Volume 40,Issue 3,2011 Table of Contents
2011, 40(3):377-383.
Abstract:
The precipitation behavior of α phase from β phase and the variation of mechanical properties during aging in the severely cold rolled alloy were studied. The results show that nanostructure is formed in some regions of the cold deformed alloy. α phases precipitating from β nanostructure region are thin-needle like during aging from 450 oC to 650 oC and those from β non-nanostructure region grow from the needle to the lath-shaped and finally become lenticular plate. After cold rolling and heat treatment at 450 oC for 4 h, the hardness of the alloy reaches the peak value (5328 MPa). The yield strength and ultimate strength of the alloy aged at 450 oC for 4 h are 1483 and 1562 MPa, respectively. The aging time for peak value is shortened and the hardness decreases sharply with the increase of aging temperature. The strength and hardness of the alloy after aging at 650 oC is lower than that before aging. This is attributed to the coarse thin-plate precipitates, the growth of nanostructure crystals and the decrease of dislocation density in the alloy during aging at 650 oC. The change tendency of the strength and the hardness of the alloy treated by different aging procedures are similar and they are related to the state of the precipitates formed during aging.
The precipitation behavior of α phase from β phase and the variation of mechanical properties during aging in the severely cold rolled alloy were studied. The results show that nanostructure is formed in some regions of the cold deformed alloy. α phases precipitating from β nanostructure region are thin-needle like during aging from 450 oC to 650 oC and those from β non-nanostructure region grow from the needle to the lath-shaped and finally become lenticular plate. After cold rolling and heat treatment at 450 oC for 4 h, the hardness of the alloy reaches the peak value (5328 MPa). The yield strength and ultimate strength of the alloy aged at 450 oC for 4 h are 1483 and 1562 MPa, respectively. The aging time for peak value is shortened and the hardness decreases sharply with the increase of aging temperature. The strength and hardness of the alloy after aging at 650 oC is lower than that before aging. This is attributed to the coarse thin-plate precipitates, the growth of nanostructure crystals and the decrease of dislocation density in the alloy during aging at 650 oC. The change tendency of the strength and the hardness of the alloy treated by different aging procedures are similar and they are related to the state of the precipitates formed during aging.
2011, 40(3):384-388.
Abstract:
The density of liquid NiCoAlMo quaternary alloy with a fixed molar ratio of Ni:Co:Al (xNi:xCo:xAl≈73:12:15) which is close to the average value of the commercial Ni-based superalloys TMS75, INCO713, CM247LC and CMSX-4, and molybdenum concentration change from 0% to 10% (mass fraction) was measured by a modified sessile drop method. It is found that the density of the liquid NiCoAlMo quaternary alloy decreases with increasing of temperature, but increases with the increase of molybdenum concentration in the alloys. The molar volume of liquid NiCoAlMo quaternary alloy increases with the increase of temperature and molybdenum concentration, and shows a negative deviation from the ideal linear mixing. The liquid density of NiCoAlMo quaternary alloy calculated from the partial molar volumes of nickel, cobalt, aluminum and molybdenum in the corresponding Ni-bases binary alloy are in good agreement with the experimental results; it means that within the error tolerance range the density of liquid Ni-based multi-component alloys can be predicted from the partial volumes of elements in Ni-based binary alloys in liquid state
The density of liquid NiCoAlMo quaternary alloy with a fixed molar ratio of Ni:Co:Al (xNi:xCo:xAl≈73:12:15) which is close to the average value of the commercial Ni-based superalloys TMS75, INCO713, CM247LC and CMSX-4, and molybdenum concentration change from 0% to 10% (mass fraction) was measured by a modified sessile drop method. It is found that the density of the liquid NiCoAlMo quaternary alloy decreases with increasing of temperature, but increases with the increase of molybdenum concentration in the alloys. The molar volume of liquid NiCoAlMo quaternary alloy increases with the increase of temperature and molybdenum concentration, and shows a negative deviation from the ideal linear mixing. The liquid density of NiCoAlMo quaternary alloy calculated from the partial molar volumes of nickel, cobalt, aluminum and molybdenum in the corresponding Ni-bases binary alloy are in good agreement with the experimental results; it means that within the error tolerance range the density of liquid Ni-based multi-component alloys can be predicted from the partial volumes of elements in Ni-based binary alloys in liquid state
2011, 40(3):389-394.
Abstract:
The inhibition performance of alloy element Na and ethanol inhibitor on lithium anode in 4 mol/L LiOH alkaline aqueous electrolytes at 30 oC was investigated using hydrogen evolution rate measurement at OCP, polarization curve, electrochemical impedance spectroscopy and voltage-time curve. The results show that alloy element Na and ethanol have inhibition effect both on anodic and cathodic reaction, but single alloy element Na or ethanol can not play an effective inhibition role on anode; only co-adding of alloy element Na and ethanol can greatly enhance the effect of inhibiting hydrogen evolution, the inhibition efficiency exceeds 80%. In addition, the property of discharge is very unstable with only adding of alloy element Na, but this problem can be resolved by adding ethanol. XRD shows that Li and Na forms perfect solid solution.
The inhibition performance of alloy element Na and ethanol inhibitor on lithium anode in 4 mol/L LiOH alkaline aqueous electrolytes at 30 oC was investigated using hydrogen evolution rate measurement at OCP, polarization curve, electrochemical impedance spectroscopy and voltage-time curve. The results show that alloy element Na and ethanol have inhibition effect both on anodic and cathodic reaction, but single alloy element Na or ethanol can not play an effective inhibition role on anode; only co-adding of alloy element Na and ethanol can greatly enhance the effect of inhibiting hydrogen evolution, the inhibition efficiency exceeds 80%. In addition, the property of discharge is very unstable with only adding of alloy element Na, but this problem can be resolved by adding ethanol. XRD shows that Li and Na forms perfect solid solution.
2011, 40(3):395-398.
Abstract:
Effects of Ni content and solution-aging treatment on transformation type and transformation temperature of Ti100-xNix (x=33.3-75) alloys were investigated by differential scanning calorimeter (DSC). The results show that one-stage transformation B2→B19′ of the solution-quenched Ti100-xNix alloys occurs. The martensitic transformation temperature TM is constant at x = 40-49, decreases sharply at x = 49-52, increases gradually at x = 52-56, and is constant again at x = 56-70. The alloys after aging at 773 K for 3.6 ks and 36 ks will have the occurrence of one-stage transformation B2→B19′ at x = 40-50.5, and the TM is constant first and then decreases suddenly with increasing of x; when x = 50.5-52, the alloys have the occurrence of two-stage transformation B2→R→B19′ and the TM decreases gradually with increasing of x; when x=53-70, the alloys have the occurrence of three-stage transformation and the TM1 and TM2 all increase first and then keep constant with increasing of x. All alloys after aging at 773 K for 360 ks have the occurrence of one-stage transformation B2→B19′ except for Ti49Ni51 and Ti47Ni53 alloy, which will have the occurrence of two-stage transformation B2→R→B19′ and three-stage transformation, respectively
Effects of Ni content and solution-aging treatment on transformation type and transformation temperature of Ti100-xNix (x=33.3-75) alloys were investigated by differential scanning calorimeter (DSC). The results show that one-stage transformation B2→B19′ of the solution-quenched Ti100-xNix alloys occurs. The martensitic transformation temperature TM is constant at x = 40-49, decreases sharply at x = 49-52, increases gradually at x = 52-56, and is constant again at x = 56-70. The alloys after aging at 773 K for 3.6 ks and 36 ks will have the occurrence of one-stage transformation B2→B19′ at x = 40-50.5, and the TM is constant first and then decreases suddenly with increasing of x; when x = 50.5-52, the alloys have the occurrence of two-stage transformation B2→R→B19′ and the TM decreases gradually with increasing of x; when x=53-70, the alloys have the occurrence of three-stage transformation and the TM1 and TM2 all increase first and then keep constant with increasing of x. All alloys after aging at 773 K for 360 ks have the occurrence of one-stage transformation B2→B19′ except for Ti49Ni51 and Ti47Ni53 alloy, which will have the occurrence of two-stage transformation B2→R→B19′ and three-stage transformation, respectively
2011, 40(3):399-402.
Abstract:
The compressive plasticity of Ti40Zr25Ni8Cu9Be18 bulk metallic glass with different specimen aspect ratio was investigated. The specimens with aspect ratios A＞1 exhibit a poor plasticity, contrariwise, showing an excellent plasticity. The maximum elongation before failure is up to about 86%. The difference in the plasticity is a result of shear bands behavior due to the geometrical constraints. The results show a linear increase in the density (spacing) of shear bands with increasing of stress, and the hardness decreases linearly with increasing of plastic strain. The results are consistent with a strain-induced local dilatation, and the free volume in the glass increases after deformation relative to the undeformed glass
The compressive plasticity of Ti40Zr25Ni8Cu9Be18 bulk metallic glass with different specimen aspect ratio was investigated. The specimens with aspect ratios A＞1 exhibit a poor plasticity, contrariwise, showing an excellent plasticity. The maximum elongation before failure is up to about 86%. The difference in the plasticity is a result of shear bands behavior due to the geometrical constraints. The results show a linear increase in the density (spacing) of shear bands with increasing of stress, and the hardness decreases linearly with increasing of plastic strain. The results are consistent with a strain-induced local dilatation, and the free volume in the glass increases after deformation relative to the undeformed glass
2011, 40(3):403-406.
