Volume 49,Issue 10,2020 Table of Contents
2020, 49(10):3285-3293.
DOI: 10.12442/j.issn.1002-185X.20200101
Abstract:
In order to accurately predict the microstructure evolution during thermo-mechanical processing of AerMet100 ultrahigh-strength steel, the dynamic recrystallization (DRX) models including DRX volume fraction and DRX grain size were established by conducting a series of isothermal hot compression tests. The hot deformation behavior of the alloy in a wide range of temperatures from 800 ?C to 1040 ?C, strain rates from 0.01 s-1 to 10 s-1 and deformation degree from 15% to 60% were analyzed. The Zener-Hollomon parameter in the constitutive model for the AerMet100 steel was obtained to establish DRX models. The effects of deformation parameters on the microstructural evolution were quantitatively predicted through the established DRX models. The microstructure observations showed that higher temperature, lower strain rate and larger deformation degree were beneficial to obtaining the homogenization and refinement of the microstructure due to the occurrence of DRX. The good agreement between the prediction and the experiment validated the accuracy of the established DRX models. And the results indicated that the DRX models could be used to quantitatively predict the microstructure evolution of AerMet100 steel components during thermo-mechanical processing at different hot deformation conditions.
In order to accurately predict the microstructure evolution during thermo-mechanical processing of AerMet100 ultrahigh-strength steel, the dynamic recrystallization (DRX) models including DRX volume fraction and DRX grain size were established by conducting a series of isothermal hot compression tests. The hot deformation behavior of the alloy in a wide range of temperatures from 800 ?C to 1040 ?C, strain rates from 0.01 s-1 to 10 s-1 and deformation degree from 15% to 60% were analyzed. The Zener-Hollomon parameter in the constitutive model for the AerMet100 steel was obtained to establish DRX models. The effects of deformation parameters on the microstructural evolution were quantitatively predicted through the established DRX models. The microstructure observations showed that higher temperature, lower strain rate and larger deformation degree were beneficial to obtaining the homogenization and refinement of the microstructure due to the occurrence of DRX. The good agreement between the prediction and the experiment validated the accuracy of the established DRX models. And the results indicated that the DRX models could be used to quantitatively predict the microstructure evolution of AerMet100 steel components during thermo-mechanical processing at different hot deformation conditions.
2020, 49(10):3294-3300.
DOI: 10.12442/j.issn.1002-185X.20200119
Abstract:
In this paper, a novel micro plastic forming technology is introduced for the forming of micro-gear using the high strength, toughness, and hard-to-deform Ti6Al4V alloy material. The experimental results showed that the Ti6Al4V alloy micro-gear can be achieved successfully from a cylindrical Ti6Al4V billet with a set of graphite die under an electric field. The Ti6Al4V material exhibits the best formability when the heating rate is 5 ℃/s, however, higher heating rate 30 ℃/s and 40 ℃/s can effectively shorten the time for pre-heating the material for deformation. The microstructure in all the formed samples have the Widmanst?tten structure. but gear center in contradiction to tooth top which exhibit a finer microstructure, and the β phase content of specimens with the heating rates of 5 ℃/s and 10 ℃/s are slightly higher than the original billet but specimens involving in heating rates 20 ℃/s, 30 ℃/s, and 40 ℃/s show nothing of the β phase from XRD analysis. Moreover, Vickers hardness of all formed samples increase than that of the original billet after an electric field, and which is independent on the heating rates.
In this paper, a novel micro plastic forming technology is introduced for the forming of micro-gear using the high strength, toughness, and hard-to-deform Ti6Al4V alloy material. The experimental results showed that the Ti6Al4V alloy micro-gear can be achieved successfully from a cylindrical Ti6Al4V billet with a set of graphite die under an electric field. The Ti6Al4V material exhibits the best formability when the heating rate is 5 ℃/s, however, higher heating rate 30 ℃/s and 40 ℃/s can effectively shorten the time for pre-heating the material for deformation. The microstructure in all the formed samples have the Widmanst?tten structure. but gear center in contradiction to tooth top which exhibit a finer microstructure, and the β phase content of specimens with the heating rates of 5 ℃/s and 10 ℃/s are slightly higher than the original billet but specimens involving in heating rates 20 ℃/s, 30 ℃/s, and 40 ℃/s show nothing of the β phase from XRD analysis. Moreover, Vickers hardness of all formed samples increase than that of the original billet after an electric field, and which is independent on the heating rates.
2020, 49(10):3301-3308.
DOI: 10.12442/j.issn.1002-185X.20190673
Abstract:
To understand the effect of pre-strain on the integrity assessment of titanium structure with crack, the dependence of tensile mechanical parameters, fracture toughness, failure assessment diagram (FAD) on pre-strain were focused. Firstly, tensile tests revealed that, the yield stress and the yield-ultimate strength ratio increased, but the ductility decreased with pre-strain value, while the fracture toughness was decreasing with pre-strain. Then, based on finite element (FE) analyses of compact tension (CT) specimen and titanium pressure vessel with crack, the plastic zone near the crack tip was decreasing with pre-strain, resulting in the decreasing of J-integral. Moreover, the failure assessment curves (FAC) of Options 1 and 3 in BS 7910: 2013 were varying with pre-strain, and the acceptable area was decreasing. Therefore, the reserve factor on yield stress increased with pre-strain, but that on fracture toughness decreased significantly. In brief, the pre-strain significantly affects the failure assessment of titanium pressure vessel with crack, and needs to be considered in the integrity assessment.
To understand the effect of pre-strain on the integrity assessment of titanium structure with crack, the dependence of tensile mechanical parameters, fracture toughness, failure assessment diagram (FAD) on pre-strain were focused. Firstly, tensile tests revealed that, the yield stress and the yield-ultimate strength ratio increased, but the ductility decreased with pre-strain value, while the fracture toughness was decreasing with pre-strain. Then, based on finite element (FE) analyses of compact tension (CT) specimen and titanium pressure vessel with crack, the plastic zone near the crack tip was decreasing with pre-strain, resulting in the decreasing of J-integral. Moreover, the failure assessment curves (FAC) of Options 1 and 3 in BS 7910: 2013 were varying with pre-strain, and the acceptable area was decreasing. Therefore, the reserve factor on yield stress increased with pre-strain, but that on fracture toughness decreased significantly. In brief, the pre-strain significantly affects the failure assessment of titanium pressure vessel with crack, and needs to be considered in the integrity assessment.
2020, 49(10):3309-3313.
DOI: 10.12442/j.issn.1002-185X.20190691
Abstract:
Wear performance and mechanism of Ti alloys strengthened by solid solute atoms Si and O from rice husk was studied from the viewpoint of wear rate, worn surface morphology and wear debris analysis. Results show that the volume wear rate of Ti alloys decreases significantly with the increase of the content of SiO2, agreeing well with the change law of hardness. There are three changes of the worn surface with the increase of SiO2 content, one is the deep grooves transferring to shallow scratches, second is the decrease of plastic deformation degree and the last one is the size and amount of adhesive debris. The decrease of debris size can be attributed to the embrittlement of wear dust due to the blending of the wear dust of counter grinding GCr15 ball as well as the Ti matrix itself. Wear mechanism also transfers from adhesive and abrasive wear of pure Ti to abrasive and oxidation wear with the increase of SiO2 content. The result of this paper provides a cheap method to produce Ti alloys with excellent combination properties by using agricultural waste rice husk, which is also benefit for the environmental protection.
Wear performance and mechanism of Ti alloys strengthened by solid solute atoms Si and O from rice husk was studied from the viewpoint of wear rate, worn surface morphology and wear debris analysis. Results show that the volume wear rate of Ti alloys decreases significantly with the increase of the content of SiO2, agreeing well with the change law of hardness. There are three changes of the worn surface with the increase of SiO2 content, one is the deep grooves transferring to shallow scratches, second is the decrease of plastic deformation degree and the last one is the size and amount of adhesive debris. The decrease of debris size can be attributed to the embrittlement of wear dust due to the blending of the wear dust of counter grinding GCr15 ball as well as the Ti matrix itself. Wear mechanism also transfers from adhesive and abrasive wear of pure Ti to abrasive and oxidation wear with the increase of SiO2 content. The result of this paper provides a cheap method to produce Ti alloys with excellent combination properties by using agricultural waste rice husk, which is also benefit for the environmental protection.
5 Hot deformation behavior of near α titanium alloy Ti-1100 prepared by TiH2-based powder metallurgy
2020, 49(10):3314-3324.
DOI: 10.12442/j.issn.1002-185X.E20200010
Abstract:
Hot deformation behavior of TiH2-based PM near α titanium alloy Ti-1100 alloys has been investigated at temperature range of 973–1173K and strain rate range of 0.01–1.0s-1 by hot compression tests. The Arrhenius constitutive equation was developed and the hot deformation activation energy was calculated to be 334.76 kJ/mol. The temperature sensitivities (θ) were calculated by a modified function and the strain rate sensitivities (m) were determined. Based on the results of temperature sensitivity and strain rate sensitivity together with microstucture at strain rate of 0.5, the hot working condition was analyzed. It was found that the instability regions is mostly appeared at strain rate of 0.01s-1 and 1s-1 over whole temperature range, while the optimal hot working conditions are obtained in the range of 1135K 0.29s-1 to 1173K 0.76s-1, and 1040 0.33 s-1 to 1096K 0.6s-1. Besides, the microstucture analysis reveals that the dynamic recrystallization (DRX) occurs at strain rate of 0.01–0.1s-1, while the formation of micro-voids is the dominant mechanism of flow softening at strain rate of 1s-1.
Hot deformation behavior of TiH2-based PM near α titanium alloy Ti-1100 alloys has been investigated at temperature range of 973–1173K and strain rate range of 0.01–1.0s-1 by hot compression tests. The Arrhenius constitutive equation was developed and the hot deformation activation energy was calculated to be 334.76 kJ/mol. The temperature sensitivities (θ) were calculated by a modified function and the strain rate sensitivities (m) were determined. Based on the results of temperature sensitivity and strain rate sensitivity together with microstucture at strain rate of 0.5, the hot working condition was analyzed. It was found that the instability regions is mostly appeared at strain rate of 0.01s-1 and 1s-1 over whole temperature range, while the optimal hot working conditions are obtained in the range of 1135K 0.29s-1 to 1173K 0.76s-1, and 1040 0.33 s-1 to 1096K 0.6s-1. Besides, the microstucture analysis reveals that the dynamic recrystallization (DRX) occurs at strain rate of 0.01–0.1s-1, while the formation of micro-voids is the dominant mechanism of flow softening at strain rate of 1s-1.
2020, 49(10):3325-3331.
DOI: 10.12442/j.issn.1002-185X.20190671
Abstract:
In this paper, in order to find out the effect of Equal Channel Angular Pressing (ECAP) on the microstructure and texture, as well as dynamic recrystallization (DRX) behavior, Mg-1Zn-1Gd alloy (wt.%) was investigated. The results show that after the equal channel angular pressing at 350℃, the microstructures of these samples is composed of fine recrystallized grains, and there are a large number of homogeneously distributed equiaxed grains in the matrix. Upon 8 passes, the uniform ultra-fine grain structure with an average grain size of 3.6 μm is obtained. The mechanism of the discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) lead to grain refinement. The micro-texture was analyzed through electron backscatter diffraction (EBSD) technique. It is revealed that after 4 passes of ECAP, a strong basal texture is achieved (multiple?random?distribution?~19.76). With the extrusion passes increasing, the grain in the basal planes of extruded alloy billet is mainly elongated along the extrusion direction, the orientation distribution changes from concentrated state to decentralized state. The texture is weakened which the maximum strength is 15.66 mrd. Finally, the texture is also related to the plane anisotropy of the Mg-1Zn-1Gd alloy.
In this paper, in order to find out the effect of Equal Channel Angular Pressing (ECAP) on the microstructure and texture, as well as dynamic recrystallization (DRX) behavior, Mg-1Zn-1Gd alloy (wt.%) was investigated. The results show that after the equal channel angular pressing at 350℃, the microstructures of these samples is composed of fine recrystallized grains, and there are a large number of homogeneously distributed equiaxed grains in the matrix. Upon 8 passes, the uniform ultra-fine grain structure with an average grain size of 3.6 μm is obtained. The mechanism of the discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) lead to grain refinement. The micro-texture was analyzed through electron backscatter diffraction (EBSD) technique. It is revealed that after 4 passes of ECAP, a strong basal texture is achieved (multiple?random?distribution?~19.76). With the extrusion passes increasing, the grain in the basal planes of extruded alloy billet is mainly elongated along the extrusion direction, the orientation distribution changes from concentrated state to decentralized state. The texture is weakened which the maximum strength is 15.66 mrd. Finally, the texture is also related to the plane anisotropy of the Mg-1Zn-1Gd alloy.
2020, 49(10):3332-3337.
