Volume 39,Issue 3,2010 Table of Contents
2010, 39(3):377-381.
Abstract:
Using magnetron sputtering method the Ge2Sb2Te5 films were deposited at different substrate temperatures (from room temperature to 300 oC) on Si substrate. The structure and the crystallization temperature of the films were determined by X-ray diffraction and Differential Scanning Calorimeter, respectively. The electrical resistance and the reflectivity of the films were measured with a four-point probe and ultraviolet photo-spectrometer, respectively. Based on the reflectivity of the films, it is found that the reflectivity contrasts of the Ge2Sb2Te5 films at the wavelengths of 405 and 650 nm change with the substrate temperature. The films prepared at room temperature are amorphous, and crystalline (fcc) at 140 oC, and a little hexagonal (hex) structure comes forth at 300 oC. At 140 oC the phase separation may take place, and exhibits significant influence on the electrical and optical properties.
Using magnetron sputtering method the Ge2Sb2Te5 films were deposited at different substrate temperatures (from room temperature to 300 oC) on Si substrate. The structure and the crystallization temperature of the films were determined by X-ray diffraction and Differential Scanning Calorimeter, respectively. The electrical resistance and the reflectivity of the films were measured with a four-point probe and ultraviolet photo-spectrometer, respectively. Based on the reflectivity of the films, it is found that the reflectivity contrasts of the Ge2Sb2Te5 films at the wavelengths of 405 and 650 nm change with the substrate temperature. The films prepared at room temperature are amorphous, and crystalline (fcc) at 140 oC, and a little hexagonal (hex) structure comes forth at 300 oC. At 140 oC the phase separation may take place, and exhibits significant influence on the electrical and optical properties.
2010, 39(3):382-387.
Abstract:
This paper presents the fatigue life of fine pitch devices with SnAgCu soldered joints calculated by experiments and numerical simulation. Special test vehicles were selected with SnAgCu soldered joints for testing, and thus the fatigue life of the SnAgCu soldered joints was 1150 cycles under –55-125 oC test condition. On the other hand finite element code ANSYS was used to simulate the stress-strain response and fatigue life of lead free soldered joints based on two sorts of constitutive models: Anand equation and Wong equation, plus two life prediction models. It is found that the similar tendency can be seen in the stress history course curves based on these constitutive models, and the values of stress based on these constitutive equation are different from each other. Two life prediction equations, comparing with thermal cycling experiments, were employed to analyze the fatigue life of fine pitch devices with SnAgCu soldered joints under thermal cycling test. It is seen that the life calculated by fatigue life prediction equations with two creep mechanism based on Wong model coincide well with that of the test data, and the life calculated by Engelmaier-modified Coffin-Mason equation calculated based on Anand model is slightly higher than that of the actual result.
This paper presents the fatigue life of fine pitch devices with SnAgCu soldered joints calculated by experiments and numerical simulation. Special test vehicles were selected with SnAgCu soldered joints for testing, and thus the fatigue life of the SnAgCu soldered joints was 1150 cycles under –55-125 oC test condition. On the other hand finite element code ANSYS was used to simulate the stress-strain response and fatigue life of lead free soldered joints based on two sorts of constitutive models: Anand equation and Wong equation, plus two life prediction models. It is found that the similar tendency can be seen in the stress history course curves based on these constitutive models, and the values of stress based on these constitutive equation are different from each other. Two life prediction equations, comparing with thermal cycling experiments, were employed to analyze the fatigue life of fine pitch devices with SnAgCu soldered joints under thermal cycling test. It is seen that the life calculated by fatigue life prediction equations with two creep mechanism based on Wong model coincide well with that of the test data, and the life calculated by Engelmaier-modified Coffin-Mason equation calculated based on Anand model is slightly higher than that of the actual result.
2010, 39(3):388-392.
Abstract:
The objective of this paper is to study the filling process of titanium alloy melt in vertical centrifugal casting, as well as the effect of processing parameters on the formation of defects of titanium alloy castings. Experimental results show that the castings obtained in the centrifugal field are better than that obtained in the gravity field. The molten metal sticks to one side of the mould which is opposite to the rotational direction to fill in the vertical centrifugal field. And the cross-sectional area of the molten metal in the runner decreases with increasing of filling length, but has a back-up trend at the inlet of ingate due to the decreases of filling velocity at the ingate. The processing parameters such as rotational direction, rotational radius and rotational velocity play an important role in the formation of defects of titanium alloy castings. Different rotational direction leads to different filling sequence of molten metal, which then affect the following solidification and the formation of the defects. Under the given rotational velocity, the volume of inner defects of castings decreases with increasing of rotational radius and rotational velocity.
The objective of this paper is to study the filling process of titanium alloy melt in vertical centrifugal casting, as well as the effect of processing parameters on the formation of defects of titanium alloy castings. Experimental results show that the castings obtained in the centrifugal field are better than that obtained in the gravity field. The molten metal sticks to one side of the mould which is opposite to the rotational direction to fill in the vertical centrifugal field. And the cross-sectional area of the molten metal in the runner decreases with increasing of filling length, but has a back-up trend at the inlet of ingate due to the decreases of filling velocity at the ingate. The processing parameters such as rotational direction, rotational radius and rotational velocity play an important role in the formation of defects of titanium alloy castings. Different rotational direction leads to different filling sequence of molten metal, which then affect the following solidification and the formation of the defects. Under the given rotational velocity, the volume of inner defects of castings decreases with increasing of rotational radius and rotational velocity.
2010, 39(3):393-396.
Abstract:
The morphology, phase, pitting corrosion behaviors and galvanic corrosion resistance behavior of the welded joint of 316L stainless steel and Ti(TA2) clad plate were studied by scanning electron microcopy (SEM), X-ray diffraction (XRD), zero-internal resistance ammeter and potentiodynamic polarization technique. The results show that the welded 316L presents severe deformation and has intermetallic phase; moreover, more δ-ferrite phase emerges at the welded seam and fusion area near 316L side. All these factors lead to the decrease of pitting corrosion resistance and galvanic corrosion resistance of the welded 316L.
The morphology, phase, pitting corrosion behaviors and galvanic corrosion resistance behavior of the welded joint of 316L stainless steel and Ti(TA2) clad plate were studied by scanning electron microcopy (SEM), X-ray diffraction (XRD), zero-internal resistance ammeter and potentiodynamic polarization technique. The results show that the welded 316L presents severe deformation and has intermetallic phase; moreover, more δ-ferrite phase emerges at the welded seam and fusion area near 316L side. All these factors lead to the decrease of pitting corrosion resistance and galvanic corrosion resistance of the welded 316L.
2010, 39(3):397-400.
Abstract:
Ga, Sn, In and Ni were added into AgCuZn cadmium-free brazing alloys. The influences of Ga, Sn, In and Ni on the microstructures and properties of AgCuZn brazing alloys were investigated. Mechanical properties of the butt and lap brazed joints were also tested. Results indicate that all AgCuZn-X(Ga, Sn, In, Ni) brazing alloys have low solidus and liquidus and acceptable mechanical properties. It is pointed out that the mechanical properties of the brazed joints are satisfactory due to the formation of fine network “characteristic gallium structure” when Ag and Ga contents are in a range of 30 wt%-56 wt% and 1 wt%-3 wt%, respectively, in the AgCuZn brazing alloy.
Ga, Sn, In and Ni were added into AgCuZn cadmium-free brazing alloys. The influences of Ga, Sn, In and Ni on the microstructures and properties of AgCuZn brazing alloys were investigated. Mechanical properties of the butt and lap brazed joints were also tested. Results indicate that all AgCuZn-X(Ga, Sn, In, Ni) brazing alloys have low solidus and liquidus and acceptable mechanical properties. It is pointed out that the mechanical properties of the brazed joints are satisfactory due to the formation of fine network “characteristic gallium structure” when Ag and Ga contents are in a range of 30 wt%-56 wt% and 1 wt%-3 wt%, respectively, in the AgCuZn brazing alloy.
2010, 39(3):401-404.
