Volume 41,Issue 5,2012 Table of Contents
2012, 41(5).
Abstract:
2012, 41(5).
Abstract:
The electrodeposition of lathanium on a Pt electrode was investigated in 0.01mol/L LaCl3－0.1mol/L LiCl－EMIMBF4 ionic liquid. The cyclic voltammetry, chronoamperometry and constant voltage electrolysis techniques were employed. The results of the cyclic voltammogram and the XRD spectrum of deposits after electrolysis under constant voltage have supported a one step electrodeposition mechanism of lanthanum, La3 3e-→La. The results also indicated that the reduction of La3 ion was irreversible. The transfer coefficient and the diffusion coefficient of La3 ion in 0.01mol/L LaCl3－0.1mol/L LiCl－EMIMBF4 ionic liquid were calculated as 0.0492 and (1.07-1.19)?0-6 cm2/s, respectively.
The electrodeposition of lathanium on a Pt electrode was investigated in 0.01mol/L LaCl3－0.1mol/L LiCl－EMIMBF4 ionic liquid. The cyclic voltammetry, chronoamperometry and constant voltage electrolysis techniques were employed. The results of the cyclic voltammogram and the XRD spectrum of deposits after electrolysis under constant voltage have supported a one step electrodeposition mechanism of lanthanum, La3 3e-→La. The results also indicated that the reduction of La3 ion was irreversible. The transfer coefficient and the diffusion coefficient of La3 ion in 0.01mol/L LaCl3－0.1mol/L LiCl－EMIMBF4 ionic liquid were calculated as 0.0492 and (1.07-1.19)?0-6 cm2/s, respectively.
2012, 41(5).
Abstract:
The Mm0.3Ml0.7Ni3.55Co0.75Mn0.4Al0.3 metal hydride electrodes were prepared at a pressure-holding time of t (t=10, 15, 20 and 25 minutes). The effects of the pressure-holding time on the activation performance, maximum discharge capacity, discharge potential characteristic and cycle stability of the electrode were investigated. The mechanism of the effects of the pressure-holding time on the electrochemical properties of metal hydride electrodes was also discussed in detail. The results show that the other electrochemical properties of the electrodes improve firstly and then degenerate with increasing pressure-holding time but to have no effect on the activation performance. The electrode at pressure-holding time of 15 min exhibits the best electrochemical properties. The improvements of the electrochemical properties are attributed to the increase of the charge-transfer reaction rate on the alloy and the decrease of the internal resistance of the electrodes.
The Mm0.3Ml0.7Ni3.55Co0.75Mn0.4Al0.3 metal hydride electrodes were prepared at a pressure-holding time of t (t=10, 15, 20 and 25 minutes). The effects of the pressure-holding time on the activation performance, maximum discharge capacity, discharge potential characteristic and cycle stability of the electrode were investigated. The mechanism of the effects of the pressure-holding time on the electrochemical properties of metal hydride electrodes was also discussed in detail. The results show that the other electrochemical properties of the electrodes improve firstly and then degenerate with increasing pressure-holding time but to have no effect on the activation performance. The electrode at pressure-holding time of 15 min exhibits the best electrochemical properties. The improvements of the electrochemical properties are attributed to the increase of the charge-transfer reaction rate on the alloy and the decrease of the internal resistance of the electrodes.
2012, 41(5):753-756.
Abstract:
Nano sheets and flower-like particles of nickel tartrate were synthesized through water-ethanol-ammonia liquid phase precipitation system. Flower-like particles of metal Ni were prepared by the thermal decomposition process, using flower-like nickel tartrate particles as precursor in an atmosphere of CO2, at temperatures of 380 °C and 420 °C, respectively. The characteristics of products were tested by means of the infrared spectrometer (IR), the differential scanning calorimeter and thermo-gravimetric analyzer (DSC-TG), the X-ray diffraction (XRD), and the scanning electron microscope (SEM). The IR studies indicate that the product is pure hydrated nickel tartrate. The studies of DSC-TG indicated that there are 2.5 moles of H2O in one mole of nickel tartrate. The analysis of XRD indicates that the silvery white powder is pure metal Ni, which has face-centered cubic crystal structure. The SEM images show that the size of the flower-like nickel tartrate particles is approximately 40 μm, and the thickness of the nano-petals is about 0.1 μm. The size of the flower-like metal Ni particles is approximately 10 μm, and thickness of the nano-petals is about 0.3 μm.
Nano sheets and flower-like particles of nickel tartrate were synthesized through water-ethanol-ammonia liquid phase precipitation system. Flower-like particles of metal Ni were prepared by the thermal decomposition process, using flower-like nickel tartrate particles as precursor in an atmosphere of CO2, at temperatures of 380 °C and 420 °C, respectively. The characteristics of products were tested by means of the infrared spectrometer (IR), the differential scanning calorimeter and thermo-gravimetric analyzer (DSC-TG), the X-ray diffraction (XRD), and the scanning electron microscope (SEM). The IR studies indicate that the product is pure hydrated nickel tartrate. The studies of DSC-TG indicated that there are 2.5 moles of H2O in one mole of nickel tartrate. The analysis of XRD indicates that the silvery white powder is pure metal Ni, which has face-centered cubic crystal structure. The SEM images show that the size of the flower-like nickel tartrate particles is approximately 40 μm, and the thickness of the nano-petals is about 0.1 μm. The size of the flower-like metal Ni particles is approximately 10 μm, and thickness of the nano-petals is about 0.3 μm.
2012, 41(5):757-761.
Abstract:
The deformation behavior and microstructure evolution in a hot compressed 2E12 alloy was investigated by constructing power dissipation map in which work efficiency can be related with microstructure evolution. Compression tests were performed in the temperature range of 250-500 °C and the strain rate ranging from 0.01 s-1 to 10 s-1 up to a true strain of 0.5. The processing maps reveal that two domains where dynamic recovery occurs comparatively: (1) 325-400 °C and 0.01-0.03 s-1, (2) 350-450 °C and 1.78-10 s-1, and partial dynamic recrystallization occurs at T≥450 °C. However, there also is evidence of redissolution of the particles and intercrystalline cracks at 500 °C and 1-10 s-1. It is shown that the volume of partial recrystallization increase with increasing of deformation temperature.
The deformation behavior and microstructure evolution in a hot compressed 2E12 alloy was investigated by constructing power dissipation map in which work efficiency can be related with microstructure evolution. Compression tests were performed in the temperature range of 250-500 °C and the strain rate ranging from 0.01 s-1 to 10 s-1 up to a true strain of 0.5. The processing maps reveal that two domains where dynamic recovery occurs comparatively: (1) 325-400 °C and 0.01-0.03 s-1, (2) 350-450 °C and 1.78-10 s-1, and partial dynamic recrystallization occurs at T≥450 °C. However, there also is evidence of redissolution of the particles and intercrystalline cracks at 500 °C and 1-10 s-1. It is shown that the volume of partial recrystallization increase with increasing of deformation temperature.
2012, 41(5):762-766.
Abstract:
The effects of size and aspect ratio (height/diameter ratio) of the specimen on the mechanical properties of a Zr56Al10.9Ni4.6Cu27.8Nb0.7 metallic glass have been investigated by uniaxial compression tests and scanning electron microscope (SEM) observations. The results show that the metallic glass with smaller size and lower aspect ratio shows an enhanced plasticity due to larger amount of free volume formed during casting. The shear-band instability index (SBI) is introduced to explain the effects of the size and aspect ratio on the plasticity of the metallic glass. Stable propagation of shear bands can be achieved for the specimen with small size and low aspect ratio, resulting in a size and aspect ratio dependance of plasticity
The effects of size and aspect ratio (height/diameter ratio) of the specimen on the mechanical properties of a Zr56Al10.9Ni4.6Cu27.8Nb0.7 metallic glass have been investigated by uniaxial compression tests and scanning electron microscope (SEM) observations. The results show that the metallic glass with smaller size and lower aspect ratio shows an enhanced plasticity due to larger amount of free volume formed during casting. The shear-band instability index (SBI) is introduced to explain the effects of the size and aspect ratio on the plasticity of the metallic glass. Stable propagation of shear bands can be achieved for the specimen with small size and low aspect ratio, resulting in a size and aspect ratio dependance of plasticity
2012, 41(5):767-771.
Abstract:
P-type Ga2Te5 based compounds with multiphase equilibrium were prepared by spark plasma sintering and their microstructures and thermoelectric properties were evaluated in the temperature range from 319 K to 549 K. Through XRD analysis, we observed the main phase Ga2Te5, a small amount of SnTe and single element Te were observed. Results indicate that the Seebeck coefficients increase and the electrical and thermal conductivities decrease with the increase of the temperature in the entire temperature range. The highest thermoelectric figure of merit ZT of 0.16 can be achieved for Ga2SnTe5 at 549 K due to relatively low thermal conductivity and high thermal conductivity.
