Volume 42,Issue 3,2013 Table of Contents
2013, 42(3):441-446.
Abstract:
The Mg/Al laminated composites were prepared by the accumulative roll bonding (ARB) at ambient temperature using the commercial pure magnesium and pure Al sheets as starting materials. Microstructure of both Mg and Al layer were refined during ARB processing. Neutron diffraction was employed to investigate the texture evolution of this kind of laminated composite. Both the Mg and Al layer of the primary sandwich exhibited dominant shear texture. During the following accumulative roll bonding, the texture of Mg layer transformed to typical rolling texture while the Al layer showed a combined texture type including evident β fiber and the Rotate Cube component
The Mg/Al laminated composites were prepared by the accumulative roll bonding (ARB) at ambient temperature using the commercial pure magnesium and pure Al sheets as starting materials. Microstructure of both Mg and Al layer were refined during ARB processing. Neutron diffraction was employed to investigate the texture evolution of this kind of laminated composite. Both the Mg and Al layer of the primary sandwich exhibited dominant shear texture. During the following accumulative roll bonding, the texture of Mg layer transformed to typical rolling texture while the Al layer showed a combined texture type including evident β fiber and the Rotate Cube component
2013, 42(3):447-451.
Abstract:
The corrosion of glassy (Ni8Nb5)99.5Sb0.5 alloy was investigated in 1, 6 mol/L HCl, 1 mol/L H2SO4 and 3% NaCl solutions, respectively, by immersion tests and electrochemical measurements and compared with that of pure Ni, Nb and Sb. The stability of passive film was studied using potentiostatic current transients and XPS depth profiling. The surface morphology of the glassy alloy after electrochemical potentiodynamic polarization test was observed using SEM. The result indicates that the Ni-Nb-Sb alloy shows good corrosion resistance in 1 mol/L HCl, 1 mol/L H2SO4 and 3 wt% NaCl solutions. The corrosion resistance, however, is poor in 6 mol/L HCl solution. The amorphous alloy is crystallized after electrochemical corrosion in chloride media. Transpassive dissolution is observed during potentiodynamic polarization test in chloride media, which appears to be associated with oxygen evolution. At low potentials, the growth of passive film is diffusion-controlled. At high potentials, however, the active corrosion is the predominant.
The corrosion of glassy (Ni8Nb5)99.5Sb0.5 alloy was investigated in 1, 6 mol/L HCl, 1 mol/L H2SO4 and 3% NaCl solutions, respectively, by immersion tests and electrochemical measurements and compared with that of pure Ni, Nb and Sb. The stability of passive film was studied using potentiostatic current transients and XPS depth profiling. The surface morphology of the glassy alloy after electrochemical potentiodynamic polarization test was observed using SEM. The result indicates that the Ni-Nb-Sb alloy shows good corrosion resistance in 1 mol/L HCl, 1 mol/L H2SO4 and 3 wt% NaCl solutions. The corrosion resistance, however, is poor in 6 mol/L HCl solution. The amorphous alloy is crystallized after electrochemical corrosion in chloride media. Transpassive dissolution is observed during potentiodynamic polarization test in chloride media, which appears to be associated with oxygen evolution. At low potentials, the growth of passive film is diffusion-controlled. At high potentials, however, the active corrosion is the predominant.
2013, 42(3):452-456.
Abstract:
Electron beam welding experiments of TiAl and TC4 titanium alloy under different welding parameters were carried out. The influence of aluminum content in the weld on the microstructure and mechanical properties of the joints were analyzed. The weld mainly consisted of the α2-Ti3Al phase and α-Ti phase, with a small quantity of B2 phase and YAlx phase when the beam acted on the contact face. In the joints the content of molten TiAl and TC4 was about 1/3 and 2/3, and the percentage of Al was about 28 wt%. This high content of Al led to the formation of a brittle α2 phase, thus the ductility and toughness of the joints decreasing. In the centered beam welding, the tensile strength of the joints was low. The fracture of the joints was the classic brittle transgranular and quasi-cleavage fracture. When the beam was deflected towards the TC4 alloy, the Al content in the weld decreased and the mechanical properties of the joints improved. When the lateral deviation hs was 0.2?mm, the highest tensile strength of the joints reached 422.2?MPa.
Electron beam welding experiments of TiAl and TC4 titanium alloy under different welding parameters were carried out. The influence of aluminum content in the weld on the microstructure and mechanical properties of the joints were analyzed. The weld mainly consisted of the α2-Ti3Al phase and α-Ti phase, with a small quantity of B2 phase and YAlx phase when the beam acted on the contact face. In the joints the content of molten TiAl and TC4 was about 1/3 and 2/3, and the percentage of Al was about 28 wt%. This high content of Al led to the formation of a brittle α2 phase, thus the ductility and toughness of the joints decreasing. In the centered beam welding, the tensile strength of the joints was low. The fracture of the joints was the classic brittle transgranular and quasi-cleavage fracture. When the beam was deflected towards the TC4 alloy, the Al content in the weld decreased and the mechanical properties of the joints improved. When the lateral deviation hs was 0.2?mm, the highest tensile strength of the joints reached 422.2?MPa.
2013, 42(3):457-461.
Abstract:
The influences of lamellar microstructure characteristics on quasi-static tensile properties and dynamic compression deformation behavior were studied for newly developed titanium alloy Ti-6Al-4V-4Zr-Mo. To tailor the microstructure characteristics, the lamellar microstructure was obtained by be solution treatment at 960 °C and underwent subsequent aging treatments at 700 and 570 °C, respectively. Results show that as the aging temperature decreases, the size of α colonies and the width of α plates present a declining trend. Correspondingly, the slip length of dislocation becomes relatively shorter, resulting in the increase of quasi-static deformation capability. Dynamic compression tests also show that the lamellar microstructure aged at 570 °C with α colonies and α plates in smaller size, which induces the propagated path of crack easily bifurcate and deflect, presents higher dynamic fracture strain, in contrast with the lamellar microstructure aged at 700 °C.
The influences of lamellar microstructure characteristics on quasi-static tensile properties and dynamic compression deformation behavior were studied for newly developed titanium alloy Ti-6Al-4V-4Zr-Mo. To tailor the microstructure characteristics, the lamellar microstructure was obtained by be solution treatment at 960 °C and underwent subsequent aging treatments at 700 and 570 °C, respectively. Results show that as the aging temperature decreases, the size of α colonies and the width of α plates present a declining trend. Correspondingly, the slip length of dislocation becomes relatively shorter, resulting in the increase of quasi-static deformation capability. Dynamic compression tests also show that the lamellar microstructure aged at 570 °C with α colonies and α plates in smaller size, which induces the propagated path of crack easily bifurcate and deflect, presents higher dynamic fracture strain, in contrast with the lamellar microstructure aged at 700 °C.
5 Synthesis of TbCu7-type Structural SmCo-based Films for Microelectromechanical System Applications
2013, 42(3):462-465.
Abstract:
Development of microelectromechanical system (MEMS) requires permanent magnetic films prepared on Si substrates with good thermal stability. The SmCo-based films were deposited on Si (100) substrates by magnetron sputtering process, and the effect of sputtering parameters on deposition rate, microstructure, crystal structure, and magnetic properties were investigated subsequently. The results show that the TbCu7-type structural SmCo-based film is obtained with adjusted sputtering parameters. The film exhibits a well preferred crystal orientation and fine microstructure, leading to better in-plane magnetic properties and a magnetization reversal process mainly controlled by domain wall pinning mechanism.
Development of microelectromechanical system (MEMS) requires permanent magnetic films prepared on Si substrates with good thermal stability. The SmCo-based films were deposited on Si (100) substrates by magnetron sputtering process, and the effect of sputtering parameters on deposition rate, microstructure, crystal structure, and magnetic properties were investigated subsequently. The results show that the TbCu7-type structural SmCo-based film is obtained with adjusted sputtering parameters. The film exhibits a well preferred crystal orientation and fine microstructure, leading to better in-plane magnetic properties and a magnetization reversal process mainly controlled by domain wall pinning mechanism.
2013, 42(3):466-469.
Abstract:
A NiAl/Al2O3 coating was prepared on an AZ91D Mg alloy substrate by laser cladding of the plasma-sprayed coating. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to identify the phases and to study the morphology, respectively. The adhesion strength and the porosity ratio of the coating material were measured by a tensile testing machine and an optical microscope (OM), respectively. The microhardness was measured using a micro Vickers hardness tester. The results show that after laser cladding metallurgical bonding occurrs at the interface between the NiAl transition layer and the substrate. The adhesion strength of the coating increases from 11.34 to 33.2 MPa. The coating became denser and the porosity ratio decrease from 10.23 % to 4.10 %. The metastable γ-Al2O3 phase in the coating without laser cladding is transformed completely into the stable α-Al2O3 phase. The microhardness HV0.05 is improved from 3290 to 5200 MPa, which is beneficial to the wear resistance.
A NiAl/Al2O3 coating was prepared on an AZ91D Mg alloy substrate by laser cladding of the plasma-sprayed coating. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to identify the phases and to study the morphology, respectively. The adhesion strength and the porosity ratio of the coating material were measured by a tensile testing machine and an optical microscope (OM), respectively. The microhardness was measured using a micro Vickers hardness tester. The results show that after laser cladding metallurgical bonding occurrs at the interface between the NiAl transition layer and the substrate. The adhesion strength of the coating increases from 11.34 to 33.2 MPa. The coating became denser and the porosity ratio decrease from 10.23 % to 4.10 %. The metastable γ-Al2O3 phase in the coating without laser cladding is transformed completely into the stable α-Al2O3 phase. The microhardness HV0.05 is improved from 3290 to 5200 MPa, which is beneficial to the wear resistance.