Abstract:
In order to improve the oxidation protective property of carbon/carbon composites at high temperature, TaSi2 coating was prepared on the surface of SiC coated carbon/carbon composites by pack cementation technique. The crystal structure and morphology of the as-obtained coating was analyzed by XRD and SEM with EDS. The isothermal oxidation test was carried out in air at 1773 K. The results show that the as-prepared coating is composed of SiC, Si and TaSi2. The multilayer coating is about 200 μm in thickness, and there are no cracks in it. The results of EDS indicate that TaSi2 can effectively fill the holes of SiC coating. There is no visible interface between the TaSi2 outer coating and the SiC inner coating. The isothermal oxidation curve of the TaSi2/SiC coated carbon/carbon composites reveals that the coating can effectively protect carbon/carbon composites for 233 h at 1773 K
In order to improve the oxidation protective property of carbon/carbon composites at high temperature, TaSi2 coating was prepared on the surface of SiC coated carbon/carbon composites by pack cementation technique. The crystal structure and morphology of the as-obtained coating was analyzed by XRD and SEM with EDS. The isothermal oxidation test was carried out in air at 1773 K. The results show that the as-prepared coating is composed of SiC, Si and TaSi2. The multilayer coating is about 200 μm in thickness, and there are no cracks in it. The results of EDS indicate that TaSi2 can effectively fill the holes of SiC coating. There is no visible interface between the TaSi2 outer coating and the SiC inner coating. The isothermal oxidation curve of the TaSi2/SiC coated carbon/carbon composites reveals that the coating can effectively protect carbon/carbon composites for 233 h at 1773 K
2011, 40(3):407-412.
Abstract:
This work aims to develop a physically based numerical model to calculate the valence electron structures and atomic bonding of the precipitates of Al-Cu-Mg-Ag alloy with high Cu/Mg ratio with the empirical electron theory of solids and molecules. The valence electron structures and the interface conjunction of W phase were calculated, and they were investigated with the phase structure factor. Accordingly, on the basis of the empirical electron theory of solid and molecules, the precipitation and stability of the precipitates and the strengthening mechanism of Al-Cu-Mg-Ag alloy were explained on the level of valence electron structure
This work aims to develop a physically based numerical model to calculate the valence electron structures and atomic bonding of the precipitates of Al-Cu-Mg-Ag alloy with high Cu/Mg ratio with the empirical electron theory of solids and molecules. The valence electron structures and the interface conjunction of W phase were calculated, and they were investigated with the phase structure factor. Accordingly, on the basis of the empirical electron theory of solid and molecules, the precipitation and stability of the precipitates and the strengthening mechanism of Al-Cu-Mg-Ag alloy were explained on the level of valence electron structure
2011, 40(3):413-417.
Abstract:
Using semi-solid isothermal heat-treatment, the behavior of grain coarsening of Al-Zn-Mg-Cu alloy at the temperatures in solid-liquid two phase region was studied. The results from regression analysis show that the relationship between the average diameter of α(Al) grains and the isothermal holding time nearly fits the formula . In the formula, the coefficient of coarsening rate K increases with the increase of the isothermal temperature, which equals to 14811.4 μm4/s at 610 oC and 17836.3 μm4/s at 620 oC, respectively. The microstructure’s polygonizing, spheroidizing and coarsening of the experimental alloy occur simultaneously; among them the coarsening is caused by the coalescence between the adjacent grains and Ostwald ripening. During the early stage of the isothermal treatment, the coarsening is governed by the coalescence growth, but the coalescence becomes more and more difficult with the increase of the liquid fraction, which results in the decrease of the coarsening rate in the late stage
Using semi-solid isothermal heat-treatment, the behavior of grain coarsening of Al-Zn-Mg-Cu alloy at the temperatures in solid-liquid two phase region was studied. The results from regression analysis show that the relationship between the average diameter of α(Al) grains and the isothermal holding time nearly fits the formula . In the formula, the coefficient of coarsening rate K increases with the increase of the isothermal temperature, which equals to 14811.4 μm4/s at 610 oC and 17836.3 μm4/s at 620 oC, respectively. The microstructure’s polygonizing, spheroidizing and coarsening of the experimental alloy occur simultaneously; among them the coarsening is caused by the coalescence between the adjacent grains and Ostwald ripening. During the early stage of the isothermal treatment, the coarsening is governed by the coalescence growth, but the coalescence becomes more and more difficult with the increase of the liquid fraction, which results in the decrease of the coarsening rate in the late stage
2011, 40(3):418-423.
Abstract:
The roles of Zn content and thermomechanical treatment in affecting microstructures and mechanical properties of Mg-x wt%Zn-1wt%Mn (x=4, 5, 6, 7, 8, 9) wrought Mg alloys were investigated. The microstructure during extrusion was extremely refined by dynamic recrystallization (DRC). As Zn content increasing, the DRC grains tended to grow up; at the same time, more second phase streamlines would be present which restricted their further growth. During solution treatment, the DRC grains would rapidly grow up; however, more Zn content could obstruct the grain boundary expanding which resulted in finer grains. The microstructures of the aged specimens were examined by transmission electron microscopy (TEM). The age-hardening resulted mainly from two metastable phases, known as β1′ and β2′, the interfaces between which and the matrix were coherent or semicoherent. β1′ phases formed as rods with their long axis parallel to the [0001]α direction of the α-Mg matrix could act as a more enormous impediment to the motion of dislocations than β2′ formed as plates on (0001)α. Based on X-ray diffraction, both phases might be the Laves phase MgZn2. Compared with the one-step aging, β1′ and β2′ in two-step aged alloys were much finer and more dispersed, since nano-sized and coherent G.P. zones formed during the pre-aging stage provided more effective nuclei for the two phases during the second stage. Higher Zn content was apt to cause overaging, so large Mg-Zn blocks were formed by consuming β1′ and β2′ after aging at 180 oC for 16 h. Mn was present as rod-shaped precipitates in the aged specimens, which could act as nuclei for β1′ and β2′ and drive them into coarser ones. The mechanical properties of as-extruded samples were not so sensitive to the changes of Zn content. The strength of as-aged samples rose as a parabolic curve with the increasing of Zn content, while Zn content exceeded its solid solution limit in Mg (6.2 wt%), strength rising became slow, and the elongation quickly deteriorated, so a Mg-Zn-Mn alloy with 6wt% Zn possessed the best mechanical properties.
The roles of Zn content and thermomechanical treatment in affecting microstructures and mechanical properties of Mg-x wt%Zn-1wt%Mn (x=4, 5, 6, 7, 8, 9) wrought Mg alloys were investigated. The microstructure during extrusion was extremely refined by dynamic recrystallization (DRC). As Zn content increasing, the DRC grains tended to grow up; at the same time, more second phase streamlines would be present which restricted their further growth. During solution treatment, the DRC grains would rapidly grow up; however, more Zn content could obstruct the grain boundary expanding which resulted in finer grains. The microstructures of the aged specimens were examined by transmission electron microscopy (TEM). The age-hardening resulted mainly from two metastable phases, known as β1′ and β2′, the interfaces between which and the matrix were coherent or semicoherent. β1′ phases formed as rods with their long axis parallel to the [0001]α direction of the α-Mg matrix could act as a more enormous impediment to the motion of dislocations than β2′ formed as plates on (0001)α. Based on X-ray diffraction, both phases might be the Laves phase MgZn2. Compared with the one-step aging, β1′ and β2′ in two-step aged alloys were much finer and more dispersed, since nano-sized and coherent G.P. zones formed during the pre-aging stage provided more effective nuclei for the two phases during the second stage. Higher Zn content was apt to cause overaging, so large Mg-Zn blocks were formed by consuming β1′ and β2′ after aging at 180 oC for 16 h. Mn was present as rod-shaped precipitates in the aged specimens, which could act as nuclei for β1′ and β2′ and drive them into coarser ones. The mechanical properties of as-extruded samples were not so sensitive to the changes of Zn content. The strength of as-aged samples rose as a parabolic curve with the increasing of Zn content, while Zn content exceeded its solid solution limit in Mg (6.2 wt%), strength rising became slow, and the elongation quickly deteriorated, so a Mg-Zn-Mn alloy with 6wt% Zn possessed the best mechanical properties.
2011, 40(3):424-428.