DOI: 10.12442/j.issn.1002-185X.20190464
Abstract:
Thermodynamic database of the Mo-RE (RE: Ce, Pr, Nd, Sm, Eu, Tb, Ho, Er, Tm, Yb, Lu) systemswas developed for the design of the Molybdenum-based refractory alloys. The thermodynamic calculation and optimization of Mo-RE binary systems have been performed using the Calculation of Phase Diagrams (CALPHAD) method on the basis of experimental data including phase equilibria and thermodynamic properties. The Gibbs energies of the liquid and solid solution phases are described by the sub-regular solution model, whereas those of the gas phases are described by the ideal gas model. The present work obtained a set of self-consistent thermodynamic parameters that reasonably describes the thermodynamic properties of the Mo-RE binary systems. A good agreement between calculation results and experimental data was reached. The utility of this database is demonstrated in the examples of thermodynamic calculations of the mixing enthalpy of liquid phase in the Mo-Ce and Mo-Pr system. Also, the 1200, 1300, 1400oC isothermal section diagrams of the Mo-Ho-Tb system and the related property diagrams like phase fraction of desired phases were depicted. Meanwhile, the Mo-Cu-Er ternary phase equilibria sections from 800 to 1000oC were extrapolated. These results show fairly good predictions and provide much-needed information for the alloy design of the Molybdenum-based refractory materials.
Thermodynamic database of the Mo-RE (RE: Ce, Pr, Nd, Sm, Eu, Tb, Ho, Er, Tm, Yb, Lu) systemswas developed for the design of the Molybdenum-based refractory alloys. The thermodynamic calculation and optimization of Mo-RE binary systems have been performed using the Calculation of Phase Diagrams (CALPHAD) method on the basis of experimental data including phase equilibria and thermodynamic properties. The Gibbs energies of the liquid and solid solution phases are described by the sub-regular solution model, whereas those of the gas phases are described by the ideal gas model. The present work obtained a set of self-consistent thermodynamic parameters that reasonably describes the thermodynamic properties of the Mo-RE binary systems. A good agreement between calculation results and experimental data was reached. The utility of this database is demonstrated in the examples of thermodynamic calculations of the mixing enthalpy of liquid phase in the Mo-Ce and Mo-Pr system. Also, the 1200, 1300, 1400oC isothermal section diagrams of the Mo-Ho-Tb system and the related property diagrams like phase fraction of desired phases were depicted. Meanwhile, the Mo-Cu-Er ternary phase equilibria sections from 800 to 1000oC were extrapolated. These results show fairly good predictions and provide much-needed information for the alloy design of the Molybdenum-based refractory materials.
2020, 49(10):3337-3352.
DOI: 10.12442/j.issn.1002-185X.20190708
Abstract:
In this paper, a novel approach to grow freestanding AlN single crystals spontaneously using the physical vapor transport method is presented. Dozens of single crystals can be obtained on the surface of a pre-sintered AlN powder source in a single growth run using this approach. In this study, the largest AlN single crystal for 100 h of growth at 2373–2523 K was 7 × 8 × 12 mm3, and the typical diameter was 5–7 mm. The surface morphologies of the as-grown crystals were investigated by scanning electron microscopy, whereas the structural quality of the crystals was characterized by Raman spectroscopy and high-resolution X-ray diffraction. Raman spectroscopy exhibited an E2 (high) full width at half maximum (FWHM) of 5.7 cm-1, whereas the high-resolution X-ray diffraction rocking curve showed a FWHM of 93.6 arcsec for the symmetric reflection. The average etch pit density revealed by preferential chemical etching was 7.5 × 104 cm-2, and the major impurities determined by evolved gas analysis and glow discharge mass spectrometry were carbon at 28 ppmw and oxygen at 120 ppmw. The proposed novel approach provides a new means of obtaining high-quality AlN single crystals, which can be cut into wafers and are ideal as seeds for subsequent homoepitaxial AlN growth. Using these small seeds, crack-free bulk AlN single crystal/wafers that have excellent deep UV transparency and are up to 60 mm in diameter were successfully prepared for the first time.
In this paper, a novel approach to grow freestanding AlN single crystals spontaneously using the physical vapor transport method is presented. Dozens of single crystals can be obtained on the surface of a pre-sintered AlN powder source in a single growth run using this approach. In this study, the largest AlN single crystal for 100 h of growth at 2373–2523 K was 7 × 8 × 12 mm3, and the typical diameter was 5–7 mm. The surface morphologies of the as-grown crystals were investigated by scanning electron microscopy, whereas the structural quality of the crystals was characterized by Raman spectroscopy and high-resolution X-ray diffraction. Raman spectroscopy exhibited an E2 (high) full width at half maximum (FWHM) of 5.7 cm-1, whereas the high-resolution X-ray diffraction rocking curve showed a FWHM of 93.6 arcsec for the symmetric reflection. The average etch pit density revealed by preferential chemical etching was 7.5 × 104 cm-2, and the major impurities determined by evolved gas analysis and glow discharge mass spectrometry were carbon at 28 ppmw and oxygen at 120 ppmw. The proposed novel approach provides a new means of obtaining high-quality AlN single crystals, which can be cut into wafers and are ideal as seeds for subsequent homoepitaxial AlN growth. Using these small seeds, crack-free bulk AlN single crystal/wafers that have excellent deep UV transparency and are up to 60 mm in diameter were successfully prepared for the first time.
2020, 49(10):3338-3346.
DOI: 10.12442/j.issn.1002-185X.20190676
Abstract:
In the range of ASTM, the effect of impurity elements on microstructure and corrosion resistance of Zr-4 alloy were studied by using sheet samples. The results show that reducing carbon content and increasing silicon content are beneficial to uniform corrosion performance of Zr-4 alloy at 400℃ steam. Microscopic analysis shows that carbon is easily enriched in the form of Zr-C on the matrix phase, and its content mainly affects the corrosion resistance by affecting the precipitation of second phase particles. The lower its content is, the easier it is to form the parallel plate (PP) structure during quenching, and the higher its content is, the more likely it is to form basketweave (BW) structure, while the second phase particles are easier to precipitate along the grain boundary of PP structure. When quenching temperature is lower than 1200℃, silicon content has no obvious effect on the formation of PP structure. Meanwhile, three-dimensional atom probe (3DAP) analysis shows that silicon tends to agglomerate in the form of SiO2 around the second phase particles, delays or weaken the oxidation of second phase particles, thus improving the corrosion resistance of Zr-4 alloy.
In the range of ASTM, the effect of impurity elements on microstructure and corrosion resistance of Zr-4 alloy were studied by using sheet samples. The results show that reducing carbon content and increasing silicon content are beneficial to uniform corrosion performance of Zr-4 alloy at 400℃ steam. Microscopic analysis shows that carbon is easily enriched in the form of Zr-C on the matrix phase, and its content mainly affects the corrosion resistance by affecting the precipitation of second phase particles. The lower its content is, the easier it is to form the parallel plate (PP) structure during quenching, and the higher its content is, the more likely it is to form basketweave (BW) structure, while the second phase particles are easier to precipitate along the grain boundary of PP structure. When quenching temperature is lower than 1200℃, silicon content has no obvious effect on the formation of PP structure. Meanwhile, three-dimensional atom probe (3DAP) analysis shows that silicon tends to agglomerate in the form of SiO2 around the second phase particles, delays or weaken the oxidation of second phase particles, thus improving the corrosion resistance of Zr-4 alloy.
2020, 49(10):3353-3360.
DOI: 10.12442/j.issn.1002-185X.20190717
Abstract:
In the present work, the effect of loading rate and holding time on the creep deformation behavior of (Zr0.6336Cu0.1452Ni0.1012Al0.12)97.4Er2.6 bulk metallic glass (BMG) was investigated by using nanoindentation technique. Experimental results demonstrate that the creep displacement of specimen increases with the increase of loading rate or holding time. On the other hand, the hardness (H) of specimen falls with the rise of loading rate or holding time. The H drops with the growth of indentation depth during the nanoindentation process, which indicates that specimen has a size effect. Specimen has a serrated flow phenomenon which has rate dependence. Specifically, as the loading rate declines, the serrated flow phenomenon becomes more obvious. The creep stress exponent of specimen goes down with the increases of loading rate or holding time.
In the present work, the effect of loading rate and holding time on the creep deformation behavior of (Zr0.6336Cu0.1452Ni0.1012Al0.12)97.4Er2.6 bulk metallic glass (BMG) was investigated by using nanoindentation technique. Experimental results demonstrate that the creep displacement of specimen increases with the increase of loading rate or holding time. On the other hand, the hardness (H) of specimen falls with the rise of loading rate or holding time. The H drops with the growth of indentation depth during the nanoindentation process, which indicates that specimen has a size effect. Specimen has a serrated flow phenomenon which has rate dependence. Specifically, as the loading rate declines, the serrated flow phenomenon becomes more obvious. The creep stress exponent of specimen goes down with the increases of loading rate or holding time.
Yunpeng Xin
,
Zhishou Zhu
,
Xinnan Wang
,
Mingbing Li
,
Gechen Liu
,
Jing Li
,
Guoqiang Shang
,
Liwei Zhu
2020, 49(10):3361-3368.
DOI: 10.12442/j.issn.1002-185X.20190733
Abstract:
The microstructure characterization and evolution behavior of TC32 titanium alloy after high-speed projectile impact were studied by optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The distribution of adiabatic shear band(ASB) and stress around the crater has always been a semi-circular diffusion. The rotating refinement process of large equiaxed grains and elongated lath subgrains in adiabatic shear band was observed. Focus ion beam (FIB) technology was used to accurately prepare TEM samples from the crack tip in the ASB. It was found that the coexistence of the amorphous regions, the amorphous-to-crystalline transition regions, the fine-scale nano-crystalline region around the crack tip. The calculation proved that the temperature rise in ASB could cause microstructure melting, the amorphous regions and small size nanocrystals were formed after fast quenching. Because the microstructure in the ASBs is fine equiaxed grains and amorphous with higher strength, the area between the deformed band and matrix is relatively weakened, and it is found that the initiation of cracks in adiabatic shear bands is mainly concentrated at the junction of deformed band and matrix, and the crack propagate in the form of microvoids rotation coupling.
The microstructure characterization and evolution behavior of TC32 titanium alloy after high-speed projectile impact were studied by optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The distribution of adiabatic shear band(ASB) and stress around the crater has always been a semi-circular diffusion. The rotating refinement process of large equiaxed grains and elongated lath subgrains in adiabatic shear band was observed. Focus ion beam (FIB) technology was used to accurately prepare TEM samples from the crack tip in the ASB. It was found that the coexistence of the amorphous regions, the amorphous-to-crystalline transition regions, the fine-scale nano-crystalline region around the crack tip. The calculation proved that the temperature rise in ASB could cause microstructure melting, the amorphous regions and small size nanocrystals were formed after fast quenching. Because the microstructure in the ASBs is fine equiaxed grains and amorphous with higher strength, the area between the deformed band and matrix is relatively weakened, and it is found that the initiation of cracks in adiabatic shear bands is mainly concentrated at the junction of deformed band and matrix, and the crack propagate in the form of microvoids rotation coupling.
2020, 49(10):3369-3376.
DOI: 10.12442/j.issn.1002-185X.20190734
Abstract:
The finite element method (FEM) and elasto-plastic self-consistent (EPSC) method were used to simulate the mechanical response of pure titanium subjected to single steel shot impacting at different shot sizes and velocities. The macroscopic and microscopic residual stresses were calculated. The results indicate that the observed macroscopic residual compressive stress increases with an increase in the shot size and impacting velocity. In addition, the macroscopic residual stress calculations correlate well with the residual elastic strain. The microscopic residual stresses lie within a range that varies with depth. Furthermore, the statistical distribution of the microscopic residual stress agrees well with the Gaussian distribution. Additionally, the dispersion of microscopic residual stresses, determined by the effective plastic deformation, is influenced by the shot size and impacting velocity. With an increase in the impacting velocity and decrease in the shot size, the standard deviation of the microscopic residual stresses at a certain depth increases.
The finite element method (FEM) and elasto-plastic self-consistent (EPSC) method were used to simulate the mechanical response of pure titanium subjected to single steel shot impacting at different shot sizes and velocities. The macroscopic and microscopic residual stresses were calculated. The results indicate that the observed macroscopic residual compressive stress increases with an increase in the shot size and impacting velocity. In addition, the macroscopic residual stress calculations correlate well with the residual elastic strain. The microscopic residual stresses lie within a range that varies with depth. Furthermore, the statistical distribution of the microscopic residual stress agrees well with the Gaussian distribution. Additionally, the dispersion of microscopic residual stresses, determined by the effective plastic deformation, is influenced by the shot size and impacting velocity. With an increase in the impacting velocity and decrease in the shot size, the standard deviation of the microscopic residual stresses at a certain depth increases.
2020, 49(10):3377-3381.
DOI: 10.12442/j.issn.1002-185X.20190766
Abstract:
The defects and microstructural evolution of cold-rolled pure zirconium with different deformation reduction were investigated using positron annihilation lifetime (PAL) and transmission electron microscopy (TEM). The results show cold-rolling deformation introduces dislocations and vacancies with high density in the pure zirconium; The mean lifetime increased with increasing amount of deformation up to 10% and then saturated. with increasing cold-rolled reduction. Furthermore, vacancy clusters in the cold-rolled pure zirconium are not formed, and they did not grow even under the isochronal annealing conditions from 298~898 K . The vacancy and dislocation densities of the cold-rolled pure zirconium decrease with increasing the annealing temperature, and they were almost recovery at 873 K.