2013, 42(3):470-473.
Abstract:
The effect of partial substitution of Al for Zr on the mechanical properties of Zr35-xTi30Cu7.5Be27.5Alx (x=0, 1, 1.5, 2, 2.5, 5, at%) bulk metallic glasses were studied by uniaxial compression test. The results showed that the compressive plasticity can be greatly improved from 0.95% (x=0) to 15.10% (x=1.5) and 3.45% (x=2) in Zr35Ti30Cu7.5Be27.5 bulk metallic glass. The fracture morphologies of the Zr35-xTi30Cu7.5Be27.5Alx bulk metallic glasses were characterized by means of scanning electron microscope (SEM). Transmission electron microscope (TEM) was employed to investigate the microstructures of the bulk metallic glasses containing different amounts of Al. It is found that the enhanced compressive plasticity could be attributed to the nanoscale heterogeneity in the bulk metallic glasses. The effect of Al addition on the microstructure and deformation behavior of the Zr-based bulk metallic glasses was discussed in terms of different critical shear stress (CSS).
The effect of partial substitution of Al for Zr on the mechanical properties of Zr35-xTi30Cu7.5Be27.5Alx (x=0, 1, 1.5, 2, 2.5, 5, at%) bulk metallic glasses were studied by uniaxial compression test. The results showed that the compressive plasticity can be greatly improved from 0.95% (x=0) to 15.10% (x=1.5) and 3.45% (x=2) in Zr35Ti30Cu7.5Be27.5 bulk metallic glass. The fracture morphologies of the Zr35-xTi30Cu7.5Be27.5Alx bulk metallic glasses were characterized by means of scanning electron microscope (SEM). Transmission electron microscope (TEM) was employed to investigate the microstructures of the bulk metallic glasses containing different amounts of Al. It is found that the enhanced compressive plasticity could be attributed to the nanoscale heterogeneity in the bulk metallic glasses. The effect of Al addition on the microstructure and deformation behavior of the Zr-based bulk metallic glasses was discussed in terms of different critical shear stress (CSS).
2013, 42(3):474-477.
Abstract:
Gold nanoparticles were prepared in an aqueous solution with polyacrylamide to reduce HAuCl4. The polyacrylamide played double roles in the preparation of Au nanoparticles. Firstly, it acted as reducing reagent; in addition, it also stabilized the Au nanoparticles to prevent agglomeration and provided environment for forming nanostructure around Au nanoparticles. UV-vis spectra of the Au nanocrystals colloids reveal the plasmon resonance peak position. TEM confirms the presence of gold nanoparticles in the fibers. This is a versatile and applicable approach to prepare many other combinations of functional fibers electrospun
Gold nanoparticles were prepared in an aqueous solution with polyacrylamide to reduce HAuCl4. The polyacrylamide played double roles in the preparation of Au nanoparticles. Firstly, it acted as reducing reagent; in addition, it also stabilized the Au nanoparticles to prevent agglomeration and provided environment for forming nanostructure around Au nanoparticles. UV-vis spectra of the Au nanocrystals colloids reveal the plasmon resonance peak position. TEM confirms the presence of gold nanoparticles in the fibers. This is a versatile and applicable approach to prepare many other combinations of functional fibers electrospun
2013, 42(3):478-482.
Abstract:
With TIG arc as heat source and AlSi5 wire as filling mental, the dissimilar material joint fabricated by TIG arc welding-brazing process between Ti-6Al-4V (TC4) and AlMg6 was studied with SEM, EDS and XRD. The temperature field and fracture behavior of the joint was investigated. The results show that aluminum side of the weld joint reveals a typical property of wire fed TIG welding, while Ti side which is base metal shows a property of brazing welding. Thickness of the weld interface increases with higher peak temperature and the interface microstructure becomes more complicated. Reducing high-temperature residence time can cut down the thickness of the interface, but with the peak temperature increasing, big cooling speed produces high stress in the joint, thus forming cracks through the grain boundary. In Ti/Al brazing weld joint, cracks which grow from gas cavity and micro-cracks in Al side are a typical hybrid composed of ductile and brittle fracture. Besides, over melting and dissolving of the Ti base metal will enlarge the size of the gas cavity, so the quantity of the heat input and melting of the base metal must be strictly controlled.
With TIG arc as heat source and AlSi5 wire as filling mental, the dissimilar material joint fabricated by TIG arc welding-brazing process between Ti-6Al-4V (TC4) and AlMg6 was studied with SEM, EDS and XRD. The temperature field and fracture behavior of the joint was investigated. The results show that aluminum side of the weld joint reveals a typical property of wire fed TIG welding, while Ti side which is base metal shows a property of brazing welding. Thickness of the weld interface increases with higher peak temperature and the interface microstructure becomes more complicated. Reducing high-temperature residence time can cut down the thickness of the interface, but with the peak temperature increasing, big cooling speed produces high stress in the joint, thus forming cracks through the grain boundary. In Ti/Al brazing weld joint, cracks which grow from gas cavity and micro-cracks in Al side are a typical hybrid composed of ductile and brittle fracture. Besides, over melting and dissolving of the Ti base metal will enlarge the size of the gas cavity, so the quantity of the heat input and melting of the base metal must be strictly controlled.
2013, 42(3):483-487.
Abstract:
The tensile mechanical properties of commercially pure titanium TA2 within the strain rate scope 1×10-4 ~1×10-2 s-1 have been tested at room temperature, and the stress-strain curves of different strain rates have also been obtained. The results show that the stress-strain curve of commercially pure titanium TA2 at room temperature is significantly sensitive to strain rate. The strength parameters such as flow stress increase with the higher strain rate, while the plastic parameters such as elongation and area reduction decrease. The strain rate sensitivity index of TA2 is great. Through the theoretical analysis of Hollomon empirical formula () and the experimental verification of TA2, it is found that the strain rate sensitivity index m and strain hardening index n are related with strain and strain rate, respectively and the relation between them is power equation. Therefore, the Hollomon empirical formula is revised, and the revised Hollomon equation of TA2 is obtained. Compared with traditional Hollomon empirical formula and Johnson-Cook model, the revised equation has better agreement with experimental results and can depict the tensile mechanical property of TA2 more accurately
The tensile mechanical properties of commercially pure titanium TA2 within the strain rate scope 1×10-4 ~1×10-2 s-1 have been tested at room temperature, and the stress-strain curves of different strain rates have also been obtained. The results show that the stress-strain curve of commercially pure titanium TA2 at room temperature is significantly sensitive to strain rate. The strength parameters such as flow stress increase with the higher strain rate, while the plastic parameters such as elongation and area reduction decrease. The strain rate sensitivity index of TA2 is great. Through the theoretical analysis of Hollomon empirical formula () and the experimental verification of TA2, it is found that the strain rate sensitivity index m and strain hardening index n are related with strain and strain rate, respectively and the relation between them is power equation. Therefore, the Hollomon empirical formula is revised, and the revised Hollomon equation of TA2 is obtained. Compared with traditional Hollomon empirical formula and Johnson-Cook model, the revised equation has better agreement with experimental results and can depict the tensile mechanical property of TA2 more accurately
2013, 42(3):488-493.
Abstract:
It is an important issue for the optimization design and refined control of extrusion process of large-diameter hard wrought alloy profiles to reveal the effects of forming parameters on the process and to determine the reasonable range of each forming parameter. And it’s also significant for the R&D, debugging and application of the large tonnage (such as 200 MN) extrusion press. Therefore, we developed an applicable and reliable FE model for the needle piercing extrusion process for Inconel690 alloy large-diameter thick-walled tube (Ф420 mm×60 mm) under the DEFORM-2D software environment. And the effects of forming parameters (i.e. extruding ratio λ, die taper angle α, sizing belt length h, billet initial temperature T and ram speed v) on the peak temperature of billet Tmax, the peak damage of billet Dmax, the uniformity of flow rate at die export Fsdv and the peak extrusion load Lmax were investigated using virtual orthogonal experiment based on the developed FE model. The results show that the order of forming parameters’ significance to Tmax, Dmax, Fsdv and Lmax are T>v>λ>h>α, α>v≈λ>T>h, h>v>T>α>λ, and λ>T>α>v>h, respectively. Comprehensively considering the quality of the extruded tube and the extrusion load, we pointed out that the reasonable ranges of forming parameters are as follows: λ=5.74~6.37, α=35°~45°, h=60~120 mm, T=1080~1180 °C, and v=150~250 mm/s.
It is an important issue for the optimization design and refined control of extrusion process of large-diameter hard wrought alloy profiles to reveal the effects of forming parameters on the process and to determine the reasonable range of each forming parameter. And it’s also significant for the R&D, debugging and application of the large tonnage (such as 200 MN) extrusion press. Therefore, we developed an applicable and reliable FE model for the needle piercing extrusion process for Inconel690 alloy large-diameter thick-walled tube (Ф420 mm×60 mm) under the DEFORM-2D software environment. And the effects of forming parameters (i.e. extruding ratio λ, die taper angle α, sizing belt length h, billet initial temperature T and ram speed v) on the peak temperature of billet Tmax, the peak damage of billet Dmax, the uniformity of flow rate at die export Fsdv and the peak extrusion load Lmax were investigated using virtual orthogonal experiment based on the developed FE model. The results show that the order of forming parameters’ significance to Tmax, Dmax, Fsdv and Lmax are T>v>λ>h>α, α>v≈λ>T>h, h>v>T>α>λ, and λ>T>α>v>h, respectively. Comprehensively considering the quality of the extruded tube and the extrusion load, we pointed out that the reasonable ranges of forming parameters are as follows: λ=5.74~6.37, α=35°~45°, h=60~120 mm, T=1080~1180 °C, and v=150~250 mm/s.
