Volume 40,Issue 1,2011 Table of Contents
2011, 40(1):1-3.
Abstract:
In order to obtain excellent comprehensive mechanical properties, it is important to control the lamellar orientation of TiAl-based alloys by directional solidification technology. The control of the lamellar orientation is related closely with the primary phase during the directional solidification of TiAl-based alloys. The identification of the primary phase in directionally solidified TiAl-based alloys is insufficient only according to an isolated two-dimensional micrograph of the lamellar orientation. In this paper, we identified accurately the primary phase according to the quasi three-dimensional micrograph of the lamellar microstructure. The results indicate that the primary phase with various lamellar orientations is β phase during the directional solidification of Ti-50Al-5Nb alloy
In order to obtain excellent comprehensive mechanical properties, it is important to control the lamellar orientation of TiAl-based alloys by directional solidification technology. The control of the lamellar orientation is related closely with the primary phase during the directional solidification of TiAl-based alloys. The identification of the primary phase in directionally solidified TiAl-based alloys is insufficient only according to an isolated two-dimensional micrograph of the lamellar orientation. In this paper, we identified accurately the primary phase according to the quasi three-dimensional micrograph of the lamellar microstructure. The results indicate that the primary phase with various lamellar orientations is β phase during the directional solidification of Ti-50Al-5Nb alloy
2011, 40(1):4-8.
Abstract:
Pure tungsten with ultra-fine grains has been fabricated by two novel sintering methods, namely spark plasma sintering (SPS) and resistance sintering under ultra high pressure (RSUHP). The sample fabricated by SPS at 1600 oC has a high density of 97.8% and tightly bound grains. However, during the SPS process the W grains obviously grew. On the contrary, the sample fabricated by RSUHP has a low density and weakly bound fine grains. The disadvantages in both the techniques can be avoided via combining the two methods by fabricating green compacts using SPS at 1400 oC followed by consolidating that by RSUHP. By employing the combined method, the product with a relative density of more than 99% and an average grain size less than 400 nm can be obtained. The consolidating mechanism has been explored and the process has been optimized. In addition, any rare earth metal element additives to prevent grains from growing are not needed during the sintering process
Pure tungsten with ultra-fine grains has been fabricated by two novel sintering methods, namely spark plasma sintering (SPS) and resistance sintering under ultra high pressure (RSUHP). The sample fabricated by SPS at 1600 oC has a high density of 97.8% and tightly bound grains. However, during the SPS process the W grains obviously grew. On the contrary, the sample fabricated by RSUHP has a low density and weakly bound fine grains. The disadvantages in both the techniques can be avoided via combining the two methods by fabricating green compacts using SPS at 1400 oC followed by consolidating that by RSUHP. By employing the combined method, the product with a relative density of more than 99% and an average grain size less than 400 nm can be obtained. The consolidating mechanism has been explored and the process has been optimized. In addition, any rare earth metal element additives to prevent grains from growing are not needed during the sintering process
2011, 40(1):9-13.
Abstract:
Nickel based superalloy AM3 was prepared in high thermal gradient directional solidification apparatus with a seeding technique. Off-axial seeds were used in the experiments to investigate the nucleation and competitive growth of stray grains. The results indicate that the local undercooling caused by off-axial dendrites could result in stray grains formation. The grains with dendrite direction close to the heat flow direction can be overgrown by those grains which have larger deviation from the heat flow direction. The results reveal that the competitive growth of stray grains depends upon the synthetical effects of the comparative position of the dendrites, the angles between the dendritic direction of the grains and the heat flow direction, and the orientations of the crystal grains.
Nickel based superalloy AM3 was prepared in high thermal gradient directional solidification apparatus with a seeding technique. Off-axial seeds were used in the experiments to investigate the nucleation and competitive growth of stray grains. The results indicate that the local undercooling caused by off-axial dendrites could result in stray grains formation. The grains with dendrite direction close to the heat flow direction can be overgrown by those grains which have larger deviation from the heat flow direction. The results reveal that the competitive growth of stray grains depends upon the synthetical effects of the comparative position of the dendrites, the angles between the dendritic direction of the grains and the heat flow direction, and the orientations of the crystal grains.
2011, 40(1):14-17.
Abstract:
In order to better understand the mechanism of the reaction characteristics of Er3Ni hydrogenation, a self-built hydrogen-adsorption experimental apparatus was used to study the effects of particle size, reaction temperature and pressure on the induction time of Er3Ni hydrogenation reaction and the hydrogen adsorption capacity, based on which the hydrogenation characteristics of Er3Ni were then discussed. The results show that activation has a great effect on hydrogen absorption capacity of Er3Ni. The influence of particle size of Er3Ni is mainly on the induction time. Lower reaction temperature needs longer induction time of accumulating energy to overcome the energy barrier of hydrogenation. The value x in Er3NiHx is insensitive to the reaction equilibrium pressure. Hydrides Er3NiHx reaches equilibrium at an extremely low pressure, about 10 kPa
In order to better understand the mechanism of the reaction characteristics of Er3Ni hydrogenation, a self-built hydrogen-adsorption experimental apparatus was used to study the effects of particle size, reaction temperature and pressure on the induction time of Er3Ni hydrogenation reaction and the hydrogen adsorption capacity, based on which the hydrogenation characteristics of Er3Ni were then discussed. The results show that activation has a great effect on hydrogen absorption capacity of Er3Ni. The influence of particle size of Er3Ni is mainly on the induction time. Lower reaction temperature needs longer induction time of accumulating energy to overcome the energy barrier of hydrogenation. The value x in Er3NiHx is insensitive to the reaction equilibrium pressure. Hydrides Er3NiHx reaches equilibrium at an extremely low pressure, about 10 kPa
2011, 40(1):18-21.
Abstract:
The molecular dynamics method was used to simulate thermodynamic properties of three binary alloys: Pb40Au60, Pb80Au20 and Pb90Au10. The energy functions, including excess free energy, cohesive energy and formation energy, were calculated. Formation energy and excess free energy are all negative values, so Pb-Au alloys belong to negative system. The atomic interactions were analyzed in macroscopic and microcosmic views. The calculated formation energy can describe the deviation degree between the actual alloy and the ideal melt quantitatively
The molecular dynamics method was used to simulate thermodynamic properties of three binary alloys: Pb40Au60, Pb80Au20 and Pb90Au10. The energy functions, including excess free energy, cohesive energy and formation energy, were calculated. Formation energy and excess free energy are all negative values, so Pb-Au alloys belong to negative system. The atomic interactions were analyzed in macroscopic and microcosmic views. The calculated formation energy can describe the deviation degree between the actual alloy and the ideal melt quantitatively
2011, 40(1):22-27.
