Volume 39,Issue 9,2010 Table of Contents
2010, 39(9):1505-1508.
Abstract:
In order to exploit the potential hot deformation ability of metalstable b titanium alloy Ti-B19 the isothermal compression behavior was investigated by a Gleeble-1500 thermal simulator in the temperature range of 750-1000 °C at an interval of 50 °C and strain rate from 0.001 to 10 s-1. The results indicate that the flow stress of the alloy increases with increasing of the strain rate at a given temperature, and decreases with the increment of temperature at a given strain rate. The processing map for the alloy obtained at strain of 0.6 can be divided into three domains. The first is the one in the temperature range of 700~800 °C and the strain rate range of 0.001-0.1 s-1, with a peak efficiency of 42% at about 750 °C and 0.01 s-1. The flow curves in this domain present a single peak or oscillation in the flow curves before continuous softening appears. The second is the one in the temperature range of 800-1000 °C and the strain rate range of 0.001-0.1 s-1, with efficiency from 29% to 36%. The flow curves in this domain present a single peak or oscillation in the flow curves before reaching steady state. Recrystallized structures can be found, which is a typical dynamic recrystallization zone. The third one is a flow instable domain at the temperature lower than 800 °C and the strain rate above 0.1 s-1, or at the temperature higher than 800 °C and strain rate above 10 s-1. The adiabatic shear bands (ASBs) and flow inhomogeneous zone of β phases can be observed.
In order to exploit the potential hot deformation ability of metalstable b titanium alloy Ti-B19 the isothermal compression behavior was investigated by a Gleeble-1500 thermal simulator in the temperature range of 750-1000 °C at an interval of 50 °C and strain rate from 0.001 to 10 s-1. The results indicate that the flow stress of the alloy increases with increasing of the strain rate at a given temperature, and decreases with the increment of temperature at a given strain rate. The processing map for the alloy obtained at strain of 0.6 can be divided into three domains. The first is the one in the temperature range of 700~800 °C and the strain rate range of 0.001-0.1 s-1, with a peak efficiency of 42% at about 750 °C and 0.01 s-1. The flow curves in this domain present a single peak or oscillation in the flow curves before continuous softening appears. The second is the one in the temperature range of 800-1000 °C and the strain rate range of 0.001-0.1 s-1, with efficiency from 29% to 36%. The flow curves in this domain present a single peak or oscillation in the flow curves before reaching steady state. Recrystallized structures can be found, which is a typical dynamic recrystallization zone. The third one is a flow instable domain at the temperature lower than 800 °C and the strain rate above 0.1 s-1, or at the temperature higher than 800 °C and strain rate above 10 s-1. The adiabatic shear bands (ASBs) and flow inhomogeneous zone of β phases can be observed.
2010, 39(9):1509-1512.
Abstract:
The behavior of hydrogen absorption/desorption of Ti600, TC21 and Ti40 alloys was studied. The results show that the initial temperatures of hydrogen absorption/desorption for Ti600, TC21 and Ti40 alloy are 573 and 578.5 °C, 580 and 628.1 °C, 515 and 540 °C, respectively. The behavior of hydrogen absorption/desorption of Ti600 alloy is similar to that of TC21 alloy. The ability of hydrogen absorption/desorption of Ti40 alloy is better than the others’.
The behavior of hydrogen absorption/desorption of Ti600, TC21 and Ti40 alloys was studied. The results show that the initial temperatures of hydrogen absorption/desorption for Ti600, TC21 and Ti40 alloy are 573 and 578.5 °C, 580 and 628.1 °C, 515 and 540 °C, respectively. The behavior of hydrogen absorption/desorption of Ti600 alloy is similar to that of TC21 alloy. The ability of hydrogen absorption/desorption of Ti40 alloy is better than the others’.
2010, 39(9):1513-1518.
Abstract:
The sintering parameters of cathode preparation for the process of electrochemical reduction of TiO2 to titanium such as the temperature and the time were investigated. The SEM and EDS methods were used to study the influences of sintering temperature and time on the microstructure and porosity of the TiO2 compacts; moreover, the influences on the microstructure and oxygen content of the electrochemical reduction products were studied. The sintering parameters mainly affect the particle size, porosity and pore distribution of the cathodes. The compact with coarser grain size can be obtained when sintered at higher temperature and for longer time; while the change of the porosity in the compact is complex under different sintering conditions. The oxygen content of the electrochemical-reduced products depends on the grain size and the porosity of the sintered compacts. The compacts with small grains, used as cathode samples can be fully reduced; both open pores and closed pores in the samples are favorable to the electro-reduction process. The proper cathode preparation condition is that the greens are sintered at 1000-1100 °C for 4 h according to the results of the experiments.
The sintering parameters of cathode preparation for the process of electrochemical reduction of TiO2 to titanium such as the temperature and the time were investigated. The SEM and EDS methods were used to study the influences of sintering temperature and time on the microstructure and porosity of the TiO2 compacts; moreover, the influences on the microstructure and oxygen content of the electrochemical reduction products were studied. The sintering parameters mainly affect the particle size, porosity and pore distribution of the cathodes. The compact with coarser grain size can be obtained when sintered at higher temperature and for longer time; while the change of the porosity in the compact is complex under different sintering conditions. The oxygen content of the electrochemical-reduced products depends on the grain size and the porosity of the sintered compacts. The compacts with small grains, used as cathode samples can be fully reduced; both open pores and closed pores in the samples are favorable to the electro-reduction process. The proper cathode preparation condition is that the greens are sintered at 1000-1100 °C for 4 h according to the results of the experiments.
2010, 39(9):1519-1524.
Abstract:
The effects of the solution treatment temperature on the microstructure, the chemical composition homogeneity and the microhardness of laser solid forming GH4169 superalloy were investigated. It is found that the grain boundaries become clearer with increasing of the solution treatment temperature. The recrystallization occurs when the samples are solution treated at 1000-1170 °C for 1 h; when the solution treatment temperature is higher than 1000 °C, a large number of twin crystals can be observed, and the grains are refined remarkably compared with the as-deposited grains. The chemical homogeneity can be achieved through solution treatment at 1100 °C for 1 h. With increasing of the solution treatment temperature, the microhardness first decreases rapidly, and then slowly when the solution treatment temperature is above 1100 °C. The variation of microhardness can be explained based on the precipitation behaviors of g ′, g " and d phases during the solution treatment. It is concluded that the temperature of 1100 °C is the low limit of solution treatment temperature range for laser solid forming GH4169 superalloy.
The effects of the solution treatment temperature on the microstructure, the chemical composition homogeneity and the microhardness of laser solid forming GH4169 superalloy were investigated. It is found that the grain boundaries become clearer with increasing of the solution treatment temperature. The recrystallization occurs when the samples are solution treated at 1000-1170 °C for 1 h; when the solution treatment temperature is higher than 1000 °C, a large number of twin crystals can be observed, and the grains are refined remarkably compared with the as-deposited grains. The chemical homogeneity can be achieved through solution treatment at 1100 °C for 1 h. With increasing of the solution treatment temperature, the microhardness first decreases rapidly, and then slowly when the solution treatment temperature is above 1100 °C. The variation of microhardness can be explained based on the precipitation behaviors of g ′, g " and d phases during the solution treatment. It is concluded that the temperature of 1100 °C is the low limit of solution treatment temperature range for laser solid forming GH4169 superalloy.
2010, 39(9):1525-1531.
Abstract:
The particle distribution of particles-reinforced metal matrix composites (MMC) plays an important role. Thus it is essential to study the effect of the particle clustering behavior on the mechanical response of MMC. This paper reported the microstructure-based finite element analysis (FEA) of MMC to evaluate the clustering behavior, in which three models were established including one-clustering, two-clustering and random particles arrangement. Based on the analysis, the distributions of the von Mises effective stress and of the strain in the matrix and in the particles were obtained and analyzed, respectively. The results show that the mechanical responses in the particles and the matrix are sensitive very much to the particle clustering. Additionally, the overall stress-strain curves of the three models were depicted. It is indicated that during the elastic deformation, the elastic responses of the composites are less affected by the particle clustering. Further, the maximum principal stress in the particles and the hydrostatic stress in the matrix for the three models were investigated. The results reveal that the percentage of the particle cracking in the particle clustering model is higher compared with that in the particle random distribution model.