2013, 42(3):494-499.
Abstract:
The influence of heat treatment techniques on medium temperature creep behaviors of the 4.5%Re single crystal nickel-base superalloy with different heat treatment regimes was investigated by means of creep curve measurement and microstructure observation. Results show that the creep property of the alloy is obviously improved with enhancing the solution temperature due to decreasing the segregation extent of the elements. After fully heat treated, the microstructure of the alloy consists of the cubic g￠ phase embedded coherent in the g matrix. During creep under the condition of 760 °C/800 MPa, no rafted structure of g￠ phase is detected, but the twisted configuration of the g￠ phase is formed in the regions near the fracture. In the ranges of the applied stresses and temperatures, the alloy displays a better creep resistance and a longer creep lifetime. And the deformation features of the alloy during creep are that the dislocations move in the g matrix channels and shear into the g￠ phase, the <110> super-dislocation shearing into the g￠ phase can be cross-slipped from {111} planes to {100} planes to form K-W locking, or the <110> super-dislocation shearing into the g￠ phase is decomposed to form the configuration of (1/3)<112> super-Shockleys partials plus the stacking fault, which may hinder dislocations movement and restrain the cross-slipping of dislocations. This is thought to be the main reason of the alloy having a better creep resistance
The influence of heat treatment techniques on medium temperature creep behaviors of the 4.5%Re single crystal nickel-base superalloy with different heat treatment regimes was investigated by means of creep curve measurement and microstructure observation. Results show that the creep property of the alloy is obviously improved with enhancing the solution temperature due to decreasing the segregation extent of the elements. After fully heat treated, the microstructure of the alloy consists of the cubic g￠ phase embedded coherent in the g matrix. During creep under the condition of 760 °C/800 MPa, no rafted structure of g￠ phase is detected, but the twisted configuration of the g￠ phase is formed in the regions near the fracture. In the ranges of the applied stresses and temperatures, the alloy displays a better creep resistance and a longer creep lifetime. And the deformation features of the alloy during creep are that the dislocations move in the g matrix channels and shear into the g￠ phase, the <110> super-dislocation shearing into the g￠ phase can be cross-slipped from {111} planes to {100} planes to form K-W locking, or the <110> super-dislocation shearing into the g￠ phase is decomposed to form the configuration of (1/3)<112> super-Shockleys partials plus the stacking fault, which may hinder dislocations movement and restrain the cross-slipping of dislocations. This is thought to be the main reason of the alloy having a better creep resistance
2013, 42(3):500-506.
Abstract:
The α+β dual phase TC4 titanium alloy hydrogenated with 0.1 wt%, 0.3 wt% and 0.5 wt% hydrogen was friction stir welded using a W-Re pin tool. Hydrogen was removed from the as-welded joints through post-weld vacuum annealing. Effects of hydrogen as a temporary alloying element on microstructure and mechanical properties of TC4 titanium alloy friction stir welded joints were investigated. Results show that hydrogen content has a significant influence on microstructure and mechanical properties in hydrogenated titanium alloy as-weld joints. Hydrogen almost does not escape from the hydrogenated titanium alloy during the friction stir welding and can be removed through post-weld vacuum annealing. The hydrogen-induced metastable phases and hydrogen-rich phases in as-welded joints decompose and transform during the dehydrogenation process. Mechanical properties of as-welded joints are also significantly recovered after dehydrogenation and the mechanical properties of dehydrogenated joints basically reach the level of the as-received unhydrogenated titanium alloy joints.
The α+β dual phase TC4 titanium alloy hydrogenated with 0.1 wt%, 0.3 wt% and 0.5 wt% hydrogen was friction stir welded using a W-Re pin tool. Hydrogen was removed from the as-welded joints through post-weld vacuum annealing. Effects of hydrogen as a temporary alloying element on microstructure and mechanical properties of TC4 titanium alloy friction stir welded joints were investigated. Results show that hydrogen content has a significant influence on microstructure and mechanical properties in hydrogenated titanium alloy as-weld joints. Hydrogen almost does not escape from the hydrogenated titanium alloy during the friction stir welding and can be removed through post-weld vacuum annealing. The hydrogen-induced metastable phases and hydrogen-rich phases in as-welded joints decompose and transform during the dehydrogenation process. Mechanical properties of as-welded joints are also significantly recovered after dehydrogenation and the mechanical properties of dehydrogenated joints basically reach the level of the as-received unhydrogenated titanium alloy joints.
2013, 42(3):507-512.
Abstract:
Ni-P alloy coatings with good adhesion and wear resistance were prepared on the surface of titanium alloy TC4 substrate using an electroless plating method. The structures of coatings after heat treatment at different temperatures were investigated by means of SEM, XRD and EDS. Furthermore, the relationship of different heat treatment temperatures, coating structure, coating hardness and wear resistance was established. The results show that the combination of double zincating and heat treatment can significantly improve the adhesive strength in the coating/substrate interface, and the adhesion of the coating reaches 35 N after heat treatment at 600 °C for 1 h. Hardness HV and wear loss of the substrate are 3780 MPa and 9.6 mg, respectively, while the hardness HV and the wear loss of the coating as plated are 5760 MPa and 7.7 mg, respectively, which indicate that electroless Ni-P coating can enhance hardness and wear resistance of TC4 titanium alloy. With the increase in temperature of heat treatment, Ni3P phase increases. The hardness shows higher values in the presence of Ni3P phase with highly-dispersed distribution, reaching the highest of 9790 MPa. Further increase in temperature results in the segregation of Ni3P phase and slowdown of dispersion degree, suggesting the hardness reduction. Wear loss of the coating decreases with increasing heat treatment temperature, revealing the wear resistance increases with the rise of heat treatment temperature. After heat treatment at 600 °C, despite the bigger grains and lower hardness of the coating, the best crystal integrity is produced, and the plasticity and the toughness of the coating are increased, so the coating shows the best wear resistance.
Ni-P alloy coatings with good adhesion and wear resistance were prepared on the surface of titanium alloy TC4 substrate using an electroless plating method. The structures of coatings after heat treatment at different temperatures were investigated by means of SEM, XRD and EDS. Furthermore, the relationship of different heat treatment temperatures, coating structure, coating hardness and wear resistance was established. The results show that the combination of double zincating and heat treatment can significantly improve the adhesive strength in the coating/substrate interface, and the adhesion of the coating reaches 35 N after heat treatment at 600 °C for 1 h. Hardness HV and wear loss of the substrate are 3780 MPa and 9.6 mg, respectively, while the hardness HV and the wear loss of the coating as plated are 5760 MPa and 7.7 mg, respectively, which indicate that electroless Ni-P coating can enhance hardness and wear resistance of TC4 titanium alloy. With the increase in temperature of heat treatment, Ni3P phase increases. The hardness shows higher values in the presence of Ni3P phase with highly-dispersed distribution, reaching the highest of 9790 MPa. Further increase in temperature results in the segregation of Ni3P phase and slowdown of dispersion degree, suggesting the hardness reduction. Wear loss of the coating decreases with increasing heat treatment temperature, revealing the wear resistance increases with the rise of heat treatment temperature. After heat treatment at 600 °C, despite the bigger grains and lower hardness of the coating, the best crystal integrity is produced, and the plasticity and the toughness of the coating are increased, so the coating shows the best wear resistance.
2013, 42(3):513-518.
Abstract:
The effects of Mo addition and aging temperatures on phase constitution, microstructure and room/high-temperature mechanical behavior of the Co-9Al-xMo-(9–x)W-2Ta-0.02 B alloys (x = 4, 9, referred as 4Mo and 9Mo alloy hereafter) prepared by arc-melting were investigated. Results show that the as-cast alloys are composed of Co-base solid solution γ phase and intermetallic Co3(Al, Me) compound γ’-phase, where Me stands for W, Mo and Ta. The γ phase is the matrix and the γ’ phase distributes on the grain boundaries of the γ matrix. While after 1350 °C/8 h solution and 800 °C/100 h aging, the cubic γ’ phase with a size of 200~300 nm homogeneously precipitates on the γ matrix for the 4Mo alloys. As for the 9Mo alloy, however, the microstructure is significantly changed, and there are a large number of needle-like and cellular к-Co3Mo precipitates besides a few cubic γ’ precipitates. After 1350 °C/8 h solution and 900 °C/100 h aging, a few of the needle-like к-Co3Mo precipitates appear in the 4Mo alloy, while the needle-like к-Co3Mo precipitates in the 9Mo alloy are coarsened. The 4Mo alloy presents excellent tensile mechanical properties, better than the 9Mo alloy at room and high temperature, and both alloys exhibit yield stress anomalies at temperatures above 600 °C
The effects of Mo addition and aging temperatures on phase constitution, microstructure and room/high-temperature mechanical behavior of the Co-9Al-xMo-(9–x)W-2Ta-0.02 B alloys (x = 4, 9, referred as 4Mo and 9Mo alloy hereafter) prepared by arc-melting were investigated. Results show that the as-cast alloys are composed of Co-base solid solution γ phase and intermetallic Co3(Al, Me) compound γ’-phase, where Me stands for W, Mo and Ta. The γ phase is the matrix and the γ’ phase distributes on the grain boundaries of the γ matrix. While after 1350 °C/8 h solution and 800 °C/100 h aging, the cubic γ’ phase with a size of 200~300 nm homogeneously precipitates on the γ matrix for the 4Mo alloys. As for the 9Mo alloy, however, the microstructure is significantly changed, and there are a large number of needle-like and cellular к-Co3Mo precipitates besides a few cubic γ’ precipitates. After 1350 °C/8 h solution and 900 °C/100 h aging, a few of the needle-like к-Co3Mo precipitates appear in the 4Mo alloy, while the needle-like к-Co3Mo precipitates in the 9Mo alloy are coarsened. The 4Mo alloy presents excellent tensile mechanical properties, better than the 9Mo alloy at room and high temperature, and both alloys exhibit yield stress anomalies at temperatures above 600 °C
2013, 42(3):519-523.