Abstract:
Hydroxyapatite coatings were fabricated on Ti substrates by laser cladding (LC) using mixed powders of CaCO3 and dicalcium phosphate dihydrate (DCPD, CaHPO4·2H2O). The effect of the mass ratio of CaCO3 to DCPD on phase and microstructure formation of the coatings was investigated. The reactions between CaCO3 and DCPD can produce high crystallized hydroxyapatite (HA, Ca5(PO4)3(OH)) in the coatings as well as tetracalcium phosphate (TTCP, Ca4P2O9), α-tricalcium phosphate (α-TCP, α-Ca3(PO4)2), β-tricalcium phosphate (β-TCP, β-Ca3(PO4)2) and Ca2P2O7. The Ca/P molar ratio (CMR) of the mixed powders (CMRP) has a great influence on the contents of the phases in the coating. HA can be produced in the coating only when the CMRP is higher than 1.54, and its content increases slowly as the CMRP increases. The coating contains only about 25wt% HA when CMRP reaches 2.00, and there exists large amount of TTCP in the coating. So a post heat treatment with furnace cooling is recommended to increase the amount of HA in the coating. All the coatings have porous structures because the reactions between the powders produce lots of gases during LC. The pore size in the coating fabricated by the powders with CMR equal to 2.00 is about 100-300 mm. CMRP also has a great influence on the bond strength, porosity and cracks of the coatings. Along with the increase of the CMRP, the bond strength and porosity decrease, whereas the number of cracks increases
Hydroxyapatite coatings were fabricated on Ti substrates by laser cladding (LC) using mixed powders of CaCO3 and dicalcium phosphate dihydrate (DCPD, CaHPO4·2H2O). The effect of the mass ratio of CaCO3 to DCPD on phase and microstructure formation of the coatings was investigated. The reactions between CaCO3 and DCPD can produce high crystallized hydroxyapatite (HA, Ca5(PO4)3(OH)) in the coatings as well as tetracalcium phosphate (TTCP, Ca4P2O9), α-tricalcium phosphate (α-TCP, α-Ca3(PO4)2), β-tricalcium phosphate (β-TCP, β-Ca3(PO4)2) and Ca2P2O7. The Ca/P molar ratio (CMR) of the mixed powders (CMRP) has a great influence on the contents of the phases in the coating. HA can be produced in the coating only when the CMRP is higher than 1.54, and its content increases slowly as the CMRP increases. The coating contains only about 25wt% HA when CMRP reaches 2.00, and there exists large amount of TTCP in the coating. So a post heat treatment with furnace cooling is recommended to increase the amount of HA in the coating. All the coatings have porous structures because the reactions between the powders produce lots of gases during LC. The pore size in the coating fabricated by the powders with CMR equal to 2.00 is about 100-300 mm. CMRP also has a great influence on the bond strength, porosity and cracks of the coatings. Along with the increase of the CMRP, the bond strength and porosity decrease, whereas the number of cracks increases
2011, 40(1):28-31.
Abstract:
Commercial pure titanium billets, grade 1 (TA1), were successfully processed by equal channel angular pressing (ECAP) for 8 passes via route BC at room temperature using a Φ=120° and ψ= 20° die. The as-processed Ti billets were smooth and free of any visible surface cracks. Special attention was paid on the microstructure evolution and mechanical properties of the ECAP samples at room temperature. The microstructure examination of the ECAP processed billets reveals that, with the pass of ECAP increasing, the initial and coarse equiaxed grains evolve into gradually the ultrafine grains with high-angle boundary composed of the subgrains and the dislocation cells, which are formed from the band structures, deformation twins and high density dislocations produced within initial several passes through the dislocations interacting and recombining. After the 8th ECAP pass, the original grains are refined to about 200 nm, and the yield strength and ultimate tensile strength is increased to 710 and 791 MPa from original 275 and 407 MPa, respectively. Meanwhile, a higher ductility of 19.0% elongation still is maintained
Commercial pure titanium billets, grade 1 (TA1), were successfully processed by equal channel angular pressing (ECAP) for 8 passes via route BC at room temperature using a Φ=120° and ψ= 20° die. The as-processed Ti billets were smooth and free of any visible surface cracks. Special attention was paid on the microstructure evolution and mechanical properties of the ECAP samples at room temperature. The microstructure examination of the ECAP processed billets reveals that, with the pass of ECAP increasing, the initial and coarse equiaxed grains evolve into gradually the ultrafine grains with high-angle boundary composed of the subgrains and the dislocation cells, which are formed from the band structures, deformation twins and high density dislocations produced within initial several passes through the dislocations interacting and recombining. After the 8th ECAP pass, the original grains are refined to about 200 nm, and the yield strength and ultimate tensile strength is increased to 710 and 791 MPa from original 275 and 407 MPa, respectively. Meanwhile, a higher ductility of 19.0% elongation still is maintained
2011, 40(1):32-35.
Abstract:
The hydrogenation/dehydrogenation processes of Zr0.9Ti0.1V2 hydrogen storage alloy were investigated by cyclic hydriding-dehydriding tests. Reversible hydrogen absorption properties were studied in three characteristic domains on P-C-T curves. Hydrogen contents is similar during each cyclic hydriding-dehydriding test including the hydrogen absorption plateau stage (0.5 H/A), the initial stage of the hydride formation (1-1.2 H/A) and the mid stage of the hydride formation (1.4 H/A). After 70 hydrogenation/dehydrogenation cycles, the regeneration hydrogen absorption capacities could reach to as large as 1.957 (H/A). The experimental Zr0.9Ti0.1V2 alloy exhibits excellent cyclic hydrogenation properties
The hydrogenation/dehydrogenation processes of Zr0.9Ti0.1V2 hydrogen storage alloy were investigated by cyclic hydriding-dehydriding tests. Reversible hydrogen absorption properties were studied in three characteristic domains on P-C-T curves. Hydrogen contents is similar during each cyclic hydriding-dehydriding test including the hydrogen absorption plateau stage (0.5 H/A), the initial stage of the hydride formation (1-1.2 H/A) and the mid stage of the hydride formation (1.4 H/A). After 70 hydrogenation/dehydrogenation cycles, the regeneration hydrogen absorption capacities could reach to as large as 1.957 (H/A). The experimental Zr0.9Ti0.1V2 alloy exhibits excellent cyclic hydrogenation properties
2011, 40(1):36-39.
Abstract:
TiFe and TiFe2 intermetallic compounds are formed at the interface of titanium alloy and steel because of diffusion and reaction, which influence the properties of the joints significantly. The valence electron structures of TiFe and TiFe2 were studied and their bond energies were calculated based on Yu’s empirical electron theory of solids and molecules (EET). The results show that their strongest bonds are Fe-Ti bonds and FeⅡ-FeⅡ bonds, respectively, and the energies of their strongest bonds are 14.77 and 26.96 kJ/mol, respectively. TiFe2 has stronger bond nets than TiFe, which results in its better hot stability. According to their valence electron structures, TiFe and TiFe2 put up eigen-brittleness
TiFe and TiFe2 intermetallic compounds are formed at the interface of titanium alloy and steel because of diffusion and reaction, which influence the properties of the joints significantly. The valence electron structures of TiFe and TiFe2 were studied and their bond energies were calculated based on Yu’s empirical electron theory of solids and molecules (EET). The results show that their strongest bonds are Fe-Ti bonds and FeⅡ-FeⅡ bonds, respectively, and the energies of their strongest bonds are 14.77 and 26.96 kJ/mol, respectively. TiFe2 has stronger bond nets than TiFe, which results in its better hot stability. According to their valence electron structures, TiFe and TiFe2 put up eigen-brittleness
2011, 40(1):40-44.
Abstract:
Ceramic oxide coatings were prepared on the Ti-6Al-2Zr-1Mo-3Nb alloy surface by micro-arc oxidation. The microstructure and phase composition of ceramic coatings were analyzed by means of scanning electron microscopy and X-ray diffraction, respectively. Bonding strength, insulating performance, the tribological properties and corrosion resistance of the coatings were also investigated. Results indicate that the oxide film is mainly composed of rutile TiO2 and anatase TiO2. The bonding strength between the Ti-6Al-2Zr-1Mo-3Nb substrate and the film is over 30 MPa. The ceramic coating shows good insulativity and excellent corrosion resistance. The wear mechanism of the micro-arc oxidation ceramic coating is characterized by slight abrasive wear and adhesive wear
Ceramic oxide coatings were prepared on the Ti-6Al-2Zr-1Mo-3Nb alloy surface by micro-arc oxidation. The microstructure and phase composition of ceramic coatings were analyzed by means of scanning electron microscopy and X-ray diffraction, respectively. Bonding strength, insulating performance, the tribological properties and corrosion resistance of the coatings were also investigated. Results indicate that the oxide film is mainly composed of rutile TiO2 and anatase TiO2. The bonding strength between the Ti-6Al-2Zr-1Mo-3Nb substrate and the film is over 30 MPa. The ceramic coating shows good insulativity and excellent corrosion resistance. The wear mechanism of the micro-arc oxidation ceramic coating is characterized by slight abrasive wear and adhesive wear
2011, 40(1):45-47.