Abstract:
Phase transformation of layered orthorhombic Li1-xMnO2 (o-Li1-xMnO2, 0≤x≤0.95) during the first charging process (lithium ion deintercalation in electrochemical system) was investigated using ex-situ high-resolution X-ray diffraction and Rietveld refinement. The results reveal that the increasing speed of the o-LiMnO2 cathode’s voltages is related to the change of its microstructure. And a succession of phase transformation of the o-LiMnO2 occurs in the first lithium deintercalation process. Rock-salt typed lithium manganese oxides emerge followed by the appearance of the spinel-like typed, which confirms the phase transition process from theoretical computation and crystallography conjecture in literatures. Only the above-stated type lithium manganese oxides (originated from o-LiMnO2) exist in the final product. Lithium ions extract from lattices of the rock-salt typed and the spinel-like typed lithium manganese oxides; both the lattice parameters become smaller and their microstructures change with the charge proceeding
Phase transformation of layered orthorhombic Li1-xMnO2 (o-Li1-xMnO2, 0≤x≤0.95) during the first charging process (lithium ion deintercalation in electrochemical system) was investigated using ex-situ high-resolution X-ray diffraction and Rietveld refinement. The results reveal that the increasing speed of the o-LiMnO2 cathode’s voltages is related to the change of its microstructure. And a succession of phase transformation of the o-LiMnO2 occurs in the first lithium deintercalation process. Rock-salt typed lithium manganese oxides emerge followed by the appearance of the spinel-like typed, which confirms the phase transition process from theoretical computation and crystallography conjecture in literatures. Only the above-stated type lithium manganese oxides (originated from o-LiMnO2) exist in the final product. Lithium ions extract from lattices of the rock-salt typed and the spinel-like typed lithium manganese oxides; both the lattice parameters become smaller and their microstructures change with the charge proceeding
2011, 40(3):429-432.
Abstract:
β γ-TiAl alloy owns excellent deformability at high temperature, so it exhibits great potential in different fields in future. Ti-45Al-9(V, Nb, Y) alloys with different x=V/Nb (x=1, 1.5, 2, 3.5) were prepared, and their cyclic oxidation behavior in static air at 800 oC was investigated. The results show that Ti-45Al-9(V, Nb,Y) alloy possesses high oxidation resistance when x=1, due to the strip-like, continuous and dense Al2O3 layer. However, the Al2O3 layer becomes thinner with increasing of x=V/Nb, resulting in poor oxidation resistance of Ti-45Al-9(V, Nb,Y) alloy
β γ-TiAl alloy owns excellent deformability at high temperature, so it exhibits great potential in different fields in future. Ti-45Al-9(V, Nb, Y) alloys with different x=V/Nb (x=1, 1.5, 2, 3.5) were prepared, and their cyclic oxidation behavior in static air at 800 oC was investigated. The results show that Ti-45Al-9(V, Nb,Y) alloy possesses high oxidation resistance when x=1, due to the strip-like, continuous and dense Al2O3 layer. However, the Al2O3 layer becomes thinner with increasing of x=V/Nb, resulting in poor oxidation resistance of Ti-45Al-9(V, Nb,Y) alloy
2011, 40(3):433-437.
Abstract:
To resolve the problem that ductile phase Cr decreases slightly the oxidation resistance of Laves phase NbCr2 alloys at 1200 oC, multiple elements Al, Si and Y were added to Cr-20Nb alloys. The results indicate that the oxidation resistance of Cr-20Nb alloys alloyed by multi elements is higher than that of unalloyed Cr-20Nb and Cr-20Nb alloyed by single element. Moreover, the oxidation resistance of Cr-20Nb alloys increases with increasing the Si content. SEM analysis shows that the additions improve the adhesion of oxide film on the matrix
To resolve the problem that ductile phase Cr decreases slightly the oxidation resistance of Laves phase NbCr2 alloys at 1200 oC, multiple elements Al, Si and Y were added to Cr-20Nb alloys. The results indicate that the oxidation resistance of Cr-20Nb alloys alloyed by multi elements is higher than that of unalloyed Cr-20Nb and Cr-20Nb alloyed by single element. Moreover, the oxidation resistance of Cr-20Nb alloys increases with increasing the Si content. SEM analysis shows that the additions improve the adhesion of oxide film on the matrix
2011, 40(3):438-442.
Abstract:
The density functional theory (DFT) of first-principles studies were adopted to calculate adsorption of H2 on Mo(001) surface. The structure parameters and the adsorption energy at three adsorption sites (top, bridge, hollow) of H2 on Mo(001) surface were obtained. The calculation results show that the highest adsorption energy is at the top site. The changes of the nearest distance between H atom and Mo atom dH-Mo with the H2 molecule bond length before and after the adsorption were analyzed. From the analysis of the density of states of H2 and the adsorption of H2 on Mo(001) surface, the adsorption reasons is the interaction between the 1s orbit of the H2 molecule and the 4d orbit of the base metal
The density functional theory (DFT) of first-principles studies were adopted to calculate adsorption of H2 on Mo(001) surface. The structure parameters and the adsorption energy at three adsorption sites (top, bridge, hollow) of H2 on Mo(001) surface were obtained. The calculation results show that the highest adsorption energy is at the top site. The changes of the nearest distance between H atom and Mo atom dH-Mo with the H2 molecule bond length before and after the adsorption were analyzed. From the analysis of the density of states of H2 and the adsorption of H2 on Mo(001) surface, the adsorption reasons is the interaction between the 1s orbit of the H2 molecule and the 4d orbit of the base metal
2011, 40(3):443-447.
Abstract:
To optimize the relationship of strength and ductility of an aluminum-lithium alloy, 2A97, a double-aging treatment was employed. The effect of double-aging processes on microstructures and tensile properties was investigated by transmission electron microscopy (TEM) and tensile tests. Results show that with the pre-aging temperature increasing, the formation of the strengthening precipitates T1 is promoted at the matrix at 155 oC, instead of the precipitation of θ"/θ′ and δ′ phases at 135 oC. It is different from that T1 precipitates nucleate and grow mainly at grain and subgrain boundaries at 135 oC. Numerous fine θ"/θ′ precipitates at the matrix at 135 oC cause the reduction of the width of θ"/θ′ precipitates-free zones adjacent to grain and subgrain boundaries and the size of equilibrium precipitates T1 at grain and subgrain boundaries. Numerous larger precipitates T1 dispersing homogeneously at matrix, combined with numerous large size θ′ and δ′ precipitates, yield higher tensile strength for the microstructure of double aging with 155 oC pre-aging than that of double aging with 135 oC pre-aging
To optimize the relationship of strength and ductility of an aluminum-lithium alloy, 2A97, a double-aging treatment was employed. The effect of double-aging processes on microstructures and tensile properties was investigated by transmission electron microscopy (TEM) and tensile tests. Results show that with the pre-aging temperature increasing, the formation of the strengthening precipitates T1 is promoted at the matrix at 155 oC, instead of the precipitation of θ"/θ′ and δ′ phases at 135 oC. It is different from that T1 precipitates nucleate and grow mainly at grain and subgrain boundaries at 135 oC. Numerous fine θ"/θ′ precipitates at the matrix at 135 oC cause the reduction of the width of θ"/θ′ precipitates-free zones adjacent to grain and subgrain boundaries and the size of equilibrium precipitates T1 at grain and subgrain boundaries. Numerous larger precipitates T1 dispersing homogeneously at matrix, combined with numerous large size θ′ and δ′ precipitates, yield higher tensile strength for the microstructure of double aging with 155 oC pre-aging than that of double aging with 135 oC pre-aging
2011, 40(3):448-452.
Abstract:
A two-step anodic oxidation process was used to prepare porous anodic aluminum oxide (AAO) template in oxalic acid electrolyte. By adjusting technological parameters including current density, oxidation time and electrolyte concentration, the AAO template possessed of uniformly distributed holes, similar aperture and hexagonal orifice was obtained. Meanwhile, by removing the barrier layer without peeling the film, the residual aluminum became basement and functioned as electrode. In the non-aqueous system, the nanowire array of Gd-Co alloy was prepared by DC electrodeposition in the AAO template. Through the observation of SEM, the aperture of AAO template is approximately 60 nm, and it changes little before and after removing the barrier layer. The prepared Gd-Co alloy nanowire is orderly and in the similar size. EDS measurement shows that nanowires are of Gd-Co alloy and a few oxides, in which Gd-Co alloy content is 90.66wt%, and the mole ratio of Gd to Co is 1:7.5. XRD analysis displays that the nanowire of Gd-Co alloy is noncrystal.
A two-step anodic oxidation process was used to prepare porous anodic aluminum oxide (AAO) template in oxalic acid electrolyte. By adjusting technological parameters including current density, oxidation time and electrolyte concentration, the AAO template possessed of uniformly distributed holes, similar aperture and hexagonal orifice was obtained. Meanwhile, by removing the barrier layer without peeling the film, the residual aluminum became basement and functioned as electrode. In the non-aqueous system, the nanowire array of Gd-Co alloy was prepared by DC electrodeposition in the AAO template. Through the observation of SEM, the aperture of AAO template is approximately 60 nm, and it changes little before and after removing the barrier layer. The prepared Gd-Co alloy nanowire is orderly and in the similar size. EDS measurement shows that nanowires are of Gd-Co alloy and a few oxides, in which Gd-Co alloy content is 90.66wt%, and the mole ratio of Gd to Co is 1:7.5. XRD analysis displays that the nanowire of Gd-Co alloy is noncrystal.
