Volume 41,Issue 9,2012 Table of Contents
2012, 41(9):1505-1510.
Abstract:
Diamond-like carbon (DLC) coatings with the thickness between 253-1880 nm were prepared on NiTi alloy by arc enhanced magnetron sputtering (AEMS). Surface profilometry, scratch tests, tribometry, and electrochemical tests were conducted to determine the mechanical properties and the corrosion behavior of the DLC-coated NiTi alloy, and it is found that DLC coatings with thickness between 700 and 1000 nm have moderate residual stress, high critical load, long wear life and good corrosion resistance. So DLC coatings with thickness between 700 and 1000 nm are suitable for improving the mechanical properties and corrosion resistance of biomedical NiTi alloy. The associated mechanisms were also discussed in detail.
Diamond-like carbon (DLC) coatings with the thickness between 253-1880 nm were prepared on NiTi alloy by arc enhanced magnetron sputtering (AEMS). Surface profilometry, scratch tests, tribometry, and electrochemical tests were conducted to determine the mechanical properties and the corrosion behavior of the DLC-coated NiTi alloy, and it is found that DLC coatings with thickness between 700 and 1000 nm have moderate residual stress, high critical load, long wear life and good corrosion resistance. So DLC coatings with thickness between 700 and 1000 nm are suitable for improving the mechanical properties and corrosion resistance of biomedical NiTi alloy. The associated mechanisms were also discussed in detail.
2012, 41(9):1511-1515.
Abstract:
Amorphous Ti3Ni2 (Ti2Ni/TiNi) alloy has been prepared by mechanical milling of crystalline Ti3Ni2 alloy, and its electrochemical properties were investigated. The results of charge and discharge test show that the amorphous Ti3Ni2 alloy can resolve the problem of extremely short cycle life of crystalline Ti3Ni2 alloy at high temperature (333 K). The capacity retention rate of amorphous Ti3Ni2 alloy is greatly increased to 88.83% at 333 K compared with the retention rate of its crystalline counterpart 39.47% after 19 cycles. Based on analysis of Tafel polarization, linear polarization, and electrochemical impedance spectroscopy, it is found that the major reason for the improvement is the presence of amorphous Ti3Ni2 alloy, which has much better corrosion resistance compared with its crystalline counterpart.
Amorphous Ti3Ni2 (Ti2Ni/TiNi) alloy has been prepared by mechanical milling of crystalline Ti3Ni2 alloy, and its electrochemical properties were investigated. The results of charge and discharge test show that the amorphous Ti3Ni2 alloy can resolve the problem of extremely short cycle life of crystalline Ti3Ni2 alloy at high temperature (333 K). The capacity retention rate of amorphous Ti3Ni2 alloy is greatly increased to 88.83% at 333 K compared with the retention rate of its crystalline counterpart 39.47% after 19 cycles. Based on analysis of Tafel polarization, linear polarization, and electrochemical impedance spectroscopy, it is found that the major reason for the improvement is the presence of amorphous Ti3Ni2 alloy, which has much better corrosion resistance compared with its crystalline counterpart.
2012, 41(9):1516-1521.
Abstract:
In order to improve the gaseous and electrochemical hydrogen storage kinetics of the Mg2Ni-type alloys, Ni in the alloy was partially substituted by element Cu. Rapid quenching technology was used for the preparation of the Mg2Ni1-xCux (x = 0, 0.1, 0.2, 0.3, 0.4) hydrogen storage alloys. The structures of the as-cast and quenched alloys were characterized by XRD, SEM and TEM. The gaseous hydrogen absorption and desorption kinetics of the alloys were measured by an automatically controlled Sieverts apparatus. The electrochemical hydrogen storage kinetics of the as-quenched alloys was tested by an automatic galvanostatic system. The results show that all the as-quenched alloys hold an entire nanocrystalline structure and are free of amorphous phase. The substitution of Cu, instead of changing the major phase Mg2Ni, leads to a visible refinement of the grains of the as-cast alloys. Furthermore, both the rapid quenching treatment and Cu substitution significantly improve the gaseous and electrochemical hydrogen storage kinetics of the alloys. As the quenching rate grows from 0 (as-cast is defined as quenching rate of 0 m/s) to 30 m/s, the hydrogen absorption saturation ratio in 5 min, for the Mg2Ni0.7Cu0.3 alloy, increases from 57.2% to 92.8%, the hydrogen desorption ratio in 20 min from 21.6% to 49.6%, the high rate discharge ability (HRD) from 40.6% to 73.1%, the hydrogen diffusion coefficient (D) from 1.02×10?11 to 4.08×10?11 cm2/s and the limiting current density (IL) from 113.0 to 715.3 mA/g.
In order to improve the gaseous and electrochemical hydrogen storage kinetics of the Mg2Ni-type alloys, Ni in the alloy was partially substituted by element Cu. Rapid quenching technology was used for the preparation of the Mg2Ni1-xCux (x = 0, 0.1, 0.2, 0.3, 0.4) hydrogen storage alloys. The structures of the as-cast and quenched alloys were characterized by XRD, SEM and TEM. The gaseous hydrogen absorption and desorption kinetics of the alloys were measured by an automatically controlled Sieverts apparatus. The electrochemical hydrogen storage kinetics of the as-quenched alloys was tested by an automatic galvanostatic system. The results show that all the as-quenched alloys hold an entire nanocrystalline structure and are free of amorphous phase. The substitution of Cu, instead of changing the major phase Mg2Ni, leads to a visible refinement of the grains of the as-cast alloys. Furthermore, both the rapid quenching treatment and Cu substitution significantly improve the gaseous and electrochemical hydrogen storage kinetics of the alloys. As the quenching rate grows from 0 (as-cast is defined as quenching rate of 0 m/s) to 30 m/s, the hydrogen absorption saturation ratio in 5 min, for the Mg2Ni0.7Cu0.3 alloy, increases from 57.2% to 92.8%, the hydrogen desorption ratio in 20 min from 21.6% to 49.6%, the high rate discharge ability (HRD) from 40.6% to 73.1%, the hydrogen diffusion coefficient (D) from 1.02×10?11 to 4.08×10?11 cm2/s and the limiting current density (IL) from 113.0 to 715.3 mA/g.
2012, 41(9):1522-1526.
Abstract:
Cast AZ31 magnesium alloy was treated by the single-pass and two-pass friction stir processing (FSP), respectively, and the microstructure and mechanical properties were investigated. The results show that FSP causes a remarkable grain refinement and homogenization, and it makes the coarse, network-like eutectic β-Mg17Al12 phase break up and dissolve into the magnesium matrix. There is no obvious preferential orientation in the cast AZ31 alloy and the single-pass FSP specimen. On the contrary, the two-pass FSP specimen exhibits the preferential grain orientation, and (0002) basal plane shows a strong tendency to be parallel to the plate surface. Further, the ultimate tensile strengths of the single-pass and the two-pass FSP specimens increase by 43 and 82 MPa, and elongations increase by 4.3% and 11.9%, respectively. In the FSP condition, the fracture surface of the AZ31 magnesium alloy exhibits ductile fracture characterization.
Cast AZ31 magnesium alloy was treated by the single-pass and two-pass friction stir processing (FSP), respectively, and the microstructure and mechanical properties were investigated. The results show that FSP causes a remarkable grain refinement and homogenization, and it makes the coarse, network-like eutectic β-Mg17Al12 phase break up and dissolve into the magnesium matrix. There is no obvious preferential orientation in the cast AZ31 alloy and the single-pass FSP specimen. On the contrary, the two-pass FSP specimen exhibits the preferential grain orientation, and (0002) basal plane shows a strong tendency to be parallel to the plate surface. Further, the ultimate tensile strengths of the single-pass and the two-pass FSP specimens increase by 43 and 82 MPa, and elongations increase by 4.3% and 11.9%, respectively. In the FSP condition, the fracture surface of the AZ31 magnesium alloy exhibits ductile fracture characterization.
2012, 41(9):1527-1530.
Abstract:
Through a mild thermal precipitation and aging process, hydrated cobalt oxalate nanorods were synthesized using CoSO3 and (NH4)2C2O4·H2O as raw materials at the reaction and aging temperature of 65 °C. Afterwards, the metal cobalt nanofibres were prepared by decomposition of cobalt oxalate nanorods precursor in Ar gas atmosphere. The composition and morphology of products were characterized by means of atomic absorption spectrometer (AAS), organic elemental analyzer (OEA), Fourier transform infrared spectroscopy (FT-IR), thermogravimetry analysis and derivative thermogravimetry (TGA-DTG), the X-ray diffraction (XRD), and scanning electron microscope (SEM). The results demonstrate that the product is hydrated cobalt oxalate, and the chemical formula CoC2O4·3H2O is confirmed. The sizes of the cobalt oxalate nanorods as-prepared are about 0.2-0.4 μm in diameter, and 1.0-5.0 μm in length; the metal nanofibres prepared via decomposition process of hydrated cobalt oxalate nanorods are about 0.2 μm in diameter, and 1.0-5.0 μm in length.
