Volume 38,Issue 2,2009 Table of Contents
2009, 38(2):189-192.
Abstract:
HfO2 gate dielectric films with a blocking layer of Al2O3 inserted between HfO2 layer and Si layer (HfO2/Si) were treated with rapid thermal annealing process at 700 ℃. The interfacial structure and electrical properties were reported. The results of X-ray photoelectron spectroscopy showed that the interfacial layer of SiOx transformed into SiO2 after the annealing treatment, and Hf-silicates and Hf-silicides were not detected. The results of high-resolution transmission electron microscopy indicated that the interfacial layer was composed of SiO2 for the annealed film with blocking layer. The results of the electrical measurements indicated that the equivalent oxide thickness decreased to 2.5 nm and the fixed charge density decreased to –4.5×1011/cm2 in comparison with the same thickness of HfO2 films without the blocking layer. Al2O3 layer could effectively prevent the diffusion of Si into HfO2 film and improve the interfacial and electrical performance of HfO2 film
HfO2 gate dielectric films with a blocking layer of Al2O3 inserted between HfO2 layer and Si layer (HfO2/Si) were treated with rapid thermal annealing process at 700 ℃. The interfacial structure and electrical properties were reported. The results of X-ray photoelectron spectroscopy showed that the interfacial layer of SiOx transformed into SiO2 after the annealing treatment, and Hf-silicates and Hf-silicides were not detected. The results of high-resolution transmission electron microscopy indicated that the interfacial layer was composed of SiO2 for the annealed film with blocking layer. The results of the electrical measurements indicated that the equivalent oxide thickness decreased to 2.5 nm and the fixed charge density decreased to –4.5×1011/cm2 in comparison with the same thickness of HfO2 films without the blocking layer. Al2O3 layer could effectively prevent the diffusion of Si into HfO2 film and improve the interfacial and electrical performance of HfO2 film
2009, 38(2):193-197.
Abstract:
The structural and electrochemical properties of La0.7Mg0.3Ni2.65Co0.75Mn0.1Al0.2Bx (x=0-0.08) hydrogen storage electrode alloys were investigated systematically. The results from XRD show that all of the alloys consist of a (La, Mg)Ni3 phase and a LaNi5 phase. With the increase of B content, the abundance of the (La, Mg)Ni3 phase increases, accordingly that of the LaNi5 phase decreases, and the cell volumes of the two phases decrease. Electrochemical studies indicate that B addition can effectively improve the high rate dischargeability (HRD) of the alloy electrode, and the optimal value of HRD1000 reaches 57.1% as x being 0.04. With the addition of small amount of B, the cycling stability and activation properties of the alloy electrodes keep almost unchanged, but the maximum discharge capacity (Cmax) decreases. In addition, the electrochemical kinetics investigations including the linear polarization and anodic polarization were also performed in detail
The structural and electrochemical properties of La0.7Mg0.3Ni2.65Co0.75Mn0.1Al0.2Bx (x=0-0.08) hydrogen storage electrode alloys were investigated systematically. The results from XRD show that all of the alloys consist of a (La, Mg)Ni3 phase and a LaNi5 phase. With the increase of B content, the abundance of the (La, Mg)Ni3 phase increases, accordingly that of the LaNi5 phase decreases, and the cell volumes of the two phases decrease. Electrochemical studies indicate that B addition can effectively improve the high rate dischargeability (HRD) of the alloy electrode, and the optimal value of HRD1000 reaches 57.1% as x being 0.04. With the addition of small amount of B, the cycling stability and activation properties of the alloy electrodes keep almost unchanged, but the maximum discharge capacity (Cmax) decreases. In addition, the electrochemical kinetics investigations including the linear polarization and anodic polarization were also performed in detail
2009, 38(2):198-202.
Abstract:
Amorphous CeMg12 was prepared by ball milled CeMg12 alloy with Ni powder. The effects of mechanical grinding and electroless deposition of nickel (EDN) on the electrochemical properties of CeMg12 composites have been studied systematically. Amorphous CeMg12 composites have a maximum discharge capacity of 1209.6 mAh/g, but their cycling stability is poor. The cycling retention rate of the electrode is 37.26% after 10 cycles. After EDN treatment, the cycling stability of CeMg12 composite is improved markedly, and the cycling retention rate increases to 63.67% after 10 cycles. The improvement of cycling retention rate can be attributed to compact nickel coating that prevents the inner Mg from further corrosion by alkali. The nickel coating also enhances the high rate discharge (HRD) property of the composite owning to the good electrochemical catalytic properties of Ni. As oxidation and corrosion is unavoidable during EDN treatment, the maximum discharge capacity decreases slightly for CeMg12 composite with EDN treatment
Amorphous CeMg12 was prepared by ball milled CeMg12 alloy with Ni powder. The effects of mechanical grinding and electroless deposition of nickel (EDN) on the electrochemical properties of CeMg12 composites have been studied systematically. Amorphous CeMg12 composites have a maximum discharge capacity of 1209.6 mAh/g, but their cycling stability is poor. The cycling retention rate of the electrode is 37.26% after 10 cycles. After EDN treatment, the cycling stability of CeMg12 composite is improved markedly, and the cycling retention rate increases to 63.67% after 10 cycles. The improvement of cycling retention rate can be attributed to compact nickel coating that prevents the inner Mg from further corrosion by alkali. The nickel coating also enhances the high rate discharge (HRD) property of the composite owning to the good electrochemical catalytic properties of Ni. As oxidation and corrosion is unavoidable during EDN treatment, the maximum discharge capacity decreases slightly for CeMg12 composite with EDN treatment
2009, 38(2):203-208.
Abstract:
A mathematical model of the direct chill (DC) casting process for superlight Mg-Li alloy (LA141) slab has been developed using the finite differential method (FDM). Thermal boundary conditions including primary and secondary cooling conditions, have been selected based on knowledges of the physical process and the literatures. The variations of heat transfer coefficient between slab and dummy block interface resulting from the deformation of the slab have been considered. By calculating the temperature distribution, solid-liquid interface shape and position, the influence of casting parameters on DC casting process, such as the pour temperature, cooling water flow rate and casting speed have been analyzed. Moreover the profiles of the solidification fronts during the casting processes for the alloys of LA141 and AZ31 are compared.
A mathematical model of the direct chill (DC) casting process for superlight Mg-Li alloy (LA141) slab has been developed using the finite differential method (FDM). Thermal boundary conditions including primary and secondary cooling conditions, have been selected based on knowledges of the physical process and the literatures. The variations of heat transfer coefficient between slab and dummy block interface resulting from the deformation of the slab have been considered. By calculating the temperature distribution, solid-liquid interface shape and position, the influence of casting parameters on DC casting process, such as the pour temperature, cooling water flow rate and casting speed have been analyzed. Moreover the profiles of the solidification fronts during the casting processes for the alloys of LA141 and AZ31 are compared.
2009, 38(2):209-213.
Abstract:
Ti metallized coating was prepared on the surface of carbon fiber reinforced silicon carbide matrix (Cf/SiC) composite by molten salt reaction to make joining the composite with high melt point metals such as Ti. The morphologies and compositions of Ti metallized coating were analyzed by SEM and EDS. The phase components were assessed by XRD. The wettability of the solder was measured by quantitative metallography. The results show that Ti metallized coating is uniform and dense, and bound with the matrix closely. Ti can infiltrate into the gaps of the fibers, and cover the surfaces of the Cf/SiC composite. The main phases of the metalized coating consist of TiC and Ti5Si3. There are three transition layers between SiC and the metallized, i. e. Ti5Si3 layer, TiC layer and Ti5Si3 layer. The wettability of Cf/SiC composites surface to Ti is greatly improved by metallization, and the contact angle is deceased from 153.9° to 13.2° at 950 oC
Ti metallized coating was prepared on the surface of carbon fiber reinforced silicon carbide matrix (Cf/SiC) composite by molten salt reaction to make joining the composite with high melt point metals such as Ti. The morphologies and compositions of Ti metallized coating were analyzed by SEM and EDS. The phase components were assessed by XRD. The wettability of the solder was measured by quantitative metallography. The results show that Ti metallized coating is uniform and dense, and bound with the matrix closely. Ti can infiltrate into the gaps of the fibers, and cover the surfaces of the Cf/SiC composite. The main phases of the metalized coating consist of TiC and Ti5Si3. There are three transition layers between SiC and the metallized, i. e. Ti5Si3 layer, TiC layer and Ti5Si3 layer. The wettability of Cf/SiC composites surface to Ti is greatly improved by metallization, and the contact angle is deceased from 153.9° to 13.2° at 950 oC
2009, 38(2):214-218.