P-type Ga2Te5 based compounds with multiphase equilibrium were prepared by spark plasma sintering and their microstructures and thermoelectric properties were evaluated in the temperature range from 319 K to 549 K. Through XRD analysis, we observed the main phase Ga2Te5, a small amount of SnTe and single element Te were observed. Results indicate that the Seebeck coefficients increase and the electrical and thermal conductivities decrease with the increase of the temperature in the entire temperature range. The highest thermoelectric figure of merit ZT of 0.16 can be achieved for Ga2SnTe5 at 549 K due to relatively low thermal conductivity and high thermal conductivity.
2012, 41(5):772-775.
Abstract:
The titanium substrates of IrO2-Ta2O5 coating anodes were manufactured into plate and expanded mesh, respectively. The coatings were prepared by conventionally thermal decomposition with a mixture of H2IrCl6·6H2O dissolved in hydrochloric acid and TaCl5 dissolved in alcohol. The microstructure and electrochemical properties of the electrodes were studied with SEM, EDX, CV and accelerated life test. Compared with plate shape anode, expanded mesh anode has a little lower electrochemical activity due to less active IrO2 crystals precipitation out on it and slender cracks. However, it has longer accelerated life time due to steady and well-distributed ingredient of the coatings and less differences of the atom ratio of Ir and Ta of bulging area and flat area.
The titanium substrates of IrO2-Ta2O5 coating anodes were manufactured into plate and expanded mesh, respectively. The coatings were prepared by conventionally thermal decomposition with a mixture of H2IrCl6·6H2O dissolved in hydrochloric acid and TaCl5 dissolved in alcohol. The microstructure and electrochemical properties of the electrodes were studied with SEM, EDX, CV and accelerated life test. Compared with plate shape anode, expanded mesh anode has a little lower electrochemical activity due to less active IrO2 crystals precipitation out on it and slender cracks. However, it has longer accelerated life time due to steady and well-distributed ingredient of the coatings and less differences of the atom ratio of Ir and Ta of bulging area and flat area.
9 Raman Spectroscopy Analysis of Oxide Film of NZ8 Alloy Corroded in 360 °C Li Water and 400 °C Steam
2012, 41(5):776-780.
Abstract:
The crystal structure of the oxide film of NZ8 alloy, corroded by static autoclave test in 360 °C Li water and 400 °C steam was investigated by Raman spectroscopy method in this paper. The results indicate that the oxide film of NZ8 alloy is mainly composed of monoclinic ZrO2, including a small amount of distorted tetragonal ZrO2. With the prolongation of corrosion time, the average content of the distorted tetragonal ZrO2 in the oxide film decreases, that of monoclinic ZrO2 increases, and tetragonal ZrO2 transforms into monoclinic ZrO2. From the oxide/metal interface to the surface of the oxide film, the content of tetragonal ZrO2 reduces gradually and it is the highest at the interface. At the same time, the tetragonal ZrO2 content at the interface of NZ8 alloy oxide film , gained in 360 °C Li water for 98 d, is much higher than that in 400 °C steam for 70 d, and tetragonal ZrO2 is not observed at the surface of the oxide film exposed to 400 °C steam. The transformation from tetragonal ZrO2 to monoclinic ZrO2 decides the corrosion properties of NZ8 alloy. Corrosion resistance is improved when the content of tetragonal ZrO2 in oxide film increases.
The crystal structure of the oxide film of NZ8 alloy, corroded by static autoclave test in 360 °C Li water and 400 °C steam was investigated by Raman spectroscopy method in this paper. The results indicate that the oxide film of NZ8 alloy is mainly composed of monoclinic ZrO2, including a small amount of distorted tetragonal ZrO2. With the prolongation of corrosion time, the average content of the distorted tetragonal ZrO2 in the oxide film decreases, that of monoclinic ZrO2 increases, and tetragonal ZrO2 transforms into monoclinic ZrO2. From the oxide/metal interface to the surface of the oxide film, the content of tetragonal ZrO2 reduces gradually and it is the highest at the interface. At the same time, the tetragonal ZrO2 content at the interface of NZ8 alloy oxide film , gained in 360 °C Li water for 98 d, is much higher than that in 400 °C steam for 70 d, and tetragonal ZrO2 is not observed at the surface of the oxide film exposed to 400 °C steam. The transformation from tetragonal ZrO2 to monoclinic ZrO2 decides the corrosion properties of NZ8 alloy. Corrosion resistance is improved when the content of tetragonal ZrO2 in oxide film increases.
2012, 41(5):781-785.
Abstract:
Based on the continuum damage mechanics (CDM) theory, a fracture prediction method for hot deformation was proposed by considering the influence of deformation history including both temperatures and strain rates effect. According to the proposed method, the fracture criterion was established for crack predication of TC11 alloy with lamellar structure during hot deformation and the materials parameters were determined using high temperature uniaxial tensile tests; the fracture criterion was then applied to simulation of isothermal compression process, and the predicted results show good agreement with experimental observations in both crack initiation and development.
Based on the continuum damage mechanics (CDM) theory, a fracture prediction method for hot deformation was proposed by considering the influence of deformation history including both temperatures and strain rates effect. According to the proposed method, the fracture criterion was established for crack predication of TC11 alloy with lamellar structure during hot deformation and the materials parameters were determined using high temperature uniaxial tensile tests; the fracture criterion was then applied to simulation of isothermal compression process, and the predicted results show good agreement with experimental observations in both crack initiation and development.
2012, 41(5):786-789.
Abstract:
In this paper, the corrosion fatigue properties of TA15 alloy in 3.5%NaCl salt spray were investigated at different stress ratio(R= –1, 0.06 and 0.5). An equation describing the Sa-Sm-N curved surface of the alloy was established on the basis of the experimental results, that is, N=1.83×1013/[888Sa /(888–Sm)–329.51]3.65. The result according to the cyclic displacement response of the fatigued alloy show that the cyclic hardening/softening characteristic of TA15 alloy in the salt is was dependent on the applied stress ratio R. SEM observations of the fracture surface indicate that the corrosion fatigue fracture of TA15 alloy presents multi-fatigue crack initiations characterized mainly by the cleavage morphology. In the crack growth zone, the fracture morphology shows that the change of deformation resistance is relative to the stress ratio.
In this paper, the corrosion fatigue properties of TA15 alloy in 3.5%NaCl salt spray were investigated at different stress ratio(R= –1, 0.06 and 0.5). An equation describing the Sa-Sm-N curved surface of the alloy was established on the basis of the experimental results, that is, N=1.83×1013/[888Sa /(888–Sm)–329.51]3.65. The result according to the cyclic displacement response of the fatigued alloy show that the cyclic hardening/softening characteristic of TA15 alloy in the salt is was dependent on the applied stress ratio R. SEM observations of the fracture surface indicate that the corrosion fatigue fracture of TA15 alloy presents multi-fatigue crack initiations characterized mainly by the cleavage morphology. In the crack growth zone, the fracture morphology shows that the change of deformation resistance is relative to the stress ratio.
2012, 41(5):790-794.
Abstract:
SiC fiber reinforced g-TiAl (Ti-43Al-9V) matrix composite was fabricated by Fiber Coating Method (MCF) plus Vacuum Hot Pressing (VHP). The interfacial reaction products of the composites were identified and the reaction kinetics was studied. According to the analysis results by means of scanning electron microscope, energy dispersive spectrometer and X-ray diffractometer, the interfacial reaction products of TiC, Ti2AlC and Ti5Si3 were formed during the consolidation and the heat treatment of the composite. The reaction products are distributed in three layers of TiC/Ti2AlC/Ti5Si3+Ti2AlC(particle) from SiC fiber side to matrix side. The growth of the interfacial reaction products is controlled by diffusion and follows a rule of parabolic rate. The activation energy Q and the pre-exponential factor k0 of SiCf/Ti-43Al-9V composite are 190 kJ/mol and 2.5×10-5 m·s-1/2, respectively. It is confirmed that the thermal stability of the interface for the present g-TiAl matrix composite is better than that for other Ti alloy matrix composites.
SiC fiber reinforced g-TiAl (Ti-43Al-9V) matrix composite was fabricated by Fiber Coating Method (MCF) plus Vacuum Hot Pressing (VHP). The interfacial reaction products of the composites were identified and the reaction kinetics was studied. According to the analysis results by means of scanning electron microscope, energy dispersive spectrometer and X-ray diffractometer, the interfacial reaction products of TiC, Ti2AlC and Ti5Si3 were formed during the consolidation and the heat treatment of the composite. The reaction products are distributed in three layers of TiC/Ti2AlC/Ti5Si3+Ti2AlC(particle) from SiC fiber side to matrix side. The growth of the interfacial reaction products is controlled by diffusion and follows a rule of parabolic rate. The activation energy Q and the pre-exponential factor k0 of SiCf/Ti-43Al-9V composite are 190 kJ/mol and 2.5×10-5 m·s-1/2, respectively. It is confirmed that the thermal stability of the interface for the present g-TiAl matrix composite is better than that for other Ti alloy matrix composites.
