Volume 46,Issue 4,2017 Table of Contents
2017, 46(4):869-875.
Abstract:
Using Cu-coated carbon fiber cloth (CFC) as reinforcement and Ti-6Al-4V (TC4) as matrix, the Cu-coated CFC/TC4 composite is fabricated by spark plasma sintering. The interface morphology, phase microstructure, phase distribution and mechanical properties of CFC/TC4 are characterized. Results show that carbon fibers are uniformly distributed in Cu-coated CFC/TC4. CuTi, Cu and very little TiC are distributed along the interface between fibers and matrix. Possessing slightly better plasticity than TC4, the yield strength and compressive strength of Cu-coated CFC/TC4 are obviously enhanced. The electroplated Cu plays important roles: (1) markedly decreases the sintering temperature of Cu-coated CFC/TC4; (2) significantly improves the wettability and interfacial bonding between carbon fibers and TC4 matrix, giving explanation to the increase of mechanical properties of Cu-coated CFC/TC4; (3) effectively inhibits the excessive generation of brittle TiC compared with uncoated CFC/TC4 composite, explaining the maintaining of good plasticity of Cu-coated CFC/TC4.
Using Cu-coated carbon fiber cloth (CFC) as reinforcement and Ti-6Al-4V (TC4) as matrix, the Cu-coated CFC/TC4 composite is fabricated by spark plasma sintering. The interface morphology, phase microstructure, phase distribution and mechanical properties of CFC/TC4 are characterized. Results show that carbon fibers are uniformly distributed in Cu-coated CFC/TC4. CuTi, Cu and very little TiC are distributed along the interface between fibers and matrix. Possessing slightly better plasticity than TC4, the yield strength and compressive strength of Cu-coated CFC/TC4 are obviously enhanced. The electroplated Cu plays important roles: (1) markedly decreases the sintering temperature of Cu-coated CFC/TC4; (2) significantly improves the wettability and interfacial bonding between carbon fibers and TC4 matrix, giving explanation to the increase of mechanical properties of Cu-coated CFC/TC4; (3) effectively inhibits the excessive generation of brittle TiC compared with uncoated CFC/TC4 composite, explaining the maintaining of good plasticity of Cu-coated CFC/TC4.
2017, 46(4):876-881.
Abstract:
Microstructure quantitatively analysis is significant for building the relationship between microstructure and properties, especially the ageing precipitation kinetics in aluminum alloys. A core parameter (aspect ratio) was introduced to describe the morphology change of precipitation. Aspect ratios of T1-plate precipitates in Al-Cu-Li-Zr alloys, S-plate precipitates in Al-Cu-Mg alloys and β-rod precipitates in Al-Mg-Si alloys were quantitatively analyzed. Results indicated that aspect ratios of precipitates increased at the early stage of ageing, then reached the peak and finally decreased slowly. The soft-impingement theory and HHC theory were introduced to model the ageing kinetics. Thermodynamics and kinetics parameters of different precipitates were also calculated in the model. Simulate results of different precipitates agree well with the experimental results.
Microstructure quantitatively analysis is significant for building the relationship between microstructure and properties, especially the ageing precipitation kinetics in aluminum alloys. A core parameter (aspect ratio) was introduced to describe the morphology change of precipitation. Aspect ratios of T1-plate precipitates in Al-Cu-Li-Zr alloys, S-plate precipitates in Al-Cu-Mg alloys and β-rod precipitates in Al-Mg-Si alloys were quantitatively analyzed. Results indicated that aspect ratios of precipitates increased at the early stage of ageing, then reached the peak and finally decreased slowly. The soft-impingement theory and HHC theory were introduced to model the ageing kinetics. Thermodynamics and kinetics parameters of different precipitates were also calculated in the model. Simulate results of different precipitates agree well with the experimental results.
2017, 46(4):882-887.
Abstract:
:Impulse pressuring diffusion bonding (IPDB) of TiC cermet to stainless steel 06Cr19Ni10 using Ti-Nb interlayer was carried out in an attempt to reduce the bonding time and alleviate the detrimental effect of interfacial reaction products on bonding strength. Successful bonding was achieved at 890℃ under a pulsed pressure of 2~10MPa within a duration of only 4~12min, which was notably shortened in comparison with conventional diffusion bonding. Microstructure characterization revealed the existence of the σ phase with a limit solubility of Nb, (β-Ti, Nb) phase, and solid solution of Ni in α β-Ti in the reaction zone. Maximum shear strength of 110MPa was obtained when the joint was bonded for 10min, indicating a robust metallurgical bonding was achieved. Upon shear loading, the joints fractured along the remnant Ti/ α β-Ti interfaceand extended to the interior of TiC cermet in a brittle cleavage manner. This technique provides a highly promising bonding method of TiC cermet and steel.
:Impulse pressuring diffusion bonding (IPDB) of TiC cermet to stainless steel 06Cr19Ni10 using Ti-Nb interlayer was carried out in an attempt to reduce the bonding time and alleviate the detrimental effect of interfacial reaction products on bonding strength. Successful bonding was achieved at 890℃ under a pulsed pressure of 2~10MPa within a duration of only 4~12min, which was notably shortened in comparison with conventional diffusion bonding. Microstructure characterization revealed the existence of the σ phase with a limit solubility of Nb, (β-Ti, Nb) phase, and solid solution of Ni in α β-Ti in the reaction zone. Maximum shear strength of 110MPa was obtained when the joint was bonded for 10min, indicating a robust metallurgical bonding was achieved. Upon shear loading, the joints fractured along the remnant Ti/ α β-Ti interfaceand extended to the interior of TiC cermet in a brittle cleavage manner. This technique provides a highly promising bonding method of TiC cermet and steel.
2017, 46(4):888-892.
Abstract:
ZnO/Graphene nano-films were directly prepared on Cu substrate via a low pressure chemical vapor deposition (LPCVD) and sol-gel method. The effects of the annealing temperature on the structural, morphology, the chemical state and component, and optical property of these ZnO/Graphene nano-films were investigated. The XRD patterns demonstrate that the ZnO/Graphene nanostructures exhibit the hexagonal wurtzite structure and the crystalline quality increases with increasing the annealing temperatures from 500 to 700 ℃. When the annealing temperature reaches at 700 ℃, SEM analysis shows that sample ?lm exhibits dense and uniform grains and smooth surface and the average grain size of film deposited 3 layers is about 35.7 nm. The PL measurement confirms that ZnO/Graphene nano-film deposited 3 layers at the annealing temperatures of 700℃ has an better optical performance, which due to the higher crystalline quality and lower defect concentration.
ZnO/Graphene nano-films were directly prepared on Cu substrate via a low pressure chemical vapor deposition (LPCVD) and sol-gel method. The effects of the annealing temperature on the structural, morphology, the chemical state and component, and optical property of these ZnO/Graphene nano-films were investigated. The XRD patterns demonstrate that the ZnO/Graphene nanostructures exhibit the hexagonal wurtzite structure and the crystalline quality increases with increasing the annealing temperatures from 500 to 700 ℃. When the annealing temperature reaches at 700 ℃, SEM analysis shows that sample ?lm exhibits dense and uniform grains and smooth surface and the average grain size of film deposited 3 layers is about 35.7 nm. The PL measurement confirms that ZnO/Graphene nano-film deposited 3 layers at the annealing temperatures of 700℃ has an better optical performance, which due to the higher crystalline quality and lower defect concentration.
2017, 46(4):893-898.
Abstract:
The quality of 3D printing parts obtained by means of droplets deposition depends strongly on the mechanism of the interaction between the molten metal droplets and the substrate to be covered. The effects of various parameters such as impact velocity, substrate temperature, droplet diameters, specific heat, thermal conductivity, latent heat on the maximum spread factor during impacting and spreading with solidification of a molten droplet onto an aluminum surface under different parameters was studied. The free surface of the droplet was tracked by the volume-of-fluid (VOF) method. The simulation model was based on the N-S equations and the energy equations which include convection and phase change. These equations were coupled with the Level Set function to track the interface between molten particles and surrounding air. The maximum spread factors were obtained and were in agreement with the experimental data available in the literature.
The quality of 3D printing parts obtained by means of droplets deposition depends strongly on the mechanism of the interaction between the molten metal droplets and the substrate to be covered. The effects of various parameters such as impact velocity, substrate temperature, droplet diameters, specific heat, thermal conductivity, latent heat on the maximum spread factor during impacting and spreading with solidification of a molten droplet onto an aluminum surface under different parameters was studied. The free surface of the droplet was tracked by the volume-of-fluid (VOF) method. The simulation model was based on the N-S equations and the energy equations which include convection and phase change. These equations were coupled with the Level Set function to track the interface between molten particles and surrounding air. The maximum spread factors were obtained and were in agreement with the experimental data available in the literature.
2017, 46(4):899-905.
Abstract:
Yttria stabilized zirconia (YSZ) nanocrystals were prepared by hydrothermal synthesis and were calcinated at different temperatures and with different isothermal hold time. X-ray diffraction via whole powder pattern modeling approach is used to study the grain growth as well as the evolution of grain size distribution of YSZ nanocrystals. Results show that YSZ nanocrystals start to grow along with the grain size distribution broadening at temperature about 300℃. The grain growth rate and the grain size distribution of YSZ nanocrystals are dependent on the calcination temperature and the isothermal hold time. The grain growth exponent and the active energy of grain growth were calculated. Grain rotation induced grain coalescence is suggested as the predominant way of grain growth of YSZ nanocrystals.
Yttria stabilized zirconia (YSZ) nanocrystals were prepared by hydrothermal synthesis and were calcinated at different temperatures and with different isothermal hold time. X-ray diffraction via whole powder pattern modeling approach is used to study the grain growth as well as the evolution of grain size distribution of YSZ nanocrystals. Results show that YSZ nanocrystals start to grow along with the grain size distribution broadening at temperature about 300℃. The grain growth rate and the grain size distribution of YSZ nanocrystals are dependent on the calcination temperature and the isothermal hold time. The grain growth exponent and the active energy of grain growth were calculated. Grain rotation induced grain coalescence is suggested as the predominant way of grain growth of YSZ nanocrystals.
2017, 46(4):906-911.
Abstract:
The microstructural characterization and interfacial shear tests of Ti/Steel bimetallic clad sheets were taken to study the interfacial bonding mechanism during explosive welding process. The wavy interface with several vortexes forms between the dissimilar metal matrixes due to the interface deformation. A significant metal flow of steel matrix caused by the severe plastic deformation induces the continuous vortexes in the interface. The TEM and XRD analysis clarify that the nanoscale interfacial interlayer contains solid solutions and a small amount of intermetallic compounds. The shear strength of the interface along the explosive welding direction is enhanced by the wavy interface. The fracture of the bonding interface presents the ductile features on the vortex and while brittle features on the smooth interface.
The microstructural characterization and interfacial shear tests of Ti/Steel bimetallic clad sheets were taken to study the interfacial bonding mechanism during explosive welding process. The wavy interface with several vortexes forms between the dissimilar metal matrixes due to the interface deformation. A significant metal flow of steel matrix caused by the severe plastic deformation induces the continuous vortexes in the interface. The TEM and XRD analysis clarify that the nanoscale interfacial interlayer contains solid solutions and a small amount of intermetallic compounds. The shear strength of the interface along the explosive welding direction is enhanced by the wavy interface. The fracture of the bonding interface presents the ductile features on the vortex and while brittle features on the smooth interface.
2017, 46(4):912-916.