Abstract:
The structural free-volume of the bulk amorphous Zr41Ti14Cu12.5Ni10Be22.5 alloy and the undercooled liquid range were investigated by X-ray diffraction (XRD) and positron annihilation techniques (PAT). The results show that the positron annihilation lifetime in the as-prepared Zr41Ti14Cu12.5Ni10Be22.5 is about 176 ps, indicating that the structural free-volume with a size larger than that of one lattice vacancy of pure Fe is available in the alloy. The positron annihilation lifetime decreases with increasing annealing time when the alloy is annealed at 400 oC in the undercooled liquid region, which reaches a value of 167 ps with annealing time of 300 min. The structure of the bulk amorphous Zr41Ti14Cu12.5Ni10Be22.5 alloy becomes more compact when annealed in the undercooled liquid region
The structural free-volume of the bulk amorphous Zr41Ti14Cu12.5Ni10Be22.5 alloy and the undercooled liquid range were investigated by X-ray diffraction (XRD) and positron annihilation techniques (PAT). The results show that the positron annihilation lifetime in the as-prepared Zr41Ti14Cu12.5Ni10Be22.5 is about 176 ps, indicating that the structural free-volume with a size larger than that of one lattice vacancy of pure Fe is available in the alloy. The positron annihilation lifetime decreases with increasing annealing time when the alloy is annealed at 400 oC in the undercooled liquid region, which reaches a value of 167 ps with annealing time of 300 min. The structure of the bulk amorphous Zr41Ti14Cu12.5Ni10Be22.5 alloy becomes more compact when annealed in the undercooled liquid region
2011, 40(1):48-51.
Abstract:
The non-active AgCu filler metal was used to join Si3N4 ceramics to TiAl-based alloys. The typical interfacial microstructure of the joints was determined as TiAl/Ti3Al+Ti(s,s)/AlCuTi/Ag(s,s)+AlCu2Ti/Ti5Si3+TiN/Si3N4 ceramics. During the brazing process, the active element Ti, which dissolves into the non-active AgCu liquid filler metal, involves in the wetting on the Si3N4 ceramic and reacts to the ceramic materials. With the increase of brazing temperature and holding time, the thickness of the TiN reaction layer close to the Si3N4 ceramic increases and AlCu2Ti compounds dispersed in the Ag-based solid solution gather greatly, which reduces the joining properties. The shear strength of the joints reaches a maximum of 124.6 MPa when the brazing temperature T = 860 oC and the holding time t=5 min. According of the thermodynamics and kinetics calculation, the activation energy Q and the growth coefficient KP of the TiN layer are 528.7 kJ/mol and 2.7×10-7 m/s1/2, respectively
The non-active AgCu filler metal was used to join Si3N4 ceramics to TiAl-based alloys. The typical interfacial microstructure of the joints was determined as TiAl/Ti3Al+Ti(s,s)/AlCuTi/Ag(s,s)+AlCu2Ti/Ti5Si3+TiN/Si3N4 ceramics. During the brazing process, the active element Ti, which dissolves into the non-active AgCu liquid filler metal, involves in the wetting on the Si3N4 ceramic and reacts to the ceramic materials. With the increase of brazing temperature and holding time, the thickness of the TiN reaction layer close to the Si3N4 ceramic increases and AlCu2Ti compounds dispersed in the Ag-based solid solution gather greatly, which reduces the joining properties. The shear strength of the joints reaches a maximum of 124.6 MPa when the brazing temperature T = 860 oC and the holding time t=5 min. According of the thermodynamics and kinetics calculation, the activation energy Q and the growth coefficient KP of the TiN layer are 528.7 kJ/mol and 2.7×10-7 m/s1/2, respectively
2011, 40(1):52-56.
Abstract:
Using the ternary microscopic phase-field model, the effect of Fe content on antisite defects NiAl and AlNi in two types of NiAlFe ternary alloys were simulated and calculated; one type is the NiAlFe alloy with Al content larger than 25%, and the other type is the NiAlFe alloy with Ni content larger than 75%. NiAl (AlNi) stands for the antisite defect which is caused by Ni(Al) atoms occupying Al(Ni) sites. The results show that, in a certain temperature range, with more Fe added, in NiAlFe alloys with Al content larger than 25% the AlNi concentration increases obviously, while the NiAl concentration increases slightly whose values are smaller than AlNi concentration; on the contrary, in NiAlFe alloys with Ni content larger than 75% the NiAl concentration increases obviously and its values are larger than AlNi concentration; at the same temperature, we made a comparison between the NiAlFe alloys with Al content larger than 25% and the NiAlFe alloys with Ni content larger than 75% to study the influence of Fe content on antisite defects in these two types of alloys, and found that AlNi concentration in the former alloys is more easier to be affected by Fe content than in the latter alloys, while NiAl concentration in the latter alloys is more easier to be affected by Fe content than in the former alloys. Besides, the concentrations of NiAl and AlNi change with timesteps gradually from an initial value to the equilibrium value; elevating the temperature causes the evolution process of antisite defects to turn slower and the equilibrium values become lager
Using the ternary microscopic phase-field model, the effect of Fe content on antisite defects NiAl and AlNi in two types of NiAlFe ternary alloys were simulated and calculated; one type is the NiAlFe alloy with Al content larger than 25%, and the other type is the NiAlFe alloy with Ni content larger than 75%. NiAl (AlNi) stands for the antisite defect which is caused by Ni(Al) atoms occupying Al(Ni) sites. The results show that, in a certain temperature range, with more Fe added, in NiAlFe alloys with Al content larger than 25% the AlNi concentration increases obviously, while the NiAl concentration increases slightly whose values are smaller than AlNi concentration; on the contrary, in NiAlFe alloys with Ni content larger than 75% the NiAl concentration increases obviously and its values are larger than AlNi concentration; at the same temperature, we made a comparison between the NiAlFe alloys with Al content larger than 25% and the NiAlFe alloys with Ni content larger than 75% to study the influence of Fe content on antisite defects in these two types of alloys, and found that AlNi concentration in the former alloys is more easier to be affected by Fe content than in the latter alloys, while NiAl concentration in the latter alloys is more easier to be affected by Fe content than in the former alloys. Besides, the concentrations of NiAl and AlNi change with timesteps gradually from an initial value to the equilibrium value; elevating the temperature causes the evolution process of antisite defects to turn slower and the equilibrium values become lager
2011, 40(1):57-62.
Abstract:
The influences of magnesium addition on the discharge performance and hydrogen evolution reaction behavior were studied via measuring discharge current, discharge potential, polarization curve and hydrogen evolution rate of lithium anodes in alkali aqueous solution. The results show that the hydrogen evolution rate is decreased by adding 0.07wt%Mg to lithium anodes. It is found that the current efficiency of lithium-magnesium alloy anodes is higher than that of lithium anodes, and the discharge current density of lithium-magnesium alloy anodes is a little lower than that of lithium anodes. The discharge potential of lithium-magnesium alloy anodes is a little more positive than that of lithium anodes when the discharge current density is high. The polarization curves show that the open circuit potential of Li-0.07wt%Mg anodes is a little more positive than that of lithium anodes. The micro-cell corrosion current density of Li-0.07wt%Mg anodes is near to that of lithium anodes. The analysis of X-ray diffraction shows that after discharge the surface film of the lithium-magnesium alloy anodes mainly consists of LiOH, LiOH·H2O and some Mg(OH)2. Scanning electron microscopy images show that the surface film of lithium-magnesium alloy anodes is less porous than that of lithium anodes after discharge, namely, the decrease of hydrogen evolution rate by magnesium addition is related to the integrity of the surface film enhanced by Mg(OH)2
The influences of magnesium addition on the discharge performance and hydrogen evolution reaction behavior were studied via measuring discharge current, discharge potential, polarization curve and hydrogen evolution rate of lithium anodes in alkali aqueous solution. The results show that the hydrogen evolution rate is decreased by adding 0.07wt%Mg to lithium anodes. It is found that the current efficiency of lithium-magnesium alloy anodes is higher than that of lithium anodes, and the discharge current density of lithium-magnesium alloy anodes is a little lower than that of lithium anodes. The discharge potential of lithium-magnesium alloy anodes is a little more positive than that of lithium anodes when the discharge current density is high. The polarization curves show that the open circuit potential of Li-0.07wt%Mg anodes is a little more positive than that of lithium anodes. The micro-cell corrosion current density of Li-0.07wt%Mg anodes is near to that of lithium anodes. The analysis of X-ray diffraction shows that after discharge the surface film of the lithium-magnesium alloy anodes mainly consists of LiOH, LiOH·H2O and some Mg(OH)2. Scanning electron microscopy images show that the surface film of lithium-magnesium alloy anodes is less porous than that of lithium anodes after discharge, namely, the decrease of hydrogen evolution rate by magnesium addition is related to the integrity of the surface film enhanced by Mg(OH)2
2011, 40(1):63-68.