Through a mild thermal precipitation and aging process, hydrated cobalt oxalate nanorods were synthesized using CoSO3 and (NH4)2C2O4·H2O as raw materials at the reaction and aging temperature of 65 °C. Afterwards, the metal cobalt nanofibres were prepared by decomposition of cobalt oxalate nanorods precursor in Ar gas atmosphere. The composition and morphology of products were characterized by means of atomic absorption spectrometer (AAS), organic elemental analyzer (OEA), Fourier transform infrared spectroscopy (FT-IR), thermogravimetry analysis and derivative thermogravimetry (TGA-DTG), the X-ray diffraction (XRD), and scanning electron microscope (SEM). The results demonstrate that the product is hydrated cobalt oxalate, and the chemical formula CoC2O4·3H2O is confirmed. The sizes of the cobalt oxalate nanorods as-prepared are about 0.2-0.4 μm in diameter, and 1.0-5.0 μm in length; the metal nanofibres prepared via decomposition process of hydrated cobalt oxalate nanorods are about 0.2 μm in diameter, and 1.0-5.0 μm in length.
2012, 41(9):1531-1534.
Abstract:
The effects of absorbed hydrogen on behavior of NZ2 zirconium alloy (Zr-1.0Sn-0.3Nb-0.3Fe-0.1Cr, in wt% designated as NZ2) were investigated. The sheet specimens were hydrided with different hydrogen contents: unhydrided (original hydrogen content), 200, 450 and 730 mg/g H and tested at room temperature and 375 °C, respectively. The results show that dynamic strain ageing (DSA) can be observed during cyclic deformation of NZ2 alloy at 375 °C. Even if the hydriding content is up to 730 mg/g it has no influence on DSA. Hydrogen can improve the fatigue life of NZ2 alloy at 375 °C and cause the cyclic softening.
The effects of absorbed hydrogen on behavior of NZ2 zirconium alloy (Zr-1.0Sn-0.3Nb-0.3Fe-0.1Cr, in wt% designated as NZ2) were investigated. The sheet specimens were hydrided with different hydrogen contents: unhydrided (original hydrogen content), 200, 450 and 730 mg/g H and tested at room temperature and 375 °C, respectively. The results show that dynamic strain ageing (DSA) can be observed during cyclic deformation of NZ2 alloy at 375 °C. Even if the hydriding content is up to 730 mg/g it has no influence on DSA. Hydrogen can improve the fatigue life of NZ2 alloy at 375 °C and cause the cyclic softening.
2012, 41(9):1535-1538.
Abstract:
Phase transformation and mechanical properties of TLM titanium alloy for orthopaedic implant application were studied. The results show that a small amount of slender α″ phase exists in the β matrix after solution treating and water quenching. The formation of α phase goes through two procedures during the aging treatment from 300 oC to 500 oC, one is β→ω→α, and the other is α″→α. While the micrographs reveal that α″ martensite hinder the nucleation and growth of metastable ω phase. The effect of the phase structures on reducing the elastic modulus is in the order of ω＞α″＞α, and the effect on improving the strength is in the order of ω＞α＞α″, and vice versa for improving the elongation of TLM alloy.
Phase transformation and mechanical properties of TLM titanium alloy for orthopaedic implant application were studied. The results show that a small amount of slender α″ phase exists in the β matrix after solution treating and water quenching. The formation of α phase goes through two procedures during the aging treatment from 300 oC to 500 oC, one is β→ω→α, and the other is α″→α. While the micrographs reveal that α″ martensite hinder the nucleation and growth of metastable ω phase. The effect of the phase structures on reducing the elastic modulus is in the order of ω＞α″＞α, and the effect on improving the strength is in the order of ω＞α＞α″, and vice versa for improving the elongation of TLM alloy.
2012, 41(9):1539-1543.
Abstract:
The friction wear properties of TC4 alloy and P110 tubing steel were comparatively studied at different temperatures. The changing rules of the wear rate, frication coefficient and topography of wear mark with the temperature were analyzed and the wear mechanism was also discussed. The results show that the wear resistance of P110 tubing steel excels obviously that of TC4 alloy. The wear resistance of TC4 changes a little with temperature rising and the wear mark is furrow morphology. The wear mechanism of TC4 alloy is delamination abrasion, adhesive abrasion and fatigue abrasion at lower temperature and delamination abrasion, adhesive abrasion and oxidation abrasion at higher temperature. The wear resistance of P110 tubing steel is decreased with temperature rising. The wear mark of P110 tubing steel is wear pit morphology and the wear mechanism is delamination abrasion and abrasive grain abrasion at lower temperature, while the wear mark is furrow morphology and the wear mechanism is delamination abrasion, adhesive abrasion and oxidation abrasion at higher temperature.
The friction wear properties of TC4 alloy and P110 tubing steel were comparatively studied at different temperatures. The changing rules of the wear rate, frication coefficient and topography of wear mark with the temperature were analyzed and the wear mechanism was also discussed. The results show that the wear resistance of P110 tubing steel excels obviously that of TC4 alloy. The wear resistance of TC4 changes a little with temperature rising and the wear mark is furrow morphology. The wear mechanism of TC4 alloy is delamination abrasion, adhesive abrasion and fatigue abrasion at lower temperature and delamination abrasion, adhesive abrasion and oxidation abrasion at higher temperature. The wear resistance of P110 tubing steel is decreased with temperature rising. The wear mark of P110 tubing steel is wear pit morphology and the wear mechanism is delamination abrasion and abrasive grain abrasion at lower temperature, while the wear mark is furrow morphology and the wear mechanism is delamination abrasion, adhesive abrasion and oxidation abrasion at higher temperature.
2012, 41(9):1544-1548.
Abstract:
Using Cu-Ti+Mo composite filler, 2D C/SiC composite was brazed to GH783 nickel-based alloy under vacuum condition. The microstructure of the joint and the effect of Mo content on microstructure and properties of joints were investigated. The results show that the joint is composed of 4 regions: interface reaction layer, stress relief layer, soft metal layer and diffusion layer, without holes, cracks or other defects. The maximal flexural strength reaches 141 MPa with 15% (mass fraction) Mo particles in the joint, and the flexural strength of the joint declines when Mo content exceeds 15%. The Mo addition releases the residual stress of the joint, and inhibits excessive reaction between Ti and C/SiC, thus effectively improving the strength of the joint.
Using Cu-Ti+Mo composite filler, 2D C/SiC composite was brazed to GH783 nickel-based alloy under vacuum condition. The microstructure of the joint and the effect of Mo content on microstructure and properties of joints were investigated. The results show that the joint is composed of 4 regions: interface reaction layer, stress relief layer, soft metal layer and diffusion layer, without holes, cracks or other defects. The maximal flexural strength reaches 141 MPa with 15% (mass fraction) Mo particles in the joint, and the flexural strength of the joint declines when Mo content exceeds 15%. The Mo addition releases the residual stress of the joint, and inhibits excessive reaction between Ti and C/SiC, thus effectively improving the strength of the joint.
2012, 41(9):1549-1554.
Abstract:
The microstructure evolution and precipitates of Cu-0.22Cr-0.05Zr-0.05Sn alloy under different thermomechanical treatments were studied by TEM and the changes of mechanical property and electrical conductivity of the alloy were explained. Results show that two kinds of precipitates of Cr and Cu4Zr consist in the matrix. Cr precipitates undergo a course of solid solution, GP zone, precipitation, coherence with the matrix and coarsening. Cu4Zr precipitates are nucleated preferentially at the pre-nucleated Cr particles, and semi-coherent with the matrix. The alloy has a better aging strengthening effect duo to that the fine precipitates are well dispersed. The alloy has an excellent combination of tensile strength and electrical conductivity reaching 400 MPa and 84%IACS respectively when subjected to the optimum thermomechanical treatment, i.e., solution-treating at 940 oC for 1 h and cold drawing to 96% strain followed by aging at 400 oC for 4 h. To this alloy, aging temperature is a key factor to determine the combination properties while the effect of aging time is unnoticeable.
