Volume 45,Issue 1,2016 Table of Contents
1 A Constitutive Model of Metal Rubber for Hysteresis Characteristics based on Meso-Mehanical Method
2016, 45(1):1-6.
Abstract:
Based on the typical mesoscopic structural characteristics of metal rubber, the mesoscopic physical mechanism was revealed, through analyzing the spatial configuration and contact mode of wire helixes for its compression deformation process. The mesoscopic structure unit based on the curved beam of variable length and the model of contact interaction between curved beams were presented, and combined with the distribution law of frictional contact points, a new constitutive model of metal rubber for hysteresis characteristics was established, which included its basic structure parameters which were the diameter and elastic modulus of wire, the diameter of wire helix, the relative density of metal rubber and so on. The model could describe the restoring force curves of metal rubber in initial loading, unloading and repeated loading phases, and theoretically explained its elastic characteristics and dry friction damping characteristics of multipoint contact. To verify the theory model, a comparison was made between the theoretical results and the experimental results for metal rubber specimens with different relative densities. The results show that theoretic calculations are consistent with the experimental data. It provides a theoretical basis for predicting the stiffness and damping of metal rubber and guiding its design.
Based on the typical mesoscopic structural characteristics of metal rubber, the mesoscopic physical mechanism was revealed, through analyzing the spatial configuration and contact mode of wire helixes for its compression deformation process. The mesoscopic structure unit based on the curved beam of variable length and the model of contact interaction between curved beams were presented, and combined with the distribution law of frictional contact points, a new constitutive model of metal rubber for hysteresis characteristics was established, which included its basic structure parameters which were the diameter and elastic modulus of wire, the diameter of wire helix, the relative density of metal rubber and so on. The model could describe the restoring force curves of metal rubber in initial loading, unloading and repeated loading phases, and theoretically explained its elastic characteristics and dry friction damping characteristics of multipoint contact. To verify the theory model, a comparison was made between the theoretical results and the experimental results for metal rubber specimens with different relative densities. The results show that theoretic calculations are consistent with the experimental data. It provides a theoretical basis for predicting the stiffness and damping of metal rubber and guiding its design.
2016, 45(1):7-12.
Abstract:
The Rare Earth (RE) containing Mg cast alloys have big potential to be used for heat-resistant applications, on condition that the RE-containing intermetallic compounds can be refined during the casting process. In this research, the effect of Ultrasonic Vibration (USV) with different powers on microstructure and mechanical properties of the semi-solid Mg-3RE-3Zn-0.7Y alloys has been investigated. The Mg alloy melt at temperature of 20?40 癈 above the liquidus was exposed to USV for 90 s with different powers from 800W to 1200W, and the USV ended about 10癈 below the liquidus. The results show that good semi-solid slurry with fine and spherical α-Mg particles could be obtained, and the primary α-Mg crystals are with average particle size of 55 μm and average shape coefficient of 0.63 after USV with 1000 W power. After USV treatment with the power of 1000 W, the ultimate tensile strength and elongation of the casting samples were 25.2% and 93.5% higher than those of the samples without USV treatment respectively. It can be concluded that ultrasonic vibration is a good method to prepare semi-solid slurry of Mg alloy with fine and relatively round primary crystals due to cavitation and acoustic streaming effects.
The Rare Earth (RE) containing Mg cast alloys have big potential to be used for heat-resistant applications, on condition that the RE-containing intermetallic compounds can be refined during the casting process. In this research, the effect of Ultrasonic Vibration (USV) with different powers on microstructure and mechanical properties of the semi-solid Mg-3RE-3Zn-0.7Y alloys has been investigated. The Mg alloy melt at temperature of 20?40 癈 above the liquidus was exposed to USV for 90 s with different powers from 800W to 1200W, and the USV ended about 10癈 below the liquidus. The results show that good semi-solid slurry with fine and spherical α-Mg particles could be obtained, and the primary α-Mg crystals are with average particle size of 55 μm and average shape coefficient of 0.63 after USV with 1000 W power. After USV treatment with the power of 1000 W, the ultimate tensile strength and elongation of the casting samples were 25.2% and 93.5% higher than those of the samples without USV treatment respectively. It can be concluded that ultrasonic vibration is a good method to prepare semi-solid slurry of Mg alloy with fine and relatively round primary crystals due to cavitation and acoustic streaming effects.
2016, 45(1):13-17.
Abstract:
The as-cast Mg-Y-Zr-xNd alloys with different Nd contents were prepared, and the effects of Nd content on microstructure, mechanical properties and electromagnetic interference (EMI)shielding properties were investigated.The results showed that the grain size was refined from 70.1 to 42.9 μm, discontinuous bone-shaped β phases formed mostly in the triple junction of grain boundaries when the content of Nd increased to 2.63 wt.%. The mechanical properties and EMI shielding capacity were both enhanced significantly by adding Nd element. The alloy with 2.63 wt.% Nd had a good combination of mechanical properties and EMI properties. T6 heat treatment was able to further improve the EMI shielding effectiveness. The above-mentioned observations are analyzed in terms of microstructural variation due to the Nd addition.
The as-cast Mg-Y-Zr-xNd alloys with different Nd contents were prepared, and the effects of Nd content on microstructure, mechanical properties and electromagnetic interference (EMI)shielding properties were investigated.The results showed that the grain size was refined from 70.1 to 42.9 μm, discontinuous bone-shaped β phases formed mostly in the triple junction of grain boundaries when the content of Nd increased to 2.63 wt.%. The mechanical properties and EMI shielding capacity were both enhanced significantly by adding Nd element. The alloy with 2.63 wt.% Nd had a good combination of mechanical properties and EMI properties. T6 heat treatment was able to further improve the EMI shielding effectiveness. The above-mentioned observations are analyzed in terms of microstructural variation due to the Nd addition.
2016, 45(1):18-22.
Abstract:
In-situ synthesis of AlN-Mg composite materials by the gas bubbling method was investigated using nitrogen as the gaseous precursor in the temperature range of 700 to 800℃. The proofs of a direct reaction of N2 and Al to form AlN in Mg-Al alloy melt were found. Microstructure analysis confirmed the formation and uniform distribution of AlN phases in the alloy. An optimum process to form in situ AlN phase in Mg-Al based alloys are obtained.
In-situ synthesis of AlN-Mg composite materials by the gas bubbling method was investigated using nitrogen as the gaseous precursor in the temperature range of 700 to 800℃. The proofs of a direct reaction of N2 and Al to form AlN in Mg-Al alloy melt were found. Microstructure analysis confirmed the formation and uniform distribution of AlN phases in the alloy. An optimum process to form in situ AlN phase in Mg-Al based alloys are obtained.
2016, 45(1):23-27.
Abstract:
Abstract: The effect of alloying element Ce on oxidation behavior and surface tension of Mg-1.2Ca alloy was investigated in order to have a further develop for the ignition-proof magnesium alloys. As the content of Ce range from 0 to 1.5wt.%, the ignition point of Mg-1.2Ca increase rapidly while the surface tension decline. The ignition point of Mg-1.2Ca-1.2Ce alloy can reach to 780℃. And the Mg-1.2Ca-1.2Ce alloy can be melt at the atmosphere without any protection method. The oxidation film of Mg-1.2Ca melt has turned to fine and close structure from porous structure with Ce addition, which can prevent magnesium alloys from further oxidation and burning. According to the test and analysis, oxide film of Mg-1.2Ca-1.2Ce alloy consists of three layers which are loose MgO in the outer layer, MgO-CaO composite oxide film in the middle layer and MgO-Ce2O3 composite oxide film in the inner layer respectively.
Abstract: The effect of alloying element Ce on oxidation behavior and surface tension of Mg-1.2Ca alloy was investigated in order to have a further develop for the ignition-proof magnesium alloys. As the content of Ce range from 0 to 1.5wt.%, the ignition point of Mg-1.2Ca increase rapidly while the surface tension decline. The ignition point of Mg-1.2Ca-1.2Ce alloy can reach to 780℃. And the Mg-1.2Ca-1.2Ce alloy can be melt at the atmosphere without any protection method. The oxidation film of Mg-1.2Ca melt has turned to fine and close structure from porous structure with Ce addition, which can prevent magnesium alloys from further oxidation and burning. According to the test and analysis, oxide film of Mg-1.2Ca-1.2Ce alloy consists of three layers which are loose MgO in the outer layer, MgO-CaO composite oxide film in the middle layer and MgO-Ce2O3 composite oxide film in the inner layer respectively.
2016, 45(1):28-31.
Abstract:
The precipitation behavior of second phases in Hastelloy C-2000 alloy matrix was studied after isothermal oxidation at 800 oC for 100 h in air. Mo-rich phases were precipitated in the alloy matrix after oxidation. It is determined that Mo-rich phases with diamond cubic structure are Mo3Ni3C type carbides. Morphology characteristics of Mo-rich phases with both no-continuous irregular strip and continuous were presented along grain boundaries and in matrix, respectively. However, some variation of morphologies will take place at both grain and grain boundaries after deep etching, i.e., a large number of white flocculent structure were distributed along grain boundaries, and corrosion pits with a diamond structure appear in intragranular. Areas of Ni and Cr-rich are more easily corroded during deep etching due to a more negative electrode potential in areas.
The precipitation behavior of second phases in Hastelloy C-2000 alloy matrix was studied after isothermal oxidation at 800 oC for 100 h in air. Mo-rich phases were precipitated in the alloy matrix after oxidation. It is determined that Mo-rich phases with diamond cubic structure are Mo3Ni3C type carbides. Morphology characteristics of Mo-rich phases with both no-continuous irregular strip and continuous were presented along grain boundaries and in matrix, respectively. However, some variation of morphologies will take place at both grain and grain boundaries after deep etching, i.e., a large number of white flocculent structure were distributed along grain boundaries, and corrosion pits with a diamond structure appear in intragranular. Areas of Ni and Cr-rich are more easily corroded during deep etching due to a more negative electrode potential in areas.
2016, 45(1):32-35.
Abstract:
Mg-Zn-Ca-Mn matrix composites reinforced with two volume fractions (1 and 3vol.%) of SiC particles (1μm) were fabricated by semisolid stirring assisted ultrasonic vibration method, and then extruded at 350℃ with the extrusion ratio of 15:1. The microstructure of materials was examined by optical microscopy (OM) and scanning electron microscope (SEM) and transmission electron microscopy（TEM）. The microstructure analysis showed that the relative uniform SiCp distribution and the refined grain were obtained in the 1vol.% SiCp/Mg-Zn-Ca-Mn and 3vol.% SiCp/Mg-Zn-Ca-Mn composites during the extrusion. The introduction of SiCp could contribute to improve the 0.2% yield strength and ultimate tensile strength. Both of the yield strength and ultimate tensile strength increased with the increase of SiCp content.