Abstract:
In order to investigate the effects of creep temperatures on the precipitation of S’ phases of Al-Cu-Mg alloys, the creep properties were measured at 125, 150, 175 and 200 oC and the difference of microstructure between the grip and the fracture area was observed through transmission electron microscopy (TEM). The results show that the length and thickness of S’ phases in the fracture area is twice as many as the grip area in the alloy crept at 150 oC under the stress of 345 MPa for 96 h. Compared with their grip areas, the length of S’ phases in the fracture areas of the sample crept at 175 oC under the stress of 265 MPa for 100 h and the sample crept at 200 oC under the stress of 210 MPa for 115 h is increased apparently, while the thickness is decreased slightly
In order to investigate the effects of creep temperatures on the precipitation of S’ phases of Al-Cu-Mg alloys, the creep properties were measured at 125, 150, 175 and 200 oC and the difference of microstructure between the grip and the fracture area was observed through transmission electron microscopy (TEM). The results show that the length and thickness of S’ phases in the fracture area is twice as many as the grip area in the alloy crept at 150 oC under the stress of 345 MPa for 96 h. Compared with their grip areas, the length of S’ phases in the fracture areas of the sample crept at 175 oC under the stress of 265 MPa for 100 h and the sample crept at 200 oC under the stress of 210 MPa for 115 h is increased apparently, while the thickness is decreased slightly
2011, 40(1):69-73.
Abstract:
The cluster rules of alloy phase structure of some typical bulk metallic glass systems were studied. The fact that the clusters share atoms each other in different ways in the alloy phase was pointed out. After sharing there are two kinds of cluster linkages: the first is the phase composition which does not need glue atoms; the other is that glue atoms are required to form phase structure, i.e. termed cluster phases. The method provides a new idea for the structure of alloy phase. In the typical bulk metallic glass system Zr-Al-Ni, there are three cluster phases, AlNiZr-Fe2P, Al2NiZr6-InMg2 and Al5Ni3Zr2-Mn23Th6. The method to determine the clusters related with metallic glass formation based on alloy phase structure was also put forward, i.e. the clusters related with the metallic glasses are generally the isolated clusters from cluster phases, which is verified very well in Zr-Al-Ni system.
The cluster rules of alloy phase structure of some typical bulk metallic glass systems were studied. The fact that the clusters share atoms each other in different ways in the alloy phase was pointed out. After sharing there are two kinds of cluster linkages: the first is the phase composition which does not need glue atoms; the other is that glue atoms are required to form phase structure, i.e. termed cluster phases. The method provides a new idea for the structure of alloy phase. In the typical bulk metallic glass system Zr-Al-Ni, there are three cluster phases, AlNiZr-Fe2P, Al2NiZr6-InMg2 and Al5Ni3Zr2-Mn23Th6. The method to determine the clusters related with metallic glass formation based on alloy phase structure was also put forward, i.e. the clusters related with the metallic glasses are generally the isolated clusters from cluster phases, which is verified very well in Zr-Al-Ni system.
2011, 40(1):74-79.
Abstract:
Pore structural parameters of 2 kinds of alumina before and after modification were reported, and with the modified alumina as coating Pd-based catalysts were prepared. The results show that the modified Al2O3-02 has specific area of 134.691 m2·g-1 and pore structure of 0.5851 cm3·g-1 and 8.6877 nm. The obtained Pd-based catalyst TWC-02 has superior properties. After calcining the catalyst at 950 oC, Pd grains homogeneously disperse in the surface of modified Al2O3-02; even ≥1050 oC, the dispersity of Pd is still good. Alumina has the effect of structure promoter on Pd-based catalyst. The superiority of the structure character of Al2O3-02 is also proved by a light-off active test.
Pore structural parameters of 2 kinds of alumina before and after modification were reported, and with the modified alumina as coating Pd-based catalysts were prepared. The results show that the modified Al2O3-02 has specific area of 134.691 m2·g-1 and pore structure of 0.5851 cm3·g-1 and 8.6877 nm. The obtained Pd-based catalyst TWC-02 has superior properties. After calcining the catalyst at 950 oC, Pd grains homogeneously disperse in the surface of modified Al2O3-02; even ≥1050 oC, the dispersity of Pd is still good. Alumina has the effect of structure promoter on Pd-based catalyst. The superiority of the structure character of Al2O3-02 is also proved by a light-off active test.
2011, 40(1):80-84.
Abstract:
Using the pseudopotential plane-wave method of the density-functional theory (DEF), the interface energy, electron structure and contour of the charge density of the Pt(100)/ZrO2(100) interface model with the bridge O and bridge Zr in ZrO2(100) were investigated. Results show that the Pt(100)/ZrO2(100)-bridge O interface energy with bridge O is 1.978 J/m2, and the Pt(100)/ZrO2(100)-bridge Zr interface energy with bridge Zr is 10.035 J/m2, indicating that the energy of bridge O is lower than the energy of bridge Zr, i.e. the ZrO2(100) with bridge Zr is easy to combine with the Pt(100). By the electron structure and contour of the charge density, there is mainly electron transfer between Zr and O with the Pt(100)/ZrO2(100)-bridge O; however, there is electron transfer between Zr and O and between Pt and Zr with the Pt(100)/ZrO2(100)-bridge Zr; between Pt and Zr there is the 4d electron orbit of Zr and the 5d and part of 6s and 5p electron orbit of Pt and they are combined. The results demonstrate that the strength of the platinum based-materials can be increased by Zr bridge interface bonding.
Using the pseudopotential plane-wave method of the density-functional theory (DEF), the interface energy, electron structure and contour of the charge density of the Pt(100)/ZrO2(100) interface model with the bridge O and bridge Zr in ZrO2(100) were investigated. Results show that the Pt(100)/ZrO2(100)-bridge O interface energy with bridge O is 1.978 J/m2, and the Pt(100)/ZrO2(100)-bridge Zr interface energy with bridge Zr is 10.035 J/m2, indicating that the energy of bridge O is lower than the energy of bridge Zr, i.e. the ZrO2(100) with bridge Zr is easy to combine with the Pt(100). By the electron structure and contour of the charge density, there is mainly electron transfer between Zr and O with the Pt(100)/ZrO2(100)-bridge O; however, there is electron transfer between Zr and O and between Pt and Zr with the Pt(100)/ZrO2(100)-bridge Zr; between Pt and Zr there is the 4d electron orbit of Zr and the 5d and part of 6s and 5p electron orbit of Pt and they are combined. The results demonstrate that the strength of the platinum based-materials can be increased by Zr bridge interface bonding.
2011, 40(1):85-89.
Abstract:
Isothermal oxidation behavior of CoNiCrAlYRe alloys with different aluminum content at 1000 oC in air was investigated by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy analysis. The results show that increasing of the aluminum content induces the Cr-rich phase to precipitate at the γ/β interfaces. The formation of the spinel oxide scales is significantly suppressed by the increase of the aluminum content. The existence of the Cr-rich layer is beneficial for the formation of a compact oxide layer of the alloy with high aluminum content, which lowers the oxidation rate and improves oxidation resistance
Isothermal oxidation behavior of CoNiCrAlYRe alloys with different aluminum content at 1000 oC in air was investigated by X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy analysis. The results show that increasing of the aluminum content induces the Cr-rich phase to precipitate at the γ/β interfaces. The formation of the spinel oxide scales is significantly suppressed by the increase of the aluminum content. The existence of the Cr-rich layer is beneficial for the formation of a compact oxide layer of the alloy with high aluminum content, which lowers the oxidation rate and improves oxidation resistance
2011, 40(1):90-95.