The microstructure evolution and precipitates of Cu-0.22Cr-0.05Zr-0.05Sn alloy under different thermomechanical treatments were studied by TEM and the changes of mechanical property and electrical conductivity of the alloy were explained. Results show that two kinds of precipitates of Cr and Cu4Zr consist in the matrix. Cr precipitates undergo a course of solid solution, GP zone, precipitation, coherence with the matrix and coarsening. Cu4Zr precipitates are nucleated preferentially at the pre-nucleated Cr particles, and semi-coherent with the matrix. The alloy has a better aging strengthening effect duo to that the fine precipitates are well dispersed. The alloy has an excellent combination of tensile strength and electrical conductivity reaching 400 MPa and 84%IACS respectively when subjected to the optimum thermomechanical treatment, i.e., solution-treating at 940 oC for 1 h and cold drawing to 96% strain followed by aging at 400 oC for 4 h. To this alloy, aging temperature is a key factor to determine the combination properties while the effect of aging time is unnoticeable.
2012, 41(9):1555-1558.
Abstract:
New type Cr-Ni-Mo and Cr-Ni-Co overlaying alloys were prepared by argon tungsten-arc welding (TIG) on 304 stainless steel, and tested by cavitation vibrating device. The cavitation erosion resistance of alloys was compared through the analysis of mass loss. The alloy layer was analyzed by scanning electron microscopy (SEM), X-ray diffractometer (XRD) and microhardness tester. Results indicate that the cavitation erosion resistance of Cr-Ni-Mo and Cr-Ni-Co overlaying alloys is better than that of 304 stainless steel, and the resistance of Cr-Ni-Co is better than Cr-Ni-Mo. In the process of cavitation the damage is preferred to appear in grain boundary. Phase transformation from austenite to martensite happens in the cavitation process of Cr-Ni-Co alloy, and it is helpful to absorb the energy and delay the process of cavitation erosion, and enhance the cavitation erosion resistance effectively. The cavitation erosion resistance of overlaying alloys is related to hardness and work hardening ability.
New type Cr-Ni-Mo and Cr-Ni-Co overlaying alloys were prepared by argon tungsten-arc welding (TIG) on 304 stainless steel, and tested by cavitation vibrating device. The cavitation erosion resistance of alloys was compared through the analysis of mass loss. The alloy layer was analyzed by scanning electron microscopy (SEM), X-ray diffractometer (XRD) and microhardness tester. Results indicate that the cavitation erosion resistance of Cr-Ni-Mo and Cr-Ni-Co overlaying alloys is better than that of 304 stainless steel, and the resistance of Cr-Ni-Co is better than Cr-Ni-Mo. In the process of cavitation the damage is preferred to appear in grain boundary. Phase transformation from austenite to martensite happens in the cavitation process of Cr-Ni-Co alloy, and it is helpful to absorb the energy and delay the process of cavitation erosion, and enhance the cavitation erosion resistance effectively. The cavitation erosion resistance of overlaying alloys is related to hardness and work hardening ability.
2012, 41(9):1559-1563.
Abstract:
Four kinds of Mo targets with different microstructures were sputtered by the same sputtering line under the same sputtering process. Microstructures (face and fractured cross-section) of sputtered films were analyzed with SEM, and the orientation of crystals and square resistance were measured with XRD and four-probe array method, respectively. Influence of Mo target’s microstructure on deposition rate and square resistance of the sputtered film were discussed. Results show that the sputtering film’s morphology of different Mo-targets is rarely different. When Mo targets are with 80% fine grains under 50 μm, the uniformity of sputtering film’s thickness and resistance are satisfied. The preferred orientation of Mo sputtered film is mostly (110). The target microstructures have little effect on sputtering film crystals’ orientation. When the Mo target’s grain size is finer and the area rate of grain boundary is higher, the sputtering film has faster deposition velocity and the sputtering film’s thickness is larger. The thickness reduction of sputtering target is more homogeneous, which raises the utilization rate of sputtering targets.
Four kinds of Mo targets with different microstructures were sputtered by the same sputtering line under the same sputtering process. Microstructures (face and fractured cross-section) of sputtered films were analyzed with SEM, and the orientation of crystals and square resistance were measured with XRD and four-probe array method, respectively. Influence of Mo target’s microstructure on deposition rate and square resistance of the sputtered film were discussed. Results show that the sputtering film’s morphology of different Mo-targets is rarely different. When Mo targets are with 80% fine grains under 50 μm, the uniformity of sputtering film’s thickness and resistance are satisfied. The preferred orientation of Mo sputtered film is mostly (110). The target microstructures have little effect on sputtering film crystals’ orientation. When the Mo target’s grain size is finer and the area rate of grain boundary is higher, the sputtering film has faster deposition velocity and the sputtering film’s thickness is larger. The thickness reduction of sputtering target is more homogeneous, which raises the utilization rate of sputtering targets.
2012, 41(9):1564-1567.
Abstract:
La2O3 doped Mo powder was pressed, sintered and cross rolled to prepare alloy plates. Then the plates were stamped to obtain molybdenum boat. The mechanical properties of the molybdenum boat were investigated under the condition of variable temperatures and loads. The influences of precipitate dispersive distribution on the mechanical properties and the influence of heating system on the stamping property were discussed for the alloy plates. And the fracture mechanism of the boat was analyzed. Results show that La2O3 of dispersive distribution increases markedly the recrystallization temperature and mechanical properties of the Mo plates. Cross rolling decreases the difference of mechanical properties between transversal and longitudinal directions, which is favorable for the stamping of Mo-La2O3 alloy plates. The maximum punch deformation can be reached when heating the 2.8 mm thick Mo-10%La2O3 alloy plate and stamping dies at 550 oC. After long-time operation of the boat in 18-tube furnace under the variable temperature and load condition, it is found that vacancy migration and dislocation slip result in dimple tear, and eventually lead to the macroscopic fracture of the molybdenum boat.
La2O3 doped Mo powder was pressed, sintered and cross rolled to prepare alloy plates. Then the plates were stamped to obtain molybdenum boat. The mechanical properties of the molybdenum boat were investigated under the condition of variable temperatures and loads. The influences of precipitate dispersive distribution on the mechanical properties and the influence of heating system on the stamping property were discussed for the alloy plates. And the fracture mechanism of the boat was analyzed. Results show that La2O3 of dispersive distribution increases markedly the recrystallization temperature and mechanical properties of the Mo plates. Cross rolling decreases the difference of mechanical properties between transversal and longitudinal directions, which is favorable for the stamping of Mo-La2O3 alloy plates. The maximum punch deformation can be reached when heating the 2.8 mm thick Mo-10%La2O3 alloy plate and stamping dies at 550 oC. After long-time operation of the boat in 18-tube furnace under the variable temperature and load condition, it is found that vacancy migration and dislocation slip result in dimple tear, and eventually lead to the macroscopic fracture of the molybdenum boat.
2012, 41(9):1568-1573.
Abstract:
The correlation between the concentration of vanadium (V) and the nucleation incubation period of L12 order phase and D022 order phase precipitated from Ni75Al25-xVx alloy was investigated by atom morphology evolution and average order parameters based on the microscopic phase dynamic model. The computer simulations demonstrate that with the variation of vanadium concentration in different ranges, the nucleation incubation periods change for L12 order phase and D022 order phase precipitated from Ni75Al25-xVx, and they present totally diverse correlation. When x is between 9.0 and 19.7, the incubation periods of two phases and V content show positive correlation, and the incubation period of D022 is longer than that of L12. When x is between 19.7 and 23.0, the incubation periods of two phases and V content show negative correlation, and the incubation period of L12 is longer than that of D022. When x is equal to 19.7, the difference between their nucleation incubation periods is not obvious.
The correlation between the concentration of vanadium (V) and the nucleation incubation period of L12 order phase and D022 order phase precipitated from Ni75Al25-xVx alloy was investigated by atom morphology evolution and average order parameters based on the microscopic phase dynamic model. The computer simulations demonstrate that with the variation of vanadium concentration in different ranges, the nucleation incubation periods change for L12 order phase and D022 order phase precipitated from Ni75Al25-xVx, and they present totally diverse correlation. When x is between 9.0 and 19.7, the incubation periods of two phases and V content show positive correlation, and the incubation period of D022 is longer than that of L12. When x is between 19.7 and 23.0, the incubation periods of two phases and V content show negative correlation, and the incubation period of L12 is longer than that of D022. When x is equal to 19.7, the difference between their nucleation incubation periods is not obvious.
15 Effect of Sm and Ti Compound Inoculation on Microstructure and Mechanical Properties of AM60 Alloy
Zhang Jinshan
,
Ji Guoqiang
,
Qiu Bin
,
Zhao Gaozhan
,
Wang Xing
,
Tao Weijian
,
Jiang Hui
,
Sun Yong
2012, 41(9):1574-1579.