2012, 41(5):795-799.
Abstract:
According to uniaxial loading-displacement curves of TC4 titanium alloy, The parameters of Gurson-Tvergaard-Needleman model (GTN model) were determined by an inverse approach. The influence of 6 different GTN model parameters on simulation results were studied by finite element method. It is found that only the parameters of f0 and fN need to be determined by the inverse approach, εn defined by tensile test, Sn determined by calculation, fc and fF could be given by simulation results directly. Voids damage evolution becomes faster with appearing of necking stages of TC4 titanium alloy, until failure fracture.
According to uniaxial loading-displacement curves of TC4 titanium alloy, The parameters of Gurson-Tvergaard-Needleman model (GTN model) were determined by an inverse approach. The influence of 6 different GTN model parameters on simulation results were studied by finite element method. It is found that only the parameters of f0 and fN need to be determined by the inverse approach, εn defined by tensile test, Sn determined by calculation, fc and fF could be given by simulation results directly. Voids damage evolution becomes faster with appearing of necking stages of TC4 titanium alloy, until failure fracture.
2012, 41(5):800-804.
Abstract:
The phase decomposition of orthorhombic martensite and the age hardening effect in TC21 alloy during aging treatment were investigated in this paper. The as-quenched alloy shows an acicular structure of orthorhombic α″ martensite. The overall decomposition reaction after aging at 300-700 °C for 4 h can be represented by the order of α″→α″+α→α+β. Aging at lower temperature, the acicular α phase firstly precipitated along with the martensite lath. With increasing of aging temperature, the fine precipitated α phase grows rapidly to lath or plate morphology. Then the much finer second α phase, about 10 nm in width and several micrometers in length, and also the densely distributed β phase, about 10-50 nm in size, were identified using dark field micrograph and selected area electron diffraction. Finally the orthorhombic α″ phase decomposed to α+β mixed phase. Significant age-hardening was observed in TC21 alloy, compared with the as-quenched alloy, the microhardness increased by 35 percent after aging at 500 °C for 4 h, the age-hardening can be attributed to the fine second α precipitates and the dispersively distributed β phase formed by the reverse transformation of orthorhombic martensite.
The phase decomposition of orthorhombic martensite and the age hardening effect in TC21 alloy during aging treatment were investigated in this paper. The as-quenched alloy shows an acicular structure of orthorhombic α″ martensite. The overall decomposition reaction after aging at 300-700 °C for 4 h can be represented by the order of α″→α″+α→α+β. Aging at lower temperature, the acicular α phase firstly precipitated along with the martensite lath. With increasing of aging temperature, the fine precipitated α phase grows rapidly to lath or plate morphology. Then the much finer second α phase, about 10 nm in width and several micrometers in length, and also the densely distributed β phase, about 10-50 nm in size, were identified using dark field micrograph and selected area electron diffraction. Finally the orthorhombic α″ phase decomposed to α+β mixed phase. Significant age-hardening was observed in TC21 alloy, compared with the as-quenched alloy, the microhardness increased by 35 percent after aging at 500 °C for 4 h, the age-hardening can be attributed to the fine second α precipitates and the dispersively distributed β phase formed by the reverse transformation of orthorhombic martensite.
2012, 41(5):805-810.
Abstract:
The effect of β stabilizing elements on the strengthening behavior of titanium α phase were investigated by selecting α' titanium alloy, though microhardness and microspecimen tensile test. Results show that the β stabilizing elements such as Mo, V, Cr and Fe present significantly higher strengthening ability than α stabilizing element Al. The hardness and strength of Ti-xMe α phase increase dramatically by addition of 6wt%Al. The strengthening ability of β stabilizing elements above keep invariant when 6wt%Al are added. The sequence of the strenghening ability of Mo, V, Cr and Fe are Fe>Cr>Mo>V. Adding of 6wt% Al into “Ti-xCr, Ti-xV”, “Ti-xMo, Ti-xV” and “Ti-xFe, Ti-xV”, the difference of strength between the two in each group decreases.
The effect of β stabilizing elements on the strengthening behavior of titanium α phase were investigated by selecting α' titanium alloy, though microhardness and microspecimen tensile test. Results show that the β stabilizing elements such as Mo, V, Cr and Fe present significantly higher strengthening ability than α stabilizing element Al. The hardness and strength of Ti-xMe α phase increase dramatically by addition of 6wt%Al. The strengthening ability of β stabilizing elements above keep invariant when 6wt%Al are added. The sequence of the strenghening ability of Mo, V, Cr and Fe are Fe>Cr>Mo>V. Adding of 6wt% Al into “Ti-xCr, Ti-xV”, “Ti-xMo, Ti-xV” and “Ti-xFe, Ti-xV”, the difference of strength between the two in each group decreases.
2012, 41(5):811-816.
Abstract:
The microstructures and fracture morphologies at the weld interfaces of near isothermally forged and heat treated Ti3Al/TC11 dual alloy after thermal exposure at 550 °C for 50 h were investigated through tensile experiment and using OM and SEM. The results indicate that under gradient heat treatment the tensile strength of dual alloy after thermal exposure increases as the increase of the deformation degree; meanwhile, the interlaced structures of the acicular α phase in weld interface decompose and coarsen, and more fined sphericity α/α2 phases precipitate in weld. The strength of the dual alloy processed by gradient heat treatment is slightly higher than that by double heat treatment after thermal exposure. α2 phase in Ti3Al HAZ of specimen processed by double heat treatment grows up during thermal exposure. Mechanical properties of the specimen without oxidation surface are superior to that with oxidation surface due to the surface microcrack caused by oxidation. It can be found that fracture predominantly occurs in Ti3Al base alloy from the facture position of specimens.
The microstructures and fracture morphologies at the weld interfaces of near isothermally forged and heat treated Ti3Al/TC11 dual alloy after thermal exposure at 550 °C for 50 h were investigated through tensile experiment and using OM and SEM. The results indicate that under gradient heat treatment the tensile strength of dual alloy after thermal exposure increases as the increase of the deformation degree; meanwhile, the interlaced structures of the acicular α phase in weld interface decompose and coarsen, and more fined sphericity α/α2 phases precipitate in weld. The strength of the dual alloy processed by gradient heat treatment is slightly higher than that by double heat treatment after thermal exposure. α2 phase in Ti3Al HAZ of specimen processed by double heat treatment grows up during thermal exposure. Mechanical properties of the specimen without oxidation surface are superior to that with oxidation surface due to the surface microcrack caused by oxidation. It can be found that fracture predominantly occurs in Ti3Al base alloy from the facture position of specimens.
2012, 41(5):817-821.
Abstract:
An amorphous Ti2Ni alloy was prepared by ball milling of a crystalline Ti2Ni alloy. XRD, charge and discharge testing, and anodic polarization curve were carried out and investigated to study the charge/discharge performances and the corrosion behaviors of Ti2Ni hydrogen storage alloy with different structures. Results show that the crystalline alloy has a charge capacity of 480 mAh/g at first cycle, while its discharge capacity is only a half of the charge capacity. A large amount of irreversible hydride is formed in the bulk alloy. However, there is no evident formation of the irreversible hydride in the subsequent cycle. The amorphous phase can restrain the formation of the irreversible hydride. And a elastic deformation occurs during the hydrogen absorption/desorption process. Moreover, the amorphous structure makes the alloy corrosion potential increasing and the alloy corrosion current density decreasing, resulting in an significant improvement of corrosion resistance of the alloy.
An amorphous Ti2Ni alloy was prepared by ball milling of a crystalline Ti2Ni alloy. XRD, charge and discharge testing, and anodic polarization curve were carried out and investigated to study the charge/discharge performances and the corrosion behaviors of Ti2Ni hydrogen storage alloy with different structures. Results show that the crystalline alloy has a charge capacity of 480 mAh/g at first cycle, while its discharge capacity is only a half of the charge capacity. A large amount of irreversible hydride is formed in the bulk alloy. However, there is no evident formation of the irreversible hydride in the subsequent cycle. The amorphous phase can restrain the formation of the irreversible hydride. And a elastic deformation occurs during the hydrogen absorption/desorption process. Moreover, the amorphous structure makes the alloy corrosion potential increasing and the alloy corrosion current density decreasing, resulting in an significant improvement of corrosion resistance of the alloy.
2012, 41(5):822-825.