Abstract:
High-temperature hot deformation experiments were conducted on the extruded alloy Mg-7.8%Li-4.6%Zn-0.96%Ce- 0.85%Y-0.30Zr at T=250-450 °C and strain rates of 0.001-10 s-1 using a Gleeble 3500 machine. The stress-strain curves of the alloy were analyzed. The curves show the characteristics of dynamic recrystallization, which is the main softening mechanism during the hot deformation processing. The peaks of the stress-strain curves become higher as the temperature decreases and the strain rate increases. The rare earth phase compound and α phases promote the dynamic recrystallization of β phases and slow down the dynamic recrystallization of α phases. In the process of the hot deformation, the dynamic recrystallization conducts quickly, the critical strain is lower in the stress-strain curves and dynamic softening covers the strain hardening effect
High-temperature hot deformation experiments were conducted on the extruded alloy Mg-7.8%Li-4.6%Zn-0.96%Ce- 0.85%Y-0.30Zr at T=250-450 °C and strain rates of 0.001-10 s-1 using a Gleeble 3500 machine. The stress-strain curves of the alloy were analyzed. The curves show the characteristics of dynamic recrystallization, which is the main softening mechanism during the hot deformation processing. The peaks of the stress-strain curves become higher as the temperature decreases and the strain rate increases. The rare earth phase compound and α phases promote the dynamic recrystallization of β phases and slow down the dynamic recrystallization of α phases. In the process of the hot deformation, the dynamic recrystallization conducts quickly, the critical strain is lower in the stress-strain curves and dynamic softening covers the strain hardening effect
2011, 40(1):96-100.
Abstract:
Glass-ceramic coating of different molar ratios deposited on the metal support (NiCrFe alloy) was prepared by a sol-gel method, with tetra-ethyl orthosilicate (TEOS) and aluminium nitrate (Al(NO3)3·9H2O) as the starting materials. The effects of different preparation parameters on the morphology, crystal quality and the bonding strength of the coating were studied. Characterization of XRD and SEM and the tests of thermal shock, ultrasonic vibration and tension show that the coating can increase the specific surface area and enhance the bonding strength between the metal support (NiCrFe alloy) of diesel engine catalytic converters and the coating. Moreover, the calcination temperature of the coating is lower and the preparation is much simpler than the traditional ones. Optimal parameters are found to be as follows: pre-oxidation of the metallic supports should be performed at 900 oC, the molar ratio of silicon to aluminum is 5:1, the coating drying is performed at 70 oC for 2 h and calcining is at 650 oC for 2 h.
Glass-ceramic coating of different molar ratios deposited on the metal support (NiCrFe alloy) was prepared by a sol-gel method, with tetra-ethyl orthosilicate (TEOS) and aluminium nitrate (Al(NO3)3·9H2O) as the starting materials. The effects of different preparation parameters on the morphology, crystal quality and the bonding strength of the coating were studied. Characterization of XRD and SEM and the tests of thermal shock, ultrasonic vibration and tension show that the coating can increase the specific surface area and enhance the bonding strength between the metal support (NiCrFe alloy) of diesel engine catalytic converters and the coating. Moreover, the calcination temperature of the coating is lower and the preparation is much simpler than the traditional ones. Optimal parameters are found to be as follows: pre-oxidation of the metallic supports should be performed at 900 oC, the molar ratio of silicon to aluminum is 5:1, the coating drying is performed at 70 oC for 2 h and calcining is at 650 oC for 2 h.
22 Effects of Carbon Nanotubes on the Corrosion Resistance of AZ31 Magnesium Alloy and Its Mechanism
2011, 40(1):101-105.
Abstract:
Carbon nanotubes (CNTs)-enforced AZ31 magnesium-based composites were fabricated by stirring-casting under the protection of Ar. Their microstructure was observed and the effect of CNTs addition on the corrosion resistance of AZ31 magnesium alloy was studied by immersing all the samples in 3.5wt% NaCl solution. The change of pH value was tested during the immersing progress. The fractographs were observed and analyzed via scanning electron microscope. Corrosion resistance mechanism of CNTs/magnesium composites was researched. The results show that CNTs addition can increase the corrosion resistance of the composites effectively. Corrosion rate changes from 3.2068 mg/(m2·s) to 1.1069 mg/(m2·s) with 1.5wt% CNTs addition
Carbon nanotubes (CNTs)-enforced AZ31 magnesium-based composites were fabricated by stirring-casting under the protection of Ar. Their microstructure was observed and the effect of CNTs addition on the corrosion resistance of AZ31 magnesium alloy was studied by immersing all the samples in 3.5wt% NaCl solution. The change of pH value was tested during the immersing progress. The fractographs were observed and analyzed via scanning electron microscope. Corrosion resistance mechanism of CNTs/magnesium composites was researched. The results show that CNTs addition can increase the corrosion resistance of the composites effectively. Corrosion rate changes from 3.2068 mg/(m2·s) to 1.1069 mg/(m2·s) with 1.5wt% CNTs addition
2011, 40(1):106-110.
Abstract:
The microstructure and interface characteristics of Mg2B2O5 whisker-reinforced magnesium matrix composites were investigated using optical microscopy, transmission electron microscopy and X-ray diffraction. It is found that the Mg2B2O5 whiskers have a twinned structure with the (202) as the twin plane and [010] as the growth direction of crystals. The MgB4O7 particles exist in some Mg2B2O5 whiskers. Equiaxial Mg2Si particles exist between the grain boundary of the matrix and the Mg2B2O5 whiskers. The MgO and MgB2 phase interface layers with different thickness are formed at the matrix-whisker interface during the vacuum-gas pressure infiltration process, which result from the interfacial reaction between Mg2B2O5 whisker and Mg matrix. The crystallographic orientation relationships between the Mg2B2O5 whisker and the interfacial reaction products are found to be [010]Mg2B2O5//[110]MgO and [110]MgO//[]MgB2, and (202)Mg2B2O5//(002)MgO and (002)MgO//(0001)MgB2, respectively. Finally, the factors that influence the microstructure of the Mg2B2O5 whiskers and the presence of the Mg2Si, MgO and MgB2 phases nearby the Mg2B2O5 whiskers were discussed.
The microstructure and interface characteristics of Mg2B2O5 whisker-reinforced magnesium matrix composites were investigated using optical microscopy, transmission electron microscopy and X-ray diffraction. It is found that the Mg2B2O5 whiskers have a twinned structure with the (202) as the twin plane and [010] as the growth direction of crystals. The MgB4O7 particles exist in some Mg2B2O5 whiskers. Equiaxial Mg2Si particles exist between the grain boundary of the matrix and the Mg2B2O5 whiskers. The MgO and MgB2 phase interface layers with different thickness are formed at the matrix-whisker interface during the vacuum-gas pressure infiltration process, which result from the interfacial reaction between Mg2B2O5 whisker and Mg matrix. The crystallographic orientation relationships between the Mg2B2O5 whisker and the interfacial reaction products are found to be [010]Mg2B2O5//[110]MgO and [110]MgO//[]MgB2, and (202)Mg2B2O5//(002)MgO and (002)MgO//(0001)MgB2, respectively. Finally, the factors that influence the microstructure of the Mg2B2O5 whiskers and the presence of the Mg2Si, MgO and MgB2 phases nearby the Mg2B2O5 whiskers were discussed.
2011, 40(1):111-114.
Abstract:
Joining samples of carbon/carbon composites (C/C composites) and Ni based high temperature alloy (GH3128) were fabricated by vacuum hot pressing joining process with the powder of Ni and Si as the interlayer material. The effects of the joining temperature on the mechanical properties and microstructure of the joints between C/C composite and GH3128 were investigated by X-ray diffraction devices, scanning electron microscopes and universal material testing machines. The results show that with the joining temperature rising, not only does the element distribution in the joints become more uniform, but also the shear strength of the joining samples increases. When the joining temperature is 1160 oC, the shear strength of the joining samples reaches up to 12.6 MPa
Joining samples of carbon/carbon composites (C/C composites) and Ni based high temperature alloy (GH3128) were fabricated by vacuum hot pressing joining process with the powder of Ni and Si as the interlayer material. The effects of the joining temperature on the mechanical properties and microstructure of the joints between C/C composite and GH3128 were investigated by X-ray diffraction devices, scanning electron microscopes and universal material testing machines. The results show that with the joining temperature rising, not only does the element distribution in the joints become more uniform, but also the shear strength of the joining samples increases. When the joining temperature is 1160 oC, the shear strength of the joining samples reaches up to 12.6 MPa
2011, 40(1):115-120.