Abstract:
Microstructures and mechanical properties of AM60 magnesium alloy with Sm and Ti addition were investigated through OM, SEM, XRD and DNS100 electronic universal testing machines and the effect of Sm and Ti addition was analyzed. The results show that the alloy grains can be refined greatly by the proper addition of Sm or Ti and reduce the precipitation of β. There are some Al3Ti phases formed after the addition of Ti. However, the β-Mg17A112 phase of the AM60 alloy changes from discontinuous netlike form to cobble or particulate form and even dispersed after 1%Sm addition. Particle phase of Al2Sm, Mg41Sm5 and spherical phase of Al18Ti2Mg3 are formed when adding Sm and Ti together. The rod-shaped phases in the alloy dismiss or transform roundly and massive particles become smaller by the inoculation of Ti and subsequent T6 process. With addition of 1.0%Sm and 0.4%Ti, the tensile strength and elongation reach 226 MPa and 6.7% , elevated by 34.5% and 39.6% respectively; the heat tensile strength and elongation at 200 oC reach 170 MPa and 10.4%, elevated by 53.2% and 82.5% respectively. T6 process can further enhance the mechanical properties of AM60 alloy.
Microstructures and mechanical properties of AM60 magnesium alloy with Sm and Ti addition were investigated through OM, SEM, XRD and DNS100 electronic universal testing machines and the effect of Sm and Ti addition was analyzed. The results show that the alloy grains can be refined greatly by the proper addition of Sm or Ti and reduce the precipitation of β. There are some Al3Ti phases formed after the addition of Ti. However, the β-Mg17A112 phase of the AM60 alloy changes from discontinuous netlike form to cobble or particulate form and even dispersed after 1%Sm addition. Particle phase of Al2Sm, Mg41Sm5 and spherical phase of Al18Ti2Mg3 are formed when adding Sm and Ti together. The rod-shaped phases in the alloy dismiss or transform roundly and massive particles become smaller by the inoculation of Ti and subsequent T6 process. With addition of 1.0%Sm and 0.4%Ti, the tensile strength and elongation reach 226 MPa and 6.7% , elevated by 34.5% and 39.6% respectively; the heat tensile strength and elongation at 200 oC reach 170 MPa and 10.4%, elevated by 53.2% and 82.5% respectively. T6 process can further enhance the mechanical properties of AM60 alloy.
2012, 41(9):1580-1585.
Abstract:
The externally solidified crystals (ESCs) and divorced eutectics in die castings of magnesium alloy have a great influence on the final performance of castings. Under the cold-chamber high pressure die casting (HPDC) process, samples were produced at different slow shot phase and fast shot phase plunger velocities to investigate the microstructure characteristics of AM60B magnesium alloy. Based on the analysis and statistics of the experimental results obtained by using OM, EBSD, XRD, SEM and EDS, it is concluded that at the slow shot phase of the HPDC process, nucleation and crystals growth occur in the melt in the shot sleeve due to the loss of superheat; the ESCs are migrating to the central region of the castings during the fast shot phase of the melt into the die cavity at high speed, which lead to a higher distribution of the ESCs at the central region than the surface layer of the castings. Besides, the percentage of the ESCs is higher at a lower slow shot phase plunger velocity, and also is higher at the area near the gate than that of the area far from the gate of the castings. Coarse dendrites are observed at the cross section of the castings at a lower fast shot phase plunger velocity. At the last stage of solidification under HPDC process, fully divorced eutectics consisting of α-Mg and β-Mg17Al12 appear at the grain boundary of the primary α-Mg. Islands of β-Mg17Al12 phase are observed at the central region of the castings, while the β-Mg17Al12 phase reveals a more dispersed and granular morphology at the surface layer. The percentage of the eutectics is higher at the central region than that at the surface layer of the castings, whilst the defect band also contains a higher percentage of the eutectics than those at the adjacent regions.
The externally solidified crystals (ESCs) and divorced eutectics in die castings of magnesium alloy have a great influence on the final performance of castings. Under the cold-chamber high pressure die casting (HPDC) process, samples were produced at different slow shot phase and fast shot phase plunger velocities to investigate the microstructure characteristics of AM60B magnesium alloy. Based on the analysis and statistics of the experimental results obtained by using OM, EBSD, XRD, SEM and EDS, it is concluded that at the slow shot phase of the HPDC process, nucleation and crystals growth occur in the melt in the shot sleeve due to the loss of superheat; the ESCs are migrating to the central region of the castings during the fast shot phase of the melt into the die cavity at high speed, which lead to a higher distribution of the ESCs at the central region than the surface layer of the castings. Besides, the percentage of the ESCs is higher at a lower slow shot phase plunger velocity, and also is higher at the area near the gate than that of the area far from the gate of the castings. Coarse dendrites are observed at the cross section of the castings at a lower fast shot phase plunger velocity. At the last stage of solidification under HPDC process, fully divorced eutectics consisting of α-Mg and β-Mg17Al12 appear at the grain boundary of the primary α-Mg. Islands of β-Mg17Al12 phase are observed at the central region of the castings, while the β-Mg17Al12 phase reveals a more dispersed and granular morphology at the surface layer. The percentage of the eutectics is higher at the central region than that at the surface layer of the castings, whilst the defect band also contains a higher percentage of the eutectics than those at the adjacent regions.
2012, 41(9):1586-1591.
Abstract:
Electrochemical behavior of AZ31 wrought magnesium alloy activated by hydrofluoric acid (HF) of different concentration was studied in an electroless nickel plating bath, using mixed potential-time curves, polarization curves and electrochemical impedance spectrum. Changes of morphologies of AZ31 samples before and after the HF activation were observed by scanning electron microscopy (SEM). The results show that the time in which the activated samples were coated completely by Ni-P layers extends with the increase of the concentration of HF. The onset reduction potential of Ni2+ in the plating bath shifts toward positive direction with an increase in the concentration of HF. The charge transfer resistance of electrode/bath interface reaction increases with an increase in the concentration of HF, and the interface reaction between the electrode and the bath is the rate-controlling step during the initial deposition stage. The shedding of Mn-Al particles in the AZ31 magnesium alloy matrix during the HF activation process results in the defect formation of the fluoride film, and the higher concentration of HF, the less defect formed on the fluoride film.
Electrochemical behavior of AZ31 wrought magnesium alloy activated by hydrofluoric acid (HF) of different concentration was studied in an electroless nickel plating bath, using mixed potential-time curves, polarization curves and electrochemical impedance spectrum. Changes of morphologies of AZ31 samples before and after the HF activation were observed by scanning electron microscopy (SEM). The results show that the time in which the activated samples were coated completely by Ni-P layers extends with the increase of the concentration of HF. The onset reduction potential of Ni2+ in the plating bath shifts toward positive direction with an increase in the concentration of HF. The charge transfer resistance of electrode/bath interface reaction increases with an increase in the concentration of HF, and the interface reaction between the electrode and the bath is the rate-controlling step during the initial deposition stage. The shedding of Mn-Al particles in the AZ31 magnesium alloy matrix during the HF activation process results in the defect formation of the fluoride film, and the higher concentration of HF, the less defect formed on the fluoride film.
2012, 41(9):1592-1596.
Abstract:
The optical microstructure, mechanical properties and high cycle tension-compression fatigue properties (R= –1) at room temperature of gravity permanent cast (GPC) and gravity sand cast (GSC) Mg-3Nd-0.2Zn-Zr (NZ30K) (wt.%) magnesium alloy were studied. Results show that GPC-NZ30K alloy has normal grain size distribution generally, with relatively fine grains, about 60 μm, while GSC-NZ30K alloy has non-uniform grain size distribution, with relatively coarse grains, about 70 μm. Finer grains in GPC-NZ30K-T6 alloy lead to higher yield strength (+6.6 MPa), higher ultimate tensile strength (+43 MPa) and higher elongation (+2.8%). However, it has a little influence on fatigue strength (+1.12 MPa). Coarse and non-uniform grain size distribution in GSC-NZ30K-T6 alloy is favor to minimize the fatigue variation of cast NZ30K-T6 alloy.
The optical microstructure, mechanical properties and high cycle tension-compression fatigue properties (R= –1) at room temperature of gravity permanent cast (GPC) and gravity sand cast (GSC) Mg-3Nd-0.2Zn-Zr (NZ30K) (wt.%) magnesium alloy were studied. Results show that GPC-NZ30K alloy has normal grain size distribution generally, with relatively fine grains, about 60 μm, while GSC-NZ30K alloy has non-uniform grain size distribution, with relatively coarse grains, about 70 μm. Finer grains in GPC-NZ30K-T6 alloy lead to higher yield strength (+6.6 MPa), higher ultimate tensile strength (+43 MPa) and higher elongation (+2.8%). However, it has a little influence on fatigue strength (+1.12 MPa). Coarse and non-uniform grain size distribution in GSC-NZ30K-T6 alloy is favor to minimize the fatigue variation of cast NZ30K-T6 alloy.
