Volume 42,Issue 6,2013 Table of Contents
2013, 42(6):1101-1104.
Abstract:
A glow plasma carburizing technique was applied to strengthen the surface of the Ti-6Al-4V alloy. The alloy was carburized at 950 oC and 30~35 Pa for 3 h using plasma of Ar gas. Graphite rod was employed as carbon supply to avoid the hydrogen brittleness which is common in traditional gas carbonization. The carburized layer was examined by an optical microscope (OM), field emission scanning electron microscope (FESEM), and X-ray diffractometer (XRD). The wear resistance under ring-block wear testing and the surface hardness were evaluated and compared to those for the untreated material. Results show that a carburized layer (416 μm thick), mainly composed of TiC and V8C7, is found. These hard carbides contributed to the imrovement of the hardness and wear resistance.
A glow plasma carburizing technique was applied to strengthen the surface of the Ti-6Al-4V alloy. The alloy was carburized at 950 oC and 30~35 Pa for 3 h using plasma of Ar gas. Graphite rod was employed as carbon supply to avoid the hydrogen brittleness which is common in traditional gas carbonization. The carburized layer was examined by an optical microscope (OM), field emission scanning electron microscope (FESEM), and X-ray diffractometer (XRD). The wear resistance under ring-block wear testing and the surface hardness were evaluated and compared to those for the untreated material. Results show that a carburized layer (416 μm thick), mainly composed of TiC and V8C7, is found. These hard carbides contributed to the imrovement of the hardness and wear resistance.
2013, 42(6):1105-1107.
Abstract:
In term of newly developed titanium alloys Ti-6Al-4V-4Zr-Mo (Ti6441) modified from the commercial Ti-6Al-4V alloys, the adiabatic shear behaviors of equiaxed and lamellar microstructures were investigated. Unlike the Ti-6Al-4V alloys, Ti6441 alloys with the lamellar microstructure are less susceptive to adiabatic shear bands (ASBs), compared with the equiaxed one. In particular, the ASBs branch off in the lamellar microstructure, requiring additional energy by consuming metal bulk plastic deformation work. Besides, forced shearing experiment results show the lamellar microstructure exhibits outstanding dynamic ductility in contrast with the equiaxed one, though both microstructures perform the same strength value.
In term of newly developed titanium alloys Ti-6Al-4V-4Zr-Mo (Ti6441) modified from the commercial Ti-6Al-4V alloys, the adiabatic shear behaviors of equiaxed and lamellar microstructures were investigated. Unlike the Ti-6Al-4V alloys, Ti6441 alloys with the lamellar microstructure are less susceptive to adiabatic shear bands (ASBs), compared with the equiaxed one. In particular, the ASBs branch off in the lamellar microstructure, requiring additional energy by consuming metal bulk plastic deformation work. Besides, forced shearing experiment results show the lamellar microstructure exhibits outstanding dynamic ductility in contrast with the equiaxed one, though both microstructures perform the same strength value.
2013, 42(6):1108-1112.
Abstract:
Tungsten heavy alloys (WHAs) with four different titanium contents (0.5%, 1.0%, 1.5%, 2.0%, wt.%) were prepared by powder metallurgy. The influence of titanium content on the microstructure and mechanical properties under high strain rates were investigated. The results show that the titanium particles disperse in the matrix with different morphology and the main effective element is the diameter of the titanium particles. There are lots of micro holes in the titanium particles when the diameter of titanium particles is larger than 20 μm. The titanium particles do not dissolve in the matrix during the sintering process and the interfaces between titanium and tungsten, titanium and matrix are good. The results of Hopkinson Striker Bar indicate that the dynamic compressive strength is highest when the content of titanium is 0.5% and the strength has little change as the content of titanium increases from 1.0% to 2.0% under 3700 s-1 strain rate. In the WHA with 2.0% titanium content, the adiabatic shear banding (ASB) is the main deformation mode and the titanium in the ASB is fragile, the temperature of thermal softening area is higher than that of the traditional WHAs because of the existence of titanium particles. The addition of titanium in the WHAs improves the adiabatic shear banding susceptivity.
Tungsten heavy alloys (WHAs) with four different titanium contents (0.5%, 1.0%, 1.5%, 2.0%, wt.%) were prepared by powder metallurgy. The influence of titanium content on the microstructure and mechanical properties under high strain rates were investigated. The results show that the titanium particles disperse in the matrix with different morphology and the main effective element is the diameter of the titanium particles. There are lots of micro holes in the titanium particles when the diameter of titanium particles is larger than 20 μm. The titanium particles do not dissolve in the matrix during the sintering process and the interfaces between titanium and tungsten, titanium and matrix are good. The results of Hopkinson Striker Bar indicate that the dynamic compressive strength is highest when the content of titanium is 0.5% and the strength has little change as the content of titanium increases from 1.0% to 2.0% under 3700 s-1 strain rate. In the WHA with 2.0% titanium content, the adiabatic shear banding (ASB) is the main deformation mode and the titanium in the ASB is fragile, the temperature of thermal softening area is higher than that of the traditional WHAs because of the existence of titanium particles. The addition of titanium in the WHAs improves the adiabatic shear banding susceptivity.
2013, 42(6):1113-1117.
Abstract:
The structure transformation from DO22 to L10 (M=1) phase in Ni64Al21V15 alloy at 1150 K was studied by the microscopic phase-field kinetic model. The results show that L10 (M=1) structure precipitates at interphase during the middle stage of the aging process with three types of the formation mechanism. Firstly, the L10 (M=1) structure which aligns along [001] direction and nucleates at the interphase of L12 and DO22 grows towards DO22 phase. Secondly, the L10 (M=1) structure which aligns along [001] direction nucleates at 90° ordered domain boundary of DO22 phase and expands to the [001] direction of DO22 phase. Thirdly, the L10 (M=1) structure which aligns along [100] direction nucleates at the interphase of two [100] aligned DO22 structure, and expands towards DO22 phase. The phase transformation from DO22 structure to L10 (M=1) structure is accomplished by atomic diffusion. In a perfect DO22 phase, the β site is mainly occupied by V atoms, while the α2 and α3 sites by Ni atoms and the α1 site by Al atoms. As the aging process proceeds, V atoms which migrate to α2 site, leading to the atomic ordering on (002) plane takes the place of both β and α2 sites ultimately, and the Ni atoms migrate from α2 to α1 site and occupy both α1 and α3 sites lastly, while Al atoms diffuse towards outside of DO22 structure facilitating the formation of highly ordered L10 (M=1) structure finally.
The structure transformation from DO22 to L10 (M=1) phase in Ni64Al21V15 alloy at 1150 K was studied by the microscopic phase-field kinetic model. The results show that L10 (M=1) structure precipitates at interphase during the middle stage of the aging process with three types of the formation mechanism. Firstly, the L10 (M=1) structure which aligns along [001] direction and nucleates at the interphase of L12 and DO22 grows towards DO22 phase. Secondly, the L10 (M=1) structure which aligns along [001] direction nucleates at 90° ordered domain boundary of DO22 phase and expands to the [001] direction of DO22 phase. Thirdly, the L10 (M=1) structure which aligns along [100] direction nucleates at the interphase of two [100] aligned DO22 structure, and expands towards DO22 phase. The phase transformation from DO22 structure to L10 (M=1) structure is accomplished by atomic diffusion. In a perfect DO22 phase, the β site is mainly occupied by V atoms, while the α2 and α3 sites by Ni atoms and the α1 site by Al atoms. As the aging process proceeds, V atoms which migrate to α2 site, leading to the atomic ordering on (002) plane takes the place of both β and α2 sites ultimately, and the Ni atoms migrate from α2 to α1 site and occupy both α1 and α3 sites lastly, while Al atoms diffuse towards outside of DO22 structure facilitating the formation of highly ordered L10 (M=1) structure finally.
2013, 42(6):1118-1122.
Abstract:
Butt joints of aluminum foam were made by three different brazing processes including brazing with multilayer filler metal in high vacuum of 10-3 (Pa) degree, brazing with multilayer filler metal in low vacuum of 1 (Pa) degree and brazing with monolayer filler metal in high vacuum of 10-3 (Pa) degree. The macrostructure and microstructure characteristics and bending strength of the joints were investigated and compared. The results indicate that the brazed specimen can achieve a satisfactory joint when brazed with multilayer filler metal in high vacuum. The bending strength of the joint is higher than that of the base metal. However, the bending strength of the joint is obviously lower than that of the base metal when brazed with multilayer filler metal in low vacuum, while it is slightly lower when brazed with monolayer filler metal in high vacuum.
Butt joints of aluminum foam were made by three different brazing processes including brazing with multilayer filler metal in high vacuum of 10-3 (Pa) degree, brazing with multilayer filler metal in low vacuum of 1 (Pa) degree and brazing with monolayer filler metal in high vacuum of 10-3 (Pa) degree. The macrostructure and microstructure characteristics and bending strength of the joints were investigated and compared. The results indicate that the brazed specimen can achieve a satisfactory joint when brazed with multilayer filler metal in high vacuum. The bending strength of the joint is higher than that of the base metal. However, the bending strength of the joint is obviously lower than that of the base metal when brazed with multilayer filler metal in low vacuum, while it is slightly lower when brazed with monolayer filler metal in high vacuum.
2013, 42(6):1123-1126.
Abstract:
Thermal exposure experiments of Ni-based cast superalloy K403 at 950 °C for 5, 50 and 100 h were conducted. The effect of thermal exposure on the microstructures and room-temperature mechanical properties of the superalloys K403 was studied. The results show that M6C carbides segregate from intra-grains and grain boundaries, and γ' phases aggregate and grow up with blunted corners. With increasing of thermal exposure time, on the one hand, γ' phases of spherical or nearly spherical shapes are formed from blunted corners and parts of the γ' phase tend to coarsen due to the connection-oriented effect. On the other hand, the offset yielding stress and the tensile strength decrease, while the plasticity improves obviously, resulting from the aggregation and coarsening of the γ' strengthening phase. The room-temperature tensile fracture surface is characterized by the dendritic structure fracture for K403 alloys before and after the thermal exposure. Whereas the intercrystalline fracture feature, and the shallow and small dimples appear on the tensile section of the thermal-exposed alloys. And the amount of dimples increases as the exposure time increases.