Abstract:
The Johnson-Cook model and the gradient-dependent plasticity were used to investigate the width of adiabatic shear band (ASB) and the strain rate effect of Ti-6Al-4V. The ASB width was defined as the width (w5%) of the region surrounding the band center over which the temperature differed from its peak value by less than 5%, similar to the viewpoint proposed by Batra and Kim. The theoretical results show that the calculated ASB widths are closer to the lower bound (12 μm) and upper bound (55μm) measured in experiments when the nominal strain rate is in the range of 800 s-1 and 1400 s-1 if the total ASB widths are 0.3235 mm and 0.0705 mm, respectively. At lower strain rates, the ASB is wider. As the strain rate increases, the ASB width rapidly decreases. However, at higher strain rates, the ASB width approaches constant. The present theoretical result is similar to the analytical result by Dodd and Bai and very consistent with the experimental result of tungsten alloy by Weerasooriya and Beaulieu, and is similar to the former part of the numerical result by Klepaczko and Rezaig
The Johnson-Cook model and the gradient-dependent plasticity were used to investigate the width of adiabatic shear band (ASB) and the strain rate effect of Ti-6Al-4V. The ASB width was defined as the width (w5%) of the region surrounding the band center over which the temperature differed from its peak value by less than 5%, similar to the viewpoint proposed by Batra and Kim. The theoretical results show that the calculated ASB widths are closer to the lower bound (12 μm) and upper bound (55μm) measured in experiments when the nominal strain rate is in the range of 800 s-1 and 1400 s-1 if the total ASB widths are 0.3235 mm and 0.0705 mm, respectively. At lower strain rates, the ASB is wider. As the strain rate increases, the ASB width rapidly decreases. However, at higher strain rates, the ASB width approaches constant. The present theoretical result is similar to the analytical result by Dodd and Bai and very consistent with the experimental result of tungsten alloy by Weerasooriya and Beaulieu, and is similar to the former part of the numerical result by Klepaczko and Rezaig
2009, 38(2):219-223.
Abstract:
An isothermal and constant strain rate compression test is carried out for the Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy with an equiaxed α+β microstructure in the temperature range of 1020~1080 ℃ and the strain rate range of 0.001~70 s-1. A power dissipation map is developed on the basis of flow stress data and by using the principles of dynamic material model. The results show that the steady state flow characteristics exist during hot compression deformation for the Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy in the temperature range 1020~1080 ℃. The dynamic recrystallization regime was identified in the power dissipation map and the microstructure examination was performed for validation. In the β phase field, the dynamic recrystallization occured in the temperature range of 1020~1080 ℃ and the strain rate range of 0.01~0.1 s-1 with the efficiency of power dissipation η mostly larger than 0.4, which is the optimum β forging processing parameters. It is proved that the power dissipation map based on dynamic material model is an effective method for successful β-forging and microstructure control
An isothermal and constant strain rate compression test is carried out for the Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy with an equiaxed α+β microstructure in the temperature range of 1020~1080 ℃ and the strain rate range of 0.001~70 s-1. A power dissipation map is developed on the basis of flow stress data and by using the principles of dynamic material model. The results show that the steady state flow characteristics exist during hot compression deformation for the Ti-6.5Al-3.5Mo-1.5Zr-0.3Si alloy in the temperature range 1020~1080 ℃. The dynamic recrystallization regime was identified in the power dissipation map and the microstructure examination was performed for validation. In the β phase field, the dynamic recrystallization occured in the temperature range of 1020~1080 ℃ and the strain rate range of 0.01~0.1 s-1 with the efficiency of power dissipation η mostly larger than 0.4, which is the optimum β forging processing parameters. It is proved that the power dissipation map based on dynamic material model is an effective method for successful β-forging and microstructure control
2009, 38(2):224-228.
Abstract:
In this article the strain controlled and stress controlled low cycle fatigue behaviors of TC21 titanium alloy were investigated. The fatigue tests were performed at room temperature and cyclic strain and stress ratio of 0.1 with triangle load wave. During the initial stage of strain controlled fatigue, the cyclic tensile stresses soften rapidly and the cyclic compressive stresses harden rapidly at the same time, the rates of cyclic softening and cyclic hardening decrease with the fatigue progress. During the overall fatigue progress, the soften rate is related to the cyclic strain but little to the cyclic stress, which is related to the macro friction stresses. Obvious cyclic creep occurs under the stress controlled low cycle fatigue conditions, and the magnitude of cyclic creep strain is related to the maximum cyclic stress. The softening of tensile friction stresses is the main factor of cyclic creep.
In this article the strain controlled and stress controlled low cycle fatigue behaviors of TC21 titanium alloy were investigated. The fatigue tests were performed at room temperature and cyclic strain and stress ratio of 0.1 with triangle load wave. During the initial stage of strain controlled fatigue, the cyclic tensile stresses soften rapidly and the cyclic compressive stresses harden rapidly at the same time, the rates of cyclic softening and cyclic hardening decrease with the fatigue progress. During the overall fatigue progress, the soften rate is related to the cyclic strain but little to the cyclic stress, which is related to the macro friction stresses. Obvious cyclic creep occurs under the stress controlled low cycle fatigue conditions, and the magnitude of cyclic creep strain is related to the maximum cyclic stress. The softening of tensile friction stresses is the main factor of cyclic creep.
2009, 38(2):229-232.
Abstract:
Multiwall carbon nanotubes (MWCNTs) were prepared by composite electrodeposit in a horizontal cathode mode. The electrodeposited MWCNTs have dense structure with a MWCNTs content of 22.45 % when using sulfuric nickel electrolyte, surface active solvent and brightener in a MWCNT content of 2~2.5 g/L and a voltaic density of 2.5 A/dm2. The SEM results show that the MWCNTs occupy the main volume of composite electrodepositing coating with sphere morphology for the Ni electrocrystallization. The crystallization occurs on the sunken part and the top of tubes where the Ni grains are connected each other to form a solid composite electrodeposits connecting the MWCNTs matrix and crystals. The MWCNTs content of composite electrodeposition are dominated by the MWCNTs concentration, the voltaic density and the brightener, while the connection of nickel deposition layer is dominated by the defects number and the connection of MWCNTs, and the shortest length of defect should be 1 nm at least for nucleation
Multiwall carbon nanotubes (MWCNTs) were prepared by composite electrodeposit in a horizontal cathode mode. The electrodeposited MWCNTs have dense structure with a MWCNTs content of 22.45 % when using sulfuric nickel electrolyte, surface active solvent and brightener in a MWCNT content of 2~2.5 g/L and a voltaic density of 2.5 A/dm2. The SEM results show that the MWCNTs occupy the main volume of composite electrodepositing coating with sphere morphology for the Ni electrocrystallization. The crystallization occurs on the sunken part and the top of tubes where the Ni grains are connected each other to form a solid composite electrodeposits connecting the MWCNTs matrix and crystals. The MWCNTs content of composite electrodeposition are dominated by the MWCNTs concentration, the voltaic density and the brightener, while the connection of nickel deposition layer is dominated by the defects number and the connection of MWCNTs, and the shortest length of defect should be 1 nm at least for nucleation
2009, 38(2):233-236.
Abstract:
Dynamic shearing experiment has been done for TC6 titanium alloy by using a split Hopkinson bar process. The fine structure of adiabatic shear band of TC6 alloy under different evolvement stages has been studied by optical microscope (OP), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It is shown that the formation of adiabatic shear band of material goes through the three processes of initiation, expansion and full evolvement, for which the fine structure is quite different. The extent of plastic deformation increases gradually from the initiation stage to the full evolvement stage, during which the dislocations play a very important role.