2012, 41(9):1597-1601.
Abstract:
Uniform microarc oxidation coatings on the friction stir weld (FSW) joint of 5083 aluminum alloy were prepared by microarc oxidation (MAO) technique. The corrosion resistance of the friction stir weld joint before and after microarc oxidation surface treatment was evaluated by potentiodynamic polarization test and electrochemical impedance spectroscopic analysis (EIS). The results show that by microarc oxidation surface treatment, the corrosion current density of friction stir weld samples is decreased, and its electrochemical impedance is increased, thus the corrosion resistance of coated samples being significantly improved. In addition, the corrosion behavior at Fsw microstructure zones without MAO surface treatment have rather obvious difference, but after MAO treatment, both the coated base metal and Fsw joint on 5083 aluminum alloy have similar surface morphology and corrosion resistance.
Uniform microarc oxidation coatings on the friction stir weld (FSW) joint of 5083 aluminum alloy were prepared by microarc oxidation (MAO) technique. The corrosion resistance of the friction stir weld joint before and after microarc oxidation surface treatment was evaluated by potentiodynamic polarization test and electrochemical impedance spectroscopic analysis (EIS). The results show that by microarc oxidation surface treatment, the corrosion current density of friction stir weld samples is decreased, and its electrochemical impedance is increased, thus the corrosion resistance of coated samples being significantly improved. In addition, the corrosion behavior at Fsw microstructure zones without MAO surface treatment have rather obvious difference, but after MAO treatment, both the coated base metal and Fsw joint on 5083 aluminum alloy have similar surface morphology and corrosion resistance.
2012, 41(9):1602-1606.
Abstract:
The low cycle fatigue (LCF) life and fracture behavior of directionally solidified superalloy DZ4 after torsional pre-deformation and heat treatment was tested and studied. The influence of different pre-deformation extents and rates on LCF life and recrystallization was analyzed. The formation mechanism of intergranular area was investigated. The results show that LCF life of directionally solidified superalloy DZ4 decreases rapidly after torsional pre-deformation and heat treatment, which is related to recrystallization texture in plastically deforming area. Cracks and damages are found on the interface of the recrystallization and the matrix caused by their inharmonious deformation, and the cracks propagate along the recrystallization boundary to form intergranular area, resulting in the decrease of LCF life. Meanwhile the life is decreased sharply with the increase of the recrystallization depth. The depth of intergranular area is in accord with the recrystallization depth when the pre-deformation is small; while when the pre-deformation is larger, the depth of intergranular area is relatively smaller. Besides, the increase of strain rate aggravates inharmonious deformation, and makes recrystallization localize, which cause more serious decrease of LCF.
The low cycle fatigue (LCF) life and fracture behavior of directionally solidified superalloy DZ4 after torsional pre-deformation and heat treatment was tested and studied. The influence of different pre-deformation extents and rates on LCF life and recrystallization was analyzed. The formation mechanism of intergranular area was investigated. The results show that LCF life of directionally solidified superalloy DZ4 decreases rapidly after torsional pre-deformation and heat treatment, which is related to recrystallization texture in plastically deforming area. Cracks and damages are found on the interface of the recrystallization and the matrix caused by their inharmonious deformation, and the cracks propagate along the recrystallization boundary to form intergranular area, resulting in the decrease of LCF life. Meanwhile the life is decreased sharply with the increase of the recrystallization depth. The depth of intergranular area is in accord with the recrystallization depth when the pre-deformation is small; while when the pre-deformation is larger, the depth of intergranular area is relatively smaller. Besides, the increase of strain rate aggravates inharmonious deformation, and makes recrystallization localize, which cause more serious decrease of LCF.
2012, 41(9):1607-1610.
Abstract:
A series of bonded magnets of (Nd,Pr)10.5(Fe,Co)83.5-xMxB6 (M=Zr, Nb, Ti) alloys were prepared by the melt-spun method. The effects of Zr, Nb and Ti element on the microstructure and magnetic properties of alloys have been investigated. The grains of (Nd,Pr)10.5(Fe,Co)83.5B6 with suitable addition of Zr, Nb, or Ti element are finer and more homogeneous. The average grain size is about 50~70 nm. Due to the combined effect of grains refining and pinning to magnetic domain wall of non-magnetic phases, the demagnetization curve rectangularity is improved notably, and the value of Hk/Hcj and other magnetic properties are also greatly increased for the bonded magnets with Zr, Nb, and Ti element addition. Compared with Nb and Ti, Zr has the best effect on refining the grains and increasing magnetic property. For the (Nd,Pr)10.5(Fe,Co)82.5Zr1B6 alloy with 1% Zr, the grains are ~60 nm and homogeneous, the demagnetization curve rectangularity is the best, the Hk/Hcj reaches to 39.9%, and Br, Hcj, and (BH)m are 0.675 T, 616 kA/m and 77 kJ/m3, respectively.
A series of bonded magnets of (Nd,Pr)10.5(Fe,Co)83.5-xMxB6 (M=Zr, Nb, Ti) alloys were prepared by the melt-spun method. The effects of Zr, Nb and Ti element on the microstructure and magnetic properties of alloys have been investigated. The grains of (Nd,Pr)10.5(Fe,Co)83.5B6 with suitable addition of Zr, Nb, or Ti element are finer and more homogeneous. The average grain size is about 50~70 nm. Due to the combined effect of grains refining and pinning to magnetic domain wall of non-magnetic phases, the demagnetization curve rectangularity is improved notably, and the value of Hk/Hcj and other magnetic properties are also greatly increased for the bonded magnets with Zr, Nb, and Ti element addition. Compared with Nb and Ti, Zr has the best effect on refining the grains and increasing magnetic property. For the (Nd,Pr)10.5(Fe,Co)82.5Zr1B6 alloy with 1% Zr, the grains are ~60 nm and homogeneous, the demagnetization curve rectangularity is the best, the Hk/Hcj reaches to 39.9%, and Br, Hcj, and (BH)m are 0.675 T, 616 kA/m and 77 kJ/m3, respectively.
2012, 41(9):1611-1614.
Abstract:
Nanocomposite NdFeB magnets were prepared by melt-spun and crystallization annealing. Effects of Co and Zr addition on the crystallization behavior, microstructure and magnetic properties of the magnets were investigated. Results show that Co addition decreases the precipitation temperature of crystalline phases and increases the remanence. After further addition of Zr, the crystallization behavior changes from a two-step to a single-step process, the coercivity is increased markedly and the grains are refined. The exchange coupling interaction between the soft magnetic phase and the hard phase is enhanced obviously; as a result, the Nd9.5Fe76Co5Zr3B6.5 alloy exhibits excellent overall properties, i.e. Jr＝0.93 T, iHc=687 kA/m and (BH)max＝129 kJ/m3.
Nanocomposite NdFeB magnets were prepared by melt-spun and crystallization annealing. Effects of Co and Zr addition on the crystallization behavior, microstructure and magnetic properties of the magnets were investigated. Results show that Co addition decreases the precipitation temperature of crystalline phases and increases the remanence. After further addition of Zr, the crystallization behavior changes from a two-step to a single-step process, the coercivity is increased markedly and the grains are refined. The exchange coupling interaction between the soft magnetic phase and the hard phase is enhanced obviously; as a result, the Nd9.5Fe76Co5Zr3B6.5 alloy exhibits excellent overall properties, i.e. Jr＝0.93 T, iHc=687 kA/m and (BH)max＝129 kJ/m3.
2012, 41(9):1615-1618.
Abstract:
i-base superalloys with different Ta contents were prepared by the screw selecting method. The effects of Ta on microstructure and creep mechanism of Ni-base single crystal superalloys were investigated. Results show that the morphology of g ￠ phase changes from ellipse to square with the increasing of Ta content. Negative mismatch of the superalloy increases due to more Ta and Mo dissolved into g phase. The creep rupture time is prolonged and dislocation net in g/g ￠ interface is improved when the content of Ta increases form 6wt% to 10wt%.
i-base superalloys with different Ta contents were prepared by the screw selecting method. The effects of Ta on microstructure and creep mechanism of Ni-base single crystal superalloys were investigated. Results show that the morphology of g ￠ phase changes from ellipse to square with the increasing of Ta content. Negative mismatch of the superalloy increases due to more Ta and Mo dissolved into g phase. The creep rupture time is prolonged and dislocation net in g/g ￠ interface is improved when the content of Ta increases form 6wt% to 10wt%.
2012, 41(9):1619-1622.