The defects and microstructural evolution of cold-rolled pure zirconium with different deformation reduction were investigated using positron annihilation lifetime (PAL) and transmission electron microscopy (TEM). The results show cold-rolling deformation introduces dislocations and vacancies with high density in the pure zirconium; The mean lifetime increased with increasing amount of deformation up to 10% and then saturated. with increasing cold-rolled reduction. Furthermore, vacancy clusters in the cold-rolled pure zirconium are not formed, and they did not grow even under the isochronal annealing conditions from 298~898 K . The vacancy and dislocation densities of the cold-rolled pure zirconium decrease with increasing the annealing temperature, and they were almost recovery at 873 K.
2020, 49(10):3382-3387.
DOI: 10.12442/j.issn.1002-185X.20190775
Abstract:
C/SiC composites were prepared by reactive melt infiltration (RMI) of molten Si into the C/C porous preform. Influences of C/C porous preform embedded in silicon powder at different positons on the capillary absorption behaviors were investigated. Lots of free Si can be found inside of C/SiC composites prepared by RMI. The free Si was decreased significantly after desilication treatment of C/SiC composite, the composite density and flexural strength decreased as well.
C/SiC composites were prepared by reactive melt infiltration (RMI) of molten Si into the C/C porous preform. Influences of C/C porous preform embedded in silicon powder at different positons on the capillary absorption behaviors were investigated. Lots of free Si can be found inside of C/SiC composites prepared by RMI. The free Si was decreased significantly after desilication treatment of C/SiC composite, the composite density and flexural strength decreased as well.
2020, 49(10):3382-3394.
DOI: 10.12442/j.issn.1002-185X.E20190101
Abstract:
In order to investigate the combing effect of Er and Sr on the microstructure and mechanical properties of A356 alloy, Al-10Er-5Sr master alloy was fabricated and its microstructure and phase compositions were investigated. The optimal percentage of Al-10Er-5Sr in A356 alloy was obtained according to the evolution of microstructure and mechanical properties. The results showed that α-Al, Al4Sr and Al3Er were the main phases in Al-10Er-5Sr. In addition, the aluminum alloy with 0.6 wt% Al-10Er-5Sr exhibited optimal microstructure and mechanical properties, with the secondary dendrite arm spacing (SDAS) decreasing to 20.2 μm and acicular-like eutectic silicon transforming to fibrous. Due to the improved microstructure, the ultimate tensile strength of the alloy (with 0.6wt% Al-10Er-5Sr) increased to 203.5 MPa, which are much better than that of untreated A356 aluminum alloy. Finally, the grain refinement and modification mechanisms were discussed.
In order to investigate the combing effect of Er and Sr on the microstructure and mechanical properties of A356 alloy, Al-10Er-5Sr master alloy was fabricated and its microstructure and phase compositions were investigated. The optimal percentage of Al-10Er-5Sr in A356 alloy was obtained according to the evolution of microstructure and mechanical properties. The results showed that α-Al, Al4Sr and Al3Er were the main phases in Al-10Er-5Sr. In addition, the aluminum alloy with 0.6 wt% Al-10Er-5Sr exhibited optimal microstructure and mechanical properties, with the secondary dendrite arm spacing (SDAS) decreasing to 20.2 μm and acicular-like eutectic silicon transforming to fibrous. Due to the improved microstructure, the ultimate tensile strength of the alloy (with 0.6wt% Al-10Er-5Sr) increased to 203.5 MPa, which are much better than that of untreated A356 aluminum alloy. Finally, the grain refinement and modification mechanisms were discussed.
2020, 49(10):3395-3401.
DOI: 10.12442/j.issn.1002-185X.20190806
Abstract:
In this paper, an over peening effect was presented based on the researches of surface integrity and internal spall of Al7050 mid-thick plates with continued multiple laser shock peening (LSP) at the same positions. The dimensions of the samples were 50 mm × 50 mm × 5 mm (Length × Width × Thickness). Laser process parameters were laser energy of 30 J, square spots of 4 mm × 4 mm, pulse width of 15 ns and continued multiple LSP at the same positions (LSP-1~LSP-8). Surface morphology, surface residual stress, and micro-hardness in depth and cross-sectional microstructure were measured by Super depth 3D microscope system, X-ray diffraction instrument, Vickers indenter and Optical Microscope (OM), respectively. The results indicated that high micro-dent depressions of 197.8 μm and ridges of 130.8 μm were generated after continued LSP-5. Surface compressive residual stress changed into tensile residual stress from continued LSP-4 to continued LSP-5. After continued LSP-5, work soft with low micro-hardness was found in the bottom layer. Continued LSP-5 was the spall threshold of Al7050 mid-thick plates. The researched results can be beneficial to avoid the spall and improve the strengthening effect in an industry application of LSP.
In this paper, an over peening effect was presented based on the researches of surface integrity and internal spall of Al7050 mid-thick plates with continued multiple laser shock peening (LSP) at the same positions. The dimensions of the samples were 50 mm × 50 mm × 5 mm (Length × Width × Thickness). Laser process parameters were laser energy of 30 J, square spots of 4 mm × 4 mm, pulse width of 15 ns and continued multiple LSP at the same positions (LSP-1~LSP-8). Surface morphology, surface residual stress, and micro-hardness in depth and cross-sectional microstructure were measured by Super depth 3D microscope system, X-ray diffraction instrument, Vickers indenter and Optical Microscope (OM), respectively. The results indicated that high micro-dent depressions of 197.8 μm and ridges of 130.8 μm were generated after continued LSP-5. Surface compressive residual stress changed into tensile residual stress from continued LSP-4 to continued LSP-5. After continued LSP-5, work soft with low micro-hardness was found in the bottom layer. Continued LSP-5 was the spall threshold of Al7050 mid-thick plates. The researched results can be beneficial to avoid the spall and improve the strengthening effect in an industry application of LSP.
2020, 49(10):3402-3411.
DOI: 10.12442/j.issn.1002-185X.20190818
Abstract:
In order to improve the mechanical properties, a new Al-5Ti-1B-1RE master alloy refiner and Al-10Sr master alloy modifier were used to composite refine and modify the as-cast A356 aluminum alloy and a novel aluminum alloy composed of as-cast A356 aluminum alloy by adding Cu, Mn, Ti and other elements in a certain proportion. The morphology distribution of the second-phase particles and strengthening mechanism of the multi-component aluminum-silicon alloy were analyzed by means of OM, SEM, TEM and the electronic universal testing machine (CSS-44100).The results showed that the second-phase eutectic silicon phase in the A356 aluminum alloy transformed from coarse lamellar to typical fibrous phase after the composite refinement and modification, and precipitated uniformly at the grain boundary of the soft-tough phase α-Al matrix. The grain size of the α-Al phase decreased significantly. It was mainly Hall-Petch grain boundary fine grain strengthening mechanism. In addition to the second-phase particle eutectic silicon in the novel aluminum alloy, there were other second-phase particles which were more dispersed in the grain boundaries or intragranular. Various strengthening mechanisms worked together. When the second-phase particles were distributed on grain boundaries, it was mainly the Hall-Petch strengthening mechanism. When the second-phase particles were distributed in intragranular, it was mainly Orowan strengthening mechanism, which became an effective obstacle to dislocation movement and played a strengthening role.
In order to improve the mechanical properties, a new Al-5Ti-1B-1RE master alloy refiner and Al-10Sr master alloy modifier were used to composite refine and modify the as-cast A356 aluminum alloy and a novel aluminum alloy composed of as-cast A356 aluminum alloy by adding Cu, Mn, Ti and other elements in a certain proportion. The morphology distribution of the second-phase particles and strengthening mechanism of the multi-component aluminum-silicon alloy were analyzed by means of OM, SEM, TEM and the electronic universal testing machine (CSS-44100).The results showed that the second-phase eutectic silicon phase in the A356 aluminum alloy transformed from coarse lamellar to typical fibrous phase after the composite refinement and modification, and precipitated uniformly at the grain boundary of the soft-tough phase α-Al matrix. The grain size of the α-Al phase decreased significantly. It was mainly Hall-Petch grain boundary fine grain strengthening mechanism. In addition to the second-phase particle eutectic silicon in the novel aluminum alloy, there were other second-phase particles which were more dispersed in the grain boundaries or intragranular. Various strengthening mechanisms worked together. When the second-phase particles were distributed on grain boundaries, it was mainly the Hall-Petch strengthening mechanism. When the second-phase particles were distributed in intragranular, it was mainly Orowan strengthening mechanism, which became an effective obstacle to dislocation movement and played a strengthening role.
Xu Jianwei
,
Zheng Jingwu
,
Chen Haibo
,
Qiao Liang
,
Ying Yao
,
Cai Wei
,
Li Wangchang
,
Yu Jing
,
Lin Min
,
Che Shenglei
2020, 49(10):3412-3418.
DOI: 10.12442/j.issn.1002-185X.20190839
Abstract:
Magnetic properties and microstructure of fully nitrided (Sm1-yCey)2Fe17Nx (y = 0, 0.20, 0.33, 0.40, 0.45, 0.50, 0.67, 0.80, 1.00) powders have been investigated. When 33 atomic% Ce is substituted for Sm, maximum energy product (BH)max changes from 17.8 MGOe to 17.6 MGOe with almost no decrease. Accordingly, performance/rare earth price ratio increases by 39.2%. According to the energy dispersive spectroscopy (EDS) analysis, Ce tends to be distributed in the REFe3/REFe2 grain boundary phase. Meanwhile, valence change of the Ce ion in (Sm1-yCey)2Fe17Nx was confirmed by XPS.
Magnetic properties and microstructure of fully nitrided (Sm1-yCey)2Fe17Nx (y = 0, 0.20, 0.33, 0.40, 0.45, 0.50, 0.67, 0.80, 1.00) powders have been investigated. When 33 atomic% Ce is substituted for Sm, maximum energy product (BH)max changes from 17.8 MGOe to 17.6 MGOe with almost no decrease. Accordingly, performance/rare earth price ratio increases by 39.2%. According to the energy dispersive spectroscopy (EDS) analysis, Ce tends to be distributed in the REFe3/REFe2 grain boundary phase. Meanwhile, valence change of the Ce ion in (Sm1-yCey)2Fe17Nx was confirmed by XPS.
2020, 49(10):3419-3424.
DOI: 10.12442/j.issn.1002-185X.20200167
Abstract:
Based on the empirical electron theory of solids and molecules, the VESs of the matrix a, Mg-Ag segregation area, W phase and the interfaces of W/Mg-Ag/a, W//a were calculated after studying the interface atom structure between the matrix a and W phase, then the relationship between the interface VESs W/Mg-Ag/a and the interface properties was analyzed in Al-Cu-Mg-Ag alloy in this paper. The results show that the continuity of the outer of W/Mg-Ag/a is better than that of the inner because that the electron density difference of Mg-Ag/a is 16.54% and that of W/Mg-Ag is 50.73%. The Mg-Ag layer makes the interface electron density difference of W/a decrease by 1.13%, while it makes the strongest covalence band force and the covalence electron density in (111)a increase by 14.52% and 146.87% respectively, it also makes the strongest covalence band force and the covalence electron density in (111)W increase by 45.85% and 45.30% respectively. The existence of Mg-Ag layer enhances the alloy strength and toughness owing to it increasing the obstruction of W phase to the dislocation, the interface continuity, the interface binding force and stability while it decreasing the interface electron density differences and the interface stress.
Based on the empirical electron theory of solids and molecules, the VESs of the matrix a, Mg-Ag segregation area, W phase and the interfaces of W/Mg-Ag/a, W//a were calculated after studying the interface atom structure between the matrix a and W phase, then the relationship between the interface VESs W/Mg-Ag/a and the interface properties was analyzed in Al-Cu-Mg-Ag alloy in this paper. The results show that the continuity of the outer of W/Mg-Ag/a is better than that of the inner because that the electron density difference of Mg-Ag/a is 16.54% and that of W/Mg-Ag is 50.73%. The Mg-Ag layer makes the interface electron density difference of W/a decrease by 1.13%, while it makes the strongest covalence band force and the covalence electron density in (111)a increase by 14.52% and 146.87% respectively, it also makes the strongest covalence band force and the covalence electron density in (111)W increase by 45.85% and 45.30% respectively. The existence of Mg-Ag layer enhances the alloy strength and toughness owing to it increasing the obstruction of W phase to the dislocation, the interface continuity, the interface binding force and stability while it decreasing the interface electron density differences and the interface stress.
2020, 49(10):3425-3432.
DOI: 10.12442/j.issn.1002-185X.20190865
Abstract:
In this article, the dissolution kinetics of copper in liquid Tin at temperatures in the range 513~573 K were investigated under the influence of a DC current by immersion method. After dissolution, the dissolution thickness and the thickness of IMC layer at Sn/Cu interface were measured and the dissolution activation energy and effective charge Z* were calculated. It is found that the current had a marked effect on the dissolution rate constant. Correspondingly, the application of the current significantly decreased the activation energy of dissolution. Similarly,the direction of the DC current was shown to have an effect on dissolution and the growth of IMC. When the electronic flow was in the direction of dissolution, a further increase in dissolution and a decrease in growth of IMC layer were observed and attributed to electromigration. When the current density was 240 A/cm2, the effective charge Z* decreased with the increased of temperature.
In this article, the dissolution kinetics of copper in liquid Tin at temperatures in the range 513~573 K were investigated under the influence of a DC current by immersion method. After dissolution, the dissolution thickness and the thickness of IMC layer at Sn/Cu interface were measured and the dissolution activation energy and effective charge Z* were calculated. It is found that the current had a marked effect on the dissolution rate constant. Correspondingly, the application of the current significantly decreased the activation energy of dissolution. Similarly,the direction of the DC current was shown to have an effect on dissolution and the growth of IMC. When the electronic flow was in the direction of dissolution, a further increase in dissolution and a decrease in growth of IMC layer were observed and attributed to electromigration. When the current density was 240 A/cm2, the effective charge Z* decreased with the increased of temperature.