2011, 40(3):453-456.
Abstract:
Tensile properties, fracture behavior and microstructure of Al-7.1Zn-1.1Mg-1.6Cu-0.14Zr alloy with T6 and T74 aging treatments were investigated by tensile testing, optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that, compared with the values in T6 state, the strength of the alloy in T74 state decreases by 15%; however, the elongation and electrical conductivity of the alloy in T74 state increases by 52% and 29%, respectively. The fracture mode of the alloy in T6 state is transgranular shearing and intergranular dimple mixed fracture. In T74 state, the fracture mode of alloy is transgranular dimple fracture. The fracture behavior of the alloy with different aging treatments is mainly determined by the coordinating interaction between movement of the dislocation and microstructures in the grain and grain boundary
Tensile properties, fracture behavior and microstructure of Al-7.1Zn-1.1Mg-1.6Cu-0.14Zr alloy with T6 and T74 aging treatments were investigated by tensile testing, optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that, compared with the values in T6 state, the strength of the alloy in T74 state decreases by 15%; however, the elongation and electrical conductivity of the alloy in T74 state increases by 52% and 29%, respectively. The fracture mode of the alloy in T6 state is transgranular shearing and intergranular dimple mixed fracture. In T74 state, the fracture mode of alloy is transgranular dimple fracture. The fracture behavior of the alloy with different aging treatments is mainly determined by the coordinating interaction between movement of the dislocation and microstructures in the grain and grain boundary
2011, 40(3):457-461.
Abstract:
Effects of microstructural type on the low cycle fatigue behavior of Ti600 alloy were investigated by Laser Scanning Confocal Microscope (LSCM) and Scanning Electron Microscope (SEM). The results demonstrate that whether specimens with LM (lamellar microstructure) or BM (bimodal microstructure) show cyclic softening within a total strain amplitude range from ±0.6% to ±1.0%. At the same total strain amplitude, the fatigue life of BM specimens is longer than that of LM specimens. The joint of cracks near the lateral surface of fatigue fracture specimens with LM lead to rupture quickly under lower cyclic stress, since the effective area for cyclic stress response is decreased rapidly.
Effects of microstructural type on the low cycle fatigue behavior of Ti600 alloy were investigated by Laser Scanning Confocal Microscope (LSCM) and Scanning Electron Microscope (SEM). The results demonstrate that whether specimens with LM (lamellar microstructure) or BM (bimodal microstructure) show cyclic softening within a total strain amplitude range from ±0.6% to ±1.0%. At the same total strain amplitude, the fatigue life of BM specimens is longer than that of LM specimens. The joint of cracks near the lateral surface of fatigue fracture specimens with LM lead to rupture quickly under lower cyclic stress, since the effective area for cyclic stress response is decreased rapidly.
2011, 40(3):462-465.
Abstract:
The phase, microstructure and absorption/desorption properties of V28Ti32Cr28Mn6Fe6 alloy prepared from FeV80 alloy were researched by XRD, SEM/EDS and PCT measurement. The prepared alloy consists of two phases, bcc main phase and C14 Laves minor phase. This alloy shows low absorption/desorption capacities and poor absorption kinetics due to the high oxygen content of 0.83wt% originated from the FeV80 source. After addition of rare-earth metal of La, the oxygen content is obviously decreased, and the mechanical properties and absorption/desorption capacities are markedly increased. The addition of 4.0wt% La brings about the optimal hydrogen absorption and desorption properties, i.e. an absorption capacity of 3.62wt% H and desorption capacity of 2.13wt% H at 293 K. The formation enthalpy of the hydride of the 4.0wt% La containing alloy is –40.0±1 kJ/mol·H2.
The phase, microstructure and absorption/desorption properties of V28Ti32Cr28Mn6Fe6 alloy prepared from FeV80 alloy were researched by XRD, SEM/EDS and PCT measurement. The prepared alloy consists of two phases, bcc main phase and C14 Laves minor phase. This alloy shows low absorption/desorption capacities and poor absorption kinetics due to the high oxygen content of 0.83wt% originated from the FeV80 source. After addition of rare-earth metal of La, the oxygen content is obviously decreased, and the mechanical properties and absorption/desorption capacities are markedly increased. The addition of 4.0wt% La brings about the optimal hydrogen absorption and desorption properties, i.e. an absorption capacity of 3.62wt% H and desorption capacity of 2.13wt% H at 293 K. The formation enthalpy of the hydride of the 4.0wt% La containing alloy is –40.0±1 kJ/mol·H2.
2011, 40(3):466-469.
Abstract:
A catalyst of the Pt-Ru/C doped with Eu for methanol electro-oxidation were synthesized by the method of pulse electro-deposition of the precursor of active material impregnated in porous carbon black layer. The active stability of Pt-Ru-Eu/C was evaluated using cyclic voltammetry. And the microstructure and composition of the catalyst surface were characterized by XRD and XPS. Results show that the performances of Pt-Ru-Eu/C for methanol electro-oxidation went down slowly during the cycles of number 15 to number 50, and then went into the steady state after the cycle of number 65. However, the electro-catalytic activity of Pt-Ru-Eu/C is still higher than that of Pt-Ru/C in all the cycles of the activity test. The main reason of the low activity for methanol electro-catalytic oxidation on the Pt-Ru-Eu/C is the serious loss of the EuOx from the top atom layer and the increasing of the size of Pt-Ru-Eu alloy particles with the activity test time prolonging
A catalyst of the Pt-Ru/C doped with Eu for methanol electro-oxidation were synthesized by the method of pulse electro-deposition of the precursor of active material impregnated in porous carbon black layer. The active stability of Pt-Ru-Eu/C was evaluated using cyclic voltammetry. And the microstructure and composition of the catalyst surface were characterized by XRD and XPS. Results show that the performances of Pt-Ru-Eu/C for methanol electro-oxidation went down slowly during the cycles of number 15 to number 50, and then went into the steady state after the cycle of number 65. However, the electro-catalytic activity of Pt-Ru-Eu/C is still higher than that of Pt-Ru/C in all the cycles of the activity test. The main reason of the low activity for methanol electro-catalytic oxidation on the Pt-Ru-Eu/C is the serious loss of the EuOx from the top atom layer and the increasing of the size of Pt-Ru-Eu alloy particles with the activity test time prolonging
2011, 40(3):470-472.
Abstract:
Compared with ordinary coarse-grained metals, the nanocrystalline metals exhibit higher strength and hardness, but have a decrease in ductility. To investigate the reasons of low ductility in nanocrystalline metals, contrastive study of mechanical behaviors between high purity, fully dense coarse-grained Ni sheets and nanocrystalline Ni sheets was carried out under uniaxial quasi-static tensile loading through digital image correlation method in this paper. From the displacement and strain fields of the two sorts of samples, uniform plastic deformation was observed in the coarse-grained Ni sample. Whereas, the nanocrystalline Ni exhibited shear localization in the form of shear band, which is the main reason of the early failure during plastic deformation in nanocrystalline Ni.
Compared with ordinary coarse-grained metals, the nanocrystalline metals exhibit higher strength and hardness, but have a decrease in ductility. To investigate the reasons of low ductility in nanocrystalline metals, contrastive study of mechanical behaviors between high purity, fully dense coarse-grained Ni sheets and nanocrystalline Ni sheets was carried out under uniaxial quasi-static tensile loading through digital image correlation method in this paper. From the displacement and strain fields of the two sorts of samples, uniform plastic deformation was observed in the coarse-grained Ni sample. Whereas, the nanocrystalline Ni exhibited shear localization in the form of shear band, which is the main reason of the early failure during plastic deformation in nanocrystalline Ni.
2011, 40(3):473-478.
Abstract:
The highly ordered mesoporous materials Zr-Ce-SBA-15 were synthesized by a hydrothermal route using tetraethyl orthosilicate (TEOS) as a silica source, Pluronic P123 as a template, zirconyl chloride and cerous nitrate as precursors under a moderate acidic condition. The main strategy of this method was to utilize the acidity self-generated in the aqueous solutions, where no addition of mineral acids was necessary. Through a simple adjustment of the initial reactant molar ratio in the synthesis gel and the crystallization temperature, the morphology of mesoporous materials could be controlled efficaciously. The as-synthesized materials were characterized by XRD, TEM, SEM, inductively coupled plasma atomic emission spectrometry (ICP-AES) and N2 adsorption. Results indicate that the Zr and Ce species are incorporated into the framework of SBA-15. The obtained Zr-Ce-SBA-15 materials with different nZr(Ce):nSi molar ratios of 0.03, 0.05 and 0.10 possess 2D-hexagonal P6mm mesoporous structure similar to SBA-15. In addition, the morphology of the bimetallic Zr-Ce-SBA-15 mesoporous materials varies with different nZr(Ce):nSi molar ratios and different crystallization temperatures. When the nZr(Ce):nSi ratio is 0.05 and the crystallization temperature 100 oC, the material of Zr-Ce-SBA-15 displays hexagonal-platelet morphology. With increasing of crystallization temperature, the morphology of the bimetallic Zr-Ce-SBA-15 mesoporous materials is changed from hexagonal-platelet to circular-platelet.