Abstract:
Single crystal superalloys have been prepared by adopting the grain selector and seeding technique in a high temperature gradient directional solidification furnace. The orientation characteristics were measured by XRD. Results indicated that for the grain selector method, the crystal solidification began at the cooling plate with random nucleation, and through mutual competitive growth at the starter block. The grains entered the spiral selector, and finally the single crystal superalloys which were close to <001> direction were obtained. By using the seeding technique, by epitaxial growth of partially melted seed crystals, single crystal superalloys which have the same orientation as the seed crystal were obtained.
Single crystal superalloys have been prepared by adopting the grain selector and seeding technique in a high temperature gradient directional solidification furnace. The orientation characteristics were measured by XRD. Results indicated that for the grain selector method, the crystal solidification began at the cooling plate with random nucleation, and through mutual competitive growth at the starter block. The grains entered the spiral selector, and finally the single crystal superalloys which were close to <001> direction were obtained. By using the seeding technique, by epitaxial growth of partially melted seed crystals, single crystal superalloys which have the same orientation as the seed crystal were obtained.
2017, 46(4):917-922.
Abstract:
Temperature of cooling roller is a key issue affecting the quality of the amorphous ribbon. To this end, heat flux distribution acting on cooling roller outer wall calculated by fluid dynamics software Fluent, cooling roller steady temperature field analyzed with Finite Element Method by heat flux boundary conditions, obtained the cooling roller inner and outer wall temperature distribution, and discussed the temperature of cooling roller as cooling roller thickness and water passage height. The results show that cooling roller outer wall temperature decreases with roller thickness and the cooling water passage height decreased; Cooling roller inner wall temperature decreases with roller thickness increased and the cooling water passage height decreased. Meantime, the appropriate roller thickness and passage height selected to keep cooling roller both inner and outer wall temperature within the certain range. The study result provided theoretical support for cooling roller design and optimization.
Temperature of cooling roller is a key issue affecting the quality of the amorphous ribbon. To this end, heat flux distribution acting on cooling roller outer wall calculated by fluid dynamics software Fluent, cooling roller steady temperature field analyzed with Finite Element Method by heat flux boundary conditions, obtained the cooling roller inner and outer wall temperature distribution, and discussed the temperature of cooling roller as cooling roller thickness and water passage height. The results show that cooling roller outer wall temperature decreases with roller thickness and the cooling water passage height decreased; Cooling roller inner wall temperature decreases with roller thickness increased and the cooling water passage height decreased. Meantime, the appropriate roller thickness and passage height selected to keep cooling roller both inner and outer wall temperature within the certain range. The study result provided theoretical support for cooling roller design and optimization.
2017, 46(4):923-927.
Abstract:
In this study, WC-12Co powder with nano WC grain size was used to deposit wear resistant coatings by AC-HVAF (Acukote High Velocity Air-Fuel) spray system. The phase compositions and micro-structure of the coatings were examined. The microhardness, fracture toughness and wear resistance were investigated. According to the X-ray Diffraction (XRD) analysis, the principal phase was WC, and its decomposition products were not found. The sprayed coating has a porosity lower than 1% and the grain sizes of coatings were among 80-100 nm which contributed to an average microhardness as high as 1940.3 HV0.3 on the surface and 1662.1 HV0.3 on the cross-section. At the load of 1.5 kg and rotational speed of 1198 r/min of WC counter body, the nano-sized coatings showed a 40% lower average weight loss and a stable friction coefficient of 0.26-0.28 (micron-sized coatings: 0.25-0.4 ) in the dry wear conditions. It was concluded that the sprayed nano structural WC-12Co coatings had a better wear resistance.
In this study, WC-12Co powder with nano WC grain size was used to deposit wear resistant coatings by AC-HVAF (Acukote High Velocity Air-Fuel) spray system. The phase compositions and micro-structure of the coatings were examined. The microhardness, fracture toughness and wear resistance were investigated. According to the X-ray Diffraction (XRD) analysis, the principal phase was WC, and its decomposition products were not found. The sprayed coating has a porosity lower than 1% and the grain sizes of coatings were among 80-100 nm which contributed to an average microhardness as high as 1940.3 HV0.3 on the surface and 1662.1 HV0.3 on the cross-section. At the load of 1.5 kg and rotational speed of 1198 r/min of WC counter body, the nano-sized coatings showed a 40% lower average weight loss and a stable friction coefficient of 0.26-0.28 (micron-sized coatings: 0.25-0.4 ) in the dry wear conditions. It was concluded that the sprayed nano structural WC-12Co coatings had a better wear resistance.
11 Study on microstructure evolution of a high zinc containing Al-Zn-Mg-Cu alloy during homogenization
2017, 46(4):928-934.
Abstract:
The microstructural evolution of a high Zn-containing Al-Zn-Mg-Cu alloy during homogenization was investigated by optical microscopy, differential scanning calorimetry, scanning electron microscope and X-ray diffraction. A homogenization kinetic equation deriving from a diffusion kinetic model was established to confirm the optimum homogenization parameter. The results showed that severe segregation exists in the as-cast alloy. The non-equilibrium eutectics consisted of α(Al), Mg(Zn,Cu,Al)2, S(Al2CuMg), θ(Al2Cu) and Fe-enriched phases. In present work, no transformation from Mg(Zn,Cu,Al)2 to S(Al2CuMg) phase occurred during homogenization and Mg(Zn,Cu,Al)2 phase directly dissolved into the matrix. θ(Al2Cu) phase dissolves into the matrix over homogenization. Fe-enriched phases still existed after homogenization, Zn and Mg elements in Fe-enriched phases were reduced or even disappeared by prolonging the holding time. In consistent with the results of homogenization kinetic analysis, the proper homogenization parameter was 440 oC×12 h 468 oC×24 h.
The microstructural evolution of a high Zn-containing Al-Zn-Mg-Cu alloy during homogenization was investigated by optical microscopy, differential scanning calorimetry, scanning electron microscope and X-ray diffraction. A homogenization kinetic equation deriving from a diffusion kinetic model was established to confirm the optimum homogenization parameter. The results showed that severe segregation exists in the as-cast alloy. The non-equilibrium eutectics consisted of α(Al), Mg(Zn,Cu,Al)2, S(Al2CuMg), θ(Al2Cu) and Fe-enriched phases. In present work, no transformation from Mg(Zn,Cu,Al)2 to S(Al2CuMg) phase occurred during homogenization and Mg(Zn,Cu,Al)2 phase directly dissolved into the matrix. θ(Al2Cu) phase dissolves into the matrix over homogenization. Fe-enriched phases still existed after homogenization, Zn and Mg elements in Fe-enriched phases were reduced or even disappeared by prolonging the holding time. In consistent with the results of homogenization kinetic analysis, the proper homogenization parameter was 440 oC×12 h 468 oC×24 h.
2017, 46(4):935-941.
Abstract:
Operating temperature waves nearly melt temperature of molten eutectic NaCl-MgCl2 which is thermal storage media at medium-high temperature. But corrosion behavior of the molten salt on metal at different temperature is not clear. Corrosion behavior and mechanism of the molten salt on Fe-14Cr-Mn alloy were studied by immersion salt corrosion method at 718K, 768K and 818K. Results show that corrosion rate increased lightly with the corrosion temperature. Corrosion kinetics characteristics obey linear law (slop is about k=-4.806E-4). At the early stage of corrosion, there was lots of vacuoles-shape, while a large number of pot hole formed after corroding 80h. Corrosion products are mainly Fe, Fe-Cr and MgO. Corrosion mechanism as follows: Absorbed oxygen on molten salt surface and oxygen atom that introduced in the form of moisture-absorbed MgCl2 is depolarizing agents. Chloride of Cr and Mn is got when oxide of Cr and Mn react with Cl-. The chloride of Cr and Mn with water (for example CrCl3.6 (H2O) and MnCl2.n (H2O)) that has low melting point will escape from corrosion system. In addition, there is a salt crust that is composed of MgCl2. (H2O) 6, NaCl and MgO on molten salt upper surface, while NaCl coexists with NaMgCl3 inside mixture salt. The study laid the foundation for the study of corrosion-resistant alloy in molten NaCl-MgCl2.
Operating temperature waves nearly melt temperature of molten eutectic NaCl-MgCl2 which is thermal storage media at medium-high temperature. But corrosion behavior of the molten salt on metal at different temperature is not clear. Corrosion behavior and mechanism of the molten salt on Fe-14Cr-Mn alloy were studied by immersion salt corrosion method at 718K, 768K and 818K. Results show that corrosion rate increased lightly with the corrosion temperature. Corrosion kinetics characteristics obey linear law (slop is about k=-4.806E-4). At the early stage of corrosion, there was lots of vacuoles-shape, while a large number of pot hole formed after corroding 80h. Corrosion products are mainly Fe, Fe-Cr and MgO. Corrosion mechanism as follows: Absorbed oxygen on molten salt surface and oxygen atom that introduced in the form of moisture-absorbed MgCl2 is depolarizing agents. Chloride of Cr and Mn is got when oxide of Cr and Mn react with Cl-. The chloride of Cr and Mn with water (for example CrCl3.6 (H2O) and MnCl2.n (H2O)) that has low melting point will escape from corrosion system. In addition, there is a salt crust that is composed of MgCl2. (H2O) 6, NaCl and MgO on molten salt upper surface, while NaCl coexists with NaMgCl3 inside mixture salt. The study laid the foundation for the study of corrosion-resistant alloy in molten NaCl-MgCl2.
2017, 46(4):942-945.
Abstract:
Silver copper oxide composites were prepared by the in-situ synthesized method. The samples were conducted by Accumulative Roll-bonding (ARB) at the temperature of 973K. The phase composition of AgSnO2 composite materials and the mechanical properties of the samples after ARB process were characterized by X-ray diffraction and optical microscope. The results show that accumulative roll-bonding produces a significant effect on the degree of homogenization AgSnO2 composite micro-structure. The density, hardness, resistivity of 4-passes ARB processed AgSnO2 composite material was studied, and the main factors affected the properties of the samples was discussed.
Silver copper oxide composites were prepared by the in-situ synthesized method. The samples were conducted by Accumulative Roll-bonding (ARB) at the temperature of 973K. The phase composition of AgSnO2 composite materials and the mechanical properties of the samples after ARB process were characterized by X-ray diffraction and optical microscope. The results show that accumulative roll-bonding produces a significant effect on the degree of homogenization AgSnO2 composite micro-structure. The density, hardness, resistivity of 4-passes ARB processed AgSnO2 composite material was studied, and the main factors affected the properties of the samples was discussed.
2017, 46(4):946-950.
Abstract:
In the investment casting of shifting fork,hot crack is the common defact.in order to analysis the hot cracking in the investment casting,The ProCAST software is adopted, the fork investment casting process is simulated,The filling field,temperature field and stress field is analysised, the cause of crack is predicted. The result shows that: as the local area is received larger tensile stress from around, the shrinkage cavity appears, leading to crack.By reducing the pouring temperature,increasing preheating temperature of the shell, increasing chamfer angle of the fork, the casting stress can be reduced, the crack can be avoided.
In the investment casting of shifting fork,hot crack is the common defact.in order to analysis the hot cracking in the investment casting,The ProCAST software is adopted, the fork investment casting process is simulated,The filling field,temperature field and stress field is analysised, the cause of crack is predicted. The result shows that: as the local area is received larger tensile stress from around, the shrinkage cavity appears, leading to crack.By reducing the pouring temperature,increasing preheating temperature of the shell, increasing chamfer angle of the fork, the casting stress can be reduced, the crack can be avoided.
2017, 46(4):951-954.