Abstract:
Film cooling as an important thermal protection technology has been widely used in gas turbine blades. However, due to stress concentration around holes, the cooling holes have become key crack nucleation regions of blades. In this paper, the crystallographic behaviors of cooling holes were analyzed by the crystallographic constitutive model. Film cooling holes in the leading edge was simplified to a flat model. The distributions of resolved shear stress along cooling holes and changes under different hole distances were obtained. The results show that stress interference exits among cooling holes clearly. Higher stress areas appear between the centerlines of the cooling holes in two adjacent columns and the lower stress regions as a diamond-shape occur between two cooling holes in the same columns. All the slip systems of octahedral, dodecahedral and hexahedral will be active. And the maximum resolved shear stresses occur at the angle 0o/20o/30o of cooling hole. With horizontal holes distance increasing, the maximum stress around cooling holes decreases. With the vertical holes distance increasing, the maximum stress around cooling holes increases. In all the slip system, the hexahedral slip systems is the most sensitive to hole distances change
Film cooling as an important thermal protection technology has been widely used in gas turbine blades. However, due to stress concentration around holes, the cooling holes have become key crack nucleation regions of blades. In this paper, the crystallographic behaviors of cooling holes were analyzed by the crystallographic constitutive model. Film cooling holes in the leading edge was simplified to a flat model. The distributions of resolved shear stress along cooling holes and changes under different hole distances were obtained. The results show that stress interference exits among cooling holes clearly. Higher stress areas appear between the centerlines of the cooling holes in two adjacent columns and the lower stress regions as a diamond-shape occur between two cooling holes in the same columns. All the slip systems of octahedral, dodecahedral and hexahedral will be active. And the maximum resolved shear stresses occur at the angle 0o/20o/30o of cooling hole. With horizontal holes distance increasing, the maximum stress around cooling holes decreases. With the vertical holes distance increasing, the maximum stress around cooling holes increases. In all the slip system, the hexahedral slip systems is the most sensitive to hole distances change
2013, 42(3):524-529.
Abstract:
TA18 titanium alloy tubes based on cold pilgering are widely used for the hydraulic system of airplanes and spacecrafts and drill pipes of oil exploration due to their high specific strength, good cold processability and reasonable texture distribution. In this study, according to the mechanical analysis of multi-strokes cold pilgering process, precision motion mode and stress state of the tube during the forming process were obtained. Furthermore, a three-dimensional FE model of multi-strokes cold pilgering of TA18 titanium alloy tube was developed in the FE software environment of ABAQUS/Explicit. Some key modeling techniques were proposed, including the implementation of virtual crank-connecting-link device, the control method of multi-strokes motion modes, the definition of complex geometric formation and the definition of rolling friction and sliding friction. The FE model was validated by energy conservation principle and experimental results, and evaluated by the distributions of equivalent stress and equivalent plastic strain during the forming process.
TA18 titanium alloy tubes based on cold pilgering are widely used for the hydraulic system of airplanes and spacecrafts and drill pipes of oil exploration due to their high specific strength, good cold processability and reasonable texture distribution. In this study, according to the mechanical analysis of multi-strokes cold pilgering process, precision motion mode and stress state of the tube during the forming process were obtained. Furthermore, a three-dimensional FE model of multi-strokes cold pilgering of TA18 titanium alloy tube was developed in the FE software environment of ABAQUS/Explicit. Some key modeling techniques were proposed, including the implementation of virtual crank-connecting-link device, the control method of multi-strokes motion modes, the definition of complex geometric formation and the definition of rolling friction and sliding friction. The FE model was validated by energy conservation principle and experimental results, and evaluated by the distributions of equivalent stress and equivalent plastic strain during the forming process.
2013, 42(3):530-535.
Abstract:
The crystal structure models of α-titanium and β-titanium with hydrogen were established and the stable structure was optimized. The variation of volume, volume expansion rate, lattice constant and ratio of lattice constant for the α-titanium and β-titanium with hydrogen were calculated with help of the first principle method. The calculated results show that the hydrogen content affects the angle of crystal axe and volume expansion. Hydrogen would occupy the tetrahedral space of β-titanium at the hydrogen content below 0.2597wt% and/or the octahedral space of β-titanium at the hydrogen content above 0.2597 wt%
The crystal structure models of α-titanium and β-titanium with hydrogen were established and the stable structure was optimized. The variation of volume, volume expansion rate, lattice constant and ratio of lattice constant for the α-titanium and β-titanium with hydrogen were calculated with help of the first principle method. The calculated results show that the hydrogen content affects the angle of crystal axe and volume expansion. Hydrogen would occupy the tetrahedral space of β-titanium at the hydrogen content below 0.2597wt% and/or the octahedral space of β-titanium at the hydrogen content above 0.2597 wt%
2013, 42(3):536-540.
Abstract:
Monofilament and multi-filament drawing processes play important roles in the manufacture of Bi-based high-temperature superconductor (HTS) tapes. In order to investigate the deformation behavior of superconducting powder, the theoretical derivation was used to analyze the drawing process of the single filament superconductor wire, and a relationship between processing parameters and powder density was determined. The experiments were applied to verify the feasibility and effectiveness of the derivation. Also, the large cross-section reduction drawing technique was employed to optimize the process and to achieve advanced energy-saving forming. For 61-filament Bi-2223/Ag wire with a diameter of 1.86 mm, the Vickers hardness of the powder cores was measured, and the finite element model of the drawing of the multi-filament superconductor wire was established. It is found that the powder density of different filaments is of inhomogeneous distribution, especially the large fluctuation in the radial distribution for layers of filaments during process, which will directly affect the ultimate quality of tapes. Meanwhile, the Gradual Racetrack-type Tri-pass Drawing process was developed to fabricate Bi-2223/Ag tapes. The experimental results show that the Racetrack drawing can increase the critical current of HTS tape by 10.1%.
Monofilament and multi-filament drawing processes play important roles in the manufacture of Bi-based high-temperature superconductor (HTS) tapes. In order to investigate the deformation behavior of superconducting powder, the theoretical derivation was used to analyze the drawing process of the single filament superconductor wire, and a relationship between processing parameters and powder density was determined. The experiments were applied to verify the feasibility and effectiveness of the derivation. Also, the large cross-section reduction drawing technique was employed to optimize the process and to achieve advanced energy-saving forming. For 61-filament Bi-2223/Ag wire with a diameter of 1.86 mm, the Vickers hardness of the powder cores was measured, and the finite element model of the drawing of the multi-filament superconductor wire was established. It is found that the powder density of different filaments is of inhomogeneous distribution, especially the large fluctuation in the radial distribution for layers of filaments during process, which will directly affect the ultimate quality of tapes. Meanwhile, the Gradual Racetrack-type Tri-pass Drawing process was developed to fabricate Bi-2223/Ag tapes. The experimental results show that the Racetrack drawing can increase the critical current of HTS tape by 10.1%.
2013, 42(3):541-544.
Abstract:
The phase diagram, liquidus projection and isothermal section (25 °C) of Au-Pd-Zr system alloys and vertical section of xAu-xPd-Zr system were calculated by Calphad soft ware Pandat and the phase equilibria and solidification sequence of the alloy 36Au-36Pd-28Zr were compared with the experimental results of OM, SEM and EDS. The results show that the calculated thermodynamic results of phase equilibria agree well with the experimental results. The solidification sequence of 36Au-36Pd-28Zr is as following: L→L+Pd3Zr→L+Pd3Zr+ ZrAu2→Pd3Zr+ZrAu2+ ZrAu3
The phase diagram, liquidus projection and isothermal section (25 °C) of Au-Pd-Zr system alloys and vertical section of xAu-xPd-Zr system were calculated by Calphad soft ware Pandat and the phase equilibria and solidification sequence of the alloy 36Au-36Pd-28Zr were compared with the experimental results of OM, SEM and EDS. The results show that the calculated thermodynamic results of phase equilibria agree well with the experimental results. The solidification sequence of 36Au-36Pd-28Zr is as following: L→L+Pd3Zr→L+Pd3Zr+ ZrAu2→Pd3Zr+ZrAu2+ ZrAu3
2013, 42(3):545-549.
Abstract:
The odtadecanethiol (ODT) was dispersed in aqueous solution with different surfactants, and then self-assembled monilayers (SAMs) were prepared on the surface of silver. The anticorrosion function and adsorption behavior of ODT SAMs on the silve surface was investigated by means of polarization curve, AC impedance and circular voltammetric methods. The results show that ODT is easy to form dense and stable SAMs on the surface of silver. It effectively suppresses silver anodic oxidation process and cathodic reduction process, and changes the surface electric double layer structure of the silver electrode. The results from electrochemical measurement indicate that the corrosion resistance of silver is improved by the ODT SAMs. Adsorption of the ODT SAMs follows the Langmuir’s adsorption isotherm, and the adsorption mechanism is typical chemisorption
The odtadecanethiol (ODT) was dispersed in aqueous solution with different surfactants, and then self-assembled monilayers (SAMs) were prepared on the surface of silver. The anticorrosion function and adsorption behavior of ODT SAMs on the silve surface was investigated by means of polarization curve, AC impedance and circular voltammetric methods. The results show that ODT is easy to form dense and stable SAMs on the surface of silver. It effectively suppresses silver anodic oxidation process and cathodic reduction process, and changes the surface electric double layer structure of the silver electrode. The results from electrochemical measurement indicate that the corrosion resistance of silver is improved by the ODT SAMs. Adsorption of the ODT SAMs follows the Langmuir’s adsorption isotherm, and the adsorption mechanism is typical chemisorption
2013, 42(3):550-554.