Mg-Zn-Ca-Mn matrix composites reinforced with two volume fractions (1 and 3vol.%) of SiC particles (1μm) were fabricated by semisolid stirring assisted ultrasonic vibration method, and then extruded at 350℃ with the extrusion ratio of 15:1. The microstructure of materials was examined by optical microscopy (OM) and scanning electron microscope (SEM) and transmission electron microscopy（TEM）. The microstructure analysis showed that the relative uniform SiCp distribution and the refined grain were obtained in the 1vol.% SiCp/Mg-Zn-Ca-Mn and 3vol.% SiCp/Mg-Zn-Ca-Mn composites during the extrusion. The introduction of SiCp could contribute to improve the 0.2% yield strength and ultimate tensile strength. Both of the yield strength and ultimate tensile strength increased with the increase of SiCp content.
2016, 45(1):36-41.
Abstract:
The composite electronic brush plating technique is facilitated to prepare the alloy nanocomposite plating with different nano-Al2O3 particles content. The effects of nanoparticles content in the electrolyte on the deposition rate, nanoparticles content, microhardness and tribological property of composite coatings are mainly discussed, measured by scanning electron microscopy, microhardness tester and attrition testing machine. It is found that, with the increase of nano-Al2O3 particles content in the solution, the deposition rate of coatings drops, the surface morphology of plating becomes flat, the microhardness is firstly enlarged and then decreased，wear scar depth is firstly reduced and then increased, friction coefficient is firstly reduced and then improved. When the nano-Al2O3 particles concentration in the electrolyte is 20g/L, the coating reaches its optimized structure and performance.
The composite electronic brush plating technique is facilitated to prepare the alloy nanocomposite plating with different nano-Al2O3 particles content. The effects of nanoparticles content in the electrolyte on the deposition rate, nanoparticles content, microhardness and tribological property of composite coatings are mainly discussed, measured by scanning electron microscopy, microhardness tester and attrition testing machine. It is found that, with the increase of nano-Al2O3 particles content in the solution, the deposition rate of coatings drops, the surface morphology of plating becomes flat, the microhardness is firstly enlarged and then decreased，wear scar depth is firstly reduced and then increased, friction coefficient is firstly reduced and then improved. When the nano-Al2O3 particles concentration in the electrolyte is 20g/L, the coating reaches its optimized structure and performance.
2016, 45(1):42-45.
Abstract:
The diffusion bonding capability between Zr41.25Ti13.75Cu12.5Ni10Be22.5 bulk metallic glass and pure Cu with and without interlayer was studied on a Gleeble3500 thermomechanical simulator. Good diffusion bonding joints without cracks and voids have been obtained under both conditions. Atomic diffusion at the interface was obviously observed using EDS and EPMA methods, while the diffusion zones were very narrow. The crystalline phases which were transformed from amorphous state accelerated the atomic diffusion at the interface.
The diffusion bonding capability between Zr41.25Ti13.75Cu12.5Ni10Be22.5 bulk metallic glass and pure Cu with and without interlayer was studied on a Gleeble3500 thermomechanical simulator. Good diffusion bonding joints without cracks and voids have been obtained under both conditions. Atomic diffusion at the interface was obviously observed using EDS and EPMA methods, while the diffusion zones were very narrow. The crystalline phases which were transformed from amorphous state accelerated the atomic diffusion at the interface.
2016, 45(1):46-50.
Abstract:
Large-area arrays of highly oriented Co-doped ZnO nanorods with hexagonal structure were grown on Zn substrates by single-step hydrothermal process. Structure analysis indicated that the as-prepared products were wurtzite structure, and no other secondary phase was found in the nanorods. The intensity of UV emission peak decreased with the Co doping concentrations increasing. When Co was doped into ZnO lattice, oxygen vacancies and Zn interstitials were created. The concentration of these defects increased with rise of the Co concentration. Magnetic measurement revealed that the Co doped ZnO nanorod arrays exhibited obvious room-temperature ferromagnetic behavior with a large coercive field Hc~660 Oe, which makes them potentially useful as building components for spintronics.
Large-area arrays of highly oriented Co-doped ZnO nanorods with hexagonal structure were grown on Zn substrates by single-step hydrothermal process. Structure analysis indicated that the as-prepared products were wurtzite structure, and no other secondary phase was found in the nanorods. The intensity of UV emission peak decreased with the Co doping concentrations increasing. When Co was doped into ZnO lattice, oxygen vacancies and Zn interstitials were created. The concentration of these defects increased with rise of the Co concentration. Magnetic measurement revealed that the Co doped ZnO nanorod arrays exhibited obvious room-temperature ferromagnetic behavior with a large coercive field Hc~660 Oe, which makes them potentially useful as building components for spintronics.
2016, 45(1):51-55.
Abstract:
Effects of electric pulse treatment on shape memory effect and microstructure in a pre-deformation Fe13Mn6Si13Cr4Ni0.1C alloy were investigated. The results indicate that electric pulse treatment can accelerate migration of Cr and C atoms and precipitation of Cr23C6 carbides, lower ageing temperature, shorten ageing time and induce nucleation of Cr23C6 carbides. Therefore, the shape recovery ratio was improved to 87.2% from 32% of a water-quenching alloy within 300 s in a Fe13Mn6Si13Cr4Ni0.1C alloy by 300 V, 1100 μf, 1 Hz electric pulse treatment after 10% tensile pre-deformation compared to alloys aged at 973 K, 1073 K respectively following the same pre-deformation.
Effects of electric pulse treatment on shape memory effect and microstructure in a pre-deformation Fe13Mn6Si13Cr4Ni0.1C alloy were investigated. The results indicate that electric pulse treatment can accelerate migration of Cr and C atoms and precipitation of Cr23C6 carbides, lower ageing temperature, shorten ageing time and induce nucleation of Cr23C6 carbides. Therefore, the shape recovery ratio was improved to 87.2% from 32% of a water-quenching alloy within 300 s in a Fe13Mn6Si13Cr4Ni0.1C alloy by 300 V, 1100 μf, 1 Hz electric pulse treatment after 10% tensile pre-deformation compared to alloys aged at 973 K, 1073 K respectively following the same pre-deformation.
2016, 45(1):56-61.
Abstract:
La(1-x)MgxNi4.25Al0.75 (x=0.0, 0.1, 0.2, 0.3) hydrogen storage alloys were synthesized by means of a three-step induction melting. Their crystal structures and hydrogen storage properties were investigated in the present work. Studies inform that alloys with x=0.0 and 0.1 Mg contain a single LaNi4Al phase, however, those alloys with x=0.2 and 0.3 are composed of LaNi4Al, (La,Mg)Ni3 and AlNi3 phases. With x increasing from 0.2 to 0.3, the abundances of the secondary phases and the plateau pressures in the pressure-composition isotherms are lifted significantly. Meanwhile, their hydrogen storage capacities are remarkably reduced. The alloy with x=0.1 possesses the fastest absorption kinetics compared to the other alloys as well as a good hydrogen capacity and a low plateau pressure.
La(1-x)MgxNi4.25Al0.75 (x=0.0, 0.1, 0.2, 0.3) hydrogen storage alloys were synthesized by means of a three-step induction melting. Their crystal structures and hydrogen storage properties were investigated in the present work. Studies inform that alloys with x=0.0 and 0.1 Mg contain a single LaNi4Al phase, however, those alloys with x=0.2 and 0.3 are composed of LaNi4Al, (La,Mg)Ni3 and AlNi3 phases. With x increasing from 0.2 to 0.3, the abundances of the secondary phases and the plateau pressures in the pressure-composition isotherms are lifted significantly. Meanwhile, their hydrogen storage capacities are remarkably reduced. The alloy with x=0.1 possesses the fastest absorption kinetics compared to the other alloys as well as a good hydrogen capacity and a low plateau pressure.
2016, 45(1):62-65.
Abstract:
Electrode materials of SnO2.xH2O are synthesized at low temperature by hydrolysis precipitation process. After calcination at various temperatures, the as-prepared powders are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA). XRD patterns confirm the structure of SnO2.xH2O powders to be tetragonal. TEM images reveal the morphology of the as-prepared SnO2?xH2O powders, and TGA shows the water content in SnO2.xH2O, which decreases as the calcination temperature increases. Electrochemical tests, such as cyclic voltammetry (CV), cycling and chronopotentiometry test are also performed to study the supercapacitor behavior of the calcined SnO2?xH2O powders. Cyclic voltammetric results indicate that SnO2?xH2O powders calcined at 200℃ has a maximum specific capacitance of 36.1 F g-1 at the scan rate of 5 mV s-1 in 0.5 M H2SO4 aqueous electrolyte. Cycling test on the same sample also shows excellent long-term cyclic stability, which has lost less than 2 % of the total specific capacitance after 2000 cycles. These results indicate that SnO2.xH2O powders prepared from hydrolysis precipitation process are excellent candidates as electrode materials towards the applications of supercapacitor.
Electrode materials of SnO2.xH2O are synthesized at low temperature by hydrolysis precipitation process. After calcination at various temperatures, the as-prepared powders are characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA). XRD patterns confirm the structure of SnO2.xH2O powders to be tetragonal. TEM images reveal the morphology of the as-prepared SnO2?xH2O powders, and TGA shows the water content in SnO2.xH2O, which decreases as the calcination temperature increases. Electrochemical tests, such as cyclic voltammetry (CV), cycling and chronopotentiometry test are also performed to study the supercapacitor behavior of the calcined SnO2?xH2O powders. Cyclic voltammetric results indicate that SnO2?xH2O powders calcined at 200℃ has a maximum specific capacitance of 36.1 F g-1 at the scan rate of 5 mV s-1 in 0.5 M H2SO4 aqueous electrolyte. Cycling test on the same sample also shows excellent long-term cyclic stability, which has lost less than 2 % of the total specific capacitance after 2000 cycles. These results indicate that SnO2.xH2O powders prepared from hydrolysis precipitation process are excellent candidates as electrode materials towards the applications of supercapacitor.
2016, 45(1):66-70.
Abstract:
In this paper, silica sol was used to seal the hole of anodic oxide film on AZ31 magnesium alloy. The immersion time, calcinating temperature and immersion times were discussed respectively. Scanning electron microscope (SEM) was employed to characterize the surface morphology of the composite film and potentiodynamic polarization curves were used to analyze the corrosion behaviors. The composition of the anodic films that sealed was studied by energy dispersion spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). It has been found that the corrosion resistance of anodic film was improved with sealing by silica sol. When the dipping time is 1.5 min and the calcination temperature is 350 ℃, the corrosion resistance of the film is the best. Times of dipping and calcination has bigger influential on the performance of the film, when the dipping- calcination was 7 times, the film has good corrosion resistance. After sealing, silica sol was adsorbed on inner hole and outside hole of the anodic oxidation film.