Abstract:
The SrFe12O19 ferrites with different amount of Bi2O3 additive were prepared by hot press sintering process at a low fired temperature of 870 °C compatible to the LTCC (low temperature co-fired ceramics) technology, and their low temperature sintering characteristics were investigated, including the crystal phase composition, sintering density, porosity, and magnetic properties. The results show that the addition of Bi2O3 promotes the formation of SrFe12O19 phase structure and increases the sintering compactness and magnetic properties for the ferrites fabricated at 870 °C. The ferrites with Bi2O3 content from 2 to 4 wt % exhibit a compact microstructure with sintering density higher than 4.65 g?cm-3 and porosity lower than 10%, which contributes to the enhanced saturation magnetization Ms and intrinsic coercivity Hci above 252.4 kA?m-1 and 312.9 kA?m-1, respectively. Moreover, the potentiality of the SrFe12O19 ferrites for use in microwave LTCC circulators is also discussed based on their low temperature sintering characteristics.
The SrFe12O19 ferrites with different amount of Bi2O3 additive were prepared by hot press sintering process at a low fired temperature of 870 °C compatible to the LTCC (low temperature co-fired ceramics) technology, and their low temperature sintering characteristics were investigated, including the crystal phase composition, sintering density, porosity, and magnetic properties. The results show that the addition of Bi2O3 promotes the formation of SrFe12O19 phase structure and increases the sintering compactness and magnetic properties for the ferrites fabricated at 870 °C. The ferrites with Bi2O3 content from 2 to 4 wt % exhibit a compact microstructure with sintering density higher than 4.65 g?cm-3 and porosity lower than 10%, which contributes to the enhanced saturation magnetization Ms and intrinsic coercivity Hci above 252.4 kA?m-1 and 312.9 kA?m-1, respectively. Moreover, the potentiality of the SrFe12O19 ferrites for use in microwave LTCC circulators is also discussed based on their low temperature sintering characteristics.
2017, 46(4):955-960.
Abstract:
Laser additive repairing technique was performed to repair the damaged aeroengine turbine blades made of K465 nickel-based superalloy. The cracks characteristics and cracking mechanism of the laser additive repaired K465 superalloy were investigated. The cracks were eliminated successfully by taking some effective measures. The results showed that the cracks originated from the heat affected zone of the laser additive repaired specimens, and extended to the repaired zone along the grain boundaries. The continuous liquid film was derived from the liquation of larger γ′ particles at the grain boundaries and γ-γ′ eutectics appeared during grain boundary liquation. Stress field simulation results obtained using the Ansys software demonstrated the existence of large thermal stresses at the zone between the substrate and the molten pool. Through preheating the substrates synchronously and adopting the optimized processing parameters, the laser additive repaired specimens with the structure of single track and multi layers without any cracks were obtained.
Laser additive repairing technique was performed to repair the damaged aeroengine turbine blades made of K465 nickel-based superalloy. The cracks characteristics and cracking mechanism of the laser additive repaired K465 superalloy were investigated. The cracks were eliminated successfully by taking some effective measures. The results showed that the cracks originated from the heat affected zone of the laser additive repaired specimens, and extended to the repaired zone along the grain boundaries. The continuous liquid film was derived from the liquation of larger γ′ particles at the grain boundaries and γ-γ′ eutectics appeared during grain boundary liquation. Stress field simulation results obtained using the Ansys software demonstrated the existence of large thermal stresses at the zone between the substrate and the molten pool. Through preheating the substrates synchronously and adopting the optimized processing parameters, the laser additive repaired specimens with the structure of single track and multi layers without any cracks were obtained.
2017, 46(4):961-965.
Abstract:
Low-density C/C composite was modified with Mo2C interlayers through molten salt method. The formation mechanism of Mo2C layers was analyzed; the effects of flux composition and reaction temperature on the abrication of Mo2C interlayers were studied; the influence of Mo2C-modification on the microstructure of C/C composite was also observed. Results show that the reaction between ammonium paramolybdate and C for the formation of Mo2C layers is mainly consist of three steps: decomposition from ammonium paramolybdate to MoO3, reduction of MoO3 to MoO2, carbonization of MoO2 to Mo2C. The appropriate flux of LiCl–KCl and the suitable reaction temperature as 1000℃ is determined according to the experimental results. Flower-like Mo2C layers are formed and then continuous Mo2C layer cover the surface of C phase with the increase of reaction time and temperature. The Mo2C/C interface showcases good bonding state. The pyrolytic carbon phase near the interface shows high order degree as the result of catalytic graphitization and stress graphitization. Modification of Mo2C interlayer for the C/C composite can facilitate the infiltration of Cu and its joining with Cu.
Low-density C/C composite was modified with Mo2C interlayers through molten salt method. The formation mechanism of Mo2C layers was analyzed; the effects of flux composition and reaction temperature on the abrication of Mo2C interlayers were studied; the influence of Mo2C-modification on the microstructure of C/C composite was also observed. Results show that the reaction between ammonium paramolybdate and C for the formation of Mo2C layers is mainly consist of three steps: decomposition from ammonium paramolybdate to MoO3, reduction of MoO3 to MoO2, carbonization of MoO2 to Mo2C. The appropriate flux of LiCl–KCl and the suitable reaction temperature as 1000℃ is determined according to the experimental results. Flower-like Mo2C layers are formed and then continuous Mo2C layer cover the surface of C phase with the increase of reaction time and temperature. The Mo2C/C interface showcases good bonding state. The pyrolytic carbon phase near the interface shows high order degree as the result of catalytic graphitization and stress graphitization. Modification of Mo2C interlayer for the C/C composite can facilitate the infiltration of Cu and its joining with Cu.
18 Effect of Electromagnetic Stirring on Melt Pool Solidification of Laser Melting TA15 Titanium Alloy
2017, 46(4):966-972.
Abstract:
In order to study the effect of electromagnetic stirring on melt pool solidification, a three-dimensional magnetic-thermal coupling numerical simulation was conducted on the process of single-pass laser melting TA15 titanium alloy with and without the magnetic field based on the finite volume method. The influence of electromagnetic field on temperature field, flow field, temperature gradient and solidification rate were analyzed. Then the numerical simulations were verified by experiment method. The results of numerical simulations showed that the melt pool maximum flow velocity increased by 20%, which promoted the function of heat exchange resulting in going down of the highest temperature of melt pool and temperature gradient on solid-liquid interface, and meanwhile the small rise in solidification rate, which were good for columnar-to-equiaxed transition at the top of melt pool. The experiment results indicated some equiaxed grains were generated at the top of melt layer with the magnetic field. Electromagnetic force was enlarged with an increase of the distance from magnetic field center, which causes equiaxed grain zone had a tendency to expand. The numerical simulations were in good agreement with the experimental results.
In order to study the effect of electromagnetic stirring on melt pool solidification, a three-dimensional magnetic-thermal coupling numerical simulation was conducted on the process of single-pass laser melting TA15 titanium alloy with and without the magnetic field based on the finite volume method. The influence of electromagnetic field on temperature field, flow field, temperature gradient and solidification rate were analyzed. Then the numerical simulations were verified by experiment method. The results of numerical simulations showed that the melt pool maximum flow velocity increased by 20%, which promoted the function of heat exchange resulting in going down of the highest temperature of melt pool and temperature gradient on solid-liquid interface, and meanwhile the small rise in solidification rate, which were good for columnar-to-equiaxed transition at the top of melt pool. The experiment results indicated some equiaxed grains were generated at the top of melt layer with the magnetic field. Electromagnetic force was enlarged with an increase of the distance from magnetic field center, which causes equiaxed grain zone had a tendency to expand. The numerical simulations were in good agreement with the experimental results.
2017, 46(4):973-978.
Abstract:
The hot deformation behaviors of β-CEZ alloy in the temperature range of 800~1000℃ and strain rate range of 0.001~10s-1 have been studied by hot compressing testing on a Gleeble-3800 simulator at the deformation degree of 0.7. The high temperature deformation behavior, the flow instability and the deformation mechanism in α β phase field and β phase field were studied by the true stress-true strain curves and processing map, which were established based on experimental data and Prasad criterion. The results shows that under the experimental conditions, β-CEZ titanium alloy shows two kinds of softening mechanism: dynamic recovery and recrystallization. The flow stress decreases continuously in α β phase field after the peak stress, decreases slightly and then tends gradually toward a constant value β phase field. The domains with high value of the efficiency of power dissipation (η) at α β phase field is 850~890℃/0.01~0.05s-1, which is the spheroidization of α lamellae area. And the domains with high value of the efficiency of power dissipation (η) at β phase field is 940~980℃/0.2~0.6s-1, which is the dynamic recrystallization area. The domains of flow instability are 800~850℃/0.1~10s-1, 850~900℃/0.1~5s-1 and 900~1000℃/1~10s-1. The manifestations of the flow instability at the α β phase field is the adiabatic shaer band, at the β phase field is the non-uniform deformation.
The hot deformation behaviors of β-CEZ alloy in the temperature range of 800~1000℃ and strain rate range of 0.001~10s-1 have been studied by hot compressing testing on a Gleeble-3800 simulator at the deformation degree of 0.7. The high temperature deformation behavior, the flow instability and the deformation mechanism in α β phase field and β phase field were studied by the true stress-true strain curves and processing map, which were established based on experimental data and Prasad criterion. The results shows that under the experimental conditions, β-CEZ titanium alloy shows two kinds of softening mechanism: dynamic recovery and recrystallization. The flow stress decreases continuously in α β phase field after the peak stress, decreases slightly and then tends gradually toward a constant value β phase field. The domains with high value of the efficiency of power dissipation (η) at α β phase field is 850~890℃/0.01~0.05s-1, which is the spheroidization of α lamellae area. And the domains with high value of the efficiency of power dissipation (η) at β phase field is 940~980℃/0.2~0.6s-1, which is the dynamic recrystallization area. The domains of flow instability are 800~850℃/0.1~10s-1, 850~900℃/0.1~5s-1 and 900~1000℃/1~10s-1. The manifestations of the flow instability at the α β phase field is the adiabatic shaer band, at the β phase field is the non-uniform deformation.
20 Crystallographic characteristics of β→α phase transformationat β grain boundaries in Ti-1300 alloy
2017, 46(4):979-984.
Abstract:
In order to obtain the essence of the nucleation phase and its variants selected of secondary α. Electronic backscatter diffraction (EBSD) has been employed to study the relationship between the crystal orientation, geometric growth direction, quantity, distribution of secondary α-phase and β-phase grain boundaries properties on nearly β-type Ti-1300 alloy. The alloy was equilibrated for 2 h at 910℃ and handled by water quenching. The alloy occurs a certain percentage of <110> 70.5° special boundaries. The alloy was slowly cooled in the furnace since 910℃, it has a significant relationship between the secondary α phase which from β→α phase transformation and β-phase grain boundaries properties. Common β/β grain boundary generated orientation is not unique, which has little effect on the nuclear of the Self -α phase grain boundary α phase variations, its relatively small number of both sides of since grain boundary α phase. The α phase grain boundary was generated by the common β/β grain boundary, its orientation was not unique. The common β/β grain boundary has little effect on the nuclear of the Self-α phase grain boundary α phase variations, and there are small number Self-α phase grain boundary both sides the α phase grain boundary. Both sides of the β grain which boundary is special high angle grain boundaries (<110>70.5°) have the same (110) plane. The orientation of the α phase grain boundary is favor for the formation of the heterogeneous nucleation of the Self-α phase grain boundary, which causes selective growth of the α variant on both sides in grain boundary; Special small-angle grain boundaries (<110>10.5°) also can cause α variant’s selective growth, but it is different from high-angle grain boundaries, the selective growth may only occur on one side of the grain boundary.
