Volume 46,Issue 6,2017 Table of Contents
1 TC4 titanium alloy microstructure and properties influenced by high frequency scan of electron beam
2017, 46(6):1457-1462.
Abstract:
In order to improve the HV hardness and microstructure on the surface of TC4 titanium alloy, the high frequency scan of electron beam had been introduced to treat TC4 titanium alloy. For acquiring excellent parameters, the energy of EB, focus current and scan times, which will influence the HV hardness and microstructres, had been studied respectively. After high frequency scan of electron beam treatment, the HV hardness, modified layer depth and microstructures of TC4 titanium alloy had been analyzed respectively. It is shown that the HV hardness on the TC4 surface treated by the high frequency scan of electron beam can be increased almost 40Mpa than original material. With energy of EB improved, the depth layer influenced is increased. The focus current adjusted at little range can acquire comparatively better HV hardness on the surface. When the scan times are increased, not only the HV hardness decreases, but also the grains grow up.
In order to improve the HV hardness and microstructure on the surface of TC4 titanium alloy, the high frequency scan of electron beam had been introduced to treat TC4 titanium alloy. For acquiring excellent parameters, the energy of EB, focus current and scan times, which will influence the HV hardness and microstructres, had been studied respectively. After high frequency scan of electron beam treatment, the HV hardness, modified layer depth and microstructures of TC4 titanium alloy had been analyzed respectively. It is shown that the HV hardness on the TC4 surface treated by the high frequency scan of electron beam can be increased almost 40Mpa than original material. With energy of EB improved, the depth layer influenced is increased. The focus current adjusted at little range can acquire comparatively better HV hardness on the surface. When the scan times are increased, not only the HV hardness decreases, but also the grains grow up.
2017, 46(6):1463-1468.
Abstract:
Significant temperature and stress dependent creep behavior of commercial pure titanium TA2 was observed at low and intermediate temperature. According to the variation of creep strain with applied stress level, the relationship between threshold stress level and the corresponding creep temperature was determined. Based on short time creep tests, the constitutive equation containing steady state creep strain rate was used to extrapolate the minimum creep rate. The existence of steady state creep of commercial pure titanium TA2 was confirmed by subsequent long time creep experiments. Through the minimum creep strain rates, creep stress exponent was obtained which also indicates the accuracy of the extrapolated minimum creep strain rates. The activation energy of primary creep (approximately 60KJ/mol) at different creep strains level was higher than the activation energy for slip controlled creep, which demonstrates the importance of twinning for the development of creep behavior of commercial pure titanium TA2 at low temperature. Moreover, according to the variation of twinning structure with deformed temperature in creep tested specimens, the temperature dependent creep behavior was interpreted and the importance of twinning for creep behavior of TA2 was confirmed.
Significant temperature and stress dependent creep behavior of commercial pure titanium TA2 was observed at low and intermediate temperature. According to the variation of creep strain with applied stress level, the relationship between threshold stress level and the corresponding creep temperature was determined. Based on short time creep tests, the constitutive equation containing steady state creep strain rate was used to extrapolate the minimum creep rate. The existence of steady state creep of commercial pure titanium TA2 was confirmed by subsequent long time creep experiments. Through the minimum creep strain rates, creep stress exponent was obtained which also indicates the accuracy of the extrapolated minimum creep strain rates. The activation energy of primary creep (approximately 60KJ/mol) at different creep strains level was higher than the activation energy for slip controlled creep, which demonstrates the importance of twinning for the development of creep behavior of commercial pure titanium TA2 at low temperature. Moreover, according to the variation of twinning structure with deformed temperature in creep tested specimens, the temperature dependent creep behavior was interpreted and the importance of twinning for creep behavior of TA2 was confirmed.
2017, 46(6):1469-1473.
Abstract:
Considering of the relationship between meso-scale accumulated damage and microstructure, external cyclic strain load was applied on 2D representative volume element (RVE) of CuW alloys, and the accumulated damage and induced crack behaviors of CuW alloy were stimulated utilizing Darveaux model. The results show that the plastic slip bands appear on the copper phase at the beginning, damage and induced cracks of CuW alloy initiate at the corners and then propagate along and edges of tungsten grains with the increase of cyclic number, the propagation path of micro-cracks is affected by the distribution of tungsten grains mainly, while the sintering necks lower the propagation speed of micro-cracks on some extents.
Considering of the relationship between meso-scale accumulated damage and microstructure, external cyclic strain load was applied on 2D representative volume element (RVE) of CuW alloys, and the accumulated damage and induced crack behaviors of CuW alloy were stimulated utilizing Darveaux model. The results show that the plastic slip bands appear on the copper phase at the beginning, damage and induced cracks of CuW alloy initiate at the corners and then propagate along and edges of tungsten grains with the increase of cyclic number, the propagation path of micro-cracks is affected by the distribution of tungsten grains mainly, while the sintering necks lower the propagation speed of micro-cracks on some extents.
2017, 46(6):1474-1479.
Abstract:
According to the sections of sintering crunode of two metal fibers, which are oval-oval geometry structure in different directions, the oval-oval model is developed based on the traditional surface diffusion mathematical model. This model is numerically solved by level set method to achieve the 2D simulations of two sintering metal fibers. Moreover, the 3D reconstitution method is proposed to depict the complex 3D geometrical structure of two sintering metal fibers. The 2D simulations and 3D reconstitution results of two metal fibers with the fiber angle 30° well agree with the experimental ones, which imply that the 2D model and 3D reconstitution method are correct. In addition, the numerical simulation results show that the growth rate of sintering neck along the directions taken from the bisector of obtuse angle to the bisector of acute angle is increased.
According to the sections of sintering crunode of two metal fibers, which are oval-oval geometry structure in different directions, the oval-oval model is developed based on the traditional surface diffusion mathematical model. This model is numerically solved by level set method to achieve the 2D simulations of two sintering metal fibers. Moreover, the 3D reconstitution method is proposed to depict the complex 3D geometrical structure of two sintering metal fibers. The 2D simulations and 3D reconstitution results of two metal fibers with the fiber angle 30° well agree with the experimental ones, which imply that the 2D model and 3D reconstitution method are correct. In addition, the numerical simulation results show that the growth rate of sintering neck along the directions taken from the bisector of obtuse angle to the bisector of acute angle is increased.
2017, 46(6):1480-1485.
Abstract:
The polypyrrole (PPy) coating and polypyrrole-molybdate (PPy-MoO42-) coating were electro-polymerized in sodium salicylate solution by using cyclic voltammetry (CV) on the AZ31 Mg alloy surface. Surface morphology of PPy coating and PPy-MoO42- coating on Mg alloy surface before and after being corrupted was observed by scanning electron microscopy (SEM). Attenuated total reflection-infrared (ATR-IR) spectra showed the characteristic ring stretching peaks of the PPy coating and PPy-MoO42- coating, and also revealed the influence of MoO42- on the characteristic ring stretching peaks for PPy. The surface resistance was measured by four-point probe method. The open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization analyzed the corrosion resistance performance of PPy coating and PPy-MoO42- coating on the Mg alloy surface in 3.5 % NaCl solution for 12 h. The results showed that the surface morphology of PPy-MoO42- coating is compact. And the corrosion current density of PPy-MoO42- coating is three orders lower than the PPy coating, the PPy-MoO42- coating on the Mg alloy surface had better corrosion resistance and smaller surface resistance than the PPy coating because of the existence of the molybdate ion.
The polypyrrole (PPy) coating and polypyrrole-molybdate (PPy-MoO42-) coating were electro-polymerized in sodium salicylate solution by using cyclic voltammetry (CV) on the AZ31 Mg alloy surface. Surface morphology of PPy coating and PPy-MoO42- coating on Mg alloy surface before and after being corrupted was observed by scanning electron microscopy (SEM). Attenuated total reflection-infrared (ATR-IR) spectra showed the characteristic ring stretching peaks of the PPy coating and PPy-MoO42- coating, and also revealed the influence of MoO42- on the characteristic ring stretching peaks for PPy. The surface resistance was measured by four-point probe method. The open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization analyzed the corrosion resistance performance of PPy coating and PPy-MoO42- coating on the Mg alloy surface in 3.5 % NaCl solution for 12 h. The results showed that the surface morphology of PPy-MoO42- coating is compact. And the corrosion current density of PPy-MoO42- coating is three orders lower than the PPy coating, the PPy-MoO42- coating on the Mg alloy surface had better corrosion resistance and smaller surface resistance than the PPy coating because of the existence of the molybdate ion.
2017, 46(6):1486-1490.
Abstract:
Hydrogenation behavior of Ti6Al4V alloy was investigated at different hydrogenation temperatures, holding time and hydrogen pressures. Distribution of hydrogen in titanium alloy was studied by OM. Results show that hydrogen content of Ti6Al4V alloy is controlled by hydrogenation temperature, hydrogen pressure and holding time. Hydrogen content increases first and then decreases with the increasing of hydrogenation temperature, increases linearly with the increasing of hydrogen pressure. The process of hydrogenation is a diffusion of hydrogen into titanium alloy, distribution of hydrogen becomes uniform with an increase of holding time.
Hydrogenation behavior of Ti6Al4V alloy was investigated at different hydrogenation temperatures, holding time and hydrogen pressures. Distribution of hydrogen in titanium alloy was studied by OM. Results show that hydrogen content of Ti6Al4V alloy is controlled by hydrogenation temperature, hydrogen pressure and holding time. Hydrogen content increases first and then decreases with the increasing of hydrogenation temperature, increases linearly with the increasing of hydrogen pressure. The process of hydrogenation is a diffusion of hydrogen into titanium alloy, distribution of hydrogen becomes uniform with an increase of holding time.
2017, 46(6):1491-1496.
Abstract:
To evaluate the mechanical properties and promote a better understanding of failure behavior of the newly developed Zr-Nb cladding tubes during reactivity initiated accidents (RIAs), burst tests were carried out with the biaxial stress state under different pressurization rates at the temperature ranging from 293 to 623 K. The influence of pressurization rate and test temperature was characterized in this test. The pressurization rates were 0.97 GPa/s at 293K, 0.62 GPa/s at 473K, and 0.49 GPa/s at 623K for the fast pressurization test, 0.23 MPs/s for the ASTM burst test. Maximum hoop stress was respectively increased by 10.61, 9.32 and 8.26 % compared to the ASTM burst test at 293K, 473K and 623K. The burst ultimate hoop stresses (UHS) at rupture decreased while the total circumferential elongation (TCE) increased monotonically with the rise of temperature, the uniform circumferential elongation (UCE) was not significantly affect by the test temperature. All the burst tests resulted ductile ballooning failure, cracks initiated and propagated along the axial direction above the maximum hoop stress. A higher pressurization rate resulted shorter but wider crack. As the test temperature raised, the ductility increased and the propagation of the axial crack was suppressed.
To evaluate the mechanical properties and promote a better understanding of failure behavior of the newly developed Zr-Nb cladding tubes during reactivity initiated accidents (RIAs), burst tests were carried out with the biaxial stress state under different pressurization rates at the temperature ranging from 293 to 623 K. The influence of pressurization rate and test temperature was characterized in this test. The pressurization rates were 0.97 GPa/s at 293K, 0.62 GPa/s at 473K, and 0.49 GPa/s at 623K for the fast pressurization test, 0.23 MPs/s for the ASTM burst test. Maximum hoop stress was respectively increased by 10.61, 9.32 and 8.26 % compared to the ASTM burst test at 293K, 473K and 623K. The burst ultimate hoop stresses (UHS) at rupture decreased while the total circumferential elongation (TCE) increased monotonically with the rise of temperature, the uniform circumferential elongation (UCE) was not significantly affect by the test temperature. All the burst tests resulted ductile ballooning failure, cracks initiated and propagated along the axial direction above the maximum hoop stress. A higher pressurization rate resulted shorter but wider crack. As the test temperature raised, the ductility increased and the propagation of the axial crack was suppressed.