In this paper, silica sol was used to seal the hole of anodic oxide film on AZ31 magnesium alloy. The immersion time, calcinating temperature and immersion times were discussed respectively. Scanning electron microscope (SEM) was employed to characterize the surface morphology of the composite film and potentiodynamic polarization curves were used to analyze the corrosion behaviors. The composition of the anodic films that sealed was studied by energy dispersion spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). It has been found that the corrosion resistance of anodic film was improved with sealing by silica sol. When the dipping time is 1.5 min and the calcination temperature is 350 ℃, the corrosion resistance of the film is the best. Times of dipping and calcination has bigger influential on the performance of the film, when the dipping- calcination was 7 times, the film has good corrosion resistance. After sealing, silica sol was adsorbed on inner hole and outside hole of the anodic oxidation film.
2016, 45(1):71-74.
Abstract:
4043 aluminum welding wire has been extensively used for welding 6000 series aluminum alloys due to the good flow ability of the fusion state and low cracking tendency during welding process. Some scratches and wear on the surface of aluminum structural components can be repaired by surface welding with the 4043 aluminum welding wires. In the present study, the influence of Si content and aging temperature on the wear resistance property of the surfacing layers welded by tungsten inert gas (TIG) welding using the 4043 aluminum welding wires has been analyzed by optical microscopy, scanning electron microscopy, hardness testing and abrasive wear testing. The results showed that increase in Si content increased the fraction of eutectic Si particles. The heat treatment spheroidized eutectic Si particles and further improved the wear resistance property of the surfacing layers.
4043 aluminum welding wire has been extensively used for welding 6000 series aluminum alloys due to the good flow ability of the fusion state and low cracking tendency during welding process. Some scratches and wear on the surface of aluminum structural components can be repaired by surface welding with the 4043 aluminum welding wires. In the present study, the influence of Si content and aging temperature on the wear resistance property of the surfacing layers welded by tungsten inert gas (TIG) welding using the 4043 aluminum welding wires has been analyzed by optical microscopy, scanning electron microscopy, hardness testing and abrasive wear testing. The results showed that increase in Si content increased the fraction of eutectic Si particles. The heat treatment spheroidized eutectic Si particles and further improved the wear resistance property of the surfacing layers.
2016, 45(1):75-78.
Abstract:
Carbon and SiC doped MgB2 bulk and wires were fabricated by a two-step reaction method. The MgB4 samples were sintered at 900 ℃ for 2 h in closed argon atmosphere, and then appropriate amount of Mg powder was added with the ground MgB4 powder to get MgB2 samples, which were sintered at 750 ℃ and 2 h for bulk samples or 680 ℃ and 2 h for wire samples in closed argon atmosphere. Carbon and SiC doped MgB2 samples were also prepared by solid state sintering for compared. The phase evolution and microstructure of MgB2 samples were characterized by means of X-ray diffraction (XRD) and scanning electron microscope (SEM). The SEM results indicate the porosity of MgB2 samples prepared by the two-step reaction method improves obviously. The carbon doping could effectively introduce the doping element into the MgB2 crystalline lattice and grain boundaries compared with SiC doping.
Carbon and SiC doped MgB2 bulk and wires were fabricated by a two-step reaction method. The MgB4 samples were sintered at 900 ℃ for 2 h in closed argon atmosphere, and then appropriate amount of Mg powder was added with the ground MgB4 powder to get MgB2 samples, which were sintered at 750 ℃ and 2 h for bulk samples or 680 ℃ and 2 h for wire samples in closed argon atmosphere. Carbon and SiC doped MgB2 samples were also prepared by solid state sintering for compared. The phase evolution and microstructure of MgB2 samples were characterized by means of X-ray diffraction (XRD) and scanning electron microscope (SEM). The SEM results indicate the porosity of MgB2 samples prepared by the two-step reaction method improves obviously. The carbon doping could effectively introduce the doping element into the MgB2 crystalline lattice and grain boundaries compared with SiC doping.
2016, 45(1):79-85.
Abstract:
By means of creep tests and microstructure observations, the effect of transverse pre-compression on high-temperature creep behavior of a [001] oriented single crystal nickel-based superalloy was studied. Results show that after being pre-compressed along [100] orientation at 1040 篊/180MPa for 40 h, the cuboidal g?phase has been transformed into one-dimensional P-type stripe-like rafts parallel to the compressive stress axis. The misorientations of the alloy and stress axis of pre-compression and tensile creep are responsible for the transverse connection of the stripe-like g?rafts. The decrease of the interfacial energy of g?g phases is the driving force of the microstructure evolution during the pre-compression treatment and the subsequent tensile creep test of the alloy. Compared to the alloy without pre-compression, the microstructure of the pre-compressed alloy makes the dislocation slip in matrix channels more easily, which has more contributions to the strain rate of the alloy along [001] orientation, so the pre-compression decreases the creep resistance of the alloy at 980 篊/200 MPa.
By means of creep tests and microstructure observations, the effect of transverse pre-compression on high-temperature creep behavior of a [001] oriented single crystal nickel-based superalloy was studied. Results show that after being pre-compressed along [100] orientation at 1040 篊/180MPa for 40 h, the cuboidal g?phase has been transformed into one-dimensional P-type stripe-like rafts parallel to the compressive stress axis. The misorientations of the alloy and stress axis of pre-compression and tensile creep are responsible for the transverse connection of the stripe-like g?rafts. The decrease of the interfacial energy of g?g phases is the driving force of the microstructure evolution during the pre-compression treatment and the subsequent tensile creep test of the alloy. Compared to the alloy without pre-compression, the microstructure of the pre-compressed alloy makes the dislocation slip in matrix channels more easily, which has more contributions to the strain rate of the alloy along [001] orientation, so the pre-compression decreases the creep resistance of the alloy at 980 篊/200 MPa.
2016, 45(1):86-91.
Abstract:
Exploring the metal flow and penetration fracture behavior is important for application of piercing extrusion process of solid ingot for high-performance seamless tube. A piercing extrusion process from solid ingot ( ) to titanium alloy tube ( ) has been studied in this paper. Based on FE soft of DEFORM-2D, a thermo-mechanical coupling model being able to describe the metal flow and penetration fracture behavior was developed for the piercing process of piercing extrusion of solid ingot. The piercing processes by using two kinds of piercing punches were analyzed. The results indicated that: at initial stage of piercing process, the deformation characteristic is similar to forward extrusion, and then metal reverse flows, and the backward extrusion is showed until the end cap is removed; the piercing force increases rapidly under forward extrusion, and backward extrusion occurs when the force rise to the stable value, the piercing force decreases rapidly at penetration fracture stage after removing the end cap; under backward extrusion, the piercing force has a little change by using cylindrical piercing punch, but the force will significantly increase again after a short stable stage by using bottle piercing punch, and thus the piercing force by using bottle piercing punch is more greater than that by using cylindrical piercing punch; at penetration fracture stage, fracture behavior by using cylindrical piercing punch is similar to that in blanking process, but the fracture face by using bottle piercing punch presents an approximate L-shaped.
Exploring the metal flow and penetration fracture behavior is important for application of piercing extrusion process of solid ingot for high-performance seamless tube. A piercing extrusion process from solid ingot ( ) to titanium alloy tube ( ) has been studied in this paper. Based on FE soft of DEFORM-2D, a thermo-mechanical coupling model being able to describe the metal flow and penetration fracture behavior was developed for the piercing process of piercing extrusion of solid ingot. The piercing processes by using two kinds of piercing punches were analyzed. The results indicated that: at initial stage of piercing process, the deformation characteristic is similar to forward extrusion, and then metal reverse flows, and the backward extrusion is showed until the end cap is removed; the piercing force increases rapidly under forward extrusion, and backward extrusion occurs when the force rise to the stable value, the piercing force decreases rapidly at penetration fracture stage after removing the end cap; under backward extrusion, the piercing force has a little change by using cylindrical piercing punch, but the force will significantly increase again after a short stable stage by using bottle piercing punch, and thus the piercing force by using bottle piercing punch is more greater than that by using cylindrical piercing punch; at penetration fracture stage, fracture behavior by using cylindrical piercing punch is similar to that in blanking process, but the fracture face by using bottle piercing punch presents an approximate L-shaped.
2016, 45(1):92-96.
Abstract:
The Ti48Zr20Nb12Cu5Be15 amorphous alloy with in-situ ?-Ti（Zr,Nb）crystal phase was prepared by copper mould injection casting. The mechanical behavior was systematically investigated under both quasi-static and dynamic compression at room temperature. Microstructure investigations were conducted by scanning electron microscopy, the result showed that the Ti48Zr20Nb12Cu5Be15 amorphous alloy is amorphous matrix and the ?-Ti (Zr,Nb) crystal phase uniformly distributed in the matrix. The fracture stress increased with increasing strain rate, revealing strain rate hardening effect for the Ti48Zr20Nb12Cu5Be15 in-situ crystal phase amorphous alloy under individual quasi-static and dynamic compression at room temperature. It was also found that the adiabatic temperature rising and the fragment of the amorphous alloys existed on dynamic compression, leading to the fracture stress and the fracture strain during dynamic compression were much lower than that during quasi-static compression at room temperature.
The Ti48Zr20Nb12Cu5Be15 amorphous alloy with in-situ ?-Ti（Zr,Nb）crystal phase was prepared by copper mould injection casting. The mechanical behavior was systematically investigated under both quasi-static and dynamic compression at room temperature. Microstructure investigations were conducted by scanning electron microscopy, the result showed that the Ti48Zr20Nb12Cu5Be15 amorphous alloy is amorphous matrix and the ?-Ti (Zr,Nb) crystal phase uniformly distributed in the matrix. The fracture stress increased with increasing strain rate, revealing strain rate hardening effect for the Ti48Zr20Nb12Cu5Be15 in-situ crystal phase amorphous alloy under individual quasi-static and dynamic compression at room temperature. It was also found that the adiabatic temperature rising and the fragment of the amorphous alloys existed on dynamic compression, leading to the fracture stress and the fracture strain during dynamic compression were much lower than that during quasi-static compression at room temperature.
2016, 45(1):97-101.
Abstract:
The type, morphology and orientation relationship of the hydride precipitates in a hydrogen absorbed Zr-4 alloy have been studied by means of transmission electron microscopy (TEM). The results show that δ-ZrH1.6 and ε-ZrH1.8 hydrides are found to precipitate successively with the increase of hydrogen absorption. For the δ-ZrH1.6 hydrides, they are mainly in the form of lath and precipitate in the orientation relationship of (0001)α//(001)δ and [2 0]α //[110]δ with the α-Zr matrix, while for the ε-ZrH1.8 hydrides, they are in acicular morphology and precipitate in the orientation relationship of ( 1 )δ //( 1 )ε and [ 12] δ//[011]ε with the δ-ZrH1.6 hydrides. The close-packed planes of these two hydrides are identified to be parallel. High-resolution TEM observation shows that there exists a great deal of distortion inside the crystal lattice of the δ-ZrH1.6 and ε-ZrH1.8 hydrides, indicating a large stress concentration produced during their precipitation.