In order to obtain the essence of the nucleation phase and its variants selected of secondary α. Electronic backscatter diffraction (EBSD) has been employed to study the relationship between the crystal orientation, geometric growth direction, quantity, distribution of secondary α-phase and β-phase grain boundaries properties on nearly β-type Ti-1300 alloy. The alloy was equilibrated for 2 h at 910℃ and handled by water quenching. The alloy occurs a certain percentage of <110> 70.5° special boundaries. The alloy was slowly cooled in the furnace since 910℃, it has a significant relationship between the secondary α phase which from β→α phase transformation and β-phase grain boundaries properties. Common β/β grain boundary generated orientation is not unique, which has little effect on the nuclear of the Self -α phase grain boundary α phase variations, its relatively small number of both sides of since grain boundary α phase. The α phase grain boundary was generated by the common β/β grain boundary, its orientation was not unique. The common β/β grain boundary has little effect on the nuclear of the Self-α phase grain boundary α phase variations, and there are small number Self-α phase grain boundary both sides the α phase grain boundary. Both sides of the β grain which boundary is special high angle grain boundaries (<110>70.5°) have the same (110) plane. The orientation of the α phase grain boundary is favor for the formation of the heterogeneous nucleation of the Self-α phase grain boundary, which causes selective growth of the α variant on both sides in grain boundary; Special small-angle grain boundaries (<110>10.5°) also can cause α variant’s selective growth, but it is different from high-angle grain boundaries, the selective growth may only occur on one side of the grain boundary.
2017, 46(4):985-989.
Abstract:
The hot compression curves of Nb bulk materials were measured by Gleeble-3500 thermal simulation machine. The flow stress behavior and the deformation microstructures of the materials were analyzed at the temperature range of 350-480 ℃ and the strain rate range of 0.001-10 S-1. It is shown that the flow stress reduces with the increasing of the deformation temperature and the strain rate. The elongated grains coarsen with the decreasing of the temperature. And dynamic recovery occurs during the hot compression. The soften mechanism also works by the dynamic recovery. Moreover, the constitutive equation of the strain rate affected by the temperature, strain and the hot deformation activation energy was deduced by the help of the modified hyperbolic sine function of Arrhenius and factor of Zener-HolIomon parameters. The simplified relation was adopted to fit the curves of the flow stress versus the strain at different temperature resulting in good effect.
The hot compression curves of Nb bulk materials were measured by Gleeble-3500 thermal simulation machine. The flow stress behavior and the deformation microstructures of the materials were analyzed at the temperature range of 350-480 ℃ and the strain rate range of 0.001-10 S-1. It is shown that the flow stress reduces with the increasing of the deformation temperature and the strain rate. The elongated grains coarsen with the decreasing of the temperature. And dynamic recovery occurs during the hot compression. The soften mechanism also works by the dynamic recovery. Moreover, the constitutive equation of the strain rate affected by the temperature, strain and the hot deformation activation energy was deduced by the help of the modified hyperbolic sine function of Arrhenius and factor of Zener-HolIomon parameters. The simplified relation was adopted to fit the curves of the flow stress versus the strain at different temperature resulting in good effect.
2017, 46(4):990-996.
Abstract:
By means of the tests of creep performance and the measurements of internal friction stresses, the effective creep parameters of the [001]-, [011]- and [111]-oriented single crystal nickel-base superalloys after being crept to steady-state stage under the conditions of high temperatures/low stresses along [001], [011] and [111] orientations respectively, and their relationship with the creep performance and deformation mechanism have been studied. Results show that, with the increase of creep temperatures and decrease of applied stresses, the internal friction stresses of the three alloys decrease. Under the same conditions, the order of the internal friction stresses is σi[001] > σi[111] > σi[011]. The inclined and continuous “roof”-type γ channels in the [011]- and [111]-oriented alloys before and after creep are responsible for the low internal friction stress and poor creep resistance of the two alloys. The effective creep activation energy of the [001] oriented alloy is Qe[001]= 281.32 KJ/mol, indicating that the deformation mechanism during steady-state creep stage is the dislocation climb controlled by element diffusion. The effective creep activation energy of the [011]-oriented alloy is Qe[011]= 139.74, and the low value is related to the open ? matrix channels possessing small resistance for dislocation slip. The effective creep activation energy of the [111]-oriented alloy is Qe[111]= 182.61 kJ/mol, and the relatively larger value compared to that of the [011]-oriented alloy is related to the lamellar γ’ rafts and the cross slip of dislocations in the [111]-oriented alloy.
By means of the tests of creep performance and the measurements of internal friction stresses, the effective creep parameters of the [001]-, [011]- and [111]-oriented single crystal nickel-base superalloys after being crept to steady-state stage under the conditions of high temperatures/low stresses along [001], [011] and [111] orientations respectively, and their relationship with the creep performance and deformation mechanism have been studied. Results show that, with the increase of creep temperatures and decrease of applied stresses, the internal friction stresses of the three alloys decrease. Under the same conditions, the order of the internal friction stresses is σi[001] > σi[111] > σi[011]. The inclined and continuous “roof”-type γ channels in the [011]- and [111]-oriented alloys before and after creep are responsible for the low internal friction stress and poor creep resistance of the two alloys. The effective creep activation energy of the [001] oriented alloy is Qe[001]= 281.32 KJ/mol, indicating that the deformation mechanism during steady-state creep stage is the dislocation climb controlled by element diffusion. The effective creep activation energy of the [011]-oriented alloy is Qe[011]= 139.74, and the low value is related to the open ? matrix channels possessing small resistance for dislocation slip. The effective creep activation energy of the [111]-oriented alloy is Qe[111]= 182.61 kJ/mol, and the relatively larger value compared to that of the [011]-oriented alloy is related to the lamellar γ’ rafts and the cross slip of dislocations in the [111]-oriented alloy.
2017, 46(4):997-1002.
Abstract:
The effect of lanthanum-cerium mischmetal on the kinetics and the microstructure of the super-cooled austenite continuous cooling transformation in 20MnCrNi2Mo wear-resistant cast steel by L78 RITA quenching thermal dilatometer, QUANTA-400 scanning electron microscope, JEM-2100 transmission electron microscope and so on. The ICP-MS inductively coupled plasma mass spectrometry was used to measure the amount of rare earth solid solution and the JEM-2100 transmission electron microscope was utilized to probe the existential state of the solid-solution rare earth. The action mechanism of the solid-solution rare earth was analyzed combined with the measurement of the interface diffusion coefficient of La. The results show that the CCT curves are moved to the bottom right, the hardenability is improved and the twin substructure in lath martensite is increased due to the effect of the rare earth. The trace amount of solid-solution rare earth can exist in grain boundary, dislocation and other crystal defects. They can reduce the grain boundary energy, block the diffusion channels and then defer the nucleation and growth of the new phase. So the phase transformation and the microstructure are influenced.
The effect of lanthanum-cerium mischmetal on the kinetics and the microstructure of the super-cooled austenite continuous cooling transformation in 20MnCrNi2Mo wear-resistant cast steel by L78 RITA quenching thermal dilatometer, QUANTA-400 scanning electron microscope, JEM-2100 transmission electron microscope and so on. The ICP-MS inductively coupled plasma mass spectrometry was used to measure the amount of rare earth solid solution and the JEM-2100 transmission electron microscope was utilized to probe the existential state of the solid-solution rare earth. The action mechanism of the solid-solution rare earth was analyzed combined with the measurement of the interface diffusion coefficient of La. The results show that the CCT curves are moved to the bottom right, the hardenability is improved and the twin substructure in lath martensite is increased due to the effect of the rare earth. The trace amount of solid-solution rare earth can exist in grain boundary, dislocation and other crystal defects. They can reduce the grain boundary energy, block the diffusion channels and then defer the nucleation and growth of the new phase. So the phase transformation and the microstructure are influenced.
2017, 46(4):1003-1007.
Abstract:
Compound modification of Al-25% Si alloy with P-Cr-Ti is utilized to study the change of the solidification microstructure and the effect mechanism of Cr and Ti elements. The results indicate that primary Si in the solidification microstructure decreases by 12.24%~51.65% in the Al-25% Si alloy modified by the compound modifier P-Cr-Ti compared with simple phosphorus modification, and the distribution of the primary Si is more uniform. The Cr and Ti elements in the Al-25%Si alloy mainly appear as compounds including TiAl3, Ti7Al5Si12, Al7Cr and Al13Cr4Si4, while a minor amount of P exists in the compounds containing Ti. Compounds containing Ti appear as long strips. Compounds containing Cr, which distribute among the primary Si, appear as granular or short rods. The number of the compounds containing Cr and Ti is increased with the increase of the cooling rate. The TiAl3 phase initiated by Al-6.5%Ti alloy wanders in the melt during the modifier process. The {110} crystal of TiAl3 phase becomes the nucleation basal of the Si phase, causing the primary Si to precipitate continuously and to refine the primary Si with a limited refining ability. Compounds containing Cr formed among the primary Si prevent the growth and gather of the primary Si during the solidification, which leads to the distribution of the primary Si more even.
Compound modification of Al-25% Si alloy with P-Cr-Ti is utilized to study the change of the solidification microstructure and the effect mechanism of Cr and Ti elements. The results indicate that primary Si in the solidification microstructure decreases by 12.24%~51.65% in the Al-25% Si alloy modified by the compound modifier P-Cr-Ti compared with simple phosphorus modification, and the distribution of the primary Si is more uniform. The Cr and Ti elements in the Al-25%Si alloy mainly appear as compounds including TiAl3, Ti7Al5Si12, Al7Cr and Al13Cr4Si4, while a minor amount of P exists in the compounds containing Ti. Compounds containing Ti appear as long strips. Compounds containing Cr, which distribute among the primary Si, appear as granular or short rods. The number of the compounds containing Cr and Ti is increased with the increase of the cooling rate. The TiAl3 phase initiated by Al-6.5%Ti alloy wanders in the melt during the modifier process. The {110} crystal of TiAl3 phase becomes the nucleation basal of the Si phase, causing the primary Si to precipitate continuously and to refine the primary Si with a limited refining ability. Compounds containing Cr formed among the primary Si prevent the growth and gather of the primary Si during the solidification, which leads to the distribution of the primary Si more even.
2017, 46(4):1008-1012.
Abstract:
Experimental object of this paper is the solution-aging and solution-large deformation (compression,ECAP)-aging of 7085 aluminum alloy. Through the tensile testing machine and scanning electron microscope (SEM) to test the tensile properties and fracture analysis. Internal dislocation density, low angle grain boundary and high angle grain boundary of 7085 aluminum alloy under different states were characterized through X-ray diffractometer (XRD) and Electron Back Scattering Diffraction (EBSD) .Combined tensile test measured yield strength, strengthen the contribution of the large deformation strengthening aluminum items of the quantitative calculation.The results show that, compared with conventional solution-aging treatment, the solution-large deformation - aging treatment can significantly refine grain size, increase the number of low angle grain boundary, prompt uniform distribution of precipitated phase so as to advance yield stress. Especially, Equal Channel Angular Pressing (ECAP) is more effective than compression in improving overall performance. Large deformation processing of 7085 aluminum alloy also makes a lot of internal accumulation of dislocations, large deformation processing was improving performance mainly depends on the alloy dislocation strengthening and small-angle grain boundary strengthening, alloy internal solid solution strengthening and second phase strengthening has been weakened by large deformation processed.