2020, 49(10):3433-3438.
DOI: 10.12442/j.issn.1002-185X.20190886
Abstract:
: The fretting fatigue characteristics of ultra-fine grain pure titanium under cylindrical-plane contact were studied by using a fretting fatigue experimental fixture designed by ourselves, and the effect of cyclic stress on its fretting fatigue life was analyzed. The fretting damage mechanism was analyzed by observing the wear and fracture morphology of the contact zone.The fretting fatigue life of ultra-fine grain pure titanium decreases with the increase of cyclic stress when the normal load is constant. The fretting fatigue crack originates at the edge of the contact zone, and the wear zone breaks seriously and has abrasive particles attached to it, which accelerates the fatigue failure of the specimen under the action of abrasive wear. The fracture surface shows both fatigue morphology and fretting morphology. The morphology changes from smooth to rough to fracture, the crack increases from small to large, the crack growth rate increases gradually, and there are secondary cracks in the crack propagation zone. Between the crack propagation zone and the fracture zone due to uneven force,there is a ridge-like morphology.
: The fretting fatigue characteristics of ultra-fine grain pure titanium under cylindrical-plane contact were studied by using a fretting fatigue experimental fixture designed by ourselves, and the effect of cyclic stress on its fretting fatigue life was analyzed. The fretting damage mechanism was analyzed by observing the wear and fracture morphology of the contact zone.The fretting fatigue life of ultra-fine grain pure titanium decreases with the increase of cyclic stress when the normal load is constant. The fretting fatigue crack originates at the edge of the contact zone, and the wear zone breaks seriously and has abrasive particles attached to it, which accelerates the fatigue failure of the specimen under the action of abrasive wear. The fracture surface shows both fatigue morphology and fretting morphology. The morphology changes from smooth to rough to fracture, the crack increases from small to large, the crack growth rate increases gradually, and there are secondary cracks in the crack propagation zone. Between the crack propagation zone and the fracture zone due to uneven force,there is a ridge-like morphology.
2020, 49(10):3439-3444.
DOI: 10.12442/j.issn.1002-185X.20190927
Abstract:
Characterizations of fatigue crackSpropagationSresistance of the key bearing structures precisely in aviation area are the basis of its service lifetime evaluation. In this work, Ti-2Al-1.5Mn titanium alloy was selected, some CT samples were prepared along different sheet orientation, the fatigue crack growth rate test was carried out, the stress intensity factor range DK at different crack stage were calculated based on full-field measurements and traditional method. It can be concluded that the fatigue crack growth rate da/dN versus DK curve and crack growth path are affected by material orientation. Compared with the traditional method, DK calculation based on full-field measurements was proved to be more efficient. For one thing, the crack shielding effect due to plastic zone in crack tip can be directly considered. For another, a more accurate DK can be got for the case that the crack path was zigzag. It has a wideSapplication in future of DK calculation based on full-field measurements.
Characterizations of fatigue crackSpropagationSresistance of the key bearing structures precisely in aviation area are the basis of its service lifetime evaluation. In this work, Ti-2Al-1.5Mn titanium alloy was selected, some CT samples were prepared along different sheet orientation, the fatigue crack growth rate test was carried out, the stress intensity factor range DK at different crack stage were calculated based on full-field measurements and traditional method. It can be concluded that the fatigue crack growth rate da/dN versus DK curve and crack growth path are affected by material orientation. Compared with the traditional method, DK calculation based on full-field measurements was proved to be more efficient. For one thing, the crack shielding effect due to plastic zone in crack tip can be directly considered. For another, a more accurate DK can be got for the case that the crack path was zigzag. It has a wideSapplication in future of DK calculation based on full-field measurements.
2020, 49(10):3445-3451.
DOI: 10.12442/j.issn.1002-185X.20190750
Abstract:
High purity zirconium was used as the base material to fabricate Zr-1.0Fe-0.2Cu alloy. The microstructure and corrosion behavior in 400 ℃/10.3 MPa superheated steam of this alloy were investigated using SEM and TEM. The results show that the Zr3Fe phase with orthogonal center structure is the typical second phase in the Zr-1.0Fe-0.2Cu alloy. Cu is prone to segregate to the Zr3Fe phase, rather than to form Zr2Cu phase. The addition of Cu element can refine the Zr3Fe phase in the alloy. When exposed to the superheated steam for 100 days, the corrosion resistance of Zr-1.0Fe-0.2Cu alloy is better than Zr-1.0Fe alloy and Zr-4 remelting alloy, which indicates that adding a small amount of Cu element is beneficial. In the oxidation process, Cu-containing Zr3Fe phase is oxidized behind the α-Zr matrix and is thus surrounded by the oxide film. As the oxidation progresses, Zr in the second phase is oxidized into tetragonal zirconia. Fe is oxidized into Fe3O4 phase with monoclinic structure. Further, the original aggregation state of Cu and Fe in the Zr3Fe phase has disappeared due to the diffusion and oxidation in the oxide film of these elements.
High purity zirconium was used as the base material to fabricate Zr-1.0Fe-0.2Cu alloy. The microstructure and corrosion behavior in 400 ℃/10.3 MPa superheated steam of this alloy were investigated using SEM and TEM. The results show that the Zr3Fe phase with orthogonal center structure is the typical second phase in the Zr-1.0Fe-0.2Cu alloy. Cu is prone to segregate to the Zr3Fe phase, rather than to form Zr2Cu phase. The addition of Cu element can refine the Zr3Fe phase in the alloy. When exposed to the superheated steam for 100 days, the corrosion resistance of Zr-1.0Fe-0.2Cu alloy is better than Zr-1.0Fe alloy and Zr-4 remelting alloy, which indicates that adding a small amount of Cu element is beneficial. In the oxidation process, Cu-containing Zr3Fe phase is oxidized behind the α-Zr matrix and is thus surrounded by the oxide film. As the oxidation progresses, Zr in the second phase is oxidized into tetragonal zirconia. Fe is oxidized into Fe3O4 phase with monoclinic structure. Further, the original aggregation state of Cu and Fe in the Zr3Fe phase has disappeared due to the diffusion and oxidation in the oxide film of these elements.
2020, 49(10):3452-3459.
DOI: 10.12442/j.issn.1002-185X.20190797
Abstract:
The metallurgical bonding of panel and core layer of aluminum foam sandwich can be realized by the powder metallurgy method, and the advantages in the preparation of near net shape aluminum foam part are prominent. Basing on the present situation of domestic research, the preparation process of aluminum foam sandwich by powder metallurgy method was improved, and the cellular structure was optimized in this paper. The results show that the foamable precursor with higher densification degree and metallurgy combination of panel and core layer can be obtained by hot-rolling of the coating panel filled with the core layer, when the density of the core layer powder is 1.12 g/cm3, and at a rolling pressure of 1500 kN, a rolling speed of 0.06 m/s and a rolling reduction rate of 55%. AlMg4Si8 aluminum alloy was selected as a core layer component, and the edge welding seal preprocessing of the steel panel was carried out. In addition, the H2 decomposed at the initial stage of foaming is wrapped by the liquid Sn when the blowing agent TiH2 was pretreated by coating of the low melting point Sn, so that the diffusion of H2 between the voids in the solid matrix was avoided and the generation of cracks was reduced, finally, aluminum foam sandwich with uniform cellular structure and 72.7% porosity can be obtained by foaming of foamable precursor at 720 °C for 300 s.
The metallurgical bonding of panel and core layer of aluminum foam sandwich can be realized by the powder metallurgy method, and the advantages in the preparation of near net shape aluminum foam part are prominent. Basing on the present situation of domestic research, the preparation process of aluminum foam sandwich by powder metallurgy method was improved, and the cellular structure was optimized in this paper. The results show that the foamable precursor with higher densification degree and metallurgy combination of panel and core layer can be obtained by hot-rolling of the coating panel filled with the core layer, when the density of the core layer powder is 1.12 g/cm3, and at a rolling pressure of 1500 kN, a rolling speed of 0.06 m/s and a rolling reduction rate of 55%. AlMg4Si8 aluminum alloy was selected as a core layer component, and the edge welding seal preprocessing of the steel panel was carried out. In addition, the H2 decomposed at the initial stage of foaming is wrapped by the liquid Sn when the blowing agent TiH2 was pretreated by coating of the low melting point Sn, so that the diffusion of H2 between the voids in the solid matrix was avoided and the generation of cracks was reduced, finally, aluminum foam sandwich with uniform cellular structure and 72.7% porosity can be obtained by foaming of foamable precursor at 720 °C for 300 s.
2020, 49(10):3460-3464.
DOI: 10.12442/j.issn.1002-185X.20190802
Abstract:
Ti-20Al-22Nb (at%) alloys were prepared by investment casting. The microstructures and tensile properties at room temperature of as-cast, hot isostatic pressing and annealed alloys were analyzed. The results show that solidified alloy has course widmanstatten structure, which consists with β matrix, fine acicular α2 phase and a small amount of O phase. The phase transformation inside original β/B2 grain was incomplete owing to non-equilibrium solidification. The loose defect and inhomogeneity of microstructures causes low plasticity of the material. The porous defects are eliminated by hot isostatic pressing in the two-phase region ofα2+β/B2. , peritectoid reaction of β/B2+α2→O promotes the formation of ring O phase around strip α2 phase, and β phase path through a process of equilibrium state transportation. The elongation of the alloy increases from 2% to 5%. Increase to 11%.
Ti-20Al-22Nb (at%) alloys were prepared by investment casting. The microstructures and tensile properties at room temperature of as-cast, hot isostatic pressing and annealed alloys were analyzed. The results show that solidified alloy has course widmanstatten structure, which consists with β matrix, fine acicular α2 phase and a small amount of O phase. The phase transformation inside original β/B2 grain was incomplete owing to non-equilibrium solidification. The loose defect and inhomogeneity of microstructures causes low plasticity of the material. The porous defects are eliminated by hot isostatic pressing in the two-phase region ofα2+β/B2. , peritectoid reaction of β/B2+α2→O promotes the formation of ring O phase around strip α2 phase, and β phase path through a process of equilibrium state transportation. The elongation of the alloy increases from 2% to 5%. Increase to 11%.
2020, 49(10):3465-3471.
DOI: 10.12442/j.issn.1002-185X.20190804
Abstract:
The mechanical properties, microstructure, fracture morphology and second phase particles of T6 state SiCp/AlMMCs were analyzed by using self-made TiB2 in situ reinforcement and 4047 welding wire as filling materials for TIG welding of T6 state SiCp/AlMMCs. The results show that the weld forming of the two kinds of welding wires is excellent, and the 4047 welding wire is more beautiful, and the tensile strength of TiB2 joint is obviously better than that of ER4047 joint, and the average strength is 171.88 MPA, which is 40.03% higher than that of 4047 joint. TIB2 particles play an in-situ strengthening role. The hardness values of the two joints are approximately symmetrical in the center of the weld, and the hardness of the weld zone is the lowest, the average value is 71.65HV,60.02HV. the "overaging" phenomenon of the hardness in the heat affected zone is obvious, the SiC particles in the weld are less, there is a serious barren zone, and no obvious Al4C3 brittleness is found. The microstructure is dendritic structure, but the dendritic grain of 4047 joint is coarse, the grain size of TiB2 joint is fine, the rare earth element Sc,Ce,Be plays the role of refining grain, and the TiB2 particles are evenly distributed in the weld, and the pores in the fracture surface of TiB2 joint are few, which is tough. The brittle mixed fracture shows that there are more particles in the second phase in the dimple, and there are more pores in the fracture surface of the 4047 joint, which is ductile fracture, and the second phase particles in the dimple are less.
The mechanical properties, microstructure, fracture morphology and second phase particles of T6 state SiCp/AlMMCs were analyzed by using self-made TiB2 in situ reinforcement and 4047 welding wire as filling materials for TIG welding of T6 state SiCp/AlMMCs. The results show that the weld forming of the two kinds of welding wires is excellent, and the 4047 welding wire is more beautiful, and the tensile strength of TiB2 joint is obviously better than that of ER4047 joint, and the average strength is 171.88 MPA, which is 40.03% higher than that of 4047 joint. TIB2 particles play an in-situ strengthening role. The hardness values of the two joints are approximately symmetrical in the center of the weld, and the hardness of the weld zone is the lowest, the average value is 71.65HV,60.02HV. the "overaging" phenomenon of the hardness in the heat affected zone is obvious, the SiC particles in the weld are less, there is a serious barren zone, and no obvious Al4C3 brittleness is found. The microstructure is dendritic structure, but the dendritic grain of 4047 joint is coarse, the grain size of TiB2 joint is fine, the rare earth element Sc,Ce,Be plays the role of refining grain, and the TiB2 particles are evenly distributed in the weld, and the pores in the fracture surface of TiB2 joint are few, which is tough. The brittle mixed fracture shows that there are more particles in the second phase in the dimple, and there are more pores in the fracture surface of the 4047 joint, which is ductile fracture, and the second phase particles in the dimple are less.
2020, 49(10):3472-3478.
