1300 ℃) for different time (0~3 h). Cube texture in the substrate was evaluated by means of X-ray diffraction and electron back-scatter diffraction, meanwhile, the hardness of the substrate was characterized. It was found that the recrystallization process was almost completed below 800 ℃ and the fraction of cube texture did not obviously change upon annealing time prolonging for 1~3 h at 980 ℃. Strong cube texture was obtained after annealing at 1100 ℃ and 1300 ℃, and the surface area fraction of the grains orientated within 8° around ideal {001}<100> texture were about 93% and 99.8% of the total grains, respectively. After the substrate trip was annealed at and below 1300 ℃, its microstructure was uniform, no abnormal grain growth was found, and the cube texture exhibited good stability at high temperature. However, abnormal grain growth and other texture components appeared in the substrate trip after annealed at 1400 ℃.
2009, 38(4):709-712.
Abstract:
The preparation technology of electrodeposited Mg-Ni hydrogen absorbing alloy was studied by using orthogonal tests in this paper. The results show that according to the purpose of higher special discharge capacity, the descending order of the influencing factors is temperature, content of MgCl2 , content of NaH2PO2 , current density and content of C6H5Na3O7. The discharge capacity of the alloy reaches 250 mAh/g under the depositing conditions of current density 100 mA/cm2, temperature 45 ℃, content of MgCl2 180 g/L, NaH2PO2·H2O 70 g/L , C6H5Na3O7·H2O 60 g/L , NiCl2 30 g/L, H3BO3 30 g/L and pH 3 ~ 4. It has obvious charge-discharge platforms and its capacity reaches the maximum in the first charge-discharge cycle but falls fast with the increase of cycles. The result of XRD shows that the alloy is composed of amorphous Mg2Ni + Ni phases.
The preparation technology of electrodeposited Mg-Ni hydrogen absorbing alloy was studied by using orthogonal tests in this paper. The results show that according to the purpose of higher special discharge capacity, the descending order of the influencing factors is temperature, content of MgCl2 , content of NaH2PO2 , current density and content of C6H5Na3O7. The discharge capacity of the alloy reaches 250 mAh/g under the depositing conditions of current density 100 mA/cm2, temperature 45 ℃, content of MgCl2 180 g/L, NaH2PO2·H2O 70 g/L , C6H5Na3O7·H2O 60 g/L , NiCl2 30 g/L, H3BO3 30 g/L and pH 3 ~ 4. It has obvious charge-discharge platforms and its capacity reaches the maximum in the first charge-discharge cycle but falls fast with the increase of cycles. The result of XRD shows that the alloy is composed of amorphous Mg2Ni + Ni phases.
2009, 38(4):713-716.
Abstract:
Using the mixed powders of Cu, Ti and graphite, Cf/SiC composite was brazed to Ti-6Al-4V alloy under vacuum condition. The joint microstructures were investigated by X-ray diffractrometry, scanning electron microscopy and energy dispersive spectrometry. The results showed that fine brazed joints of Cf/SiC composite/Ti alloy were acquired at 900~950 ℃ for 5~30 min using Cu-(15~30wt%)Ti with the addition of proper amount of graphite powder as brazing alloy. In-situ synthetic TiC which reduces the thermal stress significantly was obtained during vacuum brazing. TiC reaction layer around surplus graphite and TiC particles in the bonding layer was synthesized by interdiffusing of C element and Ti element in the liquid bonding layer. The reaction rate could be controlled by the diffusion rate of C element from graphite particles to liquid bonding layer.
Using the mixed powders of Cu, Ti and graphite, Cf/SiC composite was brazed to Ti-6Al-4V alloy under vacuum condition. The joint microstructures were investigated by X-ray diffractrometry, scanning electron microscopy and energy dispersive spectrometry. The results showed that fine brazed joints of Cf/SiC composite/Ti alloy were acquired at 900~950 ℃ for 5~30 min using Cu-(15~30wt%)Ti with the addition of proper amount of graphite powder as brazing alloy. In-situ synthetic TiC which reduces the thermal stress significantly was obtained during vacuum brazing. TiC reaction layer around surplus graphite and TiC particles in the bonding layer was synthesized by interdiffusing of C element and Ti element in the liquid bonding layer. The reaction rate could be controlled by the diffusion rate of C element from graphite particles to liquid bonding layer.
2009, 38(4):717-721.