The particle distribution of particles-reinforced metal matrix composites (MMC) plays an important role. Thus it is essential to study the effect of the particle clustering behavior on the mechanical response of MMC. This paper reported the microstructure-based finite element analysis (FEA) of MMC to evaluate the clustering behavior, in which three models were established including one-clustering, two-clustering and random particles arrangement. Based on the analysis, the distributions of the von Mises effective stress and of the strain in the matrix and in the particles were obtained and analyzed, respectively. The results show that the mechanical responses in the particles and the matrix are sensitive very much to the particle clustering. Additionally, the overall stress-strain curves of the three models were depicted. It is indicated that during the elastic deformation, the elastic responses of the composites are less affected by the particle clustering. Further, the maximum principal stress in the particles and the hydrostatic stress in the matrix for the three models were investigated. The results reveal that the percentage of the particle cracking in the particle clustering model is higher compared with that in the particle random distribution model.
2010, 39(9):1532-1535.
Abstract:
A high-concentration silver colloidal nanoparticles with a narrow size distribution were obtained using [Ag(NH3)2]+-PVP(poly (N-vinyl-2-pyrrolidone)) solution via the synergistic action of UV and heat excitation. The nucleation and growth of the silver nanoparticles were monitored by UV-vis. absorption spectroscopy. The results show surface plasma resonance peaks of silver nanoparticles are located at about 419 nm. Transmission electron microscopy (TEM) reveals that most of the particles possess spherical shape with an average size of about 1.32 nm and standard deviation 0.53 nm. Moreover, the pH value of the obtained samples is nearly neutral, which will lead to a more extensive application.
A high-concentration silver colloidal nanoparticles with a narrow size distribution were obtained using [Ag(NH3)2]+-PVP(poly (N-vinyl-2-pyrrolidone)) solution via the synergistic action of UV and heat excitation. The nucleation and growth of the silver nanoparticles were monitored by UV-vis. absorption spectroscopy. The results show surface plasma resonance peaks of silver nanoparticles are located at about 419 nm. Transmission electron microscopy (TEM) reveals that most of the particles possess spherical shape with an average size of about 1.32 nm and standard deviation 0.53 nm. Moreover, the pH value of the obtained samples is nearly neutral, which will lead to a more extensive application.
2010, 39(9):1536-1539.
Abstract:
Shot-peening was performed for TC4 titanium alloy sample and then its microstructure was analyzed by OM, SEM and TEM. The microhardness distribution along surface layer was determined and based on the results the microstructure characteristics in shot- peened layer and the mechanism of work hardening were analyzed. The results show that after shot-peening, dislocation movement and configuration change refine the microstructure and substructure of TC4 alloy surface layer, and twins are formed in the deformed area of the surface layer, resulting in significant work hardening effect.
Shot-peening was performed for TC4 titanium alloy sample and then its microstructure was analyzed by OM, SEM and TEM. The microhardness distribution along surface layer was determined and based on the results the microstructure characteristics in shot- peened layer and the mechanism of work hardening were analyzed. The results show that after shot-peening, dislocation movement and configuration change refine the microstructure and substructure of TC4 alloy surface layer, and twins are formed in the deformed area of the surface layer, resulting in significant work hardening effect.
2010, 39(9):1540-1544.
Abstract:
Effects of the isothermal forging deformation amount on the microstructure and properties of the TG6 alloy (Ti-5.8Al-4.0Sn- 4.0Zr-0.7Nb-1.5Ta-0.4Si-0.06C, mass fraction) were studied by optical microscope, SEM, EPMA, metallurgical image-analysis software and the Vikers hardness testing. The results show that with increasing of the deformation amount, both the content of primary a phases and the thickness of secondary-a phases decrease firstly and then increase; the tensile strength increases firstly and then decreases, while the plasticity is contrary. Recovery is dominant for the forging microstructure when the deformation amount is 10%, while for 30% deformation partial dynamic re-crystallization occurs in b phases and recovery is predominant in primary a phases. The lath-shaped a phases caused by the segregation of the Al element for both 10% and 30% deformation can improve the ductility significantly. When the deformation is 50%, the forging microstructure is re-crystallized completely and bimodal microstructure is formed with about 20% primary a phases; so the forging possesses good mechanical properties. Complete re-crystallization happens firstly and partial re-crystallization and recovery appears later when the deformation is 70%; the primary a phases are various and the lath-shaped a phases are caused by the assembly of the lamellar secondary-a phases. The optimal isothermal forging deformation of TG6 alloy is 50% from the analysis of the tensile properties of typical titanium alloys used at 600 °C.
Effects of the isothermal forging deformation amount on the microstructure and properties of the TG6 alloy (Ti-5.8Al-4.0Sn- 4.0Zr-0.7Nb-1.5Ta-0.4Si-0.06C, mass fraction) were studied by optical microscope, SEM, EPMA, metallurgical image-analysis software and the Vikers hardness testing. The results show that with increasing of the deformation amount, both the content of primary a phases and the thickness of secondary-a phases decrease firstly and then increase; the tensile strength increases firstly and then decreases, while the plasticity is contrary. Recovery is dominant for the forging microstructure when the deformation amount is 10%, while for 30% deformation partial dynamic re-crystallization occurs in b phases and recovery is predominant in primary a phases. The lath-shaped a phases caused by the segregation of the Al element for both 10% and 30% deformation can improve the ductility significantly. When the deformation is 50%, the forging microstructure is re-crystallized completely and bimodal microstructure is formed with about 20% primary a phases; so the forging possesses good mechanical properties. Complete re-crystallization happens firstly and partial re-crystallization and recovery appears later when the deformation is 70%; the primary a phases are various and the lath-shaped a phases are caused by the assembly of the lamellar secondary-a phases. The optimal isothermal forging deformation of TG6 alloy is 50% from the analysis of the tensile properties of typical titanium alloys used at 600 °C.
2010, 39(9):1545-4549.
Abstract:
The tensile mechanical behavior of Ti-2Al alloys containing 0.06% (extremely low content; mass fraction, similarly hereinafter), 0.16% (industrial content) and 0.30% (high content) oxygen at low temperature (77 K), room temperature and elevated temperature (673 K) was investigated. Results show that Ti-2Al-0.06O, Ti-2Al-0.16O and Ti-2Al-0.30O exhibit significant variation in strength and ductility. The strength was increased but the ductility was decreased with increasing of the oxygen concentration at room temperature and low temperature. However, there was not an obvious effect of oxygen concentration on both the strength and the ductility of these alloys at 673 K. In addition, the ductility of Ti-2Al-0.06O remained nearly invariable at different temperatures. In other words, ductility was independent on the testing temperature in the alloy with low oxygen concentration. This indicates that deterioration in ductility of Ti-2Al alloy is mainly due to excess absorption of oxygen. SEM observations reveal that a transition of fracture from brittle cleavage to dimple occurred in Ti-2Al-0.30O and Ti-2Al-0.16O as the testing temperature increased. Improvement in ductility of these alloys with high oxygen concentration can be attributed to increase in diffusivity of oxygen atoms, which leads to escape of the constrained dislocation from Cottrel atmosphere at the elevated temperature.