Dynamic shearing experiment has been done for TC6 titanium alloy by using a split Hopkinson bar process. The fine structure of adiabatic shear band of TC6 alloy under different evolvement stages has been studied by optical microscope (OP), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It is shown that the formation of adiabatic shear band of material goes through the three processes of initiation, expansion and full evolvement, for which the fine structure is quite different. The extent of plastic deformation increases gradually from the initiation stage to the full evolvement stage, during which the dislocations play a very important role.
2009, 38(2):237-241.
Abstract:
In this paper, the effects of cerium content on the structural and electrochemical properties of the La0.8-xCexMg0.2Ni3.5 (x=0, 0.05, 0.10, 0.15, 0.20) hydrogen storage alloys have been studied systematically. XRD analyses show that all these alloys consist of hexagonal Ce2Ni7-type main-phase, hexagonal CaCu5-type phase, and rhombohedral PuNi3-type phase. The P-C isotherms curves show that the plateau pressure of the hydrogen desorption increases gradually and the plateau region becomes narrower with increasing the Ce content in the alloys. It is also found that with increasing the Ce content, the discharge capacity at 303 K decreases and the cycling life can be gradually improved, but the discharge capacity at 233 K increases firstly and then decreases. The high rate dischargeability (HRD) and the exchange current density I0 increase but the hydrogen diffusion coefficient D of the alloy electrodes decreases with the increase of Ce content at 233 K. These imply that the charge-transfer reaction on the surface of alloy electrodes is the rate-determining step at 233 K
In this paper, the effects of cerium content on the structural and electrochemical properties of the La0.8-xCexMg0.2Ni3.5 (x=0, 0.05, 0.10, 0.15, 0.20) hydrogen storage alloys have been studied systematically. XRD analyses show that all these alloys consist of hexagonal Ce2Ni7-type main-phase, hexagonal CaCu5-type phase, and rhombohedral PuNi3-type phase. The P-C isotherms curves show that the plateau pressure of the hydrogen desorption increases gradually and the plateau region becomes narrower with increasing the Ce content in the alloys. It is also found that with increasing the Ce content, the discharge capacity at 303 K decreases and the cycling life can be gradually improved, but the discharge capacity at 233 K increases firstly and then decreases. The high rate dischargeability (HRD) and the exchange current density I0 increase but the hydrogen diffusion coefficient D of the alloy electrodes decreases with the increase of Ce content at 233 K. These imply that the charge-transfer reaction on the surface of alloy electrodes is the rate-determining step at 233 K
12 Microscopic Phase-Field Simulation of the Heat Treatment Process for Al-Zr Intermetallic Compound
2009, 38(2):242-246.
Abstract:
The aging processes of three different component Al-Zr alloys of Al-3at% Zr, Al-6at%Zr and Al-15at%Zr were simulated through the microscopic phase-field dynamic model. The results indicate that the precipitation mechanisms of the Al3Zr ordered phase of L12 structure are the spinodal decomposition, the mixed mechanism of spinodal decomposition and non-classical nucleation, and the non-classical nucleation for the Al-3at% Zr, Al-6at%Zr and Al-15at%Zr alloys, respectively. The ordered phase is in the order of supersaturated solid solution, G.P. zone, nonstoichiometric ordered phase, and stoichiometric ordered phase. At the initial stage of evolution, the smaller G.P. zone of lower concentration dissolved but the larger G.P. zone of higher concentration grew up to form an ordered phase at last
The aging processes of three different component Al-Zr alloys of Al-3at% Zr, Al-6at%Zr and Al-15at%Zr were simulated through the microscopic phase-field dynamic model. The results indicate that the precipitation mechanisms of the Al3Zr ordered phase of L12 structure are the spinodal decomposition, the mixed mechanism of spinodal decomposition and non-classical nucleation, and the non-classical nucleation for the Al-3at% Zr, Al-6at%Zr and Al-15at%Zr alloys, respectively. The ordered phase is in the order of supersaturated solid solution, G.P. zone, nonstoichiometric ordered phase, and stoichiometric ordered phase. At the initial stage of evolution, the smaller G.P. zone of lower concentration dissolved but the larger G.P. zone of higher concentration grew up to form an ordered phase at last
2009, 38(2):247-250.
Abstract:
Superior and inferior magnetic powders can be separated from the same batch crystallined NdFeB magnetic powders containing Zr and Co elements by magnetic separation method due to their magnetic ununiformity. The compositions and microstructures of the two powders with different magnetic properties were investigated. The results show that the superior powders contain less Zr and a relative more Fe, with integrated grains of about 20～60 nm in size and clear grain boundary without other phases. And the inferior powders contain more Zr and a relative lower Fe and metastable microstructures including the amorphous phases, the α-Fe and amorphous phases, and the un-integrated Nd2Fe14B phases of ≤10 nm in size. It is presumed that the ununiform magnetic properties are due to the elevated crystallization temperature induced by the more Zr content for the inferior powders
Superior and inferior magnetic powders can be separated from the same batch crystallined NdFeB magnetic powders containing Zr and Co elements by magnetic separation method due to their magnetic ununiformity. The compositions and microstructures of the two powders with different magnetic properties were investigated. The results show that the superior powders contain less Zr and a relative more Fe, with integrated grains of about 20～60 nm in size and clear grain boundary without other phases. And the inferior powders contain more Zr and a relative lower Fe and metastable microstructures including the amorphous phases, the α-Fe and amorphous phases, and the un-integrated Nd2Fe14B phases of ≤10 nm in size. It is presumed that the ununiform magnetic properties are due to the elevated crystallization temperature induced by the more Zr content for the inferior powders
2009, 38(2):251-254.
Abstract:
Titanium alloy castings are obtained with different rotation time in the ISM apparatus. The effects of rotation radius, riser and rotation time on the tensile strength, yield strength, specific elongation, and microhardness are investigated. The results show that the mechanical properties increase with the increase of rotation radius for the same rotation time. Excellent mechanical properties can be obtained for the casting with riser. As the rotation time is increased from 1.5 min to 15 min, the mechanical properties are greatly improved due to the finer microstructure and the strengthened grain boundary and then resulting in the increase of the resistance to dislocation slipping.
Titanium alloy castings are obtained with different rotation time in the ISM apparatus. The effects of rotation radius, riser and rotation time on the tensile strength, yield strength, specific elongation, and microhardness are investigated. The results show that the mechanical properties increase with the increase of rotation radius for the same rotation time. Excellent mechanical properties can be obtained for the casting with riser. As the rotation time is increased from 1.5 min to 15 min, the mechanical properties are greatly improved due to the finer microstructure and the strengthened grain boundary and then resulting in the increase of the resistance to dislocation slipping.
2009, 38(2):255-258.
Abstract:
Microstructure and formation characteristic of laser welded lap joints of TC4 alloy were investigated, and a parameter named join rate ψ was introduced to evaluate the welding effect of lap welding. The results indicated: the width of weld bead increases with increasing laser power or decreasing welding velocity, the top width of weld bead is larger than the bottom width and the minimum is the middle layer. And the join rate decreases as plates space or energy input increases. Microstructure of weld bead consisted of α′ martensite, and the martensite in the top portion is more concentrate than that in the bottom portion. There ate a small amount of martensite in HAZ, and distributed in gradient. For the strengthen effect of martensite, the microhardness reduces from the center of joints to base metal in cross direction, and the microhardness is higher in top weld bead
Microstructure and formation characteristic of laser welded lap joints of TC4 alloy were investigated, and a parameter named join rate ψ was introduced to evaluate the welding effect of lap welding. The results indicated: the width of weld bead increases with increasing laser power or decreasing welding velocity, the top width of weld bead is larger than the bottom width and the minimum is the middle layer. And the join rate decreases as plates space or energy input increases. Microstructure of weld bead consisted of α′ martensite, and the martensite in the top portion is more concentrate than that in the bottom portion. There ate a small amount of martensite in HAZ, and distributed in gradient. For the strengthen effect of martensite, the microhardness reduces from the center of joints to base metal in cross direction, and the microhardness is higher in top weld bead
2009, 38(2):259-262.