Abstract:
The hot sheet formability test machine and the grid measurement and analysis system were used to determine the forming limit diagram (FLD) of AZ31 magnesium alloy sheet in the forming temperature range of 150~250 °C. The deep drawing processes were simulated using DYNAFORM with the FLD and Keeler’s function as broken criterion respectively in the forming temperature range of 150~250 °C. In order to validate the simulated results, the deep drawing tests were also performed. The results show that breaking can be predicted more precisely in the forming process using the FLD as the broken criterion than using auto Keeler’s broken criterion when simulating with DYNAFORM
The hot sheet formability test machine and the grid measurement and analysis system were used to determine the forming limit diagram (FLD) of AZ31 magnesium alloy sheet in the forming temperature range of 150~250 °C. The deep drawing processes were simulated using DYNAFORM with the FLD and Keeler’s function as broken criterion respectively in the forming temperature range of 150~250 °C. In order to validate the simulated results, the deep drawing tests were also performed. The results show that breaking can be predicted more precisely in the forming process using the FLD as the broken criterion than using auto Keeler’s broken criterion when simulating with DYNAFORM
2013, 42(3):555-559.
Abstract:
A series of binary RuO2-Ta2O5 oxide composites with different Ru/Ta molar ratios were deposited on titanium substrate by a thermal decomposition method. The structure, voltametrical characteristics and capacitive properties as a function of the Ru/Ta molar ratios were investigated by X-ray diffraction (XRD), cyclic voltammetry (CV) and galvanostatic charge-discharge tests. The results show that the degree of crystallization of the Ti/RuO2-Ta2O5 electrodes decreases with the increase of Ta2O5 content in the RuO2-Ta2O5 oxide coatings. A completely amorphous structure exists as the proportion of Ta2O5 is up to 70 mol% or higher. The electrochemical performance of the Ti/RuO2-Ta2O5 electrodes is closely related with the composition and structure. The specific capacitance increases firstly and then decreases with the ratio of Ta to Ru in oxide coatings, and a maximum specific capacitance of 621.2 F·g-1(RuO2) is obtained when the Ta2O5 content is 70 mol%.
A series of binary RuO2-Ta2O5 oxide composites with different Ru/Ta molar ratios were deposited on titanium substrate by a thermal decomposition method. The structure, voltametrical characteristics and capacitive properties as a function of the Ru/Ta molar ratios were investigated by X-ray diffraction (XRD), cyclic voltammetry (CV) and galvanostatic charge-discharge tests. The results show that the degree of crystallization of the Ti/RuO2-Ta2O5 electrodes decreases with the increase of Ta2O5 content in the RuO2-Ta2O5 oxide coatings. A completely amorphous structure exists as the proportion of Ta2O5 is up to 70 mol% or higher. The electrochemical performance of the Ti/RuO2-Ta2O5 electrodes is closely related with the composition and structure. The specific capacitance increases firstly and then decreases with the ratio of Ta to Ru in oxide coatings, and a maximum specific capacitance of 621.2 F·g-1(RuO2) is obtained when the Ta2O5 content is 70 mol%.
2013, 42(3):560-564.
Abstract:
The Laves phase reinforced Nb matrix composite materials with V and Fe additions were prepared by mechanical alloying and reactive hot pressing. Microstructures and properties were investigated of Nb/NbCr2 alloys prepared from 20 h mechanically alloyed powders of Nb/NbCr2-4.0V and Nb/NbCr2-4.0Fe stoichiometric compositions by hot pressing at 1250 °C for 30 min. The results indicate that the fine dispersed ternary Laves phase Nb(Cr,V)2 and Nb(Cr, Fe)2 are synthesized in the Nb matrix by the in-situ reaction synthesis technique during hot pressing. In the ternary Laves phase V and Fe atoms preferentially occupy the Cr sites. The prepared Laves phase reinforced Nb matrix alloys with fine and uniform microstructures are nearly full-dense, and their grain sizes are less than 500 nm. The Nb/NbCr2-4.0V and Nb/NbCr2-4.0Fe alloys have fracture toughnesses of 5.3 and 6.3 MPa·m1/2 respectively. Furthermore, the Nb/NbCr2-4.0Fe alloy has a yield strength of 2094 MPa, compressive strength of 2256 MPa and plastic strain of 6.03%
The Laves phase reinforced Nb matrix composite materials with V and Fe additions were prepared by mechanical alloying and reactive hot pressing. Microstructures and properties were investigated of Nb/NbCr2 alloys prepared from 20 h mechanically alloyed powders of Nb/NbCr2-4.0V and Nb/NbCr2-4.0Fe stoichiometric compositions by hot pressing at 1250 °C for 30 min. The results indicate that the fine dispersed ternary Laves phase Nb(Cr,V)2 and Nb(Cr, Fe)2 are synthesized in the Nb matrix by the in-situ reaction synthesis technique during hot pressing. In the ternary Laves phase V and Fe atoms preferentially occupy the Cr sites. The prepared Laves phase reinforced Nb matrix alloys with fine and uniform microstructures are nearly full-dense, and their grain sizes are less than 500 nm. The Nb/NbCr2-4.0V and Nb/NbCr2-4.0Fe alloys have fracture toughnesses of 5.3 and 6.3 MPa·m1/2 respectively. Furthermore, the Nb/NbCr2-4.0Fe alloy has a yield strength of 2094 MPa, compressive strength of 2256 MPa and plastic strain of 6.03%
2013, 42(3):565-568.
Abstract:
The evolutions of the phase composition and the microstructure, as well as their effects on the magnetic performance, were investigated with a series of annealing processes using the prepared nanocrystalline single-phase SmCo7 alloy as the starting material. The SmCo7 (1:7H) phase is discovered to have a good single-phase stability from the room temperature up to 600 °C. A discontinuous nanograin growth takes place in nanocrystalline SmCo7 alloy, accompanied with the destabilization of the single 1:7H phase, resulting in the formation of the Sm2Co17 (2:17R) and SmCo5 (1:5H) phases, which exist in a form of the phase-transformation twins and the particulate precipitates respectively. The optimum magnetic performance is obtained in the nanocrystalline 1:7H single-phase alloys, and the maximum intrinsic coercivity 1164.54 kA/m and energy product 95.65 kJ/m3 are archived in SmCo7 alloys with the mean grain size of 33 nm and 29 nm, respectively.
The evolutions of the phase composition and the microstructure, as well as their effects on the magnetic performance, were investigated with a series of annealing processes using the prepared nanocrystalline single-phase SmCo7 alloy as the starting material. The SmCo7 (1:7H) phase is discovered to have a good single-phase stability from the room temperature up to 600 °C. A discontinuous nanograin growth takes place in nanocrystalline SmCo7 alloy, accompanied with the destabilization of the single 1:7H phase, resulting in the formation of the Sm2Co17 (2:17R) and SmCo5 (1:5H) phases, which exist in a form of the phase-transformation twins and the particulate precipitates respectively. The optimum magnetic performance is obtained in the nanocrystalline 1:7H single-phase alloys, and the maximum intrinsic coercivity 1164.54 kA/m and energy product 95.65 kJ/m3 are archived in SmCo7 alloys with the mean grain size of 33 nm and 29 nm, respectively.
2013, 42(3):569-573.
Abstract:
In order to enhance the corrosion resistance of 304 stainless steel, niobium was electrodeposited on its surface in air-and-water-stable 1-Ethyl-3-methylimidazolium Trifluoromethanesulfonate ([emim]OTF) ionic liquids. The electrochemical behaviors of bare and niobium coated 304 stainless steel were evaluated by electrochemical tests in simulated PEMFC environment. The results show that deposited niobium is finely dispersed on the surface of 304 stainless steel as isolated islands and that the height of isolated island is within 100 nm. The result of X-ray photoelectron spectroscopy (XPS) and X-ray diffraction analysis (XRD) manifest that the smooth and strong chemical inertness compound film is obtained on the surface of 304 stainless steel, which is mainly composed of NbO and Nb2O5. The thin composite film acts as barrier and remarkably improves the corrosion resistance of 304 stainless steel in PEMFC environment
In order to enhance the corrosion resistance of 304 stainless steel, niobium was electrodeposited on its surface in air-and-water-stable 1-Ethyl-3-methylimidazolium Trifluoromethanesulfonate ([emim]OTF) ionic liquids. The electrochemical behaviors of bare and niobium coated 304 stainless steel were evaluated by electrochemical tests in simulated PEMFC environment. The results show that deposited niobium is finely dispersed on the surface of 304 stainless steel as isolated islands and that the height of isolated island is within 100 nm. The result of X-ray photoelectron spectroscopy (XPS) and X-ray diffraction analysis (XRD) manifest that the smooth and strong chemical inertness compound film is obtained on the surface of 304 stainless steel, which is mainly composed of NbO and Nb2O5. The thin composite film acts as barrier and remarkably improves the corrosion resistance of 304 stainless steel in PEMFC environment
2013, 42(3):574-578.