Thermal exposure experiments of Ni-based cast superalloy K403 at 950 °C for 5, 50 and 100 h were conducted. The effect of thermal exposure on the microstructures and room-temperature mechanical properties of the superalloys K403 was studied. The results show that M6C carbides segregate from intra-grains and grain boundaries, and γ' phases aggregate and grow up with blunted corners. With increasing of thermal exposure time, on the one hand, γ' phases of spherical or nearly spherical shapes are formed from blunted corners and parts of the γ' phase tend to coarsen due to the connection-oriented effect. On the other hand, the offset yielding stress and the tensile strength decrease, while the plasticity improves obviously, resulting from the aggregation and coarsening of the γ' strengthening phase. The room-temperature tensile fracture surface is characterized by the dendritic structure fracture for K403 alloys before and after the thermal exposure. Whereas the intercrystalline fracture feature, and the shallow and small dimples appear on the tensile section of the thermal-exposed alloys. And the amount of dimples increases as the exposure time increases.
2013, 42(6):1127-1129.
Abstract:
AlNiCrFexMo0.2CoCu (x=0.5, 1.0, 1.5 2.0) high entropy alloys were prepared by the method of powder metallurgy. Effects of Fe content on microstructure, hardness and comprehensive mechanical properties were investigated. The XRD results show that constituent phases change from bcc+fcc+ σ at x=0.5 to bcc+fcc at x=2.0. The hardness of the alloys varies from HBW3170 MPa at x=0.5 to HBW2290 MPa at x=2.0. The fracture strengths of all the AlNiCrFexMo0.2CoCu alloys are higher than 1100 MPa, and have a good plasticity.
AlNiCrFexMo0.2CoCu (x=0.5, 1.0, 1.5 2.0) high entropy alloys were prepared by the method of powder metallurgy. Effects of Fe content on microstructure, hardness and comprehensive mechanical properties were investigated. The XRD results show that constituent phases change from bcc+fcc+ σ at x=0.5 to bcc+fcc at x=2.0. The hardness of the alloys varies from HBW3170 MPa at x=0.5 to HBW2290 MPa at x=2.0. The fracture strengths of all the AlNiCrFexMo0.2CoCu alloys are higher than 1100 MPa, and have a good plasticity.
2013, 42(6):1130-1133.
Abstract:
To improve the photoelectric conversion efficiency and reduce the cost of platinized electrodes of dye-sensitized solar cells (DSSCs), a systemic study was performed for preparing efficient platinized counter electrodes (CE) by the pyrolysis method, and an optimum process was obtained. Results indicate that the platinized CE using the optimizing pyrolysis achieves high photovoltaic efficiency close to that of the sputtering platinized electrodes, and this method may be used to economically prepare large-sized and high-performance platinum loaded CE.
To improve the photoelectric conversion efficiency and reduce the cost of platinized electrodes of dye-sensitized solar cells (DSSCs), a systemic study was performed for preparing efficient platinized counter electrodes (CE) by the pyrolysis method, and an optimum process was obtained. Results indicate that the platinized CE using the optimizing pyrolysis achieves high photovoltaic efficiency close to that of the sputtering platinized electrodes, and this method may be used to economically prepare large-sized and high-performance platinum loaded CE.
2013, 42(6):1134-1138.
Abstract:
A new thermal barrier coating system based on Dy2Zr2O7, which had a lower thermal conductivity and closer thermal expansion coefficient to nickel-based superalloys, was prepared by the air plasma spraying (APS). The microstructure, phase composition and thermal-shock resistance of the as-sprayed coatings were studied. Besides, the failure process of the coating during thermal cycles was also discussed. After 6~8 thermal-shock cycles, coatings spalled from the specimens. Micro cracks in the top coat grew and crushed the ceramic top coat in the vicinity of bond coat interface into pieces, and then led to the spallation of the top coat.
A new thermal barrier coating system based on Dy2Zr2O7, which had a lower thermal conductivity and closer thermal expansion coefficient to nickel-based superalloys, was prepared by the air plasma spraying (APS). The microstructure, phase composition and thermal-shock resistance of the as-sprayed coatings were studied. Besides, the failure process of the coating during thermal cycles was also discussed. After 6~8 thermal-shock cycles, coatings spalled from the specimens. Micro cracks in the top coat grew and crushed the ceramic top coat in the vicinity of bond coat interface into pieces, and then led to the spallation of the top coat.
2013, 42(6):1139-1145.
Abstract:
Commercially pure (CP) titanium (grade 1) was processed by equal channel angular pressing (ECAP) up to 4 passes via route C at room temperature using a die of Φ=90° and ψ= 20°. The as-processed CP-Ti billets were smooth and free of visible surface cracks. The texture evolution in CP-Ti after ECAP was investigated at room temperature. The results show that the basal and pyramidal textures gradually evolve to P (φ1=45°, φ=0°~90°, φ2=30°) texture. Basal and pyramidal textures are decreased, while prismatic texture is increased. Texture evolution in CP-Ti is caused by the dislocation multiplication in the early stage of ECAP deformation. In the later period of deformation, the shear texture is formed through the grain rotation and the basal texture is increased gradually due to grain refinement.
Commercially pure (CP) titanium (grade 1) was processed by equal channel angular pressing (ECAP) up to 4 passes via route C at room temperature using a die of Φ=90° and ψ= 20°. The as-processed CP-Ti billets were smooth and free of visible surface cracks. The texture evolution in CP-Ti after ECAP was investigated at room temperature. The results show that the basal and pyramidal textures gradually evolve to P (φ1=45°, φ=0°~90°, φ2=30°) texture. Basal and pyramidal textures are decreased, while prismatic texture is increased. Texture evolution in CP-Ti is caused by the dislocation multiplication in the early stage of ECAP deformation. In the later period of deformation, the shear texture is formed through the grain rotation and the basal texture is increased gradually due to grain refinement.
2013, 42(6):1146-1149.
Abstract:
The crystal structure and deuterium storage property of Ti36Zr40Ni20Pd4 alloy were investigated by means of X-ray diffraction and a gas-solid reaction system. Results show that before suction-casting, the alloy ingot grows into the MgZn2-typed C14 Laves phase with the coordination number of 14 and the lattice constant of a=0.5287nm, c=0.8610 nm. Through a simple activation treatment, the phase can load largely deuterium up to 10.96 mmol·D2/g·M (D2 represents the deuterium molecule and M the alloy). After one absorption-desorption cycle, the deuterium-uptake speed substantially improves, with the reaction constant reaching to 0.015 s-1. In contrast to the Ti36Zr40Ni20Pd4 quasicrystal, the present Laves phase with the same composition can load deuterium with a lower rate but in a comparable volume, indicating?its promise in storing hydrogen.
The crystal structure and deuterium storage property of Ti36Zr40Ni20Pd4 alloy were investigated by means of X-ray diffraction and a gas-solid reaction system. Results show that before suction-casting, the alloy ingot grows into the MgZn2-typed C14 Laves phase with the coordination number of 14 and the lattice constant of a=0.5287nm, c=0.8610 nm. Through a simple activation treatment, the phase can load largely deuterium up to 10.96 mmol·D2/g·M (D2 represents the deuterium molecule and M the alloy). After one absorption-desorption cycle, the deuterium-uptake speed substantially improves, with the reaction constant reaching to 0.015 s-1. In contrast to the Ti36Zr40Ni20Pd4 quasicrystal, the present Laves phase with the same composition can load deuterium with a lower rate but in a comparable volume, indicating?its promise in storing hydrogen.
2013, 42(6):1150-1153.
Abstract:
Electron beam welding of TC11 alloy was carried out to study the microstructure, mechanical properties and residual stress of the joint. In the fusion zone, typical columnar crystals with fine martensite α′ are found, in contrast with the heat affected zone where equiaxed α and martensite α′ are dispersed in the transformed β. The microhardness of the fusion zone is higher than that of the heat affected zone and the base metal. The joint impact toughness is increased by 20%, while the tensile strength remains invariable compared to the base metal. Longitudinal and transverse stresses are tensile, while the transverse stress is smaller than the longitudinal stress.
Electron beam welding of TC11 alloy was carried out to study the microstructure, mechanical properties and residual stress of the joint. In the fusion zone, typical columnar crystals with fine martensite α′ are found, in contrast with the heat affected zone where equiaxed α and martensite α′ are dispersed in the transformed β. The microhardness of the fusion zone is higher than that of the heat affected zone and the base metal. The joint impact toughness is increased by 20%, while the tensile strength remains invariable compared to the base metal. Longitudinal and transverse stresses are tensile, while the transverse stress is smaller than the longitudinal stress.
2013, 42(6):1154-1158.
Abstract:
TiNb/Zr55Cu30Al10Ni5 and TiNb/Cu46Zr42Al7Y5 bulk metallic glass composites were prepared by Spark Plasma Sintering (SPS). The compression results show that TiNb/Zr55Cu30Al10Ni5 composites get larger plasticity than TiNb/Cu46Zr42Al7Y5 composites. The reason is that Zr55Cu30Al10Ni5 bulk metallic glass is resistant to micro-crack. The fracture toughness test proves that KC of Zr55Cu30Al10Ni5 is higher than that of Cu46Zr42Al7Y5, so there is a larger length scale of plastic process zone Rp for Zr55Cu30Al10Ni5.