Abstract:
The epoxy resin (EP)/polytetrafluoroethylene (PTFE) coatings were made on the silane coupling agent modified TiNi alloy teeth corrective wires by dipping. The influence of silane coupling agent concentration on the adhesion force between the coatings and TiNi alloys was investigated, and the mechanism of the improvement of the adhesion force due to the induction of the silane coupling agent was revealed. The effect of epoxy resin (EP)/polytetrafluoroethylene (PTFE) coatings on the biocompatibility and Ni ions release from the TiNi alloys was investigated. In addition, the difference between the coated and uncoated TiNi alloy teeth corrective wires was compared. The results show that the concentation of silance coupling agent has a great influencer on the adhension force between the coating and TiNi alloy. With the increase of the concentation, the adhension force increases first, then decreases. EP/PTFE coating can inhibit Ni ions precipitation from TiNi alloy, and has a good biocompatibility.
The epoxy resin (EP)/polytetrafluoroethylene (PTFE) coatings were made on the silane coupling agent modified TiNi alloy teeth corrective wires by dipping. The influence of silane coupling agent concentration on the adhesion force between the coatings and TiNi alloys was investigated, and the mechanism of the improvement of the adhesion force due to the induction of the silane coupling agent was revealed. The effect of epoxy resin (EP)/polytetrafluoroethylene (PTFE) coatings on the biocompatibility and Ni ions release from the TiNi alloys was investigated. In addition, the difference between the coated and uncoated TiNi alloy teeth corrective wires was compared. The results show that the concentation of silance coupling agent has a great influencer on the adhension force between the coating and TiNi alloy. With the increase of the concentation, the adhension force increases first, then decreases. EP/PTFE coating can inhibit Ni ions precipitation from TiNi alloy, and has a good biocompatibility.
2012, 41(5):826-829.
Abstract:
A new-type of low density TiAlBeSc alloy system was prepared by vacuum arc melting. The lowest density is 3.289 g/cm3. Its microstructures, thermal stability were studied using SEM (EDS), XRD, nanoindentation and DTA methods. The results show that the TiAlBeSc alloy system forms stable intermetallic compound and solid solution. No transformation occurs below 1000 °C. These alloys exhibit a very high thermal stability with a melting point above 1100 °C. For the equimolar TiAlBeSc alloy, 25% (atomic percentage) beryllium is totally dissolved in scandium lattice. The dendritic TiAl phase with L10 ordered structure is uniformly distributed in α-Sc matrix which exhibits excellent mechanical properties with hardness 7330 MPa.
A new-type of low density TiAlBeSc alloy system was prepared by vacuum arc melting. The lowest density is 3.289 g/cm3. Its microstructures, thermal stability were studied using SEM (EDS), XRD, nanoindentation and DTA methods. The results show that the TiAlBeSc alloy system forms stable intermetallic compound and solid solution. No transformation occurs below 1000 °C. These alloys exhibit a very high thermal stability with a melting point above 1100 °C. For the equimolar TiAlBeSc alloy, 25% (atomic percentage) beryllium is totally dissolved in scandium lattice. The dendritic TiAl phase with L10 ordered structure is uniformly distributed in α-Sc matrix which exhibits excellent mechanical properties with hardness 7330 MPa.
2012, 41(5):830-834.
Abstract:
The precipitates and phase the transformation temperatures of both zirconium alloys, Zr-1Sn-0.3Nb-0.3Fe-0.1Cr alloy and Zr-0.8Sn-0.3Nb-0.3Fe-0.1Cr alloy were investigated. The temperatures of the phase transformation of both zirconium alloys were measured by Differential Scanning Calorimetric (DSC). The effect of Sn content on the phase transformation temperature was studied. The microstructures of the alloy specimens as 6 processed states (as hot rolled state, as hot rolled+annealed state, as cold rolled state, as cold rolled+annealed state, as final rolled state, and as final rolled+annealed state) were observed carefully by SEM, Then the sizes and the volume fractions and their distributions of the second precipitated phase in the alloys were analyzed and calculated by quantitative metallography and Energy Dispersive Spectrum (EDS). The results show that the decrease of Sn content has a obvious influence on the phase trasformation temperature of α→β, and very little effect on the spape and the structure of the precipitated particles, but their average sizes will be reduced. EDS results show that the segregation of Sn content exists in the Zr alloy to some extent.
The precipitates and phase the transformation temperatures of both zirconium alloys, Zr-1Sn-0.3Nb-0.3Fe-0.1Cr alloy and Zr-0.8Sn-0.3Nb-0.3Fe-0.1Cr alloy were investigated. The temperatures of the phase transformation of both zirconium alloys were measured by Differential Scanning Calorimetric (DSC). The effect of Sn content on the phase transformation temperature was studied. The microstructures of the alloy specimens as 6 processed states (as hot rolled state, as hot rolled+annealed state, as cold rolled state, as cold rolled+annealed state, as final rolled state, and as final rolled+annealed state) were observed carefully by SEM, Then the sizes and the volume fractions and their distributions of the second precipitated phase in the alloys were analyzed and calculated by quantitative metallography and Energy Dispersive Spectrum (EDS). The results show that the decrease of Sn content has a obvious influence on the phase trasformation temperature of α→β, and very little effect on the spape and the structure of the precipitated particles, but their average sizes will be reduced. EDS results show that the segregation of Sn content exists in the Zr alloy to some extent.
Hu Jieqiong
,
Xie Ming
,
Pan Yong
,
Liu Manmen
,
Zhang Jiming
,
Yang Youcai
,
Cui Hao
,
Chen Yongtai
2012, 41(5):835-839.
Abstract:
According to the First Principle based on Density Functional Theory (DFT), dopting the plane wave pserdopotential method in which the Local Density Approximation (LDA) and Generalized Gradient Approximation (GGA) were used respectively, the electronic structuresand the elastic constants of RhZr2 alloy with tetragonal system were calculated. The internal positions of atoms in the unit cell were optimized and the ground state properties such as band structure, density of state, charge densities difference, cohesive energies and the enthalpies of formation were calculated. The results show that the elastic constant C11, C12, C13, C33, C44 and C66 of tetragonal RhZr2 are 195.38, 176.80, 109.00, 235.65, 11.12 and 24.51 GPa, respectively, and the bulk modulus is 156.92(±2.22) GPa, the Young’s modulus is 34.77, 34.77 and 171.80 GPa for [100]、[010] and [001] directions, the shear modulus Gxy, Gzx, Gzy of RhZr2 is 24.79、14.57 and 19.68 GPa, respectively.
According to the First Principle based on Density Functional Theory (DFT), dopting the plane wave pserdopotential method in which the Local Density Approximation (LDA) and Generalized Gradient Approximation (GGA) were used respectively, the electronic structuresand the elastic constants of RhZr2 alloy with tetragonal system were calculated. The internal positions of atoms in the unit cell were optimized and the ground state properties such as band structure, density of state, charge densities difference, cohesive energies and the enthalpies of formation were calculated. The results show that the elastic constant C11, C12, C13, C33, C44 and C66 of tetragonal RhZr2 are 195.38, 176.80, 109.00, 235.65, 11.12 and 24.51 GPa, respectively, and the bulk modulus is 156.92(±2.22) GPa, the Young’s modulus is 34.77, 34.77 and 171.80 GPa for [100]、[010] and [001] directions, the shear modulus Gxy, Gzx, Gzy of RhZr2 is 24.79、14.57 and 19.68 GPa, respectively.
2012, 41(5):840-846.
Abstract:
In this paper, the influences of withdrawal rates and mold heater zone temperature on the microstructures and the properties of heat treated castings were investigated. Results show that a better aligned grain structure and a much higher thermal gradient can be obtained in castings prepared by “high superheat” technique. Moreover, with elevating of withdrawal rates and mold heater zone temperature, the dendrite structures and size of γ′ phase are refined; dendrite structures and size of γ′ phase are larger in thicker zone. With the increase of withdrawal rates, γ+γ' eutectic fractions decreases but the micro-segregation decreases initially and then increases. With elevating of heating zone temperature, the γ+γ' eutectic fraction reduces and micro-segregation becomes severe except Ta. After heat treated, the dendrite structures of the castings become ambiguous and the γ′ phase prepared with various solidification parameters have no obvious difference. The properties of castings prepared with different withdrawal rates are almost the same, but that prepared with high thermal gradient has a better high temperature rupture life.
In this paper, the influences of withdrawal rates and mold heater zone temperature on the microstructures and the properties of heat treated castings were investigated. Results show that a better aligned grain structure and a much higher thermal gradient can be obtained in castings prepared by “high superheat” technique. Moreover, with elevating of withdrawal rates and mold heater zone temperature, the dendrite structures and size of γ′ phase are refined; dendrite structures and size of γ′ phase are larger in thicker zone. With the increase of withdrawal rates, γ+γ' eutectic fractions decreases but the micro-segregation decreases initially and then increases. With elevating of heating zone temperature, the γ+γ' eutectic fraction reduces and micro-segregation becomes severe except Ta. After heat treated, the dendrite structures of the castings become ambiguous and the γ′ phase prepared with various solidification parameters have no obvious difference. The properties of castings prepared with different withdrawal rates are almost the same, but that prepared with high thermal gradient has a better high temperature rupture life.