The tensile mechanical behavior of Ti-2Al alloys containing 0.06% (extremely low content; mass fraction, similarly hereinafter), 0.16% (industrial content) and 0.30% (high content) oxygen at low temperature (77 K), room temperature and elevated temperature (673 K) was investigated. Results show that Ti-2Al-0.06O, Ti-2Al-0.16O and Ti-2Al-0.30O exhibit significant variation in strength and ductility. The strength was increased but the ductility was decreased with increasing of the oxygen concentration at room temperature and low temperature. However, there was not an obvious effect of oxygen concentration on both the strength and the ductility of these alloys at 673 K. In addition, the ductility of Ti-2Al-0.06O remained nearly invariable at different temperatures. In other words, ductility was independent on the testing temperature in the alloy with low oxygen concentration. This indicates that deterioration in ductility of Ti-2Al alloy is mainly due to excess absorption of oxygen. SEM observations reveal that a transition of fracture from brittle cleavage to dimple occurred in Ti-2Al-0.30O and Ti-2Al-0.16O as the testing temperature increased. Improvement in ductility of these alloys with high oxygen concentration can be attributed to increase in diffusivity of oxygen atoms, which leads to escape of the constrained dislocation from Cottrel atmosphere at the elevated temperature.
2010, 39(9):1550-1554.
Abstract:
Isothermal constant strain rate compression tests were carried out for Ti-6Al-2Zr-1Mo-1V alloy. The plastic flow instability was predicted by Prasad criterion and phenomenological criterion and the results were compared through the compression experiment data. It is shown that the both instability criterions predict a large region of flow instability in the high strain rate range of 0.32-10 s-1, which is likely to extend to low strain rate region with decreasing of the deformation temperature. The corresponding microstructures of deformed specimens were observed. The results indicate Prasad criterion can not predict the flow localization and kinking instability in the range of 750-800 oC and 0.001-0.0032 s-1. However, cracks and cavities at initial β boundaries and flow localization can not be predicted by phenomenological instability criterion in the range of 770-870 oC and 0.01-0.32 s-1, and in the range of 900-950 oC and 0.32-3.16 s-1. A new method to predict plastic flow instability was developed by superimposing the two instability maps of the two criterions on the basis of their merits and drawbacks.
Isothermal constant strain rate compression tests were carried out for Ti-6Al-2Zr-1Mo-1V alloy. The plastic flow instability was predicted by Prasad criterion and phenomenological criterion and the results were compared through the compression experiment data. It is shown that the both instability criterions predict a large region of flow instability in the high strain rate range of 0.32-10 s-1, which is likely to extend to low strain rate region with decreasing of the deformation temperature. The corresponding microstructures of deformed specimens were observed. The results indicate Prasad criterion can not predict the flow localization and kinking instability in the range of 750-800 oC and 0.001-0.0032 s-1. However, cracks and cavities at initial β boundaries and flow localization can not be predicted by phenomenological instability criterion in the range of 770-870 oC and 0.01-0.32 s-1, and in the range of 900-950 oC and 0.32-3.16 s-1. A new method to predict plastic flow instability was developed by superimposing the two instability maps of the two criterions on the basis of their merits and drawbacks.
2010, 39(9):1555-1560.
Abstract:
The cooling characteristic curves of the center, 1/2R and the border of the BT22 forged bars were measured. Results show there is a slow cooling stage in the 875 oC solution treatment cooling curve, due to the phase transformation. The curve exhibits one approximation flatform. The three positions have a big nonsynchronous characteristic of cooling. At the same time, microstructure development during the solution treatment cooling process at 875 and 810 oC was researched. According to the hardness test, non-uniform mechanical property of the medium forged bar after heat treatment was found.
The cooling characteristic curves of the center, 1/2R and the border of the BT22 forged bars were measured. Results show there is a slow cooling stage in the 875 oC solution treatment cooling curve, due to the phase transformation. The curve exhibits one approximation flatform. The three positions have a big nonsynchronous characteristic of cooling. At the same time, microstructure development during the solution treatment cooling process at 875 and 810 oC was researched. According to the hardness test, non-uniform mechanical property of the medium forged bar after heat treatment was found.
Yang Jingkui
,
Wang Xinhua
,
Bei Yayao
,
Pan Hongge
,
Chen Lixin
,
Li Shouquan
,
Ge Hongwei
,
Chen Changpin
2010, 39(9):1561-1564.
Abstract:
In order to improve the hydrogen storage properties of LiAlH4 and LiNH2, LiAlH4/LiNH2 composite was prepared by ball milling the mixture of LiAlH4 and LiNH2 with Ti or TiF3 as catalyst. The effects of Ti and TiF3 catalyst on the hydrogen storage properties of LiAlH4/LiNH2 composite were studied by thermogravimetry (TG), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) and hydrogen storage properties measurements. The results show that Ti or TiF3 addition significantly improves the desorption kinetics, increases the hydrogen desorption capacity, and decreases the initial hydrogen desorption temperature. For the LiAlH4/LiNH2 composite with addition of 5 mol% TiF3, the hydrogen desorption capacity of the composite increaseses from 1.27 wt% to 1.69 wt% during ball-milling process, the total hydrogen desorption capacity increases from 5.95 wt% to 6.85 wt%, and the initial hydrogen desorption temperature decreases from 150 to 75 oC.
In order to improve the hydrogen storage properties of LiAlH4 and LiNH2, LiAlH4/LiNH2 composite was prepared by ball milling the mixture of LiAlH4 and LiNH2 with Ti or TiF3 as catalyst. The effects of Ti and TiF3 catalyst on the hydrogen storage properties of LiAlH4/LiNH2 composite were studied by thermogravimetry (TG), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) and hydrogen storage properties measurements. The results show that Ti or TiF3 addition significantly improves the desorption kinetics, increases the hydrogen desorption capacity, and decreases the initial hydrogen desorption temperature. For the LiAlH4/LiNH2 composite with addition of 5 mol% TiF3, the hydrogen desorption capacity of the composite increaseses from 1.27 wt% to 1.69 wt% during ball-milling process, the total hydrogen desorption capacity increases from 5.95 wt% to 6.85 wt%, and the initial hydrogen desorption temperature decreases from 150 to 75 oC.
2010, 39(9):1565-1570.
Abstract:
Different solution treatments and aging treatments were carried out for GH864 superalloy. The change rule of g ￠ phase content and re-dissolution and precipitation rule of carbides were studied, as well as their effects on grain size, tensile property, creep property and crack growth behavior. Results indicate that by the same heat treatment schedule, the smaller and more uniform the grain sizes are, the higher the strength is; the larger the grain sizes are, the lower the crack growth rate is. In the temperature range of 960-1080 oC, g ￠ phase content decreases with increasing of the solution temperature, but the total amount of g ￠ phases is equal after dual aging treatment. But the cooling medium has no significant influence on the g ￠ content. Because of the interaction between g ￠ phase and carbides, the grain grows slowly below 1020 oC. Besides, the grain size has an obvious effect on the creep property and there is an optimum grain size to obtain the best performance.
Different solution treatments and aging treatments were carried out for GH864 superalloy. The change rule of g ￠ phase content and re-dissolution and precipitation rule of carbides were studied, as well as their effects on grain size, tensile property, creep property and crack growth behavior. Results indicate that by the same heat treatment schedule, the smaller and more uniform the grain sizes are, the higher the strength is; the larger the grain sizes are, the lower the crack growth rate is. In the temperature range of 960-1080 oC, g ￠ phase content decreases with increasing of the solution temperature, but the total amount of g ￠ phases is equal after dual aging treatment. But the cooling medium has no significant influence on the g ￠ content. Because of the interaction between g ￠ phase and carbides, the grain grows slowly below 1020 oC. Besides, the grain size has an obvious effect on the creep property and there is an optimum grain size to obtain the best performance.
2010, 39(9):1571-1574.
Abstract:
The microstructure of solid solution strengthened Hastelloy C-276 alloys before and after ruptured at 650 oC under different tensile stresses was studied by SEM and TEM. The results show that the fracture surface displays typical dimple morphology, with a few intergranular fractures. It can be concluded that the C-276 alloy has very good high-temperature toughness. A few annealing twins and plenty of dislocations exist in the initial microstructure of C-276 alloy. And after persistent tensile experiments, a large number of deformation twins are formed in C-276 crystals. Moreover, many fine and dispersive precipitations are also formed in the grain boundary and intragranular. Therefore, a good high temperature stress rupture performance of the Hastelloy C-276 alloy arises from co-effects of solid solution-strengthening, precipitation- strengthening and possible deformation twin-strengthening.