DOI: 10.12442/j.issn.1002-185X.20190819
Abstract:
In this paper, the particle shape and size of tungsten powders were quantitatively analyzed by image analysis technology, and the effect of particle shape on the rheological properties of tungsten feedstocks for metal powder injection molding (MIM) was alao investigated. The results showed that the particle size of narrow particle-sized tungsten (NPW) powder was almost the same as that of spherical tungsten (SW) powder. In contrast to NPW powders, the SW powders exhibited better sphericity, surface smoothness and dispersion. Mixing with the same binder, the solid loading of SW powders was 64%, which was higher than that of 59% of the NPW powders. The SW feedshocks showed better flow performance, i.e., lower flow behavior index and flow activation energy, and it thus was more suitable for injection molding. Particle shape affects the rheology of tungsten MIM feedstocks by changing the nature of organic binder–particle and particle–particle interactions.
In this paper, the particle shape and size of tungsten powders were quantitatively analyzed by image analysis technology, and the effect of particle shape on the rheological properties of tungsten feedstocks for metal powder injection molding (MIM) was alao investigated. The results showed that the particle size of narrow particle-sized tungsten (NPW) powder was almost the same as that of spherical tungsten (SW) powder. In contrast to NPW powders, the SW powders exhibited better sphericity, surface smoothness and dispersion. Mixing with the same binder, the solid loading of SW powders was 64%, which was higher than that of 59% of the NPW powders. The SW feedshocks showed better flow performance, i.e., lower flow behavior index and flow activation energy, and it thus was more suitable for injection molding. Particle shape affects the rheology of tungsten MIM feedstocks by changing the nature of organic binder–particle and particle–particle interactions.
2020, 49(10):3479-3483.
DOI: 10.12442/j.issn.1002-185X.20190821
Abstract:
The AZ61 magnesium alloy wires and sticks were prepared through multi-step hot rotary swaging, and the strength of AZ61 alloy is enhanced due to grain refinement and dynamic precipitation during rotary swaging process. The dynamic precipitation mechanism during hot rotary swaging is also discussed. The results show that the rotary swaged AZ61 alloys exhibited a high YS of 302MPa, a high UTS of 376MPa and a elongation of 7%. The means grain sizes in rotary swaged AZ61 alloy is 8μm. The dynamicly precipitated nanophases during rotary swaging process of AZ61 alloy include spherical Mg17Al12 particles (average size of 110nm, ~6.5 vol.%) and spherical Al6Mn particles (average size of 10nm). The dynamic precipitation mechanism during rotary swaging process is as follows: rotary swaging is a high-frequency pulse forging process (the pulse forging frequency is between 1500 and 6000 strokes per minute) during which plastic deformation intervals altered with aging intervals. These crystal defects produced during plastic deformation such as dislocations and vacancies provided large amount of nucleation sites for precipitation. The aging interval during each pulse period is as short as 0.05s and hence the dynamic precipitate phases didn’t grow to a very large size.
The AZ61 magnesium alloy wires and sticks were prepared through multi-step hot rotary swaging, and the strength of AZ61 alloy is enhanced due to grain refinement and dynamic precipitation during rotary swaging process. The dynamic precipitation mechanism during hot rotary swaging is also discussed. The results show that the rotary swaged AZ61 alloys exhibited a high YS of 302MPa, a high UTS of 376MPa and a elongation of 7%. The means grain sizes in rotary swaged AZ61 alloy is 8μm. The dynamicly precipitated nanophases during rotary swaging process of AZ61 alloy include spherical Mg17Al12 particles (average size of 110nm, ~6.5 vol.%) and spherical Al6Mn particles (average size of 10nm). The dynamic precipitation mechanism during rotary swaging process is as follows: rotary swaging is a high-frequency pulse forging process (the pulse forging frequency is between 1500 and 6000 strokes per minute) during which plastic deformation intervals altered with aging intervals. These crystal defects produced during plastic deformation such as dislocations and vacancies provided large amount of nucleation sites for precipitation. The aging interval during each pulse period is as short as 0.05s and hence the dynamic precipitate phases didn’t grow to a very large size.
2020, 49(10):3484-3489.
DOI: 10.12442/j.issn.1002-185X.20190833
Abstract:
Micro-arc oxidation (MAO) is a new technology for in-situ growth of oxide ceramic layers on valve metals( Ti, Al, Mg, Zr, Ta, etc) or their alloys. which improve the wear resistance and corrosion resistance of metals.The ZIRLO alloy was subjected to micro-arc oxidation treatment using a phosphate or silicate electrolyte system. XRD, SEM, TEM etc.were used to study the phase composition, surface morphology and cross-sectional structure of the ceramic layer. The results show that the ceramic layer prepared in the phosphate electrolyte system and the silicate electrolyte system is mainly composed of m-ZrO2. The inner surface of the ceramic layer prepared by the phosphate electrolyte system is denser than the ceramic layer prepared by the silicate electrolyte system. A small amount of β-Zr is present on the side of the substrate near the O/M interface in E sample (Micro-arc oxidation of silicate electrolyte system). ZIRLO alloy and D sample (Micro-arc oxidation of phosphorus electrolyte system) and E sample (Micro-arc oxidation of silicate electrolyte system) was studied in static autoclave at 360 °C / 18.6 MPa deionized water and 360 °C / 18.6 MPa 0.01 M LiOH aqueous solution. The corrosion weight double logarithmic curve results show that when samples corroded to 360 d in 360 °C / 18.6 MPa deionized water, the corrosion resistance of D and E samples is similar, which is better than the ZIRLO alloy sample without micro-arc oxidation; When samples corroded to 246 d in 360 °C / 18.6 MPa 0.01 M LiOH aqueous solution , the corrosion resistance of D and E samples are close to that of ZIRLO alloy samples without micro-arc oxidation treatment or even which have harmful influence on ZIRLO alloy. With the extension of corrosion time, micro-arc oxidation has limited improvement on corrosion resistance of ZIRLO alloy.
Micro-arc oxidation (MAO) is a new technology for in-situ growth of oxide ceramic layers on valve metals( Ti, Al, Mg, Zr, Ta, etc) or their alloys. which improve the wear resistance and corrosion resistance of metals.The ZIRLO alloy was subjected to micro-arc oxidation treatment using a phosphate or silicate electrolyte system. XRD, SEM, TEM etc.were used to study the phase composition, surface morphology and cross-sectional structure of the ceramic layer. The results show that the ceramic layer prepared in the phosphate electrolyte system and the silicate electrolyte system is mainly composed of m-ZrO2. The inner surface of the ceramic layer prepared by the phosphate electrolyte system is denser than the ceramic layer prepared by the silicate electrolyte system. A small amount of β-Zr is present on the side of the substrate near the O/M interface in E sample (Micro-arc oxidation of silicate electrolyte system). ZIRLO alloy and D sample (Micro-arc oxidation of phosphorus electrolyte system) and E sample (Micro-arc oxidation of silicate electrolyte system) was studied in static autoclave at 360 °C / 18.6 MPa deionized water and 360 °C / 18.6 MPa 0.01 M LiOH aqueous solution. The corrosion weight double logarithmic curve results show that when samples corroded to 360 d in 360 °C / 18.6 MPa deionized water, the corrosion resistance of D and E samples is similar, which is better than the ZIRLO alloy sample without micro-arc oxidation; When samples corroded to 246 d in 360 °C / 18.6 MPa 0.01 M LiOH aqueous solution , the corrosion resistance of D and E samples are close to that of ZIRLO alloy samples without micro-arc oxidation treatment or even which have harmful influence on ZIRLO alloy. With the extension of corrosion time, micro-arc oxidation has limited improvement on corrosion resistance of ZIRLO alloy.
2020, 49(10):3490-3497.
DOI: 10.12442/j.issn.1002-185X.20190843
Abstract:
This paper fabricated pure tungsten thin wall parts by laser single track scanning via SLM. The wall thickness and molten trace width were measured by two-dimensional imager and optical microscope, respectively, and the influence of laser power and scanning rate on the wall thickness and molten trace width were investigated. The surface 2D and 3D morphology of thin walls were detected by optical microscope. The powder adhesion on the side surface of the thin wall was detected by scanning electron microscope and the reason for powder adhesion was analyzed. The results indicated that the walls thickness was greater than molten trace width. With the increase of laser power, the wall thickness amd molten trace width increased, the surface of thin wall became smooth. With the increase of scanning rate, the wall thickness and molten trace with decreased, the molten trace became twisted first and then straight, and twisted again, the height difference of the molten trace decreased first and then increased. The thin wall consisted of complete melting zone, balling zone, semi-melting zone and unmelted zone.
This paper fabricated pure tungsten thin wall parts by laser single track scanning via SLM. The wall thickness and molten trace width were measured by two-dimensional imager and optical microscope, respectively, and the influence of laser power and scanning rate on the wall thickness and molten trace width were investigated. The surface 2D and 3D morphology of thin walls were detected by optical microscope. The powder adhesion on the side surface of the thin wall was detected by scanning electron microscope and the reason for powder adhesion was analyzed. The results indicated that the walls thickness was greater than molten trace width. With the increase of laser power, the wall thickness amd molten trace width increased, the surface of thin wall became smooth. With the increase of scanning rate, the wall thickness and molten trace with decreased, the molten trace became twisted first and then straight, and twisted again, the height difference of the molten trace decreased first and then increased. The thin wall consisted of complete melting zone, balling zone, semi-melting zone and unmelted zone.
2020, 49(10):3498-3504.
DOI: 10.12442/j.issn.1002-185X.20190844
Abstract:
The effect of high-energy helium ion pre-implantation on deuterium retention behavior in tungsten was studied by using high-energy ion implanter and linear experimental plasma system (LEPS). FIB-SEM, TEM, GD-OES and TDS measurements were used to analyze the effect of helium ion pre-implantation on deuterium retention in tungsten from both microstructure and deuterium concentration depth profile. The results show that a large number of helium bubbles are formed in the irradiated area by implantation of helium ions. After deuterium plasma exposure, the number of deuterium bubbles are was significantly lower than that of sample without helium ion pre-implantation. GD-OES analysis shows that deuterium concentration depth profile increases obviously at the helium capture position, and the helium ion pre-implantation increases the diffusion depth of deuterium in tungsten. TDS analysis also shows that helium ion pre-implantation increases the retention of deuterium in tungsten. This can be attributed to the defects formed after helium ions pre-implantation provide a large number of new trap sites for deuterium capture in tungsten, which leads to the significant increase of deuterium retention in tungsten.
The effect of high-energy helium ion pre-implantation on deuterium retention behavior in tungsten was studied by using high-energy ion implanter and linear experimental plasma system (LEPS). FIB-SEM, TEM, GD-OES and TDS measurements were used to analyze the effect of helium ion pre-implantation on deuterium retention in tungsten from both microstructure and deuterium concentration depth profile. The results show that a large number of helium bubbles are formed in the irradiated area by implantation of helium ions. After deuterium plasma exposure, the number of deuterium bubbles are was significantly lower than that of sample without helium ion pre-implantation. GD-OES analysis shows that deuterium concentration depth profile increases obviously at the helium capture position, and the helium ion pre-implantation increases the diffusion depth of deuterium in tungsten. TDS analysis also shows that helium ion pre-implantation increases the retention of deuterium in tungsten. This can be attributed to the defects formed after helium ions pre-implantation provide a large number of new trap sites for deuterium capture in tungsten, which leads to the significant increase of deuterium retention in tungsten.
du jun chen
,
Yang Haiqiong
,
Zhang Aimin
,
Guo Miaoxin
,
Zheng Tingting
,
Zhao Yunkun
,
Luo Yongming
,
Huang Weiqiang
2020, 49(10):3505-3509.
DOI: 10.12442/j.issn.1002-185X.20190856
Abstract:
Through the preparation of Pd/ZrO2-Al2O3 catalysts supported by ZrO2-Al2O3 composite oxides, the influence of the preparation of ZrO2-Al2O3 composite oxides on the low temperature CH4 oxidation activity of the catalysts were studied in a continuous flow fixed bed reactor, in order to promote the practical application of ZrO2-Al2O3 in the catalyst for natural gas vehicle exhaust purification, and to clarify the mechanism of the influence of preparation conditions on the conversion activity of the supported catalyst. The results show that the precipitation method can improve the activity of catalyst more than the impregnation method and the peptizing method; When Zr(NO3)4 is used as zirconium precursor and boehmite as aluminum precursor, high catalytic activity can be obtained; The activity of w (ZrO2): w (Al2O3)=10:90 is the highest in series of catalysts with different proportions. The structure characterization of XRD, N2 adsorption-desorption and CO pulse adsorption show that the large specific surface area, pore volume and pore diameter of ZrO2-Al2O3 composite oxides are the key factors to promote the dispersion of noble metal Pd and the conversion activity of catalyst CH4 at low temperature.
Through the preparation of Pd/ZrO2-Al2O3 catalysts supported by ZrO2-Al2O3 composite oxides, the influence of the preparation of ZrO2-Al2O3 composite oxides on the low temperature CH4 oxidation activity of the catalysts were studied in a continuous flow fixed bed reactor, in order to promote the practical application of ZrO2-Al2O3 in the catalyst for natural gas vehicle exhaust purification, and to clarify the mechanism of the influence of preparation conditions on the conversion activity of the supported catalyst. The results show that the precipitation method can improve the activity of catalyst more than the impregnation method and the peptizing method; When Zr(NO3)4 is used as zirconium precursor and boehmite as aluminum precursor, high catalytic activity can be obtained; The activity of w (ZrO2): w (Al2O3)=10:90 is the highest in series of catalysts with different proportions. The structure characterization of XRD, N2 adsorption-desorption and CO pulse adsorption show that the large specific surface area, pore volume and pore diameter of ZrO2-Al2O3 composite oxides are the key factors to promote the dispersion of noble metal Pd and the conversion activity of catalyst CH4 at low temperature.