Abstract:
The microstructure of Ti-6Al-4V joints by laser beam welding with different welding parameters was studied, and the tensile properties were investigated. The microstructure of welding seam by laser beam welding consists mainly of α′ martensite phase as well as some α″ phase. By increasing the weld heat input，the distribution of martensite becomes more dispersive and glomerate due to the molten pool stiring, the welding stress and the burning loss of alloy elements. However, the welding parameters have no obviously effects on both the phase composition and the phase ratio. The tensile strength of joints is higher than basal metal when welded with reasonable parameters
The microstructure of Ti-6Al-4V joints by laser beam welding with different welding parameters was studied, and the tensile properties were investigated. The microstructure of welding seam by laser beam welding consists mainly of α′ martensite phase as well as some α″ phase. By increasing the weld heat input，the distribution of martensite becomes more dispersive and glomerate due to the molten pool stiring, the welding stress and the burning loss of alloy elements. However, the welding parameters have no obviously effects on both the phase composition and the phase ratio. The tensile strength of joints is higher than basal metal when welded with reasonable parameters
Li Jianfeng
,
Zhang Pingxiang
,
Liu Xianghong
,
Li Jinshan
,
Feng Yong
,
Wang Tiancheng
,
Du Shejun
,
Liu Weitao
,
G. Grunblatt
,
C. Verwaerde
,
G. K. Hoang
2009, 38(2):263-265.
Abstract:
This paper shows the results of R&D program carried out to optimize NbTi wires for the Poloidal Field (PF) coils of ITER. The influence of heat treatment on the microstructure was investigated by using TEM to find the relations between the microstructure and the critical current densities at 4.2 K for NbTi superconducting composite wire. Typical microstructure (in transverse cross-section) shows α-Ti pinning centers dispersed within the superconducting β-NbTi matrix with strong fold and curl for the NbTi wire with high critical current density at 4.2 K. It is believed that the higher temperature is beneficial to a higher Jc value at 4.2 K, but the Jc values slightly decrease with increasing the heat treatment times
This paper shows the results of R&D program carried out to optimize NbTi wires for the Poloidal Field (PF) coils of ITER. The influence of heat treatment on the microstructure was investigated by using TEM to find the relations between the microstructure and the critical current densities at 4.2 K for NbTi superconducting composite wire. Typical microstructure (in transverse cross-section) shows α-Ti pinning centers dispersed within the superconducting β-NbTi matrix with strong fold and curl for the NbTi wire with high critical current density at 4.2 K. It is believed that the higher temperature is beneficial to a higher Jc value at 4.2 K, but the Jc values slightly decrease with increasing the heat treatment times
2009, 38(2):266-270.
Abstract:
The first-principles based on the density functional theory was applied to calculate the structure parameters, bond units and electronic structure of the oxidation mechanism for the Pt-Zr solid solution under high oxygen atmosphere. The calculated conclusions show that the structure parameter of the Pt-Zr solid solution was changed by the oxidation reaction of Pt-Zr, so that the expansion along c axis is larger than the b and c axis in the Pt-Zr solid solution. As the oxidation of Zr is stronger than Pt, the electrons on the 4d orbit of Zr combine the electrons on the 2p orbit of O to bond and form the oxide of Zr, but Pt just acts as a bridge function during the wholly oxidize process. It is also found that our calculated results are in good agreement with the experimental phenomenon
The first-principles based on the density functional theory was applied to calculate the structure parameters, bond units and electronic structure of the oxidation mechanism for the Pt-Zr solid solution under high oxygen atmosphere. The calculated conclusions show that the structure parameter of the Pt-Zr solid solution was changed by the oxidation reaction of Pt-Zr, so that the expansion along c axis is larger than the b and c axis in the Pt-Zr solid solution. As the oxidation of Zr is stronger than Pt, the electrons on the 4d orbit of Zr combine the electrons on the 2p orbit of O to bond and form the oxide of Zr, but Pt just acts as a bridge function during the wholly oxidize process. It is also found that our calculated results are in good agreement with the experimental phenomenon
Zhu Yingying
,
Deng Wen
,
Sun Shunping
,
Jiang Haifeng
,
Huang Yuyang
,
Cao Mingzhou
,
Xiong Liangyue
2009, 38(2):271-274.
Abstract:
The positron lifetime and coincidence Doppler broadening spectra have been measured in pure Al, Si, Ti, Cr, Nb elements and Ti50Al50, Ti50Al48Cr2, Ti50Al48Nb2 alloys. It has been found that the 3d electron signal and the electron density for binary TiAl alloy are relative low due to the Ti 3d-Al 3p interactions. The addition of Cr and Nb atoms to TiAl alloy leads to the increase of electron densities in the bulk and grain boundaries simultaneously as well as the enhancement of d-d electron interactions. The d electron signal in the spectrum of Ti50Al48Cr2 alloy is higher than that of Ti50Al48Nb2 alloy. The effects of Cr and Nb on the d electrons of TiAl alloys have been discussed
The positron lifetime and coincidence Doppler broadening spectra have been measured in pure Al, Si, Ti, Cr, Nb elements and Ti50Al50, Ti50Al48Cr2, Ti50Al48Nb2 alloys. It has been found that the 3d electron signal and the electron density for binary TiAl alloy are relative low due to the Ti 3d-Al 3p interactions. The addition of Cr and Nb atoms to TiAl alloy leads to the increase of electron densities in the bulk and grain boundaries simultaneously as well as the enhancement of d-d electron interactions. The d electron signal in the spectrum of Ti50Al48Cr2 alloy is higher than that of Ti50Al48Nb2 alloy. The effects of Cr and Nb on the d electrons of TiAl alloys have been discussed
2009, 38(2):275-280.
Abstract:
The deformation behavior and evolution process of dynamic recrystallization for GH761 superalloy were studied with isothermal compression test in the temperature range of 950 ℃~1150 ℃ and the strain rate range of 0.1 s-1~30 s-1. The effect of thermodynamic parameters on flow stress was analyzed. A constitutive relationship was proposed based on the Arrhenius equation for the GH761 superalloy. The initiation and evolution of dynamic recrystallization were investigated with quantitive microstructure analysis. The volume fracture and grain size of dynamic recrystallization were established as functions of the Zener-Hollomon parameter. It is found that the calculation results of the proposed model are well agreed with the experimental data. Therefore, the proposed model can lay foundation of the quality control and process design for the forging process of GH761 superalloy
The deformation behavior and evolution process of dynamic recrystallization for GH761 superalloy were studied with isothermal compression test in the temperature range of 950 ℃~1150 ℃ and the strain rate range of 0.1 s-1~30 s-1. The effect of thermodynamic parameters on flow stress was analyzed. A constitutive relationship was proposed based on the Arrhenius equation for the GH761 superalloy. The initiation and evolution of dynamic recrystallization were investigated with quantitive microstructure analysis. The volume fracture and grain size of dynamic recrystallization were established as functions of the Zener-Hollomon parameter. It is found that the calculation results of the proposed model are well agreed with the experimental data. Therefore, the proposed model can lay foundation of the quality control and process design for the forging process of GH761 superalloy
2009, 38(2):281-285.
Abstract:
Supersaturated CuCr solid solution was prepared by pulverization. After that, the aging dynamics were analyzed at different temperatures. The results showed that the G.P zone was presented at relatively low temperature. We could observe a coherent interface between precipitated phase and matrix. The results that were obtained both from transmission electron microscope (TEM) and Electron Energy Disperse Spectroscopy (EDS) revealed that as aging time increased, the amount of Cr metal phase also increased due to solute enrichment process. On the other hand, the activation energy for atomic diffusion was reduced at high temperature. As a result, the metal phases of Cr were formed very fast. The fractional volume of the precipitated phase was measured by EDS and then applied Avrami equation to analyze the dynamical effect of aging. Finally we concluded that the phase transition in CuCr alloy was determined by aging dynamics and diffusion was the most important effect of aging process, other factors such as solute species, impurities, vacancies, dislocations, grain boundaries and lattice distortions may be affected this process, too.