2017, 46(6):1497-1502.
Abstract:
In this study, Ti-Al-Si-Cu-N films were deposited on the AISI-304 stainless steel by reactive magnetron sputtering technology. The influences of the substrate temperature on the microstructure and properties of the films were researched by scanning electron microscope（SEM），energy disperse spectroscopy（EDS）, X-ray diffraction （XRD）, a nano-indenter, a scratch tester and a ball-on-disc rotational tribometer. The results indicated that when the deposition temperature increased from room temperature to 250 oC, the films became smoother and denser. The hardness and elastic modulus increased with the increase of the deposition temperature. The scratch test showed that when the deposition temperatures were RT, 150 oC and 250 oC, the critical load of the films was 3.85 N, 3.45 N and 5.10 N, respectively. The friction coefficient and wear rate of the Ti-Al-Si-Cu-N film deposited at 250 oC were the smallest, and the wear debris was mainly from the counterparts GCr15 stainless balls, the wear mechanism of the films deposited at lower temperatures was mainly fatigue fracture and abrasive wear, while that of the film deposited at 250 oC was abrasive wear.
In this study, Ti-Al-Si-Cu-N films were deposited on the AISI-304 stainless steel by reactive magnetron sputtering technology. The influences of the substrate temperature on the microstructure and properties of the films were researched by scanning electron microscope（SEM），energy disperse spectroscopy（EDS）, X-ray diffraction （XRD）, a nano-indenter, a scratch tester and a ball-on-disc rotational tribometer. The results indicated that when the deposition temperature increased from room temperature to 250 oC, the films became smoother and denser. The hardness and elastic modulus increased with the increase of the deposition temperature. The scratch test showed that when the deposition temperatures were RT, 150 oC and 250 oC, the critical load of the films was 3.85 N, 3.45 N and 5.10 N, respectively. The friction coefficient and wear rate of the Ti-Al-Si-Cu-N film deposited at 250 oC were the smallest, and the wear debris was mainly from the counterparts GCr15 stainless balls, the wear mechanism of the films deposited at lower temperatures was mainly fatigue fracture and abrasive wear, while that of the film deposited at 250 oC was abrasive wear.
2017, 46(6):1503-1507.
Abstract:
The treatment of hydrogen-free carburization is applied on commercial purity titanium by the technology of equipotential hollow-cathode glow discharge under the commercial purity titanium phase transition temperature. The morphology, distribution of composition, phase composition are analyzed by the scanning electron microscope, the energy dispersive spectrometer, the X-ray diffraction, respectively; the tribology capability of the sample is studied by the friction and wear tester; the corrosion resistance of the samples in 3.5% NaCl solution is studied under the normal temperature static condition by using the electrochemical workstation. The results have shown that the high hardness alloy layer is formed on the commercial purity titanium surface by the treatment of hydrogen-free caburization, and the maximum thickness of the carburized layer is 7.5 μm; and the maximum hardness is 1298 HV0.2, which is 5.43 times that of the matrix. Due to the improved surface hardness, the wear resistance on the surface of the sample is increased significantly, and the average friction coefficient is only 0.312, which is obviously decreased than 0.746 that of the original sample. The minimum annual corrosion rate of the samples is 1/11 of the original sample in 3.5 mol/L NaCl solution. So the wear resistance and corrosion resistance are obviously improved in the premise of keeping the mechanics properties of the substrate.
The treatment of hydrogen-free carburization is applied on commercial purity titanium by the technology of equipotential hollow-cathode glow discharge under the commercial purity titanium phase transition temperature. The morphology, distribution of composition, phase composition are analyzed by the scanning electron microscope, the energy dispersive spectrometer, the X-ray diffraction, respectively; the tribology capability of the sample is studied by the friction and wear tester; the corrosion resistance of the samples in 3.5% NaCl solution is studied under the normal temperature static condition by using the electrochemical workstation. The results have shown that the high hardness alloy layer is formed on the commercial purity titanium surface by the treatment of hydrogen-free caburization, and the maximum thickness of the carburized layer is 7.5 μm; and the maximum hardness is 1298 HV0.2, which is 5.43 times that of the matrix. Due to the improved surface hardness, the wear resistance on the surface of the sample is increased significantly, and the average friction coefficient is only 0.312, which is obviously decreased than 0.746 that of the original sample. The minimum annual corrosion rate of the samples is 1/11 of the original sample in 3.5 mol/L NaCl solution. So the wear resistance and corrosion resistance are obviously improved in the premise of keeping the mechanics properties of the substrate.
2017, 46(6):1508-1511.
Abstract:
A thermal-mechanical coupling model was developed based on thermal-elastic-plastic theory according the special process of plasma sprayed Hydroxyapatite (HA) coating upon Ti-6Al-4V substrate. On the one hand, the classical Fourier transient heat conduction equation was modified by introducing the effect item of deformation on temperature, on the other hand, the Johnson-Cook model, suitable for high temperature and high strain rate conditions, was used as constitutive equation after considering temperature softening effect, strain hardening effect and strain rate reinforcement effect. Based on the above coupling model, the residual stress field within the HA coating was simulated by using finite element method(FEM). Meanwhile, the substrate preheating temperature and coating thickness on the influence of residual stress components were calculated, respectively. In addition, in order to verify the reliability of calculation, the material removal measurement technique was applied to determine the residual stress of HA coating near the interface. Some important conclusions are obtained.
A thermal-mechanical coupling model was developed based on thermal-elastic-plastic theory according the special process of plasma sprayed Hydroxyapatite (HA) coating upon Ti-6Al-4V substrate. On the one hand, the classical Fourier transient heat conduction equation was modified by introducing the effect item of deformation on temperature, on the other hand, the Johnson-Cook model, suitable for high temperature and high strain rate conditions, was used as constitutive equation after considering temperature softening effect, strain hardening effect and strain rate reinforcement effect. Based on the above coupling model, the residual stress field within the HA coating was simulated by using finite element method(FEM). Meanwhile, the substrate preheating temperature and coating thickness on the influence of residual stress components were calculated, respectively. In addition, in order to verify the reliability of calculation, the material removal measurement technique was applied to determine the residual stress of HA coating near the interface. Some important conclusions are obtained.
2017, 46(6):1512-1517.
Abstract:
Titanium has been widely used for orthopedic products, however, it is bioinert and surface modification is necessary to improve its osteoconductivity. Magnesium (Mg) ions are considered to be involved in bone metabolism and plays important physiological roles in the growth and mineralization of bone tissue; therefor this study carried out a feasible treatment to modify titanium with Mg. Briefly, pure titanium was treated in condensed sodium hydroxide solution first and then transferred to diluted magnesium chloride solution to conduct ion exchange. After that, heat treatment was conducted and a nano-sized network containing magnesium titanate was obtained. Surface morphology, roughness, and chemical composition were characterized. In vivo apatite inducing ability was evaluated in simulated body fluid (SBF) and bovine serum albumin (BSA) was used as model to study protein adsorption. MC3T3-E1 cells were cultured and initial cell attachment, morphology, proliferation were evaluated. Compared with Sodium (Na) modified surface, Mg immobilization accelerated apatite formation and prompted protein adsorption, significantly. Besides, cell attachment was improved and cell spreading was enhanced on Mg-containing samples compared with Na containing samples. Increased early cellular attachment resulted in subsequent increase of number of proliferated cells on the Mg-containing surface. In conclusion, this method is expected to be an effective method to fabricate titanium implant with good bioactivity.
Titanium has been widely used for orthopedic products, however, it is bioinert and surface modification is necessary to improve its osteoconductivity. Magnesium (Mg) ions are considered to be involved in bone metabolism and plays important physiological roles in the growth and mineralization of bone tissue; therefor this study carried out a feasible treatment to modify titanium with Mg. Briefly, pure titanium was treated in condensed sodium hydroxide solution first and then transferred to diluted magnesium chloride solution to conduct ion exchange. After that, heat treatment was conducted and a nano-sized network containing magnesium titanate was obtained. Surface morphology, roughness, and chemical composition were characterized. In vivo apatite inducing ability was evaluated in simulated body fluid (SBF) and bovine serum albumin (BSA) was used as model to study protein adsorption. MC3T3-E1 cells were cultured and initial cell attachment, morphology, proliferation were evaluated. Compared with Sodium (Na) modified surface, Mg immobilization accelerated apatite formation and prompted protein adsorption, significantly. Besides, cell attachment was improved and cell spreading was enhanced on Mg-containing samples compared with Na containing samples. Increased early cellular attachment resulted in subsequent increase of number of proliferated cells on the Mg-containing surface. In conclusion, this method is expected to be an effective method to fabricate titanium implant with good bioactivity.
2017, 46(6):1518-1523.
Abstract:
To observe the dynamic mechanical response and investigate the processes of high speed stamping for C5191 phosphorus bronze, tensile properties and deformation behaviour of C5191 phosphor bronze under quasi-static tensile condition at a strain rate of 0.001 s-1 by electronic universal testing machine, and dynamic tensile condition at strain rate of 500, 1000 and 1500 s-1 by split Hopkinson tensile bar (SHTB) apparatus were studied. The effects of strain rate and the mechanism were investigated by means of SEM and TEM. The results showed that the yield strength and tensile strength of C5191 phosphor bronze under high strain rates deformation increased by 32.77% and 32.77% respectively compared with quasi-static condition, the strain hardeningSindexSincreases from 0.075 toS0.251, andSthe strength of the materialSstrain rateSsensitivity indexSchange from 0.005 toS0.022, which presented a clear sensitive to strain rates. The deformation resistance increased with increasing the strain rate due to the stronger short range resistance induced by the acceleration of dislocation motion. The ability of plastic deformation of C5191 phosphor bronze increased due to the number of movable dislocations increased significantly, started multi-line slip, and the soft effect of adiabatic temperature rise at the strain rate ranging from 500 to 1500 s-1.
To observe the dynamic mechanical response and investigate the processes of high speed stamping for C5191 phosphorus bronze, tensile properties and deformation behaviour of C5191 phosphor bronze under quasi-static tensile condition at a strain rate of 0.001 s-1 by electronic universal testing machine, and dynamic tensile condition at strain rate of 500, 1000 and 1500 s-1 by split Hopkinson tensile bar (SHTB) apparatus were studied. The effects of strain rate and the mechanism were investigated by means of SEM and TEM. The results showed that the yield strength and tensile strength of C5191 phosphor bronze under high strain rates deformation increased by 32.77% and 32.77% respectively compared with quasi-static condition, the strain hardeningSindexSincreases from 0.075 toS0.251, andSthe strength of the materialSstrain rateSsensitivity indexSchange from 0.005 toS0.022, which presented a clear sensitive to strain rates. The deformation resistance increased with increasing the strain rate due to the stronger short range resistance induced by the acceleration of dislocation motion. The ability of plastic deformation of C5191 phosphor bronze increased due to the number of movable dislocations increased significantly, started multi-line slip, and the soft effect of adiabatic temperature rise at the strain rate ranging from 500 to 1500 s-1.