The type, morphology and orientation relationship of the hydride precipitates in a hydrogen absorbed Zr-4 alloy have been studied by means of transmission electron microscopy (TEM). The results show that δ-ZrH1.6 and ε-ZrH1.8 hydrides are found to precipitate successively with the increase of hydrogen absorption. For the δ-ZrH1.6 hydrides, they are mainly in the form of lath and precipitate in the orientation relationship of (0001)α//(001)δ and [2 0]α //[110]δ with the α-Zr matrix, while for the ε-ZrH1.8 hydrides, they are in acicular morphology and precipitate in the orientation relationship of ( 1 )δ //( 1 )ε and [ 12] δ//[011]ε with the δ-ZrH1.6 hydrides. The close-packed planes of these two hydrides are identified to be parallel. High-resolution TEM observation shows that there exists a great deal of distortion inside the crystal lattice of the δ-ZrH1.6 and ε-ZrH1.8 hydrides, indicating a large stress concentration produced during their precipitation.
2016, 45(1):102-106.
Abstract:
Pure titanium TA2 alloy was tested by Split Hopkinson Pressure Bar (SHPB) under uniaxial dynamic compression conditions with different strain rates and room temperatures. Adiabatic shear bands were found in the specimens by metallographic after compression tests. As a result, we found strain and strain rate were so important for the initiation of shear bands. A critical strain must be arrived when the shear bands occur, and the larger strain rate, the smaller critical strain.
Pure titanium TA2 alloy was tested by Split Hopkinson Pressure Bar (SHPB) under uniaxial dynamic compression conditions with different strain rates and room temperatures. Adiabatic shear bands were found in the specimens by metallographic after compression tests. As a result, we found strain and strain rate were so important for the initiation of shear bands. A critical strain must be arrived when the shear bands occur, and the larger strain rate, the smaller critical strain.
2016, 45(1):107-111.
Abstract:
In order to understand the microstructure and thermophysical properties of Ag-In-Cd alloy in reactor under irradiation, the Ag-In-Cd-Sn alloy specimens were fabricated with the same composition for a given neutron irradiation condition. The microstructure, thermal diffusivity, specific heat, thermal conductivity and thermal expansion have been investigated by optical microscope (OM), scanning electron microscope (SEM), X ray diffractometer (XRD) and differential methods, differential scanning calorimeter, laser bombard method. The results show that the transformation induced by chemical modifications inside the single phase (FCC) alloy and, further, formation of two phases (FCC HCP). The second phase was Ag3In. The thermal conductivity, specific heat, thermal diffusivity and thermal expansion of Ag-In-Cd-Sn alloy increased as the temperature increased under the uniform Sn content between 25 to 600℃. However, the thermal conductivity and thermal diffusivity decreased obviously but the specific heat and thermal expansion increased appreciably as the Ag content decreased and the Sn content increased respectively.
In order to understand the microstructure and thermophysical properties of Ag-In-Cd alloy in reactor under irradiation, the Ag-In-Cd-Sn alloy specimens were fabricated with the same composition for a given neutron irradiation condition. The microstructure, thermal diffusivity, specific heat, thermal conductivity and thermal expansion have been investigated by optical microscope (OM), scanning electron microscope (SEM), X ray diffractometer (XRD) and differential methods, differential scanning calorimeter, laser bombard method. The results show that the transformation induced by chemical modifications inside the single phase (FCC) alloy and, further, formation of two phases (FCC HCP). The second phase was Ag3In. The thermal conductivity, specific heat, thermal diffusivity and thermal expansion of Ag-In-Cd-Sn alloy increased as the temperature increased under the uniform Sn content between 25 to 600℃. However, the thermal conductivity and thermal diffusivity decreased obviously but the specific heat and thermal expansion increased appreciably as the Ag content decreased and the Sn content increased respectively.
2016, 45(1):112-116.
Abstract:
The isothermal section of the Mn-Zr-Si ternary system at 600℃ was investigated by using X-ray diffraction, scanning electron microscope and energy dispersive analysis. A new termary compound was discovered. This compound was found to be isostrutural to Fe4Si7Zr4 with tetralgonal structure and cell parameters of a = 1.3027 nm, c = 0.515 nm. A quite different conclusion was obstained for the Zr-Si binary system comparing to results in the literatures. No the evidence was found to support the existence of Zr3Si at 600℃, which was taken as a stable phase in the Zr-Si system. Moreover, XRD and SEM/EDS revealed that Zr5Si3 was a stable phase at 600℃. In addition, MnSi2Zr and MnSiZr were confirmed at 600℃ while Mn4Si6Zr3 is not found in the present work.
The isothermal section of the Mn-Zr-Si ternary system at 600℃ was investigated by using X-ray diffraction, scanning electron microscope and energy dispersive analysis. A new termary compound was discovered. This compound was found to be isostrutural to Fe4Si7Zr4 with tetralgonal structure and cell parameters of a = 1.3027 nm, c = 0.515 nm. A quite different conclusion was obstained for the Zr-Si binary system comparing to results in the literatures. No the evidence was found to support the existence of Zr3Si at 600℃, which was taken as a stable phase in the Zr-Si system. Moreover, XRD and SEM/EDS revealed that Zr5Si3 was a stable phase at 600℃. In addition, MnSi2Zr and MnSiZr were confirmed at 600℃ while Mn4Si6Zr3 is not found in the present work.
2016, 45(1):117-121.
Abstract:
Adopting differential scanning calorimetry and copper-mould spray-casting methods, the near-equilibrium and sub-rapid solidification of K424 superalloy were fabricated with a wide range of cooling rate between 0.17 K/s and 100 K/s. Using OM, SEM and EDS, the evolutions of primary γ phase, precipitated γ′ phase, MC carbides and eutectic microstructure were described as a function of cooling rate. It is shown that γ phase is refined with increasing cooling rate, where the secondary dendrite spacing decreases from 84 μm for 0.17 K/s to that of 5 μm for 100 K/s. Moreover, the average size of precipitated γ′ phase decreases because of the shortened time for transformation. Precipitation process occurs once again as for heating the formed supersaturated solid solution during sub-rapid solidification. Both the refinement of γ phase and solute trapping decrease the extent of solute segregation, which leads to the reduction of the sizes of γ+γ′ eutectic and carbides.
Adopting differential scanning calorimetry and copper-mould spray-casting methods, the near-equilibrium and sub-rapid solidification of K424 superalloy were fabricated with a wide range of cooling rate between 0.17 K/s and 100 K/s. Using OM, SEM and EDS, the evolutions of primary γ phase, precipitated γ′ phase, MC carbides and eutectic microstructure were described as a function of cooling rate. It is shown that γ phase is refined with increasing cooling rate, where the secondary dendrite spacing decreases from 84 μm for 0.17 K/s to that of 5 μm for 100 K/s. Moreover, the average size of precipitated γ′ phase decreases because of the shortened time for transformation. Precipitation process occurs once again as for heating the formed supersaturated solid solution during sub-rapid solidification. Both the refinement of γ phase and solute trapping decrease the extent of solute segregation, which leads to the reduction of the sizes of γ+γ′ eutectic and carbides.
2016, 45(1):122-126.
Abstract:
The failure behavior and inducement mechanism of tungsten alloy fragments penetrating low carbon steel at high projectile velocities are investigated. The physical forms of 93W and 95W fragments after penetrating the low-carbon steel target at the velocities that higher than 1500m/s were obtained by using ballistic gun experiments. Using Scanning Electron Microscope (SEM) analyze damaged tungsten alloy fragments after the penetration, the result shows that, for low-carbon steel plate, when the penetration velocity of the tungsten alloy fragment is higher than 1500m/s, 93W tungsten particle is dimple-type transgranular fracture, 95W tungsten particle is quasi-cleavage transgranular fracture; Both 93W and 95W fragments were melted partially, the 50μm tungsten particles melted and condensed as less than 10μm spherical particles and arranged tightly. The macro phenomenon is the penetration of the whole damaged particles.
The failure behavior and inducement mechanism of tungsten alloy fragments penetrating low carbon steel at high projectile velocities are investigated. The physical forms of 93W and 95W fragments after penetrating the low-carbon steel target at the velocities that higher than 1500m/s were obtained by using ballistic gun experiments. Using Scanning Electron Microscope (SEM) analyze damaged tungsten alloy fragments after the penetration, the result shows that, for low-carbon steel plate, when the penetration velocity of the tungsten alloy fragment is higher than 1500m/s, 93W tungsten particle is dimple-type transgranular fracture, 95W tungsten particle is quasi-cleavage transgranular fracture; Both 93W and 95W fragments were melted partially, the 50μm tungsten particles melted and condensed as less than 10μm spherical particles and arranged tightly. The macro phenomenon is the penetration of the whole damaged particles.
2016, 45(1):127-131.
Abstract:
A new method of preparing Mg-Li alloys by vacuum carbothemic reduction is proposed. The thermodynamics of the reduction reactions were analyzed and the equations of the reduction reactions, the Gibbs free energy and critical temperature of reactions also have been studied. The results show that vacuum carbothermic reduction producing Mg-Li alloys had the thermodynamics feasibility. Under the condition of the other factors unchanged, with the increase of vacuum degree and reaction temperature, the Gibbs free energy of reduction reaction reduced. Under the same vacuum degree condition, the critical temperature of vacuum carbothermic reduction producing Mg-Li alloys was lower than producing metallic Mg or metallic Li, and reaction was more easily. When the vacuum degree was 10Pa and the relative proportion of Li2O was 0.1, the critical temperature of vacuum carbothermic reduction producing Mg-Li alloys was 1345K. Under the reaction temperature (about 1473K) and vacuum degree (about 13.3Pa) of conventional Pidgeon process(producing metallic magnesium by vacuum silicothermic reduction) conditions, no matter what the relative proportions of magnesium oxide and lithium oxide in the hybrid system, vacuum carbothermic reduction producing Mg-Li alloys had the thermodynamics feasibility.
A new method of preparing Mg-Li alloys by vacuum carbothemic reduction is proposed. The thermodynamics of the reduction reactions were analyzed and the equations of the reduction reactions, the Gibbs free energy and critical temperature of reactions also have been studied. The results show that vacuum carbothermic reduction producing Mg-Li alloys had the thermodynamics feasibility. Under the condition of the other factors unchanged, with the increase of vacuum degree and reaction temperature, the Gibbs free energy of reduction reaction reduced. Under the same vacuum degree condition, the critical temperature of vacuum carbothermic reduction producing Mg-Li alloys was lower than producing metallic Mg or metallic Li, and reaction was more easily. When the vacuum degree was 10Pa and the relative proportion of Li2O was 0.1, the critical temperature of vacuum carbothermic reduction producing Mg-Li alloys was 1345K. Under the reaction temperature (about 1473K) and vacuum degree (about 13.3Pa) of conventional Pidgeon process(producing metallic magnesium by vacuum silicothermic reduction) conditions, no matter what the relative proportions of magnesium oxide and lithium oxide in the hybrid system, vacuum carbothermic reduction producing Mg-Li alloys had the thermodynamics feasibility.
