Volume 47,Issue 10,2018 Table of Contents
2018, 47(10):2919-2926.
Abstract:
The thermodynamic assessment of the Co-Nb-W ternary system has been carried out by applying the CALPHAD method. A slight modification of the Co-W binary system has been performed to unify the model of μ phase in Co-Nb-W system. The three published isothermal sections at 1273, 1373 and 1473 K have been critically examined and used to optimize the model parameters. The solution phases, including αCo and BCC were modeled as substitutional solutions; the λ, χ, and Co3Nb phases have been assessed by using two-sublattice models. The Co7W6 and Co7Nb6 phases were described as (Co, Nb)1(Co, Nb, W)2(Co, Nb, W)4(Co)6. Calculated isothermal sections and vertical sections agreed well with the experimental data.
The thermodynamic assessment of the Co-Nb-W ternary system has been carried out by applying the CALPHAD method. A slight modification of the Co-W binary system has been performed to unify the model of μ phase in Co-Nb-W system. The three published isothermal sections at 1273, 1373 and 1473 K have been critically examined and used to optimize the model parameters. The solution phases, including αCo and BCC were modeled as substitutional solutions; the λ, χ, and Co3Nb phases have been assessed by using two-sublattice models. The Co7W6 and Co7Nb6 phases were described as (Co, Nb)1(Co, Nb, W)2(Co, Nb, W)4(Co)6. Calculated isothermal sections and vertical sections agreed well with the experimental data.
2018, 47(10):2927-2935.
Abstract:
Grain boundary character and microstructural evolution during hot deformation of a high Nb-containing TiAl alloy with the composition of Ti-45Al-8.5Nb-(W,B,Y) have been investigated in this work. The plasma arc-melted alloy exhibits nearly lamellar microstructures with β/B2 phase precipitating along colony boundaries. The retained β/B2 phase rich in Ti, Nb and W and poor in Al is believed to be formed by the β → α transformation during nonequilibrium solidification. This β/B2 precipitation is caused by the relative high cooling rate, low atom diffusion rate of β stabilizers and different partition coefficient of the elements. B and Y elements exist mainly as borides and Y2O3, respectively. The morphology, size, composition and stability of β/B2 phase are determined by hot deformation. The high temperature and press enhance the elements diffusion, thus the variation of the composition of β/B2 phase in deformed samples is obviously observed. When the samples are deformed in (α + γ) phase region, the transformation β/B2 → α2 takes place. Considering the different crystal structures between β/B2 and α2 phases, there is a tendency for β/B2 phase to transform to an increased close packed structure of α2 during deformation. The β/B2 → α2 transformation is promoted by the hot deformation.
Grain boundary character and microstructural evolution during hot deformation of a high Nb-containing TiAl alloy with the composition of Ti-45Al-8.5Nb-(W,B,Y) have been investigated in this work. The plasma arc-melted alloy exhibits nearly lamellar microstructures with β/B2 phase precipitating along colony boundaries. The retained β/B2 phase rich in Ti, Nb and W and poor in Al is believed to be formed by the β → α transformation during nonequilibrium solidification. This β/B2 precipitation is caused by the relative high cooling rate, low atom diffusion rate of β stabilizers and different partition coefficient of the elements. B and Y elements exist mainly as borides and Y2O3, respectively. The morphology, size, composition and stability of β/B2 phase are determined by hot deformation. The high temperature and press enhance the elements diffusion, thus the variation of the composition of β/B2 phase in deformed samples is obviously observed. When the samples are deformed in (α + γ) phase region, the transformation β/B2 → α2 takes place. Considering the different crystal structures between β/B2 and α2 phases, there is a tendency for β/B2 phase to transform to an increased close packed structure of α2 during deformation. The β/B2 → α2 transformation is promoted by the hot deformation.
2018, 47(10):2936-2941.
Abstract:
Ni7W/Ni12W/Ni7W composite substrates for YBa2Cu3O7-δ coated conductors were prepared by rolling assisted biaxially textured substrates route. A threefold intermediate annealing at different temperatures was introduced in the rolling process of Ni7W/Ni12W/Ni7W composite substrates to better its deformation texture. The recovery microstructure and the deformation texture of latitude and longitude section were studied with X-ray diffraction and electron backscattered diffraction to reveal the possible mechanism of temperature effects on rolling and strong cube texture formation processes. The results show that the highest cube area fraction is found in sample intermediately annealed at 600S°C/60Smin, in this way Ni7W/Ni12W/Ni7W composite substrates with high cube texture content of 95% (<10°) are obtained at a low recrystallization annealing temperature. Crystal orientation maps reveal that a higher amount of cube orientation exists in its recovery and initial recrystallization samples. Point to point misorientation files confirms the high grain boundary angle of these cube grains, which strongly boost the cube texture formation during subsequent recrystallization.
Ni7W/Ni12W/Ni7W composite substrates for YBa2Cu3O7-δ coated conductors were prepared by rolling assisted biaxially textured substrates route. A threefold intermediate annealing at different temperatures was introduced in the rolling process of Ni7W/Ni12W/Ni7W composite substrates to better its deformation texture. The recovery microstructure and the deformation texture of latitude and longitude section were studied with X-ray diffraction and electron backscattered diffraction to reveal the possible mechanism of temperature effects on rolling and strong cube texture formation processes. The results show that the highest cube area fraction is found in sample intermediately annealed at 600S°C/60Smin, in this way Ni7W/Ni12W/Ni7W composite substrates with high cube texture content of 95% (<10°) are obtained at a low recrystallization annealing temperature. Crystal orientation maps reveal that a higher amount of cube orientation exists in its recovery and initial recrystallization samples. Point to point misorientation files confirms the high grain boundary angle of these cube grains, which strongly boost the cube texture formation during subsequent recrystallization.
2018, 47(10):2942-2948.
Abstract:
The effects of cryogenic treatment prior hot rolling on the strength toughness and ductility of as-cast AZ31 magnesium alloy plate was investigated in this study. The cryogenic treatment conditions were ?60 °C/12 h, ?120 °C/12 h, ?180 °C/12 h, ?60 °C/2 h, and ?180 °C/2 h. Experimental results indicated that appropriate cryogenic treatment conditions can significantly refine the grain size and the strength, toughness and ductility were also improved. A large number of twins appeared in both kinds of samples cryogenically treated for 2 h. The grain size of the sample, which experienced cryogenic treatment for 12 h at ?60 °C followed by rolling process was the finest and most uniform. By increasing cryogenic treatment duration to 12 h, the yield strength of the AZ31 magnesium alloy was enhanced by 25.8% after rolling under ?60 °C cryogenic treatment temperature. Meanwhile, a four-time increase in extension rate (3.06% to 12.31%) was attained. The tensile fracture presented a mixed-mode fracture, which is characteristic of brittle and ductile fracture mechanisms.
The effects of cryogenic treatment prior hot rolling on the strength toughness and ductility of as-cast AZ31 magnesium alloy plate was investigated in this study. The cryogenic treatment conditions were ?60 °C/12 h, ?120 °C/12 h, ?180 °C/12 h, ?60 °C/2 h, and ?180 °C/2 h. Experimental results indicated that appropriate cryogenic treatment conditions can significantly refine the grain size and the strength, toughness and ductility were also improved. A large number of twins appeared in both kinds of samples cryogenically treated for 2 h. The grain size of the sample, which experienced cryogenic treatment for 12 h at ?60 °C followed by rolling process was the finest and most uniform. By increasing cryogenic treatment duration to 12 h, the yield strength of the AZ31 magnesium alloy was enhanced by 25.8% after rolling under ?60 °C cryogenic treatment temperature. Meanwhile, a four-time increase in extension rate (3.06% to 12.31%) was attained. The tensile fracture presented a mixed-mode fracture, which is characteristic of brittle and ductile fracture mechanisms.
2018, 47(10):2949-2956.
Abstract:
INCONEL 718 superalloy samples with V-grooves were experimentally repaired by electromagnetic stirring assisted laser repairing (EMS-LR) under different magnetic field currents. The effects of the magnetic field current on morphologies of single pass repaired zone (RZ), microstructure and mechanical properties of multilayer RZ were experimentally investigated. Microstructure observations show that metallurgical bonding was obtained between the RZ and the substrate when the optimized process parameter was used. The microstructure in RZ is coarse columnar crystal when no electromagnetic stirring was used, which growing epitaxially along the deposition direction. With the increase of magnetic field current, the convection of liquid metals prompts the transformation from the coarse columnar to fine equixed grains. The strong scour of liquid metal convection can affect the interdendritic g+Laves eutectic reaction and prohibit the growth of Laves phase. Electromagnetic stirring can improve the spreading of liquid metal in a certain extent. The width and deposition height of the single trace were measured and it was found that the width and deposition height ratio changed from 3.26 when no electromagnetic stirring was used to 3.33, 4.14 and 5.14 when the applied magnetic field current was 20, 40 and 60A, respectively, and the penetration was fond to be decreased inversely. The tensile strengths of repaired components increased from 487 MPa to 510, 673 and 770MPa for magnetic field currents of 0, 20, 40 and 60 A, respectively.
INCONEL 718 superalloy samples with V-grooves were experimentally repaired by electromagnetic stirring assisted laser repairing (EMS-LR) under different magnetic field currents. The effects of the magnetic field current on morphologies of single pass repaired zone (RZ), microstructure and mechanical properties of multilayer RZ were experimentally investigated. Microstructure observations show that metallurgical bonding was obtained between the RZ and the substrate when the optimized process parameter was used. The microstructure in RZ is coarse columnar crystal when no electromagnetic stirring was used, which growing epitaxially along the deposition direction. With the increase of magnetic field current, the convection of liquid metals prompts the transformation from the coarse columnar to fine equixed grains. The strong scour of liquid metal convection can affect the interdendritic g+Laves eutectic reaction and prohibit the growth of Laves phase. Electromagnetic stirring can improve the spreading of liquid metal in a certain extent. The width and deposition height of the single trace were measured and it was found that the width and deposition height ratio changed from 3.26 when no electromagnetic stirring was used to 3.33, 4.14 and 5.14 when the applied magnetic field current was 20, 40 and 60A, respectively, and the penetration was fond to be decreased inversely. The tensile strengths of repaired components increased from 487 MPa to 510, 673 and 770MPa for magnetic field currents of 0, 20, 40 and 60 A, respectively.
6 Effect of Zn content on the microstructure and mechanical properties of the extruded Mg-6Gd-4Y alloy
2018, 47(10):2957-2963.
Abstract:
Microstructures and mechanical properties of the Mg-6Gd-4Y(wt.%) alloys with and without 1% Zn additions have been investigated. The results showed that the as-cast microstructure of the Mg-6Gd-4Y alloy studied consisted of the α-Mg matrix and Mg24(GdY)5 secondary phase. However, the as-cast microstructure of the Zn-containing Mg-6Gd-4Y-1Zn alloy studied consisted of the ?-Mg matrix, Mg24(GdY)5 secondary phase and Mg12Y1Zn1 phase which had a 18R long period staking ordered (18R-LPSO) structure. After extrusion the 14H-LPSO phase had been found in the Zn-containing alloy and distributed between the 18R-LPSO strips in the as extruded microstructure. The formation mechanism of the 14H-LPSO phase is precipitation, and the reaction can be expressed as ‘α-Mg′ → α-Mg + 14H’. Zn content had no obvious effect on the precipitation of β series. Aging conducted(T6 and T5 treatment) on both the Mg-6Gd-4Y alloy and the Mg-6Gd-4Y-1Zn alloy caused the formation of β" precipitates. The T6-aging Mg-6Gd-4Y-1Zn alloy exhibited high tensile strength combined with good ductility, and the values of the yield strength (YS), ultimate tensile strength (UTS) and elongation were 309MPa, 438MPa and 6.8%, respectively. It was due to the coexistence of 18R-LPSO phase and small dispersed distribution of the 14H-LPSO phase and the β" precipitates in the microstructure.
Microstructures and mechanical properties of the Mg-6Gd-4Y(wt.%) alloys with and without 1% Zn additions have been investigated. The results showed that the as-cast microstructure of the Mg-6Gd-4Y alloy studied consisted of the α-Mg matrix and Mg24(GdY)5 secondary phase. However, the as-cast microstructure of the Zn-containing Mg-6Gd-4Y-1Zn alloy studied consisted of the ?-Mg matrix, Mg24(GdY)5 secondary phase and Mg12Y1Zn1 phase which had a 18R long period staking ordered (18R-LPSO) structure. After extrusion the 14H-LPSO phase had been found in the Zn-containing alloy and distributed between the 18R-LPSO strips in the as extruded microstructure. The formation mechanism of the 14H-LPSO phase is precipitation, and the reaction can be expressed as ‘α-Mg′ → α-Mg + 14H’. Zn content had no obvious effect on the precipitation of β series. Aging conducted(T6 and T5 treatment) on both the Mg-6Gd-4Y alloy and the Mg-6Gd-4Y-1Zn alloy caused the formation of β" precipitates. The T6-aging Mg-6Gd-4Y-1Zn alloy exhibited high tensile strength combined with good ductility, and the values of the yield strength (YS), ultimate tensile strength (UTS) and elongation were 309MPa, 438MPa and 6.8%, respectively. It was due to the coexistence of 18R-LPSO phase and small dispersed distribution of the 14H-LPSO phase and the β" precipitates in the microstructure.