2017, 46(6):1524-1528.
Abstract:
Y2O3:Eu(5％), Li(x％) thin film phosphor was fabricated via electro-deposited method. The microstructure and luminescent properties were also investigated for all samples. It is found that the Li addition is helpful for the formation of flower morphology and can enhance the photoluminescence intensity, and the optimal Li content is 15％ for Y2O3:Eu(5％), Li(x％). At the same time, during the deposition processing, the dependence of the morphology and luminescent properties for Y2O3:Eu(5％), Li(x％) thin film on deposition time and solution concentration are also studied.
Y2O3:Eu(5％), Li(x％) thin film phosphor was fabricated via electro-deposited method. The microstructure and luminescent properties were also investigated for all samples. It is found that the Li addition is helpful for the formation of flower morphology and can enhance the photoluminescence intensity, and the optimal Li content is 15％ for Y2O3:Eu(5％), Li(x％). At the same time, during the deposition processing, the dependence of the morphology and luminescent properties for Y2O3:Eu(5％), Li(x％) thin film on deposition time and solution concentration are also studied.
2017, 46(6):1530-1535.
Abstract:
To design more efficient homogenization-solution heat treatments for advanced single crystal superalloys, an experimental single crystal superalloy was studied after homogenization-solution heat treatments with different temperatures and durations. Metallographic and field emission microscope were used to observe microstructures; electron probe was applied for component analysis. The results show that no incipient melting appears when the alloy is directly heated up to 1338℃; when it is directly heated up to 1350℃, obvious incipient melting occurs, while the incipient melting microstructure gradually fades away with holding time; for an lower temperature 1328℃, although there is no risk of incipient melting, the homogenization-solution efficiency is far from satisfactory. After analyzing the results by aid of dynamics and thermodynamics calculation, it can be concluded that the single crystal superalloy owns a dynamic homogenization-solution heat treatment window: both the γ′ solvus end temperature and the incipient melting temperature increase with the homogenization process. Such dynamic characteristic is especially noticeable for advanced single crystal superalloys since the segregation is more severe. There is no need to always keep the homogenization-solution heat treatment temperature below the incipient melting temperature of the as-cast condition, but keeping it below the incipient melting temperature of the alloy at the temporal homogenous state is necessary. For advanced single crystal superalloys, elevating temperatures of each step is much more effective than prolonging duration to get better heterogeneous effect. By using above conclusions, a new approach is introduced to design effective homogenization-solution heat treatments for advanced single crystal superalloys, and it has been successfully used on the experimental single crystal superalloy.
To design more efficient homogenization-solution heat treatments for advanced single crystal superalloys, an experimental single crystal superalloy was studied after homogenization-solution heat treatments with different temperatures and durations. Metallographic and field emission microscope were used to observe microstructures; electron probe was applied for component analysis. The results show that no incipient melting appears when the alloy is directly heated up to 1338℃; when it is directly heated up to 1350℃, obvious incipient melting occurs, while the incipient melting microstructure gradually fades away with holding time; for an lower temperature 1328℃, although there is no risk of incipient melting, the homogenization-solution efficiency is far from satisfactory. After analyzing the results by aid of dynamics and thermodynamics calculation, it can be concluded that the single crystal superalloy owns a dynamic homogenization-solution heat treatment window: both the γ′ solvus end temperature and the incipient melting temperature increase with the homogenization process. Such dynamic characteristic is especially noticeable for advanced single crystal superalloys since the segregation is more severe. There is no need to always keep the homogenization-solution heat treatment temperature below the incipient melting temperature of the as-cast condition, but keeping it below the incipient melting temperature of the alloy at the temporal homogenous state is necessary. For advanced single crystal superalloys, elevating temperatures of each step is much more effective than prolonging duration to get better heterogeneous effect. By using above conclusions, a new approach is introduced to design effective homogenization-solution heat treatments for advanced single crystal superalloys, and it has been successfully used on the experimental single crystal superalloy.
2017, 46(6):1536-1542.
Abstract:
The uniformity of the pore size and the morphology of nano-porous anodic alumina (nano-PAA) can be improved by a pore-widening process. In this paper, the evolution of the pore diameter and the morphology are investigated in details and in real time. Phosphoric acid solution was used to chemically enlarge the pores of a nano-PAA prepared with oxalic acid. The pore-widening is monitored by carrying out simultaneously both top-view and cross-section analyses. From the top-view analysis, the pore diameter results to be gradually enlarged with the increasing etching time. However, such enlarging rate varies with the multilayer structure of the pore wall. From the cross-section analysis, the pores wall of a multilayered amorphous compound result to be etched in a stage-by-stage mode until almost everything is etched away. The pore-widening procedure on the upper portion is completed earlier respect to the lower portion, after some time the pore-widening becomes uniform along the axial direction. If the etching is maintained, hexagonal pore walls are destroyed and split into ultrahigh aspect ratio nanowires due to the etching anisotropy, and finally completely dissolved. This is the first experimental report on the structural evolution details of alumina nano-pores upon etching, combining analyses in the depth direction with stereoscopic 3D imaging. Results clarify the pore-widening mechanism in 3D nano-PAA and can have important practical applications.
The uniformity of the pore size and the morphology of nano-porous anodic alumina (nano-PAA) can be improved by a pore-widening process. In this paper, the evolution of the pore diameter and the morphology are investigated in details and in real time. Phosphoric acid solution was used to chemically enlarge the pores of a nano-PAA prepared with oxalic acid. The pore-widening is monitored by carrying out simultaneously both top-view and cross-section analyses. From the top-view analysis, the pore diameter results to be gradually enlarged with the increasing etching time. However, such enlarging rate varies with the multilayer structure of the pore wall. From the cross-section analysis, the pores wall of a multilayered amorphous compound result to be etched in a stage-by-stage mode until almost everything is etched away. The pore-widening procedure on the upper portion is completed earlier respect to the lower portion, after some time the pore-widening becomes uniform along the axial direction. If the etching is maintained, hexagonal pore walls are destroyed and split into ultrahigh aspect ratio nanowires due to the etching anisotropy, and finally completely dissolved. This is the first experimental report on the structural evolution details of alumina nano-pores upon etching, combining analyses in the depth direction with stereoscopic 3D imaging. Results clarify the pore-widening mechanism in 3D nano-PAA and can have important practical applications.
2017, 46(6):1543-1550.
Abstract:
A three dimensional finite element model was established to simulate the selective laser melting (SLM) of TiC/Inconel 718 composites. Latent heat of phase change, multiple heat transfer mechanisms and temperature-dependent thermal physical properties were considered. The movement of Gaussian laser source and the application of energy of multi-layers and multi-tracks were realized using APDL secondary development language. The results indicated that there was a positive corresponding relationship between the rate of temperature change and processing parameters (laser powers and scan speeds). The maximum of the rate of temperature change was 7.03×106 °C/s. A high scan speed (300 mm/s) or a low laser power (50 W) yielded an extremely short liquid lifetime (0.29 ms) and low temperarure (1991 °C), resulting in the formation of a small amount of liquid phase with a relatively high viscosity. This phenomenon was detrimental for the wettaility of the liquid phase among the pores of powders, causing the appearance of irregular pores and the attendant high porosity in SLM-produced parts. The combination of a laser power of 100 W and a scan speed of 100 mm/s contributed to achieve a sound metallurgical bonding between the neighboring layers and tracks, due to the appropriate remelted depth (15.1 μm), remelted width (35.0 μm), the rate of temperature change, the liquid lifetime (1.2 ms) and maximum temperature (2204 °C) of molten pool. The selective laser melting experiments on a TiC/Inconel 718 powder mixture were carried out and simulation results were verified to be correct.
A three dimensional finite element model was established to simulate the selective laser melting (SLM) of TiC/Inconel 718 composites. Latent heat of phase change, multiple heat transfer mechanisms and temperature-dependent thermal physical properties were considered. The movement of Gaussian laser source and the application of energy of multi-layers and multi-tracks were realized using APDL secondary development language. The results indicated that there was a positive corresponding relationship between the rate of temperature change and processing parameters (laser powers and scan speeds). The maximum of the rate of temperature change was 7.03×106 °C/s. A high scan speed (300 mm/s) or a low laser power (50 W) yielded an extremely short liquid lifetime (0.29 ms) and low temperarure (1991 °C), resulting in the formation of a small amount of liquid phase with a relatively high viscosity. This phenomenon was detrimental for the wettaility of the liquid phase among the pores of powders, causing the appearance of irregular pores and the attendant high porosity in SLM-produced parts. The combination of a laser power of 100 W and a scan speed of 100 mm/s contributed to achieve a sound metallurgical bonding between the neighboring layers and tracks, due to the appropriate remelted depth (15.1 μm), remelted width (35.0 μm), the rate of temperature change, the liquid lifetime (1.2 ms) and maximum temperature (2204 °C) of molten pool. The selective laser melting experiments on a TiC/Inconel 718 powder mixture were carried out and simulation results were verified to be correct.
2017, 46(6):1551-1558.
Abstract:
A new technology, powder thixoforming, has been proposed in this paper. Microstructural evolution during partial remelting of the SiCp/2024 aluminum composite prepared by cold pressing of alloy powders has been investigated. The effects of heating temperature and SiCp volume fractions (0%~20%) on semisolid microstructure have also been discussed. The results indicate that the microstructural evolution of the 5%SiCp/2024 composite can be divided into three stages, the initial rapid coarsening of the fine grains within 2024 powders, the formation of continuous liquid layer on the primary particle surface and finally formed the slurry needed by thixoforming with the small and spheroidal solid particles through the spheroidization during heating at 635℃ (0~60 min), which are attributed to the phase transformations of θ→α, θ + α→L and α→L, and α→L, respectively. Proper rising the partial remelting temperature is beneficial for obtaining ideal semisolid microstructure available for thixoforming. The microstructural evolution rate of the composites is slower than that of the matrix alloy. The coarsening rate of the primary particles is quite slow, one powder evolves into one primary particle with a continuous liquid layer surface.
A new technology, powder thixoforming, has been proposed in this paper. Microstructural evolution during partial remelting of the SiCp/2024 aluminum composite prepared by cold pressing of alloy powders has been investigated. The effects of heating temperature and SiCp volume fractions (0%~20%) on semisolid microstructure have also been discussed. The results indicate that the microstructural evolution of the 5%SiCp/2024 composite can be divided into three stages, the initial rapid coarsening of the fine grains within 2024 powders, the formation of continuous liquid layer on the primary particle surface and finally formed the slurry needed by thixoforming with the small and spheroidal solid particles through the spheroidization during heating at 635℃ (0~60 min), which are attributed to the phase transformations of θ→α, θ + α→L and α→L, and α→L, respectively. Proper rising the partial remelting temperature is beneficial for obtaining ideal semisolid microstructure available for thixoforming. The microstructural evolution rate of the composites is slower than that of the matrix alloy. The coarsening rate of the primary particles is quite slow, one powder evolves into one primary particle with a continuous liquid layer surface.
2017, 46(6):1559-1565.