2012, 41(5):847-850.
Abstract:
Pt+g ￠-Ni3Al+g -Ni/CMSX-4 coatings were fabricated by Pt electroplating on CMSX-4 single crystal superalloys substrate and followed by an aluminizing pack cementation process. The microstructure of the Pt+g ￠-Ni3Al+g -Ni/CMSX-4 coating was studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). TEM investigation showed that {111} twinning exists in the g ￠-Ni3Al phase, Pt was mainly distributed in the g ￠-Ni3Al. Precipitates were observed in the coatings. Selected area electron diffraction (SAED) reveals that the precipitate was the hexagonal topologically close-packed (TCP) m phase with lattice parameters a=0.473 nm, and c=2.565 nm. Twin domains parallel to (001) and (10
Pt+g ￠-Ni3Al+g -Ni/CMSX-4 coatings were fabricated by Pt electroplating on CMSX-4 single crystal superalloys substrate and followed by an aluminizing pack cementation process. The microstructure of the Pt+g ￠-Ni3Al+g -Ni/CMSX-4 coating was studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). TEM investigation showed that {111} twinning exists in the g ￠-Ni3Al phase, Pt was mainly distributed in the g ￠-Ni3Al. Precipitates were observed in the coatings. Selected area electron diffraction (SAED) reveals that the precipitate was the hexagonal topologically close-packed (TCP) m phase with lattice parameters a=0.473 nm, and c=2.565 nm. Twin domains parallel to (001) and (10
2012, 41(5):851-856.
Abstract:
Nanocrystalline Co-Ni-Fe alloys were synthesized by pulsed electrodeposition. The composition, microstructure and surface morphologies were studied by EDS、XRD, TEM and SEM. The effect of Co content and grain sizes on the electrochemical corrosion behaviour of nanocrystalline Co-Ni-Fe deposits in 3.5wt% NaCl solution were investigated using Tafel polarization curves. The results reveal that the grain sizes of the nanocrystalline fcc Co-Ni-Fe alloys descrease with increasing of the content of Co in the coating. The grain sizes of nanocrystalline Co-Ni-Fe alloys increase with increasing of the annealing temperature，showing a strong （111）texture. The corrosion rates of Co-Ni-Fe alloys decrease first and then increase with increasing of the Co content in the coating. The corrosion rates decline gradually with increasing of the annealing temperature. Comparing to the nanocrystalline deposits, the coarse grain deposit exhibits a quite a different corrosion morphologies.
Nanocrystalline Co-Ni-Fe alloys were synthesized by pulsed electrodeposition. The composition, microstructure and surface morphologies were studied by EDS、XRD, TEM and SEM. The effect of Co content and grain sizes on the electrochemical corrosion behaviour of nanocrystalline Co-Ni-Fe deposits in 3.5wt% NaCl solution were investigated using Tafel polarization curves. The results reveal that the grain sizes of the nanocrystalline fcc Co-Ni-Fe alloys descrease with increasing of the content of Co in the coating. The grain sizes of nanocrystalline Co-Ni-Fe alloys increase with increasing of the annealing temperature，showing a strong （111）texture. The corrosion rates of Co-Ni-Fe alloys decrease first and then increase with increasing of the Co content in the coating. The corrosion rates decline gradually with increasing of the annealing temperature. Comparing to the nanocrystalline deposits, the coarse grain deposit exhibits a quite a different corrosion morphologies.
2012, 41(5):857-861.
Abstract:
Based on the fundamental thermodynamic principles, the ordering behavior of the ThMn12-type intermetallics NdFe10-xCoxMo2 were studied using a general four-sublattice model supported with first-principles calculations. The results show that the 2a sublattices are occupied by the rare earth elements Nd exclusively, while the 50% of 8i sublattices are occupied by Mo atoms, 8f, 8j and the rest 50% of 8i sublattices are shared by Fe and Co atoms, which agreed well with the reported experimental results. Site occupancy fractions of Fe and Co atoms vary with temperature in the quaternary alloys due to the partial solid solution of Fe and Co atoms in sublattice 8f and 8j, while they keep constant in ternary alloys upon varying temperature. Co and Fe atoms can substitute each other without affecting the ordering behavior of the intermetallics. In the alloy NdFe5Co5Mo2, with an equal the content of Fe and Co, Fe atoms favor the occupancy of sublattice 8f, while Co atoms prefer the occupancy of sublattice 8j.
Based on the fundamental thermodynamic principles, the ordering behavior of the ThMn12-type intermetallics NdFe10-xCoxMo2 were studied using a general four-sublattice model supported with first-principles calculations. The results show that the 2a sublattices are occupied by the rare earth elements Nd exclusively, while the 50% of 8i sublattices are occupied by Mo atoms, 8f, 8j and the rest 50% of 8i sublattices are shared by Fe and Co atoms, which agreed well with the reported experimental results. Site occupancy fractions of Fe and Co atoms vary with temperature in the quaternary alloys due to the partial solid solution of Fe and Co atoms in sublattice 8f and 8j, while they keep constant in ternary alloys upon varying temperature. Co and Fe atoms can substitute each other without affecting the ordering behavior of the intermetallics. In the alloy NdFe5Co5Mo2, with an equal the content of Fe and Co, Fe atoms favor the occupancy of sublattice 8f, while Co atoms prefer the occupancy of sublattice 8j.
2012, 41(5):862-866.
Abstract:
The microstructures, hardness and electrochemical properties of AlCoCrFeNiTi0.5 high-entropy alloys fabricated by cold crucible levitation melting (CCLM) with as-cast structure and tempering treated structures were investigated. The results show that in contrast to suction casting using copper molds, CCLM causes the growth of dendrite phase and separation of ω phase. As the increase of temperature, the dendrite grains grow up, the amount of eutectic structures increases, and the intensity of BCC peak shows a rising trend after the first drop. At the temperature of 800 ℃, the dendrite grains become refined. And then, as the temperature increases, the element segregation of interdendrite is weakened. The alloy exhibits a superior resistance to tempering and softening property. Furthermore, pitting corrosions are mainly concentrated in the place between dendrite phase and eutectic α phase. The tempering treatment improves corrosion properties in a 3.5% NaCl solution, and the alloy tempered at 700 exhibits the best corrosion property among the experimental alloys.
The microstructures, hardness and electrochemical properties of AlCoCrFeNiTi0.5 high-entropy alloys fabricated by cold crucible levitation melting (CCLM) with as-cast structure and tempering treated structures were investigated. The results show that in contrast to suction casting using copper molds, CCLM causes the growth of dendrite phase and separation of ω phase. As the increase of temperature, the dendrite grains grow up, the amount of eutectic structures increases, and the intensity of BCC peak shows a rising trend after the first drop. At the temperature of 800 ℃, the dendrite grains become refined. And then, as the temperature increases, the element segregation of interdendrite is weakened. The alloy exhibits a superior resistance to tempering and softening property. Furthermore, pitting corrosions are mainly concentrated in the place between dendrite phase and eutectic α phase. The tempering treatment improves corrosion properties in a 3.5% NaCl solution, and the alloy tempered at 700 exhibits the best corrosion property among the experimental alloys.
2012, 41(5):867-871.
Abstract:
The microstructures and the creep behavior of ZK31+4Si magnesium alloy processed by Equal channel angular pressing (ECAP) were investigated. The experimental results show that the coarse Chinese script-like Mg2Si precipitates are refined to fine polygonal shape particles and redistributed dispersedly after ECAP. The creep resistance is greatly enhanced after ECAP. The ctable creep rate of the 8-pass ECAPed specimen is nearly 1/15 of that of the as-cast one, and its creep life is increased by about 8 times. The curves of the minimum strain rate versus the stress show that the alloy ECAPed either through 8 passes or through 4 passes exhibit a same stress exponent n?4. Furthermore, the theoretical calculation results according to the dislocation creep model with n=4 are well in agreement with the experimental values, indicating that the creep under the present test condition is controlled by the movement of dislocations.
The microstructures and the creep behavior of ZK31+4Si magnesium alloy processed by Equal channel angular pressing (ECAP) were investigated. The experimental results show that the coarse Chinese script-like Mg2Si precipitates are refined to fine polygonal shape particles and redistributed dispersedly after ECAP. The creep resistance is greatly enhanced after ECAP. The ctable creep rate of the 8-pass ECAPed specimen is nearly 1/15 of that of the as-cast one, and its creep life is increased by about 8 times. The curves of the minimum strain rate versus the stress show that the alloy ECAPed either through 8 passes or through 4 passes exhibit a same stress exponent n?4. Furthermore, the theoretical calculation results according to the dislocation creep model with n=4 are well in agreement with the experimental values, indicating that the creep under the present test condition is controlled by the movement of dislocations.