Supersaturated CuCr solid solution was prepared by pulverization. After that, the aging dynamics were analyzed at different temperatures. The results showed that the G.P zone was presented at relatively low temperature. We could observe a coherent interface between precipitated phase and matrix. The results that were obtained both from transmission electron microscope (TEM) and Electron Energy Disperse Spectroscopy (EDS) revealed that as aging time increased, the amount of Cr metal phase also increased due to solute enrichment process. On the other hand, the activation energy for atomic diffusion was reduced at high temperature. As a result, the metal phases of Cr were formed very fast. The fractional volume of the precipitated phase was measured by EDS and then applied Avrami equation to analyze the dynamical effect of aging. Finally we concluded that the phase transition in CuCr alloy was determined by aging dynamics and diffusion was the most important effect of aging process, other factors such as solute species, impurities, vacancies, dislocations, grain boundaries and lattice distortions may be affected this process, too.
2009, 38(2):286-290.
Abstract:
The effect of the fourth-nearest pair potentials on the precipitation mechanism of Ni75Al5V20 alloy is studied using a microscopic phase-field kinetic equation. Our simulations demonstrate that both DO22 phase and L12 phase have a mixed precipitation mechanism of non-classical nucleation growth and spinodal decomposition without changing the fourth-nearest pair potentials. When the absolute value of the fourth-nearest pair potential between Ni and Al (namely V4Ni-Al, negative) increases, the precipitation mechanism of L12 phase becomes spinodal decomposition. And when the fourth-nearest pair potential between Ni and V (namely V4Ni-V) increases, the precipitation mechanism of DO22 phase is spinodal decomposition, the L12 phase is non-classical nucleation and the Al concentration in L12 phase gains. When the absolute value of the negative V4Al-V increases, the mechanism is similar to the increase of V4Ni-V; when the positive V4Al-V increases, the mechanism is similar to the decrease of V4Ni-V
The effect of the fourth-nearest pair potentials on the precipitation mechanism of Ni75Al5V20 alloy is studied using a microscopic phase-field kinetic equation. Our simulations demonstrate that both DO22 phase and L12 phase have a mixed precipitation mechanism of non-classical nucleation growth and spinodal decomposition without changing the fourth-nearest pair potentials. When the absolute value of the fourth-nearest pair potential between Ni and Al (namely V4Ni-Al, negative) increases, the precipitation mechanism of L12 phase becomes spinodal decomposition. And when the fourth-nearest pair potential between Ni and V (namely V4Ni-V) increases, the precipitation mechanism of DO22 phase is spinodal decomposition, the L12 phase is non-classical nucleation and the Al concentration in L12 phase gains. When the absolute value of the negative V4Al-V increases, the mechanism is similar to the increase of V4Ni-V; when the positive V4Al-V increases, the mechanism is similar to the decrease of V4Ni-V
2009, 38(2):291-294.
Abstract:
Sol-gel process is used to prepare Ru-Ir-Ti/Ti electrode coating. The microstructure and morphology are examined by SEM, XRD, EPMA, and the electrochemical performance is studied by potentiodynamic polarization and current efficiency. The results show that the alloy elements in the electrode coating prepared by the sol-gel process are well distributed, more sufficient to form solid solution and with higher current efficiency than by the traditional thermal decomposition process. The deactivation effect is due to the forming of unconductive TiO2 for the sol-gel process, but due to the dissolution of active composition for the thermal decomposition process.
Sol-gel process is used to prepare Ru-Ir-Ti/Ti electrode coating. The microstructure and morphology are examined by SEM, XRD, EPMA, and the electrochemical performance is studied by potentiodynamic polarization and current efficiency. The results show that the alloy elements in the electrode coating prepared by the sol-gel process are well distributed, more sufficient to form solid solution and with higher current efficiency than by the traditional thermal decomposition process. The deactivation effect is due to the forming of unconductive TiO2 for the sol-gel process, but due to the dissolution of active composition for the thermal decomposition process.
Ji Honglin
,
Chu Chenglin
,
Wang Rumang
,
Zhang Xuhai
,
Zhang Wenyan
,
Dong Yinsheng
,
Guo Chao
,
Sheng Xiaobo
,
Lin Pinghua
,
Paul K. Chu
2009, 38(2):295-298.
Abstract:
Pure Zr metal film was deposited on the surface of NiTi shape memory alloy by balanced magnetron DC sputtering and the microstructure of the Zr film was investigated by SEM, XRD and XPS methods. It is found that the Zr film has the T-type crystal band structure with a fine and dense fibre character. There are no pores and prick form. The film has good combination with NiTi substrate and a flatness surface. The crystal structure of the film is identical with its bulk Zr target except for a little bioinert ZrO2 phase. Finally the depositing mechanism of the Zr film by magnetron sputtering is discussed.
Pure Zr metal film was deposited on the surface of NiTi shape memory alloy by balanced magnetron DC sputtering and the microstructure of the Zr film was investigated by SEM, XRD and XPS methods. It is found that the Zr film has the T-type crystal band structure with a fine and dense fibre character. There are no pores and prick form. The film has good combination with NiTi substrate and a flatness surface. The crystal structure of the film is identical with its bulk Zr target except for a little bioinert ZrO2 phase. Finally the depositing mechanism of the Zr film by magnetron sputtering is discussed.
2009, 38(2):299-302.
Abstract:
The La0.7Sr0.3MnO3/Nb-1wt%-doped SrTiO3 p-n junction fabricated by the magnetron sputtering technique exhibits excellent rectifying characteristics over the temperature range from 40 to 320 K, nearly independent of the temperature. The modulated electromagnetic property of La0.7Sr0.3MnO3 is also achieved by the built-in electric field near the interface of junction. The diffusion potential decreases almost linearly with increasing the temperatures. It can be understood by considering a picture that the depletion layer in p-n junction becomes thinner and thinner with the increase of temperature due to the thermal diffusion effect. In addition, this phenomenon is also attributed to the variation of the electronic structure of LSMO with temperature increasing. The junction resistance decreases sharply when the applied forward current increases from 1 mA to 50 mA while the insulator-metal transition temperature TP increases from around 200 K to 250 K due to the strength enhancement of the ferromagnetic double-exchange interaction
The La0.7Sr0.3MnO3/Nb-1wt%-doped SrTiO3 p-n junction fabricated by the magnetron sputtering technique exhibits excellent rectifying characteristics over the temperature range from 40 to 320 K, nearly independent of the temperature. The modulated electromagnetic property of La0.7Sr0.3MnO3 is also achieved by the built-in electric field near the interface of junction. The diffusion potential decreases almost linearly with increasing the temperatures. It can be understood by considering a picture that the depletion layer in p-n junction becomes thinner and thinner with the increase of temperature due to the thermal diffusion effect. In addition, this phenomenon is also attributed to the variation of the electronic structure of LSMO with temperature increasing. The junction resistance decreases sharply when the applied forward current increases from 1 mA to 50 mA while the insulator-metal transition temperature TP increases from around 200 K to 250 K due to the strength enhancement of the ferromagnetic double-exchange interaction
2009, 38(2):303-308.