Abstract:
The microstructure and texture variation rule and mechanism of 6016 aluminum alloy during cold rolling was studied in depth in this article, using the Electron Back-Scatter Diffraction technology (EBSD) combined with SEM and XRD. The results show that: with the increase of cold rolling passes, grains constantly elongate along the rolling direction, and inhomogeneous deformation phenomenon between different grains come first but gradually disappear later, also catenation of second phase particles are crushed by metal plastic flow; with the deformation increases, small angle dislocation interfaces increase, and they have an angle about 40°to the rolling direction from low to medium strains, but some of them are induced to large angle interfaces by large strains, which make the deformation grains occurred fragmentation; in the initial rolling stage, overall coordinate deformation and rotation of grains form some deformation texture, and in further deformation, areas near the grain boundary and interior of grains is easy to rotate from grain’s initial orientation to the β orientation line. It is the two mechanism lead the deformation textures, led by S texture, constantly increase, and the Cube texture constantly decrease.
The microstructure and texture variation rule and mechanism of 6016 aluminum alloy during cold rolling was studied in depth in this article, using the Electron Back-Scatter Diffraction technology (EBSD) combined with SEM and XRD. The results show that: with the increase of cold rolling passes, grains constantly elongate along the rolling direction, and inhomogeneous deformation phenomenon between different grains come first but gradually disappear later, also catenation of second phase particles are crushed by metal plastic flow; with the deformation increases, small angle dislocation interfaces increase, and they have an angle about 40°to the rolling direction from low to medium strains, but some of them are induced to large angle interfaces by large strains, which make the deformation grains occurred fragmentation; in the initial rolling stage, overall coordinate deformation and rotation of grains form some deformation texture, and in further deformation, areas near the grain boundary and interior of grains is easy to rotate from grain’s initial orientation to the β orientation line. It is the two mechanism lead the deformation textures, led by S texture, constantly increase, and the Cube texture constantly decrease.
2017, 46(6):1566-1571.
Abstract:
The equilibrium shape measurement (ES) has been proved to be an effective method to determine the anisotropy of crystal-melt interfacial energy. In this paper, ES method is utilized to measure the shape of liquid droplets entrained in single-phase solid, and to calculate anisotropy parameters for Al-Si and Al-Si-Sc alloys. Rod-shaped Al-2wt.%Si and Al-2wt.%Si-0.2wt.%Sc alloy specimens are produced using the directional solidification process, followed by heat treatment and quenching. Specimens are sectioned normal to the <100> direction. Optical microscopy is used to characterize 2-D droplet shapes obtained by using sequential grinding for Al-2wt.%Si and Al-2wt.%Si-0.2wt.%Sc alloys, and then anisotropy parameters of interfacial energy were calculated. 3-D morphologies of droplets sliced by using focused ion beam (FIB) for Al-2wt.%Si alloy were reconstructed with Image-J software. Anisotropy parameters of interfacial energy were calculated and the 3-D interfacial energy and interfacial stiffness were plotted by using Matlab software. Effect of equilibrium temperature and Sc element on anisotropy parameters of interfacial energy were discussed for Al-Si alloys.
The equilibrium shape measurement (ES) has been proved to be an effective method to determine the anisotropy of crystal-melt interfacial energy. In this paper, ES method is utilized to measure the shape of liquid droplets entrained in single-phase solid, and to calculate anisotropy parameters for Al-Si and Al-Si-Sc alloys. Rod-shaped Al-2wt.%Si and Al-2wt.%Si-0.2wt.%Sc alloy specimens are produced using the directional solidification process, followed by heat treatment and quenching. Specimens are sectioned normal to the <100> direction. Optical microscopy is used to characterize 2-D droplet shapes obtained by using sequential grinding for Al-2wt.%Si and Al-2wt.%Si-0.2wt.%Sc alloys, and then anisotropy parameters of interfacial energy were calculated. 3-D morphologies of droplets sliced by using focused ion beam (FIB) for Al-2wt.%Si alloy were reconstructed with Image-J software. Anisotropy parameters of interfacial energy were calculated and the 3-D interfacial energy and interfacial stiffness were plotted by using Matlab software. Effect of equilibrium temperature and Sc element on anisotropy parameters of interfacial energy were discussed for Al-Si alloys.
2017, 46(6):1572-1577.
Abstract:
TC4 titanium alloys with different grain sizes were heated to 700℃ and compressed uniaxially using a Gleeble-1500D thermal mechanical simulator. Heating rates of 0, 10℃/s, 30℃/s, 50℃/s, 70℃/s were used for the heating process. The flow stress of the TC4 titanium alloys during the high temperature compression was investigated under the effects of the current by flow stress curves, SEM and TEM. It is found that the stress can be reduced from around 1000Mpa to below 600Mpa under the application of the current. Dynamic recrystallization occurs at a low current and the stress increases rapidly with the strain at first and reaches apeak value, it then decreases quickly and eventually become steady with the further increase of the strain. Dynamic recovery takes place at a high current and dynamic recrystallization is only found at some local areas. No stress peak is noticed with a high current and the maximum stress is below 400 Mpa. In addition, a higher current can promote a more complete phase transition from β to α. In conclusion, the flow stress of the TC4 titanium alloys can be affected simulteously by the current, dynamic recrystallization and phase transition and the current can facilitate dynamic recrystallization and phase transition, leading to decreasing flow stress.
TC4 titanium alloys with different grain sizes were heated to 700℃ and compressed uniaxially using a Gleeble-1500D thermal mechanical simulator. Heating rates of 0, 10℃/s, 30℃/s, 50℃/s, 70℃/s were used for the heating process. The flow stress of the TC4 titanium alloys during the high temperature compression was investigated under the effects of the current by flow stress curves, SEM and TEM. It is found that the stress can be reduced from around 1000Mpa to below 600Mpa under the application of the current. Dynamic recrystallization occurs at a low current and the stress increases rapidly with the strain at first and reaches apeak value, it then decreases quickly and eventually become steady with the further increase of the strain. Dynamic recovery takes place at a high current and dynamic recrystallization is only found at some local areas. No stress peak is noticed with a high current and the maximum stress is below 400 Mpa. In addition, a higher current can promote a more complete phase transition from β to α. In conclusion, the flow stress of the TC4 titanium alloys can be affected simulteously by the current, dynamic recrystallization and phase transition and the current can facilitate dynamic recrystallization and phase transition, leading to decreasing flow stress.
2017, 46(6):1578-1583.
Abstract:
Based on typical FGH97 components, three P/M superalloys were designed by modifying five alloying elements. The results showed that the lattice parameters of γ phases were increased, which enhanced the effect of solid solution strengthening, increased absolute values of γ/γ′ misfit enhanced the effect of coherent strain strengthening. While the precipitation strengthening and grain boundary strengthening were ignorable. The largest contribution to the increment of tensile strength at room temperature was made by solid solution strengthening.
Based on typical FGH97 components, three P/M superalloys were designed by modifying five alloying elements. The results showed that the lattice parameters of γ phases were increased, which enhanced the effect of solid solution strengthening, increased absolute values of γ/γ′ misfit enhanced the effect of coherent strain strengthening. While the precipitation strengthening and grain boundary strengthening were ignorable. The largest contribution to the increment of tensile strength at room temperature was made by solid solution strengthening.
2017, 46(6):1584-1589.
Abstract:
The influence of strain on the plastic deformation mechanism of zirconium alloy subjected to dynamic loadings was investigated by means of the experimental design in this paper. The strain parameter of zirconium alloy subjected to dynamic loading was only separated by the strain stopping rings and the the controled strain rate, and four strain levels including 0.11, 0.21, 0.30 and 0.33 were obtained at a strain rate of 2300 s-1. The results show that the deformed bands and transformed bands were considered as the dominant plastic deformaton mechanism of zirconium alloy under different strain stages. The deformed bands were mainly composed of the severe deformed grains, and the transformed bands mainly composed of the ultrafine and equiaxed grains with the mean diameter of about 100~300 nm were confirmed. Based on microstructural characterization of zirconium alloy under high strain rate and different strains, the plastic deformation process of zirconium alloy subjected to different strain parameters was speculated.
The influence of strain on the plastic deformation mechanism of zirconium alloy subjected to dynamic loadings was investigated by means of the experimental design in this paper. The strain parameter of zirconium alloy subjected to dynamic loading was only separated by the strain stopping rings and the the controled strain rate, and four strain levels including 0.11, 0.21, 0.30 and 0.33 were obtained at a strain rate of 2300 s-1. The results show that the deformed bands and transformed bands were considered as the dominant plastic deformaton mechanism of zirconium alloy under different strain stages. The deformed bands were mainly composed of the severe deformed grains, and the transformed bands mainly composed of the ultrafine and equiaxed grains with the mean diameter of about 100~300 nm were confirmed. Based on microstructural characterization of zirconium alloy under high strain rate and different strains, the plastic deformation process of zirconium alloy subjected to different strain parameters was speculated.
2017, 46(6):1590-1595.
Abstract:
The Static softening behavior in the two-stage isothermal compression of AZ31B magnesium alloy is investigated at the deformation temperatures ranging from 250℃ to 450℃, strain rates ranging from 0.005s-1 to 1s-1 and the inter-pass times ranging from 15s to 240s after the first stage isothermal compression. The prediction model of softening rate was established. According to the essence of rolling residual strain rate, the calculation method of residual strain rate in multi pass rolling process was proposed. The results show that the static softening fraction increases with the increasing of deformation temperature, strain rate and the inter-pass times. The softening rate calculation model can be used to characterize the softening rule of AZ31B magnesium alloy, the average relative error is 12.58%.The calculation model of residual strain rate can provide technical support for solving the deformation resistance of AZ31B magnesium alloy during multi pass deformation process.
The Static softening behavior in the two-stage isothermal compression of AZ31B magnesium alloy is investigated at the deformation temperatures ranging from 250℃ to 450℃, strain rates ranging from 0.005s-1 to 1s-1 and the inter-pass times ranging from 15s to 240s after the first stage isothermal compression. The prediction model of softening rate was established. According to the essence of rolling residual strain rate, the calculation method of residual strain rate in multi pass rolling process was proposed. The results show that the static softening fraction increases with the increasing of deformation temperature, strain rate and the inter-pass times. The softening rate calculation model can be used to characterize the softening rule of AZ31B magnesium alloy, the average relative error is 12.58%.The calculation model of residual strain rate can provide technical support for solving the deformation resistance of AZ31B magnesium alloy during multi pass deformation process.
24 Microstructure and mechanical properties of laser deposition repair casting ZL114A aluminium alloy
2017, 46(6):1596-1601.
Abstract:
ZL114A casting aluminum alloy with pre-groove damage was repaired by laser deposition repair (LDR). Microstructure and distribution law of laser deposition repaired zone before and after heat treatment were analyzed, and then microhardness and room temperature tensile properties of the sample were tested. The results showed that the repaired parts and the substrate formed a good metallurgical combination, at the bottom of the deposition layer were α-Al columnar dendrites which approximately paralleled to the normal directions of the fusion line with epitaxial growth feature. The primary dendrite arm spacing is about 15.7 μm,and the distance between secondary dendrites is about 5.27 μm. Eutectic structure presented as bifurcated rod or block in shape, and continuously distributed in the gaps among dendrite crystals, and α-Al columnar dendrites transformed into equiaxed crystal at the top of the last deposition layer. After the heat treatment, secondary dendrite arm of columnar dendrite is expansive because of atomic diffusion, and eutectic Si granulation were clear to be observed, the particle size is about 4.93 μm, and part of them distributed uniformly on both sides of primary dendritic arm. The hardness of repair area increased by an average of 55.5% than substrates after heat treatment, and the room temperature tensile properties were better than casting parts.