2012, 41(5):872-876.
Abstract:
Al-Ni-Y-Co and Al-Ni-Mm-Fe amorphous and nanocrystalline composite coatings were prepared on the surface of AZ91 magnesium alloy by automatic high velocity arc spraying system. The microstructures of the composite coatings were analyzed by scanning electron microscope (SEM) and X-ray diffraction (XRD). The results show that the composite coatings compose of amorphous phases and crystalline phases. The composite coatings have a compact structure with low porosity. The Vickers microhardness HV of Al-Ni-Y-Co and Al-Ni-Mm-Fe coatings is 3117.6 MPa and 3407.2 MPa, respectively, which is about four times higher than that of the traditional Al-RE coatings and five times higher than that of the AZ91 magnesium alloy. The electrochemistry experimental results show that the corrosion resistances of the Al-Ni-Y-Co and Al-Ni-Mm-Fe amorphous and nanocrystalline composite coatings are superior to those of the traditional Al-RE coatings and AZ91 magnesium alloy.
Al-Ni-Y-Co and Al-Ni-Mm-Fe amorphous and nanocrystalline composite coatings were prepared on the surface of AZ91 magnesium alloy by automatic high velocity arc spraying system. The microstructures of the composite coatings were analyzed by scanning electron microscope (SEM) and X-ray diffraction (XRD). The results show that the composite coatings compose of amorphous phases and crystalline phases. The composite coatings have a compact structure with low porosity. The Vickers microhardness HV of Al-Ni-Y-Co and Al-Ni-Mm-Fe coatings is 3117.6 MPa and 3407.2 MPa, respectively, which is about four times higher than that of the traditional Al-RE coatings and five times higher than that of the AZ91 magnesium alloy. The electrochemistry experimental results show that the corrosion resistances of the Al-Ni-Y-Co and Al-Ni-Mm-Fe amorphous and nanocrystalline composite coatings are superior to those of the traditional Al-RE coatings and AZ91 magnesium alloy.
2012, 41(5):877-880.
Abstract:
Grain growth behavior and its kinetics during the solution treating process of hot continuous rolled (HCR) GH4169 superalloy have been investigated. The experimental results show that the d-phase dissolution temperature of HCR GH4169 superalloy is from 990 °C to 1000 °C, and the d-phase in the superalloy greatly restrains grain growth. The solution treatment at the temperature below d-phase dissolution leads to little variation of grain size, and the solution treatment at the temperature above the d-phase dissolution leads to the rapid grain growth for HCR GH4169 superalloy. The grain growth kinetics at the temperature above the d-phase dissolution shows that grain growth exponentially increases with the increasing of solution treating temperature. At the temperatures from 1000 °C to 1050 °C, the activation energy value for grain growth in HCR GH4169 superalloy is 223.849 kJ/mol, which means that the grain growth mechanism is self-diffusion-controlling process, and the grain growth kinetics eqution are given.
Grain growth behavior and its kinetics during the solution treating process of hot continuous rolled (HCR) GH4169 superalloy have been investigated. The experimental results show that the d-phase dissolution temperature of HCR GH4169 superalloy is from 990 °C to 1000 °C, and the d-phase in the superalloy greatly restrains grain growth. The solution treatment at the temperature below d-phase dissolution leads to little variation of grain size, and the solution treatment at the temperature above the d-phase dissolution leads to the rapid grain growth for HCR GH4169 superalloy. The grain growth kinetics at the temperature above the d-phase dissolution shows that grain growth exponentially increases with the increasing of solution treating temperature. At the temperatures from 1000 °C to 1050 °C, the activation energy value for grain growth in HCR GH4169 superalloy is 223.849 kJ/mol, which means that the grain growth mechanism is self-diffusion-controlling process, and the grain growth kinetics eqution are given.
2012, 41(5):881-884.
Abstract:
The electrodeposition of dysprosium on a Pt electrode from 1-ethyl-3-methyl-imidazolium tetrafluoroborate (EMIMBF4) ionic liquid was investigated. The cyclic voltammetry, chronopotentiometry and chronoamperometry were employed to examine the electrochemistry of Dy3+ in 0.01 mol/L DyCl3-0.1 mol/L LiCl-EMIMBF4 ionic liquid. The electrochemistry experiments indicate that the reduction of Dy3+ ion in 0.01 mol/L DyCl3-0.1 mol/L LiCl-EMIMBF4 ionic liquid is an irreversible process and is completed through only one step electrodeposition mechanism Dy3+ + 3e-→Dy. In 0.01 mol/L DyCl3-0.1 mol/L LiCl-EMIMBF4 ionic liquid the transfer coefficient and the diffusion coefficient of Dy3+ ion have been determined to be 0.176 and (4.87-5.04)×10-10 cm2/s, respectively. XRD pattern shows that the dysprosium deposits can be obtained, and SEM images shows that crystallites sizes of the deposits are few hundred nanometers.
The electrodeposition of dysprosium on a Pt electrode from 1-ethyl-3-methyl-imidazolium tetrafluoroborate (EMIMBF4) ionic liquid was investigated. The cyclic voltammetry, chronopotentiometry and chronoamperometry were employed to examine the electrochemistry of Dy3+ in 0.01 mol/L DyCl3-0.1 mol/L LiCl-EMIMBF4 ionic liquid. The electrochemistry experiments indicate that the reduction of Dy3+ ion in 0.01 mol/L DyCl3-0.1 mol/L LiCl-EMIMBF4 ionic liquid is an irreversible process and is completed through only one step electrodeposition mechanism Dy3+ + 3e-→Dy. In 0.01 mol/L DyCl3-0.1 mol/L LiCl-EMIMBF4 ionic liquid the transfer coefficient and the diffusion coefficient of Dy3+ ion have been determined to be 0.176 and (4.87-5.04)×10-10 cm2/s, respectively. XRD pattern shows that the dysprosium deposits can be obtained, and SEM images shows that crystallites sizes of the deposits are few hundred nanometers.
2012, 41(5):885-889.
Abstract:
The kinetics of synthesis of nanophosphor Eu0.12Y1.78La0.10O3-δ was investigated using differential thermal analysis and thermo gravimetric (DTA-TG) at different heating rates in argon gas. The results show that the precursor of nanophosphor Eu0.12Y1.78La0.10O3-δ is Y(OH)3 with hexagonal phase structure. The average apparent activation energies of the two reaction stages of the precursor were calculated using the Doyle-Ozawa and Kissinger methods they are 699.40 and 362.81 kJ·mol-1, respectively. The reaction order and frequency factor can be also determined by Kissinger method. The kinetics equations of the reaction were deduced, they are dα/dt=1.94×1046e-84120/T(1-α)1.17, dα/dt=5.89×1020e-43640/T(1-α)1.14, respectively.
The kinetics of synthesis of nanophosphor Eu0.12Y1.78La0.10O3-δ was investigated using differential thermal analysis and thermo gravimetric (DTA-TG) at different heating rates in argon gas. The results show that the precursor of nanophosphor Eu0.12Y1.78La0.10O3-δ is Y(OH)3 with hexagonal phase structure. The average apparent activation energies of the two reaction stages of the precursor were calculated using the Doyle-Ozawa and Kissinger methods they are 699.40 and 362.81 kJ·mol-1, respectively. The reaction order and frequency factor can be also determined by Kissinger method. The kinetics equations of the reaction were deduced, they are dα/dt=1.94×1046e-84120/T(1-α)1.17, dα/dt=5.89×1020e-43640/T(1-α)1.14, respectively.
2012, 41(5):890-893.
Abstract:
A first principles plane-wave method was utilized to investigate the band structure, lattice parameters and total energy for AuCd B2, γ2’ and ζ2’ structures. The results are in good agreement with experimental results. We have found that the band structures for three structures are very similar: steep profile above Fermi level, and flat blow the Fermi level. In the three structures, γ2’ phase holds the lowest energy, and the order of stability is γ2’>ζ2’> B2. AuCd γ2’ structure changes its lattice parameters according to a common principle that is lattice parameter a diminishes and b and c become larger. This result consists with the experimental result.
A first principles plane-wave method was utilized to investigate the band structure, lattice parameters and total energy for AuCd B2, γ2’ and ζ2’ structures. The results are in good agreement with experimental results. We have found that the band structures for three structures are very similar: steep profile above Fermi level, and flat blow the Fermi level. In the three structures, γ2’ phase holds the lowest energy, and the order of stability is γ2’>ζ2’> B2. AuCd γ2’ structure changes its lattice parameters according to a common principle that is lattice parameter a diminishes and b and c become larger. This result consists with the experimental result.
2012, 41(5):894-898.