2016, 45(1):132-136.
Abstract:
Three kinds of alloys were designed by making the niobium equivalent to eight approximately, compositions of alloys are Ti-45Al-8Nb-0.2B，Ti-45Al-7Nb-0.1Hf-0.1Y-0.2B，Ti-45Al-4Nb-0.5Hf-0.1Y-0.2B，(at.%). The interrupted oxidation behaviors of alloys at 900℃ in static air were studied. The results showed that combined addition of Hf and Y has been enhanced adherence between the oxide film and the substrate; Ti-45Al-4Nb-0.4Hf-0.1Y-0.2B alloy with the low Nb/Hf ratio has lower oxidation weighting and good oxidation resistance, Ti-45Al-7Nb-0.1Hf-0.1Y-0.2B alloy with the high Nb/Hf ratio has higher oxidation weighting and poor oxidation resistance. Oxidized samples were examined by scanning electron microscopy ( SEM ), energy dispersive x-ray analysis ( EDX ) and x-ray diffraction analysis( XRD), it was found that combined addition Hf and Y have been promoted the whisker growth formation of Al2O3 oxide scale, which improved adherence of the oxide film; a large number of continuous and compact Al2O3 oxide scale has found in the alloys with low Nb/Hf ratio, that has been improved oxidation resistance of alloy; in the alloy with high Nb/Hf ratio external oxidation resulted in higher oxidation weighting and poor oxidation resis-tance.
Three kinds of alloys were designed by making the niobium equivalent to eight approximately, compositions of alloys are Ti-45Al-8Nb-0.2B，Ti-45Al-7Nb-0.1Hf-0.1Y-0.2B，Ti-45Al-4Nb-0.5Hf-0.1Y-0.2B，(at.%). The interrupted oxidation behaviors of alloys at 900℃ in static air were studied. The results showed that combined addition of Hf and Y has been enhanced adherence between the oxide film and the substrate; Ti-45Al-4Nb-0.4Hf-0.1Y-0.2B alloy with the low Nb/Hf ratio has lower oxidation weighting and good oxidation resistance, Ti-45Al-7Nb-0.1Hf-0.1Y-0.2B alloy with the high Nb/Hf ratio has higher oxidation weighting and poor oxidation resistance. Oxidized samples were examined by scanning electron microscopy ( SEM ), energy dispersive x-ray analysis ( EDX ) and x-ray diffraction analysis( XRD), it was found that combined addition Hf and Y have been promoted the whisker growth formation of Al2O3 oxide scale, which improved adherence of the oxide film; a large number of continuous and compact Al2O3 oxide scale has found in the alloys with low Nb/Hf ratio, that has been improved oxidation resistance of alloy; in the alloy with high Nb/Hf ratio external oxidation resulted in higher oxidation weighting and poor oxidation resis-tance.
2016, 45(1):137-140.
Abstract:
The beta-stabilizing effects of the 3d transition metals in Ti were investigated by the first principles method. Especially, the beta-stabilizing effects of the group VIIB and group VIII metals Mn, Fe, Co and Ni in Ti were explored. The calculated results showed that Mn, Fe and Co have stronger beta-stabilizing effects than Cr and Ni in Ti, though all have the same Pauling valences. This result can be understood by the chemical bonding analysis, when the atom-size factor is proven to account little. Based on the calculated results, the valences of Mn, Fe and Co were suggested to be 6.5, 6.6 and 6.4 in the design of beta-type Ti alloy, instead of the frequently-used Pauling valence.
The beta-stabilizing effects of the 3d transition metals in Ti were investigated by the first principles method. Especially, the beta-stabilizing effects of the group VIIB and group VIII metals Mn, Fe, Co and Ni in Ti were explored. The calculated results showed that Mn, Fe and Co have stronger beta-stabilizing effects than Cr and Ni in Ti, though all have the same Pauling valences. This result can be understood by the chemical bonding analysis, when the atom-size factor is proven to account little. Based on the calculated results, the valences of Mn, Fe and Co were suggested to be 6.5, 6.6 and 6.4 in the design of beta-type Ti alloy, instead of the frequently-used Pauling valence.
2016, 45(1):141-144.
Abstract:
Copper-mold suction casting was employed for the Cu40Zr44Ti8Al8 bulk metallic glasses (BMGs) preparation. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were used to analyze the microstructure evlution and crystallization kinetics of the samples. Results show that Al3Zr and Cu10Zr7 precipetate from the amorphous matrix successively. The activation enevey of the first crystallization peak calcultaiton by the Kissinger and Ozawa method are 315.69 kJ/mol and 312.65 kJ/mol, so the BMGs are highly thermal stable. Crystallization process of the BMGs shows obvious kinetic effect. The dependence of the characteristic temperatures on the heating rate follows Lasocka equation. But crystallization mechanism of the BMGs hardly shows any kinetic effect and has nothing to do with heating rate. Parameters fitted by the GM medol under the heating rate of 30 K/min change form λi=5.2,n=3.4 to λi=2.5,n=4, indicating that the BMGs experienced an increasing nucleation and growth rates in the primary crystallization process.
Copper-mold suction casting was employed for the Cu40Zr44Ti8Al8 bulk metallic glasses (BMGs) preparation. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were used to analyze the microstructure evlution and crystallization kinetics of the samples. Results show that Al3Zr and Cu10Zr7 precipetate from the amorphous matrix successively. The activation enevey of the first crystallization peak calcultaiton by the Kissinger and Ozawa method are 315.69 kJ/mol and 312.65 kJ/mol, so the BMGs are highly thermal stable. Crystallization process of the BMGs shows obvious kinetic effect. The dependence of the characteristic temperatures on the heating rate follows Lasocka equation. But crystallization mechanism of the BMGs hardly shows any kinetic effect and has nothing to do with heating rate. Parameters fitted by the GM medol under the heating rate of 30 K/min change form λi=5.2,n=3.4 to λi=2.5,n=4, indicating that the BMGs experienced an increasing nucleation and growth rates in the primary crystallization process.
30 Effect of Ti addition on the microstructure and wear resistance of AlFeCrCoCuTiX high-entropy alloys
2016, 45(1):145-151.
Abstract:
The microstructure of AlFeCrCoCuTiX (x=0,1) high-entrophy alloys fabricated by an arc remelter with as-cast structures and 800℃ tempering treated structure were investigated by XRD,SEM,EDS and DSC. The alloys wear resistance also be tested. The result show that the AlFeCrCoCu high-entrophy alloy can posses face-centered cubic (FCC) and body-centered cubic (BCC), and with the addition of titanium, the AlFeCrCoCuTi high-entrophy alloy was composed of primary dendrite phase ( The β phase rich in Al、Co、Ti and the α phase rich in Fe、Cr eutectic structure) , interdendrite phase rich in Cu and the precipitated phase that rich in Cr2Ti,Fe2Ti intermetallic compounds. With the addition of titanium，The precipitation intermetallic compound reinforced the metal，and the alloys hardness was improved. The alloys exhibits a superior resistance to temperature and softening property. The alloy was adhesive wear behaviors, the addition of Ti, due to the effect of precipitation strengthening of the precipitated phase, the alloys wear resistance is improved. And the 800 ℃ tempering alloy wear-resisting performance is more better than that of the as-cast alloy. The main reason is that with the increase of friction time, the 800 ℃ tempering alloy generateed a layer of oxide on the surface and attached to the friction surface, improve the wear resistance of the alloy.
The microstructure of AlFeCrCoCuTiX (x=0,1) high-entrophy alloys fabricated by an arc remelter with as-cast structures and 800℃ tempering treated structure were investigated by XRD,SEM,EDS and DSC. The alloys wear resistance also be tested. The result show that the AlFeCrCoCu high-entrophy alloy can posses face-centered cubic (FCC) and body-centered cubic (BCC), and with the addition of titanium, the AlFeCrCoCuTi high-entrophy alloy was composed of primary dendrite phase ( The β phase rich in Al、Co、Ti and the α phase rich in Fe、Cr eutectic structure) , interdendrite phase rich in Cu and the precipitated phase that rich in Cr2Ti,Fe2Ti intermetallic compounds. With the addition of titanium，The precipitation intermetallic compound reinforced the metal，and the alloys hardness was improved. The alloys exhibits a superior resistance to temperature and softening property. The alloy was adhesive wear behaviors, the addition of Ti, due to the effect of precipitation strengthening of the precipitated phase, the alloys wear resistance is improved. And the 800 ℃ tempering alloy wear-resisting performance is more better than that of the as-cast alloy. The main reason is that with the increase of friction time, the 800 ℃ tempering alloy generateed a layer of oxide on the surface and attached to the friction surface, improve the wear resistance of the alloy.
31 Study on Temperature-changed Rolling Process and the Flow Stress of As-cast AZ31B Magnesium Alloy
2016, 45(1):152-158.
Abstract:
Compression tests were done at temperature ranging from 250 to 450℃,strain-rate from 0.005 to 5 s-1. The rolling test, numerical simulation and damage analysis were conducted. The thermal processing diagram was calculated by the method of dynamic material model . The material flow stress model was established by parameter method of Zener-Hollomon. Combined with the principle of heat transfer and rolling theory, the rheological stress model of hot rolling process was established. The results showed that: The model in reasonable temperature range to solve, effectively improve the prediction accuracy. The main heat transfer mechanism in forward slip area and backward slip area was different and the rolling force was mainly distributed in backward slip area, this area was the key research area of edge crack. In the rolling process, Normalized C-L damage value was maximum on sheet edge. The lower the deformation temperature and the more pass reduction, the greater the value of damage, which was consistent with the outcome of the rolling experiment. Under different rolling conditions, the results of the model solution were consistent with the numerical simulation of hot rolling process.
Compression tests were done at temperature ranging from 250 to 450℃,strain-rate from 0.005 to 5 s-1. The rolling test, numerical simulation and damage analysis were conducted. The thermal processing diagram was calculated by the method of dynamic material model . The material flow stress model was established by parameter method of Zener-Hollomon. Combined with the principle of heat transfer and rolling theory, the rheological stress model of hot rolling process was established. The results showed that: The model in reasonable temperature range to solve, effectively improve the prediction accuracy. The main heat transfer mechanism in forward slip area and backward slip area was different and the rolling force was mainly distributed in backward slip area, this area was the key research area of edge crack. In the rolling process, Normalized C-L damage value was maximum on sheet edge. The lower the deformation temperature and the more pass reduction, the greater the value of damage, which was consistent with the outcome of the rolling experiment. Under different rolling conditions, the results of the model solution were consistent with the numerical simulation of hot rolling process.
2016, 45(1):159-164.