ZL114A casting aluminum alloy with pre-groove damage was repaired by laser deposition repair (LDR). Microstructure and distribution law of laser deposition repaired zone before and after heat treatment were analyzed, and then microhardness and room temperature tensile properties of the sample were tested. The results showed that the repaired parts and the substrate formed a good metallurgical combination, at the bottom of the deposition layer were α-Al columnar dendrites which approximately paralleled to the normal directions of the fusion line with epitaxial growth feature. The primary dendrite arm spacing is about 15.7 μm,and the distance between secondary dendrites is about 5.27 μm. Eutectic structure presented as bifurcated rod or block in shape, and continuously distributed in the gaps among dendrite crystals, and α-Al columnar dendrites transformed into equiaxed crystal at the top of the last deposition layer. After the heat treatment, secondary dendrite arm of columnar dendrite is expansive because of atomic diffusion, and eutectic Si granulation were clear to be observed, the particle size is about 4.93 μm, and part of them distributed uniformly on both sides of primary dendritic arm. The hardness of repair area increased by an average of 55.5% than substrates after heat treatment, and the room temperature tensile properties were better than casting parts.
2017, 46(6):1602-1607.
Abstract:
Thin specimens in Φ3 mm for transmission electron microscopy observation were prepared using Zircaloy-4 plate. Corrosion tests of these thin specimens were conducted in the autoclave at 300 ℃/8 MPa in deionized water for short time exposure. The oxide layers formed earlier on Zircaloy-4 specimens have been investigated using optical microscopy, scanning probe microscopy and electron microscopy. The results show that the different thickness of oxide layers formed on metal grains with different orietations was in different colours. The oxide layers were mainly composed of columnar grains with m-ZrO2, but a small amount of t-ZrO2 and c-ZrO2 could be also detected. In addition, a kind of zirconia having BCC structure with a=0.88 nm was observed. Semi-coherent relationships between α-Zr matrix and the different crystal structure of zirconia with certain orietation relationship were observed：(10-11)α-Zr//(020)m-ZrO2//(002)t-ZrO2//(020)c-ZrO2. Therefore compressive deformation of 3%-7% in different directions for different crystal structure of zirconia was produced. A lot of dislocations were observed in oxide crystals and the strain in the area around the dislocations was about -4.8% to 3.5% obtained by geometric phase analysis.
Thin specimens in Φ3 mm for transmission electron microscopy observation were prepared using Zircaloy-4 plate. Corrosion tests of these thin specimens were conducted in the autoclave at 300 ℃/8 MPa in deionized water for short time exposure. The oxide layers formed earlier on Zircaloy-4 specimens have been investigated using optical microscopy, scanning probe microscopy and electron microscopy. The results show that the different thickness of oxide layers formed on metal grains with different orietations was in different colours. The oxide layers were mainly composed of columnar grains with m-ZrO2, but a small amount of t-ZrO2 and c-ZrO2 could be also detected. In addition, a kind of zirconia having BCC structure with a=0.88 nm was observed. Semi-coherent relationships between α-Zr matrix and the different crystal structure of zirconia with certain orietation relationship were observed：(10-11)α-Zr//(020)m-ZrO2//(002)t-ZrO2//(020)c-ZrO2. Therefore compressive deformation of 3%-7% in different directions for different crystal structure of zirconia was produced. A lot of dislocations were observed in oxide crystals and the strain in the area around the dislocations was about -4.8% to 3.5% obtained by geometric phase analysis.
2017, 46(6):1608-1611.
Abstract:
TC16 titanium alloy samples with a cold upset treatment carried on a fast upsetting testing machine were prepared. The properties and deformation structure of samples were analyzed by micro-hardness tester, TEM and XRD. The results demonstrated that the deformation was mainly because of the dislocation sliding, and the structure and properties of the deformation samples presented a certain extent of inhomogeneity. When the forging ratio was 1/6, the hardness was 300 HV which was stabilized. The hardness had increased 20% compared to the original sample. The original equiaxed crystals in the central part of the shearing band were stretched gradually with the increase of the deformation. Grain crack and refinement occurred when the grain width was less than 100 nm, which was the main reason of the stable hardness. Cracks were not observed in the central part of the sample under a larger deformation, due to the good plasticity of TC16 alloy. However, XRD showed that the martensite phase transformation had taken place during the process of the deformation.
TC16 titanium alloy samples with a cold upset treatment carried on a fast upsetting testing machine were prepared. The properties and deformation structure of samples were analyzed by micro-hardness tester, TEM and XRD. The results demonstrated that the deformation was mainly because of the dislocation sliding, and the structure and properties of the deformation samples presented a certain extent of inhomogeneity. When the forging ratio was 1/6, the hardness was 300 HV which was stabilized. The hardness had increased 20% compared to the original sample. The original equiaxed crystals in the central part of the shearing band were stretched gradually with the increase of the deformation. Grain crack and refinement occurred when the grain width was less than 100 nm, which was the main reason of the stable hardness. Cracks were not observed in the central part of the sample under a larger deformation, due to the good plasticity of TC16 alloy. However, XRD showed that the martensite phase transformation had taken place during the process of the deformation.
2017, 46(6):1612-1619.
Abstract:
The Al + Si codeposited coatings were prepared on DZ417G superalloy substrates by aluminization and siliconization using pack cementation. XRD, SEM and EDS were used to study the microstructure and morphology of coatings. During the co-deposition process, the phase structure formed on the coating surface changed with Al content. In addition, the post heat-treatment also had an effect on the microstructure of coatings. When the composition (in wt.%) of the packs was xAl-4NH4Cl-4Si-(92-x)Al2O3 with different Al contents (x = 1, 4 and 6), the corresponding microstructures of the coatings were NiSi and Ni2Al3 after pack cementation, respectively. When Si content increased to 6 and 10 wt.%, the microstructure of the coatings were also NiSi or Ni2Al3. After post heat-treatment, because of Ni, Cr and Mo diffusion from the substrate, NiSi was transformed to AlNi6Si3 or δ-Ni2Si, while Ni2Al3 was transformed to β-NiAl. The Si level in the β-NiAl coatings was very small. Cr or Mo dissolved into AlNi6Si3, δ-Ni2Si and β-NiAl. The results indicate that Al content plays a role for the formations of coatings. When Al content is low in the pack, the microstructure of coatings was NiSi after Al + Si codepostion. However, when the Al content was above 4 wt.%, the microstructures of coatings were Ni2Al3 after pack cementation. Cr-rich AlNi6Si3, Cr- and Mo-rich δ-Ni2Si as well as β-NiAl coatings were formed after Al + Si codepostion followed by post heat-treatment.
The Al + Si codeposited coatings were prepared on DZ417G superalloy substrates by aluminization and siliconization using pack cementation. XRD, SEM and EDS were used to study the microstructure and morphology of coatings. During the co-deposition process, the phase structure formed on the coating surface changed with Al content. In addition, the post heat-treatment also had an effect on the microstructure of coatings. When the composition (in wt.%) of the packs was xAl-4NH4Cl-4Si-(92-x)Al2O3 with different Al contents (x = 1, 4 and 6), the corresponding microstructures of the coatings were NiSi and Ni2Al3 after pack cementation, respectively. When Si content increased to 6 and 10 wt.%, the microstructure of the coatings were also NiSi or Ni2Al3. After post heat-treatment, because of Ni, Cr and Mo diffusion from the substrate, NiSi was transformed to AlNi6Si3 or δ-Ni2Si, while Ni2Al3 was transformed to β-NiAl. The Si level in the β-NiAl coatings was very small. Cr or Mo dissolved into AlNi6Si3, δ-Ni2Si and β-NiAl. The results indicate that Al content plays a role for the formations of coatings. When Al content is low in the pack, the microstructure of coatings was NiSi after Al + Si codepostion. However, when the Al content was above 4 wt.%, the microstructures of coatings were Ni2Al3 after pack cementation. Cr-rich AlNi6Si3, Cr- and Mo-rich δ-Ni2Si as well as β-NiAl coatings were formed after Al + Si codepostion followed by post heat-treatment.
2017, 46(6):1620-1625.
Abstract:
TC4 alloy was bonded by a new solid-state bonding process named as rigid restraint thermal self-compressing bonding at different heating time. Effect of heating time on bond interface, microstructure and mechanical properties was investigated through the optical microscope observation, scanning electron microscope analysis and mechanical properties test to the joints produced at different heating time. In the meantime, thermal stress-strain history during bonding was analyzed by finite element analysis. Results show that with the increase of heating time, the dwell time over high temperature, the action time of compressive stress and the transversal compressive plastic strain are increased which promote the atom diffusion between butt-specimens and thus the number of voids retained at bond interface is decreased. When the heating time is improved to more than 300s, sound solid-state joint with good bond interface, homogeneous microstructure and good mechanical properties is obtained.
TC4 alloy was bonded by a new solid-state bonding process named as rigid restraint thermal self-compressing bonding at different heating time. Effect of heating time on bond interface, microstructure and mechanical properties was investigated through the optical microscope observation, scanning electron microscope analysis and mechanical properties test to the joints produced at different heating time. In the meantime, thermal stress-strain history during bonding was analyzed by finite element analysis. Results show that with the increase of heating time, the dwell time over high temperature, the action time of compressive stress and the transversal compressive plastic strain are increased which promote the atom diffusion between butt-specimens and thus the number of voids retained at bond interface is decreased. When the heating time is improved to more than 300s, sound solid-state joint with good bond interface, homogeneous microstructure and good mechanical properties is obtained.
2017, 46(6):1626-1631.
Abstract:
In this study, the magnesium sheets in size of 160mm×8mm, 170mm×4mm and 160mm×3mm were processed experimentally by using continuous extrusion method with single and double rod modes. The influence of the process conditions, including feeding modes (single and double rod), width thickness radio and extrusion speed on the forming abilities, the microstructure distributions and the mechanical properties of the AZ31 magnesium sheets were examined. As a result, the microstructure distributions in cross-section of the sheets processed by the double rod mode show more homogeneous, comparing with the sheets processed by the single rod mode. The average tensile strength was up to 239MPa and the average elongation was 15%.The magnesium sheets with refined grains were obtained when the width thickness radio was improved to be 53.The tensile strength of AZ31 sheets decreased with increasing the wheel speed. This is because higher temperature generally leads to larger grain size.
In this study, the magnesium sheets in size of 160mm×8mm, 170mm×4mm and 160mm×3mm were processed experimentally by using continuous extrusion method with single and double rod modes. The influence of the process conditions, including feeding modes (single and double rod), width thickness radio and extrusion speed on the forming abilities, the microstructure distributions and the mechanical properties of the AZ31 magnesium sheets were examined. As a result, the microstructure distributions in cross-section of the sheets processed by the double rod mode show more homogeneous, comparing with the sheets processed by the single rod mode. The average tensile strength was up to 239MPa and the average elongation was 15%.The magnesium sheets with refined grains were obtained when the width thickness radio was improved to be 53.The tensile strength of AZ31 sheets decreased with increasing the wheel speed. This is because higher temperature generally leads to larger grain size.
2017, 46(6):1632-1637.
Abstract:
In order to study Wf/Zr-based metallic glass composites containing four kinds of tungsten fiber with different diameters, penetration experiments are taken to perforate homogeneous armor steel at velocity 1270m/s to 1600m/s. The results demonstrate that the both of the diameter of the tungsten fiber and the velocity are critical parameters for penetration ability. Firstly, the diameter of Wf/Zr-based metallic glass composites is more than 10% smaller than tungsten, which illustrates that the Wf/Zr-based metallic glass composite keeps self-sharping during the penetration process. Next, the failure mechanism of Wf/Zr-based metallic glass composite changes form adiabatic shear failure to the tungsten fiber buckling and back-flow due of the velocity increase. The diameter of tungsten fiber is smaller, the more stable the penetration process would be, because the stability of penetration is affected by the diameter of the tungsten fiber.