The microstructure of solid solution strengthened Hastelloy C-276 alloys before and after ruptured at 650 oC under different tensile stresses was studied by SEM and TEM. The results show that the fracture surface displays typical dimple morphology, with a few intergranular fractures. It can be concluded that the C-276 alloy has very good high-temperature toughness. A few annealing twins and plenty of dislocations exist in the initial microstructure of C-276 alloy. And after persistent tensile experiments, a large number of deformation twins are formed in C-276 crystals. Moreover, many fine and dispersive precipitations are also formed in the grain boundary and intragranular. Therefore, a good high temperature stress rupture performance of the Hastelloy C-276 alloy arises from co-effects of solid solution-strengthening, precipitation- strengthening and possible deformation twin-strengthening.
2010, 39(9):1575-1578.
Abstract:
Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk amorphous alloy (BAA) was prepared by arc melting and copper mold rapid casting. The crystallization process was tested by a heat expansion method, and the results were compared with that of the differential scanning calorimetry (DSC). The formation of the crystal nucleus and the crystal growth rule at the initial stage of crystallization was observed by high resolution transmission electron microscope (HRTEM). It is found that the relaxation process of the amorphous structure, glass transition, supercooled liquid region, starting temperature of crystallization and peak temperatures of the crystallization process which were tested by heat expansion are accordant with DSC results. The near-spherical nanocrystalline grains and crystal lattice stripes can be observed in HRTEM images. However, it is difficult to identify the tiny crystallization zone by HRTEM images at the initial stage of crystallization. The basic crystallization characters of the tiny zone can be observed expediently only by the fast Fourier transform (FFT) for the HRTEM image.
Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk amorphous alloy (BAA) was prepared by arc melting and copper mold rapid casting. The crystallization process was tested by a heat expansion method, and the results were compared with that of the differential scanning calorimetry (DSC). The formation of the crystal nucleus and the crystal growth rule at the initial stage of crystallization was observed by high resolution transmission electron microscope (HRTEM). It is found that the relaxation process of the amorphous structure, glass transition, supercooled liquid region, starting temperature of crystallization and peak temperatures of the crystallization process which were tested by heat expansion are accordant with DSC results. The near-spherical nanocrystalline grains and crystal lattice stripes can be observed in HRTEM images. However, it is difficult to identify the tiny crystallization zone by HRTEM images at the initial stage of crystallization. The basic crystallization characters of the tiny zone can be observed expediently only by the fast Fourier transform (FFT) for the HRTEM image.
2010, 39(9):1579-1582.
Abstract:
The high cycle fatigue behavior of die casting magnesium alloy AZ91D containing 1% mischmetal (AZ91D-1%MM) at the stress ratio of 0.1 was investigated. The microstructure difference between the skin and the core region of the die casting specimen was analyzed using optical microscopy and XRD. The ultimate tensile strength, yield strength and elongation are 185 MPa, 159 MPa and 1.5% at room temperature, respectively. The p-S-N curve (p=50%) of the die casting AZ91D-1%MM is determined and the fatigue strength at 3.8×105 cycles is 70 MPa. A linear relation between S and Np in log scale between 103 and 106 cycles is given as lgNp=17.85–6.83lgS. The fracture surfaces of some fatigue specimens at lower stress exhibit rubbing mark. The fatigue fracture surface of specimens with minor defects possesses the mixed characteristics of quasi-cleavage and gliding fracture such as tearing ridge, dimple or fatigue striation; therefore, the material belongs to lower-ductility materials.
The high cycle fatigue behavior of die casting magnesium alloy AZ91D containing 1% mischmetal (AZ91D-1%MM) at the stress ratio of 0.1 was investigated. The microstructure difference between the skin and the core region of the die casting specimen was analyzed using optical microscopy and XRD. The ultimate tensile strength, yield strength and elongation are 185 MPa, 159 MPa and 1.5% at room temperature, respectively. The p-S-N curve (p=50%) of the die casting AZ91D-1%MM is determined and the fatigue strength at 3.8×105 cycles is 70 MPa. A linear relation between S and Np in log scale between 103 and 106 cycles is given as lgNp=17.85–6.83lgS. The fracture surfaces of some fatigue specimens at lower stress exhibit rubbing mark. The fatigue fracture surface of specimens with minor defects possesses the mixed characteristics of quasi-cleavage and gliding fracture such as tearing ridge, dimple or fatigue striation; therefore, the material belongs to lower-ductility materials.
2010, 39(9):1583-1587.
Abstract:
The effect of Mg and Zn additions on the microstructure evolution and mechanical properties of an Al-Cu-Li alloy was studied by transmission electron microscopy and tensile testing. Results show that additions of Mg and Zn can accelerate the precipitation of δ′ phase nucleation and inhibit its growth, so the δ′ phase becomes finer and more dispersive. In the under-aging condition, a lot of GP zones are formed in the alloy containing Mg and Zn. The alloy only containing Mg also has many GP zones. But no GP zone is found in the alloy only containing Zn, while only a few coarse θ′ is found. The above results reveal that Mg promotes the formation of GP zones while the single role of Zn is not significant; Zn has a better effect when it acts with Mg together. As the aging proceeding, GP zones in the alloy containing Mg and Zn transforms into θ′/θ′′ phase and plenty of θ′/θ′′ phases are formed in the alloy only containing Mg, but θ′ phase dose not change obviously in the alloy only containing Zn. It indicates that Mg is the key element to accelerate θ′/θ′′ phase formation, and Zn can promote the formation only with Mg.
The effect of Mg and Zn additions on the microstructure evolution and mechanical properties of an Al-Cu-Li alloy was studied by transmission electron microscopy and tensile testing. Results show that additions of Mg and Zn can accelerate the precipitation of δ′ phase nucleation and inhibit its growth, so the δ′ phase becomes finer and more dispersive. In the under-aging condition, a lot of GP zones are formed in the alloy containing Mg and Zn. The alloy only containing Mg also has many GP zones. But no GP zone is found in the alloy only containing Zn, while only a few coarse θ′ is found. The above results reveal that Mg promotes the formation of GP zones while the single role of Zn is not significant; Zn has a better effect when it acts with Mg together. As the aging proceeding, GP zones in the alloy containing Mg and Zn transforms into θ′/θ′′ phase and plenty of θ′/θ′′ phases are formed in the alloy only containing Mg, but θ′ phase dose not change obviously in the alloy only containing Zn. It indicates that Mg is the key element to accelerate θ′/θ′′ phase formation, and Zn can promote the formation only with Mg.
2010, 39(9):1588-1592.
Abstract:
The tensile properties and electrical conductivity of 7A55 aluminum alloys at different states during RRA conventional treatment and RRA continuous treatment were tested and the microstructure evolution in the two periods was observed by TEM. The results show that either after conventional RRA treatment or after continuous RRA treatment, the alloy is composed of a large number of metstable η′ phase precipitates and a few η phase precipitates in grains; η phase precipitates are coarsened seriously and PFZ (precipitate free zone) appears at the grain boundaries; the electrical conductivity is greatly increased during the retrogression step. In addition, after the first step treatment without air cooling, heated to the retrogression temperature at a proper heating rate, the 7A55 alloy can obtain the strength near the first step aging levels together with the electrical conductivity of 38.1%IACS in continuous RRA treatment.
The tensile properties and electrical conductivity of 7A55 aluminum alloys at different states during RRA conventional treatment and RRA continuous treatment were tested and the microstructure evolution in the two periods was observed by TEM. The results show that either after conventional RRA treatment or after continuous RRA treatment, the alloy is composed of a large number of metstable η′ phase precipitates and a few η phase precipitates in grains; η phase precipitates are coarsened seriously and PFZ (precipitate free zone) appears at the grain boundaries; the electrical conductivity is greatly increased during the retrogression step. In addition, after the first step treatment without air cooling, heated to the retrogression temperature at a proper heating rate, the 7A55 alloy can obtain the strength near the first step aging levels together with the electrical conductivity of 38.1%IACS in continuous RRA treatment.