TiNb/Zr55Cu30Al10Ni5 and TiNb/Cu46Zr42Al7Y5 bulk metallic glass composites were prepared by Spark Plasma Sintering (SPS). The compression results show that TiNb/Zr55Cu30Al10Ni5 composites get larger plasticity than TiNb/Cu46Zr42Al7Y5 composites. The reason is that Zr55Cu30Al10Ni5 bulk metallic glass is resistant to micro-crack. The fracture toughness test proves that KC of Zr55Cu30Al10Ni5 is higher than that of Cu46Zr42Al7Y5, so there is a larger length scale of plastic process zone Rp for Zr55Cu30Al10Ni5.
2013, 42(6):1159-1164.
Abstract:
Micro-arc oxidation processes of the dense Ti samples and the gradient porous Ti samples in H2SO4 electrolyte were studied. The effects of pore characteristics, current density, constituents of the electrolyte on initial voltage, breakdown voltage, ignition time, the morphology and thickness of oxidation coatings were analyzed. Phase composition of micro-arc coatings was measured. The results show that the gradient porous Ti samples have higher initial voltage and breakdown voltage, longer ignition time and higher coating thickness compared with the dense Ti samples during micro-arc oxidation. With the increase of current density, micro-arc oxidation reaction becomes acute. In the oxidation coatings, the pore sizes increase and the porosity decreases. Simultaneously, the roughness and thickness of oxidation coatings both improve. When La(NO3)3·6H2O is added in H2SO4 electrolyte, the initial voltage, breakdown voltage and ignition time of the gradient porous Ti samples increase. The mean pore sizes in oxidation coatings and coatings thickness increase form 200 nm to 2 μm and from 27.6 μm to 35.6 μm, respectively. The roughness of oxidation coatings also improves. XRD analysis shows that micro-arc oxidation coatings is composed of Ti, anatase TiO2 and rutile TiO2. The main existing form of TiO2 is anatase TiO2.
Micro-arc oxidation processes of the dense Ti samples and the gradient porous Ti samples in H2SO4 electrolyte were studied. The effects of pore characteristics, current density, constituents of the electrolyte on initial voltage, breakdown voltage, ignition time, the morphology and thickness of oxidation coatings were analyzed. Phase composition of micro-arc coatings was measured. The results show that the gradient porous Ti samples have higher initial voltage and breakdown voltage, longer ignition time and higher coating thickness compared with the dense Ti samples during micro-arc oxidation. With the increase of current density, micro-arc oxidation reaction becomes acute. In the oxidation coatings, the pore sizes increase and the porosity decreases. Simultaneously, the roughness and thickness of oxidation coatings both improve. When La(NO3)3·6H2O is added in H2SO4 electrolyte, the initial voltage, breakdown voltage and ignition time of the gradient porous Ti samples increase. The mean pore sizes in oxidation coatings and coatings thickness increase form 200 nm to 2 μm and from 27.6 μm to 35.6 μm, respectively. The roughness of oxidation coatings also improves. XRD analysis shows that micro-arc oxidation coatings is composed of Ti, anatase TiO2 and rutile TiO2. The main existing form of TiO2 is anatase TiO2.
2013, 42(6):1165-1168.
Abstract:
Si-C-N nanocomposite films on titanium substrate were prepared by arc enhanced magnetron sputtering (AEMS). The microstructure and properties of Si-C-N nanocomposite films were investigated. The results show that a nanocomposite of amorphous C–C, C=C, N–C and Si–C matrix is formed for the films. The microhardness of the films is (38.2±4.1) GPa. The fracture toughness of the films is (3.68±0.32) MPa·m1/2. Si-C-N nanocomposite films have a low friction coefficient of 0.23 at room temperature. The corrosion rate of TA2 with Si-C-N nanocomposite films is 0.000 125 mm·a-1 in 3.5%NaCl water solution at 25 oC, which is 12.5% of that of pure TA2 under the same condition. The TA2 with Si-C-N nanocomposite films has better wear resistance and corrosion resistance than pure TA2.
Si-C-N nanocomposite films on titanium substrate were prepared by arc enhanced magnetron sputtering (AEMS). The microstructure and properties of Si-C-N nanocomposite films were investigated. The results show that a nanocomposite of amorphous C–C, C=C, N–C and Si–C matrix is formed for the films. The microhardness of the films is (38.2±4.1) GPa. The fracture toughness of the films is (3.68±0.32) MPa·m1/2. Si-C-N nanocomposite films have a low friction coefficient of 0.23 at room temperature. The corrosion rate of TA2 with Si-C-N nanocomposite films is 0.000 125 mm·a-1 in 3.5%NaCl water solution at 25 oC, which is 12.5% of that of pure TA2 under the same condition. The TA2 with Si-C-N nanocomposite films has better wear resistance and corrosion resistance than pure TA2.
2013, 42(6):1169-1172.
Abstract:
The tensile tests of Ti-3Al-2.5V (TA18) tubes with the diameter of 16 mm by cold rolling were accomplished on an electro-hydraulic servo material testing machine at –60, 25, 100, 200, 300 and 350 oC, respectively. Meanwhile, microstructure of TA18 titanium alloy tubes after fracture was observed by TEM when tests were carried out at different temperatures. The results indicate that the tensile strength and the elongation of TA18 titanium alloy tubes decreases with the rise of temperature. There is a large amount of mechanical twins in the specimens deformed at –60 oC, but they don’t exist at 350 oC. It is concluded that twinning plays an important role in the process of TA18 titanium alloy tubing deformation.
The tensile tests of Ti-3Al-2.5V (TA18) tubes with the diameter of 16 mm by cold rolling were accomplished on an electro-hydraulic servo material testing machine at –60, 25, 100, 200, 300 and 350 oC, respectively. Meanwhile, microstructure of TA18 titanium alloy tubes after fracture was observed by TEM when tests were carried out at different temperatures. The results indicate that the tensile strength and the elongation of TA18 titanium alloy tubes decreases with the rise of temperature. There is a large amount of mechanical twins in the specimens deformed at –60 oC, but they don’t exist at 350 oC. It is concluded that twinning plays an important role in the process of TA18 titanium alloy tubing deformation.
2013, 42(6):1173-1177.
Abstract:
Ti-29Nb-13Ta-4.6Zr alloys (wt%, TNTZ) were prepared by a spark plasma sintering (SPS) technique. The effects of the different sintering temperatures on the relative density, microstructure and mechanical properties of the alloys were investigated. In the sintering temperature range from 950 to 1150 oC, the alloys present a very high densification levels. All of the samples consist of β-Ti phase, Ti-Nb-Ta-Zr solid solution phase and some unmelted Nb, Ta, Zr metal particles. The alloys have a higher compressive strength, and they show a good room temperature compressive property. With the sintering temperatures increasing from 950 to 1150 oC, the relative density and the compressive strength of the alloys increase. The size of the matrix consisting of β-Ti phase and Ti-Nb-Ta-Zr solid solution phase increases and they bond further with each other. Furthermore, the size and the amount of the unmelted Nb, Ta, Zr metal particles decrease. The alloys exhibit low compressive elastic modulus in the range of 50~60 GPa, and it reveals the better mechanical compatibility.
Ti-29Nb-13Ta-4.6Zr alloys (wt%, TNTZ) were prepared by a spark plasma sintering (SPS) technique. The effects of the different sintering temperatures on the relative density, microstructure and mechanical properties of the alloys were investigated. In the sintering temperature range from 950 to 1150 oC, the alloys present a very high densification levels. All of the samples consist of β-Ti phase, Ti-Nb-Ta-Zr solid solution phase and some unmelted Nb, Ta, Zr metal particles. The alloys have a higher compressive strength, and they show a good room temperature compressive property. With the sintering temperatures increasing from 950 to 1150 oC, the relative density and the compressive strength of the alloys increase. The size of the matrix consisting of β-Ti phase and Ti-Nb-Ta-Zr solid solution phase increases and they bond further with each other. Furthermore, the size and the amount of the unmelted Nb, Ta, Zr metal particles decrease. The alloys exhibit low compressive elastic modulus in the range of 50~60 GPa, and it reveals the better mechanical compatibility.
2013, 42(6):1178-1184.
Abstract:
Microstructure and high temperature oxidation behaviour of Ti45Al8Nb0.5B0.2C alloy was investigated in this work. XRD, SEM, TEM and EDS analysis demonstrate that as-cast Ti46Al8Nb0.5B0.2C alloy after HIP has fully lamellar microstructure consisting of γ and α2 with point-like or ribbon-like TiB2 distributing in the colony or at grain boundary. When the alloy was treated at 1400 ℃ for 1 h and oil cooled from the single α filed leads to α→γm transformation and γm was aged in the α+γ two-phase field, alpha plates precipitated on all {111} planes of the γm to form fine microstructures. In addition to determination of the oxidation knetics by mass gain measurements, surface and cross-sectional morphologies of oxidizing layer formed was observed by SEM and the present phases in the scales were analyzed by XRD. Results show that oxidation reaction constant and power index for Ti46Al8Nb0.5B0.2C alloy oxidized at 900 ℃for 100 h were 0.00192 and 1.1381, respectively. However, oxidation reaction constant and power index for Ti46Al8Nb0.5B0.2C alloy oxidized at1000 ℃ for 100 h were 0.31637 and 2.0076, respectively. Oxidizing layer of Ti46Al8Nb0.5B0.2C alloy after 900℃, 100 h oxidation was about 4 μm and composed of four layer. The first layer is discontinous Al2O3, the second layer is the mixture of Al2O3 and TiO2, and the last is rich in Nb. Oxidizing layer of Ti46Al8Nb0.5B0.2C alloy after 1000 ℃, 100 h oxidation was about 5 μm and composed of 4 layer. The first layer is TiO2, the second layer is the mixture of Al2O3 and TiO2, and the third layer is nitride layer in sequence.