In order to study Wf/Zr-based metallic glass composites containing four kinds of tungsten fiber with different diameters, penetration experiments are taken to perforate homogeneous armor steel at velocity 1270m/s to 1600m/s. The results demonstrate that the both of the diameter of the tungsten fiber and the velocity are critical parameters for penetration ability. Firstly, the diameter of Wf/Zr-based metallic glass composites is more than 10% smaller than tungsten, which illustrates that the Wf/Zr-based metallic glass composite keeps self-sharping during the penetration process. Next, the failure mechanism of Wf/Zr-based metallic glass composite changes form adiabatic shear failure to the tungsten fiber buckling and back-flow due of the velocity increase. The diameter of tungsten fiber is smaller, the more stable the penetration process would be, because the stability of penetration is affected by the diameter of the tungsten fiber.
31 Effect of Different Fluoride on Weld Formation and Organization with A-TIG Welding of Titanium Alloy
2017, 46(6):1638-1643.
Abstract:
Nine kinds of fluoride were used for A-TIG welding of titanium alloy. Welding arc shape and electrical signals were collected by the high-speed cameras and Hannover analyser in the process. After welding, organization of welded joint was observed and analysised. The results show that: MgF2 had the apparent effect in increasing the weld penetration, it was 2 times the depth of weld without flux. KF was in the second place. LiF could decrease the weld penetration; Compared with MgF2, KF had a small weld width , narrow HAZ width and total joint width. NaF obtained the minimum HAZ width; The angle of NaF, KF, MgF2 and AlF3 between columnar crystal growth direction and weld center axis was bigger than the other fluoride. The length of the column crystal size was determined by the size of penetration, the width variation law was for AlF3＞KF＞MgF2＞NaF; the grain size of coarse grain area in HAZ was for MgF2 > NaF > AlF3 > KF.
Nine kinds of fluoride were used for A-TIG welding of titanium alloy. Welding arc shape and electrical signals were collected by the high-speed cameras and Hannover analyser in the process. After welding, organization of welded joint was observed and analysised. The results show that: MgF2 had the apparent effect in increasing the weld penetration, it was 2 times the depth of weld without flux. KF was in the second place. LiF could decrease the weld penetration; Compared with MgF2, KF had a small weld width , narrow HAZ width and total joint width. NaF obtained the minimum HAZ width; The angle of NaF, KF, MgF2 and AlF3 between columnar crystal growth direction and weld center axis was bigger than the other fluoride. The length of the column crystal size was determined by the size of penetration, the width variation law was for AlF3＞KF＞MgF2＞NaF; the grain size of coarse grain area in HAZ was for MgF2 > NaF > AlF3 > KF.
2017, 46(6):1644-1649.
Abstract:
A seriesSof TiO2 nanotube array thin films were prepared by anodic oxidation pure titanium foils under different anodization voltages and anodization times in ethylene glycol electrolyte. The surface and fracture morphology of TiO2 nanotube samples were characterized by FESEM, which was used to investigate the influence of anodization voltage and anodization time on the growth rate of TiO2 nanotubes. Photoelectrochemical properties of the TiO2 nanotubes were measured by electrochemical method. The photocatalytic activity of TiO2 nanotubes was evaluated by hydrogen production in the two-compartment photoelectrochemical cell without any external applied voltage. The results indicated that comparing to prolonging anodization time, increasing anodization voltage was more effective to obtain TiO2 nanotube arrays withShigh aspect ratio. Consequently, the photocurrent response, photoconversion efficiency and hydrogen production of TiO2 nanotube arrays were improved remarkably.
A seriesSof TiO2 nanotube array thin films were prepared by anodic oxidation pure titanium foils under different anodization voltages and anodization times in ethylene glycol electrolyte. The surface and fracture morphology of TiO2 nanotube samples were characterized by FESEM, which was used to investigate the influence of anodization voltage and anodization time on the growth rate of TiO2 nanotubes. Photoelectrochemical properties of the TiO2 nanotubes were measured by electrochemical method. The photocatalytic activity of TiO2 nanotubes was evaluated by hydrogen production in the two-compartment photoelectrochemical cell without any external applied voltage. The results indicated that comparing to prolonging anodization time, increasing anodization voltage was more effective to obtain TiO2 nanotube arrays withShigh aspect ratio. Consequently, the photocurrent response, photoconversion efficiency and hydrogen production of TiO2 nanotube arrays were improved remarkably.
2017, 46(6):1650-1655.
Abstract:
The TA15 titanium alloy specimens were prepared by laser deposition manufacturing. The effects of oxygen content in the argon shielding gas on microstructure, fracture and mechanical properties of laser deposition manufacturing TA15 titanium alloy have been investigated by optical microstructure (OM) and scanning electron microscopy (SEM). The results show that both as-deposited and annealed specimens microstructure are typically basket-weave microstructure without dramatic changes with the increasing of the oxygen content of the atmosphere. The tensile strength at room temperature of the annealed alloy is gradually on the rise while the ductility is decreasing. By considering both the ductility and strength properties, samples with the oxygen content at 0~5×10-5 have the best comprehensive mechanical properties. Microhardness of the annealed samples is lower than that of the as-deposited, and they are gradually enhancing with the increasing of oxygen content. Room temperature tensile fracture mechanism changes from ductile fracture to semi-cleavage and semi-ductile fracture with the increasing of oxygen content.
The TA15 titanium alloy specimens were prepared by laser deposition manufacturing. The effects of oxygen content in the argon shielding gas on microstructure, fracture and mechanical properties of laser deposition manufacturing TA15 titanium alloy have been investigated by optical microstructure (OM) and scanning electron microscopy (SEM). The results show that both as-deposited and annealed specimens microstructure are typically basket-weave microstructure without dramatic changes with the increasing of the oxygen content of the atmosphere. The tensile strength at room temperature of the annealed alloy is gradually on the rise while the ductility is decreasing. By considering both the ductility and strength properties, samples with the oxygen content at 0~5×10-5 have the best comprehensive mechanical properties. Microhardness of the annealed samples is lower than that of the as-deposited, and they are gradually enhancing with the increasing of oxygen content. Room temperature tensile fracture mechanism changes from ductile fracture to semi-cleavage and semi-ductile fracture with the increasing of oxygen content.
2017, 46(6):1656-1661.
Abstract:
AZ91D magnesium alloys were treated at different time by micro arc oxidation (MAO) in silicate-containing electrolyte. In this work，two types of power loading processes, named P1 mode (constant voltage) and P2 mode (variable voltage ) respectively, were used to prepare the coatings. Varitations of the thickness, surface morphology, phase composition and corrosion resistant of the coatings with treatment time were investigated and the size and amount of the micro pores on coating surface and the surface porosity were studied quantitatively. The results show that the coatings obtained under these two power loading processes had similar evolution patterns in characteristics of microstructure and the extent of which was larger in P2 mode. With prolonging treatment time, the thickness of the coatings was enlarged, with the amount of the total mircro pores and the bigger ones decreasing and increasing, respectively, and the surface porosity of the coatings increased. However, the phase composition of the coatings had no change. The corrosion resistance of the coatings increased continually under P1 mode but it firstly increased and then decreased under P2 mode with treatment time. Comparing these two processes, the P1 mode has an advantage in industrial applications because the MAO coating can grow in a larger rate during the early stage.
AZ91D magnesium alloys were treated at different time by micro arc oxidation (MAO) in silicate-containing electrolyte. In this work，two types of power loading processes, named P1 mode (constant voltage) and P2 mode (variable voltage ) respectively, were used to prepare the coatings. Varitations of the thickness, surface morphology, phase composition and corrosion resistant of the coatings with treatment time were investigated and the size and amount of the micro pores on coating surface and the surface porosity were studied quantitatively. The results show that the coatings obtained under these two power loading processes had similar evolution patterns in characteristics of microstructure and the extent of which was larger in P2 mode. With prolonging treatment time, the thickness of the coatings was enlarged, with the amount of the total mircro pores and the bigger ones decreasing and increasing, respectively, and the surface porosity of the coatings increased. However, the phase composition of the coatings had no change. The corrosion resistance of the coatings increased continually under P1 mode but it firstly increased and then decreased under P2 mode with treatment time. Comparing these two processes, the P1 mode has an advantage in industrial applications because the MAO coating can grow in a larger rate during the early stage.
2017, 46(6):1662-1667.
Abstract:
In the present work, AZ91 Mg alloy /1060 pure Al explosive composite plates were annealed. The microstructures, elemental distributions and mechanical properties of the bonding interfaces before and after annealing were studied. The results show that, Mg atoms diffuse from AZ91 to 1060 during annealing process and the diffusion layer is in 1060 near the interface. The thickness of diffusion layer and the highest hardness of composite plates increase obviously after annealing. The layer of high hardness is in AZ31 near the interface in composite plates before annealing, however after annealing the layer of high hardness is in 1060 near the interface. Before annealing the hardness increases because of work hardening and after annealing the hardness increases because solid solution and intermetallic compounds form in diffusion layers. With the increase of annealing temperature, thickness of diffusion layers increase, recrystallization tendency is more obvious and deformation bands disappear gradually.
In the present work, AZ91 Mg alloy /1060 pure Al explosive composite plates were annealed. The microstructures, elemental distributions and mechanical properties of the bonding interfaces before and after annealing were studied. The results show that, Mg atoms diffuse from AZ91 to 1060 during annealing process and the diffusion layer is in 1060 near the interface. The thickness of diffusion layer and the highest hardness of composite plates increase obviously after annealing. The layer of high hardness is in AZ31 near the interface in composite plates before annealing, however after annealing the layer of high hardness is in 1060 near the interface. Before annealing the hardness increases because of work hardening and after annealing the hardness increases because solid solution and intermetallic compounds form in diffusion layers. With the increase of annealing temperature, thickness of diffusion layers increase, recrystallization tendency is more obvious and deformation bands disappear gradually.
2017, 46(6):1668-1673.
Abstract:
The effects of cerium and different mass ratio Cu:Zn on the microstructures and mechanical properties of Mg-Zn-Cu alloys were investigated. The optical microscope, X-ray diffractometer, scanning electron microscope were introduced in the experiments. The microhardening testing, room and high temperature tensile test and creep properties test were done to study the effect of Cu content on the properties of the alloys, such as the evolution rule of its room and high temperature mechanical property, hot deformation behavior, strengthening mechanism and resistant creep behavior. The tensile strength and yield strength of extruded Mg-8Zn-8Cu-Ce are 320 MPa and 291 MPa respectively at room temperature, and its tensile strength is still higher than 220 MPa at 423 K. The alloy has best creep property; the steady creep speed rate is 1.21 × 10-8 s-1 with the creep strain 0.562% only. At the same deformation temperature, the true stress level of the as-cast Mg-7Zn-3Cu-Ce alloy increases with increasing of the strain rate. The result indicates that the alloy is strain rate sensitive material. While at the same strain rate, the true stress level of the alloy declined with the temperature increased. There is no obvious dynamic recrystallization and the softening effects.