Abstract:
Silver-modified TiO2/SnO2 thin films (Ag-TiO2/SnO2 thin films) were prepared by the photodeposition method. The effects of preparation conditions on the photocatalytic activity of Ag-TiO2/SnO2 thin films were discussed. The surface morphology, chemical composition and structure of the films were characterized by SEM and XRD, and its photocatalytic properties were evaluated with Rhodamine B as model compound. The results show that the optimum content of Ag on the film surface was 0.51at% and the diameter of Ag particles was about 30~90 nm. The photocatalytic degradation rate of Ag-TiO2/SnO2 film is 1.92 times and 2.54 times higher than the TiO2/SnO2 film and the TiO2/ITO film, respectively, mainly duo to the change in the reaction mechanism. The heterojunction of Ag-TiO2 in Ag-TiO2/SnO2 film efficiently promoted the separation of charges and accelerated the reaction of excited electrons and oxygen relatively to TiO2/SnO2 film in photocatalytic degradation for Rhodamine B
Silver-modified TiO2/SnO2 thin films (Ag-TiO2/SnO2 thin films) were prepared by the photodeposition method. The effects of preparation conditions on the photocatalytic activity of Ag-TiO2/SnO2 thin films were discussed. The surface morphology, chemical composition and structure of the films were characterized by SEM and XRD, and its photocatalytic properties were evaluated with Rhodamine B as model compound. The results show that the optimum content of Ag on the film surface was 0.51at% and the diameter of Ag particles was about 30~90 nm. The photocatalytic degradation rate of Ag-TiO2/SnO2 film is 1.92 times and 2.54 times higher than the TiO2/SnO2 film and the TiO2/ITO film, respectively, mainly duo to the change in the reaction mechanism. The heterojunction of Ag-TiO2 in Ag-TiO2/SnO2 film efficiently promoted the separation of charges and accelerated the reaction of excited electrons and oxygen relatively to TiO2/SnO2 film in photocatalytic degradation for Rhodamine B
2009, 38(2):308-312.
Abstract:
TiC/7075 composite was synthesized by melt in-situ synthesis. The TiC particulates were observed from SEM to be nearly spherical shape with an average size of less than 1.0 μm. The experimental results show that the tensile elongation of the composite is slightly decreased, but the tensile strength and yield strength are respectively improved about 35.8% and 42.2% than those of 7075 aluminum alloy, showing that the TiC particulates formed by in-suit reaction strengthen the matrix effectively. The results of wear experiment show that the wear resistance of 6wt％TiC/7075 composite is better than that of 7075 aluminum alloy under lower loading (9.1 N). The wear resistance of the same composite, however, is lower than that of 7075 aluminum alloy under higher loading (35.8 N). The effect of external load on the wear resistance of the materials was analyzed
TiC/7075 composite was synthesized by melt in-situ synthesis. The TiC particulates were observed from SEM to be nearly spherical shape with an average size of less than 1.0 μm. The experimental results show that the tensile elongation of the composite is slightly decreased, but the tensile strength and yield strength are respectively improved about 35.8% and 42.2% than those of 7075 aluminum alloy, showing that the TiC particulates formed by in-suit reaction strengthen the matrix effectively. The results of wear experiment show that the wear resistance of 6wt％TiC/7075 composite is better than that of 7075 aluminum alloy under lower loading (9.1 N). The wear resistance of the same composite, however, is lower than that of 7075 aluminum alloy under higher loading (35.8 N). The effect of external load on the wear resistance of the materials was analyzed
2009, 38(2):313-317.
Abstract:
In order to obtain LaB6 cathode with high-purity and excellent properties，La and LaH2 nanopowders were prepared by hydrogen arc plasma method, and then La-LaH2 and B nanopowders were sintered to fabricate the high-purity LaB6 polycrystal nano-bulk cathode by in situ SPS (Spark Plasma Sintering) in a oxygen free system. The effects of sintering temperature and pressure on the phases, microstructure and properties of the nano-bulk were systematically studied. The results show that the single-phase LaB6 was formed in the nano bulk with a high purity of 99.867％ and an average crystal size of about 120 nm. The relative densities of nano-bulk LaB6 is up to 99.2%, and its hardness is up to 17.4 GPa, the bend strength of the polycrystal LaB6 is as high as around 245.6 MPa, the theoretical bend strength value of single crystal
In order to obtain LaB6 cathode with high-purity and excellent properties，La and LaH2 nanopowders were prepared by hydrogen arc plasma method, and then La-LaH2 and B nanopowders were sintered to fabricate the high-purity LaB6 polycrystal nano-bulk cathode by in situ SPS (Spark Plasma Sintering) in a oxygen free system. The effects of sintering temperature and pressure on the phases, microstructure and properties of the nano-bulk were systematically studied. The results show that the single-phase LaB6 was formed in the nano bulk with a high purity of 99.867％ and an average crystal size of about 120 nm. The relative densities of nano-bulk LaB6 is up to 99.2%, and its hardness is up to 17.4 GPa, the bend strength of the polycrystal LaB6 is as high as around 245.6 MPa, the theoretical bend strength value of single crystal
29 Preparation and Cytocompatibility of Bioactive β-TCP Coatings on Porous Magnesium Scaffold Surface
2009, 38(2):318-322.
Abstract:
A chemical deposition route was employed to prepare bioactive β-TCP coatings on porous magnesium scaffold surfaces. The phase identification and surface morphology of the specimens were studied by X-ray diffraction and scanning electron microscope, respectively. The cytocompatibility of treated porous magnesium scaffolds was studied in the present paper by using human osteoblast-like UMR106 cells. It was found that the cytotoxicity was in grade 1, indicating cytotoxicity free and without damage to DNA and no change to the cell cycle for the extracted liquid of treated magnesium. All the experimental results indicate that the treated porous magnesium has a good cytocompatibility and potential to be a new type of bone tissue engineering scaffolds
A chemical deposition route was employed to prepare bioactive β-TCP coatings on porous magnesium scaffold surfaces. The phase identification and surface morphology of the specimens were studied by X-ray diffraction and scanning electron microscope, respectively. The cytocompatibility of treated porous magnesium scaffolds was studied in the present paper by using human osteoblast-like UMR106 cells. It was found that the cytotoxicity was in grade 1, indicating cytotoxicity free and without damage to DNA and no change to the cell cycle for the extracted liquid of treated magnesium. All the experimental results indicate that the treated porous magnesium has a good cytocompatibility and potential to be a new type of bone tissue engineering scaffolds
2009, 38(2):323-326.
Abstract:
The microstructure and mechanical properties of Ni56Fe17Ga27-xCox(x=0, 2, 4, 6) magnetic shape memory alloys have been studied, and the influence of Co addition on γ phase and the mechanism for increasing toughness by γ phase were revealed. The results show that the microstructure of as-melted alloys is composed of martensite phase and γ phase at room temperature. With increasing Co content, the volume of γ phase increases. For the martensite phase, the saturation solubility of Fe and Co atoms is fixed. If the total content of Fe and Co atoms exceeds 16 at %, the residual atoms will exist in the form of γ phase, which is rich in Fe and Co atoms. Besides, the saturation solubility of Fe and Co atoms in γ phase is around 23 at %. The tensile tests show that the yielding strength and fracture strength increase with increasing Co content. The fracture mechanism of martensite phase is transcrystalline fracture, and the γ phase is gliding fracture, it proves that the γ phase improves the toughness of experimental alloys
The microstructure and mechanical properties of Ni56Fe17Ga27-xCox(x=0, 2, 4, 6) magnetic shape memory alloys have been studied, and the influence of Co addition on γ phase and the mechanism for increasing toughness by γ phase were revealed. The results show that the microstructure of as-melted alloys is composed of martensite phase and γ phase at room temperature. With increasing Co content, the volume of γ phase increases. For the martensite phase, the saturation solubility of Fe and Co atoms is fixed. If the total content of Fe and Co atoms exceeds 16 at %, the residual atoms will exist in the form of γ phase, which is rich in Fe and Co atoms. Besides, the saturation solubility of Fe and Co atoms in γ phase is around 23 at %. The tensile tests show that the yielding strength and fracture strength increase with increasing Co content. The fracture mechanism of martensite phase is transcrystalline fracture, and the γ phase is gliding fracture, it proves that the γ phase improves the toughness of experimental alloys
2009, 38(2):327-330.