2018, 47(10):2964-2969.
Abstract:
At the temperature range of 760 °C to 1100 °C, the transverse tensile properties of a nickel-based third generation single crystal superalloy were studied. The microstructures and fracture surfaces were observed by optical microscopy (OM), field emission scanning electron microscopy (FESEM) and scanning transmission electron microscopy (STEM). The results show that the tensile strength of the alloy decreases as the temperature increases, while the tensile elongation of the alloy increases with the temperature increasing. The fracture surfaces of the tensile ruptured specimens are characterized by quasi-cleavage features at 760 °C and 850 °C. At the temperature range of 980 °C to 1100 °C, dendrites characteristics exhibiting the solidification direction are observed on the fracture surfaces and the proportion of dendrites characteristic on the fracture surfaces increases with the temperature increasing. The fracture surface displays mixed quasi-cleavage and dimple features at 980 °C. The fracture surfaces are characterized by dimple features at 1070 °C and 1100 °C. As the temperature increases, more slip systems tend to be activated during the plastic deformation, result in different dislocation configurations. At 760 °C, high density a/2<110> dislocations are found to distribute roughly parallel with each other in the tensile ruptured specimens. The dislocations are observed to be tangled at 980 °C and dislocation networks have formed at 1100 °C.
At the temperature range of 760 °C to 1100 °C, the transverse tensile properties of a nickel-based third generation single crystal superalloy were studied. The microstructures and fracture surfaces were observed by optical microscopy (OM), field emission scanning electron microscopy (FESEM) and scanning transmission electron microscopy (STEM). The results show that the tensile strength of the alloy decreases as the temperature increases, while the tensile elongation of the alloy increases with the temperature increasing. The fracture surfaces of the tensile ruptured specimens are characterized by quasi-cleavage features at 760 °C and 850 °C. At the temperature range of 980 °C to 1100 °C, dendrites characteristics exhibiting the solidification direction are observed on the fracture surfaces and the proportion of dendrites characteristic on the fracture surfaces increases with the temperature increasing. The fracture surface displays mixed quasi-cleavage and dimple features at 980 °C. The fracture surfaces are characterized by dimple features at 1070 °C and 1100 °C. As the temperature increases, more slip systems tend to be activated during the plastic deformation, result in different dislocation configurations. At 760 °C, high density a/2<110> dislocations are found to distribute roughly parallel with each other in the tensile ruptured specimens. The dislocations are observed to be tangled at 980 °C and dislocation networks have formed at 1100 °C.
2018, 47(10):2970-2975.
Abstract:
On ITER (International Thermal Nuclear Experimental Reactor) superconducting fusion device, the Nb3Sn composite strands have been applied to CICC (cable-in-conduit conductor) to meet the impact of the magnet field above 12 T. The strain of Nb3Sn-based conductor due to Lorentz forces leads to the change of critical current and coupling loss time constant. However, the study on critical performance degradation of CICC is still inadequate. Moreover, the most important is that the influence exploration of the contact properties with strain on coupling loss time constant is also insufficient. In order to calculate coupling loss accurately and quickly, a new calculation model of coupling loss time constant was put forward in this paper, which is expressed with a linear equation using some parameters that is the cabling sequence ratio, the contact resistance and the void fraction with strain main from electromagnetic force. In this model, not only the computation expression of cabling sequence ratio is given, but also the contact resistance and the void fraction is obtained with strain (from electromagnetic load cycle). Compared with numerical calculation using Gandalf and traditional method, the error of coupling loss calculated with the combination of the cabling sequence ratio, the contact resistance and the void fraction with strain is small, which is close to the engineering measured value.
On ITER (International Thermal Nuclear Experimental Reactor) superconducting fusion device, the Nb3Sn composite strands have been applied to CICC (cable-in-conduit conductor) to meet the impact of the magnet field above 12 T. The strain of Nb3Sn-based conductor due to Lorentz forces leads to the change of critical current and coupling loss time constant. However, the study on critical performance degradation of CICC is still inadequate. Moreover, the most important is that the influence exploration of the contact properties with strain on coupling loss time constant is also insufficient. In order to calculate coupling loss accurately and quickly, a new calculation model of coupling loss time constant was put forward in this paper, which is expressed with a linear equation using some parameters that is the cabling sequence ratio, the contact resistance and the void fraction with strain main from electromagnetic force. In this model, not only the computation expression of cabling sequence ratio is given, but also the contact resistance and the void fraction is obtained with strain (from electromagnetic load cycle). Compared with numerical calculation using Gandalf and traditional method, the error of coupling loss calculated with the combination of the cabling sequence ratio, the contact resistance and the void fraction with strain is small, which is close to the engineering measured value.
2018, 47(10):2976-2979.
Abstract:
The effects of the addition of Pr6O11 nanopowder on the critical current density (Jc), irreversibility field (Hirr) and upper critical field (Hc2) of the MgB2 bulks prepared by a Mg-diffusion method were investigated. The experimental results showed that Jc, Hirr and Hc2 of the MgB2 bulks have been enhanced systematically by Pr6O11 nanopowder doping, but the superconducting transition temperature (Tc) was little affected. At 20 K in a self-field, the Jc value for the 1 wt.% Pr6O11-doped MgB2 sample was 3.61×105A/cm2, which was nearly five times larger than the undoped sample. In addition, at 10 K, the Hc2 and Hirr of the bulk increased by 1.9 T and 2.6 T, respectively. The Pr6O11-dopingmechanism on superconductivity and flux pinning was also discussed.
The effects of the addition of Pr6O11 nanopowder on the critical current density (Jc), irreversibility field (Hirr) and upper critical field (Hc2) of the MgB2 bulks prepared by a Mg-diffusion method were investigated. The experimental results showed that Jc, Hirr and Hc2 of the MgB2 bulks have been enhanced systematically by Pr6O11 nanopowder doping, but the superconducting transition temperature (Tc) was little affected. At 20 K in a self-field, the Jc value for the 1 wt.% Pr6O11-doped MgB2 sample was 3.61×105A/cm2, which was nearly five times larger than the undoped sample. In addition, at 10 K, the Hc2 and Hirr of the bulk increased by 1.9 T and 2.6 T, respectively. The Pr6O11-dopingmechanism on superconductivity and flux pinning was also discussed.
10 Superhydrophobic Micro-nano Structures on 5A05 Al Alloy Surface with Enhanced Corrosion Resistance
2018, 47(10):2980-2985.
Abstract:
Corrosion failure is a bottleneck problem that restricts the application of Al alloys. As a stable technology for functional implementation, the superhydrophobic fabrication exactly provides an effective method to solve metallic corrosion. This work develops a simple and low-cost method to endow 5A05 Al alloy with superior superhydrophobicity and corrosion resistance. The microscale wrinkles covered with nanoscale craters are prepared by one-step wire electrical discharge machining process. Meanwhile, the wettability and corrosion resistance of as-prepared structures are investigated after the low-surface-energy modification. The results show that the modified surface exhibits excellent superhydrophobicity with a water contact angle (CA) of 152.7° and a sliding angle (SA) of 7.1°. Furthermore, its corrosion resistance is assessed by the electrochemical tests. Ultimately, owing to the trapped air in micro-nano structures, the solid-air-liquid interfaces help to resist seawater penetration on the superhydrophobic surface as well as significantly enhance its corrosion resistance. This work sheds insights into extending the applications of Al alloys in many areas especially for oceaneering fields.
Corrosion failure is a bottleneck problem that restricts the application of Al alloys. As a stable technology for functional implementation, the superhydrophobic fabrication exactly provides an effective method to solve metallic corrosion. This work develops a simple and low-cost method to endow 5A05 Al alloy with superior superhydrophobicity and corrosion resistance. The microscale wrinkles covered with nanoscale craters are prepared by one-step wire electrical discharge machining process. Meanwhile, the wettability and corrosion resistance of as-prepared structures are investigated after the low-surface-energy modification. The results show that the modified surface exhibits excellent superhydrophobicity with a water contact angle (CA) of 152.7° and a sliding angle (SA) of 7.1°. Furthermore, its corrosion resistance is assessed by the electrochemical tests. Ultimately, owing to the trapped air in micro-nano structures, the solid-air-liquid interfaces help to resist seawater penetration on the superhydrophobic surface as well as significantly enhance its corrosion resistance. This work sheds insights into extending the applications of Al alloys in many areas especially for oceaneering fields.
2018, 47(10):2986-2992.
Abstract:
A NiFeBSiNb amorphous/nanocrystalline composite coating was prepared through flame thermal spraying, where a gas atomized alloy powder substituted an amorphous powder. The microstructure and thermal behavior of the laboratory-produced powders and the produced as-sprayed coating were characterized. The results demonstrated that the powder, which was spherical or ellipsoidal, was mainly consisted of the Nb2Ni21B6 and (Ni,Fe)23B6 crystalline phases, whereas the as-sprayed coating was consisted of a glassy structure and certain nanocrystalline phases. It was observed through calculations that the Rc (critical cooling rate) of the powder and the as-sprayed coating for the amorphous phases formations were 6.01×105 K/s and 4.56×103 K/s, respectively. A probable explanation for the amorphous structure, as it occurred in the as-sprayed coating, was rapid quenching from the melt at the cooling rates which exceeded the critical cooling rate Rc. The prepared coating of these as-sprayed amorphous coatings displayed the properties of a 0.17 low friction coefficient and excellent wear resistance.
A NiFeBSiNb amorphous/nanocrystalline composite coating was prepared through flame thermal spraying, where a gas atomized alloy powder substituted an amorphous powder. The microstructure and thermal behavior of the laboratory-produced powders and the produced as-sprayed coating were characterized. The results demonstrated that the powder, which was spherical or ellipsoidal, was mainly consisted of the Nb2Ni21B6 and (Ni,Fe)23B6 crystalline phases, whereas the as-sprayed coating was consisted of a glassy structure and certain nanocrystalline phases. It was observed through calculations that the Rc (critical cooling rate) of the powder and the as-sprayed coating for the amorphous phases formations were 6.01×105 K/s and 4.56×103 K/s, respectively. A probable explanation for the amorphous structure, as it occurred in the as-sprayed coating, was rapid quenching from the melt at the cooling rates which exceeded the critical cooling rate Rc. The prepared coating of these as-sprayed amorphous coatings displayed the properties of a 0.17 low friction coefficient and excellent wear resistance.
2018, 47(10):2993-2999.
Abstract:
Calcium phosphate (Ca-P) coatings were deposited on AZ31 magnesium by hydrothermal treatment t at various pH o improve the corrosion resistance and biocompatibility of magnesium alloys. Crystal phase, morphology and composition of the coatings were investigated by XRD, SEM and EDS, respectively. The electrochemical measurements and immersion tests in Hank’s solution were performed to examine the bio-corrosion behaviors of the coated specimens. The results showed that the pH value of solutions influenced the phase composition and microstructure of the coating. And the degree of protection afforded by Ca-P coating varies with their microstructure. The deposited Ca-P coating treated at pH6 was composed of Mg3(PO4)2 and OCP. When the pH values increased, only the HA was formed. The HA coating with nano-scale and rod-like crystals prepared at pH10 can prevent the penetration of solution more effectively than the OCP at pH6 and honeycomb-like HA coating at pH8.
Calcium phosphate (Ca-P) coatings were deposited on AZ31 magnesium by hydrothermal treatment t at various pH o improve the corrosion resistance and biocompatibility of magnesium alloys. Crystal phase, morphology and composition of the coatings were investigated by XRD, SEM and EDS, respectively. The electrochemical measurements and immersion tests in Hank’s solution were performed to examine the bio-corrosion behaviors of the coated specimens. The results showed that the pH value of solutions influenced the phase composition and microstructure of the coating. And the degree of protection afforded by Ca-P coating varies with their microstructure. The deposited Ca-P coating treated at pH6 was composed of Mg3(PO4)2 and OCP. When the pH values increased, only the HA was formed. The HA coating with nano-scale and rod-like crystals prepared at pH10 can prevent the penetration of solution more effectively than the OCP at pH6 and honeycomb-like HA coating at pH8.
2018, 47(10):3000-3007.
Abstract:
The precipitation process of Ni75Al15Ti10 alloy was simulated by microscopic phase-field kinetics model. The microscopic morphology evolution is firstly studied, which indicates that the precipitation process has been divided into two stages: the first is the transformation from L10 phase to L12 phase, the second is the formation of stoichiometric L12 phase. The effect of single aging temperature on the microstructure and atomic occupation probability and atomic diffusion are subsequently investigated. The result shows that the shape of γ′ precipitates is transformed from irregular shape to regular cuboid and the degree of orientation growth enhances with the increasing of aging temperature. But the higher aging temperature, the lower occupation probability and lower order degree. Meanwhile, the path of diffusion of Al is from the interface to the internal of γ" phase, and the diffusion of Ti atom is the opposite. Furthermore, we further study the dual aging with the purpose of improving occupation probability of γ′ precipitates and discuss its influence on the γ′ phase. Dual aging can not only obtain stable γ" phase with regular shape, but also can increase the occupation probability of Al and Ti and inhibit the formation of anti-site defects. Our results provide useful information in preparing Ni-Al-Ti alloy with excellent mechanical properties to some extent.