The effects of cerium and different mass ratio Cu:Zn on the microstructures and mechanical properties of Mg-Zn-Cu alloys were investigated. The optical microscope, X-ray diffractometer, scanning electron microscope were introduced in the experiments. The microhardening testing, room and high temperature tensile test and creep properties test were done to study the effect of Cu content on the properties of the alloys, such as the evolution rule of its room and high temperature mechanical property, hot deformation behavior, strengthening mechanism and resistant creep behavior. The tensile strength and yield strength of extruded Mg-8Zn-8Cu-Ce are 320 MPa and 291 MPa respectively at room temperature, and its tensile strength is still higher than 220 MPa at 423 K. The alloy has best creep property; the steady creep speed rate is 1.21 × 10-8 s-1 with the creep strain 0.562% only. At the same deformation temperature, the true stress level of the as-cast Mg-7Zn-3Cu-Ce alloy increases with increasing of the strain rate. The result indicates that the alloy is strain rate sensitive material. While at the same strain rate, the true stress level of the alloy declined with the temperature increased. There is no obvious dynamic recrystallization and the softening effects.
2017, 46(6):1674-1678.
Abstract:
Porous Ni-Ti alloys are widely used in biomedical implant material because of its shape memory effect. In this work, porous Ni-Ti alloy with large size and complicated shape was fabricated by gel-casting of TiH2 powder and atomization nickel powder, followed by vacuum drying, thermal debinding and subsequent vacuum sintering process. Effects of sintering temperature on porosity, mechanical properties, phase composition and microstructure of porous Ni-Ti alloys were studied by XRD and SEM. With the increase of sintering temperature, the porosity of Ni-Ti alloy reduces while the compression strength and Young’s modulus increases. Under the condition of vacuum sintering at 1050 ℃ for 2h, the obtained samples with the solid loading of 45vol. % exhibits a porosity of 42.65%, compression strength of 202.65 MPa and Young’s modulus of 17.14 GPa, which match the demands of human bones.
Porous Ni-Ti alloys are widely used in biomedical implant material because of its shape memory effect. In this work, porous Ni-Ti alloy with large size and complicated shape was fabricated by gel-casting of TiH2 powder and atomization nickel powder, followed by vacuum drying, thermal debinding and subsequent vacuum sintering process. Effects of sintering temperature on porosity, mechanical properties, phase composition and microstructure of porous Ni-Ti alloys were studied by XRD and SEM. With the increase of sintering temperature, the porosity of Ni-Ti alloy reduces while the compression strength and Young’s modulus increases. Under the condition of vacuum sintering at 1050 ℃ for 2h, the obtained samples with the solid loading of 45vol. % exhibits a porosity of 42.65%, compression strength of 202.65 MPa and Young’s modulus of 17.14 GPa, which match the demands of human bones.
2017, 46(6):1679-1683.
Abstract:
In this study, Ti-60Ta powders were produced by the plasma rotating electrode processing technique. The surface and internal microstructural morphologies, phase compositions, distances between dendrites and micro-hardness have been characterized for powders with different size ranges by SEM、XRD and Vickers micro-hardness methods. Results showed that the prepared Ti-60Ta powders exhibited major β phase and a small amount of martensitic α" and ω phases; the surface of larger particles appears isometric petal-shaped dentritic microstructures, while small particles exhibit refined dendritic microstructures. Particularly, fine acicular martensitic appearance was observed on the smaller particles. As the powder particle size decreases, the martensite phases increase and accordingly Vickers micro-hardness increases.
In this study, Ti-60Ta powders were produced by the plasma rotating electrode processing technique. The surface and internal microstructural morphologies, phase compositions, distances between dendrites and micro-hardness have been characterized for powders with different size ranges by SEM、XRD and Vickers micro-hardness methods. Results showed that the prepared Ti-60Ta powders exhibited major β phase and a small amount of martensitic α" and ω phases; the surface of larger particles appears isometric petal-shaped dentritic microstructures, while small particles exhibit refined dendritic microstructures. Particularly, fine acicular martensitic appearance was observed on the smaller particles. As the powder particle size decreases, the martensite phases increase and accordingly Vickers micro-hardness increases.
2017, 46(6):1684-1688.
Abstract:
Thick plate of La0.6Pr0.4Fe11.4Si1.6B0.2 alloy was produced with industrial raw materials by induction melting method and NaZn13 type magnetocaloric phase was obtained by annealing at high temperature for short time. The annealed alloy was hydrogenated with various shapes and sizes. The bulk sample with a size of 3-5 cm was broken to powders from the outside to inside like an onion with a smooth ball shape center part left during the hydrogenation process, while the small samples with sizes less than 1 cm still hold their original shapes. The critical crack size for the La0.6Pr0.4Fe11.4Si1.6B0.2 alloy was 1 cm on hydrogenation to avoid breaking down to powders. The processing could be used to develop La0.6Pr0.4Fe11.4Si1.6B0.2Hx alloys with a certain sizes and shapes directly from casting alloy by hydrogenation absorption.
Thick plate of La0.6Pr0.4Fe11.4Si1.6B0.2 alloy was produced with industrial raw materials by induction melting method and NaZn13 type magnetocaloric phase was obtained by annealing at high temperature for short time. The annealed alloy was hydrogenated with various shapes and sizes. The bulk sample with a size of 3-5 cm was broken to powders from the outside to inside like an onion with a smooth ball shape center part left during the hydrogenation process, while the small samples with sizes less than 1 cm still hold their original shapes. The critical crack size for the La0.6Pr0.4Fe11.4Si1.6B0.2 alloy was 1 cm on hydrogenation to avoid breaking down to powders. The processing could be used to develop La0.6Pr0.4Fe11.4Si1.6B0.2Hx alloys with a certain sizes and shapes directly from casting alloy by hydrogenation absorption.
2017, 46(6):1689-1693.
Abstract:
Ti-6Al-4V alloy was thermal oxidized and subsequently vacuum diffused to prepare an oxidation coating. Dry sliding wear tests of the coating were performed at 400 ℃ in air on a high-temperature wear tester. The elevated-temperature wear behaviors and mechanism of coating were studied. The results show that the oxidation coating with a thickness of 250 μm was produced on Ti-6Al-4V alloy. The wear losses of oxidation coating were extremely low, compared with uncoated materials, its elevated-temperature wear resistance was noticeably improved. Tribo-oxide layers were always found to form on worn surfaces. The high wear resistance of coating could be ascribed to the integrated function of the hardened ceramic coating and protective tribo-layer. The predominant wear mechanism was delamination wear during dry sliding.
Ti-6Al-4V alloy was thermal oxidized and subsequently vacuum diffused to prepare an oxidation coating. Dry sliding wear tests of the coating were performed at 400 ℃ in air on a high-temperature wear tester. The elevated-temperature wear behaviors and mechanism of coating were studied. The results show that the oxidation coating with a thickness of 250 μm was produced on Ti-6Al-4V alloy. The wear losses of oxidation coating were extremely low, compared with uncoated materials, its elevated-temperature wear resistance was noticeably improved. Tribo-oxide layers were always found to form on worn surfaces. The high wear resistance of coating could be ascribed to the integrated function of the hardened ceramic coating and protective tribo-layer. The predominant wear mechanism was delamination wear during dry sliding.
2017, 46(6):1694-1698.
Abstract:
Ag-Graphene composites (Ag-RGO) were prepared using poly (N-vinyl-2-pyrrolidone) (PVP) as reductant and stabilizer under 60℃ reaction conditions. The synthesized Ag-RGO were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Uv-vis absorption spectra, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), respectively. The results showed that Ag nanoparticles with small-size and excellent dispersion were anchored firmlyon RGO sheet. The photocatalytic activity was evaluated by oxidation of AO7 under visible light irradiation. AO7 could be almost degraded completely within 120 min by 0.2Ag-RGO sample. The origin of high photocatalytic activity of Ag-RGO was discussed, which was mainly ascribed to the surface plasmo resonance effect of Ag nanoparticles in Ag-RGO composites. In addition, RGO acted as electron transmission channels. The synergistic effects induced by RGO also contributed to the high photocatalytic activity.
Ag-Graphene composites (Ag-RGO) were prepared using poly (N-vinyl-2-pyrrolidone) (PVP) as reductant and stabilizer under 60℃ reaction conditions. The synthesized Ag-RGO were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Uv-vis absorption spectra, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), respectively. The results showed that Ag nanoparticles with small-size and excellent dispersion were anchored firmlyon RGO sheet. The photocatalytic activity was evaluated by oxidation of AO7 under visible light irradiation. AO7 could be almost degraded completely within 120 min by 0.2Ag-RGO sample. The origin of high photocatalytic activity of Ag-RGO was discussed, which was mainly ascribed to the surface plasmo resonance effect of Ag nanoparticles in Ag-RGO composites. In addition, RGO acted as electron transmission channels. The synergistic effects induced by RGO also contributed to the high photocatalytic activity.
2017, 46(6):1699-1703.
Abstract:
The carbonates composite electrolytes for solid oxide cells have aroused more attention. However, the thermal stability of carbonates composite electrolytes remains in doubt due to the molten state of the carbonates at operating temperature. The novel composite electrolytes were obtained by mixing LSGM powders which were synthesized by acrylamide polymerization with binary carbonates. Ageing, cycling and longtime fuel cell performance tests were used to evaluate the stability of LSGM-(Li/Na)2CO3 composite materials. The sample shows a relatively stable conductivity of 0.07-0.09 Scm-1 during a 650 h measurement in air at 600℃.The composites keep weight stable during thermal cycling below 700℃, and demonstrate a good stability after 5 thermal cycles. The cell based on LSGM-(Li/Na)2CO3 composite electrolyte delivers an average output of 256 mWcm-2 in 1h operation corresponding to the constant current density 0.6Acm-2.
The carbonates composite electrolytes for solid oxide cells have aroused more attention. However, the thermal stability of carbonates composite electrolytes remains in doubt due to the molten state of the carbonates at operating temperature. The novel composite electrolytes were obtained by mixing LSGM powders which were synthesized by acrylamide polymerization with binary carbonates. Ageing, cycling and longtime fuel cell performance tests were used to evaluate the stability of LSGM-(Li/Na)2CO3 composite materials. The sample shows a relatively stable conductivity of 0.07-0.09 Scm-1 during a 650 h measurement in air at 600℃.The composites keep weight stable during thermal cycling below 700℃, and demonstrate a good stability after 5 thermal cycles. The cell based on LSGM-(Li/Na)2CO3 composite electrolyte delivers an average output of 256 mWcm-2 in 1h operation corresponding to the constant current density 0.6Acm-2.
2017, 46(6):1704-1708.
Abstract:
Through the ordinary moulding - presintering, sintering at 1800-1950 ℃,the fine-grained tungsten alloys were fabricated with ultrafine/nano composite powders of W-0.3%Y which were prepared by Sol-spray drying- Nano in situ composite.The microhardness and tensile strength of alloys were detected,Moreover ,Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy were used to examine fracture morphology and microstructure .The evolution of Sintering and Fracture behavior were investigated.The results show that the added trace yttrium exists in the form of Y2O3 as the second phase particles dispersing throughout grain boundary and inner grain of W, restraining tungsten grain growth and making the grains to be significantly refined,which is to improve the mechanical properties of the alloys.Besides,The fracture mode of tungsten alloy with adding trace yttrium was changed from intergranular fracture transition of pure tungsten to mainly intergranular fracture and part transgranular fracture.