Abstract:
Mg-4Al-1Si magnesium alloy melt was treated by self-designed ultrasonic treatment equipment for magnesium alloy melt. The effects of ultrasonic power, treating time and treating temperature on solidification structures of Mg-4Al-1Si magnesium alloy were investigated. The results show that ultrasonic treatment can markedly refine the grain size of Mg-4Al-1Si magnesium alloy, and the grain size is improved by enhancing ultrasonic power, elevating treating temperature, or prolonging treating time. The grain size of Mg-4Al-1Si magnesium alloy treated by 270 W ultrasonic power for 50 s at 650 °C is very fine, 107 μm, which is only 28% as that without ultrasonic treatment (383μm). In addition, the morphology of Mg2Si in Mg-4Al-1Si alloy with ultrasonic treatment changes from coarse Chinese character shape without ultrasonic treatment into tiny granulation with evenly distribution in the matrix.
Mg-4Al-1Si magnesium alloy melt was treated by self-designed ultrasonic treatment equipment for magnesium alloy melt. The effects of ultrasonic power, treating time and treating temperature on solidification structures of Mg-4Al-1Si magnesium alloy were investigated. The results show that ultrasonic treatment can markedly refine the grain size of Mg-4Al-1Si magnesium alloy, and the grain size is improved by enhancing ultrasonic power, elevating treating temperature, or prolonging treating time. The grain size of Mg-4Al-1Si magnesium alloy treated by 270 W ultrasonic power for 50 s at 650 °C is very fine, 107 μm, which is only 28% as that without ultrasonic treatment (383μm). In addition, the morphology of Mg2Si in Mg-4Al-1Si alloy with ultrasonic treatment changes from coarse Chinese character shape without ultrasonic treatment into tiny granulation with evenly distribution in the matrix.
2013, 42(3):579-584.
Abstract:
2090 Al-Li alloy electron beam welding joints were heat treated after welding, and the heat treatment scheme was 530 °C quenching for 0.5 h + 190 °C artificial aging for 12 h. Results show that the strength of 2090 Al-Li alloy joint is from 331 MPa in the as-welded state to 415 MPa under the condition of post-weld heat treatment. Therefore, the post-weld heat treatment can increase the strength of Al-Li alloy joints greatly. The observation of joint microstructure demonstrates that the grain morphology of the weldment varies form equiaxed dendrites in as-welded state into equiaxed grains after heat treatment, and the fine strengthening phases precipitate within the grain and along the grain boundary. The XRD analysis of phase constituent indicates that the main strengthening phases in Al-Li weldment are δ′(Al3Li), T1(Al2CuLi) and β′(Al3Zr), etc. The TEM observation shows that after heat treatment, many strengthening phases of spheroidal δ′ and needle-like T1 precipitate in weld metal of 2090 Al-Li alloy joint, which contribute to the joint strength. The observation of joint tensile fracture shows that the Al-Li alloy electron beam welding joint presents the characteristic of transgranular ductile fracture in the as-welded state. After post-weld heat treatment, the Al-Li alloy welded joint presents the pattern of intergranular fracture
2090 Al-Li alloy electron beam welding joints were heat treated after welding, and the heat treatment scheme was 530 °C quenching for 0.5 h + 190 °C artificial aging for 12 h. Results show that the strength of 2090 Al-Li alloy joint is from 331 MPa in the as-welded state to 415 MPa under the condition of post-weld heat treatment. Therefore, the post-weld heat treatment can increase the strength of Al-Li alloy joints greatly. The observation of joint microstructure demonstrates that the grain morphology of the weldment varies form equiaxed dendrites in as-welded state into equiaxed grains after heat treatment, and the fine strengthening phases precipitate within the grain and along the grain boundary. The XRD analysis of phase constituent indicates that the main strengthening phases in Al-Li weldment are δ′(Al3Li), T1(Al2CuLi) and β′(Al3Zr), etc. The TEM observation shows that after heat treatment, many strengthening phases of spheroidal δ′ and needle-like T1 precipitate in weld metal of 2090 Al-Li alloy joint, which contribute to the joint strength. The observation of joint tensile fracture shows that the Al-Li alloy electron beam welding joint presents the characteristic of transgranular ductile fracture in the as-welded state. After post-weld heat treatment, the Al-Li alloy welded joint presents the pattern of intergranular fracture
2013, 42(3):585-588.
Abstract:
The microstructure, nano-indentation and friction properties of the CNx/SiC (carbon nitride/silicon carbon) bilayered films (SiC as interlayer), deposited on ultrafine-grained TiNi alloy substrate using magnetron sputtering technique at room temperature, were investigated. The results show that the CNx film is not fully compact with micro-pore defections in some zones, which has been possibly caused by the breaking off of inclusions in substrates. The CNx film presents high concentration graphite, low nano-hardness (5.23 GPa), low Young's modulus (33.29 Pa), but high hardness-to-modulus ratio (0.157). As sliding against Si3N4 (silicon nitride) balls (2 mm in radius), under ambient environment and 200 g load, the CNx film exhibits the friction coefficient of about 0.173 without film cracking and interface delaminating. On the other hand, under Kokubo simulation body fluid (SBF) and 500 g load, the CNx film exhibits the friction coefficient of about 0.103, but the interface delaminating occurs that is believed to be due to that the SBF enter into the film-film-substrate interfaces through micro-pores defections and corrode the interfaces
The microstructure, nano-indentation and friction properties of the CNx/SiC (carbon nitride/silicon carbon) bilayered films (SiC as interlayer), deposited on ultrafine-grained TiNi alloy substrate using magnetron sputtering technique at room temperature, were investigated. The results show that the CNx film is not fully compact with micro-pore defections in some zones, which has been possibly caused by the breaking off of inclusions in substrates. The CNx film presents high concentration graphite, low nano-hardness (5.23 GPa), low Young's modulus (33.29 Pa), but high hardness-to-modulus ratio (0.157). As sliding against Si3N4 (silicon nitride) balls (2 mm in radius), under ambient environment and 200 g load, the CNx film exhibits the friction coefficient of about 0.173 without film cracking and interface delaminating. On the other hand, under Kokubo simulation body fluid (SBF) and 500 g load, the CNx film exhibits the friction coefficient of about 0.103, but the interface delaminating occurs that is believed to be due to that the SBF enter into the film-film-substrate interfaces through micro-pores defections and corrode the interfaces
2013, 42(3):589-592.
Abstract:
Cr-N coatings were deposited on magnesium alloy by close field unbalanced magnetron sputtering technique (CFUBMS) with different bias. The microstructure, thickness, adhesion and wear properties of the coatings were characterized. The results show that the coatings are mainly composed of Cr(N) phase and a little Cr2N phase. The coating deposited with the bias of 60 V has higher hardness, well adhesion and wear properties. With further increasing the bias voltage, the coating hardness is enhanced; however, both the adhesion and wear resistance are reduced
Cr-N coatings were deposited on magnesium alloy by close field unbalanced magnetron sputtering technique (CFUBMS) with different bias. The microstructure, thickness, adhesion and wear properties of the coatings were characterized. The results show that the coatings are mainly composed of Cr(N) phase and a little Cr2N phase. The coating deposited with the bias of 60 V has higher hardness, well adhesion and wear properties. With further increasing the bias voltage, the coating hardness is enhanced; however, both the adhesion and wear resistance are reduced
2013, 42(3):593-597.
Abstract:
Mechanical properties of as-cast and as-extruded Mg-7Zn-3Al-0~0.7Re(wt%) magnesium alloys both at room temperature and elevated temperatures were compared by means of TEM, SEM, EDS and tensile mechanical property testing, and the effects of rare-earth addition and deformation on the strength and plasticity of the alloys were analyzed. The results show that the proper addition of Er could dramatically increase the elevated temperature plasticity of as-cast Mg-Zn-Al alloy, while it would not change much the room temperature mechanical properties and the elevated temperature yield strength. It is also revealed that spherical nano-precipitates occurred during the extrusion, which increased the elevated temperature mechanical properties of the as-extruded Mg-Zn-Al-Er alloy remarkably. Compared to those of the as-cast alloy, the yield strength and elongation of the as-extruded alloy at 200 °C were increased by 105% and 120%, respectively. Furthermore, fractographs present an obvious tough fracture feature
Mechanical properties of as-cast and as-extruded Mg-7Zn-3Al-0~0.7Re(wt%) magnesium alloys both at room temperature and elevated temperatures were compared by means of TEM, SEM, EDS and tensile mechanical property testing, and the effects of rare-earth addition and deformation on the strength and plasticity of the alloys were analyzed. The results show that the proper addition of Er could dramatically increase the elevated temperature plasticity of as-cast Mg-Zn-Al alloy, while it would not change much the room temperature mechanical properties and the elevated temperature yield strength. It is also revealed that spherical nano-precipitates occurred during the extrusion, which increased the elevated temperature mechanical properties of the as-extruded Mg-Zn-Al-Er alloy remarkably. Compared to those of the as-cast alloy, the yield strength and elongation of the as-extruded alloy at 200 °C were increased by 105% and 120%, respectively. Furthermore, fractographs present an obvious tough fracture feature
2013, 42(3):598-602.