The precipitation process of Ni75Al15Ti10 alloy was simulated by microscopic phase-field kinetics model. The microscopic morphology evolution is firstly studied, which indicates that the precipitation process has been divided into two stages: the first is the transformation from L10 phase to L12 phase, the second is the formation of stoichiometric L12 phase. The effect of single aging temperature on the microstructure and atomic occupation probability and atomic diffusion are subsequently investigated. The result shows that the shape of γ′ precipitates is transformed from irregular shape to regular cuboid and the degree of orientation growth enhances with the increasing of aging temperature. But the higher aging temperature, the lower occupation probability and lower order degree. Meanwhile, the path of diffusion of Al is from the interface to the internal of γ" phase, and the diffusion of Ti atom is the opposite. Furthermore, we further study the dual aging with the purpose of improving occupation probability of γ′ precipitates and discuss its influence on the γ′ phase. Dual aging can not only obtain stable γ" phase with regular shape, but also can increase the occupation probability of Al and Ti and inhibit the formation of anti-site defects. Our results provide useful information in preparing Ni-Al-Ti alloy with excellent mechanical properties to some extent.
2018, 47(10):3008-3014.
Abstract:
In order to overcome defects of high over-potential and preparation cost existing in traditional Pb alloy anode, a new type aluminum foam/Pb-0.6wt%Ag alloy composite anode (AF/Pb-0.6 wt%Ag anode) was produced in this paper. And the electrochemical performance of AF/Pb-0.6 wt%Ag anode and traditional Pb-0.6 wt%Ag anode after 72 h galvanostic polarization were investigated comparatively in 160 g/L H2SO4 solution by chronopotentiometry(CP), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and Tafel measurements. The results show that the anodic layer of AF/Pb-0.6 wt%Ag anode is more intact than that of Pb-0.6wt%Ag anode, and exhibits better corrosion resistance. Moreover, the AF/Pb-0.6 wt%Ag anode shows a lower stable anodic potential, which is consist with the higher PbO2, lower PbO, PbO?PbSO4 content and Rct value obtained by CP and EIS measurements. It is also revealed that the AF/Pb-0.6 wt%Ag anode possesses better oxygen evolution reaction (OER).
In order to overcome defects of high over-potential and preparation cost existing in traditional Pb alloy anode, a new type aluminum foam/Pb-0.6wt%Ag alloy composite anode (AF/Pb-0.6 wt%Ag anode) was produced in this paper. And the electrochemical performance of AF/Pb-0.6 wt%Ag anode and traditional Pb-0.6 wt%Ag anode after 72 h galvanostic polarization were investigated comparatively in 160 g/L H2SO4 solution by chronopotentiometry(CP), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and Tafel measurements. The results show that the anodic layer of AF/Pb-0.6 wt%Ag anode is more intact than that of Pb-0.6wt%Ag anode, and exhibits better corrosion resistance. Moreover, the AF/Pb-0.6 wt%Ag anode shows a lower stable anodic potential, which is consist with the higher PbO2, lower PbO, PbO?PbSO4 content and Rct value obtained by CP and EIS measurements. It is also revealed that the AF/Pb-0.6 wt%Ag anode possesses better oxygen evolution reaction (OER).
Yan Xin
,
Gao Qiang
,
Hui Xiaoyan
,
Yan Congxiang
,
AiTao
,
WangZhenjun
,
Sun Guodong
,
Su Xinghua
,
Zhao Peng
2018, 47(10):3015-3020.
Abstract:
The g-C3N4/MoS2 nanosheets were prepared via a facile ball milling method. The composite photocatalysts were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), UV–vis diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) spectroscopy. The results indicated that MoS2 nanosheets were successfully coupled into the g- C3N4 to form C3N4/ MoS2 heterojunction. The photocatalytic activities were evaluated by degradation of organic Rhodamine B (RhB) under visible light irradiation. The kinetic constant of RhB degradation with g-C3N4/MoS2 nanosheets-2 wt % heterojunction (0.0368 min?1) is about 4.3 as high as that of the bulk g-C3N4 (0.00840 min?1). The enhanced photocatalytic activities can be mainly ascribed to the efficient separation and transportation of photo-induced electron-hole pairs. The possible photocatalytic mechanism of composites was proposed according to the light trapping experiment.
The g-C3N4/MoS2 nanosheets were prepared via a facile ball milling method. The composite photocatalysts were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), UV–vis diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) spectroscopy. The results indicated that MoS2 nanosheets were successfully coupled into the g- C3N4 to form C3N4/ MoS2 heterojunction. The photocatalytic activities were evaluated by degradation of organic Rhodamine B (RhB) under visible light irradiation. The kinetic constant of RhB degradation with g-C3N4/MoS2 nanosheets-2 wt % heterojunction (0.0368 min?1) is about 4.3 as high as that of the bulk g-C3N4 (0.00840 min?1). The enhanced photocatalytic activities can be mainly ascribed to the efficient separation and transportation of photo-induced electron-hole pairs. The possible photocatalytic mechanism of composites was proposed according to the light trapping experiment.
2018, 47(10):3021-3029.
Abstract:
Based on numerical model established with actual parameters of raw material and processes, micro mechanism of metal rubber’s nonlinear stiffness was researched. Numerical model was verified in some respects, such as forming force, tissue structure, size and quasi-static loading curve. Tissue structure of metal rubber was decomposed. Elastic micro structure model and its local coordinate system were set up. Spatial motion, elastic deformation on z direction, and elastic deformation in xoy plane of elastic micro structure were studied. Mathematic model of metal rubber’s nonlinear stiffness property was built. Micro mechanism of nonlinear stiffness was described. The numerical model can coincide with experimental results well and be reliable. In quasi-static loading process, elastic micro structure’s translation is the main spatial motion, and its spatial rotation is very small. The elastic deformation on z direction can be regarded as parallel connection of several curved beams. The elastic deformation in xoy plane can be treated as a curved beam’s bending deformation making the distance of two endpoints smaller. The mathematical model agrees with test results well and it contains basic structure parameters, micro feature parameters and nonlinear stiffness mechanism parameters. These parameters have clear physical significance and the mathematic model has a high accuracy. Micro mechanism of nonlinear stiffness can be explained well by theory models. The mathematic model has some guiding significance for metal rubber’s design.
Based on numerical model established with actual parameters of raw material and processes, micro mechanism of metal rubber’s nonlinear stiffness was researched. Numerical model was verified in some respects, such as forming force, tissue structure, size and quasi-static loading curve. Tissue structure of metal rubber was decomposed. Elastic micro structure model and its local coordinate system were set up. Spatial motion, elastic deformation on z direction, and elastic deformation in xoy plane of elastic micro structure were studied. Mathematic model of metal rubber’s nonlinear stiffness property was built. Micro mechanism of nonlinear stiffness was described. The numerical model can coincide with experimental results well and be reliable. In quasi-static loading process, elastic micro structure’s translation is the main spatial motion, and its spatial rotation is very small. The elastic deformation on z direction can be regarded as parallel connection of several curved beams. The elastic deformation in xoy plane can be treated as a curved beam’s bending deformation making the distance of two endpoints smaller. The mathematical model agrees with test results well and it contains basic structure parameters, micro feature parameters and nonlinear stiffness mechanism parameters. These parameters have clear physical significance and the mathematic model has a high accuracy. Micro mechanism of nonlinear stiffness can be explained well by theory models. The mathematic model has some guiding significance for metal rubber’s design.
2018, 47(10):3030-3037.
Abstract:
A mixed three-phase solidification model based on Eulerian-Eulerian approach and volume average method for macrosegregation is applied to predict segregation in three dimensional ingot of Al-4%Cu aluminum alloy during direct chill casting (DC). In addition to the thermosolutal buoyancy flow, we consider the movement of equiaxed crystal, the capture of the equiaxed crystals by growing columnar tree trunks and the interaction and impingement between columnar and equiaxed crystals in the model. The results show that the cone zone of negative segregation is obviously observed at the bottom of ingot. Negative segregation is also observed adjacent to the center, whereas positive segregation obtained in the center and middle part of the radius. This W-type segregation profile is agreement with measured experimental data obtained from literatures. At the same time, the influence of pouring temperature and casting speed on macrosegregation are studied. It indicates that casting speed has a greater impact on segregation.
A mixed three-phase solidification model based on Eulerian-Eulerian approach and volume average method for macrosegregation is applied to predict segregation in three dimensional ingot of Al-4%Cu aluminum alloy during direct chill casting (DC). In addition to the thermosolutal buoyancy flow, we consider the movement of equiaxed crystal, the capture of the equiaxed crystals by growing columnar tree trunks and the interaction and impingement between columnar and equiaxed crystals in the model. The results show that the cone zone of negative segregation is obviously observed at the bottom of ingot. Negative segregation is also observed adjacent to the center, whereas positive segregation obtained in the center and middle part of the radius. This W-type segregation profile is agreement with measured experimental data obtained from literatures. At the same time, the influence of pouring temperature and casting speed on macrosegregation are studied. It indicates that casting speed has a greater impact on segregation.
2018, 47(10):3038-3044.
Abstract:
Ultrafine grained (UFG) pure titanium was prepared by ECAP up to four passes. The hot compression tests were conducted in the different temperatures (250~450 ℃) and the strain rates of 10-5~1s-1.The artificial neural network (ANN) and Arrhenius constitutive equation were used for establishing constitutiveSmodel of UFG pure titanium, respectively. The experimental results show that the flow stress increased with the increase of strain at the beginning of the deformation, then increased slowly. Finally, the stress reached a stable value. The experimental value and the predicted value of flow stress showed that the average absolute relative errors obtained from the artificial neural network model and Arrhenius constitutive equations were 2.1% and 11.54%, respectively. The correlation coefficient of the artificial neural network model and Arrhenius constitutive equations were 0.9979 and 0.9464, respectively. It means that the artificial neural network model can more accurately describe the constitutive relations of UFG pure titanium. By comparing the error of the two models under different temperatures, it can be find that artificial neural network model has better stability under the condition of high temperature.
Ultrafine grained (UFG) pure titanium was prepared by ECAP up to four passes. The hot compression tests were conducted in the different temperatures (250~450 ℃) and the strain rates of 10-5~1s-1.The artificial neural network (ANN) and Arrhenius constitutive equation were used for establishing constitutiveSmodel of UFG pure titanium, respectively. The experimental results show that the flow stress increased with the increase of strain at the beginning of the deformation, then increased slowly. Finally, the stress reached a stable value. The experimental value and the predicted value of flow stress showed that the average absolute relative errors obtained from the artificial neural network model and Arrhenius constitutive equations were 2.1% and 11.54%, respectively. The correlation coefficient of the artificial neural network model and Arrhenius constitutive equations were 0.9979 and 0.9464, respectively. It means that the artificial neural network model can more accurately describe the constitutive relations of UFG pure titanium. By comparing the error of the two models under different temperatures, it can be find that artificial neural network model has better stability under the condition of high temperature.
2018, 47(10):3045-3051.
Abstract:
In the paper, the process of TC4 aging phase transition and diffusion bonding was studied by molecular dynamics method. the radial distribution function of TC4 ternary alloy and the relative content of different crystal structures were analyzed. At the same time, the atomic concentration distribution, diffusion connection width and diffusion coefficient of diffusion bonding process under different thermal insulation temperature are studied. The results show that the structural changes of TC4 in the aging phase transition are mainly manifested in the new a phase of metastable b phase, and the b phase content reaches 23% after the state stabilizes, which is in good agreement with the experimental results. In the process of TC4 diffusion, the titanium atoms near the interface are mainly diffused, and vanadium atomic diffusion is secondary, while aluminum atom is relatively few. Under the same conditions, the diffusion connection width and thermal insulation temperature are in a good linear relationship. The diffusion coefficient of titanium is exponentially related with the temperature of heat preservation, and the results are in accordance with the experiment.
In the paper, the process of TC4 aging phase transition and diffusion bonding was studied by molecular dynamics method. the radial distribution function of TC4 ternary alloy and the relative content of different crystal structures were analyzed. At the same time, the atomic concentration distribution, diffusion connection width and diffusion coefficient of diffusion bonding process under different thermal insulation temperature are studied. The results show that the structural changes of TC4 in the aging phase transition are mainly manifested in the new a phase of metastable b phase, and the b phase content reaches 23% after the state stabilizes, which is in good agreement with the experimental results. In the process of TC4 diffusion, the titanium atoms near the interface are mainly diffused, and vanadium atomic diffusion is secondary, while aluminum atom is relatively few. Under the same conditions, the diffusion connection width and thermal insulation temperature are in a good linear relationship. The diffusion coefficient of titanium is exponentially related with the temperature of heat preservation, and the results are in accordance with the experiment.
2018, 47(10):3052-3057.