Abstract:
The nano-silver flake with about 30 nm, was prepared by a chemical reduction method. Cetyltrimethyl ammonium bromide (CTAB) was used to prevent agglomeration of the nanoparticles by its steric hindrance. However, an excessive amount of CTAB will impede the growth of silver nanoparticles, and thus it is not beneficial to the formation of the desired morphology. When the mass ratio of CTAB to silver nitrate is 0.8, the nano-silver with flaky structure can be obtained. At temperature of 20 oC, the solubility of CTAB is low, and it is difficult to retard the agglomeration effectively. At the same time, the low reaction rate will lead to large and nonuniform nanoparticles. When the temperature is 40 oC, the increased solubility of CTAB promotes the forming of nanoparticle. Nevertheless, when the temperature reaches 60 oC, the reaction is so fast that the nucleation rate increases and thus tiny particles are formed eventually. High pH value will lead to promote the reaction and ensure the complete consumption of Ag+, but too high pH may cause damage to the double-layer electronic structure of silver particles, resulting in collapse and agglomeration of the formed particles. When the pH value is around 6, stable nano-silver flakes can be obtained in a uniform dispersed form.
The nano-silver flake with about 30 nm, was prepared by a chemical reduction method. Cetyltrimethyl ammonium bromide (CTAB) was used to prevent agglomeration of the nanoparticles by its steric hindrance. However, an excessive amount of CTAB will impede the growth of silver nanoparticles, and thus it is not beneficial to the formation of the desired morphology. When the mass ratio of CTAB to silver nitrate is 0.8, the nano-silver with flaky structure can be obtained. At temperature of 20 oC, the solubility of CTAB is low, and it is difficult to retard the agglomeration effectively. At the same time, the low reaction rate will lead to large and nonuniform nanoparticles. When the temperature is 40 oC, the increased solubility of CTAB promotes the forming of nanoparticle. Nevertheless, when the temperature reaches 60 oC, the reaction is so fast that the nucleation rate increases and thus tiny particles are formed eventually. High pH value will lead to promote the reaction and ensure the complete consumption of Ag+, but too high pH may cause damage to the double-layer electronic structure of silver particles, resulting in collapse and agglomeration of the formed particles. When the pH value is around 6, stable nano-silver flakes can be obtained in a uniform dispersed form.
2010, 39(3):405-409.
Abstract:
Rolling deformation textures and annealing textures of AgCu28 alloys were studied by means of X-ray diffraction pole figures method; ultimate tensile strength and elongation to failure of AgCu28 alloys were tested too. The results show that dominant deformation textures of Ag and Cu are {110}<112> Brass textures when AgCu28 alloy is 95% reduction by rolling, and the annealing textures are the same as the deformation textures when AgCu28 alloy is annealed at 650 ℃ for 1.5 h under H2 protection ambient atmosphere; ultimate tensile strengths of the deformed AgCu28 alloys are 750 MP along transverse direction(TD) and 680 MPa along rolling direction(RD), respectively; ultimate tensile strength of the annealed AgCu28 are 374 MPa along TD and 327 MPa along RD, respectively and its elongation to failure along TD and RD are about 12%. It is indicated that grains of two phases influence each other in binary eutectic so that their deformation textures are the same as the annealed textures, their grains are ultrafine, recrystallization temperature rises remarkably and ultimate tensile strength which is anisotropy is enhanced remarkably.
Rolling deformation textures and annealing textures of AgCu28 alloys were studied by means of X-ray diffraction pole figures method; ultimate tensile strength and elongation to failure of AgCu28 alloys were tested too. The results show that dominant deformation textures of Ag and Cu are {110}<112> Brass textures when AgCu28 alloy is 95% reduction by rolling, and the annealing textures are the same as the deformation textures when AgCu28 alloy is annealed at 650 ℃ for 1.5 h under H2 protection ambient atmosphere; ultimate tensile strengths of the deformed AgCu28 alloys are 750 MP along transverse direction(TD) and 680 MPa along rolling direction(RD), respectively; ultimate tensile strength of the annealed AgCu28 are 374 MPa along TD and 327 MPa along RD, respectively and its elongation to failure along TD and RD are about 12%. It is indicated that grains of two phases influence each other in binary eutectic so that their deformation textures are the same as the annealed textures, their grains are ultrafine, recrystallization temperature rises remarkably and ultimate tensile strength which is anisotropy is enhanced remarkably.
2010, 39(3):410-413.
Abstract:
The flow stress behavior of Ag/SnO2 composite under different deformation condition was investigated by isothermal constant speed compression test, and then the parameters of the kinetic equation of dynamic recrystallization and the equation of the recrystallized grain size were identified according to the experimental data. By finite element simulation of extrusion process, the grain-size evolution and final grain size of Ag/SnO2 composite by reactive synthesis were obtained. Compared with SEM images of extruded sample, it is found that the process simulation is well consistent with the experiment. Finally, the change mechanism and characteristic for the grain size in the extrusion process were revealed.
The flow stress behavior of Ag/SnO2 composite under different deformation condition was investigated by isothermal constant speed compression test, and then the parameters of the kinetic equation of dynamic recrystallization and the equation of the recrystallized grain size were identified according to the experimental data. By finite element simulation of extrusion process, the grain-size evolution and final grain size of Ag/SnO2 composite by reactive synthesis were obtained. Compared with SEM images of extruded sample, it is found that the process simulation is well consistent with the experiment. Finally, the change mechanism and characteristic for the grain size in the extrusion process were revealed.
2010, 39(3):414-417.
Abstract:
According to the empirical electron theory (EET) of solids and molecules, the valence electron structures of (Mo1-x,Wx)Si2 solid solutions were analyzed using the average atom model, and they were compared with those of MoSi2 and WSi2 matrix. Results show that with x value increasing, the bond energy of the main bond branch, the covalence electron number on the strongest bond and the percentage of total covalence electron number of (Mo1-x,Wx)Si2 solid solutions all increased gradually, indicating the increase of melting point, hardness and strength of (Mo1-x,Wx)Si2 solid solutions.
According to the empirical electron theory (EET) of solids and molecules, the valence electron structures of (Mo1-x,Wx)Si2 solid solutions were analyzed using the average atom model, and they were compared with those of MoSi2 and WSi2 matrix. Results show that with x value increasing, the bond energy of the main bond branch, the covalence electron number on the strongest bond and the percentage of total covalence electron number of (Mo1-x,Wx)Si2 solid solutions all increased gradually, indicating the increase of melting point, hardness and strength of (Mo1-x,Wx)Si2 solid solutions.
2010, 39(3):418-422.
Abstract:
By means of creep property test, microstructure observation and FEM analysis of the stress field near the voids, the influence of the microstructure defects on creep behavior and microstructure evolution of single crystal nickel-based superalloys was investigated. Results show that the plasticity and creep lifetime of the single crystal nickel-based superalloys are obviously decreased by microstructure defects. During high temperature creep, the stress isoline near the voids displays the feature of acetabuliform distribution, and possesses bigger values in the direction of 45° angle to the applied stress axis. That results in the g￠ phase transformed into the rafted structure in the direction of 45° angle to the applied stress axis, and the circular voids defects are elongated into the ellipse in the applied stress axis direction. During creep, smaller values of the stress distribution are in the up and down regions of the circular voids, and the maximum value of the stress distribution appears in the apices region at the sides of the void. Furthermore, the fact that the value of the stress distribution increases as creep goes on results in the germination there and expanding vertically to the stress axis of the cracks, which is a main reason of creep lifetime decrease of the alloys.
By means of creep property test, microstructure observation and FEM analysis of the stress field near the voids, the influence of the microstructure defects on creep behavior and microstructure evolution of single crystal nickel-based superalloys was investigated. Results show that the plasticity and creep lifetime of the single crystal nickel-based superalloys are obviously decreased by microstructure defects. During high temperature creep, the stress isoline near the voids displays the feature of acetabuliform distribution, and possesses bigger values in the direction of 45° angle to the applied stress axis. That results in the g￠ phase transformed into the rafted structure in the direction of 45° angle to the applied stress axis, and the circular voids defects are elongated into the ellipse in the applied stress axis direction. During creep, smaller values of the stress distribution are in the up and down regions of the circular voids, and the maximum value of the stress distribution appears in the apices region at the sides of the void. Furthermore, the fact that the value of the stress distribution increases as creep goes on results in the germination there and expanding vertically to the stress axis of the cracks, which is a main reason of creep lifetime decrease of the alloys.