The highly ordered mesoporous materials Zr-Ce-SBA-15 were synthesized by a hydrothermal route using tetraethyl orthosilicate (TEOS) as a silica source, Pluronic P123 as a template, zirconyl chloride and cerous nitrate as precursors under a moderate acidic condition. The main strategy of this method was to utilize the acidity self-generated in the aqueous solutions, where no addition of mineral acids was necessary. Through a simple adjustment of the initial reactant molar ratio in the synthesis gel and the crystallization temperature, the morphology of mesoporous materials could be controlled efficaciously. The as-synthesized materials were characterized by XRD, TEM, SEM, inductively coupled plasma atomic emission spectrometry (ICP-AES) and N2 adsorption. Results indicate that the Zr and Ce species are incorporated into the framework of SBA-15. The obtained Zr-Ce-SBA-15 materials with different nZr(Ce):nSi molar ratios of 0.03, 0.05 and 0.10 possess 2D-hexagonal P6mm mesoporous structure similar to SBA-15. In addition, the morphology of the bimetallic Zr-Ce-SBA-15 mesoporous materials varies with different nZr(Ce):nSi molar ratios and different crystallization temperatures. When the nZr(Ce):nSi ratio is 0.05 and the crystallization temperature 100 oC, the material of Zr-Ce-SBA-15 displays hexagonal-platelet morphology. With increasing of crystallization temperature, the morphology of the bimetallic Zr-Ce-SBA-15 mesoporous materials is changed from hexagonal-platelet to circular-platelet.
2011, 40(3):479-482.
Abstract:
A series of photoluminescence materials of red-orange-blue three lights emission, Ce/Mn:Cd0.5Zn0.5B4O7 were prepared via a high-temperature solid-state method for the first time. The crystal system, point group and cell parameters of (Cd0.38Ce0.06/ Mn0.03)Zn0.5B4O7 were confirmed by X-ray diffraction. The phosphor belongs to orthorhombic crystal system with Pbca space group. Spectral characteristics of Ce/Mn:Cd0.5Zn0.5B4O7 indicate that excited by 285 nm UV, the emission mainly presents 4T1(4G)→6A1(6S) of Mn2+; excited by 370 nm UV, the emission is mainly 5d→2F5/2, 2F7/2 of Ce3+; excited by 296 nm UV, it shows compound light-emitting of 470 nm and 630 nm with similar emission intensity ratio. Ce3+ and Mn2+ co-exist, and they are the activator and the sensitizer of each other. In the phosphors Ce/MnCd0.5Zn0.5B4O7 there are multiple energy transfers among the host, Ce3+ and Mn2+, which are rarely found. The major energy transfer is Ce3+?Mn2+. Flux CaF2 and KCl can reduce the synthesis temperature and increase the luminous intensity, but they have different effects for Ce3+ and Mn2+ emission spectra
A series of photoluminescence materials of red-orange-blue three lights emission, Ce/Mn:Cd0.5Zn0.5B4O7 were prepared via a high-temperature solid-state method for the first time. The crystal system, point group and cell parameters of (Cd0.38Ce0.06/ Mn0.03)Zn0.5B4O7 were confirmed by X-ray diffraction. The phosphor belongs to orthorhombic crystal system with Pbca space group. Spectral characteristics of Ce/Mn:Cd0.5Zn0.5B4O7 indicate that excited by 285 nm UV, the emission mainly presents 4T1(4G)→6A1(6S) of Mn2+; excited by 370 nm UV, the emission is mainly 5d→2F5/2, 2F7/2 of Ce3+; excited by 296 nm UV, it shows compound light-emitting of 470 nm and 630 nm with similar emission intensity ratio. Ce3+ and Mn2+ co-exist, and they are the activator and the sensitizer of each other. In the phosphors Ce/MnCd0.5Zn0.5B4O7 there are multiple energy transfers among the host, Ce3+ and Mn2+, which are rarely found. The major energy transfer is Ce3+?Mn2+. Flux CaF2 and KCl can reduce the synthesis temperature and increase the luminous intensity, but they have different effects for Ce3+ and Mn2+ emission spectra
Yu Fengdan
,
Chu Chenglin
,
Ji Honglin
,
Rao Xi
,
Zhang Wenyan
,
Dong Yinsheng
,
Guo Chao
,
Sheng Xiaobo
,
Lin Pinghua
,
Paul K. Chu
2011, 40(3):483-486.
Abstract:
Zr-Ti film was deposited on the surface of NiTi shape memory alloy (SMA) by balanced magnetron DC sputtering. The results of SEM, XRD and XPS indicate that the Zr-Ti film has the T-type crystal band structure with a fine and dense fibre character. The film has a good combination with NiTi substrate and a small amount of bioinert ZrO2 and TiO2 ceramics phases is found in the film. Blood compatibility was evaluated by hemolysis test and platelet adhesion test. The hemolysis of Zr-Ti film is less than that of NiTi SMA. And the number of platelets on the sample surface is also less than that of Zr-Ti film, which indicates the blood compatibility of NiTi SMA could be improved by the Zr-Ti film. Finally the depositing mechanism of the Zr-Ti film by magnetron sputtering was discussed
Zr-Ti film was deposited on the surface of NiTi shape memory alloy (SMA) by balanced magnetron DC sputtering. The results of SEM, XRD and XPS indicate that the Zr-Ti film has the T-type crystal band structure with a fine and dense fibre character. The film has a good combination with NiTi substrate and a small amount of bioinert ZrO2 and TiO2 ceramics phases is found in the film. Blood compatibility was evaluated by hemolysis test and platelet adhesion test. The hemolysis of Zr-Ti film is less than that of NiTi SMA. And the number of platelets on the sample surface is also less than that of Zr-Ti film, which indicates the blood compatibility of NiTi SMA could be improved by the Zr-Ti film. Finally the depositing mechanism of the Zr-Ti film by magnetron sputtering was discussed
2011, 40(3):487-490.
Abstract:
(ZrTi)V2 alloy was prepared by vacuum induction melting method and then annealed at 950 oC for a long time. The phase composition and hydrogen absorption property were investigated. Results show that (ZrTi)V2 alloy is composed of C15 Laves phase, α-Zr phase, Zr3V3O phase and V-based solid solution phase. The α-Zr phase and V-based solid solution phase decrease after heat treatment. The experimental alloy is easy to be activated. The best activation effect can be obtained by the process of removing gas at 400 oC for 1 h and a hydrogenation cycle. The equilibrium pressure is 8.1×10-14 Pa at room temperature extrapolated by Van’t Hoff line
(ZrTi)V2 alloy was prepared by vacuum induction melting method and then annealed at 950 oC for a long time. The phase composition and hydrogen absorption property were investigated. Results show that (ZrTi)V2 alloy is composed of C15 Laves phase, α-Zr phase, Zr3V3O phase and V-based solid solution phase. The α-Zr phase and V-based solid solution phase decrease after heat treatment. The experimental alloy is easy to be activated. The best activation effect can be obtained by the process of removing gas at 400 oC for 1 h and a hydrogenation cycle. The equilibrium pressure is 8.1×10-14 Pa at room temperature extrapolated by Van’t Hoff line
2011, 40(3):491-494.
Abstract:
High-strength SiC fibre (W core) was fabricated by DC heating chemical vapor deposition (CVD) method. The morphology, microstructure and fracture characteristics of the fiber were characterized by X-ray Diffraction (XRD), Scanning Electron Microscope (SEM) and Transmission Electron Microscopy (TEM). The strength of the fibre was also analyzed by tensile tests. The results show that the CVD-SiC fibre mainly consists of β-SiC. The interfacial reaction layer between W core and SiC layer is 300 nm in thickness and there is great thermo-residual tensile stress, which leads to the tensile strength degradation. High-strength SiC fibre cracking origin is in the W/SiC interfacial reaction zone while low-strength SiC fibre cracking is generated in the inside of W core or on the surface of the fibre. The existence of defects at W core or on SiC fibre surface leads to low tensile strength
High-strength SiC fibre (W core) was fabricated by DC heating chemical vapor deposition (CVD) method. The morphology, microstructure and fracture characteristics of the fiber were characterized by X-ray Diffraction (XRD), Scanning Electron Microscope (SEM) and Transmission Electron Microscopy (TEM). The strength of the fibre was also analyzed by tensile tests. The results show that the CVD-SiC fibre mainly consists of β-SiC. The interfacial reaction layer between W core and SiC layer is 300 nm in thickness and there is great thermo-residual tensile stress, which leads to the tensile strength degradation. High-strength SiC fibre cracking origin is in the W/SiC interfacial reaction zone while low-strength SiC fibre cracking is generated in the inside of W core or on the surface of the fibre. The existence of defects at W core or on SiC fibre surface leads to low tensile strength
26 Preparation and Electrochemical Corrosion Behavior of Amorphous and Nanocrystalline Fe-Based Alloys
2011, 40(3):495-498.