Through the ordinary moulding - presintering, sintering at 1800-1950 ℃,the fine-grained tungsten alloys were fabricated with ultrafine/nano composite powders of W-0.3%Y which were prepared by Sol-spray drying- Nano in situ composite.The microhardness and tensile strength of alloys were detected,Moreover ,Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy were used to examine fracture morphology and microstructure .The evolution of Sintering and Fracture behavior were investigated.The results show that the added trace yttrium exists in the form of Y2O3 as the second phase particles dispersing throughout grain boundary and inner grain of W, restraining tungsten grain growth and making the grains to be significantly refined,which is to improve the mechanical properties of the alloys.Besides,The fracture mode of tungsten alloy with adding trace yttrium was changed from intergranular fracture transition of pure tungsten to mainly intergranular fracture and part transgranular fracture.
2017, 46(6):1709-1713.
Abstract:
Highly ordered Au@Al2O33DOM composites with different pore diameters, including0.48, 0.96, 1.27, 1.49 and 1.65μm, were prepared via infilling Al2O3 into the gaps of PS colloidal crystal templates with colloidal crystal template techniquce. The morphology characters and catalytic activity of Au@Al2O3 3DOM composites were characterized by SEM, XRD and UV-Vis spectrometer, respectively. It was found that Au@Al2O33DOM composites had excellent catalytic performance. As the pore diameters increased, the catalytic performance increasedSrapidly and then decreased gradually. The catalytic activity was highest, when the pore size of the composite material reached1.27 μm. The results of theoretical analysis indicated that effective active area and channel transmission efficiency varied with the change of the microstructure, and the competition between the effective active area and the channel transmission efficiency resulted in the chang of the catalytic performance.
Highly ordered Au@Al2O33DOM composites with different pore diameters, including0.48, 0.96, 1.27, 1.49 and 1.65μm, were prepared via infilling Al2O3 into the gaps of PS colloidal crystal templates with colloidal crystal template techniquce. The morphology characters and catalytic activity of Au@Al2O3 3DOM composites were characterized by SEM, XRD and UV-Vis spectrometer, respectively. It was found that Au@Al2O33DOM composites had excellent catalytic performance. As the pore diameters increased, the catalytic performance increasedSrapidly and then decreased gradually. The catalytic activity was highest, when the pore size of the composite material reached1.27 μm. The results of theoretical analysis indicated that effective active area and channel transmission efficiency varied with the change of the microstructure, and the competition between the effective active area and the channel transmission efficiency resulted in the chang of the catalytic performance.
2017, 46(6):1714-1718.
Abstract:
ITO nanopowders were prepared by chemical coprecipitation , NH4Cl-NH3H2O,(NH4)2SO4-NH3H2O and NH4AC solution were used as buffer solution to remain the pH value unchanged, simultaneously, the powders were prepared with different dispersants, the effects of buffer solution and dispersant on pHase structure,morpHology ,conductivity and the dispersion were characterized by XRD, TEM,FourSpoint probe and BET .The results show that the powders prepared with the buffer solution is single-pHase In2O3 structure.When the nanopowders prepared under the conditions of NH4AC as buffer solution, soluble starches as dispersant, the pH value 6 to 7, the obtained powder is with about 10 nm particle size,uniform particle size, and good dispersibility ,and simultaneously the powders is inerratic cubic shape with relatively good electrical conductivity.
ITO nanopowders were prepared by chemical coprecipitation , NH4Cl-NH3H2O,(NH4)2SO4-NH3H2O and NH4AC solution were used as buffer solution to remain the pH value unchanged, simultaneously, the powders were prepared with different dispersants, the effects of buffer solution and dispersant on pHase structure,morpHology ,conductivity and the dispersion were characterized by XRD, TEM,FourSpoint probe and BET .The results show that the powders prepared with the buffer solution is single-pHase In2O3 structure.When the nanopowders prepared under the conditions of NH4AC as buffer solution, soluble starches as dispersant, the pH value 6 to 7, the obtained powder is with about 10 nm particle size,uniform particle size, and good dispersibility ,and simultaneously the powders is inerratic cubic shape with relatively good electrical conductivity.
2017, 46(6):1719-1722.
Abstract:
Due to high surface activity of nano Sn powder, the mixture powders containing in-situ nano Mg2Sn phase were synthesized efficiently by milling micro Mg powders and nano Sn powders. High-performance Mg2Sn/Mg composites were then prepared by hot-press sintering from the milled mixture powders. Effect of milling time on microstructure and properties of Mg2Sn/Mg composites were investigated comparatively. The results show that, with the increase of milling time, the size of Mg2Sn clusters consisting of Mg2Sn nanophase decreases continuously, and Mg2Sn clusters are distributed uniformly in the matrix. Moreover, the mechanical properties of sintered Mg2Sn/Mg composites are also gradually improved.
Due to high surface activity of nano Sn powder, the mixture powders containing in-situ nano Mg2Sn phase were synthesized efficiently by milling micro Mg powders and nano Sn powders. High-performance Mg2Sn/Mg composites were then prepared by hot-press sintering from the milled mixture powders. Effect of milling time on microstructure and properties of Mg2Sn/Mg composites were investigated comparatively. The results show that, with the increase of milling time, the size of Mg2Sn clusters consisting of Mg2Sn nanophase decreases continuously, and Mg2Sn clusters are distributed uniformly in the matrix. Moreover, the mechanical properties of sintered Mg2Sn/Mg composites are also gradually improved.
2017, 46(6):1723-1726.
Abstract:
For preventing hydrogen lossing from zirconium hydride, zirconium oxide films were prepared on the surface of zirconium hydride by Sol-Gel method. Zirconium n-propoxide was precursor in reaction system. The influence of heat treatment temperature on phase composition, surface morphologies, cross-sectional morphologies and hydrogen resistance performance of zirconium oxide films were researched in this paper. The phase composition, surface morphologies and cross-sectional morphologies were characterized by X-ray diffractometer(XRD) , confocal laser scanning microscope(CLSM) and scanning election microscopy(SEM), respectively. Hydrogen resistance performance was evaluated by the experiment of vacuum dehydrogenation testing. The results showed that the continuous and dense zirconium oxide films are formed on the surface of zirconium hydride when heat treatment temperature is 600℃. The PRF values of zirconium oxide films present the trend that increase at first,then decrease with increasing of heat treatment temperature. The maximum PRF value of zirconium oxide films reach 8.6 at 600℃. The phase structure of zirconium oxide films is both tetragonal phase T-ZrO1.8 and monoclinic phase M-ZrO1.8, and the films is mainly composed of monoclinic phase M-ZrO1.8.
For preventing hydrogen lossing from zirconium hydride, zirconium oxide films were prepared on the surface of zirconium hydride by Sol-Gel method. Zirconium n-propoxide was precursor in reaction system. The influence of heat treatment temperature on phase composition, surface morphologies, cross-sectional morphologies and hydrogen resistance performance of zirconium oxide films were researched in this paper. The phase composition, surface morphologies and cross-sectional morphologies were characterized by X-ray diffractometer(XRD) , confocal laser scanning microscope(CLSM) and scanning election microscopy(SEM), respectively. Hydrogen resistance performance was evaluated by the experiment of vacuum dehydrogenation testing. The results showed that the continuous and dense zirconium oxide films are formed on the surface of zirconium hydride when heat treatment temperature is 600℃. The PRF values of zirconium oxide films present the trend that increase at first,then decrease with increasing of heat treatment temperature. The maximum PRF value of zirconium oxide films reach 8.6 at 600℃. The phase structure of zirconium oxide films is both tetragonal phase T-ZrO1.8 and monoclinic phase M-ZrO1.8, and the films is mainly composed of monoclinic phase M-ZrO1.8.
2017, 46(6):1727-1730.
Abstract:
An alumina coating with a thickness of 65μm was prepared on depleted uranium surface by cathodic microarc desposition in 1mol/L Al(NO3)3.9H2O ethanol solution. The morphology, composition and phase constituent of alumina coating were analyzed by SEM, XRDand EDS. The corrosion resistance were determined by electrochemical integrated test system. The results show that the coating, which is composed of α-Al2O3and γ- Al2O3, remain a good adhesion to depleted uranium substrate. The coating contains a little uranium element, which confirms that depleted uranium substrate near the coating /uranium also takes part in the sintering process of coating under cathodic microarc discharge. The coating reduce the depleted corrosion current by two orders-of-magnitude, which shows the good corrosion resistance.
An alumina coating with a thickness of 65μm was prepared on depleted uranium surface by cathodic microarc desposition in 1mol/L Al(NO3)3.9H2O ethanol solution. The morphology, composition and phase constituent of alumina coating were analyzed by SEM, XRDand EDS. The corrosion resistance were determined by electrochemical integrated test system. The results show that the coating, which is composed of α-Al2O3and γ- Al2O3, remain a good adhesion to depleted uranium substrate. The coating contains a little uranium element, which confirms that depleted uranium substrate near the coating /uranium also takes part in the sintering process of coating under cathodic microarc discharge. The coating reduce the depleted corrosion current by two orders-of-magnitude, which shows the good corrosion resistance.
2017, 46(6):1731-1733.
Abstract:
Tritium titanium target is an important assembly used in a D-T type neutron generator, and the problem is the coexistence of the decayed helium and hydrogen isotope is inevitable in tritium-contained materials, and the stability of the tritium titanium target is influenced by the inner evolution of helium bubbles. It is therefore of essence to study the effect of ion irradiations on the lifetime of tritium titanium targets with a long storage time in a neutron generator. Both surface morphologies, surface element types and surface phase structures were measured for the original or irradiated tritide targets. Results reflected that Mo and Ti were the main elements remained on the irradiated surface, and hardly any trace of Ti or TiTx could be detected on the surface. It finally arrived that after a storage time of nearly 12 years, the main part of the tritide film were striped by inner evolved helium bubbles.
Tritium titanium target is an important assembly used in a D-T type neutron generator, and the problem is the coexistence of the decayed helium and hydrogen isotope is inevitable in tritium-contained materials, and the stability of the tritium titanium target is influenced by the inner evolution of helium bubbles. It is therefore of essence to study the effect of ion irradiations on the lifetime of tritium titanium targets with a long storage time in a neutron generator. Both surface morphologies, surface element types and surface phase structures were measured for the original or irradiated tritide targets. Results reflected that Mo and Ti were the main elements remained on the irradiated surface, and hardly any trace of Ti or TiTx could be detected on the surface. It finally arrived that after a storage time of nearly 12 years, the main part of the tritide film were striped by inner evolved helium bubbles.
2017, 46(6):1734-1748.
Abstract:
As a novel kind of titanium alloy materials, titanium foams or porous titanium has been obtained a rapid development in recent years. They are attractive for aerospace, biomedical, submarine, automobile and environmental protection applications because of their double attribute of structural and functional properties. This paper attempts to give a review on the newly-presented preparation methods of titanium foams or porous titanium since 2004. The methods are divided into two categories. A first group is based on powder metallurgy and the another is based on physical or chemical synthesis. The preparation process, technology characteristics, pore structure and properties of obtained titanium foams or porous titanium of each method are introduced in detail and its development tendency was as-pointed out through a comparative analysis.
As a novel kind of titanium alloy materials, titanium foams or porous titanium has been obtained a rapid development in recent years. They are attractive for aerospace, biomedical, submarine, automobile and environmental protection applications because of their double attribute of structural and functional properties. This paper attempts to give a review on the newly-presented preparation methods of titanium foams or porous titanium since 2004. The methods are divided into two categories. A first group is based on powder metallurgy and the another is based on physical or chemical synthesis. The preparation process, technology characteristics, pore structure and properties of obtained titanium foams or porous titanium of each method are introduced in detail and its development tendency was as-pointed out through a comparative analysis.