2010, 39(9):1593-1597.
Abstract:
The deposition process of electroless plating of Ni-P on AZ91D magnesium alloy was investigated by metallographic microscope, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Results show that the initial deposition mechanisms of Ni-P coating in different places of the activated surface are different. There is only nickel (Ni) deposition but no P on “massive object” generated after activation, mainly due to the dissolution of the fluorides and the replacement of Mg for Ni. For β phase and the edge of α phase, adjacent Ni2+ would gain a few electrons lost by Mg and be reduced because of electrochemical effect. The Ni nucleus with high catalytic activity provides the catalysis condition for the reduction of P and Ni.
The deposition process of electroless plating of Ni-P on AZ91D magnesium alloy was investigated by metallographic microscope, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Results show that the initial deposition mechanisms of Ni-P coating in different places of the activated surface are different. There is only nickel (Ni) deposition but no P on “massive object” generated after activation, mainly due to the dissolution of the fluorides and the replacement of Mg for Ni. For β phase and the edge of α phase, adjacent Ni2+ would gain a few electrons lost by Mg and be reduced because of electrochemical effect. The Ni nucleus with high catalytic activity provides the catalysis condition for the reduction of P and Ni.
2010, 39(9):1598-1603.
Abstract:
SEM-BSE, TEM and EDS techniques were applied to investigate the effect of Zn content on formation of precipitate phases and long-period stacking structure in MgGd3Nd0.3Znx alloys (x=0-1.25, at%) during aging at 400 oC. The results show that the alloys with x≤0.62 precipitate equilibrium β-phases around the as-cast secondary phases which remain stable at 400 oC, while for those with x≥1.06, the precipitation of β-phases does not take place in the Mg matrix. In the high Zn-content alloys, the as-cast secondary phases are no longer stable; they turn to decompose, and this leads to the formation of Zn- and RE-rich transition regions containing both stacking faults of high density and LPS between those undecomposed secondary phases and Mg matrix. With the aid of the compositional analysis of secondary phases, transition regions and Mg matrix in heat-treated MgGd3Nd0.3Znx alloys, the formation reason and process of the LPS in the high Zn-content alloys were discussed.
SEM-BSE, TEM and EDS techniques were applied to investigate the effect of Zn content on formation of precipitate phases and long-period stacking structure in MgGd3Nd0.3Znx alloys (x=0-1.25, at%) during aging at 400 oC. The results show that the alloys with x≤0.62 precipitate equilibrium β-phases around the as-cast secondary phases which remain stable at 400 oC, while for those with x≥1.06, the precipitation of β-phases does not take place in the Mg matrix. In the high Zn-content alloys, the as-cast secondary phases are no longer stable; they turn to decompose, and this leads to the formation of Zn- and RE-rich transition regions containing both stacking faults of high density and LPS between those undecomposed secondary phases and Mg matrix. With the aid of the compositional analysis of secondary phases, transition regions and Mg matrix in heat-treated MgGd3Nd0.3Znx alloys, the formation reason and process of the LPS in the high Zn-content alloys were discussed.
2010, 39(9):1604-1608.
Abstract:
Aluminum-based composites, using Al72Ni12Co16 decagonal quasicrystalline as reinforcing particles and pure Al and Al-5.5%Zn alloys (mass fraction) as base alloy, were fabricated. The microstructure and the particle distribution of the composite were analyzed by scanning electron microscopy (SEM) and energy dispersive spectrum (EDS). Results show that the phase transition occurs because the decagonal quaicrystalline particles are unstable in the melt. Regular polygon-like θ-phase distributes in the Al matrix, with particle sizes mainly ranging from 3.45-40 μm. At the same time, fine strip-like γ-phase with the size of 1.15-8.57 μm are formed along the grain boundaries. Mechanical property testing results reveal that, due to the existence of the final crystallized phases, yield strength, ultimate tensile strength and Young’s modulus of the composites are improved, but the elongation is decreased rapidly.
Aluminum-based composites, using Al72Ni12Co16 decagonal quasicrystalline as reinforcing particles and pure Al and Al-5.5%Zn alloys (mass fraction) as base alloy, were fabricated. The microstructure and the particle distribution of the composite were analyzed by scanning electron microscopy (SEM) and energy dispersive spectrum (EDS). Results show that the phase transition occurs because the decagonal quaicrystalline particles are unstable in the melt. Regular polygon-like θ-phase distributes in the Al matrix, with particle sizes mainly ranging from 3.45-40 μm. At the same time, fine strip-like γ-phase with the size of 1.15-8.57 μm are formed along the grain boundaries. Mechanical property testing results reveal that, due to the existence of the final crystallized phases, yield strength, ultimate tensile strength and Young’s modulus of the composites are improved, but the elongation is decreased rapidly.
2010, 39(9):1609-1613.
Abstract:
Amorphous electrode active material, nickel hydroxide powder codoped with PO43- and Mg2+ was synthesized by the method of quick cryoprecipatation. Its microstructure and electrochemical performance were studied. Results show that the shape of the amorphous sample codoped with 5wt% PO43- and 2wt% Mg2+ is abnormal, the randomness is strong and it contains a large amount of crystal water up to 31%. As the positive active material of MH-Ni battery, the discharge specific capacity of the codoped sample is 347 mAh·g-1, and the discharge mean voltage reaches to 1.29 V. The discharge rate has a little effect on the discharge specific capacity of the electrode sample. The stability of electrode material is good after the 50 times circulation of charging and discharging and the capacity decrement is only 3.5%; the proton diffusion coefficient is 9.22×10-10 cm2·s-1 and the electrochemical impedance in the electrochemical reaction is small. The electrochemical performances of the sample are much better than those of β-Ni(OH)2 applied in MH-Ni production.
Amorphous electrode active material, nickel hydroxide powder codoped with PO43- and Mg2+ was synthesized by the method of quick cryoprecipatation. Its microstructure and electrochemical performance were studied. Results show that the shape of the amorphous sample codoped with 5wt% PO43- and 2wt% Mg2+ is abnormal, the randomness is strong and it contains a large amount of crystal water up to 31%. As the positive active material of MH-Ni battery, the discharge specific capacity of the codoped sample is 347 mAh·g-1, and the discharge mean voltage reaches to 1.29 V. The discharge rate has a little effect on the discharge specific capacity of the electrode sample. The stability of electrode material is good after the 50 times circulation of charging and discharging and the capacity decrement is only 3.5%; the proton diffusion coefficient is 9.22×10-10 cm2·s-1 and the electrochemical impedance in the electrochemical reaction is small. The electrochemical performances of the sample are much better than those of β-Ni(OH)2 applied in MH-Ni production.
2010, 39(9):1614-1617.
Abstract:
Microcrystalline Ni (MC-Ni), ultrafine grained Ni (UFG-Ni) and nanocrystalline Ni (NC-Ni) with mean grain sizes of 2 μm, 120.7 nm and 22.4 nm, respectively were prepared by a pulsed electrodeposition method. The room-temperature one-way tensile tests show that the yield strength and the ultimate tensile strength of the three kinds of Ni deposits increase with decreasing of the grain size. The ductility of UFG-Ni decreases to 7.9% compared with 11.1% of the MC-Ni, while the UFG Ni shows a higher uniform elongation than MC-Ni. However, the ductility of NC-Ni is only 4.1%.
Microcrystalline Ni (MC-Ni), ultrafine grained Ni (UFG-Ni) and nanocrystalline Ni (NC-Ni) with mean grain sizes of 2 μm, 120.7 nm and 22.4 nm, respectively were prepared by a pulsed electrodeposition method. The room-temperature one-way tensile tests show that the yield strength and the ultimate tensile strength of the three kinds of Ni deposits increase with decreasing of the grain size. The ductility of UFG-Ni decreases to 7.9% compared with 11.1% of the MC-Ni, while the UFG Ni shows a higher uniform elongation than MC-Ni. However, the ductility of NC-Ni is only 4.1%.