Abstract:
In this study, the effect of thermal mismatch stress on the surface crack propagation of thermal barrier coatings was investigated by using extended finite element method (XFEM). The results show that the location, slope angle and length of crack have a significant impact on crack propagation length, energy release rate and stress level at crack tip under the influence of thermal mismatch stress. The crack length is the longest and the energy release rate is the largest in the valley for the same initial crack. The larger the slope angle is, the shorter the length of crack expansion is but the larger the strain energy is. The larger the initial crack length is, the longer the crack growth length and the faster the expansion rate is, and the greater the energy release rate is. The crack propagation affects each other under the condition of multiple cracks.
In this study, the effect of thermal mismatch stress on the surface crack propagation of thermal barrier coatings was investigated by using extended finite element method (XFEM). The results show that the location, slope angle and length of crack have a significant impact on crack propagation length, energy release rate and stress level at crack tip under the influence of thermal mismatch stress. The crack length is the longest and the energy release rate is the largest in the valley for the same initial crack. The larger the slope angle is, the shorter the length of crack expansion is but the larger the strain energy is. The larger the initial crack length is, the longer the crack growth length and the faster the expansion rate is, and the greater the energy release rate is. The crack propagation affects each other under the condition of multiple cracks.
2018, 47(10):3058-3062.
Abstract:
Based on the experimental orientation relationship, first-principles density function theory calculations were performed to study the α/ω interface in titanium. With different surface termination and interface coordination types, a total of 24 possible atomistic interface models of the α{1-100}/ω{1-100} were constructed and calculated. Five interface structures were favored in energy and may co-present in titanium, and the average interface energy was predicted as 0.100 J/m2 with including the misfit strain energy, and 0.029 J/m2 without including the misfit strain energy, respectively. These results are helpful in supporting the future phase-field simulations and in clarifying the phase transformation mechanisms in titanium.
Based on the experimental orientation relationship, first-principles density function theory calculations were performed to study the α/ω interface in titanium. With different surface termination and interface coordination types, a total of 24 possible atomistic interface models of the α{1-100}/ω{1-100} were constructed and calculated. Five interface structures were favored in energy and may co-present in titanium, and the average interface energy was predicted as 0.100 J/m2 with including the misfit strain energy, and 0.029 J/m2 without including the misfit strain energy, respectively. These results are helpful in supporting the future phase-field simulations and in clarifying the phase transformation mechanisms in titanium.
2018, 47(10):3063-3071.
Abstract:
The vacuum gas pressure infiltration was performed for the continuous Al2O3f/Al composite with the volume fraction of 40%, of which the reinforced material was Nextel610-Al2O3 fiber, Al2O3 fibers were extracted using NaOH solution, the matrix alloys were 1A99, ZL210A, ZL301 and 7075 alloys, the effects of matrix alloy on the density, fiber damage and tensile strength of continuous Al2O3f/Al composites were studied. The results showed that different matrix alloys have obvious influence on the density and microstructure of the composites. The density of continuous Al2O3f/ZL301 composite is highest as 99.2%, and it has the least defect, the density of continuous Al2O3f/1A99 composite is lowest as 96.8%, the main reason for this difference is the wettability between the matrix and the fiber is different. The degree of interface reaction between different matrix and fiber is different. Eventually, the damage degree of the fiber is different. The tensile strength of continuous Al2O3f/1A99, Al2O3f/ZL210A, Al2O3f/ZL301 and Al2O3f/7075 were 465MPa, 479MPa, 680MPa and 389MPa, respectively. The defect, interfacial reaction degree and the fiber damage are the main factors to determine the tensile strength of the composite.
The vacuum gas pressure infiltration was performed for the continuous Al2O3f/Al composite with the volume fraction of 40%, of which the reinforced material was Nextel610-Al2O3 fiber, Al2O3 fibers were extracted using NaOH solution, the matrix alloys were 1A99, ZL210A, ZL301 and 7075 alloys, the effects of matrix alloy on the density, fiber damage and tensile strength of continuous Al2O3f/Al composites were studied. The results showed that different matrix alloys have obvious influence on the density and microstructure of the composites. The density of continuous Al2O3f/ZL301 composite is highest as 99.2%, and it has the least defect, the density of continuous Al2O3f/1A99 composite is lowest as 96.8%, the main reason for this difference is the wettability between the matrix and the fiber is different. The degree of interface reaction between different matrix and fiber is different. Eventually, the damage degree of the fiber is different. The tensile strength of continuous Al2O3f/1A99, Al2O3f/ZL210A, Al2O3f/ZL301 and Al2O3f/7075 were 465MPa, 479MPa, 680MPa and 389MPa, respectively. The defect, interfacial reaction degree and the fiber damage are the main factors to determine the tensile strength of the composite.
2018, 47(10):3072-3079.
Abstract:
FeSiAl magnetically soft alloy hollow microspheres were prepared by self-reactive quenching technology based on Fe+Si+Al and Fe+Si+Al+KNO3 reactive systems, respectively, in order to obtain absorbents with light weight, low frequency and high efficiency. Effect of reaction heat-releasing on their density, morphology, phase and microwave absorption properties in low frequency band was studied by SEM, XRD and vector network analyzer. The results show that, chemical reactions can not happen without KNO3. In addition, the quenching products consist of spherical particles, near-spherical particles, irregular particles and lamellar particles. The phase components are Fe, Si, Al and Fe0.9Si0.1. FeSiAl alloys are not formed and their microwave absorption properties do not exist basically. After adding KNO3, the quenching products mainly consist of hollow microspheres with uniform particle size distribution. The phases are made up of Fe3Si0.5Al0.5, Fe3Si0.7Al0.3, Fe0.9Si0.1 and Fe. FeSiAl alloys are obtained. The minimum reflectivity of the absorbent sample at 5 mm is -22.1 dB, and the corresponding frequency is 7.0 GHz. The effective absorption frequency band lower than -10 dB is 5.3-8.5 GHz, with the bandwidth of 3.2 GHz. The high heat-releasing and large amount of gas from the decomposition of KNO3 makes the reaction temperature be higher. In addition, the target products are obtained and then melt. Moreover, the spherical rate and hollow rate are both improved. These are the reasons for obvious improvement of microwave absorption properties in low frequency. Compared with flake FeSiAl magnetically soft alloy prepared by mechanical alloying method, FeSiAl hollow microspheres prepared by self-reactive quenching technology have a broader absorption frequency band in low frequency. In addition, the density of the material has decreased by 38 %. So the characteristics of new absorbents in low frequency including “thin, broad, light and strong”are effectively realized.
FeSiAl magnetically soft alloy hollow microspheres were prepared by self-reactive quenching technology based on Fe+Si+Al and Fe+Si+Al+KNO3 reactive systems, respectively, in order to obtain absorbents with light weight, low frequency and high efficiency. Effect of reaction heat-releasing on their density, morphology, phase and microwave absorption properties in low frequency band was studied by SEM, XRD and vector network analyzer. The results show that, chemical reactions can not happen without KNO3. In addition, the quenching products consist of spherical particles, near-spherical particles, irregular particles and lamellar particles. The phase components are Fe, Si, Al and Fe0.9Si0.1. FeSiAl alloys are not formed and their microwave absorption properties do not exist basically. After adding KNO3, the quenching products mainly consist of hollow microspheres with uniform particle size distribution. The phases are made up of Fe3Si0.5Al0.5, Fe3Si0.7Al0.3, Fe0.9Si0.1 and Fe. FeSiAl alloys are obtained. The minimum reflectivity of the absorbent sample at 5 mm is -22.1 dB, and the corresponding frequency is 7.0 GHz. The effective absorption frequency band lower than -10 dB is 5.3-8.5 GHz, with the bandwidth of 3.2 GHz. The high heat-releasing and large amount of gas from the decomposition of KNO3 makes the reaction temperature be higher. In addition, the target products are obtained and then melt. Moreover, the spherical rate and hollow rate are both improved. These are the reasons for obvious improvement of microwave absorption properties in low frequency. Compared with flake FeSiAl magnetically soft alloy prepared by mechanical alloying method, FeSiAl hollow microspheres prepared by self-reactive quenching technology have a broader absorption frequency band in low frequency. In addition, the density of the material has decreased by 38 %. So the characteristics of new absorbents in low frequency including “thin, broad, light and strong”are effectively realized.
2018, 47(10):3080-3087.
Abstract:
The interpenetrating (HA+β-TCP)/Mg-3Zn composites were fabricated by infiltrating Mg-3Zn alloy into porous HA+β-TCP with different HA content using suction casting technique, the microstructure, mechanical properties and corrosion behaviors of the composites have been evaluated. It presented that the molten Mg-3Zn alloy had infiltrated not only into the pores but also into the struts of the porous HA+β-TCP scaffold to forming a compact composite. The Mg-3Zn alloy contacted to the HA+β-TCP scaffold closely, and no reaction layer can be found. The compressive strength of the (HA+β-TCP)/Mg-3Zn composite with different HA content were 115~196 MPa, which were about 350-fold higher than that of the original porous HA+β-TCP scaffold and 44 %-75 % of the strength of the Mg-3Zn bulk alloy. The corrosion resistance of the composites was better than that of the Mg-3Zn bulk alloy, and the mechanical and corrosive behavior of the composites were controled by the choice of HA /β-TCp ratio.
The interpenetrating (HA+β-TCP)/Mg-3Zn composites were fabricated by infiltrating Mg-3Zn alloy into porous HA+β-TCP with different HA content using suction casting technique, the microstructure, mechanical properties and corrosion behaviors of the composites have been evaluated. It presented that the molten Mg-3Zn alloy had infiltrated not only into the pores but also into the struts of the porous HA+β-TCP scaffold to forming a compact composite. The Mg-3Zn alloy contacted to the HA+β-TCP scaffold closely, and no reaction layer can be found. The compressive strength of the (HA+β-TCP)/Mg-3Zn composite with different HA content were 115~196 MPa, which were about 350-fold higher than that of the original porous HA+β-TCP scaffold and 44 %-75 % of the strength of the Mg-3Zn bulk alloy. The corrosion resistance of the composites was better than that of the Mg-3Zn bulk alloy, and the mechanical and corrosive behavior of the composites were controled by the choice of HA /β-TCp ratio.
2018, 47(10):3088-3095.
Abstract:
Tensile tests, optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were carried out to characterize the mechanical properties and microstructure of 7056 aluminum alloy plates, which were 40 mm thick by hot rolling. The results show that the microstructure of 7056 hot rolling plate is inhomogeneous in different layers. The second phase particles in surface distribute dispersively, and the size is relatively small, while are concentrated in the centre, and the size is relatively large. From surface to centre, The shear texture is gradually reduced. The content of deformation texture in the center layer is the largest, and the difference of cube texture in each layer is not significant. After solution treatment, the recrystallization texture increased and the shear texture decreased in the surface, and the deformation texture of the central layer increased. After aging, a large amount of homogeneous and fine η" phase appeared in the surface layer and the center layer, while discontinuous precipitates and a certain width of precipitation-free zone can be observed at grain boundaries. Optimal solution treatment of 40 mm thick 7056 plate is 470℃ for 3h. After aging, the yield strength of the surface layer is 605MPa and the tensile strength is 628MPa. The yield strength of T / 4 layer is 626MPa and the tensile strength is 643MPa. The yield strength of the center layer is 623MPa and the tensile strength is 639MPa.
Tensile tests, optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were carried out to characterize the mechanical properties and microstructure of 7056 aluminum alloy plates, which were 40 mm thick by hot rolling. The results show that the microstructure of 7056 hot rolling plate is inhomogeneous in different layers. The second phase particles in surface distribute dispersively, and the size is relatively small, while are concentrated in the centre, and the size is relatively large. From surface to centre, The shear texture is gradually reduced. The content of deformation texture in the center layer is the largest, and the difference of cube texture in each layer is not significant. After solution treatment, the recrystallization texture increased and the shear texture decreased in the surface, and the deformation texture of the central layer increased. After aging, a large amount of homogeneous and fine η" phase appeared in the surface layer and the center layer, while discontinuous precipitates and a certain width of precipitation-free zone can be observed at grain boundaries. Optimal solution treatment of 40 mm thick 7056 plate is 470℃ for 3h. After aging, the yield strength of the surface layer is 605MPa and the tensile strength is 628MPa. The yield strength of T / 4 layer is 626MPa and the tensile strength is 643MPa. The yield strength of the center layer is 623MPa and the tensile strength is 639MPa.
26 Deformation Structure and Mechanical Properties of Single Crystal Copper Deformed by Route Bc ECAP
2018, 47(10):3096-3103.
Abstract:
The deformation structure of single crystal copper during 4 passes equal channel angular pressing (ECAP) througth route Bc were investigated by electron backscatter diffraction (EBSD) and XRD methods, and the mechanical properties of the deformed material were measured. The results show that the macroscopic orientation of single crystal under low pass deformation was not changed. After 2 passes，orientation-ordered shear bands appeared and inclined at angles in the range of 15°–20°from the ED direction，deformation texture {111}<112> appeared on grains；After 4 passes，the angle between the shear band and the ED direction was constant , the inclined direction was opposite to that of the 2 passes，the texture of the material was still in texture of {111}<112>，and large angle grain boundary was not presented；The tensile strength increased from 168MPa to 395MPa, the elongation decreased from 63% to 26.5%, the material hardness increased from 60Hv to 125Hv and then was tended to be changed little. Because of dislocation accumulation, the plastic deformation capability of the material becomes worse and the necking area increases. ECAP has positive effect on enhanceing the strength of single crystal copper with not broken grains.