Abstract:
Using sodium hypophosphite as the reducing agent, polyvinyl pyrrolidone as the protecting agent, the nanosized silver powder was synthesized by chemical reduction method in a highly concentrated silver nitrate solution. Using the orthogonal design method of three factors and three levels, the optimal conditions to prepare the nanosized silver powder were obtained by studying the effects of following factors, such as the concentration of reducing agent, the doses of protecting agent and the temperature, on the particles size and morphology of silver powder. The pure nanosized silver powders with qusai-spherical shapes and homogeneous distribution and diameter of 30 nm to 50 nm were synthesized under the conditions of AgNO3 concentration of 1.0 mol/L, NaH2PO2·H2O concentration of 0.1 mol/L, PVP/AgNO3 weight ratio of 1∶1, pH=1~2 and at 40 ℃
Using sodium hypophosphite as the reducing agent, polyvinyl pyrrolidone as the protecting agent, the nanosized silver powder was synthesized by chemical reduction method in a highly concentrated silver nitrate solution. Using the orthogonal design method of three factors and three levels, the optimal conditions to prepare the nanosized silver powder were obtained by studying the effects of following factors, such as the concentration of reducing agent, the doses of protecting agent and the temperature, on the particles size and morphology of silver powder. The pure nanosized silver powders with qusai-spherical shapes and homogeneous distribution and diameter of 30 nm to 50 nm were synthesized under the conditions of AgNO3 concentration of 1.0 mol/L, NaH2PO2·H2O concentration of 0.1 mol/L, PVP/AgNO3 weight ratio of 1∶1, pH=1~2 and at 40 ℃
2009, 38(2):331-334.
Abstract:
Formation and mechanical properties of ZrCuAlSi metallic glass alloy was investigated by using differential scanning calorimetry (DSC), X-ray diffraction (XRD), microhardness test, and compression test. When the samples were prepared by using the simple copper mould casting, the maximum diameter of glassy rods increased from 4 mm for the Zr47Cu44Al9 alloy to 6 mm for the (Zr47Cu44Al9)98.5Si1.5 alloy without detectable crystal. Properly adding Si can enhance the GFA of the (Zr47Cu44Al9)100-xSix alloy and increase the microhardness(Hv) form 5850 MPa for the Zr47Cu44Al9 alloy to 6220 MPa for the (Zr47Cu44Al9)98.5Si1.5 alloy due to the suppression to form the primary CuZr phase. The compression test at room temperature shows that the (Zr47Cu44Al9)98.5Si1.5 alloy has the high fracture strength of 1862 MPa
Formation and mechanical properties of ZrCuAlSi metallic glass alloy was investigated by using differential scanning calorimetry (DSC), X-ray diffraction (XRD), microhardness test, and compression test. When the samples were prepared by using the simple copper mould casting, the maximum diameter of glassy rods increased from 4 mm for the Zr47Cu44Al9 alloy to 6 mm for the (Zr47Cu44Al9)98.5Si1.5 alloy without detectable crystal. Properly adding Si can enhance the GFA of the (Zr47Cu44Al9)100-xSix alloy and increase the microhardness(Hv) form 5850 MPa for the Zr47Cu44Al9 alloy to 6220 MPa for the (Zr47Cu44Al9)98.5Si1.5 alloy due to the suppression to form the primary CuZr phase. The compression test at room temperature shows that the (Zr47Cu44Al9)98.5Si1.5 alloy has the high fracture strength of 1862 MPa
2009, 38(2):335-338.
Abstract:
Micro-arc oxide (MAO) films were prepared on AZ91D magnesium alloy in an electrolyte bath of aluminate and sodium hydroxide with different additives such as montmorillonite, EDTA and arabin. The effects of additives on the chemical composition and corrosion resistance of MAO films were examined by means of SEM, EDS, XRD and potentiodynamic polarization in a 3.5% NaCl solution. The results show that the morphology of MAO films is like alveolate, and the microstructure is consisted of MgAl2O4, MgO and Mg2SiO4 phases. Compared with the untreated magnesium alloy, the MAO treated specimen exhibits higher corrosion resistance, especially for the films using montmorillonite as additive
Micro-arc oxide (MAO) films were prepared on AZ91D magnesium alloy in an electrolyte bath of aluminate and sodium hydroxide with different additives such as montmorillonite, EDTA and arabin. The effects of additives on the chemical composition and corrosion resistance of MAO films were examined by means of SEM, EDS, XRD and potentiodynamic polarization in a 3.5% NaCl solution. The results show that the morphology of MAO films is like alveolate, and the microstructure is consisted of MgAl2O4, MgO and Mg2SiO4 phases. Compared with the untreated magnesium alloy, the MAO treated specimen exhibits higher corrosion resistance, especially for the films using montmorillonite as additive
2009, 38(2):339-342.
Abstract:
In order to evaluate the effects of ultrasonic deep rolling process on the reducing surface roughness and healing surface scar or micro-damage, some line type surface notches and pit like surface caves were prepared and followed by ultrasonic deep rolling treatment on Ti-6Al-4V plate to simulate the foreign object damage. The surface roughness and geometry were evaluated by a surface profile tester and SEM observation for both the treated and untreated specimens. Results show that the surface roughness of the specimen can be reduced from Ra 2.32 μm to 0.11 μm by the ultrasonic deep rolling process. Some line type surface notches and pit like surface caves were significantly attenuated. The above results are expected to improve the anti-fatigue performance of parts effectively or to restore the fatigue resistance of the FOD damaged surface
In order to evaluate the effects of ultrasonic deep rolling process on the reducing surface roughness and healing surface scar or micro-damage, some line type surface notches and pit like surface caves were prepared and followed by ultrasonic deep rolling treatment on Ti-6Al-4V plate to simulate the foreign object damage. The surface roughness and geometry were evaluated by a surface profile tester and SEM observation for both the treated and untreated specimens. Results show that the surface roughness of the specimen can be reduced from Ra 2.32 μm to 0.11 μm by the ultrasonic deep rolling process. Some line type surface notches and pit like surface caves were significantly attenuated. The above results are expected to improve the anti-fatigue performance of parts effectively or to restore the fatigue resistance of the FOD damaged surface
2009, 38(2):343-347.
Abstract:
Mg2Si/AM60 composites were fabricated by in situ synthesis, and their microstructures and properties were investigated for the composites adding different Si contents. The results indicate that some fine Mg2Si particles of cosh shape and chinese script shape appeared in the microstructure by adding crystal Si, but were changed to irregular bulks when the content of Si is high. The composites with more homogeneous distribution of Mg2Si particles were produced by mechanical stirring. The ultimate tensile strength and hardness of composites were increased with the increase of Si, but the elongation was reduced. The ultimate tensile strength increased by 12 % for 1.0 % Si addition and the hardness increased by 48.6 % for 5 % Si addition
Mg2Si/AM60 composites were fabricated by in situ synthesis, and their microstructures and properties were investigated for the composites adding different Si contents. The results indicate that some fine Mg2Si particles of cosh shape and chinese script shape appeared in the microstructure by adding crystal Si, but were changed to irregular bulks when the content of Si is high. The composites with more homogeneous distribution of Mg2Si particles were produced by mechanical stirring. The ultimate tensile strength and hardness of composites were increased with the increase of Si, but the elongation was reduced. The ultimate tensile strength increased by 12 % for 1.0 % Si addition and the hardness increased by 48.6 % for 5 % Si addition
2009, 38(2):348-352.
Abstract:
A chemical co-precipitation method was used in this study to prepare W-Cu composite oxide powder firstly, and then the nanoscale W-20%Cu composite powder through hydrogen reduction. The W-Cu alloy of ultrafine dispersion structure was obtained by forming and sintering the composite powder. The results show that the W grains have polygonal shape with a particle size of 30 nm ~50 nm after hydrogen reduction. Furthermore, the Cu phase disperses evenly in the W phase to bind some W particles together. The W-20%Cu composite powder prepared by this process showed a good sintering activity with a relative density of 99.7% and a thermal conductivity of 223.1 W?m-1?K-1 when the W-Cu nanoscale composite power was sintered at 1250 ℃. Other performances such as electrical conductivity, bend strength, hardness were also increased greatly if compared with the traditional W-20%Cu products.
A chemical co-precipitation method was used in this study to prepare W-Cu composite oxide powder firstly, and then the nanoscale W-20%Cu composite powder through hydrogen reduction. The W-Cu alloy of ultrafine dispersion structure was obtained by forming and sintering the composite powder. The results show that the W grains have polygonal shape with a particle size of 30 nm ~50 nm after hydrogen reduction. Furthermore, the Cu phase disperses evenly in the W phase to bind some W particles together. The W-20%Cu composite powder prepared by this process showed a good sintering activity with a relative density of 99.7% and a thermal conductivity of 223.1 W?m-1?K-1 when the W-Cu nanoscale composite power was sintered at 1250 ℃. Other performances such as electrical conductivity, bend strength, hardness were also increased greatly if compared with the traditional W-20%Cu products.