2010, 39(3):423-426.
Abstract:
Viscosity change rules of Ga-Sb melts with different composition were studied by a viscometer. The results show that the viscosity of Ga-Sb melts increases generally with the temperature decreasing, and the change curves have the feature of exponential change. It is distinct that there is abnormal discontinuous change at 830 ℃ for Ga36.5Sb63.5 melt, which divides the viscosity-temperature curve into two segments, i.e. low temperature segment and high temperature segment. According to the microstructure feature of the melts, the experimental results were discussed.
Viscosity change rules of Ga-Sb melts with different composition were studied by a viscometer. The results show that the viscosity of Ga-Sb melts increases generally with the temperature decreasing, and the change curves have the feature of exponential change. It is distinct that there is abnormal discontinuous change at 830 ℃ for Ga36.5Sb63.5 melt, which divides the viscosity-temperature curve into two segments, i.e. low temperature segment and high temperature segment. According to the microstructure feature of the melts, the experimental results were discussed.
2010, 39(3):427-432.
Abstract:
Cold worked CRAs (Corrosion Resistance Alloys) have been successfully used for corrosive sour gas wells for many years. However, the locally activated pitting and the consequential stress concentration is one of the main mechanisms of stress corrosion cracking failure of cold worked CRAs. The corrosion behavior of Ni-base alloy 028 was simulated in the environment with high temperatures and high partial pressures of H2S/CO2. The results show that the general corrosion of Ni-base alloy 028 was slight, but pitting corrosion happened on the surface of the alloy, and the pitting corrosion of the sample with precipitated phase was more obvious. The XPS results indicate that after corrosion, the element sulfur enriched only in the surface layer of the passive film, and the passive film which can protect the matrix was mainly composed of oxides and hydroxides. But the EDS analysis results of the cross section of pitting corrosion indicate that element sulfur enriched inside of the pitting, resulting in local acidification; consequently, the growth of the pitting was accelerated.
Cold worked CRAs (Corrosion Resistance Alloys) have been successfully used for corrosive sour gas wells for many years. However, the locally activated pitting and the consequential stress concentration is one of the main mechanisms of stress corrosion cracking failure of cold worked CRAs. The corrosion behavior of Ni-base alloy 028 was simulated in the environment with high temperatures and high partial pressures of H2S/CO2. The results show that the general corrosion of Ni-base alloy 028 was slight, but pitting corrosion happened on the surface of the alloy, and the pitting corrosion of the sample with precipitated phase was more obvious. The XPS results indicate that after corrosion, the element sulfur enriched only in the surface layer of the passive film, and the passive film which can protect the matrix was mainly composed of oxides and hydroxides. But the EDS analysis results of the cross section of pitting corrosion indicate that element sulfur enriched inside of the pitting, resulting in local acidification; consequently, the growth of the pitting was accelerated.
2010, 39(3):433-436.
Abstract:
The superplastic deformation behavior and mechanism of burn-resistant Ti40 alloy with large grains at elevated temperature were investigated by OM and TEM. Results show that Ti40 alloy exhibits excellent superplastic behavior in the strain rate range from 5×10-5 to 1×10-2 s-1 at 920 ℃. All of the tensile elongations exceed 250% while the strain rate sensitivity index m is over 0.3. Optical microstructure shows that the large equiaxed gains are refined after superplastic deformation. TEM observation indicates that an unstable subgrain boundary formed by dislocation during superplastic deformation. The subgrain boundaries were transformed into low- and even high-angle grain boundaries by absorbing gliding dislocations. The superplastic behavior of large-grained Ti40 alloy could be explained by dynamic recovery and recrystallization.
The superplastic deformation behavior and mechanism of burn-resistant Ti40 alloy with large grains at elevated temperature were investigated by OM and TEM. Results show that Ti40 alloy exhibits excellent superplastic behavior in the strain rate range from 5×10-5 to 1×10-2 s-1 at 920 ℃. All of the tensile elongations exceed 250% while the strain rate sensitivity index m is over 0.3. Optical microstructure shows that the large equiaxed gains are refined after superplastic deformation. TEM observation indicates that an unstable subgrain boundary formed by dislocation during superplastic deformation. The subgrain boundaries were transformed into low- and even high-angle grain boundaries by absorbing gliding dislocations. The superplastic behavior of large-grained Ti40 alloy could be explained by dynamic recovery and recrystallization.
2010, 39(3):437-441.
Abstract:
Microstructure evolution and hardness distribution of as-deposited Ti2A1Nb-based alloy by laser solid forming (LSF) was investigated through SEM, XRD and TEM. The results indicate that the LSFed Ti2A1Nb-based alloy was constituted of B2/β0 phase (ordered-bbc) and O phase (orthorhombic). The as-deposited phase in the bottom and top area of the LSF Ti2A1Nb-based alloy sample is B2 phase (Nb-based solid solution), while the phase in the middle area is O phase Widmanstǎttem. The phase evolution through bottom→middle→top is B2/β0→B2/β0+O→B2/β0. Therefore, the microhardness of the middle area for LSFed as-deposited Ti2AlNb-based alloy is maximum, and that of the top and bottom is similar. The microhardness of the alloys increases with the laser power increasing.
Microstructure evolution and hardness distribution of as-deposited Ti2A1Nb-based alloy by laser solid forming (LSF) was investigated through SEM, XRD and TEM. The results indicate that the LSFed Ti2A1Nb-based alloy was constituted of B2/β0 phase (ordered-bbc) and O phase (orthorhombic). The as-deposited phase in the bottom and top area of the LSF Ti2A1Nb-based alloy sample is B2 phase (Nb-based solid solution), while the phase in the middle area is O phase Widmanstǎttem. The phase evolution through bottom→middle→top is B2/β0→B2/β0+O→B2/β0. Therefore, the microhardness of the middle area for LSFed as-deposited Ti2AlNb-based alloy is maximum, and that of the top and bottom is similar. The microhardness of the alloys increases with the laser power increasing.
2010, 39(3):442-446.
Abstract:
The thermal stability of Ti14, a novel α+Ti2Cu burn resistant titanium alloy, after semi-solid forging (SSF) with different deformation amount from 45% to 75% was investigated. Effects of deformation amount on the thermal stability were analyzed. The results show that the deformation amount significantly affects the morphology of precipitates and grain size, leading to change of thermal stability. With the deformation amount increasing, the strength of Ti14 alloy after thermal exposure decreases first and then increases, and the plasticity was improved. When the deformation amount was 45%, the microstructure consisted of coarse grains and strip-like Ti2Cu precipitates in the grain boundary. As deformation amount increases to 75%, the microstructure changed to refined grains and granular or/and short rod-like Ti2Cu, inducing the improvement of strength and plasticity. Fracture analyses show that the fracture has lots of tearing ridges for small deformation amount; when the deformation amount reaches 75%, the fracture are mainly dimples. It indicates the precipitates and grain size determine the thermal stability of Ti14 alloy together.
The thermal stability of Ti14, a novel α+Ti2Cu burn resistant titanium alloy, after semi-solid forging (SSF) with different deformation amount from 45% to 75% was investigated. Effects of deformation amount on the thermal stability were analyzed. The results show that the deformation amount significantly affects the morphology of precipitates and grain size, leading to change of thermal stability. With the deformation amount increasing, the strength of Ti14 alloy after thermal exposure decreases first and then increases, and the plasticity was improved. When the deformation amount was 45%, the microstructure consisted of coarse grains and strip-like Ti2Cu precipitates in the grain boundary. As deformation amount increases to 75%, the microstructure changed to refined grains and granular or/and short rod-like Ti2Cu, inducing the improvement of strength and plasticity. Fracture analyses show that the fracture has lots of tearing ridges for small deformation amount; when the deformation amount reaches 75%, the fracture are mainly dimples. It indicates the precipitates and grain size determine the thermal stability of Ti14 alloy together.