The deformation structure of single crystal copper during 4 passes equal channel angular pressing (ECAP) througth route Bc were investigated by electron backscatter diffraction (EBSD) and XRD methods, and the mechanical properties of the deformed material were measured. The results show that the macroscopic orientation of single crystal under low pass deformation was not changed. After 2 passes，orientation-ordered shear bands appeared and inclined at angles in the range of 15°–20°from the ED direction，deformation texture {111}<112> appeared on grains；After 4 passes，the angle between the shear band and the ED direction was constant , the inclined direction was opposite to that of the 2 passes，the texture of the material was still in texture of {111}<112>，and large angle grain boundary was not presented；The tensile strength increased from 168MPa to 395MPa, the elongation decreased from 63% to 26.5%, the material hardness increased from 60Hv to 125Hv and then was tended to be changed little. Because of dislocation accumulation, the plastic deformation capability of the material becomes worse and the necking area increases. ECAP has positive effect on enhanceing the strength of single crystal copper with not broken grains.
2018, 47(10):3104-3111.
Abstract:
The effect of processing parameters on deformation behavior and microstructures of TC4 titanium alloy were investigated by using simulated compression tests. Select the best hot-work parameters and ultra-fine grained TC4 sheets with high strength were manufactured by accumulative roll-bonding in this work. The results showed that the flow stress of TC4 alloys increased quickly to a peak and then decreased to a steady value with strain increasing. The steady and peak stress obviously decreased as deformation temperatures increased and strain rates decreased. The accumulative rolling were finally conducted at about 700℃ with rolling speed less than 0.5m/s to prepare sheets without cracking and interface oxidizing. As the accumulative layers increased to 16, the grain sizes were refined to 500nm and high-quality interfaces were obtained. The ultra-fine grain structure of TC4 alloy was fabricated by accumulative rolling bonding process, during which the hot deformation process and the ARB processed window were studied, and the effect of the ARB parameters and the heat treatment process on the interface bonding and the microstructure was investigated. The stress-strain curve takes on the dynamic recovery process, and the high temperature (≥700℃) and deformation rates (≤0.1s-1) can promote the fine grains and the sheet quality. Finally the excellent interface bonding and the sheet quality can be obtained at the temperature of 720℃ and the low rolling rate (≤0.5m/s) with the anti-oxidation treatment of the contact interface. The deformation during ARB process is composed with the cooperation deformation of α/β grains and the shear deformation, and the elongated band structure and the shear bands are observed in the ARB processed TC4 alloy. The band structure spacing decrease gradually with the increase of the ARB layers, and the bands spacing of 200nm~500nm can be obtained after the 16 layers ARB process. Simultinately the increasing heating temperature during the heat treatment can promote the solutes diffusion and the recrystallization process, which can be consisted with the matrix structure. Finally the ultra-fine grain with 300nm~600nm can be obtained with the heating temperature of 700℃ and the holding time of 60min for the ARB processed TC4 alloy.
The effect of processing parameters on deformation behavior and microstructures of TC4 titanium alloy were investigated by using simulated compression tests. Select the best hot-work parameters and ultra-fine grained TC4 sheets with high strength were manufactured by accumulative roll-bonding in this work. The results showed that the flow stress of TC4 alloys increased quickly to a peak and then decreased to a steady value with strain increasing. The steady and peak stress obviously decreased as deformation temperatures increased and strain rates decreased. The accumulative rolling were finally conducted at about 700℃ with rolling speed less than 0.5m/s to prepare sheets without cracking and interface oxidizing. As the accumulative layers increased to 16, the grain sizes were refined to 500nm and high-quality interfaces were obtained. The ultra-fine grain structure of TC4 alloy was fabricated by accumulative rolling bonding process, during which the hot deformation process and the ARB processed window were studied, and the effect of the ARB parameters and the heat treatment process on the interface bonding and the microstructure was investigated. The stress-strain curve takes on the dynamic recovery process, and the high temperature (≥700℃) and deformation rates (≤0.1s-1) can promote the fine grains and the sheet quality. Finally the excellent interface bonding and the sheet quality can be obtained at the temperature of 720℃ and the low rolling rate (≤0.5m/s) with the anti-oxidation treatment of the contact interface. The deformation during ARB process is composed with the cooperation deformation of α/β grains and the shear deformation, and the elongated band structure and the shear bands are observed in the ARB processed TC4 alloy. The band structure spacing decrease gradually with the increase of the ARB layers, and the bands spacing of 200nm~500nm can be obtained after the 16 layers ARB process. Simultinately the increasing heating temperature during the heat treatment can promote the solutes diffusion and the recrystallization process, which can be consisted with the matrix structure. Finally the ultra-fine grain with 300nm~600nm can be obtained with the heating temperature of 700℃ and the holding time of 60min for the ARB processed TC4 alloy.
28 Effect of the second phases on corrosion behavior of the magnesium alloys with different Ca contents
2018, 47(10):3112-3119.
Abstract:
The microstructure of Mg-Al-Zn-xCa (x=0%, 1.25%, 1.74%, 2.53%) alloy before and corroded has been characterized by XRD, SEM, TEM and EDS. And the corrosion behavior has been studied by weight-loss, electrochemical method and SPM. Results shown that the phase composition consists mainly of α-Mg, β-Mg17Al12, Al2Ca and (Mg, Al)2Ca. With the increasing of Ca, the size of dendritic arm decreased, and the scale and number of Mg17Al12 phase decreased gradually. The shape of Al2Ca phase transformed from bonelike to network on grain boundary, and (Mg, Al)2Ca phase increased gradually. The result of corrosion behavior testing shown that the content of α+β eutectic reduced by addition of Ca, and therefore led to the corrosion channel narrowed and the proportion decreased. The formed Al2Ca cathode phase inhibited the hydrogen precipitation process and adding Ca led to an increase in anodic corrosion potential. The potential differences of Al2Ca and α-Mg are lower than β-Mg17Al12and α-Mg.
The microstructure of Mg-Al-Zn-xCa (x=0%, 1.25%, 1.74%, 2.53%) alloy before and corroded has been characterized by XRD, SEM, TEM and EDS. And the corrosion behavior has been studied by weight-loss, electrochemical method and SPM. Results shown that the phase composition consists mainly of α-Mg, β-Mg17Al12, Al2Ca and (Mg, Al)2Ca. With the increasing of Ca, the size of dendritic arm decreased, and the scale and number of Mg17Al12 phase decreased gradually. The shape of Al2Ca phase transformed from bonelike to network on grain boundary, and (Mg, Al)2Ca phase increased gradually. The result of corrosion behavior testing shown that the content of α+β eutectic reduced by addition of Ca, and therefore led to the corrosion channel narrowed and the proportion decreased. The formed Al2Ca cathode phase inhibited the hydrogen precipitation process and adding Ca led to an increase in anodic corrosion potential. The potential differences of Al2Ca and α-Mg are lower than β-Mg17Al12and α-Mg.
2018, 47(10):3120-3126.
Abstract:
In the study, a temperature acquisition system was used to measure average solidification cooling rate of GE81 alloys under different cooling conditions, such as furnace-cooled in graphite mould, air-cooled in graphite mould, air-cooled in steel mould and air-cooled in copper mould. The connection between cooling rate and grain density was studied on the basis of classical nucleation theory. The optical microscope (OM) and scanning electron microscope (SEM) were used to observe the microstructure of as-cast GE81 alloys (Mg-8%Gd-1%Er, mass fraction) under various cooling rate in order to establish the relationship between solidification cooling rate, grain density, hardness and volume fraction of secondary phases. The results showed that the solidification cooling rate of GE81 alloy in the four moulds was 0.23, 0.46 2.17 and 3.88 K·s-1, respectively. The cooling rate is linear with the undercooling and the formula was ?T=13.5664v+6.9655. With the increasing cooling rate, the α-Mg grains were refined obviously. The relationship between the cooling rate and the grain density could be described as Nv=1.1135×1012exp(-46.8344/(13.5664v+6.9655)). Moreover, the secondary phases distributed more homogeneously and their volume fraction decreased so that the hardness of GE81 alloy increased significantly. The relationship between the hardness and the cooling rate could be expressed as HV=72.1772-12.6895/(1+exp(v-2.2570)).
In the study, a temperature acquisition system was used to measure average solidification cooling rate of GE81 alloys under different cooling conditions, such as furnace-cooled in graphite mould, air-cooled in graphite mould, air-cooled in steel mould and air-cooled in copper mould. The connection between cooling rate and grain density was studied on the basis of classical nucleation theory. The optical microscope (OM) and scanning electron microscope (SEM) were used to observe the microstructure of as-cast GE81 alloys (Mg-8%Gd-1%Er, mass fraction) under various cooling rate in order to establish the relationship between solidification cooling rate, grain density, hardness and volume fraction of secondary phases. The results showed that the solidification cooling rate of GE81 alloy in the four moulds was 0.23, 0.46 2.17 and 3.88 K·s-1, respectively. The cooling rate is linear with the undercooling and the formula was ?T=13.5664v+6.9655. With the increasing cooling rate, the α-Mg grains were refined obviously. The relationship between the cooling rate and the grain density could be described as Nv=1.1135×1012exp(-46.8344/(13.5664v+6.9655)). Moreover, the secondary phases distributed more homogeneously and their volume fraction decreased so that the hardness of GE81 alloy increased significantly. The relationship between the hardness and the cooling rate could be expressed as HV=72.1772-12.6895/(1+exp(v-2.2570)).
2018, 47(10):3127-3133.
Abstract:
Aiming at improving the corrosion resistance of 45 steel used in maritime works, an Al-Cr composite alloyed layer is deposited on the surface of 45 steel via a composite technique of plasma ion implantation (PII) and double glow plasma surface metallurgy (DGPSM). Element distributions and phase structures of the Al-Cr composite alloyed layer are investigated via X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Atomic force microscope (AFM), Scanning electron microscope (SEM) and Energy dispersive spectroscopy (EDS). Polarization curves and electrochemical impedance spectroscopy (EIS) are used to study the corrosion resistance and the corrosion mechanisms of the Al-Cr composite alloyed layer, the Al implanted layer and 45 steel in 3.5 wt% NaCl solution. The results show that the Al-Cr composite alloyed layer reveals the best corrosion resistance. The formation of Cr2O3 and Al2O3 as passive films on the surface of the Al-Cr composite alloyed layer, and the inner Fe2AlCr and Al8Cr5 phases with excellent corrosion resistance, hindering the corrosion of Cl- ions effectively. The Al implanted layer exhibits moderate corrosion resistance due to the formation of Al2O3 passive film. The substrate of 45 steel shows the worst corrosion resistance.
Aiming at improving the corrosion resistance of 45 steel used in maritime works, an Al-Cr composite alloyed layer is deposited on the surface of 45 steel via a composite technique of plasma ion implantation (PII) and double glow plasma surface metallurgy (DGPSM). Element distributions and phase structures of the Al-Cr composite alloyed layer are investigated via X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Atomic force microscope (AFM), Scanning electron microscope (SEM) and Energy dispersive spectroscopy (EDS). Polarization curves and electrochemical impedance spectroscopy (EIS) are used to study the corrosion resistance and the corrosion mechanisms of the Al-Cr composite alloyed layer, the Al implanted layer and 45 steel in 3.5 wt% NaCl solution. The results show that the Al-Cr composite alloyed layer reveals the best corrosion resistance. The formation of Cr2O3 and Al2O3 as passive films on the surface of the Al-Cr composite alloyed layer, and the inner Fe2AlCr and Al8Cr5 phases with excellent corrosion resistance, hindering the corrosion of Cl- ions effectively. The Al implanted layer exhibits moderate corrosion resistance due to the formation of Al2O3 passive film. The substrate of 45 steel shows the worst corrosion resistance.
2018, 47(10):3134-3140.
Abstract:
Ni-Ti-O nanosheets were fabricated on 3D porous nickel foam by hydrothermal synthesis and thermal diffusion metallizing. Scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) were used to investigate the micro morphology and phase of NiO and Ni-Ti-O nanostructure. The methanol catalytsis performance and capacitance properties of these electrodes were investigated by cyclic voltammetry and charge- discharge tests. The results show that the phase of Ni-Ti-O nanosheets fabricated on 3D porous nickel foam are NiO and TiO with polycrystalline form; The permeation of Ti result in oxygen vacancies in NiO nanosheets and produce synergistic effect with Ni, which makes that the electrocatalytic property of methanol oxidation of Ni-Ti-O nanosheet electrode is much larger than that of Ni(OH)2 and NiO electrode; When the the mass ratio of Ni foam and Ti powder (RNi/Ti) is 1:24, at a current density of 5 mA?cm-2, the area specific capacitance of Ni-Ti-O electrode is 2.15 F?cm-2, which is 3 times more than that of Ni(OH)2/Ni foam electrode (0.67 F?cm-2).