Abstract:
Vanadium dioxide (VO2) films were deposited on 300 ℃ SiO2 coated soda-lime glass substrates by rf-reactive magnetron sputtering. The influences of sputtering time (from 5 to 35 min) on the microstructure, the morphology and electrical and optical performances of the films were investigated and characterized by X-ray diffraction, scanning electron microscopy, resistance testing, ultraviolet-visible spectrometry and doubled beam infrared spectrometry. The obtained results show that the films present a distortion rutile structure and preferred orientation of (011), the crystalline growth trends to completion, and the grains size increase with the increase of sputtering time. Heat-treating the films from room temperature to 90 ℃ for 35 min, the change of the film sheet resistance is nearly 103 magnitudes. The films have low visible transmittance due to the intrinsic absorption, and the visible transmittance decreases with the increase of film thickness. In the range from 1500 to 4000 cm-1, the infrared reflectance of the films heat-treated at 20 ℃ and 80 ℃ shows that the variation of reflectance increases with the increase of film thickness, and the maximum of which is as high as 59%.
Vanadium dioxide (VO2) films were deposited on 300 ℃ SiO2 coated soda-lime glass substrates by rf-reactive magnetron sputtering. The influences of sputtering time (from 5 to 35 min) on the microstructure, the morphology and electrical and optical performances of the films were investigated and characterized by X-ray diffraction, scanning electron microscopy, resistance testing, ultraviolet-visible spectrometry and doubled beam infrared spectrometry. The obtained results show that the films present a distortion rutile structure and preferred orientation of (011), the crystalline growth trends to completion, and the grains size increase with the increase of sputtering time. Heat-treating the films from room temperature to 90 ℃ for 35 min, the change of the film sheet resistance is nearly 103 magnitudes. The films have low visible transmittance due to the intrinsic absorption, and the visible transmittance decreases with the increase of film thickness. In the range from 1500 to 4000 cm-1, the infrared reflectance of the films heat-treated at 20 ℃ and 80 ℃ shows that the variation of reflectance increases with the increase of film thickness, and the maximum of which is as high as 59%.
2009, 38(4):722-725.
Abstract:
The polyurethane sponge impregnation method was used to prepare copper foam with a high porosity (85%~95%) and open-cell structure. The sintering technology was discussed in accordance with the characteristics of this method. Additionally, the composition of copper foam was analyzed and the microstructure and compressive performances of copper foam fabricated by single-impregnating and double-impregnating were measured and compared. It is indicated that the microstructure at cell wall of the copper foam can be changed and the porosity decreases slightly after treatment of double impregnating, but the compressive stress level increases from 0.5 MPa to 1 MPa which is of great importance for improving the performance of material energy absorption.
The polyurethane sponge impregnation method was used to prepare copper foam with a high porosity (85%~95%) and open-cell structure. The sintering technology was discussed in accordance with the characteristics of this method. Additionally, the composition of copper foam was analyzed and the microstructure and compressive performances of copper foam fabricated by single-impregnating and double-impregnating were measured and compared. It is indicated that the microstructure at cell wall of the copper foam can be changed and the porosity decreases slightly after treatment of double impregnating, but the compressive stress level increases from 0.5 MPa to 1 MPa which is of great importance for improving the performance of material energy absorption.
2009, 38(4):726-729.
Abstract:
Nano-crystalline SmN/α-Fe and SmO/α-Fe double phase composite with electromagnetic (EM) wave absorption property was prepared by hydrogenization and dehydrogenization followed by nitrogenation and oxidation treatment. The results show that the measured real part and imaginary part of dielectric constant for SmN/α-Fe are higher than that for SmO/α-Fe, but the complex EM permeability of SmO/α-Fe is higher than that of SmN/α-Fe, their imaginary parts of the relative permeability μ″ exhibit two resonant peaks and high values over the 0.5~18 GHz range. Because the match between the permeability and the dielectric constant for SmO/α-Fe is better than that for SmN/α-Fe, therefore the former has better EM wave absorption property and its RL (reflection loss) is less than –20 dB with absorber match thickness of 1.60~3.95 mm in the frequency range of 3.30~10.65 GHz. The minimum RL is –50 dB, absorber match thickness is 2.92 mm at 4.8 GHz.