Abstract:
Direct diffusion bonding of hydrogenated TC4 alloy to Al2O3 ceramic was achieved. The typical interfacial microstructure of TC4/Al2O3 joint was TC4/α-Ti/Ti3Al + Al2TiO5/Al2O3, which was confirmed by means of OM, SEM coupled with EDS and XRD. The effect of the bonding temperature on the microstructure of joints was investigated. Results show that the phase constitution of reaction layers dose not change when the bonding temperature is changed. However, with an increase of the diffusion temperature, the thickness of each reaction layer increases. The activation energy of Ti3Al + Al2TiO5 layer are 213, 172 and 152 kJ/mol, respectively when the hydrogen contents are 0 wt%, 0.3 wt% and 0.4 wt%. The maximum shear strength of the joint reaches 128 MPa when the bonding temperature is 840 °C for 90 min and the hydrogen content in TC4 is 0.4 wt%. Moreover, fracture analysis shows that fracture occurs in the Al2O3 base metal side
Direct diffusion bonding of hydrogenated TC4 alloy to Al2O3 ceramic was achieved. The typical interfacial microstructure of TC4/Al2O3 joint was TC4/α-Ti/Ti3Al + Al2TiO5/Al2O3, which was confirmed by means of OM, SEM coupled with EDS and XRD. The effect of the bonding temperature on the microstructure of joints was investigated. Results show that the phase constitution of reaction layers dose not change when the bonding temperature is changed. However, with an increase of the diffusion temperature, the thickness of each reaction layer increases. The activation energy of Ti3Al + Al2TiO5 layer are 213, 172 and 152 kJ/mol, respectively when the hydrogen contents are 0 wt%, 0.3 wt% and 0.4 wt%. The maximum shear strength of the joint reaches 128 MPa when the bonding temperature is 840 °C for 90 min and the hydrogen content in TC4 is 0.4 wt%. Moreover, fracture analysis shows that fracture occurs in the Al2O3 base metal side
2013, 42(3):603-606.
Abstract:
T800 alloy is a good wear-resistant coating material for tip shrouds of turbine blades operated at high temperature. In order to make clear the best serving state of T800 alloy, microstructure and high-temperature fretting wear behavior of T800 alloy in casting and cladding state were studied. During welding, alloying elements of K417G alloy substrate diffused into welding melting pool, which resulted in that there was a decrease in the alloying elements of the T800 clad. Laves phases were dissolved completely and then precipitated to form fine Laves phases in matrix during solidification. As a result, as-cast T800 possessed larger volume fraction and size of Laves phases, higher hardness and high-temperature fretting wear resistance than T800 cladding
T800 alloy is a good wear-resistant coating material for tip shrouds of turbine blades operated at high temperature. In order to make clear the best serving state of T800 alloy, microstructure and high-temperature fretting wear behavior of T800 alloy in casting and cladding state were studied. During welding, alloying elements of K417G alloy substrate diffused into welding melting pool, which resulted in that there was a decrease in the alloying elements of the T800 clad. Laves phases were dissolved completely and then precipitated to form fine Laves phases in matrix during solidification. As a result, as-cast T800 possessed larger volume fraction and size of Laves phases, higher hardness and high-temperature fretting wear resistance than T800 cladding
2013, 42(3):607-610.
Abstract:
The influences of controlled over-pressure sintering on the critical current density and mechanical properties of the Bi-2223/Ag high-temperature superconducting tape have been investigated. XRD and SEM were used to analyze the reasons of the improvement of the tape’s properties. The results show that the critical current density of the tape is promoted by more than 30% while the tensile strength and critical bending strain are improved to 104 MPa and 0.91% respectively. The Bi-2223 content is increased and the FWMH value of the tape is lowered from 6.5° to 5.6° by the controlled over-pressure sintering process. Besides, the densities of the ceramic cores are improved. Due to the higher Bi-2223 content, better grain alignment and higher core density, the critical current density and mechanical property are improved
The influences of controlled over-pressure sintering on the critical current density and mechanical properties of the Bi-2223/Ag high-temperature superconducting tape have been investigated. XRD and SEM were used to analyze the reasons of the improvement of the tape’s properties. The results show that the critical current density of the tape is promoted by more than 30% while the tensile strength and critical bending strain are improved to 104 MPa and 0.91% respectively. The Bi-2223 content is increased and the FWMH value of the tape is lowered from 6.5° to 5.6° by the controlled over-pressure sintering process. Besides, the densities of the ceramic cores are improved. Due to the higher Bi-2223 content, better grain alignment and higher core density, the critical current density and mechanical property are improved
2013, 42(3):611-615.
Abstract:
Anodic coatings of the oxides of Ru-Ir-Ti with different layer numbers were prepared by a pyrolysis method. The anodic coatings’ electrochemical characteristics were studied by electrochemical methods. The surface topography and the microstructure of the coatings were also studied. The results show that when the Ru-Ir-Ti oxide coating is coated with 30 layers (15.55 μm), it has better adhesive force and better catalytic selectivity. Meanwhile, the coating’s chlorine evolution potential, oxygen evolution potential and current efficiency are 1.02 V, 1.52 V and 94.5%, respectively. At the same time, the coating’s cyclic voltammetry charge is up to 35 mC/cm2 and its accelerated durability is about 525 h. When the coating layer number reaches up to 40 (22.6 μm), the anodic coating has rough surface and poor binding force and the cracks on the coating surface become deeper and wider
Anodic coatings of the oxides of Ru-Ir-Ti with different layer numbers were prepared by a pyrolysis method. The anodic coatings’ electrochemical characteristics were studied by electrochemical methods. The surface topography and the microstructure of the coatings were also studied. The results show that when the Ru-Ir-Ti oxide coating is coated with 30 layers (15.55 μm), it has better adhesive force and better catalytic selectivity. Meanwhile, the coating’s chlorine evolution potential, oxygen evolution potential and current efficiency are 1.02 V, 1.52 V and 94.5%, respectively. At the same time, the coating’s cyclic voltammetry charge is up to 35 mC/cm2 and its accelerated durability is about 525 h. When the coating layer number reaches up to 40 (22.6 μm), the anodic coating has rough surface and poor binding force and the cracks on the coating surface become deeper and wider
2013, 42(3):616-620.
Abstract:
Iridium catalyst was prepared by a direct gas phase reduction method. The phase composition of iridium was analyzed by X-ray diffraction, and the electrochemical performance was evaluated by cyclic voltammetry (CV) and linear scanning voltage (LSV). The result of XRD shows that iridium is transformed completely from iridium oxides after 400 °C reduction for 3 h under ammonia atmosphere. According to the result of CV and LSV, iridium possesses favorable electrocatalytic activity for oxygen reduction. The onset potential of iridium for oxygen reduction reaction (ORR) achieves 0.51 V (vs. SCE). From the viewpoint of atomic states, the number of d-band vacancy of iridium is more than that of platinum which leads to the lower electrocatalytic activity of iridium than that of platinum, but the two electrocatalysts have the similar electrocatalytic paths for ORR
Iridium catalyst was prepared by a direct gas phase reduction method. The phase composition of iridium was analyzed by X-ray diffraction, and the electrochemical performance was evaluated by cyclic voltammetry (CV) and linear scanning voltage (LSV). The result of XRD shows that iridium is transformed completely from iridium oxides after 400 °C reduction for 3 h under ammonia atmosphere. According to the result of CV and LSV, iridium possesses favorable electrocatalytic activity for oxygen reduction. The onset potential of iridium for oxygen reduction reaction (ORR) achieves 0.51 V (vs. SCE). From the viewpoint of atomic states, the number of d-band vacancy of iridium is more than that of platinum which leads to the lower electrocatalytic activity of iridium than that of platinum, but the two electrocatalysts have the similar electrocatalytic paths for ORR
2013, 42(3):621-624.
Abstract:
Using DC pulse mode, a microarc oxidation (MAO) composite coating containing Cr2O3 particles on TC4 titanium alloy was prepared by adding 1.5 g/L Cr2O3 microparticles into the Na2SiO3-(NaPO3)6 electrolyte. The morphology and microstructure was analyzed by SEM, EDS and XRD. The dry wear behavior of the composite coating was investigated at room temperature. The results show that the surface pores of composite coating are filled with tiny Cr2O3 particles, and only a small amount of micropores can be observed on the coating surface. The composite coating has a large number of Cr2O3 phase besides rutile-TiO2, anatase-TiO2, Al2TiO5 phase and some amorphous compounds. The MAO composite coating containing Cr2O3 particles has smaller friction coefficient, lower wear loss and better wear resistance under the same wear condition. The composite coating only produces slight adhesive wear, almost without abrasive wear under the load of 10 N. However, the abrasive wear is somewhat intensified, and the loss of second-phase particles appears under the load of 50 N. Cr2O3 particles can reduce the friction coefficient and wear loss and improve the wear resistance of the composite coating by filling the pores of MAO coating, transferring load of Cr2O3 particles and the dispersion strengthening
Using DC pulse mode, a microarc oxidation (MAO) composite coating containing Cr2O3 particles on TC4 titanium alloy was prepared by adding 1.5 g/L Cr2O3 microparticles into the Na2SiO3-(NaPO3)6 electrolyte. The morphology and microstructure was analyzed by SEM, EDS and XRD. The dry wear behavior of the composite coating was investigated at room temperature. The results show that the surface pores of composite coating are filled with tiny Cr2O3 particles, and only a small amount of micropores can be observed on the coating surface. The composite coating has a large number of Cr2O3 phase besides rutile-TiO2, anatase-TiO2, Al2TiO5 phase and some amorphous compounds. The MAO composite coating containing Cr2O3 particles has smaller friction coefficient, lower wear loss and better wear resistance under the same wear condition. The composite coating only produces slight adhesive wear, almost without abrasive wear under the load of 10 N. However, the abrasive wear is somewhat intensified, and the loss of second-phase particles appears under the load of 50 N. Cr2O3 particles can reduce the friction coefficient and wear loss and improve the wear resistance of the composite coating by filling the pores of MAO coating, transferring load of Cr2O3 particles and the dispersion strengthening
2013, 42(3):625-628.