Ni-Ti-O nanosheets were fabricated on 3D porous nickel foam by hydrothermal synthesis and thermal diffusion metallizing. Scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) were used to investigate the micro morphology and phase of NiO and Ni-Ti-O nanostructure. The methanol catalytsis performance and capacitance properties of these electrodes were investigated by cyclic voltammetry and charge- discharge tests. The results show that the phase of Ni-Ti-O nanosheets fabricated on 3D porous nickel foam are NiO and TiO with polycrystalline form; The permeation of Ti result in oxygen vacancies in NiO nanosheets and produce synergistic effect with Ni, which makes that the electrocatalytic property of methanol oxidation of Ni-Ti-O nanosheet electrode is much larger than that of Ni(OH)2 and NiO electrode; When the the mass ratio of Ni foam and Ti powder (RNi/Ti) is 1:24, at a current density of 5 mA?cm-2, the area specific capacitance of Ni-Ti-O electrode is 2.15 F?cm-2, which is 3 times more than that of Ni(OH)2/Ni foam electrode (0.67 F?cm-2).
2018, 47(10):3141-3147.
Abstract:
Aim at the fatigue fracture fault of aero-engine directional solidified turbine blade, laser shock peening was suggested to be conducted on the DZ17G superalloy simulated blades to improve fatigue performance. However, in order to avoid the occurrence of grain refinement in the columnar crystals,a special laser shock treatment method, high frequency shock without ablation coating underwater based on micro-scale laser shock peening, was proposed. In this method, short laser pulse width micro-scale laser beam was conducted to decrease the plastically degree and affected depth, and high frequency shock without ablation coating was conducted to form a uniform plastically strengthening layer. The experiment results indicate that there are high density disloactions and dislocation tangles generated in the shallow layer of DZ17G superalloy simulated blade, but no grain refinement, and the density of dislocations decrease with the depth sharply. High density disloactions and dislocation tangles result in a high improvement of hardness, increased by 30%. However, There is a 180 thick hardened layer generated. The fatigue strength of DZ17G superalloy simulated blades is improved form 257.00 MPa to 302.00 MPa, increased by 17.5%. There is still a improvement of 11.7% on fatigue strength after thermal insulation for 2h under 800℃. High density disloactions and dislocation tangles are the immanent cause of fatigue performance improvement.
Aim at the fatigue fracture fault of aero-engine directional solidified turbine blade, laser shock peening was suggested to be conducted on the DZ17G superalloy simulated blades to improve fatigue performance. However, in order to avoid the occurrence of grain refinement in the columnar crystals,a special laser shock treatment method, high frequency shock without ablation coating underwater based on micro-scale laser shock peening, was proposed. In this method, short laser pulse width micro-scale laser beam was conducted to decrease the plastically degree and affected depth, and high frequency shock without ablation coating was conducted to form a uniform plastically strengthening layer. The experiment results indicate that there are high density disloactions and dislocation tangles generated in the shallow layer of DZ17G superalloy simulated blade, but no grain refinement, and the density of dislocations decrease with the depth sharply. High density disloactions and dislocation tangles result in a high improvement of hardness, increased by 30%. However, There is a 180 thick hardened layer generated. The fatigue strength of DZ17G superalloy simulated blades is improved form 257.00 MPa to 302.00 MPa, increased by 17.5%. There is still a improvement of 11.7% on fatigue strength after thermal insulation for 2h under 800℃. High density disloactions and dislocation tangles are the immanent cause of fatigue performance improvement.
2018, 47(10):3148-3154.
Abstract:
Co doped Zn1-xCoxS nanorods with different concentration ratio (x=0, 0.01, 0.03, 0.05 and 0.07) were successfully synthesized by hydrothermal method using ethylenediamine as a modifier. The crystal microstructure, morphology and optical properties of the samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), X-ray energy dispersive spectrometry (XEDS), Ultraviolet–visible Diffuse Reflectance spectroscopy (UV–vis DRS), photoluminescence spectra (PL) and Fourier transform Infrared spectroscopy (FTIR). The experiment results show that all samples synthesized by this method possess wurtzite structure with good crystallization, which indicates that all Co2+ successfully substituted for the lattice site of Zn2+ and generate single-phase Zn1-xCoxS. The morphology is one-dimensional rod-like shape with good dispersion. The the grain size increases, the cell volume decreases and the lattice constant occurs shrink with the increase of Co content. UV–vis spectra reveals the band gap of doped Zn1-xCoxS nanorods occurs red shift compare to that of the pure ZnS. PL spectra shows that the samples have obvious violet (402nm), blue (470nm, yellow (600nm) and infrared (826nm) emission peaks, the luminescence intensity decreases with the increase of the Co doping concentration.The FTIR spectrum shows that the absorption peak position does not change with the increase of the Co doping concentration.
Co doped Zn1-xCoxS nanorods with different concentration ratio (x=0, 0.01, 0.03, 0.05 and 0.07) were successfully synthesized by hydrothermal method using ethylenediamine as a modifier. The crystal microstructure, morphology and optical properties of the samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), X-ray energy dispersive spectrometry (XEDS), Ultraviolet–visible Diffuse Reflectance spectroscopy (UV–vis DRS), photoluminescence spectra (PL) and Fourier transform Infrared spectroscopy (FTIR). The experiment results show that all samples synthesized by this method possess wurtzite structure with good crystallization, which indicates that all Co2+ successfully substituted for the lattice site of Zn2+ and generate single-phase Zn1-xCoxS. The morphology is one-dimensional rod-like shape with good dispersion. The the grain size increases, the cell volume decreases and the lattice constant occurs shrink with the increase of Co content. UV–vis spectra reveals the band gap of doped Zn1-xCoxS nanorods occurs red shift compare to that of the pure ZnS. PL spectra shows that the samples have obvious violet (402nm), blue (470nm, yellow (600nm) and infrared (826nm) emission peaks, the luminescence intensity decreases with the increase of the Co doping concentration.The FTIR spectrum shows that the absorption peak position does not change with the increase of the Co doping concentration.
2018, 47(10):3155-3160.
Abstract:
A Y2Ti2O7/316L stainless steel functionally graded composite material was fabricated through powder lamination and hot-press sintering processing, and its microstructure and some mechanical properties were investigated. The observations of optical microscopy, X-ray diffractometry, and electron probe microanalysis all confirmed the formation of compositional and microstructural gradients in the transition region between the metal and oxide halves. Some mechanical properties of the graded composite were also preliminarily evaluated, by performing the mechanical testing on homogeneous composite samples with different volume fractions of Y2Ti2O7. The results suggested that some mechanical properties vary in the same gradient of composition and microstructure, i.e. relative density and bending strength increase gradually while Vickers hardness decreases gradually with the increase of metal content in the transition region.
A Y2Ti2O7/316L stainless steel functionally graded composite material was fabricated through powder lamination and hot-press sintering processing, and its microstructure and some mechanical properties were investigated. The observations of optical microscopy, X-ray diffractometry, and electron probe microanalysis all confirmed the formation of compositional and microstructural gradients in the transition region between the metal and oxide halves. Some mechanical properties of the graded composite were also preliminarily evaluated, by performing the mechanical testing on homogeneous composite samples with different volume fractions of Y2Ti2O7. The results suggested that some mechanical properties vary in the same gradient of composition and microstructure, i.e. relative density and bending strength increase gradually while Vickers hardness decreases gradually with the increase of metal content in the transition region.
2018, 47(10):3161-3166.
Abstract:
5000 series (Al-Mg) aluminum alloy for shipbuilding with thickness of 5mm was successfully welded by variable polarity plasma welding process at vertical-up position. The microstructure and mechanical properties of the joint were investigated. The ultimate tensile strength of the joint was 295MPa, the elongation was 10%, and the location of fracture was near the partly melted zone. The micro hardness of fusion line and heat affected zone was lower than the base metal, and the lowest hardness appeared in the center of the weld. The optical micrographs of the joint shown that the weld microstructure near the fusion line was coarse equiaxed grain structure and most of the weld region was cellular dendritic structure which grown from the two sides to the middle, while the microstructure of heat affected zone was typical recrystallization structure. The composition around the tensile fracture position was analyzed by EPMA, and the results revealed that the content of Mg was low and heterogeneously distributed. The lack and segregation of Mg and non-homogeneous microstructure decreased solution strengthening and resulted in a weak zone of the joint.
5000 series (Al-Mg) aluminum alloy for shipbuilding with thickness of 5mm was successfully welded by variable polarity plasma welding process at vertical-up position. The microstructure and mechanical properties of the joint were investigated. The ultimate tensile strength of the joint was 295MPa, the elongation was 10%, and the location of fracture was near the partly melted zone. The micro hardness of fusion line and heat affected zone was lower than the base metal, and the lowest hardness appeared in the center of the weld. The optical micrographs of the joint shown that the weld microstructure near the fusion line was coarse equiaxed grain structure and most of the weld region was cellular dendritic structure which grown from the two sides to the middle, while the microstructure of heat affected zone was typical recrystallization structure. The composition around the tensile fracture position was analyzed by EPMA, and the results revealed that the content of Mg was low and heterogeneously distributed. The lack and segregation of Mg and non-homogeneous microstructure decreased solution strengthening and resulted in a weak zone of the joint.
2018, 47(10):3167-3172.
Abstract:
High strength 7055 aluminum alloy were produced by spray forming. The microstructures and properties of alloy after forging and extrusion were investigated using tensile test, electrochemical workstation, OM, SEM, TEM. The results indicate that the corrosion –resistance of extruded aluminum alloy is superior to forged aluminum alloy; at room temperature, the tensile strength of the extruded alloy can reach 642 MPa, the yield strength can reach to 574 MPa, the tensile strength and yield strength of the forged alloy decrease, but the elongation、electrical conductivity and hardness have increased, the alloys both exhibit a ductile fracture; element distribution of the alloys in the grain boundary and grain interior is no difference, but have small fluctuation, and this phenomenon is more apparent under the forged alloy; in T74 condition the main precipitates are GP zones and η′ phase in the matrix, and the grain boundary precipitates distribute interrupted，precipitated phases of grain boundary of the forged alloy is more than that of the extruded alloy, but precipitated phases of grain interior have coarsened.
High strength 7055 aluminum alloy were produced by spray forming. The microstructures and properties of alloy after forging and extrusion were investigated using tensile test, electrochemical workstation, OM, SEM, TEM. The results indicate that the corrosion –resistance of extruded aluminum alloy is superior to forged aluminum alloy; at room temperature, the tensile strength of the extruded alloy can reach 642 MPa, the yield strength can reach to 574 MPa, the tensile strength and yield strength of the forged alloy decrease, but the elongation、electrical conductivity and hardness have increased, the alloys both exhibit a ductile fracture; element distribution of the alloys in the grain boundary and grain interior is no difference, but have small fluctuation, and this phenomenon is more apparent under the forged alloy; in T74 condition the main precipitates are GP zones and η′ phase in the matrix, and the grain boundary precipitates distribute interrupted，precipitated phases of grain boundary of the forged alloy is more than that of the extruded alloy, but precipitated phases of grain interior have coarsened.
2018, 47(10):3173-3178.
Abstract:
In this paper, the photoelectrode of CdS QDs/CdTe NRAs are prepared by using chemical deposition for CdS and RF sputtering for CdTe. The achieved samples are investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), uv-vis absorption spectroscopy (UV vis) and optical electrode electrochemical workstation, respectively. The SEM results confirm that the photoelectrode is consisted of CdS quantum dots and CdTe nanorods. The XRD results showed that CdTe nanorods grow along the preferred orientation of (111) direction. The novel pyroelectric phenomenon is found in the photoelectrode. The best results are achieved in the photoelectrode with 25 cycle CdS QDs, and the open circuit voltage and the short-circuit current is 0.49 V and 71.09 μA, respectively. The photoelectric ratio between the on and off is six. We also found the current reverse phenomenon caused by the pyroelectric property, and it has the important significance for improving photoelectric device performance.
In this paper, the photoelectrode of CdS QDs/CdTe NRAs are prepared by using chemical deposition for CdS and RF sputtering for CdTe. The achieved samples are investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), uv-vis absorption spectroscopy (UV vis) and optical electrode electrochemical workstation, respectively. The SEM results confirm that the photoelectrode is consisted of CdS quantum dots and CdTe nanorods. The XRD results showed that CdTe nanorods grow along the preferred orientation of (111) direction. The novel pyroelectric phenomenon is found in the photoelectrode. The best results are achieved in the photoelectrode with 25 cycle CdS QDs, and the open circuit voltage and the short-circuit current is 0.49 V and 71.09 μA, respectively. The photoelectric ratio between the on and off is six. We also found the current reverse phenomenon caused by the pyroelectric property, and it has the important significance for improving photoelectric device performance.
2018, 47(10):3179-3184.