Nano-crystalline SmN/α-Fe and SmO/α-Fe double phase composite with electromagnetic (EM) wave absorption property was prepared by hydrogenization and dehydrogenization followed by nitrogenation and oxidation treatment. The results show that the measured real part and imaginary part of dielectric constant for SmN/α-Fe are higher than that for SmO/α-Fe, but the complex EM permeability of SmO/α-Fe is higher than that of SmN/α-Fe, their imaginary parts of the relative permeability μ″ exhibit two resonant peaks and high values over the 0.5~18 GHz range. Because the match between the permeability and the dielectric constant for SmO/α-Fe is better than that for SmN/α-Fe, therefore the former has better EM wave absorption property and its RL (reflection loss) is less than –20 dB with absorber match thickness of 1.60~3.95 mm in the frequency range of 3.30~10.65 GHz. The minimum RL is –50 dB, absorber match thickness is 2.92 mm at 4.8 GHz.
2009, 38(4):730-733.
Abstract:
The densification of W-Cu thin green by continuous liquid phase sintering was studied by means of DTA, XRD, density measurement and microstructure observation. The theory of pore reverse direction migration can explain exactly the densification behaviour of W-Cu thin green in the process continuous liquid phase sintering.
The densification of W-Cu thin green by continuous liquid phase sintering was studied by means of DTA, XRD, density measurement and microstructure observation. The theory of pore reverse direction migration can explain exactly the densification behaviour of W-Cu thin green in the process continuous liquid phase sintering.
2009, 38(4):734-737.
Abstract:
A biomorphic carbon retaining its anatomical feature was prepared by carbonizing wood through controlling heating rates. Then Pt particles were electrodeposited onto the synthesized carbon materials. The C/Pt composite materials were modified onto the surface of GC electrode by means of chitosan. The modified electrode showed good response to H2O2 due to the good electrochemical properties of the hybrid.
A biomorphic carbon retaining its anatomical feature was prepared by carbonizing wood through controlling heating rates. Then Pt particles were electrodeposited onto the synthesized carbon materials. The C/Pt composite materials were modified onto the surface of GC electrode by means of chitosan. The modified electrode showed good response to H2O2 due to the good electrochemical properties of the hybrid.
2009, 38(4):738-741.
Abstract:
The mixed powder of W-40Cu ball-milled for different time was cold-pressed into a compact, then it was hot-extruded into W-40Cu composite. The effects of the mechanical ball milling on the microstructure and the performance of the composite were investigated. The results show that ball milling for long time has unbenefical effect on the microstructure and the performance of the composite. With prolonging of ball milling, the inhomogeneity of tungsten phase size within the composite appears obviously, the density and specific conductance of the composite decrease, and the hardness increases.
The mixed powder of W-40Cu ball-milled for different time was cold-pressed into a compact, then it was hot-extruded into W-40Cu composite. The effects of the mechanical ball milling on the microstructure and the performance of the composite were investigated. The results show that ball milling for long time has unbenefical effect on the microstructure and the performance of the composite. With prolonging of ball milling, the inhomogeneity of tungsten phase size within the composite appears obviously, the density and specific conductance of the composite decrease, and the hardness increases.
2009, 38(4):742-747.
Abstract:
The current application of microwave energy to preparing metallic products is one of the important projects in materials research. With analyzing the interaction between microwave field and metals, the microwave energy applications in intermetallic synthesis, metallic PM parts sintering, molting and joining of metallic materials etc. are introduced in this review.
The current application of microwave energy to preparing metallic products is one of the important projects in materials research. With analyzing the interaction between microwave field and metals, the microwave energy applications in intermetallic synthesis, metallic PM parts sintering, molting and joining of metallic materials etc. are introduced in this review.
2009, 38(4):748-752.
Abstract:
Silver coated glass fiber has some attractive performances such as antistatic, anti-electromagnetic-radiation, deodorization, antibacterium and radar-reflection. The technology of the electroless silver plating on glass fiber has the advantages of simple fabrication, and uniform coating with strong adhesion, and receives more and more attention in recent years. The preparation methods and applications of elctroless silver plating on glass fiber are introduced, the influence factors of electroless silver plating on glass fiber are discussed in detail. Finally some problems in preparation and application are suggested.
Silver coated glass fiber has some attractive performances such as antistatic, anti-electromagnetic-radiation, deodorization, antibacterium and radar-reflection. The technology of the electroless silver plating on glass fiber has the advantages of simple fabrication, and uniform coating with strong adhesion, and receives more and more attention in recent years. The preparation methods and applications of elctroless silver plating on glass fiber are introduced, the influence factors of electroless silver plating on glass fiber are discussed in detail. Finally some problems in preparation and application are suggested.