Abstract:
As a good film electrode material for supercapacitor (Ru-Sn)O2·nH2O film was deposited on tantalum foils with aqueous solution of (Ru-Sn)Clx as reservoir by galvanostatic-differential pulse voltammetry and heat treatment. The surface morphology, phase transition of precursor (Ru-Sn)Clx to amorphous (Ru-Sn)O2·nH2O and capacitance of the film were studied by scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electrochemical analyzer, respectively. Results show that the precursor (Ru-Sn)Clx transforms into (Ru-Sn)O2·nH2O film by the proper heat treatment, and the adhesive force of the film with Ta substrate is improved significantly which is measured to be 12.3 MPa. The binding force is improved with addition of SnCl2 into solution. With more addition of SnCl2, the surface mass per unit area is increased; the capacitance of the film per unit area is increased at first and then decreased gradually with a maximum value of 1.9 F/cm2 while the special capacitance drops continuously
As a good film electrode material for supercapacitor (Ru-Sn)O2·nH2O film was deposited on tantalum foils with aqueous solution of (Ru-Sn)Clx as reservoir by galvanostatic-differential pulse voltammetry and heat treatment. The surface morphology, phase transition of precursor (Ru-Sn)Clx to amorphous (Ru-Sn)O2·nH2O and capacitance of the film were studied by scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and electrochemical analyzer, respectively. Results show that the precursor (Ru-Sn)Clx transforms into (Ru-Sn)O2·nH2O film by the proper heat treatment, and the adhesive force of the film with Ta substrate is improved significantly which is measured to be 12.3 MPa. The binding force is improved with addition of SnCl2 into solution. With more addition of SnCl2, the surface mass per unit area is increased; the capacitance of the film per unit area is increased at first and then decreased gradually with a maximum value of 1.9 F/cm2 while the special capacitance drops continuously
2011, 40(1):121-125.
Abstract:
A sodium sulfite leaching method was adopted to purify selenium. Effects of concentration of sodium sulfite solution, leaching temperature, leaching time, stirring speed in selenium leaching process and concentration of sodium sulfide solution in the purification process on selenium purification were studied. The sample was analyzed by XRD and SEM. The results show that under the conditions of sodium sulfite solution of 300g/L, leaching temperature of 98 oC, leaching time of 2 h, stirring speed of 150 r/min and sodium sulfide solution of 2 g/L, the integrated effect of selenium purification is best. The leaching rate of selenium is 98.6% and the purity of fine selenium is 99.98%. XRD analysis shows that the purity of the sample is further improved. SEM analysis shows that the as-prepared selenium powders are shuttle-like and in homogeneous distribution.
A sodium sulfite leaching method was adopted to purify selenium. Effects of concentration of sodium sulfite solution, leaching temperature, leaching time, stirring speed in selenium leaching process and concentration of sodium sulfide solution in the purification process on selenium purification were studied. The sample was analyzed by XRD and SEM. The results show that under the conditions of sodium sulfite solution of 300g/L, leaching temperature of 98 oC, leaching time of 2 h, stirring speed of 150 r/min and sodium sulfide solution of 2 g/L, the integrated effect of selenium purification is best. The leaching rate of selenium is 98.6% and the purity of fine selenium is 99.98%. XRD analysis shows that the purity of the sample is further improved. SEM analysis shows that the as-prepared selenium powders are shuttle-like and in homogeneous distribution.
27 Research on Internal Stress in Electrodeposited Cu Films on Ni Substrates Based on Electron Theory
2011, 40(1):126-129.
Abstract:
Electroplating was employed to prepare Cu film on the surface of Ni substrate. Deflection of Ni substrate with Cu film coating was measured in situ by a cantilever beam method. Based on the measured deflection, average internal stress and distributed internal stress in Cu film were calculated. The results show that average internal stress and distributed internal stress in the Cu film decrease abruptly with the thickness of Cu film increasing. Interfacial stress of Cu film is very large while growth stress is small. Average internal stress in Cu film, which is caused by the adjustment of the electron densities at both sides of the interface, was roughly calculated using the modified Thomas-Feimi-Dirac-Cheng (TFDC) electron theory. The calculated result of TFDC electron theory is close to that of the experiment, indicating that the calculation model of electron theory is of high accuracy
Electroplating was employed to prepare Cu film on the surface of Ni substrate. Deflection of Ni substrate with Cu film coating was measured in situ by a cantilever beam method. Based on the measured deflection, average internal stress and distributed internal stress in Cu film were calculated. The results show that average internal stress and distributed internal stress in the Cu film decrease abruptly with the thickness of Cu film increasing. Interfacial stress of Cu film is very large while growth stress is small. Average internal stress in Cu film, which is caused by the adjustment of the electron densities at both sides of the interface, was roughly calculated using the modified Thomas-Feimi-Dirac-Cheng (TFDC) electron theory. The calculated result of TFDC electron theory is close to that of the experiment, indicating that the calculation model of electron theory is of high accuracy
2011, 40(1):130-133.
Abstract:
The effects of carbon content on the crystal structure, the lattice parameters, the density and the average particle size of the lithium vanadium phosphate cathode materials (Li3V2(PO4)3) were investigated. It is found that amorphous carbon can not change the crystal structure and the lattice parameters of the Li3V2(PO4)3 cathode materials, but it has effects on their density and the average particle size. The density and the average particle size of the Li3V2(PO4)3 are both reduced as the carbon content is increased. In addition, the electrochemical performance of the Li3V2(PO4)3 cathode materials was tested in CR2032 button battery. The tests show that when the materials are charged/discharged at low C-rate, their electrochemical performance is improved gradually as the carbon content is increased and it becomes best at 10% carbon-content; the materials require more carbon as the C-rate is increased
The effects of carbon content on the crystal structure, the lattice parameters, the density and the average particle size of the lithium vanadium phosphate cathode materials (Li3V2(PO4)3) were investigated. It is found that amorphous carbon can not change the crystal structure and the lattice parameters of the Li3V2(PO4)3 cathode materials, but it has effects on their density and the average particle size. The density and the average particle size of the Li3V2(PO4)3 are both reduced as the carbon content is increased. In addition, the electrochemical performance of the Li3V2(PO4)3 cathode materials was tested in CR2032 button battery. The tests show that when the materials are charged/discharged at low C-rate, their electrochemical performance is improved gradually as the carbon content is increased and it becomes best at 10% carbon-content; the materials require more carbon as the C-rate is increased
2011, 40(1):134-137.
Abstract:
Magnetic annealing were carried out for Nd0.75Mg0.25(Ni0.8Co0.2)3.8 hydrogen storage alloys at different temperatures. The electrochemical properties, magnetic properties, phase composition and lattice parameters of alloys were systematically investigated. The results show that magnetic annealing has little influence on phase composition of alloys, which includes Ce2Ni7 type (Nd,Mg)2(Ni,Co)7 phase and CaCu5 type NdNi5 phase. Magnetic annealing results in the orientation of easy magnetization axis along c axis. As the annealing temperature increases, the lattice parameter c is increased, which coincides with the extension of tetrahedral interstitials along c axis. Additionally, the obstacle of transportation for hydrogen proton decreases and the rate properties are improved with the annealing temperature increasing
Magnetic annealing were carried out for Nd0.75Mg0.25(Ni0.8Co0.2)3.8 hydrogen storage alloys at different temperatures. The electrochemical properties, magnetic properties, phase composition and lattice parameters of alloys were systematically investigated. The results show that magnetic annealing has little influence on phase composition of alloys, which includes Ce2Ni7 type (Nd,Mg)2(Ni,Co)7 phase and CaCu5 type NdNi5 phase. Magnetic annealing results in the orientation of easy magnetization axis along c axis. As the annealing temperature increases, the lattice parameter c is increased, which coincides with the extension of tetrahedral interstitials along c axis. Additionally, the obstacle of transportation for hydrogen proton decreases and the rate properties are improved with the annealing temperature increasing
2011, 40(1):138-141.