Abstract:
In this study, as-cast WE43 alloy was subjected to submerged friction stir processing (SFSP). Microstructural evolution during SFSP and effect of aging treatment on mechanical properties of SFSP specimens were investigated. The results showed that the microstructure of cast WE43 alloy was significantly refined and the mechanical properties were greatly enhanced. After subsequent artificial aging treatment at 66 h for 150 ℃ and 54 h for 180 ℃, strengths of the peak–aged specimens were further increased, which was attributed to the large quantity of β′′ and β1 precipitates, respectively. Meanwhile, elongations of the peak-aged specimens were both decreased, since more crack nucleation sites were provided with the increased precipitates. The failure mechanism of SFSP specimen was ductile fracture mode, while the peak-aged specimens were all mixed ductile–brittle fracture mode.
In this study, as-cast WE43 alloy was subjected to submerged friction stir processing (SFSP). Microstructural evolution during SFSP and effect of aging treatment on mechanical properties of SFSP specimens were investigated. The results showed that the microstructure of cast WE43 alloy was significantly refined and the mechanical properties were greatly enhanced. After subsequent artificial aging treatment at 66 h for 150 ℃ and 54 h for 180 ℃, strengths of the peak–aged specimens were further increased, which was attributed to the large quantity of β′′ and β1 precipitates, respectively. Meanwhile, elongations of the peak-aged specimens were both decreased, since more crack nucleation sites were provided with the increased precipitates. The failure mechanism of SFSP specimen was ductile fracture mode, while the peak-aged specimens were all mixed ductile–brittle fracture mode.
2018, 47(10):3185-3190.
Abstract:
The microstructure and texture of the Ni47Ti44Nb9 ingots under the condition of fast and slowly cooling rate were studied through optical microscope (OM), scanning electronic microscope (SEM) and X-ray diffraction (XRD). And then the effect mechanism of solidification rate on microstructure and texture was discussed. The results indicated that the preferred growth direction of Ni47Ti44Nb9 cast alloy is <113> and there is an important impact of solidification rate on the microstructure and texture of Ni47Ti44Nb9 cast alloy. In detail, when the cooling rate is fast, uniform dendrites with texture of {113} can be achieved, while in the case of slowly cooling, columnar dendrites with specific direction can be obtained and the main textures of vertical section are close to {113}<361>, {113}<332> and {113}<141>. In addition, the directional growth of dendrites induced by directional heat conduction during the process of solidification is found the main reason for the formation of cast microstructure and texture.
The microstructure and texture of the Ni47Ti44Nb9 ingots under the condition of fast and slowly cooling rate were studied through optical microscope (OM), scanning electronic microscope (SEM) and X-ray diffraction (XRD). And then the effect mechanism of solidification rate on microstructure and texture was discussed. The results indicated that the preferred growth direction of Ni47Ti44Nb9 cast alloy is <113> and there is an important impact of solidification rate on the microstructure and texture of Ni47Ti44Nb9 cast alloy. In detail, when the cooling rate is fast, uniform dendrites with texture of {113}
2018, 47(10):3191-3196.
Abstract:
AlCoCrFeNi high entropy alloy was prepared by vacuum arc melting furnace and annealed at 600 ℃, 800 ℃ and 1000 ℃ for 10h. The microstructure of the alloys before and after annealing and their ?corrosion resistance in 3.5% NaCl solution, 0.5 mol/L NaOH solution and 0.5 mol/L H2SO4 solution were studied Using XRD, SEM, EDS and electrochemical corrosion test. Organizational analysis shows that there is no complex intermetallic compound in as-cast and annealing states; the alloys in as-cast and 600 ℃ and 800 ℃ annealing states are composed of simple BCC crystal structure and have the branch crystal morphology; in 1000 ℃ annealing state the alloy consists of BCC + FCC and Short rod-like FCC precipitate phase and BCC substrates arrange alternately; in as-cast and three temperature annealing states, Co, Fe and Ni distributions are uniform and Cr, Al are certain segregation; Al segregation in as-cast is the most serious and Cr segregation in 800 ℃ annealing state is the most serious. Electrochemical corrosion test results show that AlCoCrFeNi alloys in as-cast and three temperature annealing states have excellent corrosion resistance in 3.5% NaCl solution and 0.5 mol/L NaOH solution; in 3.5% NaCl solution, the 1000 ℃ annealing alloy has the best corrosion resistance; in 0.5 mol/L NaOH solution, the four states of the alloy have similar corrosion resistance; in 0.5 mol/L H2SO4 solution, the four states of the alloy have occurred the phenomenon of passivation and 1000 ℃ annealing state has the minimum dimension passive current density and the highest break blunt potential, and its corrosion resistance is best.
AlCoCrFeNi high entropy alloy was prepared by vacuum arc melting furnace and annealed at 600 ℃, 800 ℃ and 1000 ℃ for 10h. The microstructure of the alloys before and after annealing and their ?corrosion resistance in 3.5% NaCl solution, 0.5 mol/L NaOH solution and 0.5 mol/L H2SO4 solution were studied Using XRD, SEM, EDS and electrochemical corrosion test. Organizational analysis shows that there is no complex intermetallic compound in as-cast and annealing states; the alloys in as-cast and 600 ℃ and 800 ℃ annealing states are composed of simple BCC crystal structure and have the branch crystal morphology; in 1000 ℃ annealing state the alloy consists of BCC + FCC and Short rod-like FCC precipitate phase and BCC substrates arrange alternately; in as-cast and three temperature annealing states, Co, Fe and Ni distributions are uniform and Cr, Al are certain segregation; Al segregation in as-cast is the most serious and Cr segregation in 800 ℃ annealing state is the most serious. Electrochemical corrosion test results show that AlCoCrFeNi alloys in as-cast and three temperature annealing states have excellent corrosion resistance in 3.5% NaCl solution and 0.5 mol/L NaOH solution; in 3.5% NaCl solution, the 1000 ℃ annealing alloy has the best corrosion resistance; in 0.5 mol/L NaOH solution, the four states of the alloy have similar corrosion resistance; in 0.5 mol/L H2SO4 solution, the four states of the alloy have occurred the phenomenon of passivation and 1000 ℃ annealing state has the minimum dimension passive current density and the highest break blunt potential, and its corrosion resistance is best.
2018, 47(10):3197-3202.
Abstract:
Al alloy and Mg alloy, which have advantages of low density and high specific strength, are widely applied in aerospace industry, yet easily generate brittle intermetallic compound during welding, thereby causing great difficulty in acquisition of joints with excellent performance. Therefore, during soldering, choose of soldering filler metal which can avoid generation of harmful intermetallic compound is key to acquisition of high grade Al/Mg dissimilar metal joint. In this work, Sn-based and Zn-based soldering filling metals are chosen, 6063 Al alloy and AZ31B Mg alloy are welded by ultrasonic-assisted soldering at atmosphere, and contrastive analysis is carried out to the two solder joint microstructures of soldering filler metals by OM, SEM and EDS spectrum. The results indicated that when Sn-based soldering filler metal is adopted, the joint cannot generate Mg-Al brittle intermetallic compound, Al elements which dissolve in soldering seams exist in the joint in form of Al-Sn-Zn and Ag (Al) phases, and when the ultrasonic action time reaches 4.5s, the Al elements are uniformly distributed in the whole soldering seam. When Zn-based soldering filler metal is adopted, large amount of brittle Mg/Al intermetallic compound generate in the joint, and second-phased low-melting-point Sn particles disperse at the grain boundary of the soldering seam.
Al alloy and Mg alloy, which have advantages of low density and high specific strength, are widely applied in aerospace industry, yet easily generate brittle intermetallic compound during welding, thereby causing great difficulty in acquisition of joints with excellent performance. Therefore, during soldering, choose of soldering filler metal which can avoid generation of harmful intermetallic compound is key to acquisition of high grade Al/Mg dissimilar metal joint. In this work, Sn-based and Zn-based soldering filling metals are chosen, 6063 Al alloy and AZ31B Mg alloy are welded by ultrasonic-assisted soldering at atmosphere, and contrastive analysis is carried out to the two solder joint microstructures of soldering filler metals by OM, SEM and EDS spectrum. The results indicated that when Sn-based soldering filler metal is adopted, the joint cannot generate Mg-Al brittle intermetallic compound, Al elements which dissolve in soldering seams exist in the joint in form of Al-Sn-Zn and Ag (Al) phases, and when the ultrasonic action time reaches 4.5s, the Al elements are uniformly distributed in the whole soldering seam. When Zn-based soldering filler metal is adopted, large amount of brittle Mg/Al intermetallic compound generate in the joint, and second-phased low-melting-point Sn particles disperse at the grain boundary of the soldering seam.
2018, 47(10):3203-3207.
Abstract:
FeCrCoNiMnBx (x=0, 0.05, 0.1, 0.15, 0.2 where, x is the mole percentage) were prepared by vacuum arc melting.The microstructure and mechanical property of FeCrCoNiMnBx high-entropy alloys were investigated.The results show thatwithout boron addition, the alloy is composed of simple fcc solid solution structure and the cellular crystal structures form . When the content of B in the alloys was higher than 0.05, (Fe, Co) 2B with shape of dendritic and nano granular can be observed. With the increase of B content, the tensile strength of the alloy increases gradually. When the content of boron is 0.2, the tensile strength of the alloy is 610 MPa, but the elongation is only 7%. The proper amount of B element can improve the comprehensive mechanical properties of high entropy alloy.When the content of B is 0.1, the tensile strength is 550 MPa, and the elongation is 20%.proper amount of B element can improve the comprehensive mechanical properties of high entropy alloy.When the content of B is 0.1, the tensile strength is 550 MPa, and the elongation is 20%.
FeCrCoNiMnBx (x=0, 0.05, 0.1, 0.15, 0.2 where, x is the mole percentage) were prepared by vacuum arc melting.The microstructure and mechanical property of FeCrCoNiMnBx high-entropy alloys were investigated.The results show thatwithout boron addition, the alloy is composed of simple fcc solid solution structure and the cellular crystal structures form . When the content of B in the alloys was higher than 0.05, (Fe, Co) 2B with shape of dendritic and nano granular can be observed. With the increase of B content, the tensile strength of the alloy increases gradually. When the content of boron is 0.2, the tensile strength of the alloy is 610 MPa, but the elongation is only 7%. The proper amount of B element can improve the comprehensive mechanical properties of high entropy alloy.When the content of B is 0.1, the tensile strength is 550 MPa, and the elongation is 20%.proper amount of B element can improve the comprehensive mechanical properties of high entropy alloy.When the content of B is 0.1, the tensile strength is 550 MPa, and the elongation is 20%.
43 Effect of quenching parameters on magnetic property and microstructure of the Nd9.5Fe84B6.5 alloy
2018, 47(10):3208-3212.
Abstract:
The Nd9.5Fe84B6.5 ribbons were prepared by melt-spinning. The effects of the chamber pressure and wheel speed on the magnetic property and microstructure of the Nd9.5Fe84B6.5 alloy were investigated. A complementary relationship between the chamber pressure and the wheel speed in rapid solidification of melt-spinning is proposed. The values of thickness and magnetic property in the ribbon sample prepared at the chamber pressure of 0.03 MPa and the wheel speed of 19 m/s are similar to that in the ribbon prepared at the chamber pressure of 0.05 MPa and the wheel speed of 15 m/s. XRD and TEM results show that the ribbons prepared at two conditions have same phase constitution and similar microstructure. Our work indicate that the melt-spun Nd9.5Fe84B6.5 ribbons with similar magnetic property and microstructure are obtained by controlling the chamber pressure and the wheel speed in rapid solidification, which can be used to serve as a guide in achieving permanent materials with good magnetic property in mass production.
The Nd9.5Fe84B6.5 ribbons were prepared by melt-spinning. The effects of the chamber pressure and wheel speed on the magnetic property and microstructure of the Nd9.5Fe84B6.5 alloy were investigated. A complementary relationship between the chamber pressure and the wheel speed in rapid solidification of melt-spinning is proposed. The values of thickness and magnetic property in the ribbon sample prepared at the chamber pressure of 0.03 MPa and the wheel speed of 19 m/s are similar to that in the ribbon prepared at the chamber pressure of 0.05 MPa and the wheel speed of 15 m/s. XRD and TEM results show that the ribbons prepared at two conditions have same phase constitution and similar microstructure. Our work indicate that the melt-spun Nd9.5Fe84B6.5 ribbons with similar magnetic property and microstructure are obtained by controlling the chamber pressure and the wheel speed in rapid solidification, which can be used to serve as a guide in achieving permanent materials with good magnetic property in mass production.
2018, 47(10):3213-3217.
Abstract:
The gel was prepared by sol-gel method using metal nitrate as raw materials. All kinds of dry gel precursors were obtained under different drying conditions, then the CaMnO3 polycrystalline powders were obtained by calcinating the dry gel. This paper studies the effects of different drying processes on preparation of CaMnO3 powder, and the obtained powders were characterized by XRD, SEM, TEM and laser particle size analyzer. The results show that the continuous heating step for various drying temperatures is beneficial to obtain dry gel precursor with complete dehydration.The drying process of 90℃+120℃+140℃+160℃ is the best among the four processes. The CaMnO3 polycrystalline powder with good crystallinity, uniform particles and regular morphology was obtained after calcining the dry gel at 950℃, the CaMnO3 polycrystalline particles were composed by single-crystals with different orientations.