2010, 39(3):447-451.
Abstract:
The microstructure and phase composition of semi-solid Ti14 alloy (α-Ti+Ti2Cu) with different cooling modes (furnace cooling—FC, air cooling—AC and water quenching—WQ) were investigated by OM, SEM and XRD. The results show that the three cooling modes have no effects on the phase composition of Ti14, but influence the morphology and distribution of Ti2Cu. The microstructure of Ti14 after furnace cooling consisted of granular Ti2Cu precipitates, which distributed in a certain direction presenting strip and dentritic structure. After air cooling, Ti2Cu precipitates were granular or lamellar in the grains and grain boundaries; while after water quenching, the microstructure was composed of coarse grain boundary, and no evident precipitates were observed. The semi-solid Ti14 alloy undergoes peritectic solidification during cooling process. The peritectic reaction occurs in the liquid/β/Ti2Cu trijunctions region, which makes the solute distribution there irregular, and the trijunctions dynamics quite complicated. Meanwhile the cooling modes also influence the peritectic reaction extent, and thus affect the following eutectoid, resulting in different microstructure with different cooling modes.
The microstructure and phase composition of semi-solid Ti14 alloy (α-Ti+Ti2Cu) with different cooling modes (furnace cooling—FC, air cooling—AC and water quenching—WQ) were investigated by OM, SEM and XRD. The results show that the three cooling modes have no effects on the phase composition of Ti14, but influence the morphology and distribution of Ti2Cu. The microstructure of Ti14 after furnace cooling consisted of granular Ti2Cu precipitates, which distributed in a certain direction presenting strip and dentritic structure. After air cooling, Ti2Cu precipitates were granular or lamellar in the grains and grain boundaries; while after water quenching, the microstructure was composed of coarse grain boundary, and no evident precipitates were observed. The semi-solid Ti14 alloy undergoes peritectic solidification during cooling process. The peritectic reaction occurs in the liquid/β/Ti2Cu trijunctions region, which makes the solute distribution there irregular, and the trijunctions dynamics quite complicated. Meanwhile the cooling modes also influence the peritectic reaction extent, and thus affect the following eutectoid, resulting in different microstructure with different cooling modes.
2010, 39(3):452-456.
Abstract:
In the present paper, the microstructure and mechanical properties of as-deposited and duplex-annealing treated laser solid formed (LSF) Ti60 alloy at room temperature and 600 oC were investigated. It was found that Ti60 alloy is inclined to form equiaxed grains during laser solid forming due to a high proportion of the equiaxed grains in the molten pool and uncompletely remelting when new layer was deposited on prior layer. For the as-deposited sample, the microstructure is composed of Widmanst?tten α laths in prior equiaxed β grain. Through duplex-annealing treatment, the continuous prior β boundary was broken up, the α laths have an obvious tendency to coarsen and part of them were spheroidized. The ultimate tensile strength of the as-deposited LSF sample at room temperature and 600 oC are both higher than wrought, while the plasticity of room temperature is lower than wrought. The fractography shows toughness fracture character, and the plasticity of 600 oC approach those of wrought. The comprehensive mechanical properties of laser formed samples are improved obviously through duplex-annealing treatment.
In the present paper, the microstructure and mechanical properties of as-deposited and duplex-annealing treated laser solid formed (LSF) Ti60 alloy at room temperature and 600 oC were investigated. It was found that Ti60 alloy is inclined to form equiaxed grains during laser solid forming due to a high proportion of the equiaxed grains in the molten pool and uncompletely remelting when new layer was deposited on prior layer. For the as-deposited sample, the microstructure is composed of Widmanst?tten α laths in prior equiaxed β grain. Through duplex-annealing treatment, the continuous prior β boundary was broken up, the α laths have an obvious tendency to coarsen and part of them were spheroidized. The ultimate tensile strength of the as-deposited LSF sample at room temperature and 600 oC are both higher than wrought, while the plasticity of room temperature is lower than wrought. The fractography shows toughness fracture character, and the plasticity of 600 oC approach those of wrought. The comprehensive mechanical properties of laser formed samples are improved obviously through duplex-annealing treatment.
2010, 39(3):457-459.
Abstract:
Porous metal foams are excellent engineering materials with dual attributes of structural and functional characteristics, and they may suffer shearing loads when they are used as engineering components. The mechanical behavior within the component is investigated for these materials under shearing loads, and the corresponding mechanical relationship is derived from mathematical-physical deduction, using a simple manner of segregating analysis. The results display that the maximal nominal shearing stress within the component can be described with the porosity of the porous body and the inherent characteristic parameters of the metal foam itself when it endures the fracture resulting from shearing loads. From this mathematical-physical relation, the strength criterion may be directly achieved for these materials under shearing loads.
Porous metal foams are excellent engineering materials with dual attributes of structural and functional characteristics, and they may suffer shearing loads when they are used as engineering components. The mechanical behavior within the component is investigated for these materials under shearing loads, and the corresponding mechanical relationship is derived from mathematical-physical deduction, using a simple manner of segregating analysis. The results display that the maximal nominal shearing stress within the component can be described with the porosity of the porous body and the inherent characteristic parameters of the metal foam itself when it endures the fracture resulting from shearing loads. From this mathematical-physical relation, the strength criterion may be directly achieved for these materials under shearing loads.
2010, 39(3):460-463.
Abstract:
Changes of hardness of B2-NiAl(Fe) intermetallic compounds in Ni-Al-Fe system with aging time and changes of yield strength of aged B2-NiAl(Fe) intermetallic compounds containing α-Fe precipitates with temperatures were investigated. Results show that the yield strength of B2-NiAl(Fe) intermetallic compounds containing α-Fe precipitates is higher than that of single phase NiAl at all the testing temperatures. It is revealed that the precipitates are disordered bcc Fe phase. The shape of α-Fe precipitates is sphericity and keeps coherent with the matrix in the initial aging period. With prolonging the aging time, the precipitates are platelet in shape, nearly parallel to the {100} planes of the B2-ordered matrix. TEM observation determines that the Burgers vector of the slipping dislocation is <111>. Although the hardness of α-Fe precipitates is lower than that of B2-NiAl(Fe) matrix, the pinning effect of the α-Fe precipitates on moving dislocation plays an important role in hardening of the B2-NiAl(Fe) matrix.
Changes of hardness of B2-NiAl(Fe) intermetallic compounds in Ni-Al-Fe system with aging time and changes of yield strength of aged B2-NiAl(Fe) intermetallic compounds containing α-Fe precipitates with temperatures were investigated. Results show that the yield strength of B2-NiAl(Fe) intermetallic compounds containing α-Fe precipitates is higher than that of single phase NiAl at all the testing temperatures. It is revealed that the precipitates are disordered bcc Fe phase. The shape of α-Fe precipitates is sphericity and keeps coherent with the matrix in the initial aging period. With prolonging the aging time, the precipitates are platelet in shape, nearly parallel to the {100} planes of the B2-ordered matrix. TEM observation determines that the Burgers vector of the slipping dislocation is <111>. Although the hardness of α-Fe precipitates is lower than that of B2-NiAl(Fe) matrix, the pinning effect of the α-Fe precipitates on moving dislocation plays an important role in hardening of the B2-NiAl(Fe) matrix.
2010, 39(3):464-468.
Abstract:
Based on orthogonal experimental results of porous Si3N4 ceramics by gel casting preparation, a three-layer back propagation (BP) artificial neural network (BP ANN) was developed for prediction of the flexural strength and porosity. The BP ANN is composed of three neurons in the input layer, two neurons in the output layer and six neurons the hidden layer. This study demonstrates that the proposed neural network approach can predict the performances of porous Si3N4 ceramics by gel casting preparation to a high degree of accuracy, and the neural network is a very useful and accurate tool for performances analysis of porous Si3N4 ceramics. By the proposed neural network prediction and analysis, the results suggest that the porosity monotonically decreases with the increase of solid loading, flexural strength is low when solid loading was too low or too high, and flexural strength has an optimum value.