2020, 49(10):3510-3518.
DOI: 10.12442/j.issn.1002-185X.20190866
Abstract:
In order to improve the performance of the welded joint and prolong its service life, the industrial pure titanium TA2 welded joint was strengthened by ultrasonic shot peening (USSP) with a shot peening strength of 0.15A. The microstructure and corrosion morphology of TA2 welded joints were observed by OM, SEM and TEM. The residual stress values and surface roughness of different treated samples were measured, the surface of the samples after ultrasonic shot peening were heat treated. And surface grinding, the electrochemical corrosion performance of different surface residual stress and surface roughness on the welded joint weld zone in 80 ° C 10% HCl solution was studied. The results show that the corrosion resistance of the USSP intensive treatment of pure titanium welded joints has been improved. After annealing, the corrosion resistance first increases and then decreases with the increase of annealing time. When annealing for 0.5h, the natural corrosion potential was the highest, the current density was the lowest, and the corrosion resistance was optimal. After surface grinding, the corrosion rate is mainly controlled by the diffusion step, resulting in concentration polarization. As the polishing strengthening layer increases, the diffusion rate increases, and the corrosion resistance has been improved. When polished to 2/5 of the strengthening layer, the corrosion resistance has been improved significantly.
In order to improve the performance of the welded joint and prolong its service life, the industrial pure titanium TA2 welded joint was strengthened by ultrasonic shot peening (USSP) with a shot peening strength of 0.15A. The microstructure and corrosion morphology of TA2 welded joints were observed by OM, SEM and TEM. The residual stress values and surface roughness of different treated samples were measured, the surface of the samples after ultrasonic shot peening were heat treated. And surface grinding, the electrochemical corrosion performance of different surface residual stress and surface roughness on the welded joint weld zone in 80 ° C 10% HCl solution was studied. The results show that the corrosion resistance of the USSP intensive treatment of pure titanium welded joints has been improved. After annealing, the corrosion resistance first increases and then decreases with the increase of annealing time. When annealing for 0.5h, the natural corrosion potential was the highest, the current density was the lowest, and the corrosion resistance was optimal. After surface grinding, the corrosion rate is mainly controlled by the diffusion step, resulting in concentration polarization. As the polishing strengthening layer increases, the diffusion rate increases, and the corrosion resistance has been improved. When polished to 2/5 of the strengthening layer, the corrosion resistance has been improved significantly.
2020, 49(10):3519-3527.
DOI: 10.12442/j.issn.1002-185X.20190870
Abstract:
The isothermal oxidation behavior of GH3535 alloy before and after shot peening at 900 °C was investigated by using discontinuous increasing weight method. The results show that the samples of Weight gain of the 0.45 Nmm shot peening strength was reduced by 79.7% compared to the unshot sample at 900℃. The main oxide products of unshot GH3535 alloy are NiCr2O4，MoO2，NiMoO4； While the surface oxide film products of GH3535 alloy is composed of NiO, NiFe2O4, Cr2O3 and NiCr2O4 after shot peening treatments. Plastic deformation was performed on the surface of GH3535 alloy and refined the grains due to shot peening The main reason for the increase of Cr atom diffusion flux is that the dislocations and grain boundaries of the plastic deformation zone of the alloy surface act as a fast diffusion path of Cr atoms, and the Cr2O3 layer is more quickly formed, which promotes the diffusion of Cr to the surface to form Cr-rich oxides, and reduce the transient oxidation period
The isothermal oxidation behavior of GH3535 alloy before and after shot peening at 900 °C was investigated by using discontinuous increasing weight method. The results show that the samples of Weight gain of the 0.45 Nmm shot peening strength was reduced by 79.7% compared to the unshot sample at 900℃. The main oxide products of unshot GH3535 alloy are NiCr2O4，MoO2，NiMoO4； While the surface oxide film products of GH3535 alloy is composed of NiO, NiFe2O4, Cr2O3 and NiCr2O4 after shot peening treatments. Plastic deformation was performed on the surface of GH3535 alloy and refined the grains due to shot peening The main reason for the increase of Cr atom diffusion flux is that the dislocations and grain boundaries of the plastic deformation zone of the alloy surface act as a fast diffusion path of Cr atoms, and the Cr2O3 layer is more quickly formed, which promotes the diffusion of Cr to the surface to form Cr-rich oxides, and reduce the transient oxidation period
2020, 49(10):3528-3535.
DOI: 10.12442/j.issn.1002-185X.20190874
Abstract:
In this paper, the addition of Er element in the alloy of Al10Si1.5Fe2.25Co was carried out to study the effect of different mass fractions of Er on the refinement and mechanical properties of the microstructure. The research shows that the cerium element can effectively refine the eutectic silicon structure in the high-iron aluminum-silicon alloy after Co metamorphism. When the addition amount of element Er is 0.5wt.%, the eutectic silicon has the best refining effect; At the same time, α-Al also obtained a certain refinement, and excessive Er will lead to the precipitation of acicular Al3Er phase, but the element Er has no obvious refinement effect on the bulk iron-rich phase. With the refinement of eutectic silicon, the plasticity of the alloy is enhanced and the tensile strength is also improved. When the Er content is 0.5%, the maximum tensile strength is 160.8 MPa and the elongation after fracture is 1.89%. The alloy was increased by 5% and 19.6% compared to the alloy without Er added, and the excess of Er resulted in a decrease in strength and ductility. At the same time, with the increase of Er content in the alloy, the wear rate and friction coefficient of the alloy increased. When Er content is 0.5wt%, the relative wear resistance of the alloy reaches the best.
In this paper, the addition of Er element in the alloy of Al10Si1.5Fe2.25Co was carried out to study the effect of different mass fractions of Er on the refinement and mechanical properties of the microstructure. The research shows that the cerium element can effectively refine the eutectic silicon structure in the high-iron aluminum-silicon alloy after Co metamorphism. When the addition amount of element Er is 0.5wt.%, the eutectic silicon has the best refining effect; At the same time, α-Al also obtained a certain refinement, and excessive Er will lead to the precipitation of acicular Al3Er phase, but the element Er has no obvious refinement effect on the bulk iron-rich phase. With the refinement of eutectic silicon, the plasticity of the alloy is enhanced and the tensile strength is also improved. When the Er content is 0.5%, the maximum tensile strength is 160.8 MPa and the elongation after fracture is 1.89%. The alloy was increased by 5% and 19.6% compared to the alloy without Er added, and the excess of Er resulted in a decrease in strength and ductility. At the same time, with the increase of Er content in the alloy, the wear rate and friction coefficient of the alloy increased. When Er content is 0.5wt%, the relative wear resistance of the alloy reaches the best.
2020, 49(10):3536-3543.
DOI: 10.12442/j.issn.1002-185X.20190882
Abstract:
Flexible microelectrode array (fMEA) is one of the key devices for neural stimulation and recording. For its specific implantation environment, its design and manufacture should meet the requirements of biocompatibility, high resolution, flexibility and low impedance to ensure safe and long-term effective stimulation. In this paper, an fMEA fabrication process was proposed by using flexible polyimide matrix with a variety of 3D platinum nanostructure coatings were fabricated by electrochemical plating at 200 mm stimulation site. Compared with the surface of bare platinum coating, the impedance of 3D micro-structure coating decreased by 94.77% at 1 kHz, reaching 0.824 kΩ and breaking through the limit of 1 kΩ. Compared with other coated electrodes, the CSCc of the novel barrier crystal morphology coated electrodes can be increased by 6.67 times to 13.47 mC cm-2. The safe charge injection ability is 19.6 times higher than that of Pt-gray, reaching 2.53 mC cm-2. Therefore, this electroplating coating structure and process is promising for effective nerve stimulation/recording in various applications, and have broad application prospects in biomedical fields.
Flexible microelectrode array (fMEA) is one of the key devices for neural stimulation and recording. For its specific implantation environment, its design and manufacture should meet the requirements of biocompatibility, high resolution, flexibility and low impedance to ensure safe and long-term effective stimulation. In this paper, an fMEA fabrication process was proposed by using flexible polyimide matrix with a variety of 3D platinum nanostructure coatings were fabricated by electrochemical plating at 200 mm stimulation site. Compared with the surface of bare platinum coating, the impedance of 3D micro-structure coating decreased by 94.77% at 1 kHz, reaching 0.824 kΩ and breaking through the limit of 1 kΩ. Compared with other coated electrodes, the CSCc of the novel barrier crystal morphology coated electrodes can be increased by 6.67 times to 13.47 mC cm-2. The safe charge injection ability is 19.6 times higher than that of Pt-gray, reaching 2.53 mC cm-2. Therefore, this electroplating coating structure and process is promising for effective nerve stimulation/recording in various applications, and have broad application prospects in biomedical fields.
2020, 49(10):3544-3551.
DOI: 10.12442/j.issn.1002-185X.20190894
Abstract:
In this paper, the effects of deformation temperature, strain rate and deformation on the hot deformation behavior and microstructure of as-extruded ZA21 magnesium alloy were investigated. The processing map was established, and the immersion weight loss and electrochemical tests were carried out on the unstable zone, the safe zone and the best processing zone to study the corrosion behavior in different regions of ZA21 magnesium alloy. The results show that the dynamic softening mechanism of ZA21 magnesium alloy is mainly dynamic recovery at high temperature and low strain rate, and dynamic recrystallization is dominant at low temperature and high strain rate; The optimum processing temperature is 300~350 °C, and the strain rate is 0.001~0.01s-1, which is mainly related to the generation of complete dynamic recrystallization; Under the same processing technology, with the increase of deformation, the self-corrosion potential of ZA21 magnesium alloy is obviously positively shifted, and the self-corrosion current density is significantly decreased. When the amount of deformation increases to 60%, the self-corrosion current density can be reduced by 3~4 orders of magnitude. This is mainly because the grain refinement leads to a denser oxide film on the surface of the alloy; However , the microstructure of the processing instability zone has wedge cracks and obvious pores, so the corrosion rate is relatively large.
In this paper, the effects of deformation temperature, strain rate and deformation on the hot deformation behavior and microstructure of as-extruded ZA21 magnesium alloy were investigated. The processing map was established, and the immersion weight loss and electrochemical tests were carried out on the unstable zone, the safe zone and the best processing zone to study the corrosion behavior in different regions of ZA21 magnesium alloy. The results show that the dynamic softening mechanism of ZA21 magnesium alloy is mainly dynamic recovery at high temperature and low strain rate, and dynamic recrystallization is dominant at low temperature and high strain rate; The optimum processing temperature is 300~350 °C, and the strain rate is 0.001~0.01s-1, which is mainly related to the generation of complete dynamic recrystallization; Under the same processing technology, with the increase of deformation, the self-corrosion potential of ZA21 magnesium alloy is obviously positively shifted, and the self-corrosion current density is significantly decreased. When the amount of deformation increases to 60%, the self-corrosion current density can be reduced by 3~4 orders of magnitude. This is mainly because the grain refinement leads to a denser oxide film on the surface of the alloy; However , the microstructure of the processing instability zone has wedge cracks and obvious pores, so the corrosion rate is relatively large.
2020, 49(10):3552-3561.
DOI: 10.12442/j.issn.1002-185X.20190901
Abstract:
The isothermal compression tests of Ti60 alloy were conducted on the Thermecmaster-Z thermal simulator at deformation temperature of 600～950℃, strain rate 0.001～10s-1. The hot deformation behavior of Ti60 alloy were investigated, by analyzing the flow stress behavior, calculating the strain rate sensitive exponent m and strain hardening exponent n, along with the processing map and deformation microstructure, to optimize processing parameter. The results show that the flow stress-strain curve of Ti60 alloy presents flow steady state and flow softening respectively at different processing parameters. The strain rate sensitivity exponent m increases with the increase of deformation temperature and decrease of strain rate. The strain hardening exponent n decreases with the increase of deformation temperature. With the increase of strain rate, n increases in the low strain rate (0.001～0.1s-1) and decreases in the high strain rate (1～10s-1). With the increase of strain, n decreased slowly at the low strain rate (0.001～0.1s-1), the high temperature (800～950℃), while which decreased significantly at the high strain rate (1～10s-1) , the high temperature section (800～950℃) and all the strain rates (0.001～10s-1), the low temperature (600～750℃). Ti60 alloy has two peak power dissipation efficiency regions, whose corresponding processing parameter Windows : temperature 725～875℃, strain rate ≤0.003s-1 and temperature 875～938℃, strain rate ≤0.04s-1, respectively. Considering the flow stress behavior, strain rate sensitivity exponent m, strain hardening exponent n and processing map, the optimal thermal processing parameters of Ti60 alloy: temperature 800～875℃, strain rate 0.001～0.003s-1, or temperature 875～938℃, strain rate 0.001～0.04s-1.