Experimental object of this paper is the solution-aging and solution-large deformation (compression,ECAP)-aging of 7085 aluminum alloy. Through the tensile testing machine and scanning electron microscope (SEM) to test the tensile properties and fracture analysis. Internal dislocation density, low angle grain boundary and high angle grain boundary of 7085 aluminum alloy under different states were characterized through X-ray diffractometer (XRD) and Electron Back Scattering Diffraction (EBSD) .Combined tensile test measured yield strength, strengthen the contribution of the large deformation strengthening aluminum items of the quantitative calculation.The results show that, compared with conventional solution-aging treatment, the solution-large deformation - aging treatment can significantly refine grain size, increase the number of low angle grain boundary, prompt uniform distribution of precipitated phase so as to advance yield stress. Especially, Equal Channel Angular Pressing (ECAP) is more effective than compression in improving overall performance. Large deformation processing of 7085 aluminum alloy also makes a lot of internal accumulation of dislocations, large deformation processing was improving performance mainly depends on the alloy dislocation strengthening and small-angle grain boundary strengthening, alloy internal solid solution strengthening and second phase strengthening has been weakened by large deformation processed.
2017, 46(4):1013-1019.
Abstract:
Because of its superior high-temperature creep strength in combination with good workability and low cost compared to its Ni-Co-Cr based counterparts, GH 2984 alloy is evaluated to be a candidate material for applying as superheater/ reheater in 700℃ ultra-supercritical coal-fired power plants. At such high temperature (up to 700-760℃), the corrosion behavior of the alloy in steam is of great concern mainly due to the thickness of the oxide scales that are formed. In the present work, the oxidation behavior of GH 2984 alloy in pure steam at 750℃ has been investigated by using scanning electron microscope and X-ray diffractometer. The results show that a single Cr2O3 layer is formed with minor TiO2 solid soluted in it. Ti and Al are internally oxidized into TiO2 and Al2O3, respectively, preferentially along grain boundaries in the alloy underneath the Cr2O3 scale. The oxidation kinetic of the alloy observes a parabolic law. Investigation on the morphology evolution figures out that Cr2O3 blades formed initially which decreased in number and length and finally evolved into short rod-like ones with increasing oxidation time. The reason for the Cr2O3 nodules and blades formation and the oxidation mechanism of GH 2984 alloy in pure steam is discussed in detail.
Because of its superior high-temperature creep strength in combination with good workability and low cost compared to its Ni-Co-Cr based counterparts, GH 2984 alloy is evaluated to be a candidate material for applying as superheater/ reheater in 700℃ ultra-supercritical coal-fired power plants. At such high temperature (up to 700-760℃), the corrosion behavior of the alloy in steam is of great concern mainly due to the thickness of the oxide scales that are formed. In the present work, the oxidation behavior of GH 2984 alloy in pure steam at 750℃ has been investigated by using scanning electron microscope and X-ray diffractometer. The results show that a single Cr2O3 layer is formed with minor TiO2 solid soluted in it. Ti and Al are internally oxidized into TiO2 and Al2O3, respectively, preferentially along grain boundaries in the alloy underneath the Cr2O3 scale. The oxidation kinetic of the alloy observes a parabolic law. Investigation on the morphology evolution figures out that Cr2O3 blades formed initially which decreased in number and length and finally evolved into short rod-like ones with increasing oxidation time. The reason for the Cr2O3 nodules and blades formation and the oxidation mechanism of GH 2984 alloy in pure steam is discussed in detail.
2017, 46(4):1020-1025.
Abstract:
In this paper, the Ag-doped titania nanotube arrays was successfully fabricated by steps of preparation of titania nanotube arrays on the surface of pure titania and the Ag-doped technology of thermal drive, which has excellent bioactive and antibacterial performance. The researches show that the mechanism of thermal drive Ag-doped is the collaboration of thermal decomposition of silver nitrate in the limited space with the phase transition of titania at low temperature. After being soaked in saturated silver nitrate and annealed at 300℃, the titania nanotube arrays can realize not only the low temperature phase transition from amorphous to rutile, but also the low temperature decomposition of silver nitrate within it.
In this paper, the Ag-doped titania nanotube arrays was successfully fabricated by steps of preparation of titania nanotube arrays on the surface of pure titania and the Ag-doped technology of thermal drive, which has excellent bioactive and antibacterial performance. The researches show that the mechanism of thermal drive Ag-doped is the collaboration of thermal decomposition of silver nitrate in the limited space with the phase transition of titania at low temperature. After being soaked in saturated silver nitrate and annealed at 300℃, the titania nanotube arrays can realize not only the low temperature phase transition from amorphous to rutile, but also the low temperature decomposition of silver nitrate within it.
2017, 46(4):1026-1032.
Abstract:
TiCN coatings have been deposited on 304 stainless steel by newly developed cathodic arc deposition enhanced by additional electric field. The effect of the current of additional electrode on cathode arc discharge, film microstructure, cross-sectional morphology, wear resistance and adhesion between film and substrate have been investigated. The experimental results show the plasma density has been substantially increased after introduction of additional electrode in the chamber and the substrate current is improved by nearly 100%. Only a properly higher current of additional electrode may effectively decrease the crystal size and make the film structure much denser, consequently the critical load of deposited films has been enhanced. The sample deposited at a 30A-current of additional electrode possesses the highest adhesion force between film and substrate (HF1), best wear-resistance featured by narrowest wear track. The friction coefficient may decrease by 33% compared to the sample fabricated without the assistance of additional electrode. In summary cathodic arc deposition enhanced by additional electric field is an effective tool to fabricate TiCN films.
TiCN coatings have been deposited on 304 stainless steel by newly developed cathodic arc deposition enhanced by additional electric field. The effect of the current of additional electrode on cathode arc discharge, film microstructure, cross-sectional morphology, wear resistance and adhesion between film and substrate have been investigated. The experimental results show the plasma density has been substantially increased after introduction of additional electrode in the chamber and the substrate current is improved by nearly 100%. Only a properly higher current of additional electrode may effectively decrease the crystal size and make the film structure much denser, consequently the critical load of deposited films has been enhanced. The sample deposited at a 30A-current of additional electrode possesses the highest adhesion force between film and substrate (HF1), best wear-resistance featured by narrowest wear track. The friction coefficient may decrease by 33% compared to the sample fabricated without the assistance of additional electrode. In summary cathodic arc deposition enhanced by additional electric field is an effective tool to fabricate TiCN films.
2017, 46(4):1033-1042.
Abstract:
In the present study, ZrC nanocrystalline coating was synthesized on Ti-6A1-4V alloy as bipolar plates for PEMFC by a double glow discharge plasma technique. The microstructure of as-prepared ZrC coating was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM). Electrochemical measurements were carried out on a CHI604D electrochemical workstation in the simulated PEMFC anodic and cathodic environments. The hydrophilicity and interfacial contact resistance of the ZrC nanocrystalline coating were also evaluated. The microstructure of as-prepared ZrC coating consists of deposited layer and diffusion layer. The 10 μm thick deposited layer shows a dense columnar microstructure, composed of equiaxed grains with an average grain size of ~12 nm, whereas the 4 μm thick diffusion layer with the gradient distribution of alloying elements offers a smooth transition of mechanical properties, which is beneficial to improve the adhesion strength of the ZrC coating on the Ti-6A1-4V substrate. The Ecorr of the as-deposited ZrC nanocrystalline coating is obviously higher than that of Ti-6A1-4V alloy in a simuiated PEMFC environment. At applied cathode ( 0.6 V) potential for PEMFC, ZrC nanocrystalline coating is in passive region, and the passive current density is four orders of magnitude lower than that of Ti-6A1-4V alloy. At applied anode (-0.1 V) potentia, ZrC nanocrystalline coating exhibits the characteristic of cathodic protection. The results of OCP and EIS showed that the higher the temperature, the worse the corrosion resistance of bipolar plates. And the temperature corrosion susceptibility of ZrC nanocrystalline coating is obviously lower than Ti-6A1-4V alloy. Moreover, ZrC nanocrystalline coating can effectively improve conductivity and hydrophobic nature of Ti-6A1-4V alloy bipolar plate.
In the present study, ZrC nanocrystalline coating was synthesized on Ti-6A1-4V alloy as bipolar plates for PEMFC by a double glow discharge plasma technique. The microstructure of as-prepared ZrC coating was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscopy (TEM). Electrochemical measurements were carried out on a CHI604D electrochemical workstation in the simulated PEMFC anodic and cathodic environments. The hydrophilicity and interfacial contact resistance of the ZrC nanocrystalline coating were also evaluated. The microstructure of as-prepared ZrC coating consists of deposited layer and diffusion layer. The 10 μm thick deposited layer shows a dense columnar microstructure, composed of equiaxed grains with an average grain size of ~12 nm, whereas the 4 μm thick diffusion layer with the gradient distribution of alloying elements offers a smooth transition of mechanical properties, which is beneficial to improve the adhesion strength of the ZrC coating on the Ti-6A1-4V substrate. The Ecorr of the as-deposited ZrC nanocrystalline coating is obviously higher than that of Ti-6A1-4V alloy in a simuiated PEMFC environment. At applied cathode ( 0.6 V) potential for PEMFC, ZrC nanocrystalline coating is in passive region, and the passive current density is four orders of magnitude lower than that of Ti-6A1-4V alloy. At applied anode (-0.1 V) potentia, ZrC nanocrystalline coating exhibits the characteristic of cathodic protection. The results of OCP and EIS showed that the higher the temperature, the worse the corrosion resistance of bipolar plates. And the temperature corrosion susceptibility of ZrC nanocrystalline coating is obviously lower than Ti-6A1-4V alloy. Moreover, ZrC nanocrystalline coating can effectively improve conductivity and hydrophobic nature of Ti-6A1-4V alloy bipolar plate.
2017, 46(4):1043-1048.
Abstract:
W-Cu-Zn alloy with Cu-Zn matrix and low W-W contiguity was prepared by electroless copper plating combined with SPS solid-phase sintering processes. The influence of heat treatment on the microstructure and mechanical properties of the alloy was investigated. Microstructure analysis reveals that tungsten particles distributed in the Cu-Zn matrix phase homogeneously. The Cu-Zn matrix phase is α-phase solid solution. The distribution of tungsten particles and Cu-Zn matrix phase has not changed after the normalizing heat treatment. However, the mechanical properties of W-Cu-Zn alloy has has evidently improved after annealing heat treatment at 870℃ followed by furnace cooling. Under quasi-static compression, the strength of W-Cu-Zn alloy increases from 650 MPa to 750MPa, and the critical failure strain increases from 0.18 to 0.26. Under dynamic compression, the strength of W-Cu-Zn alloy increases from 710 MPa to 900MPa, and the critical failure strain increases from 0.18 to 0.26. The hardness increases from 143.8HV to 172.3HV. Mechanism analysis reveals that there are two factors contributing to improvement of the mechanical properties of W-Cu-Zn alloy. Firstly, the distribution of elenment Zn is unhomogeneously within the original W-Cu-Zn alloy. The specimen processed by annealing heat treatment at 870℃ followed by furnace cooling exhibites advantage of homogeneous distribution of Zn within the matrix. Secontlly, a large number of fine Cu3Zn precipitates are formed uniformly in the Cu-Zn matrix phase of W-Cu-Zn alloy after annealing heat treatment at 870℃ followed by furnace cooling, which plays the role of dispersion strengthening.