Microstructure and high temperature oxidation behaviour of Ti45Al8Nb0.5B0.2C alloy was investigated in this work. XRD, SEM, TEM and EDS analysis demonstrate that as-cast Ti46Al8Nb0.5B0.2C alloy after HIP has fully lamellar microstructure consisting of γ and α2 with point-like or ribbon-like TiB2 distributing in the colony or at grain boundary. When the alloy was treated at 1400 ℃ for 1 h and oil cooled from the single α filed leads to α→γm transformation and γm was aged in the α+γ two-phase field, alpha plates precipitated on all {111} planes of the γm to form fine microstructures. In addition to determination of the oxidation knetics by mass gain measurements, surface and cross-sectional morphologies of oxidizing layer formed was observed by SEM and the present phases in the scales were analyzed by XRD. Results show that oxidation reaction constant and power index for Ti46Al8Nb0.5B0.2C alloy oxidized at 900 ℃for 100 h were 0.00192 and 1.1381, respectively. However, oxidation reaction constant and power index for Ti46Al8Nb0.5B0.2C alloy oxidized at1000 ℃ for 100 h were 0.31637 and 2.0076, respectively. Oxidizing layer of Ti46Al8Nb0.5B0.2C alloy after 900℃, 100 h oxidation was about 4 μm and composed of four layer. The first layer is discontinous Al2O3, the second layer is the mixture of Al2O3 and TiO2, and the last is rich in Nb. Oxidizing layer of Ti46Al8Nb0.5B0.2C alloy after 1000 ℃, 100 h oxidation was about 5 μm and composed of 4 layer. The first layer is TiO2, the second layer is the mixture of Al2O3 and TiO2, and the third layer is nitride layer in sequence.
2013, 42(6):1185-1189.
Abstract:
Ru-La oxide coatings were prepared by thermal decomposition of the metal chlorides in the precursor solution of RuCl3×3H2O and LaCl3×7H2O. The electrochemical activity, structure and morphology of the coatings were characterized by cyclic voltammetry (CV), DSC-TG, XRD and atomic force microscope (AFM). The results show that the Ru-La oxide coatings exhibit a large electrochemical activity because of the smaller crystallite size and the larger surface active areas caused by the addition of La. The La addition increases the heat decomposing temperature of RuCl3 and restrains the crystallization and growth of RuO2 and RuOx (x>2). The mixed oxides mainly exist in the form of amorphous phase. The average crystallite size reaches a minimum value at the nominal La content of 30 mol%, while the oxide coating shows the highest electrochemical activity.
Ru-La oxide coatings were prepared by thermal decomposition of the metal chlorides in the precursor solution of RuCl3×3H2O and LaCl3×7H2O. The electrochemical activity, structure and morphology of the coatings were characterized by cyclic voltammetry (CV), DSC-TG, XRD and atomic force microscope (AFM). The results show that the Ru-La oxide coatings exhibit a large electrochemical activity because of the smaller crystallite size and the larger surface active areas caused by the addition of La. The La addition increases the heat decomposing temperature of RuCl3 and restrains the crystallization and growth of RuO2 and RuOx (x>2). The mixed oxides mainly exist in the form of amorphous phase. The average crystallite size reaches a minimum value at the nominal La content of 30 mol%, while the oxide coating shows the highest electrochemical activity.
2013, 42(6):1190-1193.
Abstract:
The effect of hydrogenation on microstructure and phase transformation of TB8 alloy was investigated by OM, SEM and XRD, and the variation of hardness after hydrogenation was studied. The result reveals that the amount of β phase increases gradually as the hydrogen content increases and hydrogenation reduces the critical cooling rate of ω phase. The hardness of TB8 alloy first increases and then decreases with increasing of hydrogen, which is attributed to the interaction of hardening phase ω, hydride δ, softening phase β and solid solution strengthening of H.
The effect of hydrogenation on microstructure and phase transformation of TB8 alloy was investigated by OM, SEM and XRD, and the variation of hardness after hydrogenation was studied. The result reveals that the amount of β phase increases gradually as the hydrogen content increases and hydrogenation reduces the critical cooling rate of ω phase. The hardness of TB8 alloy first increases and then decreases with increasing of hydrogen, which is attributed to the interaction of hardening phase ω, hydride δ, softening phase β and solid solution strengthening of H.
2013, 42(6):1194-1198.
Abstract:
Microscopic phase-field model was used to study the effect of atomic structure of interfaces, composition of alloys and elastic strain energy on the compositions of ordered domain interfaces formed between L12-Ni3Al phases in Ni75AlxV25-x alloys. The results demonstrate that the depletion degree of Ni is the lowest, and the depletion degree of Al and the segregation degree of V are the highest at the interface (100)//(200)·?[001]; the depletion degree of Ni is the highest, and the depletion degree of Al and the segregation degree of V are the lowest at the interface (200)//(200) among the three kinds of interfaces formed between L12-Ni3Al phases. With the Al concentration of alloys increasing, the concentration of Al increases while the concentrations of Ni and V decrease at the ordered domain boundaries formed between L12-Ni3Al phases. When the elastic strain energy is considered during the simulation, the concentrations of Ni and Al increase while the concentration of V decrease at the three kinds of ordered domain interfaces. The effect of elastic strain energy on the composition of (200)//(200)·?[001] and (100)//(200)·?[001] is much more remarkable than on that of (200)//(200).
Microscopic phase-field model was used to study the effect of atomic structure of interfaces, composition of alloys and elastic strain energy on the compositions of ordered domain interfaces formed between L12-Ni3Al phases in Ni75AlxV25-x alloys. The results demonstrate that the depletion degree of Ni is the lowest, and the depletion degree of Al and the segregation degree of V are the highest at the interface (100)//(200)·?[001]; the depletion degree of Ni is the highest, and the depletion degree of Al and the segregation degree of V are the lowest at the interface (200)//(200) among the three kinds of interfaces formed between L12-Ni3Al phases. With the Al concentration of alloys increasing, the concentration of Al increases while the concentrations of Ni and V decrease at the ordered domain boundaries formed between L12-Ni3Al phases. When the elastic strain energy is considered during the simulation, the concentrations of Ni and Al increase while the concentration of V decrease at the three kinds of ordered domain interfaces. The effect of elastic strain energy on the composition of (200)//(200)·?[001] and (100)//(200)·?[001] is much more remarkable than on that of (200)//(200).
2013, 42(6):1199-1204.
Abstract:
Hot deformation behavior of GH738 superalloy was studied in the temperature range of 1000~1160 oC, strain rate range of 0.01 ~10 s-1 and engineering strain range 15%~70% by the Gleeble-1500 simulator. The hot deformation equation was determined to characterize the dependence of peak stress on the temperature and strain rate. Processing maps for hot working were established on the basis of the variations of efficiency of power dissipation with temperature and strain rate, and interpreted according to the microstructure observation. The apparent activation energy Q of GH738 superalloy is about 499 kJ/mol. The maps obtained in true strain range from 0.2 to 0.8 are essentially different, and the efficiency of power dissipation increases gradually with the increase of temperature and the decrease of strain rate. An optimum zone named safe area is obtained for GH738 alloy deformation. The above results can be used as a reference for hot working of GH738 superalloy.
Hot deformation behavior of GH738 superalloy was studied in the temperature range of 1000~1160 oC, strain rate range of 0.01 ~10 s-1 and engineering strain range 15%~70% by the Gleeble-1500 simulator. The hot deformation equation was determined to characterize the dependence of peak stress on the temperature and strain rate. Processing maps for hot working were established on the basis of the variations of efficiency of power dissipation with temperature and strain rate, and interpreted according to the microstructure observation. The apparent activation energy Q of GH738 superalloy is about 499 kJ/mol. The maps obtained in true strain range from 0.2 to 0.8 are essentially different, and the efficiency of power dissipation increases gradually with the increase of temperature and the decrease of strain rate. An optimum zone named safe area is obtained for GH738 alloy deformation. The above results can be used as a reference for hot working of GH738 superalloy.
2013, 42(6):1205-1209.
Abstract:
The growth and melting of nuclei with different radii in liquid Ni have been investigated by molecular dynamics simulation. The result shows that a critical nucleus is not stable and will either grow or melt at certain undercooling temperature. By calculating the upper limit of the growth temperature and the lower limit of the melt temperature, the critical nucleation temperatures for different nucleus radii can be determined, which has a linear relationship with the inverse of the nucleus radius, in accordance with classical nucleation theory and Gibbs-Thomson model. The Gibbs-Thomson coefficient of 1.56×10-7 K·m and the crystal-melt interfacial free energy of 0.211 J/m2 are obtained based on the molecular dynamics simulation of critical nucleus evolution for Ni system, consistent with the experimental results.
The growth and melting of nuclei with different radii in liquid Ni have been investigated by molecular dynamics simulation. The result shows that a critical nucleus is not stable and will either grow or melt at certain undercooling temperature. By calculating the upper limit of the growth temperature and the lower limit of the melt temperature, the critical nucleation temperatures for different nucleus radii can be determined, which has a linear relationship with the inverse of the nucleus radius, in accordance with classical nucleation theory and Gibbs-Thomson model. The Gibbs-Thomson coefficient of 1.56×10-7 K·m and the crystal-melt interfacial free energy of 0.211 J/m2 are obtained based on the molecular dynamics simulation of critical nucleus evolution for Ni system, consistent with the experimental results.
2013, 42(6):1210-1214.