Abstract:
Dehydrogenation performances of NaAlH4 doped with transition metal oxides (TiO2, ZrO2, Cr2O3, ZnO) were studied by PCT (Pressure-Content-Temperature), XRD and SEM. The results indicate that the dehydrogenation performances of NaAlH4 doped with TiO2 or ZrO2 are preferable. In addition, the study on different ball-milling methods shows that the ball milling leads to a marked increase of dehydrogenation amount. SEM results show that with prolonging the milling time from 1 to 3 h, the size of the complex became smaller, and these particles were scattered on larger globes. However, those particles would reunite again if the milling time was prolonged from 3 to 6 h. The ball milling does not cause evident structure change, indicating that NaAlH4 has good stability.
Dehydrogenation performances of NaAlH4 doped with transition metal oxides (TiO2, ZrO2, Cr2O3, ZnO) were studied by PCT (Pressure-Content-Temperature), XRD and SEM. The results indicate that the dehydrogenation performances of NaAlH4 doped with TiO2 or ZrO2 are preferable. In addition, the study on different ball-milling methods shows that the ball milling leads to a marked increase of dehydrogenation amount. SEM results show that with prolonging the milling time from 1 to 3 h, the size of the complex became smaller, and these particles were scattered on larger globes. However, those particles would reunite again if the milling time was prolonged from 3 to 6 h. The ball milling does not cause evident structure change, indicating that NaAlH4 has good stability.
2012, 41(9):1623-1627.
Abstract:
Micro-sized silver power was prepared from AgNO3 power by chemical reduction, and the technique was optimized by orthogonal experiment. The silver sol was obtained from silver nitrate via chemical reduction in ultrasonic wave and alkaline environment using polyethylene glycol (PEG-10000) as dispersant and alcohol as antifoam agent, and after agitation, the sol was filtered, washed and dried at constant temperature to obtain silver powder. Effects of reagents adding order, pH and dosage of alcohol on the silver particle size were investigated. The silver powders were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results show that with 0.3 mol/L AgNO3 solution, 25 mL ethanol, T=40 oC, pH=7 and 10 min ultrasonic wave vibration, spherical silver power of about 1.13 mm particle size and narrow particle size distribution was prepared.
Micro-sized silver power was prepared from AgNO3 power by chemical reduction, and the technique was optimized by orthogonal experiment. The silver sol was obtained from silver nitrate via chemical reduction in ultrasonic wave and alkaline environment using polyethylene glycol (PEG-10000) as dispersant and alcohol as antifoam agent, and after agitation, the sol was filtered, washed and dried at constant temperature to obtain silver powder. Effects of reagents adding order, pH and dosage of alcohol on the silver particle size were investigated. The silver powders were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results show that with 0.3 mol/L AgNO3 solution, 25 mL ethanol, T=40 oC, pH=7 and 10 min ultrasonic wave vibration, spherical silver power of about 1.13 mm particle size and narrow particle size distribution was prepared.
2012, 41(9):1628-1632.
Abstract:
Tin nano-array electrodes were assembled by electrochemical deposition using alumina anodic oxide (AAO) as templates. Morphology and structure of the tin electrodes were characterized by SEM and XRD. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were applied to reveal the electrochemical performance of the electrodes used as anode of Li-ion battery. Compared to electrodes of tin film and tin foil from rolling, the electrodes of tin nano-arrays are very active. The EIS spectra of tin nano-array electrodes show different characters from electrodes of tin film and tin foil. A medium-frequency area has been found which is ascribed to the large charge transfer area across the electrode/electrolyte interface. The lithium ion transporting in solid-electrolyte ion surface layer are controlled by structure of electrodes. The surface resistances for nano-arrays observed from high frequency ace are between 19.8 and 14.6 Ω·cm2. The highest diffusion coefficient is 10-10 cm2·s-1 for nano-array electrode, at potential of 0.2 V. The nano-array structure can lead to high electrochemical activity of the electrodes.
Tin nano-array electrodes were assembled by electrochemical deposition using alumina anodic oxide (AAO) as templates. Morphology and structure of the tin electrodes were characterized by SEM and XRD. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were applied to reveal the electrochemical performance of the electrodes used as anode of Li-ion battery. Compared to electrodes of tin film and tin foil from rolling, the electrodes of tin nano-arrays are very active. The EIS spectra of tin nano-array electrodes show different characters from electrodes of tin film and tin foil. A medium-frequency area has been found which is ascribed to the large charge transfer area across the electrode/electrolyte interface. The lithium ion transporting in solid-electrolyte ion surface layer are controlled by structure of electrodes. The surface resistances for nano-arrays observed from high frequency ace are between 19.8 and 14.6 Ω·cm2. The highest diffusion coefficient is 10-10 cm2·s-1 for nano-array electrode, at potential of 0.2 V. The nano-array structure can lead to high electrochemical activity of the electrodes.
2012, 41(9):1633-1637.
Abstract:
The activity loss of anode PtRu/C catalyst in direct methanol fuel cell (DMFC) was examined by an electrochemical aging test. The results show that after the aging test, the activity of PtRu/C catalyst toward methanol oxidation decreased obviously. The transmission electron microscopy and X-ray diffraction analysis display that catalyst particles experienced Otswald ripening and directional migration under the electric field during the aging test. The electrochemical impedance spectra show that after the aging test, both the ohmic resistance and the polarization impedance increased remarkably, which is related to the loss of active components. The energy dispersive X-ray analysis shows that the mass ratio of Pt to Ru in the catalyst layer increased noticeably after the test. It is suggested that the loss of active components due to the potential fluctuation is an important factor responsible for the activity loss of the anode catalyst in DMFC.
The activity loss of anode PtRu/C catalyst in direct methanol fuel cell (DMFC) was examined by an electrochemical aging test. The results show that after the aging test, the activity of PtRu/C catalyst toward methanol oxidation decreased obviously. The transmission electron microscopy and X-ray diffraction analysis display that catalyst particles experienced Otswald ripening and directional migration under the electric field during the aging test. The electrochemical impedance spectra show that after the aging test, both the ohmic resistance and the polarization impedance increased remarkably, which is related to the loss of active components. The energy dispersive X-ray analysis shows that the mass ratio of Pt to Ru in the catalyst layer increased noticeably after the test. It is suggested that the loss of active components due to the potential fluctuation is an important factor responsible for the activity loss of the anode catalyst in DMFC.
2012, 41(9):1638-1641.
Abstract:
Based on the transition feature in procedure of producing stacking fault in hexagonal close-packed (hcp) metals that the atoms arrangement changes from AB (hcp) to ABC (fcc), the stacking fault energy (SFE) of hcp metals has been calculated from the energy of phase transition. In addition, the factors of vacancy defect and temperature have also been taken into account. Based on the thermodynamic model of stacking fault energy, the SFE of pure hcp metals Mg, Zn and Ti has been calculated. The equation of the influence of temperature on the SFE has also been established and finally the values of the equation have been calculated. The result shows that the thermodynamic model is fit perfectly for the pure hcp metals and the calculated results agree with the results calculated by first principle. The SFE of hcp metals is decreased gradually with the increasing temperature. The chemical free energy is also the key influence factor on SFE. In addition, vacancy can reduce the stacking fault energy of pure metals. The density of vacancy is increased with the increasing temperature and the devotion to the change of SFE is also increased.
Based on the transition feature in procedure of producing stacking fault in hexagonal close-packed (hcp) metals that the atoms arrangement changes from AB (hcp) to ABC (fcc), the stacking fault energy (SFE) of hcp metals has been calculated from the energy of phase transition. In addition, the factors of vacancy defect and temperature have also been taken into account. Based on the thermodynamic model of stacking fault energy, the SFE of pure hcp metals Mg, Zn and Ti has been calculated. The equation of the influence of temperature on the SFE has also been established and finally the values of the equation have been calculated. The result shows that the thermodynamic model is fit perfectly for the pure hcp metals and the calculated results agree with the results calculated by first principle. The SFE of hcp metals is decreased gradually with the increasing temperature. The chemical free energy is also the key influence factor on SFE. In addition, vacancy can reduce the stacking fault energy of pure metals. The density of vacancy is increased with the increasing temperature and the devotion to the change of SFE is also increased.
2012, 41(9):1642-1645.
Abstract:
Be/HR-1 and Be/Cu/HR-1 stainless steel were bonded respectively by vacuum hot pressing. The hot deformation microstructures and mechanical properties of their joints in the diffusion zone were analyzed by means of optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) and material testing machines. The relationship between deformation microstructures as well as pressure and properties were discussed. Results show that hot pressing can lead to diffusion creep and grain boundary slip of the materials, and influence the grain size and amounts of intermetallic compounds in the diffusion bonding zones. Hot pressing should not be conducted under the critical pressure or critical strain which will cause maximum grain size in the matrix. The intermetallic compounds along grain boundary can be reduced by reducing holding pressure or time, and the bonding strength can be improved. The melting points of the phases formed through reactive diffusion of Be/Cu/HR-l are much lower than that of the matrix, and the deformation can be controlled by reducing holding pressure or temperature.