Abstract:
Amorphous Fe73.5Si13.5B9Nb3Cu1 alloy was prepared by the chill block melt-spinning process and the nanocrystalline alloy was obtained by amorphous crystallization annealing. The crystallization behavior was analysed by DSC, XRD and TEM. The electrochemical corrosion behavior in different annealed states was investigated by linear polarization method and electrochemical impedance spectroscopy in 1 mol/L HCl solution. The results show that the crystallization of the amorphous alloy occurs in the two steps. Some nanometer crystals appear when annealed at 550 oC and 600 oC with grain size of 13 nm and 15 nm, respectively. The nanocrystalline alloy has higher corrosion potential and lower anodic current density than amorphous alloy. It indicates that nanocrystalline alloy has a higher corrosion resistance. Amorphous and nanocrystalline Fe73.5Si13.5B9Nb3Cu1 alloys both consist of only single semi-circle. The charge transfer reaction resistances increases as the annealing temperature rises.
Amorphous Fe73.5Si13.5B9Nb3Cu1 alloy was prepared by the chill block melt-spinning process and the nanocrystalline alloy was obtained by amorphous crystallization annealing. The crystallization behavior was analysed by DSC, XRD and TEM. The electrochemical corrosion behavior in different annealed states was investigated by linear polarization method and electrochemical impedance spectroscopy in 1 mol/L HCl solution. The results show that the crystallization of the amorphous alloy occurs in the two steps. Some nanometer crystals appear when annealed at 550 oC and 600 oC with grain size of 13 nm and 15 nm, respectively. The nanocrystalline alloy has higher corrosion potential and lower anodic current density than amorphous alloy. It indicates that nanocrystalline alloy has a higher corrosion resistance. Amorphous and nanocrystalline Fe73.5Si13.5B9Nb3Cu1 alloys both consist of only single semi-circle. The charge transfer reaction resistances increases as the annealing temperature rises.
2011, 40(3):499-502.
Abstract:
The corrosion behavior of AZ91D magnesium alloy was studied in atmosphere containing 4×10-6 SO2 (volume fraction) by indoor simulation experiment. Corrosion morphology was observed by atomic force microscopy (AFM), optical microscopy (OM) and scanning electron microscopy (SEM). Corrosion products were analyzed by X-ray diffraction (XRD). The mass gain of AZ91D magnesium alloy during the corrosion period of 1200 h can be divided into two stages. The first stage accords with linear increase law, and the second stage accords with exponential decrease law. β phase is protected as cathode, and granular corrosion products are formed in α phase as anode. The corrosion products grow outward until the continuous corrosion layer is formed. Meanwhile, large granular corrosion products appear in the cracks of corrosion layer. The corrosion products mainly consist of MgO, Mg(OH)2, MgSO3·6H2O and MgSO4·6H2O. The quantity of MgO and Mg(OH)2 is decreased, while the quantity of MgSO3·6H2O and MgSO4·6H2O is increased for a longer corrosion time
The corrosion behavior of AZ91D magnesium alloy was studied in atmosphere containing 4×10-6 SO2 (volume fraction) by indoor simulation experiment. Corrosion morphology was observed by atomic force microscopy (AFM), optical microscopy (OM) and scanning electron microscopy (SEM). Corrosion products were analyzed by X-ray diffraction (XRD). The mass gain of AZ91D magnesium alloy during the corrosion period of 1200 h can be divided into two stages. The first stage accords with linear increase law, and the second stage accords with exponential decrease law. β phase is protected as cathode, and granular corrosion products are formed in α phase as anode. The corrosion products grow outward until the continuous corrosion layer is formed. Meanwhile, large granular corrosion products appear in the cracks of corrosion layer. The corrosion products mainly consist of MgO, Mg(OH)2, MgSO3·6H2O and MgSO4·6H2O. The quantity of MgO and Mg(OH)2 is decreased, while the quantity of MgSO3·6H2O and MgSO4·6H2O is increased for a longer corrosion time
2011, 40(3):503-506.
Abstract:
Silver nanoparticles with uniform diameters were obtained in dodecyl trimethyl ammonium bromide (DTAB) solution at room temperature under magnetic stirring through hydrazine reducing AgNO3. The products were characterized by XRD, SEM and UV-vis absorption spectra. Results show that the silver nanoparticles are not from the direction reduction of Ag+ by hydrazine, but the products of the reduced silver bromide which are generated early. As the reaction time increasing, silver bromide of uniform sphere-like structure is gradually converted into nano-polyhedron silver bromide, and into silver nanoparticles finally
Silver nanoparticles with uniform diameters were obtained in dodecyl trimethyl ammonium bromide (DTAB) solution at room temperature under magnetic stirring through hydrazine reducing AgNO3. The products were characterized by XRD, SEM and UV-vis absorption spectra. Results show that the silver nanoparticles are not from the direction reduction of Ag+ by hydrazine, but the products of the reduced silver bromide which are generated early. As the reaction time increasing, silver bromide of uniform sphere-like structure is gradually converted into nano-polyhedron silver bromide, and into silver nanoparticles finally
2011, 40(3):507-510.
Abstract:
The spherical tungsten powder was fabricated by spray-drying method combined with hydrogen reduction using ammonium metatungstate (AMT) as raw materials. The powder morphology, mean particle size, particle size distribution and phase transformation process of reduction were characterized by SEM, TEM, XRD and laser diffraction particle size analyzer, respectively. Results show that the morphology of the powder prepared by spray drying is hollow sphere, and both of AMT and WO3 powder has similar good spherical structure with smooth surface. TEM results indicate that the process parameters, such as the slurry concentration, compressed air flow rate, and liquid feeding rate, play important roles in controlling the performance of AMT microspheres, such as the size distribution. It is found that calcination has no effect on the particle morphology and phase composition. The mean size is increased with the increase of the slurry concentration and compressed air flow rate, but the size distribution changes slightly with different liquid feed rates. The X-ray diffraction patterns indicate that α-W phase is obtained after reduction at 550 oC for 2 h in hydrogen atmosphere, but WO3 still exists; after reduction at 750 oC for 2 h, WO3 disappears, and α-W phase exists in the powder
The spherical tungsten powder was fabricated by spray-drying method combined with hydrogen reduction using ammonium metatungstate (AMT) as raw materials. The powder morphology, mean particle size, particle size distribution and phase transformation process of reduction were characterized by SEM, TEM, XRD and laser diffraction particle size analyzer, respectively. Results show that the morphology of the powder prepared by spray drying is hollow sphere, and both of AMT and WO3 powder has similar good spherical structure with smooth surface. TEM results indicate that the process parameters, such as the slurry concentration, compressed air flow rate, and liquid feeding rate, play important roles in controlling the performance of AMT microspheres, such as the size distribution. It is found that calcination has no effect on the particle morphology and phase composition. The mean size is increased with the increase of the slurry concentration and compressed air flow rate, but the size distribution changes slightly with different liquid feed rates. The X-ray diffraction patterns indicate that α-W phase is obtained after reduction at 550 oC for 2 h in hydrogen atmosphere, but WO3 still exists; after reduction at 750 oC for 2 h, WO3 disappears, and α-W phase exists in the powder
2011, 40(3):511-514.
Abstract:
Porosity is important to osteogenesis for porous titanium implants. Higher porosity is good for enhancement of osteogenesis. But the mechanical properties of porous titanium must rapidly decrease when its porosity increases. The puzzle now is to find a porous titanium implant with high mechanical properties as well as high porosity. The novel porous titanium which fit for bone ingrowth was fabricated by traditional slurry foaming, with CeO2 as additive. Microstructure and mechanical properties were studied by scanning electronic microscope (SEM) and compression tests respectively. The results show that the pores mainly in 100-700 μm of porous titanium with the porosity of 71.6%-73.5% are all interconnected and there are many microspores (about 10 μm) on the wall of macrospores. The porous titanium enhanced by 0.2wt%CeO2 presents optimal biomechanical compatibility, whose Young’s modulus and compressive strength are 2.08 GPa and 60.19 MPa, respectively, similar to that of cortical bone
Porosity is important to osteogenesis for porous titanium implants. Higher porosity is good for enhancement of osteogenesis. But the mechanical properties of porous titanium must rapidly decrease when its porosity increases. The puzzle now is to find a porous titanium implant with high mechanical properties as well as high porosity. The novel porous titanium which fit for bone ingrowth was fabricated by traditional slurry foaming, with CeO2 as additive. Microstructure and mechanical properties were studied by scanning electronic microscope (SEM) and compression tests respectively. The results show that the pores mainly in 100-700 μm of porous titanium with the porosity of 71.6%-73.5% are all interconnected and there are many microspores (about 10 μm) on the wall of macrospores. The porous titanium enhanced by 0.2wt%CeO2 presents optimal biomechanical compatibility, whose Young’s modulus and compressive strength are 2.08 GPa and 60.19 MPa, respectively, similar to that of cortical bone
2011, 40(3):515-518.