W-Cu-Zn alloy with Cu-Zn matrix and low W-W contiguity was prepared by electroless copper plating combined with SPS solid-phase sintering processes. The influence of heat treatment on the microstructure and mechanical properties of the alloy was investigated. Microstructure analysis reveals that tungsten particles distributed in the Cu-Zn matrix phase homogeneously. The Cu-Zn matrix phase is α-phase solid solution. The distribution of tungsten particles and Cu-Zn matrix phase has not changed after the normalizing heat treatment. However, the mechanical properties of W-Cu-Zn alloy has has evidently improved after annealing heat treatment at 870℃ followed by furnace cooling. Under quasi-static compression, the strength of W-Cu-Zn alloy increases from 650 MPa to 750MPa, and the critical failure strain increases from 0.18 to 0.26. Under dynamic compression, the strength of W-Cu-Zn alloy increases from 710 MPa to 900MPa, and the critical failure strain increases from 0.18 to 0.26. The hardness increases from 143.8HV to 172.3HV. Mechanism analysis reveals that there are two factors contributing to improvement of the mechanical properties of W-Cu-Zn alloy. Firstly, the distribution of elenment Zn is unhomogeneously within the original W-Cu-Zn alloy. The specimen processed by annealing heat treatment at 870℃ followed by furnace cooling exhibites advantage of homogeneous distribution of Zn within the matrix. Secontlly, a large number of fine Cu3Zn precipitates are formed uniformly in the Cu-Zn matrix phase of W-Cu-Zn alloy after annealing heat treatment at 870℃ followed by furnace cooling, which plays the role of dispersion strengthening.
2017, 46(4):1049-1053.
Abstract:
FeSiB soft magnetic composites (SMCs) were prepared via powder metallurgy. Influences of passivator solvent, content of the passivator as well as annealing temperature on the morphology and properties of the samples have been investigated. Alcohol has been used to dissolve phosphoric acid as the surface passivator and its effect has been compared with water and acetone. The results show that the magnetic powders tend to be oxidized with water, while acetone hinders the complete surface passivation as a result of limited reaction time caused by low boiling point and strong volatility of the acetone. Uniform insulating coating can be achieved using alcohol as the passivator solvent for decreased core loss. With the content of orthophosphoric acid varied between 0.2~0.8 wt% in alcohol, lowest core loss (187 mW/cm3 measured at 50 kHz, 50 mT) can be obtained with 0.6 wt% of orthophosphoric acid. Annealing temperatures below 400 ℃ are insufficient for complete stress relaxation for the SMCs, resulting in low permeability and high core loss, whle precipitation of the α-Fe phase occurs with annealing temperatures higher than 425 ℃. Optimized properties of the FeSiB SMCs can be achieved by annealing at 400 ℃ for 1 h.
FeSiB soft magnetic composites (SMCs) were prepared via powder metallurgy. Influences of passivator solvent, content of the passivator as well as annealing temperature on the morphology and properties of the samples have been investigated. Alcohol has been used to dissolve phosphoric acid as the surface passivator and its effect has been compared with water and acetone. The results show that the magnetic powders tend to be oxidized with water, while acetone hinders the complete surface passivation as a result of limited reaction time caused by low boiling point and strong volatility of the acetone. Uniform insulating coating can be achieved using alcohol as the passivator solvent for decreased core loss. With the content of orthophosphoric acid varied between 0.2~0.8 wt% in alcohol, lowest core loss (187 mW/cm3 measured at 50 kHz, 50 mT) can be obtained with 0.6 wt% of orthophosphoric acid. Annealing temperatures below 400 ℃ are insufficient for complete stress relaxation for the SMCs, resulting in low permeability and high core loss, whle precipitation of the α-Fe phase occurs with annealing temperatures higher than 425 ℃. Optimized properties of the FeSiB SMCs can be achieved by annealing at 400 ℃ for 1 h.
2017, 46(4):1054-1060.
Abstract:
The metal bond diamond wheels adding 3wt% brittle Na2O-B2O3-SiO2-Al2O3-Li2O glass bond were fabricated by hot pressed sintering technique at different sintering temperature. Using the methods of scan-electroscope, energy spectrum analysis, X-diffraction analysis, XPS analysis, rockwell hardness test and three-point bending test, the effect of different sintering temperatures on the microstructure, interface structure,hardness and the bending strength of glass/metal composite bond were discussed. Meanwhile, the grinding performance of cylinder of the diamond wheels was also studied. The results showed that, at 850℃, a thin FeAl2O4 transition layer formed and enhanced the interfacial adhesion toughness between metal and ceramic phase, and the bending strength of composite bond reached the maximum value826MPa, and the hardness was HRB94. At 900℃, the brittle and thickening FeAl2O4 transition layer decreased the bending strength of composite bond. When the sintering temperature was 850℃, comparing with metal bond diamond wheel, the average value of the roundness and straightness tolerance of the cylinder grinded by the diamond wheel with 3wt% glass bond reduced from 3.1μm and 2.5μm to 2.7μm and 2.1μm.
The metal bond diamond wheels adding 3wt% brittle Na2O-B2O3-SiO2-Al2O3-Li2O glass bond were fabricated by hot pressed sintering technique at different sintering temperature. Using the methods of scan-electroscope, energy spectrum analysis, X-diffraction analysis, XPS analysis, rockwell hardness test and three-point bending test, the effect of different sintering temperatures on the microstructure, interface structure,hardness and the bending strength of glass/metal composite bond were discussed. Meanwhile, the grinding performance of cylinder of the diamond wheels was also studied. The results showed that, at 850℃, a thin FeAl2O4 transition layer formed and enhanced the interfacial adhesion toughness between metal and ceramic phase, and the bending strength of composite bond reached the maximum value826MPa, and the hardness was HRB94. At 900℃, the brittle and thickening FeAl2O4 transition layer decreased the bending strength of composite bond. When the sintering temperature was 850℃, comparing with metal bond diamond wheel, the average value of the roundness and straightness tolerance of the cylinder grinded by the diamond wheel with 3wt% glass bond reduced from 3.1μm and 2.5μm to 2.7μm and 2.1μm.
2017, 46(4):1061-1066.
Abstract:
Gelcasting was employed to fabricate Si3N4/SiC whisker (SiCw) composite ceramics. SEM showed the effects of heat-treatment temperature on the length-to-diameter ratio of the whiskers. The open porosity of composite ceramics declined and density increased as the whisker content raised when the sintering temperature increased. Study also showed that both the real (ε￠) and imaginary (ε2) permittivity of Si3N4/SiC whisker (SiCw) composite ceramics decreased with increasing frequency and increased as the whisker content raised in the frequency range of 8.2~12.4GHz. As the whisker content increased from 5 wt% to 15
Gelcasting was employed to fabricate Si3N4/SiC whisker (SiCw) composite ceramics. SEM showed the effects of heat-treatment temperature on the length-to-diameter ratio of the whiskers. The open porosity of composite ceramics declined and density increased as the whisker content raised when the sintering temperature increased. Study also showed that both the real (ε￠) and imaginary (ε2) permittivity of Si3N4/SiC whisker (SiCw) composite ceramics decreased with increasing frequency and increased as the whisker content raised in the frequency range of 8.2~12.4GHz. As the whisker content increased from 5 wt% to 15
2017, 46(4):1067-1073.
Abstract:
Ti-12Nb-12Zr-2Mo alloy has been prepared by water jacketed copper crucible induction melting furnace. The heat treatment was processed using a vacuum furnace. Microstructure and mechanical properties of as-cast and heat treated alloy were systematic invested using XRD, SEM, TEM and mechanical test. The results show that microstructure of as-cast and annealed alloy were composed of α and β phase, while for quenched alloy was α′ and β phase. Heat treatment is conductive to improve strength and remain elastic modulus the same.
Ti-12Nb-12Zr-2Mo alloy has been prepared by water jacketed copper crucible induction melting furnace. The heat treatment was processed using a vacuum furnace. Microstructure and mechanical properties of as-cast and heat treated alloy were systematic invested using XRD, SEM, TEM and mechanical test. The results show that microstructure of as-cast and annealed alloy were composed of α and β phase, while for quenched alloy was α′ and β phase. Heat treatment is conductive to improve strength and remain elastic modulus the same.
2017, 46(4):1074-1079.
Abstract:
F101 Ni-based alloy coating and F101 Ni-based alloy coating with 2%wt La2O3 were fabricated on TC4 titanium alloy, under proper laser cladding parameter, using F101 Ni-based fluxed alloy powder and F101 Ni-based fluxed alloy powder with 2%wt La2O3. Macro morphology, phase composition, microstructure, microhardness and friction properties of 2 kinds of the coatings were compared and analysed. The results show that: adding rare-earth La2O3 effectively improves the absorption rate of laser irradiation; more Ti-rich phases are formed and the uniformity and densification of the microstructure are improved; To some extent, the hardness and friction property of the coating are reduced due to the excessive elements diffusion from TC4 matrix into the coating, but compared with TC4, the friction coefficient of the coating is reduced (0.41 vs 0.45) and the friction property is still 2.89 times of TC4.
F101 Ni-based alloy coating and F101 Ni-based alloy coating with 2%wt La2O3 were fabricated on TC4 titanium alloy, under proper laser cladding parameter, using F101 Ni-based fluxed alloy powder and F101 Ni-based fluxed alloy powder with 2%wt La2O3. Macro morphology, phase composition, microstructure, microhardness and friction properties of 2 kinds of the coatings were compared and analysed. The results show that: adding rare-earth La2O3 effectively improves the absorption rate of laser irradiation; more Ti-rich phases are formed and the uniformity and densification of the microstructure are improved; To some extent, the hardness and friction property of the coating are reduced due to the excessive elements diffusion from TC4 matrix into the coating, but compared with TC4, the friction coefficient of the coating is reduced (0.41 vs 0.45) and the friction property is still 2.89 times of TC4.
36 Effect of tungsten fiber diameter on penetration ability of the Zr-based metallic glass composites
2017, 46(4):1080-1085.
Abstract:
Penetration experiments are studied for Zr-based metallic glass composites containing four kinds of tungsten fiber with different diameters to perforate homogeneous armorSsteel at velocity 1270m/s±40m/s, in which the characteristics and depths of penetration is analyzed compared with the tungsten alloy. The results demonstrate that under the same preparation technology, the diameter of the tungsten fiber is a critical parameter for penetration ability. Firstly, the curve of the diameter of the tungsten with the penetration depth is convex when it perforates ideally and the composite containing 0.7mm tungsten fiber obtain the maximum penetration depth of 55mm which is increased by 25% compared with tungsten alloy because the failure mode is failed with adiabatic shear failure during the penetration similar with the depleted uranium alloy appearing a crater 90° at bottom. Secondly, the diameter of tungsten fiber influences the failure mode of the head of the composites significantly. As the increasing of the tungsten fiber diameter , the failure mode ranges from composite failure mode that includes deformation, splitting, bending and crack to adiabatic shear failure and then it turns to composite failure mode again.
Penetration experiments are studied for Zr-based metallic glass composites containing four kinds of tungsten fiber with different diameters to perforate homogeneous armorSsteel at velocity 1270m/s±40m/s, in which the characteristics and depths of penetration is analyzed compared with the tungsten alloy. The results demonstrate that under the same preparation technology, the diameter of the tungsten fiber is a critical parameter for penetration ability. Firstly, the curve of the diameter of the tungsten with the penetration depth is convex when it perforates ideally and the composite containing 0.7mm tungsten fiber obtain the maximum penetration depth of 55mm which is increased by 25% compared with tungsten alloy because the failure mode is failed with adiabatic shear failure during the penetration similar with the depleted uranium alloy appearing a crater 90° at bottom. Secondly, the diameter of tungsten fiber influences the failure mode of the head of the composites significantly. As the increasing of the tungsten fiber diameter , the failure mode ranges from composite failure mode that includes deformation, splitting, bending and crack to adiabatic shear failure and then it turns to composite failure mode again.
2017, 46(4):1086-1091.