Abstract:
The effect of Cu content on the corrosion resistance of Zr-0.80Sn-0.4Nb-0.4Fe-0.10Cr-xCu alloys (x=0.05~0.5, mass fraction, %) was investigated in superheated steam at 400 oC and 10.3 MPa by autoclave tests. The microstructure of the alloys and the fracture surface of oxide films on the corroded specimens were observed by TEM and SEM, respectively. The results show that when the addition of Cu is below 0.2%, the second phase particles (SPPs) are mainly Zr(Fe,Cr,Nb)2 in smaller size, and few Zr3Fe with Cu. When the addition of Cu is above 0.2%, the SPPs of Zr2Cu are precipitated. The Zr2Cu particles become larger in size and more in amount with the increase of Cu content. The precipitates containing Cu are found in the alloy even with 0.05% Cu, which indicates that the Cu concentration in α-Zr matrix is very small. Cu addition of 0.05%~0.35% has little effect on the corrosion resistance of the alloys, but when the addition of Cu reaches 0.5%, the corrosion resistance of the alloy decreases, which is the worst one among the alloys.
The effect of Cu content on the corrosion resistance of Zr-0.80Sn-0.4Nb-0.4Fe-0.10Cr-xCu alloys (x=0.05~0.5, mass fraction, %) was investigated in superheated steam at 400 oC and 10.3 MPa by autoclave tests. The microstructure of the alloys and the fracture surface of oxide films on the corroded specimens were observed by TEM and SEM, respectively. The results show that when the addition of Cu is below 0.2%, the second phase particles (SPPs) are mainly Zr(Fe,Cr,Nb)2 in smaller size, and few Zr3Fe with Cu. When the addition of Cu is above 0.2%, the SPPs of Zr2Cu are precipitated. The Zr2Cu particles become larger in size and more in amount with the increase of Cu content. The precipitates containing Cu are found in the alloy even with 0.05% Cu, which indicates that the Cu concentration in α-Zr matrix is very small. Cu addition of 0.05%~0.35% has little effect on the corrosion resistance of the alloys, but when the addition of Cu reaches 0.5%, the corrosion resistance of the alloy decreases, which is the worst one among the alloys.
2013, 42(6):1215-1220.
Abstract:
The first-principles calculations were performed to investigate the electronic structure and the optical properties of the MgxTi(1-x)H2 (x = 0.25, 0.5, 0.75, 0.875) systems with different Ti contents by the pseudopotential plane-wave method based on density functional theory. The electronic densities of state reveal that the MgxTi(1-x)H2 hydrides exhibit metallic characteristics by adding Ti atom to MgH2 hydride. It originates from the increasing of the valence electrons at Fermi level and the vanishing of band gap near Fermi level. The bonding nature of the hydrides was investigated by analyzing the charge distribution of MgxTi(1-x)H2, and it shows stronger covalent bonding between Ti and H than between Mg and H. The calculated results from the optical properties of MgxTi(1-x)H2 show that Ti content in MgxTi(1-x)H2 systems has an important influence on the optical properties near visible light energy region. For the lower Ti content in MgxTi(1-x)H2 such as x=0.875, it is not favorable to improve absorption over the whole visible region. Whereas the reflection is high for the higher Ti content, such as x=0.25. The calculated results provide a theoretical basis for preparing Mg-Ti-H photoelectric materials with excellent absorption and photoelectric conversion efficiency over the whole visible region.
The first-principles calculations were performed to investigate the electronic structure and the optical properties of the MgxTi(1-x)H2 (x = 0.25, 0.5, 0.75, 0.875) systems with different Ti contents by the pseudopotential plane-wave method based on density functional theory. The electronic densities of state reveal that the MgxTi(1-x)H2 hydrides exhibit metallic characteristics by adding Ti atom to MgH2 hydride. It originates from the increasing of the valence electrons at Fermi level and the vanishing of band gap near Fermi level. The bonding nature of the hydrides was investigated by analyzing the charge distribution of MgxTi(1-x)H2, and it shows stronger covalent bonding between Ti and H than between Mg and H. The calculated results from the optical properties of MgxTi(1-x)H2 show that Ti content in MgxTi(1-x)H2 systems has an important influence on the optical properties near visible light energy region. For the lower Ti content in MgxTi(1-x)H2 such as x=0.875, it is not favorable to improve absorption over the whole visible region. Whereas the reflection is high for the higher Ti content, such as x=0.25. The calculated results provide a theoretical basis for preparing Mg-Ti-H photoelectric materials with excellent absorption and photoelectric conversion efficiency over the whole visible region.
2013, 42(6):1221-1225.
Abstract:
A sol-gel method was used to improve the interface of whisker reinforced magnesium matrix composite via coating CuO on the surface of Mg2B2O5 whisker. Phase, morphology and interfacial characteristics of CuO-coated Mg2B2O5 whisker and magnesium matrix were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. Results indicate that CuO is coated on the surface of the Mg2B2O5 whisker and the interfacial products are MgCu2 and MgO in the CuO-coated Mg2B2O5 whisker reinforced magnesium matrix composite, which result from the interfacial reaction between the magnesium and CuO. The precipitate phase MgZn2 parallel grows on the both sides of whisker and has the crystallographic orientation relationship at the special position between the MgZn2 and Mg2B2O5 whisker, namely, [001] Mg2B2O5//[53] MgZn2 and (100) Mg2B2O5//(011)MgZn2. The ultimate tensile strength and the elongation of the CuO-coated Mg2B2O5 whisker reinforced composite have increased by 37.6% and 35.7%, respectively.
A sol-gel method was used to improve the interface of whisker reinforced magnesium matrix composite via coating CuO on the surface of Mg2B2O5 whisker. Phase, morphology and interfacial characteristics of CuO-coated Mg2B2O5 whisker and magnesium matrix were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), respectively. Results indicate that CuO is coated on the surface of the Mg2B2O5 whisker and the interfacial products are MgCu2 and MgO in the CuO-coated Mg2B2O5 whisker reinforced magnesium matrix composite, which result from the interfacial reaction between the magnesium and CuO. The precipitate phase MgZn2 parallel grows on the both sides of whisker and has the crystallographic orientation relationship at the special position between the MgZn2 and Mg2B2O5 whisker, namely, [001] Mg2B2O5//[53] MgZn2 and (100) Mg2B2O5//(011)MgZn2. The ultimate tensile strength and the elongation of the CuO-coated Mg2B2O5 whisker reinforced composite have increased by 37.6% and 35.7%, respectively.
2013, 42(6):1226-1230.
Abstract:
As-cast ingots of Mg-8Li-4Zn-xY magnesium alloy were prepared by lithium flux protection in an electric-resistance furnace, and 1 mm thick sheets were prepared by forward extrusion. Microstructures and mechanical properties of the alloy were investigated with OM, SEM equipped with an energy-dispersive X-ray spectroscopy (EDS), XRD and the HV-120 hardness Vickers. The results show that the matrix of as-cast Mg-8Li-4Zn-xY alloy consists of α-Mg (hexagonal close-packed) and β-Li (body-centered cubic) phase. The precipitation strengthening phase particles and compounds are Mg2Zn11, Mg72.05Zn27.95, MgZn, Mg2Y, MgY and unknown phase. The matrixes of Mg-8Li-4Zn-xY magnesium alloy ingots are refined and the amount of the precipitation strengthening phase are enhanced along with the yttrium content increasing, but there is no appreciable changing of the matrix size, appearance and dispersion precipitation phases in β-Li phase. On the contrary, the α-Mg phases wrapped by β-Li phase are elongated and refined during the extrusion process, and paralleled to the extrusion direction as stripped. The β-Li phases could coordinate plastic deformation and synchronize dynamic recrystallization, and the strengthening phases are of uniform distribution on the crystal boundary. The ingots and 1 mm thick sheets of Mg-8Li-4Zn-xY alloys are strengthened and the hardnesses are also enhanced in different extent along with the yttrium content increasing.
As-cast ingots of Mg-8Li-4Zn-xY magnesium alloy were prepared by lithium flux protection in an electric-resistance furnace, and 1 mm thick sheets were prepared by forward extrusion. Microstructures and mechanical properties of the alloy were investigated with OM, SEM equipped with an energy-dispersive X-ray spectroscopy (EDS), XRD and the HV-120 hardness Vickers. The results show that the matrix of as-cast Mg-8Li-4Zn-xY alloy consists of α-Mg (hexagonal close-packed) and β-Li (body-centered cubic) phase. The precipitation strengthening phase particles and compounds are Mg2Zn11, Mg72.05Zn27.95, MgZn, Mg2Y, MgY and unknown phase. The matrixes of Mg-8Li-4Zn-xY magnesium alloy ingots are refined and the amount of the precipitation strengthening phase are enhanced along with the yttrium content increasing, but there is no appreciable changing of the matrix size, appearance and dispersion precipitation phases in β-Li phase. On the contrary, the α-Mg phases wrapped by β-Li phase are elongated and refined during the extrusion process, and paralleled to the extrusion direction as stripped. The β-Li phases could coordinate plastic deformation and synchronize dynamic recrystallization, and the strengthening phases are of uniform distribution on the crystal boundary. The ingots and 1 mm thick sheets of Mg-8Li-4Zn-xY alloys are strengthened and the hardnesses are also enhanced in different extent along with the yttrium content increasing.
2013, 42(6):1231-1235.
Abstract:
Al element was substituted for In in the (In2Te3)0.09 (SnTe)0.91 compound with the same molar fraction and (In2Te3)0.09 (SnTe)0.91 and (In1.9Al0.1Te3)0.09(SnTe)0.91 compounds were prepared by spark plasma sintering. The microstructure and the thermoelectric property of the compounds were investigated. Results show that although the Seebeck coefficient of the sample is almost unchanged after Al doping, the electrical conductivity increases to 1×105 W-1·m-1 at 321 K and to 2.3×105 W-1·m-1 at 705 K, being at least 2.4~3 times that of Al free (In2Te3)0.09(SnTe)0.91 compound, and the lattice thermal conductivity is significantly decreased. The highest ZT value of 0.4 is obtained at 693 K, which is approximately 2 times as large as that of the Al-free (In2Te3)0.09(SnTe)0.91 compound at the same temperature.