Abstract:
The quality of electro-less Ni-P plating is dependent on the process of pretreatment. In this paper, phosphating pretreatment was preformed for electro-less Ni-P plating on Zr-8.8Al alloy. The effect of phosphating process on the microstructure, microhardness and corrosion resistance in 3.5 wt% NaCl solution of electro-less Ni-P plating was investigated. The results show that the phosphating film obtained at 45℃ for 2min was uniform and even. The electro-less Ni-P plating has amorphous cellular structure and was about 25μm thickness. Compared with that of nonplated alloy, the microhardness of electroless Ni-P plating after phosphating pretreatment was improved by 60 percent. The corrosion potential of electro-less Ni-P plating after phosphating pretreatment in 3.5 wt% NaCl solution shift positively. The plating after corrosion is still complete, which shows that the corrosion resistance of electroless Ni-P plating after phosphating pretreatment is excellent.
The quality of electro-less Ni-P plating is dependent on the process of pretreatment. In this paper, phosphating pretreatment was preformed for electro-less Ni-P plating on Zr-8.8Al alloy. The effect of phosphating process on the microstructure, microhardness and corrosion resistance in 3.5 wt% NaCl solution of electro-less Ni-P plating was investigated. The results show that the phosphating film obtained at 45℃ for 2min was uniform and even. The electro-less Ni-P plating has amorphous cellular structure and was about 25μm thickness. Compared with that of nonplated alloy, the microhardness of electroless Ni-P plating after phosphating pretreatment was improved by 60 percent. The corrosion potential of electro-less Ni-P plating after phosphating pretreatment in 3.5 wt% NaCl solution shift positively. The plating after corrosion is still complete, which shows that the corrosion resistance of electroless Ni-P plating after phosphating pretreatment is excellent.
2016, 45(1):165-170.
Abstract:
Al-5.3 wt% Cu composite reinforced with 3.0 wt% h-BN with nearly full desification was fabricated by the process of liquid-phase forging. The powder morphology and comparative structural characteristics were analyzed using X-ray diffraction, scanning and transmission electron microscopy, and the composite hardness was measured by Brinell tester. Special attention was paid to the effects of the technique on the densification and the interface bonding of as-forged composites. These revealed the composite densification can be promoted effectively with plenty of embedded liquid phase under pressure. The composites fabricated using aluminium powder with different granularity showed different grain characteristics, and in situ recrystallization occurred inside the original grains with 35 μm aluminium powder. Moreover, a good interface consisted of Al/Al2O3/BN was apparent in the composite. Compared with the basis alloy, the composite hardness was increased nearly by 15%, and the composite with 2 μm aluminium powder showed the better performance.
Al-5.3 wt% Cu composite reinforced with 3.0 wt% h-BN with nearly full desification was fabricated by the process of liquid-phase forging. The powder morphology and comparative structural characteristics were analyzed using X-ray diffraction, scanning and transmission electron microscopy, and the composite hardness was measured by Brinell tester. Special attention was paid to the effects of the technique on the densification and the interface bonding of as-forged composites. These revealed the composite densification can be promoted effectively with plenty of embedded liquid phase under pressure. The composites fabricated using aluminium powder with different granularity showed different grain characteristics, and in situ recrystallization occurred inside the original grains with 35 μm aluminium powder. Moreover, a good interface consisted of Al/Al2O3/BN was apparent in the composite. Compared with the basis alloy, the composite hardness was increased nearly by 15%, and the composite with 2 μm aluminium powder showed the better performance.
2016, 45(1):171-176.
Abstract:
A non-cyanide sulfite bath pulse electroplating process for Au-Pd-Cu alloy was investigated. Thinking about the coating’s surface morphology and the plating’s deposition rate, the optimized electroplating parameters were found as follows: current density 0.25A/dm2, duty ratio 10%, pulse frequency 900Hz, temperature 60℃. Tra-depth microscope was used to observe coating’s surface morphology, and X-ray diffraction was used to analyze the phase components. Meanwhile, the coating’s binding force was tested by means of thermal shock test and root bend test.Furthermore, the coating’s hardness was meatured by Vickers. The results showed that there were only Au, Pd and Cu in the coating without any impurity elements and the coating had fine and uniform grains, with high hardness, excellent adhesion, low porosity, good smoothness and free of cracks.
A non-cyanide sulfite bath pulse electroplating process for Au-Pd-Cu alloy was investigated. Thinking about the coating’s surface morphology and the plating’s deposition rate, the optimized electroplating parameters were found as follows: current density 0.25A/dm2, duty ratio 10%, pulse frequency 900Hz, temperature 60℃. Tra-depth microscope was used to observe coating’s surface morphology, and X-ray diffraction was used to analyze the phase components. Meanwhile, the coating’s binding force was tested by means of thermal shock test and root bend test.Furthermore, the coating’s hardness was meatured by Vickers. The results showed that there were only Au, Pd and Cu in the coating without any impurity elements and the coating had fine and uniform grains, with high hardness, excellent adhesion, low porosity, good smoothness and free of cracks.
2016, 45(1):177-181.
Abstract:
In this work the effect of heat treatment on microstructure of Ti-48Al-4Cr(at.%) alloy rapidly solidified at the wheel speed of 10m/s were experimentally investigated by using the single roller melt-spinning technique. The results indicate that after rapid solidification, the microstructures mainly consist of equiaxed γ phase, few volume fraction of α2, B2 phase particles and lamellar structures exists in the γ phase matrix. After heat treament at 723℃/1h, α2 particles becomes unstable. Annealing at 932℃ for 1h, the α2 plate in lamallar strucctures becomes unstable. The α2 plate in the lamellar structures is subdivided into rod-shaped α2 phase and α2 particles. Annealing at 995℃/1h, large volume fraction of lamellar structures dissolved, however, rod shaped α2 phase still exists. B2 phase is being precipatated at the grain boundary. This research has provided the basis of further studying on the microstructures and phase transformation of rapidly solidified Ti-Al intermetallics and enriched the theory of rapid solidification.
In this work the effect of heat treatment on microstructure of Ti-48Al-4Cr(at.%) alloy rapidly solidified at the wheel speed of 10m/s were experimentally investigated by using the single roller melt-spinning technique. The results indicate that after rapid solidification, the microstructures mainly consist of equiaxed γ phase, few volume fraction of α2, B2 phase particles and lamellar structures exists in the γ phase matrix. After heat treament at 723℃/1h, α2 particles becomes unstable. Annealing at 932℃ for 1h, the α2 plate in lamallar strucctures becomes unstable. The α2 plate in the lamellar structures is subdivided into rod-shaped α2 phase and α2 particles. Annealing at 995℃/1h, large volume fraction of lamellar structures dissolved, however, rod shaped α2 phase still exists. B2 phase is being precipatated at the grain boundary. This research has provided the basis of further studying on the microstructures and phase transformation of rapidly solidified Ti-Al intermetallics and enriched the theory of rapid solidification.
2016, 45(1):182-186.
Abstract:
In the present research, W particles were coated using Ni electroless plating technique, and the Ni coated W powders were mixed uniformly with copper powders. 65W-25Cu-10Ni alloy with low W-W contiguity was successfully prepared by SPS method using the composite powders, and the quasistatic mechanical properties were studied. The results show that, after the Ni electroless plating process, Ni is uniformly distributed on the surface of W particles, and the integrating force is strong. The 65W-25Cu-10Ni alloy prepared by SPS method is uniform and dense in microstructure. Compared with 65W-35Cu alloy, 65W-25Cu-10Ni alloy exhibits higher strength and better ductility under quasistatic compression condition, and exhibits higher strength under quasistatic tensile condition, but the ductility under quasistatic tensile condition is not obviously improved. The analysis of the failure mechanism shows that, compared with 65W-35Cu alloy, W-W contiguity is evidently decreased in the 65W-25Cu-10Ni alloy, the matrix is replaced by Cu0.81Ni0.19 solid solution, and metallurgical bonding is formed between W and the matrix, all these above are benefit to increase the strength of 65W-25Cu-10Ni alloy. Meanwhile, the decrease of W-W contiguity and the increase of the interfacial strength are account for ductility increase of 65W-25Cu-10Ni alloy under quasistatic compression condition.
In the present research, W particles were coated using Ni electroless plating technique, and the Ni coated W powders were mixed uniformly with copper powders. 65W-25Cu-10Ni alloy with low W-W contiguity was successfully prepared by SPS method using the composite powders, and the quasistatic mechanical properties were studied. The results show that, after the Ni electroless plating process, Ni is uniformly distributed on the surface of W particles, and the integrating force is strong. The 65W-25Cu-10Ni alloy prepared by SPS method is uniform and dense in microstructure. Compared with 65W-35Cu alloy, 65W-25Cu-10Ni alloy exhibits higher strength and better ductility under quasistatic compression condition, and exhibits higher strength under quasistatic tensile condition, but the ductility under quasistatic tensile condition is not obviously improved. The analysis of the failure mechanism shows that, compared with 65W-35Cu alloy, W-W contiguity is evidently decreased in the 65W-25Cu-10Ni alloy, the matrix is replaced by Cu0.81Ni0.19 solid solution, and metallurgical bonding is formed between W and the matrix, all these above are benefit to increase the strength of 65W-25Cu-10Ni alloy. Meanwhile, the decrease of W-W contiguity and the increase of the interfacial strength are account for ductility increase of 65W-25Cu-10Ni alloy under quasistatic compression condition.
2016, 45(1):187-191.
Abstract:
Effects of borides and Ce-Rich mischmetal on the modification of Fe-rich intermetallics in secondary Al-Si alloys are studied in this paper.Microstructure morphology is observed by optical microscope(OM) and scanning electric microscope(SEM) , phases and compositions of phases are analyzed by X-ray diffraction(XRD)and energy dispersive X-ray (EDS) respectively.Phase transition temperature is measured by differential scanning calorimeter(DSC).It is indicated that borides can prompt transformation from needle-like β-Fe phase to primary α-Fe phase. And the size of primary α-Fe phase increases with the addition of borides. When the borides（KBF4）reaches 1.0%, Chinese script-type α-Fe phase begins to precipitate. Nucleation of Chinese script-type α-Fe phase are based on primary α-Fe phase. Ce-rich mischmetal can inhibit the growth of the primary α-Fe phase and the formation of Chinese script-type α-Fe phase.
Effects of borides and Ce-Rich mischmetal on the modification of Fe-rich intermetallics in secondary Al-Si alloys are studied in this paper.Microstructure morphology is observed by optical microscope(OM) and scanning electric microscope(SEM) , phases and compositions of phases are analyzed by X-ray diffraction(XRD)and energy dispersive X-ray (EDS) respectively.Phase transition temperature is measured by differential scanning calorimeter(DSC).It is indicated that borides can prompt transformation from needle-like β-Fe phase to primary α-Fe phase. And the size of primary α-Fe phase increases with the addition of borides. When the borides（KBF4）reaches 1.0%, Chinese script-type α-Fe phase begins to precipitate. Nucleation of Chinese script-type α-Fe phase are based on primary α-Fe phase. Ce-rich mischmetal can inhibit the growth of the primary α-Fe phase and the formation of Chinese script-type α-Fe phase.