2010, 39(9):1618-1622.
Abstract:
A systematic thermodynamic description for the Mg-rich corner of La-Mg-Ni ternary system has been obtained using the CALPHAD approach. The substitutional solution model, the three-sublattice model and the stoichiometric compound model were used to describe the liquid, La2Mg17-xNix and LaMg2Ni phases, respectively. The model parameters were then optimized using the experimental information. Calculations were compared with the experimental data for the enthalpy of mixing in liquid, isothermal sections at 673 and 773 K, invariant reactions and partial liquidus surface. The calculation and the experimental data are in good agreement.
A systematic thermodynamic description for the Mg-rich corner of La-Mg-Ni ternary system has been obtained using the CALPHAD approach. The substitutional solution model, the three-sublattice model and the stoichiometric compound model were used to describe the liquid, La2Mg17-xNix and LaMg2Ni phases, respectively. The model parameters were then optimized using the experimental information. Calculations were compared with the experimental data for the enthalpy of mixing in liquid, isothermal sections at 673 and 773 K, invariant reactions and partial liquidus surface. The calculation and the experimental data are in good agreement.
2010, 39(9):1623-1626.
Abstract:
Mo thin films were fabricated on Si(100) substrates using a pulsed laser deposition (PLD) technique. The relation between crystallinity of films and laser fluence was investigated; the growth mechanism of films and the action of particle energy on the film growth were discussed. The AFM images show that the Mo films are flat and smooth, whose RMS (root-mean-square) roughness is less than 2 nm. XRD results show that with the laser fluence increasing, diffraction peaks of Mo films become narrow and surface roughness rises. Furthermore, Mo films convert into polycrystal state from amorphous state, and the grain sizes increase gradually.
Mo thin films were fabricated on Si(100) substrates using a pulsed laser deposition (PLD) technique. The relation between crystallinity of films and laser fluence was investigated; the growth mechanism of films and the action of particle energy on the film growth were discussed. The AFM images show that the Mo films are flat and smooth, whose RMS (root-mean-square) roughness is less than 2 nm. XRD results show that with the laser fluence increasing, diffraction peaks of Mo films become narrow and surface roughness rises. Furthermore, Mo films convert into polycrystal state from amorphous state, and the grain sizes increase gradually.
2010, 39(9):1627-1630.
Abstract:
The corrosion inhibition behavior of LaFe11.6Si1.4 alloy in water solution was studied by electrochemical measurements and scanning electron microscope. The results show that the corrosion behavior is inhibited remarkably by Na2WO4 solution with different concentrations or NaH2PO4 solution with low concentration. The inhibition effect is due to the slow anodic dissolution reaction, and the slow diffusion at low concentration of inhibitor.
The corrosion inhibition behavior of LaFe11.6Si1.4 alloy in water solution was studied by electrochemical measurements and scanning electron microscope. The results show that the corrosion behavior is inhibited remarkably by Na2WO4 solution with different concentrations or NaH2PO4 solution with low concentration. The inhibition effect is due to the slow anodic dissolution reaction, and the slow diffusion at low concentration of inhibitor.
2010, 39(9):1631-1635.
Abstract:
The pack boronizing experiment was carried out on TC4 titanium alloy surface with a method of solid powder boronizing. By means of XRD, SEM and EDS, phase composition, microstructure and morphology of the TC4 titanium alloy after boronizing were investigated. Diffusion behavior of elements in boronizing process was discussed. Results show that after holding at 1000, 1050 and 1100 oC for 5 h and 20 h, the thickness of diffusion layer ranges from 0.8 μm to 15 μm. The outer surface is TiB2 and the inner surface is TiB whiskers. XRD patterns reveal TiB-TiB2 biphasic B-Ti compounds layer is formed after boronizing of TC4 alloy and the peak position of TiB2 and TiB increases with the temperature rising. Furthermore, EDS shows, after having been absorbed by TC4, surface B atoms react with Ti of the matrix resulting in the reduction of Ti in transition region. At the same time, Al and V elements begin to diffuse into the matrix and enrich in the near-interface region. Microhardness of the diffusion layer is of gradient distribution; the hardness value of TiB2 to TiB whiskers ranges from HV0.01 22 000 MPa to HV0.01 11 000 MPa and the hardness value in the transition region is higher than that in the matrix.
The pack boronizing experiment was carried out on TC4 titanium alloy surface with a method of solid powder boronizing. By means of XRD, SEM and EDS, phase composition, microstructure and morphology of the TC4 titanium alloy after boronizing were investigated. Diffusion behavior of elements in boronizing process was discussed. Results show that after holding at 1000, 1050 and 1100 oC for 5 h and 20 h, the thickness of diffusion layer ranges from 0.8 μm to 15 μm. The outer surface is TiB2 and the inner surface is TiB whiskers. XRD patterns reveal TiB-TiB2 biphasic B-Ti compounds layer is formed after boronizing of TC4 alloy and the peak position of TiB2 and TiB increases with the temperature rising. Furthermore, EDS shows, after having been absorbed by TC4, surface B atoms react with Ti of the matrix resulting in the reduction of Ti in transition region. At the same time, Al and V elements begin to diffuse into the matrix and enrich in the near-interface region. Microhardness of the diffusion layer is of gradient distribution; the hardness value of TiB2 to TiB whiskers ranges from HV0.01 22 000 MPa to HV0.01 11 000 MPa and the hardness value in the transition region is higher than that in the matrix.
28 Effects of Different Solution Treatments on Microstructure and Phases of Ti50Ni24.9Cu25Y0.1 Alloy
2010, 39(9):1636-1639.
Abstract:
The effects of different cooling methods on the microstructure and phases of the Ti50Ni24.9Cu25Y0.1 alloy (at%) after the solution treatment at 900 oC for 9 h were studied by Optics Microscope and X-ray diffraction. The regularity of element distribution of the alloy during the solidification process was analyzed by energy dispersive spectrometer (EDS). Results show that there is obvious microsegregation of the alloy during the solidification process. Ni element is rich inside the grains, and Cu element is rich at the grain boundaries. Pure titanium precipitates both inside the grains and at the grain boundaries, which are of faceted crystal growth. The solution treatment at 900 oC for 9 h can effectively reduce the microsegregation of the alloy. XRD analysis reveals that the microstructure of the alloy after the solution treatment at 900 oC for 9 h followed by watering quenching (WQ) is composed of monoclinic B19’ martensite and a few fcc Ti2(Ni,Cu), while only B19’ martensite appears for the solution treated alloy after air cooling or furnace cooling. High-temperature XRD shows that there is only one-step B19’-B2 martensitic transformation.
The effects of different cooling methods on the microstructure and phases of the Ti50Ni24.9Cu25Y0.1 alloy (at%) after the solution treatment at 900 oC for 9 h were studied by Optics Microscope and X-ray diffraction. The regularity of element distribution of the alloy during the solidification process was analyzed by energy dispersive spectrometer (EDS). Results show that there is obvious microsegregation of the alloy during the solidification process. Ni element is rich inside the grains, and Cu element is rich at the grain boundaries. Pure titanium precipitates both inside the grains and at the grain boundaries, which are of faceted crystal growth. The solution treatment at 900 oC for 9 h can effectively reduce the microsegregation of the alloy. XRD analysis reveals that the microstructure of the alloy after the solution treatment at 900 oC for 9 h followed by watering quenching (WQ) is composed of monoclinic B19’ martensite and a few fcc Ti2(Ni,Cu), while only B19’ martensite appears for the solution treated alloy after air cooling or furnace cooling. High-temperature XRD shows that there is only one-step B19’-B2 martensitic transformation.
2010, 39(9):1640-1645.