Al element was substituted for In in the (In2Te3)0.09 (SnTe)0.91 compound with the same molar fraction and (In2Te3)0.09 (SnTe)0.91 and (In1.9Al0.1Te3)0.09(SnTe)0.91 compounds were prepared by spark plasma sintering. The microstructure and the thermoelectric property of the compounds were investigated. Results show that although the Seebeck coefficient of the sample is almost unchanged after Al doping, the electrical conductivity increases to 1×105 W-1·m-1 at 321 K and to 2.3×105 W-1·m-1 at 705 K, being at least 2.4~3 times that of Al free (In2Te3)0.09(SnTe)0.91 compound, and the lattice thermal conductivity is significantly decreased. The highest ZT value of 0.4 is obtained at 693 K, which is approximately 2 times as large as that of the Al-free (In2Te3)0.09(SnTe)0.91 compound at the same temperature.
2013, 42(6):1236-1240.
Abstract:
Amorphous alloy Fe73.5Cu1Nb3Si13.5B9 was treated by low frequency pulsating magnetic field. The microstructure of the amorphous alloy sample was analyzed by M?ssbauer spectroscopy and TEM. The results show that the initial nano-crystallozation occurs in the ample during the pulsating magnetic field treatment at room temperature. By means of the alternating gradient magnetic meter and self-made magnetostrictive coefficient measuring instrument, coercive force Hc, saturation magnetization strength Ms, initial superconducting rate μi, and magnetostrictive coefficient λs of the samples were measured before and after low frequency pulsating magnetic field treatment. Results show that the overall μi increases after low frequency pulsating magnetic field treatment, while Hc and λs are smaller than those of the as-prepared amorphous alloy. It indicates that low frequency pulsating magnetic field treatment can optimize comprehensive soft magnetic properties of amorphous alloys, and the optimization degree of soft magnetic properties is relevant with the parameters of plused magnetic field. The soft magnetic properties of the sample reach the best when the pulsating magnetic field strength Hp=250×79.6 A/m, pulsating frequency f =30 Hz and disposing time t=4 min.
Amorphous alloy Fe73.5Cu1Nb3Si13.5B9 was treated by low frequency pulsating magnetic field. The microstructure of the amorphous alloy sample was analyzed by M?ssbauer spectroscopy and TEM. The results show that the initial nano-crystallozation occurs in the ample during the pulsating magnetic field treatment at room temperature. By means of the alternating gradient magnetic meter and self-made magnetostrictive coefficient measuring instrument, coercive force Hc, saturation magnetization strength Ms, initial superconducting rate μi, and magnetostrictive coefficient λs of the samples were measured before and after low frequency pulsating magnetic field treatment. Results show that the overall μi increases after low frequency pulsating magnetic field treatment, while Hc and λs are smaller than those of the as-prepared amorphous alloy. It indicates that low frequency pulsating magnetic field treatment can optimize comprehensive soft magnetic properties of amorphous alloys, and the optimization degree of soft magnetic properties is relevant with the parameters of plused magnetic field. The soft magnetic properties of the sample reach the best when the pulsating magnetic field strength Hp=250×79.6 A/m, pulsating frequency f =30 Hz and disposing time t=4 min.
2013, 42(6):1241-1245.
Abstract:
The pulsed laser welding of 0.5 mm thick Hastelloy C-276 was carried out and the weld joint with less than 1 mm width was obtained, and then the tensile test and XRD analysis were conducted. The results indicate that the yield strength of as-welded sample is nearly the same as that of the base metal, and the tensile strength is just 88.6% of that of the base metal. In the fracture, the enrichment of brittle phase isn’t found. Their comparable yield strength is due to the similar effect of solution strengthening of the base metal and grain refining of the as-welded sample. The reduced tensile strength of the welded sample is attributed to the favorable formation of micro-fracture during the tensile test.
The pulsed laser welding of 0.5 mm thick Hastelloy C-276 was carried out and the weld joint with less than 1 mm width was obtained, and then the tensile test and XRD analysis were conducted. The results indicate that the yield strength of as-welded sample is nearly the same as that of the base metal, and the tensile strength is just 88.6% of that of the base metal. In the fracture, the enrichment of brittle phase isn’t found. Their comparable yield strength is due to the similar effect of solution strengthening of the base metal and grain refining of the as-welded sample. The reduced tensile strength of the welded sample is attributed to the favorable formation of micro-fracture during the tensile test.
2013, 42(6):1246-1249.
Abstract:
Hydrogen permeation through a Pd8Y0.23Ru alloy membrane at 300 oC~450 oC has been investigated in the presence of CO2. The results show that the hydrogen permeability is greatly decreased by CO2 addition. The higher the CO2 concentration is, the more significant the reduction of hydrogen permeation will be. The coexisting CO2 gas has a poison effect on Pd8Y0.23Ru alloy membrane. The poison effect at 450 oC is stronger than at 300 oC. The reduction rate of hydrogen permeation decreases with the permeation duration. Besides poison effect, the negative effects of CO2 on H2 permeation are also caused by two other factors. Firstly, for higher concentration of CO2 (>3%), mass transfer of H2 ?is blocked by CO2 barrier layer near the membrane surface, which is the main reason for hydrogen permeation reduction. Secondly for lower concentrations (<1%), the main reason is the effects of CO2 adsorbing on the membrane and occupying active dissociation sites of hydrogen.
Hydrogen permeation through a Pd8Y0.23Ru alloy membrane at 300 oC~450 oC has been investigated in the presence of CO2. The results show that the hydrogen permeability is greatly decreased by CO2 addition. The higher the CO2 concentration is, the more significant the reduction of hydrogen permeation will be. The coexisting CO2 gas has a poison effect on Pd8Y0.23Ru alloy membrane. The poison effect at 450 oC is stronger than at 300 oC. The reduction rate of hydrogen permeation decreases with the permeation duration. Besides poison effect, the negative effects of CO2 on H2 permeation are also caused by two other factors. Firstly, for higher concentration of CO2 (>3%), mass transfer of H2 ?is blocked by CO2 barrier layer near the membrane surface, which is the main reason for hydrogen permeation reduction. Secondly for lower concentrations (<1%), the main reason is the effects of CO2 adsorbing on the membrane and occupying active dissociation sites of hydrogen.
2013, 42(6):1250-1253.
Abstract:
The stress relaxation processes of prestressed cylindrical specimens were simulated by FEM. Assuming the creep of material obeys the Norton creep law: (is the creep strain rate, B is a material and temperature dependent constant, and σ is the applied stress), we proposed two approaches to determine the creep stress exponent using the stress relaxation method. The first method requires a single stress relaxation curve. The second requires extracting the initial stress relaxation rate by an extrapolation method, and multiple stress relaxation curves are needed to yield the creep stress exponent. The present work provides some new notions on the determination of creep properties of materials which usually serve at high temperature.
The stress relaxation processes of prestressed cylindrical specimens were simulated by FEM. Assuming the creep of material obeys the Norton creep law: (is the creep strain rate, B is a material and temperature dependent constant, and σ is the applied stress), we proposed two approaches to determine the creep stress exponent using the stress relaxation method. The first method requires a single stress relaxation curve. The second requires extracting the initial stress relaxation rate by an extrapolation method, and multiple stress relaxation curves are needed to yield the creep stress exponent. The present work provides some new notions on the determination of creep properties of materials which usually serve at high temperature.
2013, 42(6):1254-1257.
Abstract:
Copper and cerium were metallized into 304 stainless steel by the double glow plasma technique combined with the copper hollow cathode effect. Microstructure of the samples was investigated by metallographic microscope, scanning electron microscopy, energy spectrum analyzer and X-ray diffraction. The reasons why diffusion layers are divided into white layer and dark layer, of the segregation of carbon and chromium to the surface layer and the distribution variation of other elements were explained. Antibacterial experiments show that 304 stainless steel after infiltration has good antibacterial property to E. coli and S. aureus.
Copper and cerium were metallized into 304 stainless steel by the double glow plasma technique combined with the copper hollow cathode effect. Microstructure of the samples was investigated by metallographic microscope, scanning electron microscopy, energy spectrum analyzer and X-ray diffraction. The reasons why diffusion layers are divided into white layer and dark layer, of the segregation of carbon and chromium to the surface layer and the distribution variation of other elements were explained. Antibacterial experiments show that 304 stainless steel after infiltration has good antibacterial property to E. coli and S. aureus.
He Jing
,
Wang Xiaoneng
,
Liu Minghai
,
Wang Jimin
,
Tang Motang
,
Lu Junle
,
Wang Tao
,
Luo Chao
,
Guo Rui
,
Lan Mingyan
2013, 42(6):1258-1263.
Abstract:
In order to provide a theoretical basis to improve the leaching rate of germanium in vacuum slag, the leaching kinetics of germanium in vacuum slag was investigated in hydrochloric acid-calcium chloride solution. The results show that the leaching process fits the generation of solid products of unreacted-core shrinking model. The kinetics equation is 1–2/3x–(1–x)2/3=4.66×10-3CHCl1.027CCaCl21.046d-0.862exp(–21068/RT)t. The leaching process is controlled by the diffusion of the lixiviant and the activation energy is determined to be 21.068 kJ/mol. The leaching speed and the leaching rate of germanium are increased by increasing the hydrochloric acid concentration, the calcium chloride concentration, the leaching temperature and the liquid-solid ratio and decreasing the particle size of the sample.
In order to provide a theoretical basis to improve the leaching rate of germanium in vacuum slag, the leaching kinetics of germanium in vacuum slag was investigated in hydrochloric acid-calcium chloride solution. The results show that the leaching process fits the generation of solid products of unreacted-core shrinking model. The kinetics equation is 1–2/3x–(1–x)2/3=4.66×10-3CHCl1.027CCaCl21.046d-0.862exp(–21068/RT)t. The leaching process is controlled by the diffusion of the lixiviant and the activation energy is determined to be 21.068 kJ/mol. The leaching speed and the leaching rate of germanium are increased by increasing the hydrochloric acid concentration, the calcium chloride concentration, the leaching temperature and the liquid-solid ratio and decreasing the particle size of the sample.