2016, 45(1):192-196.
Abstract:
The effects of three different pretreatments on direct electroless nickel plating of magnesium alloys have been studied by several methods and techniques in order to obtain an environmentally friendly process of pretreatment. The reason of different pretreatments lead to different deposition rates on magnesium alloy was clarified by open circuit potential-time curves. The surface morphology, chemical composition and structure of these coatings were characterized using SEM, EDX and XRD. The results show that all of these nickel coatings have high P content (about 11%), similar surface morphology and structure. Polarization curves show that the corrosion resistance of the coating obtained by H3PO4+HNO3 pickling, K4P2O7 and NH4HF2 activation, respectively, was slightly stronger than the traditional chromic acid methods. The mechanical occlusive force between the coatings and the substrates was increased result from the etched deep cavities by the new pretreatment. Thus, the adherence between the coating and the substrate was improved ultimately.
The effects of three different pretreatments on direct electroless nickel plating of magnesium alloys have been studied by several methods and techniques in order to obtain an environmentally friendly process of pretreatment. The reason of different pretreatments lead to different deposition rates on magnesium alloy was clarified by open circuit potential-time curves. The surface morphology, chemical composition and structure of these coatings were characterized using SEM, EDX and XRD. The results show that all of these nickel coatings have high P content (about 11%), similar surface morphology and structure. Polarization curves show that the corrosion resistance of the coating obtained by H3PO4+HNO3 pickling, K4P2O7 and NH4HF2 activation, respectively, was slightly stronger than the traditional chromic acid methods. The mechanical occlusive force between the coatings and the substrates was increased result from the etched deep cavities by the new pretreatment. Thus, the adherence between the coating and the substrate was improved ultimately.
39 The study of the factors influence the mechanical properties of the Ta/W composite prepared by CVD
2016, 45(1):197-201.
Abstract:
The factors influence the mechanical properties of the Ta/W composite prepared by CVD was investigated by tensile test, optical microscopy(OM), scanning electron microscope(SEM ). The results show that the volume fraction of W, the time and temperature of heat treatment affect the mechanical properties of Ta/W composite observably. The composite with 13%W could afford perfect Tensile strength and ductility. The appropriate heat treatment is 1600×2h which could more powerful to enhance the mechanical properties of the Ta/W composite, and the essence of heat treatment influence the mechanical properties of the Ta/W composite was changed the size of composite grain and the thickness of diffusion layer.
The factors influence the mechanical properties of the Ta/W composite prepared by CVD was investigated by tensile test, optical microscopy(OM), scanning electron microscope(SEM ). The results show that the volume fraction of W, the time and temperature of heat treatment affect the mechanical properties of Ta/W composite observably. The composite with 13%W could afford perfect Tensile strength and ductility. The appropriate heat treatment is 1600×2h which could more powerful to enhance the mechanical properties of the Ta/W composite, and the essence of heat treatment influence the mechanical properties of the Ta/W composite was changed the size of composite grain and the thickness of diffusion layer.
2016, 45(1):202-206.
Abstract:
The effects of electric pulse heat treatment performed by SPS equipment on mechanical properties and the susceptibility to adiabatic shear bands of hot-rolled TC4 alloy were systematically studied. The results show that electric pulse heat treatment has little effect on the strength and ductility of TC4 at the static compression loading,and it also has little effect on the yielding strength at the dynamic compression loading, but the heat treatment has evidently effects on the susceptibility to adiabatic shear bands of the hot-rolled TC4.After electric pulse heat treatment at 900℃, TC4 alloy exhibits the highest adiabatic shear failure strain under the dynamic compression loading and the highest energy absorption of unit volume before fracture. Compared with the hot-rolled TC4 alloy, the adiabatic shear failure strain of heat -treated TC4 increases by 57% and the energy absorption of unit volume increases by 42%, indicating that the susceptibility to adiabatic shear bands of TC4 is significantly decreased. The microstructure analysis results show that electric pulse heat treatment has obviously influences on the prior β grain size and the detailed microstructure characteristics of TC4. After the heat treatment at 900℃, the oprior β grain size shows decreasing tendency, while the transformed β colony size shows increasing tendency, but the width of α plate shows no change.
The effects of electric pulse heat treatment performed by SPS equipment on mechanical properties and the susceptibility to adiabatic shear bands of hot-rolled TC4 alloy were systematically studied. The results show that electric pulse heat treatment has little effect on the strength and ductility of TC4 at the static compression loading,and it also has little effect on the yielding strength at the dynamic compression loading, but the heat treatment has evidently effects on the susceptibility to adiabatic shear bands of the hot-rolled TC4.After electric pulse heat treatment at 900℃, TC4 alloy exhibits the highest adiabatic shear failure strain under the dynamic compression loading and the highest energy absorption of unit volume before fracture. Compared with the hot-rolled TC4 alloy, the adiabatic shear failure strain of heat -treated TC4 increases by 57% and the energy absorption of unit volume increases by 42%, indicating that the susceptibility to adiabatic shear bands of TC4 is significantly decreased. The microstructure analysis results show that electric pulse heat treatment has obviously influences on the prior β grain size and the detailed microstructure characteristics of TC4. After the heat treatment at 900℃, the oprior β grain size shows decreasing tendency, while the transformed β colony size shows increasing tendency, but the width of α plate shows no change.
2016, 45(1):207-211.
Abstract:
Using solid-state method, a solid solution of LiFexMn1-xPO4 is generated as introducing iron into crystalline LiMnPO4 for electrochemical property improvement, and phenolic resin is added as the reducing agent and carbon sources. The Fe-to-Mn ratio that affects the electrochemical performance is also investigated, and the optimized ratio is determined. The synthesized samples have similar spherical morphology with particle size of 300~500nm, and are uniformly distributed. The results show that the electrochemical performance of LiFexMn1-xPO4 decreases continuously with increasing Mn content. The oxidation and reduction of Fe2 /Fe3 and Mn3 /Mn2 shift accordingly. The electrochemical performance by charge-discharge measurement shows: when x=0.5, the LiFe0.5Mn0.5PO4/C sample calcined at 600℃ for 10h has better performance, exhibits 147.3mAh/g at 0.1C, after 100 cycles, the discharge capacity of 115.2mAh/g becomes 112.7mAh/g, the capacity retention rate is 97.8%, illustrating well expressing its electrochemical performance at 2C. At high rate, like 10C, the capacity retention rate is 89.6% after 200 cycles.
Using solid-state method, a solid solution of LiFexMn1-xPO4 is generated as introducing iron into crystalline LiMnPO4 for electrochemical property improvement, and phenolic resin is added as the reducing agent and carbon sources. The Fe-to-Mn ratio that affects the electrochemical performance is also investigated, and the optimized ratio is determined. The synthesized samples have similar spherical morphology with particle size of 300~500nm, and are uniformly distributed. The results show that the electrochemical performance of LiFexMn1-xPO4 decreases continuously with increasing Mn content. The oxidation and reduction of Fe2 /Fe3 and Mn3 /Mn2 shift accordingly. The electrochemical performance by charge-discharge measurement shows: when x=0.5, the LiFe0.5Mn0.5PO4/C sample calcined at 600℃ for 10h has better performance, exhibits 147.3mAh/g at 0.1C, after 100 cycles, the discharge capacity of 115.2mAh/g becomes 112.7mAh/g, the capacity retention rate is 97.8%, illustrating well expressing its electrochemical performance at 2C. At high rate, like 10C, the capacity retention rate is 89.6% after 200 cycles.
2016, 45(1):212-216.
Abstract:
A series of Ti3AlC2/ZA27 composites have been successfully synthesized by mechanical alloying and pressureless sintering, which use the mixed powder of Ti3AlC2 and ZA27 as raw material. The effects of sintering temperature on composition, microstructure and mechanical property were investigated. The results showed that the relative density, Vickers hardness, bending strength and tensile strength were improved with increasing sintering temperature from 600?C to 870?C. Both the bending strength and tensile strength reached the maximum values of 592 MPa and 324MPa, respectively, at the temperature of 870?C. A weak reaction between Ti3AlC2 and ZA27 took palce at 870?C and led to the good bonding between the reinforcements and the matrix.
A series of Ti3AlC2/ZA27 composites have been successfully synthesized by mechanical alloying and pressureless sintering, which use the mixed powder of Ti3AlC2 and ZA27 as raw material. The effects of sintering temperature on composition, microstructure and mechanical property were investigated. The results showed that the relative density, Vickers hardness, bending strength and tensile strength were improved with increasing sintering temperature from 600?C to 870?C. Both the bending strength and tensile strength reached the maximum values of 592 MPa and 324MPa, respectively, at the temperature of 870?C. A weak reaction between Ti3AlC2 and ZA27 took palce at 870?C and led to the good bonding between the reinforcements and the matrix.
2016, 45(1):217-221.
Abstract:
In this study, highly stable SF-Au NPs were obtained using regenerated protein silk fibroin (SF) to stabilize gold nanoparticles (Au NPs), which were prepared through citrate reduction method. The stability of SF-Au NPs in buffer solutions with different pH conditions and different KCl concentrations were systematically investigated. Ultraviolet-visible spectroscopy (UV-Vis)、 transmission electron microscopy (TEM) and fourier transform infrared spectroscopy (FTIR) were employed to characterize the SF-Au NPs system. The results revealed that SF afforded the Au NPs with remarkable stability in the pH range of 3 to 11 and salt concentrations range of 50 mM to 1000 mM. Taking citrate and BSA stabilized gold nanoparticles as controls, the results indicated that steric hindrance may play an dominated role for the stability of SF-Au NPs. The proposed method was simpler, more efficient, and more cost effective than the conventional modification strategies for Au NPs; thus, SF–Au NPs can be potentially used in biomedical applications.
In this study, highly stable SF-Au NPs were obtained using regenerated protein silk fibroin (SF) to stabilize gold nanoparticles (Au NPs), which were prepared through citrate reduction method. The stability of SF-Au NPs in buffer solutions with different pH conditions and different KCl concentrations were systematically investigated. Ultraviolet-visible spectroscopy (UV-Vis)、 transmission electron microscopy (TEM) and fourier transform infrared spectroscopy (FTIR) were employed to characterize the SF-Au NPs system. The results revealed that SF afforded the Au NPs with remarkable stability in the pH range of 3 to 11 and salt concentrations range of 50 mM to 1000 mM. Taking citrate and BSA stabilized gold nanoparticles as controls, the results indicated that steric hindrance may play an dominated role for the stability of SF-Au NPs. The proposed method was simpler, more efficient, and more cost effective than the conventional modification strategies for Au NPs; thus, SF–Au NPs can be potentially used in biomedical applications.
2016, 45(1):222-226.