Abstract:
Co-Ti co-doped cathode material LiNi0.8Co0.2-xTixO2 (0≤x≤0.1) with a high tamping-density for Li ion battery was prepared by a molten-salt synthesis method using eutectic molten salt 0.62LiNO3-0.38LiOH, high-density precursor Co-doped Ni(OH)2 and TiO2 powder. X-ray diffraction analysis shows that the synthesized material has a well-developed layered α-NaFeO2 structure. LiNi0.8Co0.2-xTixO2 has homogeneous particles with average sizes of 1-5 μm and the particles become smaller with Ti content increasing. The tamping-density of LiNi0.8Co0.15Ti0.05O2 reaches to 3.17 g·cm-3. Charge-discharge tests show that LiNi0.8Co0.15Ti0.05O2 has an initial discharge capacity as high as 169 mAh·g-1 and excellent capacity retention in the range 3.0-4.3 V at a specific current of 0.2 C.
Co-Ti co-doped cathode material LiNi0.8Co0.2-xTixO2 (0≤x≤0.1) with a high tamping-density for Li ion battery was prepared by a molten-salt synthesis method using eutectic molten salt 0.62LiNO3-0.38LiOH, high-density precursor Co-doped Ni(OH)2 and TiO2 powder. X-ray diffraction analysis shows that the synthesized material has a well-developed layered α-NaFeO2 structure. LiNi0.8Co0.2-xTixO2 has homogeneous particles with average sizes of 1-5 μm and the particles become smaller with Ti content increasing. The tamping-density of LiNi0.8Co0.15Ti0.05O2 reaches to 3.17 g·cm-3. Charge-discharge tests show that LiNi0.8Co0.15Ti0.05O2 has an initial discharge capacity as high as 169 mAh·g-1 and excellent capacity retention in the range 3.0-4.3 V at a specific current of 0.2 C.
2010, 39(9):1646-1650.
Abstract:
The microstructures and mechanical properties of retrogression and re-aging (RRA) treated ultrahigh strength Al-Zn-Mg-Cu-Zr alloy containing Sc were investigated using transmission electron microscopy and tests for tensile properties and electric conductivity. The results show that the alloy maintains similar strength of T6 state and presents high conductivity after RRA treatment of (120 oC, 24 h pre-ageing) +( 180 oC, 30 min retrogression) + (120 oC, 24 h re-ageing); the intercrystalline microstructures are similar to those of the T6 state alloy and the grain boundary precipitates are aggregated and coarsened, similar to those of duplex over-aged microstructure.
The microstructures and mechanical properties of retrogression and re-aging (RRA) treated ultrahigh strength Al-Zn-Mg-Cu-Zr alloy containing Sc were investigated using transmission electron microscopy and tests for tensile properties and electric conductivity. The results show that the alloy maintains similar strength of T6 state and presents high conductivity after RRA treatment of (120 oC, 24 h pre-ageing) +( 180 oC, 30 min retrogression) + (120 oC, 24 h re-ageing); the intercrystalline microstructures are similar to those of the T6 state alloy and the grain boundary precipitates are aggregated and coarsened, similar to those of duplex over-aged microstructure.
2010, 39(9):1651-1654.
Abstract:
High Jc MgB2 superconducting bulks doped with carbon nano-tubes (CNTs) were prepared by a diffusion method, and their superconductivity was compared with that of CNTs-doped MgB2 prepared by a conventional solid-state reaction method. Results show that the novel diffusion method can increase the density of MgB2 bulks remarkably and reduce the adverse effect of oxygen in Mg powder. The MgB2 bulks prepared by the diffusion method are more uniform with less MgO impurity, so that they have higher critical current density in the self field. But the properties are improved a little in high field; however, MgB2 can overcome the shortcomings in high-field notably by CNTs doping. For the MgB2- sample with 0.5% CNTs doping under the condition of 10 K and 4 T, Jc is as high as 1.0×104 A/cm2 and it reaches 0.46 MA/cm2 in zero field, which is 2 to 3 times higher than that of the MgB2 samples by the solid-state reaction under the same condition.
High Jc MgB2 superconducting bulks doped with carbon nano-tubes (CNTs) were prepared by a diffusion method, and their superconductivity was compared with that of CNTs-doped MgB2 prepared by a conventional solid-state reaction method. Results show that the novel diffusion method can increase the density of MgB2 bulks remarkably and reduce the adverse effect of oxygen in Mg powder. The MgB2 bulks prepared by the diffusion method are more uniform with less MgO impurity, so that they have higher critical current density in the self field. But the properties are improved a little in high field; however, MgB2 can overcome the shortcomings in high-field notably by CNTs doping. For the MgB2- sample with 0.5% CNTs doping under the condition of 10 K and 4 T, Jc is as high as 1.0×104 A/cm2 and it reaches 0.46 MA/cm2 in zero field, which is 2 to 3 times higher than that of the MgB2 samples by the solid-state reaction under the same condition.
2010, 39(9):1655-1658.
Abstract:
A novel bulk amorphous alloy Mg70Ni15Gd10Ag5 (at%)was prepared by copper-mold casting, and its critical size was no less than 5 mm, which is the largest value of preparation size for Mg-Ni based alloys at present. The crystallization behavior of the bulk amorphous alloy during continuous heating was studied by differential scanning calorimeter (DSC). Results show that the crystallization of the amorphous alloy is multiple. With increasing of the heating rate, all the characteristic temperatures including glass transition temperature Tg, onset crystallization temperature Tx, peak crystallization temperatures Tp (Tp1, Tp2, Tp3 and Tp4), melting-starting temperature Tm and liquidus temperature Tl shift to higher temperatures. The crystallization has remarkable dynamic characteristics. The activation energies Eg, Ex and Ep, corresponding to characteristic temperatures Tg, Tx and Tp were obtained by Kissinger equation, as Eg=188.05 kJ/mol, Ex=144.79 kJ/mol, Ep1=138 kJ/mol, Ep2=142.40 kJ/mol, Ep3=119.10 kJ/mol and Ep4=72.86 kJ/mol.
A novel bulk amorphous alloy Mg70Ni15Gd10Ag5 (at%)was prepared by copper-mold casting, and its critical size was no less than 5 mm, which is the largest value of preparation size for Mg-Ni based alloys at present. The crystallization behavior of the bulk amorphous alloy during continuous heating was studied by differential scanning calorimeter (DSC). Results show that the crystallization of the amorphous alloy is multiple. With increasing of the heating rate, all the characteristic temperatures including glass transition temperature Tg, onset crystallization temperature Tx, peak crystallization temperatures Tp (Tp1, Tp2, Tp3 and Tp4), melting-starting temperature Tm and liquidus temperature Tl shift to higher temperatures. The crystallization has remarkable dynamic characteristics. The activation energies Eg, Ex and Ep, corresponding to characteristic temperatures Tg, Tx and Tp were obtained by Kissinger equation, as Eg=188.05 kJ/mol, Ex=144.79 kJ/mol, Ep1=138 kJ/mol, Ep2=142.40 kJ/mol, Ep3=119.10 kJ/mol and Ep4=72.86 kJ/mol.
Li Zhihui
,
Zhang Yongan
,
Xiong Baiqing
,
Zhu Baohong
,
Liu Hongwei
,
Wang Feng
,
Wei Yanguang
,
Zhang Jishan
2010, 39(9):1659-1663.
Abstract:
According to the application demand of novel integrated structural-functional materials for electronic packaging in electronic information industry, high-silicon aluminum alloys (50%-70%Si, mass fraction) were fabricated by a combination method of spray forming and hot compression. The microstructure, thermal-physical and mechanical properties were studied by optical microscopy, scanning electronic microscopy, hardness meter and Formastor-Digital equipment. The results show that the as-deposited microstructure of the spray-formed high-silicon aluminum alloy is fine and dispersive, and the primary silicon phases which are irregular distribute homogenously in the aluminum matrix. The appropriate hot compression process of the as-deposited preform can eliminate basically the porosities generated by spary-forming process to improve the relative density of the alloy. The spray-formed silicon aluminum alloys with hot compression process exhibit excellent thermal-physical properties and good mechanical performance, which is a new family of integrated structural-functional materials for electronic packaging.