The isothermal compression tests of Ti60 alloy were conducted on the Thermecmaster-Z thermal simulator at deformation temperature of 600～950℃, strain rate 0.001～10s-1. The hot deformation behavior of Ti60 alloy were investigated, by analyzing the flow stress behavior, calculating the strain rate sensitive exponent m and strain hardening exponent n, along with the processing map and deformation microstructure, to optimize processing parameter. The results show that the flow stress-strain curve of Ti60 alloy presents flow steady state and flow softening respectively at different processing parameters. The strain rate sensitivity exponent m increases with the increase of deformation temperature and decrease of strain rate. The strain hardening exponent n decreases with the increase of deformation temperature. With the increase of strain rate, n increases in the low strain rate (0.001～0.1s-1) and decreases in the high strain rate (1～10s-1). With the increase of strain, n decreased slowly at the low strain rate (0.001～0.1s-1), the high temperature (800～950℃), while which decreased significantly at the high strain rate (1～10s-1) , the high temperature section (800～950℃) and all the strain rates (0.001～10s-1), the low temperature (600～750℃). Ti60 alloy has two peak power dissipation efficiency regions, whose corresponding processing parameter Windows : temperature 725～875℃, strain rate ≤0.003s-1 and temperature 875～938℃, strain rate ≤0.04s-1, respectively. Considering the flow stress behavior, strain rate sensitivity exponent m, strain hardening exponent n and processing map, the optimal thermal processing parameters of Ti60 alloy: temperature 800～875℃, strain rate 0.001～0.003s-1, or temperature 875～938℃, strain rate 0.001～0.04s-1.
2020, 49(10):3562-3568.
DOI: 10.12442/j.issn.1002-185X.20190909
Abstract:
In this paper, the sintering densification process of (Ti,W,Mo,Ta, Nb,Zr)(C,N)-(Co,Ni) based cermet was studied. The effects of sintering process on composition, microstructure and properties were discussed. The results show that during the densification process of (Ti,W,Mo,Ta,Nb,Zr)(C,N)-(Co,Ni) based cermets, the mass loss caused by sintering basically ends at the solid phase sintering stage. When the sintering temperature is above 1340℃, the volume shrinkage and density of the alloy increase sharply due to the appearance of liquid phase. The change of nitrogen content in cermet during the sintering process is consistent with the change of magnetic properties of the alloy, and the nitrogen content has a significant effect on the formation of solid solution. When the sintering temperature is 1490 ℃, the comprehensive mechanical properties of (Ti,W,Mo,Ta,Nb,Zr)(C,N)-(Co,Ni) cermets are the best, and the strength and toughness of the cermets can be further improved by the appropriate control of N2 partial pressure at sintering temperature.
In this paper, the sintering densification process of (Ti,W,Mo,Ta, Nb,Zr)(C,N)-(Co,Ni) based cermet was studied. The effects of sintering process on composition, microstructure and properties were discussed. The results show that during the densification process of (Ti,W,Mo,Ta,Nb,Zr)(C,N)-(Co,Ni) based cermets, the mass loss caused by sintering basically ends at the solid phase sintering stage. When the sintering temperature is above 1340℃, the volume shrinkage and density of the alloy increase sharply due to the appearance of liquid phase. The change of nitrogen content in cermet during the sintering process is consistent with the change of magnetic properties of the alloy, and the nitrogen content has a significant effect on the formation of solid solution. When the sintering temperature is 1490 ℃, the comprehensive mechanical properties of (Ti,W,Mo,Ta,Nb,Zr)(C,N)-(Co,Ni) cermets are the best, and the strength and toughness of the cermets can be further improved by the appropriate control of N2 partial pressure at sintering temperature.
2020, 49(10):3569-3575.
DOI: 10.12442/j.issn.1002-185X.20190913
Abstract:
The effects of the stirring current and frequency on the microstructure of the semi-solid 2A50 alloy at the central and peripheral parts of the billet were studied. Results showed that the coarse dendritic particles were the main constituent of the microstructure without electromagnetic stirring, where the length of the dendrite arm was larger than 200 μm. This type of semi-solid billet was unqualified for the semi-solid forming. With the increase in stirring current or stirring frequency, the average size of the grains located at the central and peripheral regions decreased first and then slightly increased when the stirring current and stirring frequency is over 30A and 30Hz, respecitvely; the shape factors at centeral and center parts gradually increased and then slightly decreased when the stirring current is 40A or the stirring frequency is 40 Hz; Furthermore, the uniformity of the grain size and shape at the central and peripheral parts was improved with the increase in the stirring current or the frequency. The optimal average grain size and the shape factor were able to be obtained as 75.6 μm and 0.73, respectively under the stirring current of 30A and stirring frequency of 30Hz.
The effects of the stirring current and frequency on the microstructure of the semi-solid 2A50 alloy at the central and peripheral parts of the billet were studied. Results showed that the coarse dendritic particles were the main constituent of the microstructure without electromagnetic stirring, where the length of the dendrite arm was larger than 200 μm. This type of semi-solid billet was unqualified for the semi-solid forming. With the increase in stirring current or stirring frequency, the average size of the grains located at the central and peripheral regions decreased first and then slightly increased when the stirring current and stirring frequency is over 30A and 30Hz, respecitvely; the shape factors at centeral and center parts gradually increased and then slightly decreased when the stirring current is 40A or the stirring frequency is 40 Hz; Furthermore, the uniformity of the grain size and shape at the central and peripheral parts was improved with the increase in the stirring current or the frequency. The optimal average grain size and the shape factor were able to be obtained as 75.6 μm and 0.73, respectively under the stirring current of 30A and stirring frequency of 30Hz.
2020, 49(10):3576-3581.
DOI: 10.12442/j.issn.1002-185X.20190924
Abstract:
Magnesium alloys, as a new type of biodegradable medical metal material, have a promising application in the field of vascular stents. However, the poor deformability of Mg alloys due to hexagonal close-packed (hcp) structure makes it difficult to fabricate their thin tube. In this study, the micro-tubes of Mg-4Zn-0.2Mn-0.2Ca alloy, a new type of degradable magnesium alloy, with 3.1～3.6 mm in outer diameter and 0.25～0.4 mm in thickness were prepared by hot extrusion-drawing composite process. The microstructure evolution and mechanical properties of the one with 3.6 mm in outer diameter, 0.4 mm in thickness showed that the crystal slip, twins and recrystallization occurred during the plastic deformation of the tubes, and the work hardening was significant. This drawn tube exhibited a tensile strength of 427.3 MPa, yield strength of 383.4 MPa, and elongation of 5.2%. After annealing at 300℃ for 30 min, the microstructure became uniform and the elongation increased to 18.0%, which is conducive to the fabrication of vascular stents.
Magnesium alloys, as a new type of biodegradable medical metal material, have a promising application in the field of vascular stents. However, the poor deformability of Mg alloys due to hexagonal close-packed (hcp) structure makes it difficult to fabricate their thin tube. In this study, the micro-tubes of Mg-4Zn-0.2Mn-0.2Ca alloy, a new type of degradable magnesium alloy, with 3.1～3.6 mm in outer diameter and 0.25～0.4 mm in thickness were prepared by hot extrusion-drawing composite process. The microstructure evolution and mechanical properties of the one with 3.6 mm in outer diameter, 0.4 mm in thickness showed that the crystal slip, twins and recrystallization occurred during the plastic deformation of the tubes, and the work hardening was significant. This drawn tube exhibited a tensile strength of 427.3 MPa, yield strength of 383.4 MPa, and elongation of 5.2%. After annealing at 300℃ for 30 min, the microstructure became uniform and the elongation increased to 18.0%, which is conducive to the fabrication of vascular stents.
2020, 49(10):3582-3589.
DOI: 10.12442/j.issn.1002-185X.20190930
Abstract:
Al-Mg-Ga-Sn alloys with six different Al/Ga weight ratio were prepared by casting. The hydrogen production behavior of these alloys in simulated seawater (3.5% NaCl) solution at 30 ° C, 50 ° C, 70 ° C and 90 ° C was investigated, respectively, where quantitative analysis of hydrogen production rate, hydrogen yield, energy density and conversion rate, and qualitative analysis of microstructure and electrochemical performance were conducted. XRD analysis combined with SEM revealed that composition phase of Al-Mg-Ga-Sn alloys are related to the Al/Ga weight ratio. If Al/Ga＝17/1, Alss and Mg2Sn dominate; if Al/Ga≤14/1, composition phases contain Alss, Mg2Sn and Ga5Mg2. In addition to NaCl, the reaction product of Al-Mg-Ga-Sn alloy/seawater include Alss、Mg2Sn and Al(OH)3 at 30 °C-70 °C; and Alss, and AlO(OH) at 90 °C. The polarization resistance of Al-Mg-Ga-Sn alloy in the 3.5%NaCl solution at room temperature gradually increases as the Al/Ga ratio increases, and the corrosion current is related to the microstructure. At 90 ° C, when Al/Ga = 8 / 1, hydrogen production rate is 19.36mL / (min ? g), hydrogen yield is 1.156×103 mL / g, energy density is 3.515×1010J / m3, and conversion rate is up to 97.6%.
Al-Mg-Ga-Sn alloys with six different Al/Ga weight ratio were prepared by casting. The hydrogen production behavior of these alloys in simulated seawater (3.5% NaCl) solution at 30 ° C, 50 ° C, 70 ° C and 90 ° C was investigated, respectively, where quantitative analysis of hydrogen production rate, hydrogen yield, energy density and conversion rate, and qualitative analysis of microstructure and electrochemical performance were conducted. XRD analysis combined with SEM revealed that composition phase of Al-Mg-Ga-Sn alloys are related to the Al/Ga weight ratio. If Al/Ga＝17/1, Alss and Mg2Sn dominate; if Al/Ga≤14/1, composition phases contain Alss, Mg2Sn and Ga5Mg2. In addition to NaCl, the reaction product of Al-Mg-Ga-Sn alloy/seawater include Alss、Mg2Sn and Al(OH)3 at 30 °C-70 °C; and Alss, and AlO(OH) at 90 °C. The polarization resistance of Al-Mg-Ga-Sn alloy in the 3.5%NaCl solution at room temperature gradually increases as the Al/Ga ratio increases, and the corrosion current is related to the microstructure. At 90 ° C, when Al/Ga = 8 / 1, hydrogen production rate is 19.36mL / (min ? g), hydrogen yield is 1.156×103 mL / g, energy density is 3.515×1010J / m3, and conversion rate is up to 97.6%.
2020, 49(10):3590-3596.
DOI: 10.12442/j.issn.1002-185X.20190941
Abstract:
In order to explain the reason why the columnar crystal precious metal has excellent ultra-fine wire processing property and high resistance, three kinds of Ag-28Cu-0.75Ni alloy bars, columnar crystal of 20 μm×60 μm, equiaxed crystal of 10 μm, and tri-crystal zone with surface fine crystal of 5 μm + columnar crystal with length diameter ratio of around 3 + core equiaxed crystal of 30 μm, were obtained by horizontal continuous casting, water-cooled copper die casting, and graphite die casting, respectively. The effects of grain morphology and size on the ultra-fine wire processability and resistivity of Ag-28Cu-0.75Ni alloy bars were studied. The results show that, compared with the equiaxed crystal bar and the tri-crystal zone bar, the columnar crystal bar has the lower dislocation density (1.78×1015 m-2), the lowest ratio of micro-hardness change (33.3%), and no cleavage step after the tensile test, thus, it presents the lowest work hardening rate. Besides, the axial tensile strength of as-cast columnar crystal bar is up to 384.6 MPa. Therefore, the ultra-fine wire with the diameter of 0.05 mm and the length of 100 meters or more can be obtained by the high-efficiency continuous wire drawing of the columnar crystal bar. The resistivity of processed and annealed Ag-28Cu-0.75Ni alloy ultra-fine wires that drawn from the columnar crystal bar are higher, after two times continuous annealing, the resistivity of columnar crystal Ag-28Cu-0.75Ni alloy ultra-fine wire is up to 3.68 μΩ.cm, which is related to the lower dislocation density and work hardening rate.
In order to explain the reason why the columnar crystal precious metal has excellent ultra-fine wire processing property and high resistance, three kinds of Ag-28Cu-0.75Ni alloy bars, columnar crystal of 20 μm×60 μm, equiaxed crystal of 10 μm, and tri-crystal zone with surface fine crystal of 5 μm + columnar crystal with length diameter ratio of around 3 + core equiaxed crystal of 30 μm, were obtained by horizontal continuous casting, water-cooled copper die casting, and graphite die casting, respectively. The effects of grain morphology and size on the ultra-fine wire processability and resistivity of Ag-28Cu-0.75Ni alloy bars were studied. The results show that, compared with the equiaxed crystal bar and the tri-crystal zone bar, the columnar crystal bar has the lower dislocation density (1.78×1015 m-2), the lowest ratio of micro-hardness change (33.3%), and no cleavage step after the tensile test, thus, it presents the lowest work hardening rate. Besides, the axial tensile strength of as-cast columnar crystal bar is up to 384.6 MPa. Therefore, the ultra-fine wire with the diameter of 0.05 mm and the length of 100 meters or more can be obtained by the high-efficiency continuous wire drawing of the columnar crystal bar. The resistivity of processed and annealed Ag-28Cu-0.75Ni alloy ultra-fine wires that drawn from the columnar crystal bar are higher, after two times continuous annealing, the resistivity of columnar crystal Ag-28Cu-0.75Ni alloy ultra-fine wire is up to 3.68 μΩ.cm, which is related to the lower dislocation density and work hardening rate.