The gel was prepared by sol-gel method using metal nitrate as raw materials. All kinds of dry gel precursors were obtained under different drying conditions, then the CaMnO3 polycrystalline powders were obtained by calcinating the dry gel. This paper studies the effects of different drying processes on preparation of CaMnO3 powder, and the obtained powders were characterized by XRD, SEM, TEM and laser particle size analyzer. The results show that the continuous heating step for various drying temperatures is beneficial to obtain dry gel precursor with complete dehydration.The drying process of 90℃+120℃+140℃+160℃ is the best among the four processes. The CaMnO3 polycrystalline powder with good crystallinity, uniform particles and regular morphology was obtained after calcining the dry gel at 950℃, the CaMnO3 polycrystalline particles were composed by single-crystals with different orientations.
2018, 47(10):3218-3222.
Abstract:
Magnesium matrix composite was fabricated by vacuum hot pressing technique utilizingTiNishape memory alloy as reinforcement and AZ31 plate as matrix. The microstructure and mechanical properties of the composites at room temperature and elevated temperature were studied by optical microscope, SEM, EDS, DSC and tensile test. The results show：The interfacial bonding of the composites was good. The Mg element in the matrix and the Ti and Ni elements in the TiNi alloy diffused to form an interdiffusion layer of about 1 μm. The mechanical properties of the composites at elevated temperature were better than those at room temperature. The yield strength, tensile strength and elastic modulus of the composites were increased by 61MPa、41MPa and 6.05GPa respectively at 100℃ than at room temperature. The yield strength, tensile strength and elastic modulus of the composites were increased by 39MPa、72MPaand 12.19GPa respectively at 150℃ than at room temperature.
Magnesium matrix composite was fabricated by vacuum hot pressing technique utilizingTiNishape memory alloy as reinforcement and AZ31 plate as matrix. The microstructure and mechanical properties of the composites at room temperature and elevated temperature were studied by optical microscope, SEM, EDS, DSC and tensile test. The results show：The interfacial bonding of the composites was good. The Mg element in the matrix and the Ti and Ni elements in the TiNi alloy diffused to form an interdiffusion layer of about 1 μm. The mechanical properties of the composites at elevated temperature were better than those at room temperature. The yield strength, tensile strength and elastic modulus of the composites were increased by 61MPa、41MPa and 6.05GPa respectively at 100℃ than at room temperature. The yield strength, tensile strength and elastic modulus of the composites were increased by 39MPa、72MPaand 12.19GPa respectively at 150℃ than at room temperature.
2018, 47(10):3223-3227.
Abstract:
The effects of different amounts of Li addition on the microstructure and mechanical properties of Mg96.5Gd2.5Zn1 alloy by rapid solidification are investigated. The results indicate that the supersaturation of Gd and Zn solute atoms in the Mg matrix grain in the as-cast alloys decreased, (Mg, Zn) 3Gd precipitates located at the grain boundaries increased and the grain size of Mg matrix was reduced with Li addition. After solid-solution treatment, the formation of 14H type of long-period stacking phase in the alloys was inhibited and the nano- or submicron (Mg, Zn) 3Gd phase precipitated in large amounts with the increase of Li addition. And the Li content is 7.6 at. %, there is no LPSO formation in the alloy. After hot extrusion deformation, the block 14H phase in the alloys was kinked and delaminated, and lamellar 14H was dissolved in the matrix to some extent and (Mg,Zn)3Gd phase was fragmented and refined, the recrystallization occurred in the matrix in different extents. Mg96.5Gd2.5Zn1 alloy exhibits the best comprehensive mechanical property with the UTS of 325MPa and the EL of 9.5 %, whereas the mechanical properties of the alloys without Li addition decline gradually with the increase of Li addition. The microstructural evolution mechanism and mechanical behavior response under various conditions are analyzed.
The effects of different amounts of Li addition on the microstructure and mechanical properties of Mg96.5Gd2.5Zn1 alloy by rapid solidification are investigated. The results indicate that the supersaturation of Gd and Zn solute atoms in the Mg matrix grain in the as-cast alloys decreased, (Mg, Zn) 3Gd precipitates located at the grain boundaries increased and the grain size of Mg matrix was reduced with Li addition. After solid-solution treatment, the formation of 14H type of long-period stacking phase in the alloys was inhibited and the nano- or submicron (Mg, Zn) 3Gd phase precipitated in large amounts with the increase of Li addition. And the Li content is 7.6 at. %, there is no LPSO formation in the alloy. After hot extrusion deformation, the block 14H phase in the alloys was kinked and delaminated, and lamellar 14H was dissolved in the matrix to some extent and (Mg,Zn)3Gd phase was fragmented and refined, the recrystallization occurred in the matrix in different extents. Mg96.5Gd2.5Zn1 alloy exhibits the best comprehensive mechanical property with the UTS of 325MPa and the EL of 9.5 %, whereas the mechanical properties of the alloys without Li addition decline gradually with the increase of Li addition. The microstructural evolution mechanism and mechanical behavior response under various conditions are analyzed.
2018, 47(10):3228-3232.
Abstract:
In order to examine the brittle-ductile transition mechanism, nano-scratch experiment was conducted on (100), (110) and (111) crystal plane by using nano-indenter, and scratch morphology was observed by using atomic force microscopy and scanning electron microscope. The critical load and critical depth of brittle-ductile transition of each crystal plane were obtained by analyzing the depth-scratch distance curve and the scratch morphology. The results showed that single crystal germanium has strong anisotropy, the critical load of brittle-ductile transition on (100), (110) and (111) crystal plane are 37.6 mN, 30.5 mN and 32.4 mN, the critical depths are 594.7 nm, 512.5 nm and 536.6 nm respectively. A most plastic remove and least brittle-ductile transition on (100) crystal plane during the process of nano-scratch is due to its minimum hardness and deepest depth of brittle-ductile transition, and with the increase of speed of scratches, critical depth and critical load of brittle-ductile transition are increased. At last, the correctness of critical load and critical depth of brittle-ductile transition was verified through constant load scratch experiments.
In order to examine the brittle-ductile transition mechanism, nano-scratch experiment was conducted on (100), (110) and (111) crystal plane by using nano-indenter, and scratch morphology was observed by using atomic force microscopy and scanning electron microscope. The critical load and critical depth of brittle-ductile transition of each crystal plane were obtained by analyzing the depth-scratch distance curve and the scratch morphology. The results showed that single crystal germanium has strong anisotropy, the critical load of brittle-ductile transition on (100), (110) and (111) crystal plane are 37.6 mN, 30.5 mN and 32.4 mN, the critical depths are 594.7 nm, 512.5 nm and 536.6 nm respectively. A most plastic remove and least brittle-ductile transition on (100) crystal plane during the process of nano-scratch is due to its minimum hardness and deepest depth of brittle-ductile transition, and with the increase of speed of scratches, critical depth and critical load of brittle-ductile transition are increased. At last, the correctness of critical load and critical depth of brittle-ductile transition was verified through constant load scratch experiments.
2018, 47(10):3233-3237.
Abstract:
Commercially?pure?zirconium?was?strengthened?by?using?the?surface?mechanical?attraction?treatment?(SMAT).?Grains?in?the?surface?have?been?refined?and?compressive?residual?stress?has?been?induced.?Then,?heat?treatment?was?conducted?to?release?the?residual?stress?while?the?refined?microstructure?remained.?surface?microstructures?were?examined?by?optical?microscope?(OM)?and?transmission?electron?microscope?(TEM).?Residual?stresses?at?different?depths?were?measured?by?X-ray?diffraction?method.?Fatigue?properties?were?evaluated?by?four-point?bending?fatigue?test.?Morphology?of?the?fracture?surface?was?observed?by?scanning?electron?microscope?(SEM).?And?influence?mechanism?of?fatigue?properties?was?analyzed.?Based?on?the?experiments,?it?can?be?found?that?the?deformation?layer?with?the?depth?of?150μmwere?formed?after?SMAT.?Average?grain?size?of?surface?was?refined?to?35?nm.?And?a?residual?stress?field?with?depth?of?334?μmand?the?maximum?stress?of?-695.5MPa?can?be?obtained.?After?heat?treatment,?the?depth?of?residual?stress?field?reduced?to?115?μmand?the?maximum?stress?turned?into?-148.8MPa.It?is?found?that?residual?compressive?stress?can?improve?the?fatigue?limit?and?affect?the?location?of?crack?source?significantly.?The?fatigue?limit?of?SMATed?samples?was?increased?by?23%?compared?with?untreated?samples.?After?heat?treatment,?the?fatigue?limit?of?was?increased?by?13%?compared?with?the?samples?before?SMAT.
Commercially?pure?zirconium?was?strengthened?by?using?the?surface?mechanical?attraction?treatment?(SMAT).?Grains?in?the?surface?have?been?refined?and?compressive?residual?stress?has?been?induced.?Then,?heat?treatment?was?conducted?to?release?the?residual?stress?while?the?refined?microstructure?remained.?surface?microstructures?were?examined?by?optical?microscope?(OM)?and?transmission?electron?microscope?(TEM).?Residual?stresses?at?different?depths?were?measured?by?X-ray?diffraction?method.?Fatigue?properties?were?evaluated?by?four-point?bending?fatigue?test.?Morphology?of?the?fracture?surface?was?observed?by?scanning?electron?microscope?(SEM).?And?influence?mechanism?of?fatigue?properties?was?analyzed.?Based?on?the?experiments,?it?can?be?found?that?the?deformation?layer?with?the?depth?of?150μmwere?formed?after?SMAT.?Average?grain?size?of?surface?was?refined?to?35?nm.?And?a?residual?stress?field?with?depth?of?334?μmand?the?maximum?stress?of?-695.5MPa?can?be?obtained.?After?heat?treatment,?the?depth?of?residual?stress?field?reduced?to?115?μmand?the?maximum?stress?turned?into?-148.8MPa.It?is?found?that?residual?compressive?stress?can?improve?the?fatigue?limit?and?affect?the?location?of?crack?source?significantly.?The?fatigue?limit?of?SMATed?samples?was?increased?by?23%?compared?with?untreated?samples.?After?heat?treatment,?the?fatigue?limit?of?was?increased?by?13%?compared?with?the?samples?before?SMAT.
2018, 47(10):3238-3242.
Abstract:
This paper mainly adopted a hybrid molecular dynamics simulation method with the classical diffusion theory, in order to reveal the micro-scale diffusion characteristics of the welding interface, the molecular dynamics simulation of the explosive welding interface of shape memory alloy Ni50Ti50 and Cu was carried out by means of the embedded potential function (EAM potential). The micro-morphology and physical characteristics of the explosive welding interface were analyzed by means of SEM and EDX. The pressure oscillation of Ni50Ti50-Cu alloy system becomes smaller and smaller under the impact condition of uz=1500 m/s and ux=700 m/s. The temperature of the system is about 1350 K and the pressure is about 28GPa after 120ps. The atomic concentration of Cu on both sides of the diffusion layer is about 5% and that of Ni and Ti is about 5%. The interfacial diffusion layer thickness ranged from 1.03 to 1.45um. The thickness of the interfacial diffusion layer was about 1.56um, which was verified to the results of the SEM and EDS.
This paper mainly adopted a hybrid molecular dynamics simulation method with the classical diffusion theory, in order to reveal the micro-scale diffusion characteristics of the welding interface, the molecular dynamics simulation of the explosive welding interface of shape memory alloy Ni50Ti50 and Cu was carried out by means of the embedded potential function (EAM potential). The micro-morphology and physical characteristics of the explosive welding interface were analyzed by means of SEM and EDX. The pressure oscillation of Ni50Ti50-Cu alloy system becomes smaller and smaller under the impact condition of uz=1500 m/s and ux=700 m/s. The temperature of the system is about 1350 K and the pressure is about 28GPa after 120ps. The atomic concentration of Cu on both sides of the diffusion layer is about 5% and that of Ni and Ti is about 5%. The interfacial diffusion layer thickness ranged from 1.03 to 1.45um. The thickness of the interfacial diffusion layer was about 1.56um, which was verified to the results of the SEM and EDS.
2018, 47(10):3243-3250.
Abstract:
Roll bonding technology is one of the main preparation technologies of the bimetal laminated composite plate, and the history of its research and application over 100 years. It includes many methods, such as cold-roll bonding, hot-roll bonging, explosive rolling bonding, asymmetric rolling bonding, and so on. Firstly, the surface treatment methods of the rolling pieces were briefly introduced. Then, the technics characterizations, interface bonding theories and application of the roll bonding technology were summarized. The research status of the hot-roll bonding method and the asymmetric rolling bonding method was elaborated, especially. Last, the prospect of the technology was outlook.
Roll bonding technology is one of the main preparation technologies of the bimetal laminated composite plate, and the history of its research and application over 100 years. It includes many methods, such as cold-roll bonding, hot-roll bonging, explosive rolling bonding, asymmetric rolling bonding, and so on. Firstly, the surface treatment methods of the rolling pieces were briefly introduced. Then, the technics characterizations, interface bonding theories and application of the roll bonding technology were summarized. The research status of the hot-roll bonding method and the asymmetric rolling bonding method was elaborated, especially. Last, the prospect of the technology was outlook.