2013, 42(6):1264-1267.
Abstract:
TiAl alloy powder was prepared by high-energy ball milling and heat preservation under the condition of low temperature and high vacuum with titanium powder of 43 μm and aluminium powder of 9~12 μm as starting materials. After heat treated for different time and at different temperatures, the alloying of blended powder of titanium and aluminium was investigated. The results show that the alloy powder with the main intermetallic compounds of TiAl and a small quantity of Ti3Al can be obtained through 1 h high-energy ball milling and heat preservation at 500 oC for 2 h, and 600 oC for 3 h in high vacuum. The particle size of the prepared alloy powder is about 20 μm.
TiAl alloy powder was prepared by high-energy ball milling and heat preservation under the condition of low temperature and high vacuum with titanium powder of 43 μm and aluminium powder of 9~12 μm as starting materials. After heat treated for different time and at different temperatures, the alloying of blended powder of titanium and aluminium was investigated. The results show that the alloy powder with the main intermetallic compounds of TiAl and a small quantity of Ti3Al can be obtained through 1 h high-energy ball milling and heat preservation at 500 oC for 2 h, and 600 oC for 3 h in high vacuum. The particle size of the prepared alloy powder is about 20 μm.
36 Microstructure and Mechanical Properties of Mg2Si Reinforced ZK60 Magnesium Alloy Deformed by ECAP
2013, 42(6):1268-1273.
Abstract:
The effects of Equal Channel Angular Pressing (ECAP) on microstructure, mechanical properties at room temperature and high-temperature creep resistance of ZK60+2Si alloy were investigated. Results show that the components of as-cast alloy are mainly a-Mg matrix, Mg2Si and MgZn secondary phases. During ECAP processing, the original coarse Chinese-script Mg2Si phases are obviously broken into particles which tend to dispersively redistribute and the matrix is also been refined. After 4 passes of EACP, the tensile strength and the elongation of the alloy at room temperature increases from 154.8 MPa and 4.5% to 270 MPa and 17.5%, respectively. After 6 passes of EACP, the elongation further increases to 21%, but the tensile strength drops to 261 MPa. The high-temperature creep life of the alloy is extended from 20 h to 203 h, and the steady creep rate decreases by an order of magnitude. It is mainly because the tiny Mg2Si particles prevent grain boundary sliding effectively.
The effects of Equal Channel Angular Pressing (ECAP) on microstructure, mechanical properties at room temperature and high-temperature creep resistance of ZK60+2Si alloy were investigated. Results show that the components of as-cast alloy are mainly a-Mg matrix, Mg2Si and MgZn secondary phases. During ECAP processing, the original coarse Chinese-script Mg2Si phases are obviously broken into particles which tend to dispersively redistribute and the matrix is also been refined. After 4 passes of EACP, the tensile strength and the elongation of the alloy at room temperature increases from 154.8 MPa and 4.5% to 270 MPa and 17.5%, respectively. After 6 passes of EACP, the elongation further increases to 21%, but the tensile strength drops to 261 MPa. The high-temperature creep life of the alloy is extended from 20 h to 203 h, and the steady creep rate decreases by an order of magnitude. It is mainly because the tiny Mg2Si particles prevent grain boundary sliding effectively.
2013, 42(6):1274-1277.
Abstract:
Y0.9Gd0.1Ba2Cu3Oy films were prepared by the chemical solution deposition method. The effect of intermediate annealing on the phase, texture and superconducting properties of the films were evaluated. The results show that the intermediate annealing process is beneficial to achieve highly c-axis oriented YGdBCO film. The YGdBCO film prepared with intermediate annealing temperature of 400 oC has demonstrated high performance Jc (77 K, self field) = 2.4 MA/cm2.
Y0.9Gd0.1Ba2Cu3Oy films were prepared by the chemical solution deposition method. The effect of intermediate annealing on the phase, texture and superconducting properties of the films were evaluated. The results show that the intermediate annealing process is beneficial to achieve highly c-axis oriented YGdBCO film. The YGdBCO film prepared with intermediate annealing temperature of 400 oC has demonstrated high performance Jc (77 K, self field) = 2.4 MA/cm2.
2013, 42(6):1278-1281.
Abstract:
MgB2 superconductors were prepared by two-step PIT with B (crystalline or amorphous) and Mg as starting materials. The first step was mixing B (crystalline or amorphous) and Mg with the molar ratio of Mg:B=1:4. For the doping samples, 5wt% and 8wt% SiC were added to the mixture. Pressed pellets were treated at 900 oC for 30 min or 800 oC for 1 h. The second step was adding Mg to get the molar ratio of Mg:B=1:2. The tubes filled with the ground powders were treated at 750 oC for 2.5 h. The phase identities and the microstructure were investigated by X-ray diffraction (XRD) and Scanning Electronic Microscopy (SEM), respectively. Voltage dependence of the current of MgB2 wire was measured by a standard four-probe method. The results demonstrate that lots of MgB4 in low energy is synthesized by crystalline B and Mg at the first step. The sample prepared from crystalline B exhibits an excellent grain connection and stable I-V characteristics.
MgB2 superconductors were prepared by two-step PIT with B (crystalline or amorphous) and Mg as starting materials. The first step was mixing B (crystalline or amorphous) and Mg with the molar ratio of Mg:B=1:4. For the doping samples, 5wt% and 8wt% SiC were added to the mixture. Pressed pellets were treated at 900 oC for 30 min or 800 oC for 1 h. The second step was adding Mg to get the molar ratio of Mg:B=1:2. The tubes filled with the ground powders were treated at 750 oC for 2.5 h. The phase identities and the microstructure were investigated by X-ray diffraction (XRD) and Scanning Electronic Microscopy (SEM), respectively. Voltage dependence of the current of MgB2 wire was measured by a standard four-probe method. The results demonstrate that lots of MgB4 in low energy is synthesized by crystalline B and Mg at the first step. The sample prepared from crystalline B exhibits an excellent grain connection and stable I-V characteristics.
2013, 42(6):1282-1286.
Abstract:
Under microwave irradiation, the nanocomposite of Ag/TiO2 was prepared by a sol-gel method combined with temperature-programmed treatment in the presence of the triblock copolymer surfactant EO20PO70EO20 (P123). The phase composition, structure and morphology of the nanocomposite Ag/TiO2 were characterized by XRD, XPS, TEM, N2 adsorption-desorption tests and SEM-EDS. The results show that the silver species in the nanocomposite Ag/TiO2 by microwave irradiation is metallic Ag0. The phase of Ag/TiO2 with 5 min microwave irradiation is the best, whose surface area is 100.64 m2·g-1, and the average diameter is ca. 6.9 nm. Compared with the composite without microwave irradiation, the composite with microwave irradiation has small size, good structure and orderly distribution of particles. The photocatalytic activities of the as-prepared materials were studied by the UV irradiation photodegradation of methyl orange. The results show that Ag/TiO2 obtains the highest catalytic activity, when its microwave power is 200 W, and microwave irradiation time is 5 min. Moreover, it is still able to degrade 80% after three cycles.
Under microwave irradiation, the nanocomposite of Ag/TiO2 was prepared by a sol-gel method combined with temperature-programmed treatment in the presence of the triblock copolymer surfactant EO20PO70EO20 (P123). The phase composition, structure and morphology of the nanocomposite Ag/TiO2 were characterized by XRD, XPS, TEM, N2 adsorption-desorption tests and SEM-EDS. The results show that the silver species in the nanocomposite Ag/TiO2 by microwave irradiation is metallic Ag0. The phase of Ag/TiO2 with 5 min microwave irradiation is the best, whose surface area is 100.64 m2·g-1, and the average diameter is ca. 6.9 nm. Compared with the composite without microwave irradiation, the composite with microwave irradiation has small size, good structure and orderly distribution of particles. The photocatalytic activities of the as-prepared materials were studied by the UV irradiation photodegradation of methyl orange. The results show that Ag/TiO2 obtains the highest catalytic activity, when its microwave power is 200 W, and microwave irradiation time is 5 min. Moreover, it is still able to degrade 80% after three cycles.
2013, 42(6):1287-1290.
Abstract:
LaNi4.1Al0.3Mn0.4Si0.2Fex (x=0~0.4) hydrogen storage alloys were prepared by inductive melting. The crystal structure and phase composition of alloys were determined by XRD and SEM, and the electrochemical properties were also investigated. The results show that the alloys are composed of LaNi5 as main phase. When x≥0.1, some grey secondary phases are distributed on the main LaNi5 phase. With the increase of Fe content, the maximum discharge capacity decreases from 295.4 mAh/g (x=0) to 278.2 mAh/g (x=0.4), and the activity times increase from 10 to 18. Meanwhile the capacity retention rate increases from 66.85% (x=0) to 93.33% (x=0.4) after the charge/discharge cycle of 200 times.
LaNi4.1Al0.3Mn0.4Si0.2Fex (x=0~0.4) hydrogen storage alloys were prepared by inductive melting. The crystal structure and phase composition of alloys were determined by XRD and SEM, and the electrochemical properties were also investigated. The results show that the alloys are composed of LaNi5 as main phase. When x≥0.1, some grey secondary phases are distributed on the main LaNi5 phase. With the increase of Fe content, the maximum discharge capacity decreases from 295.4 mAh/g (x=0) to 278.2 mAh/g (x=0.4), and the activity times increase from 10 to 18. Meanwhile the capacity retention rate increases from 66.85% (x=0) to 93.33% (x=0.4) after the charge/discharge cycle of 200 times.