Based on orthogonal experimental results of porous Si3N4 ceramics by gel casting preparation, a three-layer back propagation (BP) artificial neural network (BP ANN) was developed for prediction of the flexural strength and porosity. The BP ANN is composed of three neurons in the input layer, two neurons in the output layer and six neurons the hidden layer. This study demonstrates that the proposed neural network approach can predict the performances of porous Si3N4 ceramics by gel casting preparation to a high degree of accuracy, and the neural network is a very useful and accurate tool for performances analysis of porous Si3N4 ceramics. By the proposed neural network prediction and analysis, the results suggest that the porosity monotonically decreases with the increase of solid loading, flexural strength is low when solid loading was too low or too high, and flexural strength has an optimum value.
2010, 39(3):469-472.
Abstract:
A meso-scale numerical constitutive model was established by the theory of crystal plasticity and the finite element method to describe the mechanical behavior of the hexagonal close-packed (hcp) metal. Based on this model, the one-way tensile experiment on a single crystal of titanium at elevated temperature was simulated. The simulated results are consistent with the experimental ones, indicating that the model is reliable. The calculated results also reveal the action of each slip system in deformation process of single crystal titanium. The meso-scale deformation evolution, including grid slipping and crystal lattice reorientation, during the tensile deformation was also analyzed.
A meso-scale numerical constitutive model was established by the theory of crystal plasticity and the finite element method to describe the mechanical behavior of the hexagonal close-packed (hcp) metal. Based on this model, the one-way tensile experiment on a single crystal of titanium at elevated temperature was simulated. The simulated results are consistent with the experimental ones, indicating that the model is reliable. The calculated results also reveal the action of each slip system in deformation process of single crystal titanium. The meso-scale deformation evolution, including grid slipping and crystal lattice reorientation, during the tensile deformation was also analyzed.
2010, 39(3):473-476.
Abstract:
The method of electro-deoxidation was used to reduce solid TiO2 to titanium in CaCl2 molten salt at 900 ℃. The sintered TiO2 samples acted as the cathode and graphite as the anode. The formation and transportation process of O2- in the electrolytic system with molten salts were studied. Results show that the experiment high-temperature promotes the formation of oxygen vacancies in TiO2 structure and occurrence of O2-; O2- transfer from the cathode inside to outside through the oxygen vacancies; the calcium titanate is necessary intermediate product in the electrolysis process; the dense layer of metal titanium on the cathode surface hinders O2- from transformation.
The method of electro-deoxidation was used to reduce solid TiO2 to titanium in CaCl2 molten salt at 900 ℃. The sintered TiO2 samples acted as the cathode and graphite as the anode. The formation and transportation process of O2- in the electrolytic system with molten salts were studied. Results show that the experiment high-temperature promotes the formation of oxygen vacancies in TiO2 structure and occurrence of O2-; O2- transfer from the cathode inside to outside through the oxygen vacancies; the calcium titanate is necessary intermediate product in the electrolysis process; the dense layer of metal titanium on the cathode surface hinders O2- from transformation.
2010, 39(3):477-481.
Abstract:
Effect of rare earth Ce on microstructure and properties of Cr2O3/Cu composite was studied by internal oxidization of Cu-Cr-Ce prealloyed powder. The results show that the appropriate Ce addition into prealloyed powder can increase the properties of Cr2O3/Cu composite, improve Cr2O3 distribution in Cu matrix and refine Cr2O3 particles. Meanwhile, Ce addition can increase the yield rate of Cr2O3 and promote internal oxidization of Cr. Under the condition of this experiment, the optimum Ce addition is 0.1% (mass fraction).
Effect of rare earth Ce on microstructure and properties of Cr2O3/Cu composite was studied by internal oxidization of Cu-Cr-Ce prealloyed powder. The results show that the appropriate Ce addition into prealloyed powder can increase the properties of Cr2O3/Cu composite, improve Cr2O3 distribution in Cu matrix and refine Cr2O3 particles. Meanwhile, Ce addition can increase the yield rate of Cr2O3 and promote internal oxidization of Cr. Under the condition of this experiment, the optimum Ce addition is 0.1% (mass fraction).
2010, 39(3):482-485.
Abstract:
Effect of Ag content on the evaluated-temperature mechanical properties of a series of Al-Cu-Mg-Ag alloys was studied by means of tensile tests, endurance tests, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that tensile strength and ultimate endurance strength increased dramatically with Ag content increasing. SEM observations suggest a plastic transgranular manner of tensile fractures. TEM results reveal that increasing Ag content promoted the nucleation of the Ω phase, which was the dominant strengthening phase in matrix. Furthermore, Ω precipitates were not coarsened on a large scale after long time endurance at evaluated temperature.
Effect of Ag content on the evaluated-temperature mechanical properties of a series of Al-Cu-Mg-Ag alloys was studied by means of tensile tests, endurance tests, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that tensile strength and ultimate endurance strength increased dramatically with Ag content increasing. SEM observations suggest a plastic transgranular manner of tensile fractures. TEM results reveal that increasing Ag content promoted the nucleation of the Ω phase, which was the dominant strengthening phase in matrix. Furthermore, Ω precipitates were not coarsened on a large scale after long time endurance at evaluated temperature.
2010, 39(3):486-489.
Abstract:
Sn-2.8Ag0.5CuX modified hypoeutectic solder was prepared by a new method. The processing properties of the liquid solder were studied. The results show that atomic-doping can significantly improve the oxidation resistance, wettability and overflowing ability of melting solder. The hypoeutectic component can reduce the solder cost and extend the stability of the liquid solder in the using process. In the air atmosphere at 265 ℃, the formation rate of oxide slag on liquid solder surface is only 0.36 mg/cm2·min. When using RMA-flux, the wetting time t0 is 0.82 s, wetting force F3 is 0.75 mN, and the rate of spread is about 78% for the solder on copper.
Sn-2.8Ag0.5CuX modified hypoeutectic solder was prepared by a new method. The processing properties of the liquid solder were studied. The results show that atomic-doping can significantly improve the oxidation resistance, wettability and overflowing ability of melting solder. The hypoeutectic component can reduce the solder cost and extend the stability of the liquid solder in the using process. In the air atmosphere at 265 ℃, the formation rate of oxide slag on liquid solder surface is only 0.36 mg/cm2·min. When using RMA-flux, the wetting time t0 is 0.82 s, wetting force F3 is 0.75 mN, and the rate of spread is about 78% for the solder on copper.
2010, 39(3):490-493.
Abstract:
The effects of Hf content on the as-cast microstructures were investigated in DD6 single crystal superalloy by OM, SEM and EDS. The results show that with the Hf content increasing, primary dendrite arm spacing increases first and decreases afterwards, and the volume fraction of γ/γ′ eutectic increases. The size of γ′ phase particles of dendritic core has no obvious change while that of interdendritic decreases a little. Microporosity has no apparent change and extent of elements segregation slightly decreases. There are two kinds of carbides with different color shades in alloys.
The effects of Hf content on the as-cast microstructures were investigated in DD6 single crystal superalloy by OM, SEM and EDS. The results show that with the Hf content increasing, primary dendrite arm spacing increases first and decreases afterwards, and the volume fraction of γ/γ′ eutectic increases. The size of γ′ phase particles of dendritic core has no obvious change while that of interdendritic decreases a little. Microporosity has no apparent change and extent of elements segregation slightly decreases. There are two kinds of carbides with different color shades in alloys.
2010, 39(3):494-497.
Abstract:
Effects of different solution heat treatment technology, including solution at R.T., pre-precipitation at high temperature and partial resolution, on microstructure, strength and exfoliation corrosion properties of AA7085 aluminum alloys were investigated by tensile testing, conductivity testing, exfoliation corrosion experiment, optical microscope and transmission electron microscopy (TEM). Results show that the partial resolution heat treatment combined with aging treatment decreases the tensile strength, but increases the conductivity and exfoliation corrosion resistance properties of the AA7085 aluminum alloys significantly. The microscope analyses show that with partial resolution heat treatment combined with aging treatment the alloy could produce discontinuous and fine grain boundary precipitates η phase, so that the corrosion resistance is enhanced.