Abstract:
Porous SiC was prepared by liquid Si infiltration and mixture acid (HNO3+HF) etching. SEM observation reveals that the porous SiC possesses irregular, interconnected and porous morphology, which comes from the porous carbon perform derived by filter paper and phenolic resin. Open porosity of the porous SiC is up to 62%. The bending strength and the fracture toughness of the porous SiC are lower than that of SiC/Si composites. The etching mechanism of free Si can be explained by the repeated oxidation-etching process
Porous SiC was prepared by liquid Si infiltration and mixture acid (HNO3+HF) etching. SEM observation reveals that the porous SiC possesses irregular, interconnected and porous morphology, which comes from the porous carbon perform derived by filter paper and phenolic resin. Open porosity of the porous SiC is up to 62%. The bending strength and the fracture toughness of the porous SiC are lower than that of SiC/Si composites. The etching mechanism of free Si can be explained by the repeated oxidation-etching process
2011, 40(1):141-147.
Abstract:
The effects of heat treatment on the microstructures and mechanical properties of TAl5 titanium alloys fabricated by laser solid forming (LSF) were investigated. The microstructure of the as-deposited sample is composed of Widmanst?tten α+β laths of different orientations, and there is certain anisotropy in the tensile properties of LSFed samples. There is no obvious change in the microstructure by annealing treatment, but the plasticity of LSFed samples is increased obviously accompanied with a little decrease of the tensile strength. The annealed sample presents good comprehensive tensile properties, which can satisfy the tensile properties standard of annealed TA15 wrought. After solution-aging treatment, the microstructure consists of coarse primary α and α', and the strength of LSFed samples is significantly improved. The microstructure of coarse primary α, refined secondary α and α' can be obtained by double solution-aging treatment, which results in a slight decrease in the tensile strength. Compared with room temperature tensile properties, all of LSFed sample in the four kinds of treatment states show a lower strength and a higher plasticity at high temperature. The hardness of LSFed samples is ranged from 30 HRC to 45 HRC for the different heat treatments, and the change trend of hardness after different heat treatments is in agreement with that of tensile strength.
The effects of heat treatment on the microstructures and mechanical properties of TAl5 titanium alloys fabricated by laser solid forming (LSF) were investigated. The microstructure of the as-deposited sample is composed of Widmanst?tten α+β laths of different orientations, and there is certain anisotropy in the tensile properties of LSFed samples. There is no obvious change in the microstructure by annealing treatment, but the plasticity of LSFed samples is increased obviously accompanied with a little decrease of the tensile strength. The annealed sample presents good comprehensive tensile properties, which can satisfy the tensile properties standard of annealed TA15 wrought. After solution-aging treatment, the microstructure consists of coarse primary α and α', and the strength of LSFed samples is significantly improved. The microstructure of coarse primary α, refined secondary α and α' can be obtained by double solution-aging treatment, which results in a slight decrease in the tensile strength. Compared with room temperature tensile properties, all of LSFed sample in the four kinds of treatment states show a lower strength and a higher plasticity at high temperature. The hardness of LSFed samples is ranged from 30 HRC to 45 HRC for the different heat treatments, and the change trend of hardness after different heat treatments is in agreement with that of tensile strength.
2011, 40(1):148-151.
Abstract:
The thermal and chemical stabilities of the colloid silver nanoparticles prepared by bioreduction were investigated in virtue of UV-Vis spectrometer. The results indicate that UV-Vis spectra of silver colloid prepared by bioreduction have not significant change after heat treatment at 100 oC for 6 h. Hydrogen ion and the electrolyte with multivalent cation markedly influence stabilities of the silver colloid, while hydroxide anion has a weak influence on its stability. Thermal and chemical stabilities of the silver colloid prepared by bioreduction are superior to that of the silver colloid prepared by the sodium citrate reduction method
The thermal and chemical stabilities of the colloid silver nanoparticles prepared by bioreduction were investigated in virtue of UV-Vis spectrometer. The results indicate that UV-Vis spectra of silver colloid prepared by bioreduction have not significant change after heat treatment at 100 oC for 6 h. Hydrogen ion and the electrolyte with multivalent cation markedly influence stabilities of the silver colloid, while hydroxide anion has a weak influence on its stability. Thermal and chemical stabilities of the silver colloid prepared by bioreduction are superior to that of the silver colloid prepared by the sodium citrate reduction method
2011, 40(1):152-155.
Abstract:
Thermal fatigue properties of DZ40M directionally solidified cobalt-base superalloy was investigated by scanning electric microscope. The results show that the crack propagation rate increases and the thermal fatigue resistance decreases with the rise of the upper temperature. Resistance of thermal fatigue is improved with the holding time prolonging at the same upper temperature, which is caused by the formation of uniform and compact film of oxide on the surface. Due to different thermal expanding coefficients of the matrix and the carbides, crack holes are easily formed in the boundary of the matrix and carbides at alternating temperatures during thermal fatigue; as a result, cracks of thermal fatigue initiate. The interconnection of crack holes makes thermal fatigue crack propagate.
Thermal fatigue properties of DZ40M directionally solidified cobalt-base superalloy was investigated by scanning electric microscope. The results show that the crack propagation rate increases and the thermal fatigue resistance decreases with the rise of the upper temperature. Resistance of thermal fatigue is improved with the holding time prolonging at the same upper temperature, which is caused by the formation of uniform and compact film of oxide on the surface. Due to different thermal expanding coefficients of the matrix and the carbides, crack holes are easily formed in the boundary of the matrix and carbides at alternating temperatures during thermal fatigue; as a result, cracks of thermal fatigue initiate. The interconnection of crack holes makes thermal fatigue crack propagate.
2011, 40(1):156-160.
Abstract:
The effects of Nd on the corrosion resistant property of as-extruded AZ31 magnesium alloys were investigated by salt spray corrosion and a potentiodynamic scanning method. The micromorphology of the corroded samples of the alloys were studied by scanning electron microscope (SEM), and the phase composition and corrosion products of the alloys were analyzed by X-ray diffractometer (XRD). The results show that Nd addition can obviously improve the corrosion resistance of AZ31 magnesium alloys and the corrosion rate changes with the Nd addition. The result of salt spray corrosion is the same as that of potentiodynamic scanning
The effects of Nd on the corrosion resistant property of as-extruded AZ31 magnesium alloys were investigated by salt spray corrosion and a potentiodynamic scanning method. The micromorphology of the corroded samples of the alloys were studied by scanning electron microscope (SEM), and the phase composition and corrosion products of the alloys were analyzed by X-ray diffractometer (XRD). The results show that Nd addition can obviously improve the corrosion resistance of AZ31 magnesium alloys and the corrosion rate changes with the Nd addition. The result of salt spray corrosion is the same as that of potentiodynamic scanning
2011, 40(1):161-164.
Abstract:
The selective laser melting of a blended powder system consisting of 96wt% 316L stainless steel and 4wt% NH4HCO3 was performed to prepare porous materials. The SEM characterizations show the formation of a honeycomb-like porous structure at a relatively high laser power of 800 W. The pore sizes of the porous structure distribute homogeneously, typically in a range of 2-5 μm. The average pore size is about 3.5 μm. The effects of laser power on the microstructural characteristics of the as-obtained microcellular structures were investigated. The formation mechanisms of the honeycomb-like porous structure during selective laser melting were also discussed.
The selective laser melting of a blended powder system consisting of 96wt% 316L stainless steel and 4wt% NH4HCO3 was performed to prepare porous materials. The SEM characterizations show the formation of a honeycomb-like porous structure at a relatively high laser power of 800 W. The pore sizes of the porous structure distribute homogeneously, typically in a range of 2-5 μm. The average pore size is about 3.5 μm. The effects of laser power on the microstructural characteristics of the as-obtained microcellular structures were investigated. The formation mechanisms of the honeycomb-like porous structure during selective laser melting were also discussed.