2013, 42(6):1291-1294.
Abstract:
Spherical micro-sized titanium powder was synthesized by (RF) plasma with large TiH2 powder as starting material. The phase, morphology and particle size distribution of the powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and laser micron sizer (LMS), respectively. The dehydrogenation, hydrogen decrepitation and spheroidization of TiH2 feedstock take place in one-step by RF plasma processing and the prepared spherical powder possesses favorable dispersity and smooth surface. The prepared fine spherical powder is composed of Ti and residual TiH. Pure single-phase spherical titanium powder is obtained after further vacuum (1.3×10-4 Pa) dehydrogenation treatment at 750 oC for 2 h. The average size of Ti powder is reduced from 100~150 μm of TiH2 powders to 20~50 μm after the treatment in the plasma. The spheroidization efficiency is almost 100% at feeding rate of 15 g/min. The RF plasma-assisted argon dehydrogenation and decomposition of TiH2 is an ideal route for large-scale synthesis of well- spherical metallic titanium powder.
Spherical micro-sized titanium powder was synthesized by (RF) plasma with large TiH2 powder as starting material. The phase, morphology and particle size distribution of the powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and laser micron sizer (LMS), respectively. The dehydrogenation, hydrogen decrepitation and spheroidization of TiH2 feedstock take place in one-step by RF plasma processing and the prepared spherical powder possesses favorable dispersity and smooth surface. The prepared fine spherical powder is composed of Ti and residual TiH. Pure single-phase spherical titanium powder is obtained after further vacuum (1.3×10-4 Pa) dehydrogenation treatment at 750 oC for 2 h. The average size of Ti powder is reduced from 100~150 μm of TiH2 powders to 20~50 μm after the treatment in the plasma. The spheroidization efficiency is almost 100% at feeding rate of 15 g/min. The RF plasma-assisted argon dehydrogenation and decomposition of TiH2 is an ideal route for large-scale synthesis of well- spherical metallic titanium powder.
2013, 42(6):1295-1299.
Abstract:
The SnCo1-xYx/C (x=0, 0.03, 0.1, 0.3, 0.5) anode materials for Li-ion batteries were synthesized by solid-state sintering followed by ball milling. The influences of Y contents on structures and electrochemical properties of the materials were investigated. Structure analyses reveal that SnCo/C consists of CoSn phase and carbon black. For SnCo1-xYx/C samples, CoSn2 phase appears when x is 0.03. When Y content is higher, a little amount of Sn and Y2O3 forms. Nano-crystalline CoSn and CoSn2 phase co-exist homogeneously in internal particles. A small amount of Y dissolve into CoSn and CoSn2 phase and exist in their grain boundaries and phase boundaries, and most of other Y reacts with O to form Y2O3 distributing at edges of particles. Electrochemical analysis shows that with Y content increasing, the discharge capacity and cycle performance of SnCo1-xYx/C both increase firstly and then decrease. As x is 0.1, the discharge capacity is 378 mA·h/g, close to the maximum, and the cycle performance reaches to the maximum that the capacity retention is above 87.6% after 50 cycles.
The SnCo1-xYx/C (x=0, 0.03, 0.1, 0.3, 0.5) anode materials for Li-ion batteries were synthesized by solid-state sintering followed by ball milling. The influences of Y contents on structures and electrochemical properties of the materials were investigated. Structure analyses reveal that SnCo/C consists of CoSn phase and carbon black. For SnCo1-xYx/C samples, CoSn2 phase appears when x is 0.03. When Y content is higher, a little amount of Sn and Y2O3 forms. Nano-crystalline CoSn and CoSn2 phase co-exist homogeneously in internal particles. A small amount of Y dissolve into CoSn and CoSn2 phase and exist in their grain boundaries and phase boundaries, and most of other Y reacts with O to form Y2O3 distributing at edges of particles. Electrochemical analysis shows that with Y content increasing, the discharge capacity and cycle performance of SnCo1-xYx/C both increase firstly and then decrease. As x is 0.1, the discharge capacity is 378 mA·h/g, close to the maximum, and the cycle performance reaches to the maximum that the capacity retention is above 87.6% after 50 cycles.
2013, 42(6):1300-1305.
Abstract:
Mg-3.13Nd-0.16Zn-0.41Zr (wt%, JDBM) alloy was chosen and the cell toxicity and corrosion property of the as-extruded JDBM were studied. Magnesium tube was prepared by hot extrusion processing and the microstructure of the tube was observed. The cardiovascular stent was prepared by laser cutting and electrochemical polishing processes. The surface roughness and radial expansion force were tested. The results show that JDBM magnesium alloy exhibits no cell toxicity of Endothelial cell, good corrosion resistance and corrosion mode. The radial expansion force of the prepared cardiovascular stents is over 4 times than that of the maximal vascular compression pressure of normal adult, which meets the requirement of the mechanical properties for cardiovascular stents.
Mg-3.13Nd-0.16Zn-0.41Zr (wt%, JDBM) alloy was chosen and the cell toxicity and corrosion property of the as-extruded JDBM were studied. Magnesium tube was prepared by hot extrusion processing and the microstructure of the tube was observed. The cardiovascular stent was prepared by laser cutting and electrochemical polishing processes. The surface roughness and radial expansion force were tested. The results show that JDBM magnesium alloy exhibits no cell toxicity of Endothelial cell, good corrosion resistance and corrosion mode. The radial expansion force of the prepared cardiovascular stents is over 4 times than that of the maximal vascular compression pressure of normal adult, which meets the requirement of the mechanical properties for cardiovascular stents.
2013, 42(6):1306-1309.
Abstract:
Zn0.95-xLixMn0.05O (x=0, 0.05) films were deposited on p-Si(110) by magnetron sputtering, and their structure, and electrical and magnetic properties were investigated. X-ray diffraction (XRD) results show that the films prefer the orientation along the c-axis and no second phase is found. The surfaces become smoother and denser with Li substitution.?The?Hall Effect measurement indicates the doping of Li in Mn-ZnO increases the concentration of the carrier without changing the n type conductivity. Li doping increases the magnetic property of the film at room temperature, which could be explained by a bound magnetic polaron model.
Zn0.95-xLixMn0.05O (x=0, 0.05) films were deposited on p-Si(110) by magnetron sputtering, and their structure, and electrical and magnetic properties were investigated. X-ray diffraction (XRD) results show that the films prefer the orientation along the c-axis and no second phase is found. The surfaces become smoother and denser with Li substitution.?The?Hall Effect measurement indicates the doping of Li in Mn-ZnO increases the concentration of the carrier without changing the n type conductivity. Li doping increases the magnetic property of the film at room temperature, which could be explained by a bound magnetic polaron model.
2013, 42(6):1310-1315.
Abstract:
The microstructure of Ag-Sn-La alloy powder after oxidation was investigated by XRD, OM and SEM. The results show that Ag, SnO2 and La2Sn2O7 phases are formed in Ag-Sn-La alloy powder after oxidation. Ag-Sn-La alloy powder has different oxidation kinetic characters, oxidation microstructures and oxidation mechanisms due to the different contents of alloying agent. The starting oxidation temperature of Ag-5.2Sn-3.4La alloy powder is 350 oC and the oxidation velocity is fast. Both element Sn and La are oxidized in situ and strip oxides are formed due to the fast oxidation of element La during the oxidation of Ag-5.2Sn-3.4La alloy powder. The oxidation velocity of Ag-6.87Sn-1.28La alloy powder is slow when the temperature is from room temperature to 300 oC and that is fast when the temperature is above 300 oC. Both element Sn and La are oxidized in situ and the formed oxides are uniformly distributed in the silver matrix. The starting oxidation temperature of Ag-9.26Sn-0.44La alloy powder is 567 oC and the oxidation velocity is slow. Element La is oxidized in situ and element Sn diffuses from the inner to the surface due to the driving of concentration gradient. La oxides are uniformly distributed in the silver matrix and Sn oxides are mainly distributed on the grain boundary after Ag-9.26Sn-0.44La alloy powder oxidation.
The microstructure of Ag-Sn-La alloy powder after oxidation was investigated by XRD, OM and SEM. The results show that Ag, SnO2 and La2Sn2O7 phases are formed in Ag-Sn-La alloy powder after oxidation. Ag-Sn-La alloy powder has different oxidation kinetic characters, oxidation microstructures and oxidation mechanisms due to the different contents of alloying agent. The starting oxidation temperature of Ag-5.2Sn-3.4La alloy powder is 350 oC and the oxidation velocity is fast. Both element Sn and La are oxidized in situ and strip oxides are formed due to the fast oxidation of element La during the oxidation of Ag-5.2Sn-3.4La alloy powder. The oxidation velocity of Ag-6.87Sn-1.28La alloy powder is slow when the temperature is from room temperature to 300 oC and that is fast when the temperature is above 300 oC. Both element Sn and La are oxidized in situ and the formed oxides are uniformly distributed in the silver matrix. The starting oxidation temperature of Ag-9.26Sn-0.44La alloy powder is 567 oC and the oxidation velocity is slow. Element La is oxidized in situ and element Sn diffuses from the inner to the surface due to the driving of concentration gradient. La oxides are uniformly distributed in the silver matrix and Sn oxides are mainly distributed on the grain boundary after Ag-9.26Sn-0.44La alloy powder oxidation.
2013, 42(6):1316-1320.
Abstract:
The composition characteristics, microstructure and properties, current development situation, application prospect and preparation techniques are summarized for FeCo crystal, amorphous and nanocrystalline alloys. The developing trend of FeCo soft magnetic materials is also prospected.
The composition characteristics, microstructure and properties, current development situation, application prospect and preparation techniques are summarized for FeCo crystal, amorphous and nanocrystalline alloys. The developing trend of FeCo soft magnetic materials is also prospected.