Abstract:
Effects of reciprocating extrusion on the microstructures and mechanical properties of as-cast Mg-0.85Zn-0.15Y-0.6Zr alloys enforced by quasicrystal particles were investigated by OM, SEM and XRD. The results show that the reciprocating extrusion can greatly refine the microstructure of as-cast Mg-0.85Zn-0.15Y-0.6Zr alloy, and make I phase relatively uniformly distribute in the α-Mg matrix. Compared with that of the as-cast alloy, the yield strength, tensile strength and elongation of the Mg-0.85Zn-0.15Y-0.6Zr magnesium alloys after reciprocating extrusion are increased by 75.8%, 43.2% and 35%, respectively
Effects of reciprocating extrusion on the microstructures and mechanical properties of as-cast Mg-0.85Zn-0.15Y-0.6Zr alloys enforced by quasicrystal particles were investigated by OM, SEM and XRD. The results show that the reciprocating extrusion can greatly refine the microstructure of as-cast Mg-0.85Zn-0.15Y-0.6Zr alloy, and make I phase relatively uniformly distribute in the α-Mg matrix. Compared with that of the as-cast alloy, the yield strength, tensile strength and elongation of the Mg-0.85Zn-0.15Y-0.6Zr magnesium alloys after reciprocating extrusion are increased by 75.8%, 43.2% and 35%, respectively
2011, 40(3):519-522.
Abstract:
Effects of reciprocating extrusion on the microstructure and mechanical properties of the as-cast Mg-6%Si alloy were studied. Results show that the microstructures of the Mg-6%Si alloy are refined markedly after reciprocating extrusion with 4 passes; the coarse dendritic primary Mg2Si phase changes into fine granules, the size of the Chinese-character-like eutectic Mg2Si phase also decreases gradually and more uniform distribution of the granular Mg2Si phase in the matrix is obtained. After reciprocating extrusion with 4 passes, the tensile strength and the elongation are increased by 82.3% and 810.9%, respectively, compared with those of the as-cast alloy. Fracture analysis shows that the fracture mode of the alloy changes from brittle fracture to ductile-brittle fracture after reciprocating extrusion
Effects of reciprocating extrusion on the microstructure and mechanical properties of the as-cast Mg-6%Si alloy were studied. Results show that the microstructures of the Mg-6%Si alloy are refined markedly after reciprocating extrusion with 4 passes; the coarse dendritic primary Mg2Si phase changes into fine granules, the size of the Chinese-character-like eutectic Mg2Si phase also decreases gradually and more uniform distribution of the granular Mg2Si phase in the matrix is obtained. After reciprocating extrusion with 4 passes, the tensile strength and the elongation are increased by 82.3% and 810.9%, respectively, compared with those of the as-cast alloy. Fracture analysis shows that the fracture mode of the alloy changes from brittle fracture to ductile-brittle fracture after reciprocating extrusion
2011, 40(3):523-525.
Abstract:
A naocrystalline layer (thickness of about 30 μm) was prepared by surface mechanical attrition treatment (SMAT) on commercial pure Ti, and the mean grain size on top-surface was about 30 nm. The SMAT Ti was then treated by immersing in H2O2 solution at 25 oC followed by calcination at 400 °C for 1 h. XPS was used to analyze the SMAT Ti structure layer by layer. The results show that obvious differences of the oxidation layer structure exist between SMAT Ti and CG (coarse grain) counterpart
A naocrystalline layer (thickness of about 30 μm) was prepared by surface mechanical attrition treatment (SMAT) on commercial pure Ti, and the mean grain size on top-surface was about 30 nm. The SMAT Ti was then treated by immersing in H2O2 solution at 25 oC followed by calcination at 400 °C for 1 h. XPS was used to analyze the SMAT Ti structure layer by layer. The results show that obvious differences of the oxidation layer structure exist between SMAT Ti and CG (coarse grain) counterpart
2011, 40(3):526-529.
Abstract:
Fly ash microspheres and carbon black were taken as raw materials to prepare SiC/Mullite microspheres by microwave heating carbon thermal reduction. X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) were applied to characterize the phase composition and microstructure of SiC/Mullite spheres.The phase composition and the structure were characterized by XRD and FESEM. The results show that the reaction mechanism mainly associates with solid-solid reaction between C(s) and SiO2(s) on the surface of fly ash microspheres with its spherical shape unchanging when the temperature is between 1100-1300 oC. When the temperature is higher than 1300 oC, SiC has easier orientation growth into whisker through VLS mechanism for the presence of liquid phase. Mullite is involved in the reaction; therefore, fly ash microspheres cannot maintain its spherical shape. The optimum conditions of our experiments are n(C):n(SiO2)=4.2, 1200 oC and 1 h
Fly ash microspheres and carbon black were taken as raw materials to prepare SiC/Mullite microspheres by microwave heating carbon thermal reduction. X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) were applied to characterize the phase composition and microstructure of SiC/Mullite spheres.The phase composition and the structure were characterized by XRD and FESEM. The results show that the reaction mechanism mainly associates with solid-solid reaction between C(s) and SiO2(s) on the surface of fly ash microspheres with its spherical shape unchanging when the temperature is between 1100-1300 oC. When the temperature is higher than 1300 oC, SiC has easier orientation growth into whisker through VLS mechanism for the presence of liquid phase. Mullite is involved in the reaction; therefore, fly ash microspheres cannot maintain its spherical shape. The optimum conditions of our experiments are n(C):n(SiO2)=4.2, 1200 oC and 1 h
2011, 40(3):530-533.
Abstract:
The microstructure, phase composition and properties of Mg-(RE)-Zn alloys under different conditions were investigated, i.e. as-cast alloys and annealed alloys at 560 oC for 7 h. The results show that the as-cast Mg-(RE)-Zn alloy contains mainly the α-Mg(RE) solid solution and the GdMg phase, which distributes predominantly in the eutectic structure, but the eutectic microstructure completely disappears and there is no deposition in the grain boundary after annealing at 560 oC for 7 h. The annealed Mg-(RE)-Zn alloy involving the α-Mg (RE) phase, the MgGd3 phase and the MgZn2 phase, has a higher hardness, a higher ultimate tensile strength and a better elongation compared with the as-cast Mg-(RE)-Zn alloy. There is a significant difference in the fracture mode for the two alloys after a uniaxial tensile test. The fracture of the as-cast Mg-(RE)-Zn alloy exhibits an intergranular mode, while the fracture of the annealed Mg-(RE)-Zn alloy shows a transgranular mode induced by microvoid coalescence
The microstructure, phase composition and properties of Mg-(RE)-Zn alloys under different conditions were investigated, i.e. as-cast alloys and annealed alloys at 560 oC for 7 h. The results show that the as-cast Mg-(RE)-Zn alloy contains mainly the α-Mg(RE) solid solution and the GdMg phase, which distributes predominantly in the eutectic structure, but the eutectic microstructure completely disappears and there is no deposition in the grain boundary after annealing at 560 oC for 7 h. The annealed Mg-(RE)-Zn alloy involving the α-Mg (RE) phase, the MgGd3 phase and the MgZn2 phase, has a higher hardness, a higher ultimate tensile strength and a better elongation compared with the as-cast Mg-(RE)-Zn alloy. There is a significant difference in the fracture mode for the two alloys after a uniaxial tensile test. The fracture of the as-cast Mg-(RE)-Zn alloy exhibits an intergranular mode, while the fracture of the annealed Mg-(RE)-Zn alloy shows a transgranular mode induced by microvoid coalescence
2011, 40(3):534-537.
Abstract:
The infrared emissivity characteristics and change mechanism of the superalloy K424 deposited with Ni/Au/Pt multilayer films were studied. After heat processing at 600 oC for 150 h, the films were analyzed by X-ray diffraction (XRD), SEM and EDS. The results show that the main compositions on the surface are Au0.7Cr0.3 and Pt, indicating that the substrate elements diffuse into the multilayer films. SEM analysis shows that there are lots of fine cracks on the rough sample, but oxides are not detected, while the surface of the polished samples is integrity after heat processing. The infrared emissivity was tested by spectral radiometer SR5000. The results show that both the surface state and heat processing have an important influence on the infrared emissivity
The infrared emissivity characteristics and change mechanism of the superalloy K424 deposited with Ni/Au/Pt multilayer films were studied. After heat processing at 600 oC for 150 h, the films were analyzed by X-ray diffraction (XRD), SEM and EDS. The results show that the main compositions on the surface are Au0.7Cr0.3 and Pt, indicating that the substrate elements diffuse into the multilayer films. SEM analysis shows that there are lots of fine cracks on the rough sample, but oxides are not detected, while the surface of the polished samples is integrity after heat processing. The infrared emissivity was tested by spectral radiometer SR5000. The results show that both the surface state and heat processing have an important influence on the infrared emissivity
2011, 40(3):538-542.