2011, 40(1):165-168.
Abstract:
The influence of medium-frequency sputtering process on the structure of Ni-AlN composite films and graded Ni-AlN selective absorbers was studied. Results show that the critical nitrogen flow rates are decreased corresponding to the change of aluminum sputtering mode from metallic mode to reactive mode with increasing nickel target current and decreasing aluminum target current; the nickel content in Ni-AlN composite films is increased with the rise of nickel target current, while the variety of the aluminum content and N/Al atomic ratio with nickel target current is inverse; metallic aluminum phase is apt to be formed in the Ni-AlN composite films deposited at higher nickel target current. When the deposition duration for a Ni-AlN composite layer is increased, the composition distribution of Ni-AlN selective absorbers in depth is shifted from the gradual changing to the stepped changing, and the visible light reflectivity is decreased. A visible light reflectivity of about 10% and a good spectral selectivity is obtained when the deposition duration for a Ni-AlN composite layer is 10 min
The influence of medium-frequency sputtering process on the structure of Ni-AlN composite films and graded Ni-AlN selective absorbers was studied. Results show that the critical nitrogen flow rates are decreased corresponding to the change of aluminum sputtering mode from metallic mode to reactive mode with increasing nickel target current and decreasing aluminum target current; the nickel content in Ni-AlN composite films is increased with the rise of nickel target current, while the variety of the aluminum content and N/Al atomic ratio with nickel target current is inverse; metallic aluminum phase is apt to be formed in the Ni-AlN composite films deposited at higher nickel target current. When the deposition duration for a Ni-AlN composite layer is increased, the composition distribution of Ni-AlN selective absorbers in depth is shifted from the gradual changing to the stepped changing, and the visible light reflectivity is decreased. A visible light reflectivity of about 10% and a good spectral selectivity is obtained when the deposition duration for a Ni-AlN composite layer is 10 min
2011, 40(1):169-172.
Abstract:
The direct synthesis of TiFe intermetallics from the mixed oxide precursors was studied by the solid oxide membrane process (SOM). Fe2O3 and TiO2 were mixed in molar proportions of 1:2 and 1:1, sintered at 1150 oC for 2 h, electrolyzed in molten CaCl2 at 1100 oC using a YSZ anode at a potential of 3.5 V for 2-6 h. The product was examined by SEM, EDS and XRD. The results show that TiO2 and Fe2O3 oxides are electrochemically reduced to TiFe and Fe2Ti alloy in molten CaCl2. Direct synthesis of TiFe alloy from the mixed oxide precursors is feasible
The direct synthesis of TiFe intermetallics from the mixed oxide precursors was studied by the solid oxide membrane process (SOM). Fe2O3 and TiO2 were mixed in molar proportions of 1:2 and 1:1, sintered at 1150 oC for 2 h, electrolyzed in molten CaCl2 at 1100 oC using a YSZ anode at a potential of 3.5 V for 2-6 h. The product was examined by SEM, EDS and XRD. The results show that TiO2 and Fe2O3 oxides are electrochemically reduced to TiFe and Fe2Ti alloy in molten CaCl2. Direct synthesis of TiFe alloy from the mixed oxide precursors is feasible
Zhao Yanchun
,
Kou Shengzhong
,
Wang Renjun
,
Suo Hongli
,
Ding Yutian
,
Li Na
,
Xue Shuwei
,
Liu Guangqiao
2011, 40(1):173-176.
Abstract:
Overheating has a pronounced effect on the thermal stability and mechanical properties of Cu36Zr48Ag8Al8 bulk metallic glass. Higher overheated temperature can enhance the thermal stability of bulk amorphous alloys, corresponding to higher specific-heat capacity and smaller initial defect concentration. Bulk amorphous alloys exhibit good compressive plasticity at small overheated levels, whereas the compressive fracture strength and microhardness show a significant increase followed by a slight decrease. The mechanical properties of bulk metallic glasses fabricated by different casting process are influenced by the interaction of the free volume and residual stresses
Overheating has a pronounced effect on the thermal stability and mechanical properties of Cu36Zr48Ag8Al8 bulk metallic glass. Higher overheated temperature can enhance the thermal stability of bulk amorphous alloys, corresponding to higher specific-heat capacity and smaller initial defect concentration. Bulk amorphous alloys exhibit good compressive plasticity at small overheated levels, whereas the compressive fracture strength and microhardness show a significant increase followed by a slight decrease. The mechanical properties of bulk metallic glasses fabricated by different casting process are influenced by the interaction of the free volume and residual stresses
Zhu Yonghua
,
Suo Hongli
,
Zhao Yue
,
Gao Mangmang
,
Cheng Yanling
,
Ma Lin
,
Gao Peikuo
,
Wang Jianhong
,
Ji Yuan
,
Zhou Meiling
2011, 40(1):177-182.
Abstract:
The cube textured Ni-7at%W(Ni7W) substrates were prepared starting from spark plasma sintered ingot, followed by Rolling-Assisted Biaxially Textured Substrate (RABiTS) processing. According to the EBSD and XRD analyses of the fully annealed tape, the cube grain content of the tape reaches as high as 99.4% within a tolerance angle of less than 10o and the grain boundary length content is 93.6% within a tolerance angle of less than 10o, while the FWHM values of the in-plane and out-of-plane orientations are about 6.32o by (111) Phi-scan and 5.4o by (200) ω-scan, respectively, indicating that the tapes have sharp cube texture. The Ni7W substrate has a uniform grain size and high quality of cube texture. The La2Zr2O7 (LZO) buffer layer fabricated on Ni7W substrates shows that the epitaxially textured LZO buffer layer could be formed on the as-obtained Ni7W substrate. The FWHM values of (222) φ-scan and (400) ω-scan are 7.57° and 5.73°, respectively
The cube textured Ni-7at%W(Ni7W) substrates were prepared starting from spark plasma sintered ingot, followed by Rolling-Assisted Biaxially Textured Substrate (RABiTS) processing. According to the EBSD and XRD analyses of the fully annealed tape, the cube grain content of the tape reaches as high as 99.4% within a tolerance angle of less than 10o and the grain boundary length content is 93.6% within a tolerance angle of less than 10o, while the FWHM values of the in-plane and out-of-plane orientations are about 6.32o by (111) Phi-scan and 5.4o by (200) ω-scan, respectively, indicating that the tapes have sharp cube texture. The Ni7W substrate has a uniform grain size and high quality of cube texture. The La2Zr2O7 (LZO) buffer layer fabricated on Ni7W substrates shows that the epitaxially textured LZO buffer layer could be formed on the as-obtained Ni7W substrate. The FWHM values of (222) φ-scan and (400) ω-scan are 7.57° and 5.73°, respectively
2011, 40(1):183-188.
Abstract:
Friction stir processing (FSP) was summarized in detail. Its effect on properties of materials and the research on preparation of composites and alloys were also introduced. In addition, the problems of FSP research, the prospect and the future development were pointed out. The influencing factors and formation mechanism of the abnormal grain growth need further studies. FSP combined with melt welding can meet the requirement of welding of high strength materials such as titanium alloys. There will be a good application future for FSP to prepare nano-particles enforced metal matrix composites (MMCs) and intermetallic composites (IMCs). An inventive technique to fabricate materials with homogeneous microstructure by adopting the concepts of FSP is pivotal for its applications
Friction stir processing (FSP) was summarized in detail. Its effect on properties of materials and the research on preparation of composites and alloys were also introduced. In addition, the problems of FSP research, the prospect and the future development were pointed out. The influencing factors and formation mechanism of the abnormal grain growth need further studies. FSP combined with melt welding can meet the requirement of welding of high strength materials such as titanium alloys. There will be a good application future for FSP to prepare nano-particles enforced metal matrix composites (MMCs) and intermetallic composites (IMCs). An inventive technique to fabricate materials with homogeneous microstructure by adopting the concepts of FSP is pivotal for its applications