Abstract:
The bulk thermoelectric materials of Bi2Te3-Sb2Te3 ternary alloy were prepared using a vertical Bridgman method at solidification rates ranging from 5 μm/s to 1000 μm/s. The directionally solidified microstructures with the composition of 25% Bi2Te3-75% Sb2Te3 alloy were investigated and the corresponding thermoelectric properties were measured. The results shows that the directionally solidified microstructures of 25% Bi2Te3-75% Sb2Te3 alloy only consist of Bi0.5Sb1.5Te3 single phase. At a low solidification rate of 5 μm/s, the cellular structures appear due to the solid/liquid interface losing its stabilization, and the increase of the solidification rate results in decreasing cellular structures. Additionally, the values of Seebeck coefficient and the resistivity of directionally solidified 25% Bi2Te3-75% Sb2Te3 alloys tend to a increase with increasing of the solidification rate. Under the solidification rate of 50 μm/s, the Power Factor (PF) of the alloy maintains (4.6-5.01)×10-3 W/(K2·m) in the temperature range of 300-450 K, and its maximum value reaches 5.01×10-3 W/(K2·m) at 350 K. Besides, at a higher solidification rate of 500 μm/s, the maximal PF value can be measured to be 4.5×10-3 W/(K2·m). It seems that the Bridgman method employing high temperature gradient with rapid solidification rate is a promising approach for the preparation of thermoelectric materials with high performance.
The bulk thermoelectric materials of Bi2Te3-Sb2Te3 ternary alloy were prepared using a vertical Bridgman method at solidification rates ranging from 5 μm/s to 1000 μm/s. The directionally solidified microstructures with the composition of 25% Bi2Te3-75% Sb2Te3 alloy were investigated and the corresponding thermoelectric properties were measured. The results shows that the directionally solidified microstructures of 25% Bi2Te3-75% Sb2Te3 alloy only consist of Bi0.5Sb1.5Te3 single phase. At a low solidification rate of 5 μm/s, the cellular structures appear due to the solid/liquid interface losing its stabilization, and the increase of the solidification rate results in decreasing cellular structures. Additionally, the values of Seebeck coefficient and the resistivity of directionally solidified 25% Bi2Te3-75% Sb2Te3 alloys tend to a increase with increasing of the solidification rate. Under the solidification rate of 50 μm/s, the Power Factor (PF) of the alloy maintains (4.6-5.01)×10-3 W/(K2·m) in the temperature range of 300-450 K, and its maximum value reaches 5.01×10-3 W/(K2·m) at 350 K. Besides, at a higher solidification rate of 500 μm/s, the maximal PF value can be measured to be 4.5×10-3 W/(K2·m). It seems that the Bridgman method employing high temperature gradient with rapid solidification rate is a promising approach for the preparation of thermoelectric materials with high performance.
2012, 41(5):899-904.
Abstract:
Rutile, ilmenite and Al powder were used to prepare high titanium ferrous alloy by thermit-SHS(self -propagating high-temperature synthesis) reduction method. The thermodynamic and dynamic of the relative reaction systems were studied. The effects of charge ratio, slag type and heating agent on the thermit-SHS reduction process were investigated and the high titanium ferrous alloys were characterized by XRD，SEM and chemical compositions analysis technologies. The results indicate that the adiabatic temperatures of all reaction systems are higher than 1800 K, so all of the reactions can be kept up by self. The apparent activation energy is 93.676 kJ·mol-1 and reaction order is 0.01, the apparent activation energy for Al reducing TiO2 and Fe2O3 is 300.740 kJ·mol-1 and the reaction order is 1.20. The high titanium ferrous alloys consist mainly of TiFe2, TiFe and Fe2TiO0.13 ilmenites solid solution with low oxygen content. The oxide inclusions exist in the alloy which results directly in the high oxygen content and micro-structural defects in the alloys. The contents of titanium, aluminum, ferrous and silicon in the alloy are 60.0%-62%, 7.0%-11.0%, 21.0%-25.0% and 3.0% about, respectively. The lowest oxygen content in the alloy is 1.85% which is removed effectively.
Rutile, ilmenite and Al powder were used to prepare high titanium ferrous alloy by thermit-SHS(self -propagating high-temperature synthesis) reduction method. The thermodynamic and dynamic of the relative reaction systems were studied. The effects of charge ratio, slag type and heating agent on the thermit-SHS reduction process were investigated and the high titanium ferrous alloys were characterized by XRD，SEM and chemical compositions analysis technologies. The results indicate that the adiabatic temperatures of all reaction systems are higher than 1800 K, so all of the reactions can be kept up by self. The apparent activation energy is 93.676 kJ·mol-1 and reaction order is 0.01, the apparent activation energy for Al reducing TiO2 and Fe2O3 is 300.740 kJ·mol-1 and the reaction order is 1.20. The high titanium ferrous alloys consist mainly of TiFe2, TiFe and Fe2TiO0.13 ilmenites solid solution with low oxygen content. The oxide inclusions exist in the alloy which results directly in the high oxygen content and micro-structural defects in the alloys. The contents of titanium, aluminum, ferrous and silicon in the alloy are 60.0%-62%, 7.0%-11.0%, 21.0%-25.0% and 3.0% about, respectively. The lowest oxygen content in the alloy is 1.85% which is removed effectively.
Xiao Ling
,
Sun Yanhua
,
Liu Xiajing
,
Ding Chunhua
,
Qi Shemiao
,
Geng Haipeng
,
Yu Lie
,
Ding Binjun
2012, 41(5):905-909.
Abstract:
IS304 coating was been prepared by high energy ball milling and induction sintering. The microstructure of IS304 was fine and dense, the sizes of self lubricating particles were very small. Ag particles were about 5 μm, BaF2/CaF2 particles less than 2 μm, while some BaF2/CaF2 particles were located in Cr2O3 particles to form composite structure. Results show that the temperature and microstructure have great effect on the wear rates of the IS304. At 20 °C, the friction coefficient is great. The worn surface showes that the brittle fracture is the dominant wear mechanism. With the increase of temperature, IS304 exhibits an improved friction coefficient in the temperature range from 300 to 350 °C due to the formation of self-lubricating fluoride films. The existence of fluoride film on the worn surface of IS304 is attributed to the size refinement and the appropriate distribution of fluorides, resulting in a higher temperature rise at the instantaneous contacting surface in comparison to that of the PM304. The finite element models with different microstructures were built to simulate the flash temperature.
IS304 coating was been prepared by high energy ball milling and induction sintering. The microstructure of IS304 was fine and dense, the sizes of self lubricating particles were very small. Ag particles were about 5 μm, BaF2/CaF2 particles less than 2 μm, while some BaF2/CaF2 particles were located in Cr2O3 particles to form composite structure. Results show that the temperature and microstructure have great effect on the wear rates of the IS304. At 20 °C, the friction coefficient is great. The worn surface showes that the brittle fracture is the dominant wear mechanism. With the increase of temperature, IS304 exhibits an improved friction coefficient in the temperature range from 300 to 350 °C due to the formation of self-lubricating fluoride films. The existence of fluoride film on the worn surface of IS304 is attributed to the size refinement and the appropriate distribution of fluorides, resulting in a higher temperature rise at the instantaneous contacting surface in comparison to that of the PM304. The finite element models with different microstructures were built to simulate the flash temperature.
2012, 41(5):910-913.
Abstract:
In order to improve the hydrgen storage properties of LiAlH4 and LiNH2, LiAlH4/2LiNH2 composite was prepared by ball milling LiAlH4 and LiNH2 with a molar ratio of 1:2. The hydrogen storage properties and the microstructure change during dehydrogenation process were studied by using TG/DSC/MS, XRD, FTIR and NMR. Based on the hydrogen desorption properties and microstructure analysis, the dehydrogenation mechanism of LiAlH4/2LiNH2 composite was discussed. The experimental results show that the dehydrogenation reaction path of LiAlH4 is changed by addition of LiNH2, and the final product is Li3AlN2.
In order to improve the hydrgen storage properties of LiAlH4 and LiNH2, LiAlH4/2LiNH2 composite was prepared by ball milling LiAlH4 and LiNH2 with a molar ratio of 1:2. The hydrogen storage properties and the microstructure change during dehydrogenation process were studied by using TG/DSC/MS, XRD, FTIR and NMR. Based on the hydrogen desorption properties and microstructure analysis, the dehydrogenation mechanism of LiAlH4/2LiNH2 composite was discussed. The experimental results show that the dehydrogenation reaction path of LiAlH4 is changed by addition of LiNH2, and the final product is Li3AlN2.
2012, 41(5):914-919.