According to the application demand of novel integrated structural-functional materials for electronic packaging in electronic information industry, high-silicon aluminum alloys (50%-70%Si, mass fraction) were fabricated by a combination method of spray forming and hot compression. The microstructure, thermal-physical and mechanical properties were studied by optical microscopy, scanning electronic microscopy, hardness meter and Formastor-Digital equipment. The results show that the as-deposited microstructure of the spray-formed high-silicon aluminum alloy is fine and dispersive, and the primary silicon phases which are irregular distribute homogenously in the aluminum matrix. The appropriate hot compression process of the as-deposited preform can eliminate basically the porosities generated by spary-forming process to improve the relative density of the alloy. The spray-formed silicon aluminum alloys with hot compression process exhibit excellent thermal-physical properties and good mechanical performance, which is a new family of integrated structural-functional materials for electronic packaging.
2010, 39(9):1664-1667.
Abstract:
A LiPON solid electrolyte film was prepared, and then a lithium metal electrode protected by the LiPON film was obtained through an electrodeposition method. The electrochemical behaviors of the electrode were tested in nonaqueous organic electrolyte. Results show that because of LiPON film the non-Faraday reactions between the lithium electrode and the electrolyte were depressed, resulting in a more stable lithium/electrolyte interface. As a result of the LiPON protection, the lithium electrode present excellent interface stability during charge/discharge cycles; therefore higher Coulombic cycle efficiency and longer cycle-life are obtained.
A LiPON solid electrolyte film was prepared, and then a lithium metal electrode protected by the LiPON film was obtained through an electrodeposition method. The electrochemical behaviors of the electrode were tested in nonaqueous organic electrolyte. Results show that because of LiPON film the non-Faraday reactions between the lithium electrode and the electrolyte were depressed, resulting in a more stable lithium/electrolyte interface. As a result of the LiPON protection, the lithium electrode present excellent interface stability during charge/discharge cycles; therefore higher Coulombic cycle efficiency and longer cycle-life are obtained.
2010, 39(9):1668-1671.
Abstract:
Pure BiFeO3 (BFO) film and 10%Co-doped BiFeO3 (BFCO) film were deposited on indium tin oxide (ITO)/glass substrates by a polymer-assisted sol-gel process. XRD results confirm that both the films are warping rhombohedral perovskite structure. SEM observation indicates that BFCO film possesses smoother surface and less pinhole than the pure BFO ?lm. Ferroelectric tests show that substitution of Co enhances obviously ferroelectricity and remanent polarization with decrease of leakage current density. The magnetic tests indicate that the magnetic properties of BFCO film are enhanced compared with that of BFO film.
Pure BiFeO3 (BFO) film and 10%Co-doped BiFeO3 (BFCO) film were deposited on indium tin oxide (ITO)/glass substrates by a polymer-assisted sol-gel process. XRD results confirm that both the films are warping rhombohedral perovskite structure. SEM observation indicates that BFCO film possesses smoother surface and less pinhole than the pure BFO ?lm. Ferroelectric tests show that substitution of Co enhances obviously ferroelectricity and remanent polarization with decrease of leakage current density. The magnetic tests indicate that the magnetic properties of BFCO film are enhanced compared with that of BFO film.
2010, 39(9):1672-1675.
Abstract:
Rod-shaped gold nanoparticles were prepared by a seed-mediated growth method with Ag+ as assistant ion, CTAB as surfactant and ascorbic acid as weak reductant. The effect of amount of seeds on the rod aspect ratio and the yield was studied. The morphology and crystal structure of rod-shaped gold nanoparticles were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The optical properties were tested by UV-Vis spectroscopy. The results indicate that the rod-shaped Au particles were fcc structure. UV-Vis absorption spectra show a transverse plasmon absorption band at 530 nm and a longitude plasmon absorption band at 970-980 nm. Aspect ratios of the rod-shaped nanoparticles increased first, and then decreased with the amount of Au seeds increasing. Meanwhile, an increase in the proportion of spherical gold nanoparticles was observed when the Au seeds were added excessively. Finally, the growth mechanism of the products was discussed.
Rod-shaped gold nanoparticles were prepared by a seed-mediated growth method with Ag+ as assistant ion, CTAB as surfactant and ascorbic acid as weak reductant. The effect of amount of seeds on the rod aspect ratio and the yield was studied. The morphology and crystal structure of rod-shaped gold nanoparticles were characterized by transmission electron microscopy (TEM) and X-ray diffraction (XRD). The optical properties were tested by UV-Vis spectroscopy. The results indicate that the rod-shaped Au particles were fcc structure. UV-Vis absorption spectra show a transverse plasmon absorption band at 530 nm and a longitude plasmon absorption band at 970-980 nm. Aspect ratios of the rod-shaped nanoparticles increased first, and then decreased with the amount of Au seeds increasing. Meanwhile, an increase in the proportion of spherical gold nanoparticles was observed when the Au seeds were added excessively. Finally, the growth mechanism of the products was discussed.
2010, 39(9):1676-1681.
Abstract:
By use of octadecanethiol adsorption onto silver in aqueous micellar solution, self-assembled monolayers (SAMs), which were dense, smooth and hydrophobic, were obtained. EMPA and XPS tests show that the surfactants including CTAB, TX-100, PLE and PE6400, as the dispersants of octadecanethiol, play a role of transfer during the self-assembling process; they do not take part in monolayer formation themselves but they can influence the thickness and tilt angle of SAMs. Ag2O on the surface is reduced by H-S bond of the thiol, and Ag-S-C18H37 is formed at the same time.
By use of octadecanethiol adsorption onto silver in aqueous micellar solution, self-assembled monolayers (SAMs), which were dense, smooth and hydrophobic, were obtained. EMPA and XPS tests show that the surfactants including CTAB, TX-100, PLE and PE6400, as the dispersants of octadecanethiol, play a role of transfer during the self-assembling process; they do not take part in monolayer formation themselves but they can influence the thickness and tilt angle of SAMs. Ag2O on the surface is reduced by H-S bond of the thiol, and Ag-S-C18H37 is formed at the same time.
2010, 39(9):1682-1686.
Abstract:
The research progress on Ni-free Ti based shape memory alloys at home and abroad in recent years is reviewed. The shape memory properties and superelastic behavior of Ti-Nb- and Ti-Mo- based binary or ternary alloys are mainly introduced, as well as the microstructure, martensitic transformation behavior and mechanical properties. Some attractive points for the future research are proposed.
The research progress on Ni-free Ti based shape memory alloys at home and abroad in recent years is reviewed. The shape memory properties and superelastic behavior of Ti-Nb- and Ti-Mo- based binary or ternary alloys are mainly introduced, as well as the microstructure, martensitic transformation behavior and mechanical properties. Some attractive points for the future research are proposed.
2010, 39(9):1687-1692.
Abstract:
The history and recent development of sintering stress of powder metallurgical materials are introduced systemically. The methods of the sintering stress calculation, including the energy difference method, the curvature method and the force balance method are stated. The present attention on the sintering stress is the ideal two-sphere model and the repeating unit cell model. But all these calculation methods or models can not reflect the sintering stress of porous materials in the factual sintering condition. So, it is essential to construct a sintering model and to develop a method to calculate the un-identical sphere model to describe the factual sintering stress. Computer simulation of sintering stress is the direction of further investigation on the un-identical sphere model.
The history and recent development of sintering stress of powder metallurgical materials are introduced systemically. The methods of the sintering stress calculation, including the energy difference method, the curvature method and the force balance method are stated. The present attention on the sintering stress is the ideal two-sphere model and the repeating unit cell model. But all these calculation methods or models can not reflect the sintering stress of porous materials in the factual sintering condition. So, it is essential to construct a sintering model and to develop a method to calculate the un-identical sphere model to describe the factual sintering stress. Computer simulation of sintering stress is the direction of further investigation on the un-identical sphere model.