Abstract:
Under a temperature gradient of 300 K/cm, NiAl-1.5at%W eutectic samples were directionally solidified at the different drawing rates to analyze the effect of the drawing rates on the spacing and the size of W fiber phases. Moreover. the NiAl matrix was selectively etched by using a solution of HCl:H2O2 to prepare the tunsten fiber filaments with the equivalent diameter less than 500 nm. The research results show that the roundness of W fiber phase cross-section increases, the spacing and the equivalent diameter of W fiber phase both decreases, the ratio between them is in the range of 6.12 to 7.54, as increasing the drawing rate; and that the tungsten fibers obtained by selective dissolution have the diversiform three-dimensional morphologies, such as the thin strip, pearl string and lapping state, which have been found that those shapes have a relationship with the drawing rate.
Under a temperature gradient of 300 K/cm, NiAl-1.5at%W eutectic samples were directionally solidified at the different drawing rates to analyze the effect of the drawing rates on the spacing and the size of W fiber phases. Moreover. the NiAl matrix was selectively etched by using a solution of HCl:H2O2 to prepare the tunsten fiber filaments with the equivalent diameter less than 500 nm. The research results show that the roundness of W fiber phase cross-section increases, the spacing and the equivalent diameter of W fiber phase both decreases, the ratio between them is in the range of 6.12 to 7.54, as increasing the drawing rate; and that the tungsten fibers obtained by selective dissolution have the diversiform three-dimensional morphologies, such as the thin strip, pearl string and lapping state, which have been found that those shapes have a relationship with the drawing rate.
2016, 45(1):227-231.
Abstract:
Precision glass moulding is a replicative process that allows the production of high precision optical components from glass without grinding and polishing. In order to enhance the mould insert"s lifetime, protective coatings can be applied. In this study, Re, Ir monolayer and Re/Ir multilayer were deposited on the WC substrate by RF magnetron sputtering deposition system respectively. SEM, XRD, Nano Indenter and contour graph were used to characterize those protective coatings. The wetting angle at high temperature was adopted to evaluate the sticking situation between mould and D-ZK3 glass. The results demonstrated that the mechanical property and antistick performance of the mould after coating were both improved significantly. Re/Ir multilayer shows best antistik capability as well as mechanical property among these three types of coating. Meanwhile, the glass after wetting contact test with Re/Ir multilayer coating still have high transparency, which demonstrate that almost no interfacial reaction between glass gob and protective coating happened. This study displays a promising application of Re/Ir multilayer protective coating in glass moulding technology.
Precision glass moulding is a replicative process that allows the production of high precision optical components from glass without grinding and polishing. In order to enhance the mould insert"s lifetime, protective coatings can be applied. In this study, Re, Ir monolayer and Re/Ir multilayer were deposited on the WC substrate by RF magnetron sputtering deposition system respectively. SEM, XRD, Nano Indenter and contour graph were used to characterize those protective coatings. The wetting angle at high temperature was adopted to evaluate the sticking situation between mould and D-ZK3 glass. The results demonstrated that the mechanical property and antistick performance of the mould after coating were both improved significantly. Re/Ir multilayer shows best antistik capability as well as mechanical property among these three types of coating. Meanwhile, the glass after wetting contact test with Re/Ir multilayer coating still have high transparency, which demonstrate that almost no interfacial reaction between glass gob and protective coating happened. This study displays a promising application of Re/Ir multilayer protective coating in glass moulding technology.
2016, 45(1):232-235.
Abstract:
The Two-Step Sintering processed of AgSnO2 electric contact materials was studied. By the discussion for the effect of pre-sintering temperature, pre-sintering time and heating rate on the properties of AgSnO2 electric contact materials, we confirm the optimal pre-sintering temperature and pre-sintering time are 700℃ for 0.5h and the beat heating rate are 15K per minute before pre-sintering and 3K per minute after pre-sintering. By the comparative study on properties and microstructures of AgSnO2 electric contact materials prepared by two step sintering process and the traditional one-step sintering process, The results indicate that two-step sintering processed AgSnO2 electric contact material possesses improved sintering activity of AgSnO2 power and promotes its densification in the high-temperature-sintering stage which eventually improved the microstructure and performance of AgSnO2 electric contact materials.
The Two-Step Sintering processed of AgSnO2 electric contact materials was studied. By the discussion for the effect of pre-sintering temperature, pre-sintering time and heating rate on the properties of AgSnO2 electric contact materials, we confirm the optimal pre-sintering temperature and pre-sintering time are 700℃ for 0.5h and the beat heating rate are 15K per minute before pre-sintering and 3K per minute after pre-sintering. By the comparative study on properties and microstructures of AgSnO2 electric contact materials prepared by two step sintering process and the traditional one-step sintering process, The results indicate that two-step sintering processed AgSnO2 electric contact material possesses improved sintering activity of AgSnO2 power and promotes its densification in the high-temperature-sintering stage which eventually improved the microstructure and performance of AgSnO2 electric contact materials.
2016, 45(1):236-239.
Abstract:
Comparing the catalysts’ performance of palladium on carbon applied in the catalytic hydrogenation synthesis of indoxacarb intermediate, the effects of the carriers of catalysts and pretreatment were investigated in this paper. The results showed that nitric acid reflux treatment with ultrasound can effectively remove the ash of activated carbon and reduce the impact of those impurities on properties of catalysts. And in the catalytic reaction of indoxacarb intermediate, the Pd/C catalyst on activated carbon with large average pore size and high specific surface area exhibited better catalytic reactivity and selectivity.
Comparing the catalysts’ performance of palladium on carbon applied in the catalytic hydrogenation synthesis of indoxacarb intermediate, the effects of the carriers of catalysts and pretreatment were investigated in this paper. The results showed that nitric acid reflux treatment with ultrasound can effectively remove the ash of activated carbon and reduce the impact of those impurities on properties of catalysts. And in the catalytic reaction of indoxacarb intermediate, the Pd/C catalyst on activated carbon with large average pore size and high specific surface area exhibited better catalytic reactivity and selectivity.
2016, 45(1):240-243.
Abstract:
YAG transparent ceramic has been successfully fabricated by the vacuum sintering technique, with MgO as sintering aids. Thermal expansion curves of the green samples, optical transmittance spectrum, and surface microstructure of the prepared YAG ceramics were measured. The effect of MgO content on the microstructure, in-line transmittance of the samples was systematically studied. Transparent ceramics with high optical quality were obtained after vacuum sintered at 1780 ℃ for 6 h. Ceramics with MgO at the level above 0.1 wt.% were easy to densify, however, the second phase and pores appeared then, which did harm for the optical quality of the samples. 0.03 wt.% of MgO content benefited the sintering process most. Uniform grains with about 10μm were gained, with neither inner nor intergranular pores. The in-line transmittace of the ceramic at 1100 nm reached 82%.
YAG transparent ceramic has been successfully fabricated by the vacuum sintering technique, with MgO as sintering aids. Thermal expansion curves of the green samples, optical transmittance spectrum, and surface microstructure of the prepared YAG ceramics were measured. The effect of MgO content on the microstructure, in-line transmittance of the samples was systematically studied. Transparent ceramics with high optical quality were obtained after vacuum sintered at 1780 ℃ for 6 h. Ceramics with MgO at the level above 0.1 wt.% were easy to densify, however, the second phase and pores appeared then, which did harm for the optical quality of the samples. 0.03 wt.% of MgO content benefited the sintering process most. Uniform grains with about 10μm were gained, with neither inner nor intergranular pores. The in-line transmittace of the ceramic at 1100 nm reached 82%.
2016, 45(1):244-247.
Abstract:
La0.8Ce0.2(Fe11.5-xCox)Si1.5(x=0、0.3、0.5、0.7) ribbons were prepared by melt spinning. The phases and the magnetic property were characterized by X-ray diffraction and a vibrating sample magnetometer. The results show that Co and high quenched-speed help form the NaZn13-type phase. The substitution of Fe by Co can enhance the Curie temperature. The maximum magnetic entropy changes and the magnetic hysteresis decrease because of the substitution of Fe by Co. However, the magnetic hysteresis increases with quenched-speed rising. The quenched-speeds have little effect on maximum magnetic entropy changes and the Curie temperature.
La0.8Ce0.2(Fe11.5-xCox)Si1.5(x=0、0.3、0.5、0.7) ribbons were prepared by melt spinning. The phases and the magnetic property were characterized by X-ray diffraction and a vibrating sample magnetometer. The results show that Co and high quenched-speed help form the NaZn13-type phase. The substitution of Fe by Co can enhance the Curie temperature. The maximum magnetic entropy changes and the magnetic hysteresis decrease because of the substitution of Fe by Co. However, the magnetic hysteresis increases with quenched-speed rising. The quenched-speeds have little effect on maximum magnetic entropy changes and the Curie temperature.
2016, 45(1):248-253.
Abstract:
High strength and high conductivity Cu-Ag material is a kind of structural material with excellent physical properties and mechanical properties. In this paper, the developments of microstructure, strengthening mechanism, conductivity characteristics and Cu-Ag UFG materials by severe plastic deformation are introduced. Moreover, the possible future research directions are revealed.
High strength and high conductivity Cu-Ag material is a kind of structural material with excellent physical properties and mechanical properties. In this paper, the developments of microstructure, strengthening mechanism, conductivity characteristics and Cu-Ag UFG materials by severe plastic deformation are introduced. Moreover, the possible future research directions are revealed.
2016, 45(1):254-260.
Abstract:
Because of their excellent low temperature comprehensive properties, titanium alloys have gradually attracted considerable attention as important engineering materials at low temperatures. The application situation of titanium alloys at cryogenic temperatures in recent years is critically reviewed. The recent progress of deformation mechanisms of titanium alloys at low temperatures, including alpha titanium alloys, alpha/ beta double phases and beta titanium alloys, is then overviewed and concluded. Different influences of temperatures, alloy composition, deformation factors and microstructure on plastic deformation mechanisms of titanium alloys at cryogenic temperatures are summarized. Finally, the development trend of titanium alloys used at cryogenic temperatures is also discussed, in order to provide some valuable references to design and explore new titanium alloys with better comprehensive performance at cryogenic temperatures.
Because of their excellent low temperature comprehensive properties, titanium alloys have gradually attracted considerable attention as important engineering materials at low temperatures. The application situation of titanium alloys at cryogenic temperatures in recent years is critically reviewed. The recent progress of deformation mechanisms of titanium alloys at low temperatures, including alpha titanium alloys, alpha/ beta double phases and beta titanium alloys, is then overviewed and concluded. Different influences of temperatures, alloy composition, deformation factors and microstructure on plastic deformation mechanisms of titanium alloys at cryogenic temperatures are summarized. Finally, the development trend of titanium alloys used at cryogenic temperatures is also discussed, in order to provide some valuable references to design and explore new titanium alloys with better comprehensive performance at cryogenic temperatures.