Abstract:
The effects of ultrasonic power, duration and treatment temperature on molten Mg-3Ca alloy degassing and solidification structure were investigated. The results indicate that applying of ultrasonic treatment technology can effectively remove gas and increase the density of Mg-3Ca alloy. Ultrasonic degassing effect is closely related with ultrasonic power, duration and treatment temperature. Too low ultrasonic power, too short or too long ultrasonic duration and too high or too low temperature are not beneficial to degassing effect. Under this experiment condition, when ultrasonic power is 150 W, ultrasonic duration is 120 s and treatment temperature is 700 ℃, the optimum degassing effect can be obtained and the degassing efficiency reaches 53.8%. In addition, ultrasound not only removes gas in melt, but also obtains the uniform refining solidification structure of ingot at the same time. Coarsened dendrite is adverse to bubbles rising and melt feeding. However, uniform refining equiaxed grain is beneficial to bubbles rising and melts feeding.
The effects of ultrasonic power, duration and treatment temperature on molten Mg-3Ca alloy degassing and solidification structure were investigated. The results indicate that applying of ultrasonic treatment technology can effectively remove gas and increase the density of Mg-3Ca alloy. Ultrasonic degassing effect is closely related with ultrasonic power, duration and treatment temperature. Too low ultrasonic power, too short or too long ultrasonic duration and too high or too low temperature are not beneficial to degassing effect. Under this experiment condition, when ultrasonic power is 150 W, ultrasonic duration is 120 s and treatment temperature is 700 ℃, the optimum degassing effect can be obtained and the degassing efficiency reaches 53.8%. In addition, ultrasound not only removes gas in melt, but also obtains the uniform refining solidification structure of ingot at the same time. Coarsened dendrite is adverse to bubbles rising and melt feeding. However, uniform refining equiaxed grain is beneficial to bubbles rising and melts feeding.
2012, 41(5):920-924.
Abstract:
Fe/Pt multiplayer coatings were prepared via an electrodeposition process, where FeSO4·7H2O and H2PtCl6·6H2O solution were used as Fe2+source and Pt4+source, respectively, and Fe/Pt=100:1, pH=2.5. Then Platinum chip and pure copper chip were used as anode and cathode, respectively, in the above mixture solution. The Fe/Pt multiplayer coatings were obtained through adjusting the parameters of pulse potential which results in the deposits of Fe and Pt reduplicatively. The results show that the surface morphologies of the Fe/Pt multiplayer coatings changes with the variety of Fe-rich layer potentials. The Fe/Pt multiplayer coatings, where the Fe/Pt ratio is close to 3:1, have been prepared in the conditions of –2 V, 6 min for the Pt-rich layer, –5 V, 3 min for Fe-rich layer, and 4-cycle deposits. The coercivity and saturation magnetization of the as-prepared multiplayer coatings increase from 5.12 kA/m to 42.18 kA/m and from 43.1 kA/m to 459.1 kA/m, respectively, after annealing at 550 °C for 30 min.
Fe/Pt multiplayer coatings were prepared via an electrodeposition process, where FeSO4·7H2O and H2PtCl6·6H2O solution were used as Fe2+source and Pt4+source, respectively, and Fe/Pt=100:1, pH=2.5. Then Platinum chip and pure copper chip were used as anode and cathode, respectively, in the above mixture solution. The Fe/Pt multiplayer coatings were obtained through adjusting the parameters of pulse potential which results in the deposits of Fe and Pt reduplicatively. The results show that the surface morphologies of the Fe/Pt multiplayer coatings changes with the variety of Fe-rich layer potentials. The Fe/Pt multiplayer coatings, where the Fe/Pt ratio is close to 3:1, have been prepared in the conditions of –2 V, 6 min for the Pt-rich layer, –5 V, 3 min for Fe-rich layer, and 4-cycle deposits. The coercivity and saturation magnetization of the as-prepared multiplayer coatings increase from 5.12 kA/m to 42.18 kA/m and from 43.1 kA/m to 459.1 kA/m, respectively, after annealing at 550 °C for 30 min.
2012, 41(5):925-928.
Abstract:
SrHfON thin films were prepared on p-type Si substrates by reactive radio-frequency sputtering deposition. The effects of annealing on the interface between SrHfON film and Si substrate, the structure and the electrical properties of the as-deposited and annealed ?lms have been investigated systematically. The results of XRD and HRTEM show that the SrHfON films are amorphous even after annealing at 900 °C. The interface between SrHfON film and Si substrate is composed of HfSixOy and SiO2 confirmed by XPS. The measurements indicate that MOS capacitors using the SrHfON films as gate dielectrics have lower leakage current densities and the leakage current densities decrease with increasing of RTA temperatures. The leakage current densities at Vg=+1 V for the as-deposited and annealed ?lms are 4.3×10-6 A/cm2 and 1.2×10-7 A/cm2, respectively. The analyses results show that SrHfON films will be a promising candidate for replacing SiO2 gate dielectric.
SrHfON thin films were prepared on p-type Si substrates by reactive radio-frequency sputtering deposition. The effects of annealing on the interface between SrHfON film and Si substrate, the structure and the electrical properties of the as-deposited and annealed ?lms have been investigated systematically. The results of XRD and HRTEM show that the SrHfON films are amorphous even after annealing at 900 °C. The interface between SrHfON film and Si substrate is composed of HfSixOy and SiO2 confirmed by XPS. The measurements indicate that MOS capacitors using the SrHfON films as gate dielectrics have lower leakage current densities and the leakage current densities decrease with increasing of RTA temperatures. The leakage current densities at Vg=+1 V for the as-deposited and annealed ?lms are 4.3×10-6 A/cm2 and 1.2×10-7 A/cm2, respectively. The analyses results show that SrHfON films will be a promising candidate for replacing SiO2 gate dielectric.
2012, 41(5):929-931.
Abstract:
The effects of 0-2.5wt%Zn addition on the anti-tarnishing of 925 silver alloys were investigated. The results of phase analysising, casting analysising, microstructure observation, and anti-tarnishing performance test show that adding of 0.5wt%~1wt% Zn will improve the anti-tarnishing of 925 silver alloy obviously which is attributed to a layer of zinc oxide film formed on the surface. Adding of Zn can play a role of brightening effect and improve the casting properties.
The effects of 0-2.5wt%Zn addition on the anti-tarnishing of 925 silver alloys were investigated. The results of phase analysising, casting analysising, microstructure observation, and anti-tarnishing performance test show that adding of 0.5wt%~1wt% Zn will improve the anti-tarnishing of 925 silver alloy obviously which is attributed to a layer of zinc oxide film formed on the surface. Adding of Zn can play a role of brightening effect and improve the casting properties.
2012, 41(5):932-935.
Abstract:
The microstructure evolution was analysised by heat treatment process at different solution temperatures and different cooling rates above or below βtransform temperature. The microstructure parameters such as grain size, total α phase area, thicknesses of lamellar α phase, primary α phase area and secondary α phase area were measured by software Image Proplus. The results show that for the heat treatment above βtransform temperature with furnace cooling, the grain size increases with the increase of temperature, its growth is bigger than that under BC cooling condition at the same solution temperature. During the heat treatment below βtransform temperature, for BC cooling condition, the total α phase area increases with increasing of temperature (800-850 °C), while it decreases as result of the secondary α phase disappearance (after 900-930 °C solution treatment). Moreover, for FC cooling condition (900-930 °C), the total α phase area increases as result of the largely precipitation of feathery lamellar α phase. The evolution?mechanism of?the grain?and the?volume fraction of?α phase?were analysised by the dynamics?theory.
The microstructure evolution was analysised by heat treatment process at different solution temperatures and different cooling rates above or below βtransform temperature. The microstructure parameters such as grain size, total α phase area, thicknesses of lamellar α phase, primary α phase area and secondary α phase area were measured by software Image Proplus. The results show that for the heat treatment above βtransform temperature with furnace cooling, the grain size increases with the increase of temperature, its growth is bigger than that under BC cooling condition at the same solution temperature. During the heat treatment below βtransform temperature, for BC cooling condition, the total α phase area increases with increasing of temperature (800-850 °C), while it decreases as result of the secondary α phase disappearance (after 900-930 °C solution treatment). Moreover, for FC cooling condition (900-930 °C), the total α phase area increases as result of the largely precipitation of feathery lamellar α phase. The evolution?mechanism of?the grain?and the?volume fraction of?α phase?were analysised by the dynamics?theory.
2012, 41(5):936-940.
Abstract:
The latest research work of La-Rh-O, Bi-Rh-O, Cu-Rh-O, Ca-Rh-O, Zn-Rh-O, Li-Rh-O were introduced, and the effects of their crystal structures, preparation methods, doped elements, on thermoelectric properties were studied. Rhodium oxide thermoelectric materials are considered as a new type of potential thermoelectric materials today.
The latest research work of La-Rh-O, Bi-Rh-O, Cu-Rh-O, Ca-Rh-O, Zn-Rh-O, Li-Rh-O were introduced, and the effects of their crystal structures, preparation methods, doped elements, on thermoelectric properties were studied. Rhodium oxide thermoelectric materials are considered as a new type of potential thermoelectric materials today.