2009, 38(2):353-357.
Abstract:
A ‘panoramic effect’ of oxygen impurity on the thermal stability and GFA of Vitreloy 105 metallic glass was investigated based on the construction of TTT diagram and the kinetics analysis of primary phase precipitation. It was found that the oxygen impurity has different influences on the alloy’s thermal stability and GFA in the content range of 0.015 %~0.045 % (mass) because the primary phase was changed. The oxygen decreases the alloy’s GFA during continuously cooling crystallization for the oxygen-induced f.c.c.-Zr2Ni precipitates as the primary phase. However, the oxygen retards the precipitation of b.c.t.-Zr2Ni phase and enhances the alloy’s thermal stability during the reheating recrystallization of glassy alloy for the b.c.t.-Zr2Ni as the initial precipitation phase. The crystal structure of primary phases depends on the conditions for oxygen diffusion during the crystallization above nose temperature, Tn, and the recrystallization below Tn
A ‘panoramic effect’ of oxygen impurity on the thermal stability and GFA of Vitreloy 105 metallic glass was investigated based on the construction of TTT diagram and the kinetics analysis of primary phase precipitation. It was found that the oxygen impurity has different influences on the alloy’s thermal stability and GFA in the content range of 0.015 %~0.045 % (mass) because the primary phase was changed. The oxygen decreases the alloy’s GFA during continuously cooling crystallization for the oxygen-induced f.c.c.-Zr2Ni precipitates as the primary phase. However, the oxygen retards the precipitation of b.c.t.-Zr2Ni phase and enhances the alloy’s thermal stability during the reheating recrystallization of glassy alloy for the b.c.t.-Zr2Ni as the initial precipitation phase. The crystal structure of primary phases depends on the conditions for oxygen diffusion during the crystallization above nose temperature, Tn, and the recrystallization below Tn
2009, 38(2):358-360.
Abstract:
In this paper, a deaggregation technology and its mechanism were studied for the Ag/ZnO nanocomposite antibacterial agent added with PVPK17 by sedimentation experiment, laser scattering particle size analysis and transmission electron microscopy (TEM). The minimum inhibitory concentration of the fore-aft deaggregation Ag/ZnO nanocomposite antibacterial agent was tested. The results showed that the Ag/ZnO nanocomposite antibacterial agent in isopropanol could be stable suspension more than 6 days after deaggregation with PVPk17, the average particle size was smaller than 51.3 nm. The dispersion effect was the best when the mass % of PVPk17 was 40%. TEM results show that the Ag/ZnO nanocomposite antibacterial agent is kindly dispersed. Then, a model of deaggregation mechanism was built. The MIC of Ag/ZnO nanocomposite antibacterial agent was 50 mg/L after deaggregation, with good antibacterial property
In this paper, a deaggregation technology and its mechanism were studied for the Ag/ZnO nanocomposite antibacterial agent added with PVPK17 by sedimentation experiment, laser scattering particle size analysis and transmission electron microscopy (TEM). The minimum inhibitory concentration of the fore-aft deaggregation Ag/ZnO nanocomposite antibacterial agent was tested. The results showed that the Ag/ZnO nanocomposite antibacterial agent in isopropanol could be stable suspension more than 6 days after deaggregation with PVPk17, the average particle size was smaller than 51.3 nm. The dispersion effect was the best when the mass % of PVPk17 was 40%. TEM results show that the Ag/ZnO nanocomposite antibacterial agent is kindly dispersed. Then, a model of deaggregation mechanism was built. The MIC of Ag/ZnO nanocomposite antibacterial agent was 50 mg/L after deaggregation, with good antibacterial property
2009, 38(2):361-364.
Abstract:
La-modified TiAl3 intermetallics were prepared by combined processing of mechanical alloying and annealing. The effects of adding lanthanum on the microstructure and mechanical properties of TiAl3 were investigated by XRD, particle size and distribution analysis, TEM, the tests of hardness, elongation and fracture toughness. The results show that adding trace element lanthanum can make the DO22 type TiAl3 crystal structure transform into the related cubic L12 structure. The fracture toughness of alloys modified by adding La can be increased by 143.75%. However, the Vickers hardness of the Al-Ti-La powders is smaller than that of the Al-Ti powders
La-modified TiAl3 intermetallics were prepared by combined processing of mechanical alloying and annealing. The effects of adding lanthanum on the microstructure and mechanical properties of TiAl3 were investigated by XRD, particle size and distribution analysis, TEM, the tests of hardness, elongation and fracture toughness. The results show that adding trace element lanthanum can make the DO22 type TiAl3 crystal structure transform into the related cubic L12 structure. The fracture toughness of alloys modified by adding La can be increased by 143.75%. However, the Vickers hardness of the Al-Ti-La powders is smaller than that of the Al-Ti powders
2009, 38(2):365-367.
Abstract:
The Mg-8 mol% LaNi0.5 hydrogen storage materials were prepared by mechanically milling at cryogenic temperature (cryomilling). The phase structure and surface morphology of the materials were studied by XRD and SEM, the granularity distribution was determined by laser method, the hydrogen storage performance of the materials were studied by an equipment of PCT (pressure-composition-Temperature). The results showed that a small amount of the alloy phase appeared after ten hours. The average particle size of the materials is 10 μm. The materials had a flat platform of hydrogen absorption and desorption, the hydrogen storage capacity is 2.33 wt% at 573 K. Under 4.0 MPa hydrogen pressure, the materials can absorb more than 80% of their full hydrogen capacity in 3 min to 5 min at 523 K~653 K. The materials prepared by cryomilling had better activation performance, without activation, and fine platform performance, and the dynamic performance was improved
The Mg-8 mol% LaNi0.5 hydrogen storage materials were prepared by mechanically milling at cryogenic temperature (cryomilling). The phase structure and surface morphology of the materials were studied by XRD and SEM, the granularity distribution was determined by laser method, the hydrogen storage performance of the materials were studied by an equipment of PCT (pressure-composition-Temperature). The results showed that a small amount of the alloy phase appeared after ten hours. The average particle size of the materials is 10 μm. The materials had a flat platform of hydrogen absorption and desorption, the hydrogen storage capacity is 2.33 wt% at 573 K. Under 4.0 MPa hydrogen pressure, the materials can absorb more than 80% of their full hydrogen capacity in 3 min to 5 min at 523 K~653 K. The materials prepared by cryomilling had better activation performance, without activation, and fine platform performance, and the dynamic performance was improved
2009, 38(2):368-372.
Abstract:
Noble metal core-shell nanoparticles have attracted much attention due to their unique optical, electric and catalytic properties, they can be applied in material sciences, biophysics, molecular electronics and fluorescence-spectral engineering based on surface- enhancement. In this paper, a comprehensive review is presented on noble metal core-shell nanoparticles including preparation, application, and then the development trends of noble metal core-shell materials were also proposed
Noble metal core-shell nanoparticles have attracted much attention due to their unique optical, electric and catalytic properties, they can be applied in material sciences, biophysics, molecular electronics and fluorescence-spectral engineering based on surface- enhancement. In this paper, a comprehensive review is presented on noble metal core-shell nanoparticles including preparation, application, and then the development trends of noble metal core-shell materials were also proposed
2009, 38(2):373-376.
Abstract:
Introduce the application area of rhenium including petrochemical, aeronautics and astronautics, metallurgy and electron industry and others. Systemic summarize and analyzed the main preparation methods of rhenium products, point out various preparation methods of rhenium and rhenium alloys
Introduce the application area of rhenium including petrochemical, aeronautics and astronautics, metallurgy and electron industry and others. Systemic summarize and analyzed the main preparation methods of rhenium products, point out various preparation methods of rhenium and rhenium alloys