Effects of different solution heat treatment technology, including solution at R.T., pre-precipitation at high temperature and partial resolution, on microstructure, strength and exfoliation corrosion properties of AA7085 aluminum alloys were investigated by tensile testing, conductivity testing, exfoliation corrosion experiment, optical microscope and transmission electron microscopy (TEM). Results show that the partial resolution heat treatment combined with aging treatment decreases the tensile strength, but increases the conductivity and exfoliation corrosion resistance properties of the AA7085 aluminum alloys significantly. The microscope analyses show that with partial resolution heat treatment combined with aging treatment the alloy could produce discontinuous and fine grain boundary precipitates η phase, so that the corrosion resistance is enhanced.
2010, 39(3):498-501.
Abstract:
Non-equilibrium coatings were prepared from Zn-Al-Mg-RE-Si powder core spun alloy by electric arc spraying, and the corrosion resistances of non-equilibrium coatings were investigated by copper accelerated acetic acid salt spray test (CASS), mass-loss test, XRD, SEM, polarization curves and electrochemical impedance spectroscopy. The results show that the obtained Zn-Al-Mg-RE-Si coatings are non-equilibrium texture like glassy state but not amorphous texture, and their corrosion rate is obviously slower than that of normal coatings due to large quantity of compact corrosion products attaching to the surface of coatings and preventing breakage of coatings, which indicates the self-sealing effectiveness of non-equilibrium coatings. While the corrosion potential of non-equilibrium coatings is more positive than that of normal coatings, and the corrosion current is only half of that of normal coatings. Furthermore, the charge-transfer resistance is twice as big as that of normal coatings which shows that the corrosion resistance of non-equilibrium coatings is superior to that of normal coatings.
Non-equilibrium coatings were prepared from Zn-Al-Mg-RE-Si powder core spun alloy by electric arc spraying, and the corrosion resistances of non-equilibrium coatings were investigated by copper accelerated acetic acid salt spray test (CASS), mass-loss test, XRD, SEM, polarization curves and electrochemical impedance spectroscopy. The results show that the obtained Zn-Al-Mg-RE-Si coatings are non-equilibrium texture like glassy state but not amorphous texture, and their corrosion rate is obviously slower than that of normal coatings due to large quantity of compact corrosion products attaching to the surface of coatings and preventing breakage of coatings, which indicates the self-sealing effectiveness of non-equilibrium coatings. While the corrosion potential of non-equilibrium coatings is more positive than that of normal coatings, and the corrosion current is only half of that of normal coatings. Furthermore, the charge-transfer resistance is twice as big as that of normal coatings which shows that the corrosion resistance of non-equilibrium coatings is superior to that of normal coatings.
2010, 39(3):502-506.
Abstract:
Mg-8Gd-3Y-0.5Zr(GW83K) alloys were prepared by means of the atmosphere protection method and then chamber die cast into tensile samples with cold mould. The microstructures and mechanical properties of alloys in die-cast state and different heat treatment states were investigated by optical microscopy, scanning electron microscopy and mechanical property testing. The results show that the mechanical properties of the cold-mould die-cast GW83K alloys after heat treatment are improved. In particular, the die-cast GW83K alloy after short-time low-temperature solid solution treatment (T4) has a little variation in grain size and more uniform microstructure, lamellar eutectic disappears and the second phases distribute in the grain boundary in discontinuous rod shape or granule shape. Due to microstructure improvement of GW83K-T4 alloy, the mechanical properties of the alloy at room temperature are improved such as: σb=261.7 MPa, σs=240.8 MPa and δs=6.0%, which are increased by 21%, 28.4% and 30.4% compared with those of die-cast GW83K alloy respectively, and GW83K-T4 alloy has better elevated temperature mechanical properties.
Mg-8Gd-3Y-0.5Zr(GW83K) alloys were prepared by means of the atmosphere protection method and then chamber die cast into tensile samples with cold mould. The microstructures and mechanical properties of alloys in die-cast state and different heat treatment states were investigated by optical microscopy, scanning electron microscopy and mechanical property testing. The results show that the mechanical properties of the cold-mould die-cast GW83K alloys after heat treatment are improved. In particular, the die-cast GW83K alloy after short-time low-temperature solid solution treatment (T4) has a little variation in grain size and more uniform microstructure, lamellar eutectic disappears and the second phases distribute in the grain boundary in discontinuous rod shape or granule shape. Due to microstructure improvement of GW83K-T4 alloy, the mechanical properties of the alloy at room temperature are improved such as: σb=261.7 MPa, σs=240.8 MPa and δs=6.0%, which are increased by 21%, 28.4% and 30.4% compared with those of die-cast GW83K alloy respectively, and GW83K-T4 alloy has better elevated temperature mechanical properties.
2010, 39(3):507-510.
Abstract:
Sn film electrodes with different thickness (2, 0.5, 0.25, 0.12 μm), as anode materials for lithium-ion batteries were prepared by electrodeposition onto copper foil collector. Their microstructures were observed by SEM and the performances were studied through charging-discharge experiments. Result show that the performances of Sn film electrodes can be improved by the thickness decrease, but the first reversible capacity loss was increased at the same time. The electrode of 0.5 μm thickness shows the highest discharge capacity and better cyclic stability: its discharge capacity is 749 mAh/g for the first cycle and keeps 578 mAh/g after 40 cycles.
Sn film electrodes with different thickness (2, 0.5, 0.25, 0.12 μm), as anode materials for lithium-ion batteries were prepared by electrodeposition onto copper foil collector. Their microstructures were observed by SEM and the performances were studied through charging-discharge experiments. Result show that the performances of Sn film electrodes can be improved by the thickness decrease, but the first reversible capacity loss was increased at the same time. The electrode of 0.5 μm thickness shows the highest discharge capacity and better cyclic stability: its discharge capacity is 749 mAh/g for the first cycle and keeps 578 mAh/g after 40 cycles.
2010, 39(3):511-514.
Abstract:
A nanostructured surface layer was induced on the surface of Zr-4 alloy with typical hcp structure by the method of surface mechanical attrition treatment (SMAT). XRD was applied to identify the average surface grain size of specimens processed for different duration. The results show that the minimum average grain size was about 20 nm for 15 min SMAT. Optical microsco(OM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HREM) were adopted to observe the microstructure of nanocrystallized surface layer, and the grain refinement mechanism of Zr-4 was studied.
A nanostructured surface layer was induced on the surface of Zr-4 alloy with typical hcp structure by the method of surface mechanical attrition treatment (SMAT). XRD was applied to identify the average surface grain size of specimens processed for different duration. The results show that the minimum average grain size was about 20 nm for 15 min SMAT. Optical microsco(OM), transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HREM) were adopted to observe the microstructure of nanocrystallized surface layer, and the grain refinement mechanism of Zr-4 was studied.
2010, 39(3):515-518.
Abstract:
In order to improve the electrochemical properties of LiNi0.5Mn1.5O4, a series of Li-ion batteries cathode materials LiMgxNi0.5-xMn1.5O4 (x=0, 0.05, 0.1) were prepared by rheological method. XRD results reveal that the synthesized compounds had the spinel structure. Electrochemical tests show that when x was 0.1 the sample LiMg0.1Ni0.4Mn1.5O4 had excellent cycle ability in the potential range from 3.5 to 4.9 V. When the charge and discharge current was 1 C, the LiMg0.1Ni0.4Mn1.5O4 electrode delivered the initial discharge capacity of 110.22 mAh/g. Its capacity decline rate after 30 cycles was only 7.7%.