Be/HR-1 and Be/Cu/HR-1 stainless steel were bonded respectively by vacuum hot pressing. The hot deformation microstructures and mechanical properties of their joints in the diffusion zone were analyzed by means of optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) and material testing machines. The relationship between deformation microstructures as well as pressure and properties were discussed. Results show that hot pressing can lead to diffusion creep and grain boundary slip of the materials, and influence the grain size and amounts of intermetallic compounds in the diffusion bonding zones. Hot pressing should not be conducted under the critical pressure or critical strain which will cause maximum grain size in the matrix. The intermetallic compounds along grain boundary can be reduced by reducing holding pressure or time, and the bonding strength can be improved. The melting points of the phases formed through reactive diffusion of Be/Cu/HR-l are much lower than that of the matrix, and the deformation can be controlled by reducing holding pressure or temperature.
2012, 41(9):1646-1650.
Abstract:
The crystal structure, magnetic properties and crystallization kinetics of the Fe3B/Pr2Fe14B nanocomposite prepared from lean rare-earth Pr4.5Fe77B18.5 amorphous alloy have been investigated by X-ray diffractometer (XRD), transmission electron microscope (TEM), vibrating sample magnetometer (VSM) and differential thermal analysis (DTA). The results indicate that the phases of this sample are composed of Fe3B soft-magnetic phase and Pr2Fe14B hard-magnetic phase as the alloy annealed at 650 oC for 10 min, and the grains are very small and homogeneously distributed in this nannocomposite alloys. The result of VSM analysis presents a single hard-magnetic phase behavior in this alloy. The study on crystallization kinetics for the Fe3B/Pr2Fe14B nanocomposite alloy indicates that the crystallization behavior with easy nucleation and difficult growth of Fe3B phase and with difficult nucleation and easy growth of Pr2Fe14B phase, essentially results in a stronger exchange-coupling effect in Fe3B/Pr2Fe14B nanocomposite.
The crystal structure, magnetic properties and crystallization kinetics of the Fe3B/Pr2Fe14B nanocomposite prepared from lean rare-earth Pr4.5Fe77B18.5 amorphous alloy have been investigated by X-ray diffractometer (XRD), transmission electron microscope (TEM), vibrating sample magnetometer (VSM) and differential thermal analysis (DTA). The results indicate that the phases of this sample are composed of Fe3B soft-magnetic phase and Pr2Fe14B hard-magnetic phase as the alloy annealed at 650 oC for 10 min, and the grains are very small and homogeneously distributed in this nannocomposite alloys. The result of VSM analysis presents a single hard-magnetic phase behavior in this alloy. The study on crystallization kinetics for the Fe3B/Pr2Fe14B nanocomposite alloy indicates that the crystallization behavior with easy nucleation and difficult growth of Fe3B phase and with difficult nucleation and easy growth of Pr2Fe14B phase, essentially results in a stronger exchange-coupling effect in Fe3B/Pr2Fe14B nanocomposite.
2012, 41(9):1651-1656.
Abstract:
By means of the creep properties measurement and microstructure observation of the isothermally forged GH4169 alloy and the hot continuous rolled (HCR) alloy, the influence of the deformation technology on the microstructure and creep behavior of GH4169 alloy was investigated. Results show that the deformation features of the alloy during hot continuous rolling are identified as the twinning and dislocation slipping within the twins. Compared with the isothermally forged alloy, the denser dislocations formed during hot continuous rolling possess have an effect of deformed strengthening, which can improve the creep resistance of the alloy. Only the twinning deformation occurs in the forged alloy during creep, but the deformation mechanism of HCRed alloy during creep is thought to be the twinning and dislocation slipping within the twins. Thereinto, the denser dislocations formed during HCR of the alloy may promote the single/multi-systems slipping of creep dislocation activated within the twins, which may weaken the stress concentration to restrain or delay the initiation of the cracks in the grain boundaries. It is thought to be a main reason of prolonging the creep lifetime of the alloy. In the later period of creep, the micro-cracks are formed in the grain boundary regions vertical to the applied stress axis, and propagate along the grain boundary to produce the cleavage fracture, which is a main mechanism of creep fracture for the alloys prepared by the two kinds of technology.
By means of the creep properties measurement and microstructure observation of the isothermally forged GH4169 alloy and the hot continuous rolled (HCR) alloy, the influence of the deformation technology on the microstructure and creep behavior of GH4169 alloy was investigated. Results show that the deformation features of the alloy during hot continuous rolling are identified as the twinning and dislocation slipping within the twins. Compared with the isothermally forged alloy, the denser dislocations formed during hot continuous rolling possess have an effect of deformed strengthening, which can improve the creep resistance of the alloy. Only the twinning deformation occurs in the forged alloy during creep, but the deformation mechanism of HCRed alloy during creep is thought to be the twinning and dislocation slipping within the twins. Thereinto, the denser dislocations formed during HCR of the alloy may promote the single/multi-systems slipping of creep dislocation activated within the twins, which may weaken the stress concentration to restrain or delay the initiation of the cracks in the grain boundaries. It is thought to be a main reason of prolonging the creep lifetime of the alloy. In the later period of creep, the micro-cracks are formed in the grain boundary regions vertical to the applied stress axis, and propagate along the grain boundary to produce the cleavage fracture, which is a main mechanism of creep fracture for the alloys prepared by the two kinds of technology.
2012, 41(9):1657-1660.
Abstract:
Porous pieces were prepared with the alloy powder (TLM:Ti-Zr-Sn-Mo-Nb) and centre stick by means of sintering. The surface of porous pieces was modified with MAO. Another composite coating with BMP was prepared. The surface morphology, microstructure and composition of the three kinds of test pieces were analyzed. The new bone tissue around the coatings of these test pieces were evaluated according to animal implantation experiment. The results show that all of the three surface coatings have good biocompatibility. The PCI/HA group and PCI/HA/BMP group have excellent osteoconductivity and a good prospect of clinical application.
Porous pieces were prepared with the alloy powder (TLM:Ti-Zr-Sn-Mo-Nb) and centre stick by means of sintering. The surface of porous pieces was modified with MAO. Another composite coating with BMP was prepared. The surface morphology, microstructure and composition of the three kinds of test pieces were analyzed. The new bone tissue around the coatings of these test pieces were evaluated according to animal implantation experiment. The results show that all of the three surface coatings have good biocompatibility. The PCI/HA group and PCI/HA/BMP group have excellent osteoconductivity and a good prospect of clinical application.
2012, 41(9):1661-1665.
Abstract:
Self-assembled TiO2-based air-water interfacial particles with nano structure were soaked into silver nitrate (AgNO3) aqueous solution and Ag-TiO2 composite nanoparticles were obtained by the heat-treatment at 400 oC. The composite nanoparticles were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and ultraviolet visible spectrum (UV-Vis). The results show that the Ag-TiO2 particles at 400 oC could significantly enhance the photocatalytic activity of the TiO2 particles. Methyl orange was used as the degradable agent in photocatalytic experiment. The results indicate that methyl orange could be degraded 96.25% by Ag-TiO2 nanoparticles under the optimal conditions. It is concluded that the Ag-TiO2 composite nanoparticles posses good photocatalysis activity.
Self-assembled TiO2-based air-water interfacial particles with nano structure were soaked into silver nitrate (AgNO3) aqueous solution and Ag-TiO2 composite nanoparticles were obtained by the heat-treatment at 400 oC. The composite nanoparticles were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and ultraviolet visible spectrum (UV-Vis). The results show that the Ag-TiO2 particles at 400 oC could significantly enhance the photocatalytic activity of the TiO2 particles. Methyl orange was used as the degradable agent in photocatalytic experiment. The results indicate that methyl orange could be degraded 96.25% by Ag-TiO2 nanoparticles under the optimal conditions. It is concluded that the Ag-TiO2 composite nanoparticles posses good photocatalysis activity.
2012, 41(9):1666-1671.
Abstract:
The Cr2Nb/CuCr composites with different Cr2Nb contents were prepared by the vacuum sintering and infiltration method. The microstructure of the composites was characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM), and the effects of in-situ synthesized Cr2Nb on the surface arc motion and erosion morphology of the composites were studied by high speed photography and scanning electron microscope (SEM). The results show that the addition of Cr-Nb composite powder causes a significant improvement in the hardness, conductivity, chopping current, arcing life and breakdown strength. The addition of 7wt% Cr-Nb composite powder can make the cathode spots of the Cr2Nb/CuCr composite distribute more dispersively, decrease the chopping current and prolong the arcing life obviously. In comparison with conventional CuCr alloys, the Cr2Nb/CuCr composites present better overall performance.