Abstract:
According to the deformation processing of TA18 titanium tubes of different compositions, deformation ratios and annealing temperatures, the relations of deformation ratio, annealing temperature, compositions and mechanical properties were studied and their relation curves were drawn. Results show that change of V and Al content has different effects on mechanical properties. Al content can produce a great effect on strength increase and plasticity decrease. When the composition is designed in definite ranges (Al: 2.8 wt%~3.2 wt%, V: 2.30 wt%~2.70 wt%, O: 0.07 wt%~0.09 wt%), Q value is not larger than 1.14 and similar deformation ratio (0%~70%) are confirmed, TA18 titanium tube can reach the strength level of AMS4946B and the military standard under two annealing systems (380~580 °C, 650~750 °C)
According to the deformation processing of TA18 titanium tubes of different compositions, deformation ratios and annealing temperatures, the relations of deformation ratio, annealing temperature, compositions and mechanical properties were studied and their relation curves were drawn. Results show that change of V and Al content has different effects on mechanical properties. Al content can produce a great effect on strength increase and plasticity decrease. When the composition is designed in definite ranges (Al: 2.8 wt%~3.2 wt%, V: 2.30 wt%~2.70 wt%, O: 0.07 wt%~0.09 wt%), Q value is not larger than 1.14 and similar deformation ratio (0%~70%) are confirmed, TA18 titanium tube can reach the strength level of AMS4946B and the military standard under two annealing systems (380~580 °C, 650~750 °C)
2013, 42(3):629-633.
Abstract:
A Ni-1.76 wt%W alloy liner for shaped charge was prepared by means of electrodeposition. The microstructure of the as-deposited and as-annealed alloys was examined by X-ray diffraction, transmission electron microscope and Auger electron spectroscopy technique. Mechanical properties of alloys were evaluated by tensile tests. The results demonstrate that the electrodeposited alloy has high strength, fine grains and a strong (111) texture. The prepared Ni-W alloy still has fcc structure and W is solid solutioned in Ni lattice. By annealing at 300 °C, abnormal grain growth appears in the sample. (111) texture weakens and (220) texture tends to appear. At 500 °C, sulfur segregation at grain boundary has a detrimental effect on the tensile properties of the alloy.
A Ni-1.76 wt%W alloy liner for shaped charge was prepared by means of electrodeposition. The microstructure of the as-deposited and as-annealed alloys was examined by X-ray diffraction, transmission electron microscope and Auger electron spectroscopy technique. Mechanical properties of alloys were evaluated by tensile tests. The results demonstrate that the electrodeposited alloy has high strength, fine grains and a strong (111) texture. The prepared Ni-W alloy still has fcc structure and W is solid solutioned in Ni lattice. By annealing at 300 °C, abnormal grain growth appears in the sample. (111) texture weakens and (220) texture tends to appear. At 500 °C, sulfur segregation at grain boundary has a detrimental effect on the tensile properties of the alloy.
2013, 42(3):634-638.
Abstract:
The effects of deformation temperature and deformation degree on the microstructure and mechanical properties of TC18 titanium alloy during the β isothermal forging were studied. Results show that the microstructure of TC18 titanium alloy is sensitive to the variation of isothermal forging temperature. Deforming in (α+β)-phase gets a typical bi-modal microstructure while deforming in β-phase gets a net-shaped microstructure. When deforming above the β-transus temperature, the forging shows higher strength, fracture toughness and lower plasticity. With higher deformation temperature, both the strength and the plasticity decrease while the fracture toughness increases a little. Deforming above the β-transus temperature, typical Widmanstatten, coarse β grains, and the highest fracture toughness are obtained in small deformation degree. When the deformation degree reaches 60%, grains crack seriously, secondary lamellar α further globalize and disperse, and the microstructure becomes even fine, so the alloy’s strength and plasticity maintain good matching, fracture toughness is better and the best comprehensive properties are achieved
The effects of deformation temperature and deformation degree on the microstructure and mechanical properties of TC18 titanium alloy during the β isothermal forging were studied. Results show that the microstructure of TC18 titanium alloy is sensitive to the variation of isothermal forging temperature. Deforming in (α+β)-phase gets a typical bi-modal microstructure while deforming in β-phase gets a net-shaped microstructure. When deforming above the β-transus temperature, the forging shows higher strength, fracture toughness and lower plasticity. With higher deformation temperature, both the strength and the plasticity decrease while the fracture toughness increases a little. Deforming above the β-transus temperature, typical Widmanstatten, coarse β grains, and the highest fracture toughness are obtained in small deformation degree. When the deformation degree reaches 60%, grains crack seriously, secondary lamellar α further globalize and disperse, and the microstructure becomes even fine, so the alloy’s strength and plasticity maintain good matching, fracture toughness is better and the best comprehensive properties are achieved
2013, 42(3):639-643.
Abstract:
The web AuSn solders and AuSn/Ni joints were prepared by a rolling-annealing method and reflow process, respectively. The effects of the reflow time on the microstructure and the shear properties of the AuSn/Ni joints were investigated. The results show that the molten temperature and chemical composition of the AuSn solder prepared by rolling-annealing method are close to those of the common Au-20Sn eutectic alloy solder. The AuSn/Ni joint formed a fine lamellar eutectic ζ-(Au, Ni)5Sn+δ-(Au, Ni)Sn microstructure after reflow at 330 °C for 30 s. After reflowing for 60 s, a thin and flat layer of (Ni, Au)3Sn2 intermetallic compound (IMC) was formed with some needle-like (Ni,Au)3Sn2 intermetallics. Keeping increasing the reflow time, the (Ni, Au)3Sn2 IMC layer and intermetallics grew significantly. The shear strength of AuSn/Ni joints was improved with reflow time at the beginning, up to the best shear strength of 12.49 MPa at the point of 90 s, and then went down again with further increasing the reflow time.
The web AuSn solders and AuSn/Ni joints were prepared by a rolling-annealing method and reflow process, respectively. The effects of the reflow time on the microstructure and the shear properties of the AuSn/Ni joints were investigated. The results show that the molten temperature and chemical composition of the AuSn solder prepared by rolling-annealing method are close to those of the common Au-20Sn eutectic alloy solder. The AuSn/Ni joint formed a fine lamellar eutectic ζ-(Au, Ni)5Sn+δ-(Au, Ni)Sn microstructure after reflow at 330 °C for 30 s. After reflowing for 60 s, a thin and flat layer of (Ni, Au)3Sn2 intermetallic compound (IMC) was formed with some needle-like (Ni,Au)3Sn2 intermetallics. Keeping increasing the reflow time, the (Ni, Au)3Sn2 IMC layer and intermetallics grew significantly. The shear strength of AuSn/Ni joints was improved with reflow time at the beginning, up to the best shear strength of 12.49 MPa at the point of 90 s, and then went down again with further increasing the reflow time.
2013, 42(3):644-648.
Abstract:
The theory of molecular dynamics and the developments of composites’ interface simulation, which conducted by molecular dynamics method in recent years, are summarized briefly. The modeling and computation of various composite interface problems are reviewed, including atomistic configuration, electron structures, interface interaction energy, stress and load transfer, interface mechanical constants, and the deformation and failure of interface. The interfacial issues which can be solved by molecular dynamics simulation are summed up, and the method’s future application and developments are also anticipated.
The theory of molecular dynamics and the developments of composites’ interface simulation, which conducted by molecular dynamics method in recent years, are summarized briefly. The modeling and computation of various composite interface problems are reviewed, including atomistic configuration, electron structures, interface interaction energy, stress and load transfer, interface mechanical constants, and the deformation and failure of interface. The interfacial issues which can be solved by molecular dynamics simulation are summed up, and the method’s future application and developments are also anticipated.
2013, 42(3):649-654.
Abstract:
The research progress of the electro-deposition technology under the external magnetic field is introduced. During the electroplating process, the external magnetic field has an effect on solution properties, mass transfer, charge transfer, crystal growth and crystal orientation, etc. The magnetic field’s working principle during the material preparation is illustrated, and its specific impact during the electroplating is also classified and summarized. The problems in the field of the electroplating and the development prospects of the magnetic field application are also expatiated.
The research progress of the electro-deposition technology under the external magnetic field is introduced. During the electroplating process, the external magnetic field has an effect on solution properties, mass transfer, charge transfer, crystal growth and crystal orientation, etc. The magnetic field’s working principle during the material preparation is illustrated, and its specific impact during the electroplating is also classified and summarized. The problems in the field of the electroplating and the development prospects of the magnetic field application are also expatiated.
2013, 42(3):655-660.
Abstract:
During the process of laser welding for Ti6Al4V alloy, there is large temperature gradient in the weld and the narrow area nearby because of high heat source density, which causes a large gradient of microstructure, properties and residual stress across welded joint. Based on the domestic and foreign literatures, this paper synthetically researches the heterogeneous gradient features of temperature, microstructure, mechanical properties and residual stress of titanium alloy with laser welding. The results show that the studies for large gradient features of welded joint mainly focus on the heterogeneity analysis but not on quantitative analysis and evaluation. Therefore, the method of making a quantitative characterization efficiently and intuitively for the gradient of microstructure, properties and residual stress after welding is very significant for evaluation of overall performance and safety of laser welded joints.
During the process of laser welding for Ti6Al4V alloy, there is large temperature gradient in the weld and the narrow area nearby because of high heat source density, which causes a large gradient of microstructure, properties and residual stress across welded joint. Based on the domestic and foreign literatures, this paper synthetically researches the heterogeneous gradient features of temperature, microstructure, mechanical properties and residual stress of titanium alloy with laser welding. The results show that the studies for large gradient features of welded joint mainly focus on the heterogeneity analysis but not on quantitative analysis and evaluation. Therefore, the method of making a quantitative characterization efficiently and intuitively for the gradient of microstructure, properties and residual stress after welding is very significant for evaluation of overall performance and safety of laser welded joints.