In order to improve the electrochemical properties of LiNi0.5Mn1.5O4, a series of Li-ion batteries cathode materials LiMgxNi0.5-xMn1.5O4 (x=0, 0.05, 0.1) were prepared by rheological method. XRD results reveal that the synthesized compounds had the spinel structure. Electrochemical tests show that when x was 0.1 the sample LiMg0.1Ni0.4Mn1.5O4 had excellent cycle ability in the potential range from 3.5 to 4.9 V. When the charge and discharge current was 1 C, the LiMg0.1Ni0.4Mn1.5O4 electrode delivered the initial discharge capacity of 110.22 mAh/g. Its capacity decline rate after 30 cycles was only 7.7%.
2010, 39(3):519-522.
Abstract:
Two kinds of palladium methanol decomposition catalysts were prepared by immersion method with γ-Al2O3 and Ce0.65Zr0.35O2 as supports, respectively. XRD, XPS, H2-TPR (H2-Temperature-Programmed-Redution) and NH3-TPD (NH3-Temperature- Programmed Desorption) techniques were used to study the microstructure and performance of catalyst samples and the activity of methanol low-temperature decomposition for the catalysts was also investigated. Testing results show that the Pd/Ce0.65Zr0.35O2 catalyst possesses weak surface acidity and good low-temperature reducibility. XPS results confirm that palladium of the two catalysts exist as oxidation state. Combining with catalytic activity, it can be known that Pd+ is advantageous in the methanol decomposition. High dispersion of palladium in ceria-zirconia solid solution and strong interaction between Pd and supports can decrease activation energy which results in high catalytic activity for methanol decomposition. The conversion of methanol nearly achieved 100% at 220 ℃ for Pd/Ce0.65Zr0.35O2.
Two kinds of palladium methanol decomposition catalysts were prepared by immersion method with γ-Al2O3 and Ce0.65Zr0.35O2 as supports, respectively. XRD, XPS, H2-TPR (H2-Temperature-Programmed-Redution) and NH3-TPD (NH3-Temperature- Programmed Desorption) techniques were used to study the microstructure and performance of catalyst samples and the activity of methanol low-temperature decomposition for the catalysts was also investigated. Testing results show that the Pd/Ce0.65Zr0.35O2 catalyst possesses weak surface acidity and good low-temperature reducibility. XPS results confirm that palladium of the two catalysts exist as oxidation state. Combining with catalytic activity, it can be known that Pd+ is advantageous in the methanol decomposition. High dispersion of palladium in ceria-zirconia solid solution and strong interaction between Pd and supports can decrease activation energy which results in high catalytic activity for methanol decomposition. The conversion of methanol nearly achieved 100% at 220 ℃ for Pd/Ce0.65Zr0.35O2.
2010, 39(3):523-527.
Abstract:
In order to extend the application of Mo2C as electric materials, the preparation of RE molybdenum carbide LnxMoyC by means of rare earth co-permeation with (NH4)3[CrMo6O24H6]·7H2O as the precursor and its conductivity were studied. XRD, EDS, XPS and four-probe poles were used to characterize the structure, element content, valences and conductivity of LnxMoyC. Results show that the structure of the prepared LnxMoyC is single hexagonal close-packed (hcp) and some rare earth elements such as Nd, Gd, La and Sm permeated into crystal phase of molybdenum carbide have influence on its conductivity. The conductivity of LNSGMC (La0.00593Nd0.00562Sm0.00502Gd0.00500Mo1.98C ) at room temperature is 4.692×102 S·cm-1, which is 4.6 times higher than the highest value (1.025×102 S·cm-1) by conventional methods. In the range of 289-490 K, it shows metallic conductivity while in 490-550 K range it shows obvious semiconductor conductivity.
In order to extend the application of Mo2C as electric materials, the preparation of RE molybdenum carbide LnxMoyC by means of rare earth co-permeation with (NH4)3[CrMo6O24H6]·7H2O as the precursor and its conductivity were studied. XRD, EDS, XPS and four-probe poles were used to characterize the structure, element content, valences and conductivity of LnxMoyC. Results show that the structure of the prepared LnxMoyC is single hexagonal close-packed (hcp) and some rare earth elements such as Nd, Gd, La and Sm permeated into crystal phase of molybdenum carbide have influence on its conductivity. The conductivity of LNSGMC (La0.00593Nd0.00562Sm0.00502Gd0.00500Mo1.98C ) at room temperature is 4.692×102 S·cm-1, which is 4.6 times higher than the highest value (1.025×102 S·cm-1) by conventional methods. In the range of 289-490 K, it shows metallic conductivity while in 490-550 K range it shows obvious semiconductor conductivity.
2010, 39(3):528-530.
Abstract:
Thermal variation of the Co79.5Sn20.5 alloy during the cooling process was analyzed by the differential scanning calorimeter (DSC) and its equivalent magnetic susceptibility change during the process was measured using a new device. The magnetic susceptibility and the heat of the alloy will change abruptly when there are structure changes. During the disorder-order phase transition in the solid state, the structure and the equivalent magnetic susceptibility were studied. Moreover, the comparison among the microstructure changes by different physical properties indicates that the solid-liquid transition, the Curie transition and the disorder-order solid transformation can be well characterized by the variations of the equivalent magnetic susceptibility.
Thermal variation of the Co79.5Sn20.5 alloy during the cooling process was analyzed by the differential scanning calorimeter (DSC) and its equivalent magnetic susceptibility change during the process was measured using a new device. The magnetic susceptibility and the heat of the alloy will change abruptly when there are structure changes. During the disorder-order phase transition in the solid state, the structure and the equivalent magnetic susceptibility were studied. Moreover, the comparison among the microstructure changes by different physical properties indicates that the solid-liquid transition, the Curie transition and the disorder-order solid transformation can be well characterized by the variations of the equivalent magnetic susceptibility.
2010, 39(3):531-533.
Abstract:
Objective criterion for the preparation process of W-Cu green sheet by powder rolling was investigated, and an objective methodology frame for the preparation was obtained. Based on the change tendency of mixed behavior, the optimum ratio between powder and adhesive was obtained. Based on differential thermal and thermo-gravimetric analysis results, the drying temperature and drying time of powder was determined. Based on the law of conservation of mass, the density of the powder-rolled green sheet was determined. According to materials’ own physical and chemical property index, the effect of human elements can be weakened, and thus the stability of preparation process of green sheet by powder rolling can be increased.
Objective criterion for the preparation process of W-Cu green sheet by powder rolling was investigated, and an objective methodology frame for the preparation was obtained. Based on the change tendency of mixed behavior, the optimum ratio between powder and adhesive was obtained. Based on differential thermal and thermo-gravimetric analysis results, the drying temperature and drying time of powder was determined. Based on the law of conservation of mass, the density of the powder-rolled green sheet was determined. According to materials’ own physical and chemical property index, the effect of human elements can be weakened, and thus the stability of preparation process of green sheet by powder rolling can be increased.
37 Research on Combination Stirring Fabrication Technology of Nano-CeO2/Zn-4.5Al-RE-Mg-Ti Composites
2010, 39(3):534-537.
Abstract:
The prime mixture of Zn-4.5Al-RE-Mg-Ti alloy (ZA) and nano-CeO2 clusters was prepared by mechanical stirring method with high engulfing ability. Then the engulfed nano-CeO2 clusters were dispersed by high-intensity ultrasonic to obtain nano-CeO2/ZA composites (ZACs) with the nominal mass fractions of 1%-6%. The optical microscope observations show that the microstructure of ZACs at room temperature consists of island-like eutectoid structure α(Al)+β(Zn) and lamellar structure α+β. Based on the FE-SEM results, nano-CeO2 particulates could be homogeneously distributed in the ZACs prepared by the combination stirring technology.
The prime mixture of Zn-4.5Al-RE-Mg-Ti alloy (ZA) and nano-CeO2 clusters was prepared by mechanical stirring method with high engulfing ability. Then the engulfed nano-CeO2 clusters were dispersed by high-intensity ultrasonic to obtain nano-CeO2/ZA composites (ZACs) with the nominal mass fractions of 1%-6%. The optical microscope observations show that the microstructure of ZACs at room temperature consists of island-like eutectoid structure α(Al)+β(Zn) and lamellar structure α+β. Based on the FE-SEM results, nano-CeO2 particulates could be homogeneously distributed in the ZACs prepared by the combination stirring technology.