2020, 49(10):3597-3603.
DOI: 10.12442/j.issn.1002-185X.20190943
Abstract:
Ti45Al-6Nb-xCo (x=0, 0.5, 1, 2 and4 at.%) alloys were prepared using non- consumable arc melting method by three times of remelts. The microstructure and high temperature oxidation behavior of the alloys with different Co concentrations were investigated. The results show that increase of Co concentration in the alloy can significantly refine the α2+γ lamellaer, promote the formation of γ and B2 phases while inhibit the formation of α2 phase. Co-rich precipitates and microstructure coarsening were observed when concentration of Co is higher than 2 at.% in the alloy. The static oxidation results at 1000 ℃ in air show that the oxidation resistance of TiAl-Nb alloy has been remarkably improved by appropriate Co alloying. The oxidation parabolic rate constant of the Ti45Al-6Nb-1Co alloy is about 1.36×10-2mg2/cm4h, lower than that of the Ti45Al-Nb alloy by about one order of magnitude. However, once the concentration of Co exceeds 2 at.%, increase of Co concentration in the alloy lead to an increase of the oxidation rate of the alloy.
Ti45Al-6Nb-xCo (x=0, 0.5, 1, 2 and4 at.%) alloys were prepared using non- consumable arc melting method by three times of remelts. The microstructure and high temperature oxidation behavior of the alloys with different Co concentrations were investigated. The results show that increase of Co concentration in the alloy can significantly refine the α2+γ lamellaer, promote the formation of γ and B2 phases while inhibit the formation of α2 phase. Co-rich precipitates and microstructure coarsening were observed when concentration of Co is higher than 2 at.% in the alloy. The static oxidation results at 1000 ℃ in air show that the oxidation resistance of TiAl-Nb alloy has been remarkably improved by appropriate Co alloying. The oxidation parabolic rate constant of the Ti45Al-6Nb-1Co alloy is about 1.36×10-2mg2/cm4h, lower than that of the Ti45Al-Nb alloy by about one order of magnitude. However, once the concentration of Co exceeds 2 at.%, increase of Co concentration in the alloy lead to an increase of the oxidation rate of the alloy.
2020, 49(10):3604-3611.
DOI: 10.12442/j.issn.1002-185X.20190944
Abstract:
In order to study the influence of WC content on the corrosion resistance of Ni60 alloy coating and the related mechanism, WC with the different mass fraction was added to Ni60 self-fused alloy powder, Ni60/WC directional structure composite coatings with different WC contents were prepared on 45 steel by induction remelting and forced cooling technology. The corrosion resistance and mechanism of WC particles reinforced Ni60 alloy directional structure composite coatings were investigated by SEM, EDS, XRD, electrochemical test and immersion corrosion. Results showed that the polarization resistance of composite coatings increased first and then decreased with the increase of WC, and the maximum polarization resistance reached 9710.8 Ω when the WC addition amount was 10%. The corrosion current density of composite coatings decreased first and then increased, and the minimum current density reached 1.34×10-6 A/cm2 with 10% WC content. The WC content had the important effect on microstructures, element distribution, phases of composite coatings, and further affected the corrosion resistance.
In order to study the influence of WC content on the corrosion resistance of Ni60 alloy coating and the related mechanism, WC with the different mass fraction was added to Ni60 self-fused alloy powder, Ni60/WC directional structure composite coatings with different WC contents were prepared on 45 steel by induction remelting and forced cooling technology. The corrosion resistance and mechanism of WC particles reinforced Ni60 alloy directional structure composite coatings were investigated by SEM, EDS, XRD, electrochemical test and immersion corrosion. Results showed that the polarization resistance of composite coatings increased first and then decreased with the increase of WC, and the maximum polarization resistance reached 9710.8 Ω when the WC addition amount was 10%. The corrosion current density of composite coatings decreased first and then increased, and the minimum current density reached 1.34×10-6 A/cm2 with 10% WC content. The WC content had the important effect on microstructures, element distribution, phases of composite coatings, and further affected the corrosion resistance.
2020, 49(10):3612-3619.
DOI: 10.12442/j.issn.1002-185X.20190946
Abstract:
Two different hydrogen evolution inhibitor Bi2O3 and In2O3/sisal fiber-based carbon composites were prepared by in-situ synthesis of carbon. The carbon composites were characterized by XRD, SEM, EDS and N2 adsorption-desorption curves. The results of SEM and XRD indicate that the composites have a good degree of crystallization. A large amount of hydrogen evolution inhibitor particles embedded in the fiber surface can be observed on the surface of the sisal fiber-based carbon material, and the distribution is uniform. The prepared carbon composite material was mixed with a battery auxiliary agent to prepare a lead carbon battery anode material. The electrochemical test results show that the anode material of the In2O3/sisal fiber-based carbon composite material has a longer cycle life and better electrochemistry. Performance, the final capacity can reach 102.25 mAh / g, after 150 cycles, the specific capacity accounts for 79.8% of the initial specific capacity.
Two different hydrogen evolution inhibitor Bi2O3 and In2O3/sisal fiber-based carbon composites were prepared by in-situ synthesis of carbon. The carbon composites were characterized by XRD, SEM, EDS and N2 adsorption-desorption curves. The results of SEM and XRD indicate that the composites have a good degree of crystallization. A large amount of hydrogen evolution inhibitor particles embedded in the fiber surface can be observed on the surface of the sisal fiber-based carbon material, and the distribution is uniform. The prepared carbon composite material was mixed with a battery auxiliary agent to prepare a lead carbon battery anode material. The electrochemical test results show that the anode material of the In2O3/sisal fiber-based carbon composite material has a longer cycle life and better electrochemistry. Performance, the final capacity can reach 102.25 mAh / g, after 150 cycles, the specific capacity accounts for 79.8% of the initial specific capacity.
2020, 49(10):3620-3626.
DOI: 10.12442/j.issn.1002-185X.20190947
Abstract:
γ＇-Ir3(Al,W) phase-strengthed Ir-13W-6Al(at.%) Superalloys exhibit promising applications for aerospace industry. An experimental set-up was based on Ir-13W-6Al ternary superalloy and 2, 5, 8 at.% Ta elements were added. In order to research the effect of Ta, the microstructure evolution, the amount of γ＇ strengthening phase, the precipitation behavior, room-/high- temperature mechanical properties and fracture characteristics of γ+γ＇ two-phase Ir-based superalloys were investigated. The results show that with Ta content increasing, the volume fraction of γ＇strengthening phase increases and the vickers hardness/nano-hardness are higher than the Ir-13W-6Al ternary superalloy. The addition of Ta improves the high-temperature mechanical properties of Ir-13W-6Al superalloys at 1300 ℃, and the increased compressive strength can be attributed to the precipitation of γ＇-Ir3(Al,W) phase and solid-solution strengthening. Ta effectively improves the room- and high-temperature properties of Ir-13W-6Al superalloys. This study provides experimental and theoretical guide for the development of novel γ+γ＇ two-phase Ir-based superalloys.
γ＇-Ir3(Al,W) phase-strengthed Ir-13W-6Al(at.%) Superalloys exhibit promising applications for aerospace industry. An experimental set-up was based on Ir-13W-6Al ternary superalloy and 2, 5, 8 at.% Ta elements were added. In order to research the effect of Ta, the microstructure evolution, the amount of γ＇ strengthening phase, the precipitation behavior, room-/high- temperature mechanical properties and fracture characteristics of γ+γ＇ two-phase Ir-based superalloys were investigated. The results show that with Ta content increasing, the volume fraction of γ＇strengthening phase increases and the vickers hardness/nano-hardness are higher than the Ir-13W-6Al ternary superalloy. The addition of Ta improves the high-temperature mechanical properties of Ir-13W-6Al superalloys at 1300 ℃, and the increased compressive strength can be attributed to the precipitation of γ＇-Ir3(Al,W) phase and solid-solution strengthening. Ta effectively improves the room- and high-temperature properties of Ir-13W-6Al superalloys. This study provides experimental and theoretical guide for the development of novel γ+γ＇ two-phase Ir-based superalloys.
2020, 49(10):3627-3632.
DOI: 10.12442/j.issn.1002-185X.20190951
Abstract:
The powder metallurgy method of raw material powder mixing, billet pressing and sintering molding is widely used in the preparation process of molybdenum alloys. Therefore, the uniformity, purity, powder size and morphology of the raw material powder have an important influence on the properties of the molybdenum alloy product. In this paper, the precursor powder was prepared by solution spray drying, and the precursor powder was reduced to molybdenum-tungsten alloy powder or molybdenum-niobium-nickel composite powder by high temperature reduction under hydrogen atmosphere. They were studied that the effects of the spray drying process parameters (solution concentration, feed rate, drying temperature, etc) and reduction heat treatment process parameters (reduction atmosphere, temperature, time, etc.) on the particle size, composition and morphology of molybdenum alloy micropowder. Furthermore, the brazing property of molybdenum-niobium-nickel composite powder was analyzed. The result show that spherical molybdenum-tungsten solid solution alloy powder with the particle size of 0.5~3μm and spherical molybdenum-niobium-nickel composite powder with the particle size of 0.5~2μm can be obtained by solution spray drying combined with reduction heat treatment. Molybdenum-niobium-nickel composite powder has excellent wettability when it was brazed on molybdenum plate.
The powder metallurgy method of raw material powder mixing, billet pressing and sintering molding is widely used in the preparation process of molybdenum alloys. Therefore, the uniformity, purity, powder size and morphology of the raw material powder have an important influence on the properties of the molybdenum alloy product. In this paper, the precursor powder was prepared by solution spray drying, and the precursor powder was reduced to molybdenum-tungsten alloy powder or molybdenum-niobium-nickel composite powder by high temperature reduction under hydrogen atmosphere. They were studied that the effects of the spray drying process parameters (solution concentration, feed rate, drying temperature, etc) and reduction heat treatment process parameters (reduction atmosphere, temperature, time, etc.) on the particle size, composition and morphology of molybdenum alloy micropowder. Furthermore, the brazing property of molybdenum-niobium-nickel composite powder was analyzed. The result show that spherical molybdenum-tungsten solid solution alloy powder with the particle size of 0.5~3μm and spherical molybdenum-niobium-nickel composite powder with the particle size of 0.5~2μm can be obtained by solution spray drying combined with reduction heat treatment. Molybdenum-niobium-nickel composite powder has excellent wettability when it was brazed on molybdenum plate.
Chang Haitao
,
Huo Xiaofeng
,
Li Wangpeng
,
Yang Tao
,
J C Huang
,
Wu Baolin
,
Duan Guosheng
,
Du Xinghao
2020, 49(10):3633-3645.
DOI: 10.12442/j.issn.1002-185X.20190857
Abstract:
As a kind of multi-principal-element alloys, high-entropy alloys exhibit usually different deformation mechanisms and strengthening mechanisms with respect to the traditional single-principal-element alloys. The current researches show that the high-entropy alloys have better strengthening and toughening capacity than the traditional alloys, presenting a bright future as a kind of newly structural materials. In this paper, recent researching results on the strengthening mechanisms of high-entropy alloys are reviewed. Various strengthening mechanisms of high-entropy alloys are discussed and analyzed, and the factors affecting the strenghening effect of high-entropy alloys are indicated. Finally, the possible future development direction to strengthen the high-entropy alloys is also given.
As a kind of multi-principal-element alloys, high-entropy alloys exhibit usually different deformation mechanisms and strengthening mechanisms with respect to the traditional single-principal-element alloys. The current researches show that the high-entropy alloys have better strengthening and toughening capacity than the traditional alloys, presenting a bright future as a kind of newly structural materials. In this paper, recent researching results on the strengthening mechanisms of high-entropy alloys are reviewed. Various strengthening mechanisms of high-entropy alloys are discussed and analyzed, and the factors affecting the strenghening effect of high-entropy alloys are indicated. Finally, the possible future development direction to strengthen the high-entropy alloys is also given.
2020, 49(10):3646-3652.
DOI: 10.12442/j.issn.1002-185X.20190881
Abstract:
Due to the increasing demand for higher operating temperatures in gas turbine engines, a reliability problem has emerged on TBCs by the attack of calcium-magnesium-alumino-silicate (CMAS) deposits. These contaminants yield glassy melts adhering to the TBC surface at high temperatures, followed by infiltrating and interacting into/with TBC, which result in its severe degradation and premature failure. The adhesion of molten CMAS and the protection methods are hot and difficult points in the field of thermal barrier coatings. In this paper, the latest research results on CMAS adhesion, infiltration and corrosion resistance of plasma spray-physical vapor deposited thermal barrier coatings are reviewed. The approaches for developing corrosion-resistant TBCs were proposed.
Due to the increasing demand for higher operating temperatures in gas turbine engines, a reliability problem has emerged on TBCs by the attack of calcium-magnesium-alumino-silicate (CMAS) deposits. These contaminants yield glassy melts adhering to the TBC surface at high temperatures, followed by infiltrating and interacting into/with TBC, which result in its severe degradation and premature failure. The adhesion of molten CMAS and the protection methods are hot and difficult points in the field of thermal barrier coatings. In this paper, the latest research results on CMAS adhesion, infiltration and corrosion resistance of plasma spray-physical vapor deposited thermal barrier coatings are reviewed. The approaches for developing corrosion-resistant TBCs were proposed.
