Volume 39,Issue 10,2010 Table of Contents
2010, 39(10):1693-1696.
Abstract:
Four groups of transmission electron microscopy (TEM) specimens of Zr52.5Cu17.9Ni14.6Al10Ti5 metallic glass were prepared by double-jet electropolishing, dimpling and ion milling. TEM observations indicate that the microstructures in electron-transparent areas change sensitively with ion milling conditions. Detailed comparisons between the selected area electron diffraction patterns of TEM specimens and the X-ray diffraction patterns of thermally annealed samples of the same composition show that significant heating effects exist in some severe milling processes, resulting in the formation of various ordered structures in thin areas. In TEM specimens prepared by intentionally long time ion milling, the peak temperature locally reached is estimated as high as 780 K, far above the glass transition temperature of this metallic glass. The results suggest that precautions must be taken to prepare TEM specimens of amorphous alloys by ion milling, particularly when the induced microstructure changes may lead to invalid judgments
Four groups of transmission electron microscopy (TEM) specimens of Zr52.5Cu17.9Ni14.6Al10Ti5 metallic glass were prepared by double-jet electropolishing, dimpling and ion milling. TEM observations indicate that the microstructures in electron-transparent areas change sensitively with ion milling conditions. Detailed comparisons between the selected area electron diffraction patterns of TEM specimens and the X-ray diffraction patterns of thermally annealed samples of the same composition show that significant heating effects exist in some severe milling processes, resulting in the formation of various ordered structures in thin areas. In TEM specimens prepared by intentionally long time ion milling, the peak temperature locally reached is estimated as high as 780 K, far above the glass transition temperature of this metallic glass. The results suggest that precautions must be taken to prepare TEM specimens of amorphous alloys by ion milling, particularly when the induced microstructure changes may lead to invalid judgments
2010, 39(10):1697-1701.
Abstract:
One of the direct metal forming techniques, electron beam melting (EBM) process, was used to fabricate Ti6Al4V implants with controllable porous structure. The micro-structural pore characterization, porosity and mechanical properties of the fabricated implants were investigated. Scanning electron microscope (SEM) observation shows that the porous structure of fabricated samples coincide with the designed architecture. It is demonstrated that EBM process can provide accurate control over the internal pore architectures of the implant. The compressive strength of the implant with porosity of 60.1% is 163 MPa. The Young's modulus is 14 GPa, which is similar to that of cortical bone. The surface modification by improved alkali-heat treatment induces apatite formation in simulated body fluid (SBF). In vitro cell culture experiment results reveal that osteoblasts will spread and proliferate on the surface of modified specimens over a culture time of 7 d
One of the direct metal forming techniques, electron beam melting (EBM) process, was used to fabricate Ti6Al4V implants with controllable porous structure. The micro-structural pore characterization, porosity and mechanical properties of the fabricated implants were investigated. Scanning electron microscope (SEM) observation shows that the porous structure of fabricated samples coincide with the designed architecture. It is demonstrated that EBM process can provide accurate control over the internal pore architectures of the implant. The compressive strength of the implant with porosity of 60.1% is 163 MPa. The Young's modulus is 14 GPa, which is similar to that of cortical bone. The surface modification by improved alkali-heat treatment induces apatite formation in simulated body fluid (SBF). In vitro cell culture experiment results reveal that osteoblasts will spread and proliferate on the surface of modified specimens over a culture time of 7 d
2010, 39(10):1702-1706.
Abstract:
The influences of different Ag contents on the properties of Sn-9Zn lead-free solder were investigated. The results indicate that Ag plays an important role not only in the solderability and the structure of the solder, but also in the mechanical property of the soldered joint. In particular, adding 0.3% (mass fraction) Ag can improve the oxidation resistance of the solder, so the solderability of the solder is significantly improved. Sn-9Zn-0.3Ag shows finer and more uniform microstructure than Sn-9Zn. Results also indicate that when the content of Ag is 0.3%, the best mechanical property of the soldered joint can be obtained, and the fracture micrographs show that plenty of small and uniform dimples are found on the soldered joints fractures. Some Cu-Zn and Ag-Zn intermetallic compounds appear at the bottom of dimples when the content of Ag is up to 1%, and the mechanical property of the soldered joint is reduced
The influences of different Ag contents on the properties of Sn-9Zn lead-free solder were investigated. The results indicate that Ag plays an important role not only in the solderability and the structure of the solder, but also in the mechanical property of the soldered joint. In particular, adding 0.3% (mass fraction) Ag can improve the oxidation resistance of the solder, so the solderability of the solder is significantly improved. Sn-9Zn-0.3Ag shows finer and more uniform microstructure than Sn-9Zn. Results also indicate that when the content of Ag is 0.3%, the best mechanical property of the soldered joint can be obtained, and the fracture micrographs show that plenty of small and uniform dimples are found on the soldered joints fractures. Some Cu-Zn and Ag-Zn intermetallic compounds appear at the bottom of dimples when the content of Ag is up to 1%, and the mechanical property of the soldered joint is reduced
2010, 39(10):1707-1710.