2010, 39(3):538-541.
Abstract:
Variation of the free volume of Zr60Al15Ni25 amorphous alloy during rolling plastic deformation and its influence on the mechanical property were investigated by differential scanning calorimetry (DSC). Results show that the Vickers microhardness decreases with increment of deformation degree ε, and the maximum reduction reaches about 10% from as-cast state to ε=95%. However, in the DSC curves the released energy due to relaxation before glassy transformation increases with ε increasing. It is concluded that the free volume in the amorphous alloy increases after plastic deformation. The excess free volume in shear zone maybe coalesces into nano-sized voids as deformation ceases. The existence of those voids leads to the decrease of the viscosity, i.e., the decline of the Vickers hardness.
Variation of the free volume of Zr60Al15Ni25 amorphous alloy during rolling plastic deformation and its influence on the mechanical property were investigated by differential scanning calorimetry (DSC). Results show that the Vickers microhardness decreases with increment of deformation degree ε, and the maximum reduction reaches about 10% from as-cast state to ε=95%. However, in the DSC curves the released energy due to relaxation before glassy transformation increases with ε increasing. It is concluded that the free volume in the amorphous alloy increases after plastic deformation. The excess free volume in shear zone maybe coalesces into nano-sized voids as deformation ceases. The existence of those voids leads to the decrease of the viscosity, i.e., the decline of the Vickers hardness.
2010, 39(3):542-544.
Abstract:
Praseodymium oxide nanorod Nanorods Nanocomposite were prepared and the silver was loaded on them by immersion method. Then the nanocomposite was obtained with high stability. The nanocomposite was characterized by XRD, TEM and HRTEM. Pr6O11/Ag nanocomposite was used as catalyst for the epoxidation reaction of cyclohexene, indicating its superior catalytic activity.
Praseodymium oxide nanorod Nanorods Nanocomposite were prepared and the silver was loaded on them by immersion method. Then the nanocomposite was obtained with high stability. The nanocomposite was characterized by XRD, TEM and HRTEM. Pr6O11/Ag nanocomposite was used as catalyst for the epoxidation reaction of cyclohexene, indicating its superior catalytic activity.
2010, 39(3):545-548.
Abstract:
The film of LaMgNi4 alloy was prepared by constant-current electrodeposition method in an aqueous solution. The electrochemical performance, surface morphology and structure of the film were studied by cyclic voltammetry, charge-discharge cycle, SEM and XRD. The results show that as a hydrogen storage electrode, the film has good electrochemical activity with no need for an activation procedure and the capacity reached 398 mAh/g in the first cycle.
The film of LaMgNi4 alloy was prepared by constant-current electrodeposition method in an aqueous solution. The electrochemical performance, surface morphology and structure of the film were studied by cyclic voltammetry, charge-discharge cycle, SEM and XRD. The results show that as a hydrogen storage electrode, the film has good electrochemical activity with no need for an activation procedure and the capacity reached 398 mAh/g in the first cycle.
2010, 39(3):549-551.
Abstract:
(Mn1-xFex)5Sn3 (x=0.1-0.5) alloys were prepared by powder metallurgy method with magnetic field pressing and sintering. The crystal structure, Curie temperature and magnetic entropy change of the alloys were studied. XRD patterns reveal that all samples of this system maintain a hexagonal InNi2-type structure with space group P63/mmc. The lattice parameter and cell volumes of the (Mn1-xFex)5Sn3 alloys decrease with x increasing by calculation, while the Curie temperature of these alloys increases almost linearly and is tunable continually from 244 K to 391 K by M-T curves. The Curie temperature of (Mn0.70Fe0.30)5Sn3 is about 295 K close to room temperature, and the maximum magnetic entropy change is 0.87 (kg·K)-1 with a field change from 0 to 1.5 T. The curve of magnetic entropy change of (Mn0.70Fe0.30)5Sn3 is flat in a wide temperature range. It is indicated that the (Mn1-xFex)5Sn3 alloy is a suitable candidate with low cost for Ericsson cycle.
(Mn1-xFex)5Sn3 (x=0.1-0.5) alloys were prepared by powder metallurgy method with magnetic field pressing and sintering. The crystal structure, Curie temperature and magnetic entropy change of the alloys were studied. XRD patterns reveal that all samples of this system maintain a hexagonal InNi2-type structure with space group P63/mmc. The lattice parameter and cell volumes of the (Mn1-xFex)5Sn3 alloys decrease with x increasing by calculation, while the Curie temperature of these alloys increases almost linearly and is tunable continually from 244 K to 391 K by M-T curves. The Curie temperature of (Mn0.70Fe0.30)5Sn3 is about 295 K close to room temperature, and the maximum magnetic entropy change is 0.87 (kg·K)-1 with a field change from 0 to 1.5 T. The curve of magnetic entropy change of (Mn0.70Fe0.30)5Sn3 is flat in a wide temperature range. It is indicated that the (Mn1-xFex)5Sn3 alloy is a suitable candidate with low cost for Ericsson cycle.
2010, 39(3):552-555.
Abstract:
By means of hot compression and tension test on a Gleeble-1500 equipment for the as-forged V-5Cr-5Ti alloys, the effect of the deformation temperature on the critical deformation and critical deformation resistance in the compression process were studied, its effect on the yield strength and percentage reduction of area in the tension process were also studied. The deformation microstructure of hot compression specimen was analyzed by OM. Results show that the V-5Cr-5Ti alloys have high deformation resistance and low plasticity. In order to improve the hot workability, the hot-working temperature range must be strictly selected and controlled. The optimum hot-working temperature range of V-5Cr-5Ti alloys should be 1150-1250 ℃, and the deformation amount should be below 30% to get satisfactory alloys.
By means of hot compression and tension test on a Gleeble-1500 equipment for the as-forged V-5Cr-5Ti alloys, the effect of the deformation temperature on the critical deformation and critical deformation resistance in the compression process were studied, its effect on the yield strength and percentage reduction of area in the tension process were also studied. The deformation microstructure of hot compression specimen was analyzed by OM. Results show that the V-5Cr-5Ti alloys have high deformation resistance and low plasticity. In order to improve the hot workability, the hot-working temperature range must be strictly selected and controlled. The optimum hot-working temperature range of V-5Cr-5Ti alloys should be 1150-1250 ℃, and the deformation amount should be below 30% to get satisfactory alloys.
2010, 39(3):556-560.
Abstract:
Thermoelectric materials and the related devices which are environmentally friendly have attracted increasing attention due to the development of modern technologies and the intensification of energy and environment crisis. Recent theoretical and experimental studies have demonstrated that it is promising to decrease the dimensions and the sizes in the research and development of thermoelectric materials. The research progress of the influencing factor on thermoelectric performance, material preparation and measurement technology of low-dimensional thermoelectric materials are introduced and reviewed. The research and development trends of low-dimensional thermoelectric materials are further discussed.
Thermoelectric materials and the related devices which are environmentally friendly have attracted increasing attention due to the development of modern technologies and the intensification of energy and environment crisis. Recent theoretical and experimental studies have demonstrated that it is promising to decrease the dimensions and the sizes in the research and development of thermoelectric materials. The research progress of the influencing factor on thermoelectric performance, material preparation and measurement technology of low-dimensional thermoelectric materials are introduced and reviewed. The research and development trends of low-dimensional thermoelectric materials are further discussed.
2010, 39(3):561-564.
Abstract:
Compressive property of porous metals was analyzed and the latest research progress of this field in recent years was emphatically introduced. Moreover, effects of compressive property on performance of porous metals were discussed. The energy absorption capacity of porous metals in compression process was emphasized. Finally, limitation of research on compressive property for porous metals was put forward.
Compressive property of porous metals was analyzed and the latest research progress of this field in recent years was emphatically introduced. Moreover, effects of compressive property on performance of porous metals were discussed. The energy absorption capacity of porous metals in compression process was emphasized. Finally, limitation of research on compressive property for porous metals was put forward.