Abstract:
In-situ β-Zr/ Zr-based metallic glass matrix composites with diameter of 3 mm were fabricated by conventional Cu-mold casting method and the wear behavior underSdrySslidingScondition of the composites were investigated. The results indicate that compared to the pure BMG, the composites exhibited a markedly improved wear resistance. The composites showed lower friction coefficient and wear rate than the pure BMG. The lowest wear rate in these composites is 48.1% lower than that of the pure BMG. Meanwhile, the worn surface of a proper amount of composite is less severe and there were shallow grooves with some fine wear debris on the worn surface, which exhibited the characteristic of mild abrasive, whereas that of the pure BMG is characterized by flakes, delamination, pile-up and deep grooves which show a severe abrasive wear mode. The improvement of the wear resistance of the composites is attributed to the fact that the β-Zr crystalline phase distributed in the amorphous matrix has some effective load bearing, plastic deformation and work hardening ability to decrease strain accumulation and the release of strain energy in the glassy matrix, restrict the expanding of shear bands and cracks, and occur plastic deformation homogeneously.
In-situ β-Zr/ Zr-based metallic glass matrix composites with diameter of 3 mm were fabricated by conventional Cu-mold casting method and the wear behavior underSdrySslidingScondition of the composites were investigated. The results indicate that compared to the pure BMG, the composites exhibited a markedly improved wear resistance. The composites showed lower friction coefficient and wear rate than the pure BMG. The lowest wear rate in these composites is 48.1% lower than that of the pure BMG. Meanwhile, the worn surface of a proper amount of composite is less severe and there were shallow grooves with some fine wear debris on the worn surface, which exhibited the characteristic of mild abrasive, whereas that of the pure BMG is characterized by flakes, delamination, pile-up and deep grooves which show a severe abrasive wear mode. The improvement of the wear resistance of the composites is attributed to the fact that the β-Zr crystalline phase distributed in the amorphous matrix has some effective load bearing, plastic deformation and work hardening ability to decrease strain accumulation and the release of strain energy in the glassy matrix, restrict the expanding of shear bands and cracks, and occur plastic deformation homogeneously.
2017, 46(4):1092-1096.
Abstract:
With the secondary sphericity particles mading of 1~2μm size Ta powder as raw material,Tantalum porous material was prepared by compression molding, vacuum sintering. The effect of sintering temperature on Ta porous material performance was researched. The results show that the Ta green body occur shrinkage because of sintering-neck come into being and growing up during the sinter. The porosity and penetrate coefficient of decrease and the shear strength improved with increase the sintering temperature. Ta porous material was provided with favorable three-dimensional meshwork in connection with big and small pore while maximum pore size is the minimum for 1600℃sintering temperature. The pore size less than 3.1μm is proportion of 98%.
With the secondary sphericity particles mading of 1~2μm size Ta powder as raw material,Tantalum porous material was prepared by compression molding, vacuum sintering. The effect of sintering temperature on Ta porous material performance was researched. The results show that the Ta green body occur shrinkage because of sintering-neck come into being and growing up during the sinter. The porosity and penetrate coefficient of decrease and the shear strength improved with increase the sintering temperature. Ta porous material was provided with favorable three-dimensional meshwork in connection with big and small pore while maximum pore size is the minimum for 1600℃sintering temperature. The pore size less than 3.1μm is proportion of 98%.
2017, 46(4):1097-1102.
Abstract:
The microstructure and mechanical properties of Mg94Y4Zn1Ni1 alloy in as-cast, as-annealed, as-extruded and aged stages were inverstigated by OM, SEM, TEM and electronic universal testing machine. The results show that the as-cast alloy is composed of α-Mg matrix, 18R LPSO structure and Mg24(Y,Zn,Ni)5 phase. During hot extrusion, the 18R phases become stripy shape and are aligned in lines along extrusion direction. The ultimate tensile strength of as-extruded alloy reaches 417 MPa. After aging, a large number of coherent β'' phases are precipitated in α-Mg matrix, and because of which, the strength of the alloy is enhanced further. The T5-treated and T6 treated alloys exhibit ultimate tensile strength of 434 MPa and 432 MPa, respectively.
The microstructure and mechanical properties of Mg94Y4Zn1Ni1 alloy in as-cast, as-annealed, as-extruded and aged stages were inverstigated by OM, SEM, TEM and electronic universal testing machine. The results show that the as-cast alloy is composed of α-Mg matrix, 18R LPSO structure and Mg24(Y,Zn,Ni)5 phase. During hot extrusion, the 18R phases become stripy shape and are aligned in lines along extrusion direction. The ultimate tensile strength of as-extruded alloy reaches 417 MPa. After aging, a large number of coherent β'' phases are precipitated in α-Mg matrix, and because of which, the strength of the alloy is enhanced further. The T5-treated and T6 treated alloys exhibit ultimate tensile strength of 434 MPa and 432 MPa, respectively.
2017, 46(4):1103-1109.
Abstract:
To further improve the quality and performance of oxidation film，AZ31 magnesium alloy were anodized in NaOH Na2SiO3 base electrolyte with different aminoacetic acid as organic additives. The effects of different amino acids on the thickness, morphology, structure and corrosion resistance of anodizing films were investigated. The mechanisms of organic amino acids additives were discussed. Results show that there are different effects on the anodizing of magnesium alloy after adding different amino acids in electrolyte. EDTA and L-Orn have remarkable effect on arc restraining, which resulted in an increase in the thickness of anodizing films and a decrease in the surface micro-hole size and porosity, and finally the improvement in corrosion resistance. Organic additives, mainly through the combined effect of inhibition, arc suppression, and surfactant, affect the anodizing process and the performance of oxide film.
To further improve the quality and performance of oxidation film，AZ31 magnesium alloy were anodized in NaOH Na2SiO3 base electrolyte with different aminoacetic acid as organic additives. The effects of different amino acids on the thickness, morphology, structure and corrosion resistance of anodizing films were investigated. The mechanisms of organic amino acids additives were discussed. Results show that there are different effects on the anodizing of magnesium alloy after adding different amino acids in electrolyte. EDTA and L-Orn have remarkable effect on arc restraining, which resulted in an increase in the thickness of anodizing films and a decrease in the surface micro-hole size and porosity, and finally the improvement in corrosion resistance. Organic additives, mainly through the combined effect of inhibition, arc suppression, and surfactant, affect the anodizing process and the performance of oxide film.
2017, 46(4):1110-1114.
Abstract:
The effect of 0.5, 1.5 and 4.5 (wt.%) Sm addition on microstructure and mechanical properties of extruded Mg-6Al-1.0Ca-0.5Mn alloys was investigated. With increasing the content of Sm, the Al2Sm phase precipitates in the matrix and the amount of the phase increases but that of Mg17Al12 phase decreases. The grains of alloys are refined due to the sufficient occurrence of dynamic recrystallization during extrusion process. The result of tensile tests shows that the alloy containing 1.5wt.% Sm exhibits the best mechanical properties. The improved mechanical properties of the alloy are mainly attributed to grain refinement, the precipitation strengthening of a large number of Al2Sm particles and the decrease of Mg17Al12 phase in the matrix.
The effect of 0.5, 1.5 and 4.5 (wt.%) Sm addition on microstructure and mechanical properties of extruded Mg-6Al-1.0Ca-0.5Mn alloys was investigated. With increasing the content of Sm, the Al2Sm phase precipitates in the matrix and the amount of the phase increases but that of Mg17Al12 phase decreases. The grains of alloys are refined due to the sufficient occurrence of dynamic recrystallization during extrusion process. The result of tensile tests shows that the alloy containing 1.5wt.% Sm exhibits the best mechanical properties. The improved mechanical properties of the alloy are mainly attributed to grain refinement, the precipitation strengthening of a large number of Al2Sm particles and the decrease of Mg17Al12 phase in the matrix.
2017, 46(4):1115-1119.
Abstract:
The influence of microstructures, matrix precipitates, grain boundary precipitates and precipitate free zone on the strength and fracture toughness of 7055 aluminum alloy after peak aging and secondary T7951 heat treatments was studied through mechanical property tests, microstructures and fractography analysis. The results showed that strength of 7055-T7951 would not decrease dramatically compared to the peak aging material because of the competition between the softening effect of η phase precipitating and the strengthening effects of dislocation and fine grains. The main reason for the improvement of fracture toughness after secondary aging was the aggregation and coarsening of grain boundary precipitates. Fractographic analysis showed that the fracture mechanism was mixed fracture containing both ductile and brittle features, but with more ductile features in the secondary aging materials.
The influence of microstructures, matrix precipitates, grain boundary precipitates and precipitate free zone on the strength and fracture toughness of 7055 aluminum alloy after peak aging and secondary T7951 heat treatments was studied through mechanical property tests, microstructures and fractography analysis. The results showed that strength of 7055-T7951 would not decrease dramatically compared to the peak aging material because of the competition between the softening effect of η phase precipitating and the strengthening effects of dislocation and fine grains. The main reason for the improvement of fracture toughness after secondary aging was the aggregation and coarsening of grain boundary precipitates. Fractographic analysis showed that the fracture mechanism was mixed fracture containing both ductile and brittle features, but with more ductile features in the secondary aging materials.
2017, 46(4):1120-1125.
Abstract:
YG15 cemented carbides and 35CrMo steel were brazed with different content of element Ni in the article. The effect of the content of element Ni, brazing temperature and ultrasonic vibration on the mechanical properties and microstructure of the joints was investigated. It shows that continued α-Cu solution layers can be obtained by increasing the content of element Ni, and the shear strength peaked at 295 Mpa with the 4.7 wt.% Ni content filler metal at the brazing temperature of 800°C. It found that the brazing temperature influence the depleted zone width of element Co of joints through the impact on the diffusion of element Ni. The minimum of the depleted zone width of element Co is observed in the joints at the brazing temperature of 730°C, and the shear strength of the joints reached maximum 350 MPa. The brazing process with ultrasonic vibration can enlarge the width of the depleted zone of element Co of the joints, decrease the content of eutectic structure, and drive the WC particles migration into the bonds. The maximum shear strength of the joints with 17.5 μm depleted zone of element Co was obtained at 378 Mpa with ultrasonic brazing for 30s, increasing the shear strength of the joints by 6% than the joints without ultrasound.
YG15 cemented carbides and 35CrMo steel were brazed with different content of element Ni in the article. The effect of the content of element Ni, brazing temperature and ultrasonic vibration on the mechanical properties and microstructure of the joints was investigated. It shows that continued α-Cu solution layers can be obtained by increasing the content of element Ni, and the shear strength peaked at 295 Mpa with the 4.7 wt.% Ni content filler metal at the brazing temperature of 800°C. It found that the brazing temperature influence the depleted zone width of element Co of joints through the impact on the diffusion of element Ni. The minimum of the depleted zone width of element Co is observed in the joints at the brazing temperature of 730°C, and the shear strength of the joints reached maximum 350 MPa. The brazing process with ultrasonic vibration can enlarge the width of the depleted zone of element Co of the joints, decrease the content of eutectic structure, and drive the WC particles migration into the bonds. The maximum shear strength of the joints with 17.5 μm depleted zone of element Co was obtained at 378 Mpa with ultrasonic brazing for 30s, increasing the shear strength of the joints by 6% than the joints without ultrasound.
2017, 46(4):1126-1131.