The Cr2Nb/CuCr composites with different Cr2Nb contents were prepared by the vacuum sintering and infiltration method. The microstructure of the composites was characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM), and the effects of in-situ synthesized Cr2Nb on the surface arc motion and erosion morphology of the composites were studied by high speed photography and scanning electron microscope (SEM). The results show that the addition of Cr-Nb composite powder causes a significant improvement in the hardness, conductivity, chopping current, arcing life and breakdown strength. The addition of 7wt% Cr-Nb composite powder can make the cathode spots of the Cr2Nb/CuCr composite distribute more dispersively, decrease the chopping current and prolong the arcing life obviously. In comparison with conventional CuCr alloys, the Cr2Nb/CuCr composites present better overall performance.
2012, 41(9):1672-1675.
Abstract:
Silver nanoparticles were synthesized by a totally green approach with silver nitrate (AgNO3) as precursor and ascorbic acid (Vc) as reducing agent. The nano-silver particles had narrow particle size distribution. The feature, structure and optical absorption properties of silver nanoparticles were characterized by X-ray diffraction (XRD), Raman spectra, ultraviolet visible spectrum (UV-Vis), scanning electron microscope (SEM) and transmission electron microscope (TEM). Surface-enhanced Raman scattering (SERS) on the prepared nano-silver particles as substrate was investigated by pyridine as the probe molecule. The results show that the detection limit is down to 10-10 mol·L-1. The variation tendency of Raman signal is stable with the change of the probe molecule concentration, which can be used for the study of the quantitative analysis.
Silver nanoparticles were synthesized by a totally green approach with silver nitrate (AgNO3) as precursor and ascorbic acid (Vc) as reducing agent. The nano-silver particles had narrow particle size distribution. The feature, structure and optical absorption properties of silver nanoparticles were characterized by X-ray diffraction (XRD), Raman spectra, ultraviolet visible spectrum (UV-Vis), scanning electron microscope (SEM) and transmission electron microscope (TEM). Surface-enhanced Raman scattering (SERS) on the prepared nano-silver particles as substrate was investigated by pyridine as the probe molecule. The results show that the detection limit is down to 10-10 mol·L-1. The variation tendency of Raman signal is stable with the change of the probe molecule concentration, which can be used for the study of the quantitative analysis.
2012, 41(9):1676-1679.
Abstract:
Flake-like diatomite was used as forming templates to prepare the core-shell functional particles by the electroless silver plating method. The effects of electroless plating process on the silver content and surface morphology of diatomite were discussed. The dielectric properties of silver-coated diatomite particles were also analyzed. The results indicate that the silver content of diatomite increases with increasing plating time and load. At the silver content of 34.65% (mass fraction), the silver coating is fairly homogeneous, continuous and compact, and the micropores on the surface of diatomite are completely covered by the coating. The dielectric properties of silver-coated diatomite particles are related with silver content, coating morphology and volume concentration. Furthermore, the imaginary parts of dielectric constant of all the samples are lower than the real parts. It shows that all the samples do not exhibit percolation phenomenon.
Flake-like diatomite was used as forming templates to prepare the core-shell functional particles by the electroless silver plating method. The effects of electroless plating process on the silver content and surface morphology of diatomite were discussed. The dielectric properties of silver-coated diatomite particles were also analyzed. The results indicate that the silver content of diatomite increases with increasing plating time and load. At the silver content of 34.65% (mass fraction), the silver coating is fairly homogeneous, continuous and compact, and the micropores on the surface of diatomite are completely covered by the coating. The dielectric properties of silver-coated diatomite particles are related with silver content, coating morphology and volume concentration. Furthermore, the imaginary parts of dielectric constant of all the samples are lower than the real parts. It shows that all the samples do not exhibit percolation phenomenon.
2012, 41(9):1680-1683.
Abstract:
Effects of vacuum heat treatment on microstructure and mechanical properties of extruded rods of 93W-Ni-Fe alloy sintered by microwave were studied. Fracture morphology and microstructure were observed by SEM and optical microscope, respectively. Quantitative analysis of each element of the samples before and after vacuum heat treatment was performed by energy spectrum analyzer. Relative density, tensile strength, elongation and hardness of samples were measured. The results show that the mechanical properties of the tungsten-based alloy are increased after vacuum heat treatment. Tensile strength and elongation are improved markedly, which are increased from 920 MPa to 988 MPa and from 9.7% to 18.6%, respectively. After vacuum heat treatment connectivity of tungsten grains is reduced, and transgranular cleavage fracture of tungsten grains and ductile tearing of binding phase are increased evidently. The content of tungsten element in binding phase is obviously reduced after vacuum heat treatment.
Effects of vacuum heat treatment on microstructure and mechanical properties of extruded rods of 93W-Ni-Fe alloy sintered by microwave were studied. Fracture morphology and microstructure were observed by SEM and optical microscope, respectively. Quantitative analysis of each element of the samples before and after vacuum heat treatment was performed by energy spectrum analyzer. Relative density, tensile strength, elongation and hardness of samples were measured. The results show that the mechanical properties of the tungsten-based alloy are increased after vacuum heat treatment. Tensile strength and elongation are improved markedly, which are increased from 920 MPa to 988 MPa and from 9.7% to 18.6%, respectively. After vacuum heat treatment connectivity of tungsten grains is reduced, and transgranular cleavage fracture of tungsten grains and ductile tearing of binding phase are increased evidently. The content of tungsten element in binding phase is obviously reduced after vacuum heat treatment.
2012, 41(9):1684-1688.
Abstract:
Beryllium thin films with a thickness of 400~2100 nm and root of mean square roughness Rq<6.0 nm were grown on the SiO2 substrate by the evaporation deposition method. X-ray diffraction analysis indicates that Be thin films with different thickness consist of hcp structure α-Be phase. As the evaporation temperature increases from 1243 to 1403 K, the deposition rate of Be atom increases rapidly, the average diameter of α-Be crystalline grain becomes 3 times larger, and its preferential orientation changes remarkably. The island grains on the thin film surface show a transition from polygon grain to hexagon grain. Otherwise, cross section microstructures of thin films are mainly characterized by column crystal, and they are perpendicular to the SiO2 substrate and of directional array. Furthermore, the calculated growth velocities of Be thin films are in good agreement with experimental results. The growth velocities are directly proportional to the equilibrium vapor pressure, and increase dramatically with the evaporation temperatures rising.
Beryllium thin films with a thickness of 400~2100 nm and root of mean square roughness Rq<6.0 nm were grown on the SiO2 substrate by the evaporation deposition method. X-ray diffraction analysis indicates that Be thin films with different thickness consist of hcp structure α-Be phase. As the evaporation temperature increases from 1243 to 1403 K, the deposition rate of Be atom increases rapidly, the average diameter of α-Be crystalline grain becomes 3 times larger, and its preferential orientation changes remarkably. The island grains on the thin film surface show a transition from polygon grain to hexagon grain. Otherwise, cross section microstructures of thin films are mainly characterized by column crystal, and they are perpendicular to the SiO2 substrate and of directional array. Furthermore, the calculated growth velocities of Be thin films are in good agreement with experimental results. The growth velocities are directly proportional to the equilibrium vapor pressure, and increase dramatically with the evaporation temperatures rising.
2012, 41(9):1689-1692.
Abstract:
Inhomogeneous deformation and cracking could easily appear during forging for powder metallurgy (P/M for short) superalloy. OM, SEM and TEM were employed to find the reasons of inhomogeneous deformation. The action of annealing on improving the microstructure and malleability was explored preliminarily. The results indicate that inhomogeneous microscopic deformation caused by grains turn and non-uniform secondary particles can lead to inhomogeneous deformation. Through the multistage annealing before forging, equiaxed fine grain layer appeared in the junction of three grains and made secondary particles disperse, which is attributed to homogeneous deformation of P/M superalloy.
Inhomogeneous deformation and cracking could easily appear during forging for powder metallurgy (P/M for short) superalloy. OM, SEM and TEM were employed to find the reasons of inhomogeneous deformation. The action of annealing on improving the microstructure and malleability was explored preliminarily. The results indicate that inhomogeneous microscopic deformation caused by grains turn and non-uniform secondary particles can lead to inhomogeneous deformation. Through the multistage annealing before forging, equiaxed fine grain layer appeared in the junction of three grains and made secondary particles disperse, which is attributed to homogeneous deformation of P/M superalloy.