Abstract:
Talcum powder has potential application in the field of conductive fillers preparation because of its particular structure. The conductive talcum powder was prepared by electroless silver plating with the way of silver ammonic solution dipping into the reduction solution with formaldehyde as reductant. The conditions of electroless silver plating for talcum powder were studied. Effects of pH value of the silver ammonic solution, concentration of the silver nitrate and formaldehyde, loadage of the powder and plating reaction time on the powder mass gain of coated silver were discussed. With the aid of FESEM, the morphology of talcum powder after silver plating was characterized; the rate of mass gain and the resistivity of the compacted talcum after silver-plating were tested. On the basis of the above analysis, the best conditions of electroless silver plating on talcum powder are drawn: pH value of silver ammonic solution 11.7, concentration of silver nitrate 10 g/L and that of formaldehyde 13 mL/L, loadage 25 g/L, and reaction time 60 min. Under these conditions, the resistivity of the compacted talcum powder after silver plating was 23.6 Ω×cm.
Talcum powder has potential application in the field of conductive fillers preparation because of its particular structure. The conductive talcum powder was prepared by electroless silver plating with the way of silver ammonic solution dipping into the reduction solution with formaldehyde as reductant. The conditions of electroless silver plating for talcum powder were studied. Effects of pH value of the silver ammonic solution, concentration of the silver nitrate and formaldehyde, loadage of the powder and plating reaction time on the powder mass gain of coated silver were discussed. With the aid of FESEM, the morphology of talcum powder after silver plating was characterized; the rate of mass gain and the resistivity of the compacted talcum after silver-plating were tested. On the basis of the above analysis, the best conditions of electroless silver plating on talcum powder are drawn: pH value of silver ammonic solution 11.7, concentration of silver nitrate 10 g/L and that of formaldehyde 13 mL/L, loadage 25 g/L, and reaction time 60 min. Under these conditions, the resistivity of the compacted talcum powder after silver plating was 23.6 Ω×cm.
2011, 40(3):543-546.
Abstract:
Effects of fluorination treatment on electrochemical properties of La0.67Mg0.33Ni2.25Co0.75 hydrogen storage alloy were investigated, using scanning electron microscopy, charge and discharge testing, linear polarization and potential-step measurement. The results show that cycling stability is improved by fluorination treatment. The cycling capacity retention rate S50 increases greatly after fluorination treatment. Moreover, fluorination treatment contributes to an increase in exchange current density, a decrease in charge- transfer resistance and the facility of hydrogen diffusion within the bulk alloy, leading to an obvious improvement on high rate dischargeability (HRD).
Effects of fluorination treatment on electrochemical properties of La0.67Mg0.33Ni2.25Co0.75 hydrogen storage alloy were investigated, using scanning electron microscopy, charge and discharge testing, linear polarization and potential-step measurement. The results show that cycling stability is improved by fluorination treatment. The cycling capacity retention rate S50 increases greatly after fluorination treatment. Moreover, fluorination treatment contributes to an increase in exchange current density, a decrease in charge- transfer resistance and the facility of hydrogen diffusion within the bulk alloy, leading to an obvious improvement on high rate dischargeability (HRD).
2011, 40(3):547-550.
Abstract:
The complex hydride LiAlH4 doped with rare earths (RE) catalysts of LaCl3, CeCl3 and Ce(SO4)2, respectively were prepared by ball milling. The effects of RE catalysts on the dehydriding properties and phase structures of the complex hydride LiAlH4 were investigated. The results show that the doped Ce(SO4)2 has little effect on the dehydrogenation of LiAlH4 in the ball milling process. However, the doped LaCl3 and CeCl3 cause dehydrogenation of the partial LiAlH4, resulting in LiCl and Al3RE (RE=La, Ce). The doped RE catalysts decrease the dehydriging start temperature of LiAlH4, especially Ce(SO4)2, which decreases the dehydriging start temperature by about 25 oC. RE catalysts help to speed up the decomposition reaction rate of LiAlH4 and improve the dehydriding properties of LiAlH4
The complex hydride LiAlH4 doped with rare earths (RE) catalysts of LaCl3, CeCl3 and Ce(SO4)2, respectively were prepared by ball milling. The effects of RE catalysts on the dehydriding properties and phase structures of the complex hydride LiAlH4 were investigated. The results show that the doped Ce(SO4)2 has little effect on the dehydrogenation of LiAlH4 in the ball milling process. However, the doped LaCl3 and CeCl3 cause dehydrogenation of the partial LiAlH4, resulting in LiCl and Al3RE (RE=La, Ce). The doped RE catalysts decrease the dehydriging start temperature of LiAlH4, especially Ce(SO4)2, which decreases the dehydriging start temperature by about 25 oC. RE catalysts help to speed up the decomposition reaction rate of LiAlH4 and improve the dehydriding properties of LiAlH4
2011, 40(3):551-554.
Abstract:
Highly ordered TiO2 nanotubes (TiO2-NTs) were grown from Ti substrate. More load sites for specified metal were provided by this nanotube structure. TiO2-NTs/Pt electrodes for electrocatalytic oxidation were prepared through hydrothermal reaction between TiO2 nanotubes and H2PtCl6·6H2O. Characterization of the electrodes by scanning electron microscope (SEM) and X-ray diffraction (XRD) illustrates that Pt nanoparticles with an average size of 20-30 nm are dispersed on the surface or in the pore of TiO2 nanotube. The results of cyclic voltammetry (CV) show that in the system without dyes the current density at the oxidation peak of 0.13 V of TiO2-NTs/Pt electrodes is 9 times greater than that of Pt bulk electrode; while in the system with dyes, the oxidation peak current density of the TiO2-NTs/Pt electrodes to acid scarlet GR is 4.2 times that of Pt bulk electrodes. The results of degradation to acid scarlet GR show that TiO2-NTs/Pt electrodes possess high catalytic activity and high-efficiency degradation ability
Highly ordered TiO2 nanotubes (TiO2-NTs) were grown from Ti substrate. More load sites for specified metal were provided by this nanotube structure. TiO2-NTs/Pt electrodes for electrocatalytic oxidation were prepared through hydrothermal reaction between TiO2 nanotubes and H2PtCl6·6H2O. Characterization of the electrodes by scanning electron microscope (SEM) and X-ray diffraction (XRD) illustrates that Pt nanoparticles with an average size of 20-30 nm are dispersed on the surface or in the pore of TiO2 nanotube. The results of cyclic voltammetry (CV) show that in the system without dyes the current density at the oxidation peak of 0.13 V of TiO2-NTs/Pt electrodes is 9 times greater than that of Pt bulk electrode; while in the system with dyes, the oxidation peak current density of the TiO2-NTs/Pt electrodes to acid scarlet GR is 4.2 times that of Pt bulk electrodes. The results of degradation to acid scarlet GR show that TiO2-NTs/Pt electrodes possess high catalytic activity and high-efficiency degradation ability
2011, 40(3):555-558.
Abstract:
In order to meet the need of high temperature thermal protection, Ni3Al coating was prepared by plasmas spraying technology. The microstructure, bond strength, thermal shock and anti-oxidation properties of the coating were studied. The results show that due to the full contact between the nickel powder and the aluminum powder, the Ni3Al intermetallic compound are completely formed during plasma spraying and a lot of heat is released. The coating and the matrix are of micro metallurgic bonding. The coating shows high thermal shock and anti-oxidation properties and its bond strength is 30% to 40% higher than that of the commercial NiAl coating
In order to meet the need of high temperature thermal protection, Ni3Al coating was prepared by plasmas spraying technology. The microstructure, bond strength, thermal shock and anti-oxidation properties of the coating were studied. The results show that due to the full contact between the nickel powder and the aluminum powder, the Ni3Al intermetallic compound are completely formed during plasma spraying and a lot of heat is released. The coating and the matrix are of micro metallurgic bonding. The coating shows high thermal shock and anti-oxidation properties and its bond strength is 30% to 40% higher than that of the commercial NiAl coating
2011, 40(3):559-564.
Abstract:
The interaction of the metallic surface or nanoparticles with nearby fluorophores broadens the applications of the metallic nanostructures in biological assays and biotechnology, and promotes the development of novel ultrabright fluorescence probes. This paper aims to introduce the mechanism of metal-enhanced fluorescence and its research progress at home and abroad. The factors influencing the efficiency of the fluorescence emission were reviewed, and the unresolved problems and the direction of development in metal-enhanced fluorescence were also present.
The interaction of the metallic surface or nanoparticles with nearby fluorophores broadens the applications of the metallic nanostructures in biological assays and biotechnology, and promotes the development of novel ultrabright fluorescence probes. This paper aims to introduce the mechanism of metal-enhanced fluorescence and its research progress at home and abroad. The factors influencing the efficiency of the fluorescence emission were reviewed, and the unresolved problems and the direction of development in metal-enhanced fluorescence were also present.