Abstract:
The aim of the research is to study the effects of casting tungsten carbide powder on wear resistance of ceramic particle reinforced Fe matrix composites by laser cladding. The tungsten carbide powders with different particle size preapred by different methods were added into Fe alloy powders. The laser cladding technique was used to form alloyed layer with high hardness and wear resistance on 45# steel with such mixed powders. The microscope, SEM, XRD and hardness tester were used to investigate microstructure, phase composition and microhardness of cladding layer. The wheel wear test machine was used to test their wear resistance. The result shows the cladding layer is mainly composed of ledeburite phase. The difference of tungsten carbide powder makes important effects on wear resistance. The tungsten carbide powder prapared by plasma rotating electrode process can increase wear resistance mostly. The increasing effect of fine tungsten carbide powder on wear resistance is more remarkable than the coarse powder.
The aim of the research is to study the effects of casting tungsten carbide powder on wear resistance of ceramic particle reinforced Fe matrix composites by laser cladding. The tungsten carbide powders with different particle size preapred by different methods were added into Fe alloy powders. The laser cladding technique was used to form alloyed layer with high hardness and wear resistance on 45# steel with such mixed powders. The microscope, SEM, XRD and hardness tester were used to investigate microstructure, phase composition and microhardness of cladding layer. The wheel wear test machine was used to test their wear resistance. The result shows the cladding layer is mainly composed of ledeburite phase. The difference of tungsten carbide powder makes important effects on wear resistance. The tungsten carbide powder prapared by plasma rotating electrode process can increase wear resistance mostly. The increasing effect of fine tungsten carbide powder on wear resistance is more remarkable than the coarse powder.
2017, 46(4):1132-1135.
Abstract:
Nanocomposite Nd8.5Fe77Co5Zr3B6.5 alloys were prepared by melt-spinning under different melt temperatures. The effect of melt temperature on the microstructure and magnetic properties of alloys was investigated. The results show that the melt temperature is a key factor that affects the microstructure and magnetic properties of as-quenched and also as-annealed alloys. The as-quenched alloys melt-spun at 1210 °C are composed of amorphous phase and Nd2Fe14B phase. The relative content of amorphous phase in as-quenched alloys increases as melt temperature increases. As-spun alloys with high content of amorphous phase show soft magnetic properties. Subsequent annealing of as-spun alloys initiates the formation of nanocrystalline Nd2Fe14B phase and precipitation of a small amount of soft magnetic phase. Alloys with finer microstructure and more favorable magnetic properties are obtained by crystallizing the as-quenched alloys melt spun at lower melt temperature. The as-annealed alloys melt-spun at 1210 °C shows optimum magnetic properties with an intrinsic coercivity of 559.2 kA/m, remanence of 0.98 T, and maximum energy product of 127.8 kJ/m3.
Nanocomposite Nd8.5Fe77Co5Zr3B6.5 alloys were prepared by melt-spinning under different melt temperatures. The effect of melt temperature on the microstructure and magnetic properties of alloys was investigated. The results show that the melt temperature is a key factor that affects the microstructure and magnetic properties of as-quenched and also as-annealed alloys. The as-quenched alloys melt-spun at 1210 °C are composed of amorphous phase and Nd2Fe14B phase. The relative content of amorphous phase in as-quenched alloys increases as melt temperature increases. As-spun alloys with high content of amorphous phase show soft magnetic properties. Subsequent annealing of as-spun alloys initiates the formation of nanocrystalline Nd2Fe14B phase and precipitation of a small amount of soft magnetic phase. Alloys with finer microstructure and more favorable magnetic properties are obtained by crystallizing the as-quenched alloys melt spun at lower melt temperature. The as-annealed alloys melt-spun at 1210 °C shows optimum magnetic properties with an intrinsic coercivity of 559.2 kA/m, remanence of 0.98 T, and maximum energy product of 127.8 kJ/m3.
2017, 46(4):1136-1142.
Abstract:
A new Ni-Fe based wrought superalloy for 700℃ advanced ultra-supercritical steam turbine rotor application was developed. The effects of B and P on the microstructure and mechanical properties of the alloy were investigated. The results show that the major precipitates in the alloy were γ′, MC, M23C6 and M3B2. B restrains the precipitation and growth of the M23C6, increasing the binding force of grain boundaries and obstacles intergranular crack initiation. P accelerates the precipitation and growth of the M23C6, and suppress crack initiation and propagation in the surface. B and P play an even more significant role in strengthening grain boundaries at 700 ℃ than at room temperature, they improve not only the strength but also the high-temperature ductility of the alloy. But However, high B content impairs the beneficial effect of P element. reducing the tensile strength and rupture life of the alloy.
A new Ni-Fe based wrought superalloy for 700℃ advanced ultra-supercritical steam turbine rotor application was developed. The effects of B and P on the microstructure and mechanical properties of the alloy were investigated. The results show that the major precipitates in the alloy were γ′, MC, M23C6 and M3B2. B restrains the precipitation and growth of the M23C6, increasing the binding force of grain boundaries and obstacles intergranular crack initiation. P accelerates the precipitation and growth of the M23C6, and suppress crack initiation and propagation in the surface. B and P play an even more significant role in strengthening grain boundaries at 700 ℃ than at room temperature, they improve not only the strength but also the high-temperature ductility of the alloy. But However, high B content impairs the beneficial effect of P element. reducing the tensile strength and rupture life of the alloy.
Wang Wei
,
Huang Xi-wen
,
Liu Xin-yu
,
Chen Guang-ming
,
Li bo
,
Cai Ding-yun
,
Zhang Tian-jin
,
Wang Zhen-yu
2017, 46(4):1143-1147.
Abstract:
In this paper, the research on the Oxide Sintered Integration of AgSn Alloy Billet .X-ray diffraction analysis (XRD) and scanning electron microscope (SEM) observation were carried out to characterize the as prepared AgSn powder. System inspected the oxidation temperature, oxidation time, forming pressure and sintering temperature and sintering time on the AgSn alloy billet oxidation rate, the influence of relative density and bending strength. To determine the best oxidation temperature and time are 700 ℃ for 2h, the best sintering temperature and time are 900℃ for 3h, and best compacting pressure to 250 MPa. The results showed that: AgSn alloy blank oxide sintered sintering process integration can not only simplify traditional powder metallurgy process, improve the production efficiency, and can improve the powder sintering activity.
In this paper, the research on the Oxide Sintered Integration of AgSn Alloy Billet .X-ray diffraction analysis (XRD) and scanning electron microscope (SEM) observation were carried out to characterize the as prepared AgSn powder. System inspected the oxidation temperature, oxidation time, forming pressure and sintering temperature and sintering time on the AgSn alloy billet oxidation rate, the influence of relative density and bending strength. To determine the best oxidation temperature and time are 700 ℃ for 2h, the best sintering temperature and time are 900℃ for 3h, and best compacting pressure to 250 MPa. The results showed that: AgSn alloy blank oxide sintered sintering process integration can not only simplify traditional powder metallurgy process, improve the production efficiency, and can improve the powder sintering activity.
2017, 46(4):1148-1155.
Abstract:
NiCoCrAlYTa splats and coatings were deposited on K4169 substrates by low pressure plasma spray (LPPS) and atmospheric plasma spray (APS), respectively. The microstructures of the splats, and some fundamental properties of the coatings were evaluated in detail. The results show that the splats collected by LPPS performed as disk-shaped ones, while the coating was quite dense with low oxygen content. On the contrary, the splats caught by APS mainly deposited as splash shapes, while the coating has high porosity and oxygen content. 7YSZ splats were deposited on the mirror polished K4169 substrate and low pressure plasma sprayed NiCoCrAlYTa coating respectively, the microstructures of 7YSZ splats were also observed. Typical disk-shaped 7YSZ splat with network of fine cracks and macro circle crack could be found on the K4169 substrate; while the 7YSZ splat deposited on the NiCoCrAlYTa coating has some splash fingers surround the central solidification core, the macro circle cracks almost disappear and less network fine crack could be found, because the intermetallic bond coating can fill the thermal expansion mismatch between substrate and ceramic splat.
NiCoCrAlYTa splats and coatings were deposited on K4169 substrates by low pressure plasma spray (LPPS) and atmospheric plasma spray (APS), respectively. The microstructures of the splats, and some fundamental properties of the coatings were evaluated in detail. The results show that the splats collected by LPPS performed as disk-shaped ones, while the coating was quite dense with low oxygen content. On the contrary, the splats caught by APS mainly deposited as splash shapes, while the coating has high porosity and oxygen content. 7YSZ splats were deposited on the mirror polished K4169 substrate and low pressure plasma sprayed NiCoCrAlYTa coating respectively, the microstructures of 7YSZ splats were also observed. Typical disk-shaped 7YSZ splat with network of fine cracks and macro circle crack could be found on the K4169 substrate; while the 7YSZ splat deposited on the NiCoCrAlYTa coating has some splash fingers surround the central solidification core, the macro circle cracks almost disappear and less network fine crack could be found, because the intermetallic bond coating can fill the thermal expansion mismatch between substrate and ceramic splat.
2017, 46(4):1156-1161.
Abstract:
Solution treatment was conducted on Mg-(4-x)Nd-xGd-0.3Sr-0.2Zn-0.4Zr(mass fractuon, %, x=0, 1, 3). The microstructures and phases were studied using scanning electron microscope (SEM), energy dispersive spectrometer and X-ray diffraction. The corrosion rates of the alloys in simulated body fluid were evaluated by mass loss and hydrogen evolution tests, and the corrosion morphologies of the alloys were observed by SEM. It is found that the grain size of the alloy with 1%Gd addition is the finest, as well as the lowest corrosion rate, and the second phase was located relatively continuously around the matrix. While the grain size of the alloy with 3%Gd addition is the coarsest and the corrosion rate is the highest. The alloys exhibit relatively uniform corrosion morphologies, and thus, they are desirable biodegradable materials.
Solution treatment was conducted on Mg-(4-x)Nd-xGd-0.3Sr-0.2Zn-0.4Zr(mass fractuon, %, x=0, 1, 3). The microstructures and phases were studied using scanning electron microscope (SEM), energy dispersive spectrometer and X-ray diffraction. The corrosion rates of the alloys in simulated body fluid were evaluated by mass loss and hydrogen evolution tests, and the corrosion morphologies of the alloys were observed by SEM. It is found that the grain size of the alloy with 1%Gd addition is the finest, as well as the lowest corrosion rate, and the second phase was located relatively continuously around the matrix. While the grain size of the alloy with 3%Gd addition is the coarsest and the corrosion rate is the highest. The alloys exhibit relatively uniform corrosion morphologies, and thus, they are desirable biodegradable materials.
2017, 46(4):1162-1168.
Abstract:
Addittive manufactureing (AM) processes have been a major concern in most countries since 1990s. Powers are the main raw materials for AM, and qualities of powders effect the part fabricated by AM significantly. Spherical-shaped metal powders are ideal raw materials for AM due to the properties of excellent fluidity, spreadability, and high bulk density. State of the art on two technologies preparing spherical-shaped powders of atomization and spheroidization are presented. Methods such as conventional water/gas atomization, Electrode Induction-melting Inert Gas Atomization, and plasma rotating electrode process are specified and compared. According to the requirement of metal AM, the trends of spherical powder fabrication technology are proposed.
Addittive manufactureing (AM) processes have been a major concern in most countries since 1990s. Powers are the main raw materials for AM, and qualities of powders effect the part fabricated by AM significantly. Spherical-shaped metal powders are ideal raw materials for AM due to the properties of excellent fluidity, spreadability, and high bulk density. State of the art on two technologies preparing spherical-shaped powders of atomization and spheroidization are presented. Methods such as conventional water/gas atomization, Electrode Induction-melting Inert Gas Atomization, and plasma rotating electrode process are specified and compared. According to the requirement of metal AM, the trends of spherical powder fabrication technology are proposed.