Abstract:
Microstructure evolutions of Ti-27Nb-8Zr (mass fraction, %) biomedical alloy subjected to different aging treatments after solution treatment were studied by optical microscopy, scanning electron microscopy and X-ray diffraction, and the influence of various microstructures on the elastic modulus and tensile strength was discussed. The results indicate that the Ti-27Nb-8Zr alloy after solution treatment consists of β+α” phases and has relatively lower elastic modulus and tensile strength, while for the alloy after aging treatment, it contains β, α and ω phases and exhibits significantly higher elastic modulus and tensile strength. With increasing of the aging temperature, the microstructure became coarser and the elastic modulus and tensile strength became lower. It is recommended that a Ti-27Nb-8Zr alloy with comparatively lower elastic modulus (85.5 GPa) and optimal comprehensive properties can be obtained by adopting following process: solution treatment at 800 oC for 1 h and then quenched, aged at 500 oC for 12 h then air-cooled
Microstructure evolutions of Ti-27Nb-8Zr (mass fraction, %) biomedical alloy subjected to different aging treatments after solution treatment were studied by optical microscopy, scanning electron microscopy and X-ray diffraction, and the influence of various microstructures on the elastic modulus and tensile strength was discussed. The results indicate that the Ti-27Nb-8Zr alloy after solution treatment consists of β+α” phases and has relatively lower elastic modulus and tensile strength, while for the alloy after aging treatment, it contains β, α and ω phases and exhibits significantly higher elastic modulus and tensile strength. With increasing of the aging temperature, the microstructure became coarser and the elastic modulus and tensile strength became lower. It is recommended that a Ti-27Nb-8Zr alloy with comparatively lower elastic modulus (85.5 GPa) and optimal comprehensive properties can be obtained by adopting following process: solution treatment at 800 oC for 1 h and then quenched, aged at 500 oC for 12 h then air-cooled
2010, 39(10):1711-1714.
Abstract:
Oil-soluble Cu nanoparticles were prepared by an oil-water interface growth method, using ascorbic acid as a reductant, polyethylene glycol (PEG-2000) as a modifier, and 1-butanol as growth agent. The particle size distribution of the obtained nanoparticles was between 18.2-80.2 nm, and the average size was 44.7 nm. The microstructures of these nanoparticles were characterized by XRD, TEM and high-concentration laser granularity scatter analyzer. The XRD patterns indicate that the lattice parameters of these Cu nanoparticles are enlarged by about 1.478%. The anti-wear and friction performance of SF15W/40 lubricating oil with these Cu nanoparticles were measured by ball-on-disk UMT-Ⅱ tribometer. It is found that the oil-soluble Cu nanoparticles have wetting effect and can be kept in dispersing form for long-term in SF15W/40 lubricating oil; the tribological performance of SF15W/40 lubricating oil with nano-Cu is improved. The best additive content of oil-soluble nano-Cu in SF15W/40 is 0.8% (mass fraction), and in such case the friction coefficient and wear loss are the lowest
Oil-soluble Cu nanoparticles were prepared by an oil-water interface growth method, using ascorbic acid as a reductant, polyethylene glycol (PEG-2000) as a modifier, and 1-butanol as growth agent. The particle size distribution of the obtained nanoparticles was between 18.2-80.2 nm, and the average size was 44.7 nm. The microstructures of these nanoparticles were characterized by XRD, TEM and high-concentration laser granularity scatter analyzer. The XRD patterns indicate that the lattice parameters of these Cu nanoparticles are enlarged by about 1.478%. The anti-wear and friction performance of SF15W/40 lubricating oil with these Cu nanoparticles were measured by ball-on-disk UMT-Ⅱ tribometer. It is found that the oil-soluble Cu nanoparticles have wetting effect and can be kept in dispersing form for long-term in SF15W/40 lubricating oil; the tribological performance of SF15W/40 lubricating oil with nano-Cu is improved. The best additive content of oil-soluble nano-Cu in SF15W/40 is 0.8% (mass fraction), and in such case the friction coefficient and wear loss are the lowest
6 Oxalate Coprecipitation Process Synthesis of 5 V Cathode Material LiNi0.5Mn1.5O4 and Its Performance
2010, 39(10):1715-1718.
Abstract:
5 V cathode material LiNi0.5Mn1.5O4 was synthesized via an oxalate co-precipitation process. The synthesized product was characterized by XRD, SEM, charge/discharge test and cyclic voltammetry. XRD and SEM results indicate that the synthesized product LiNi0.5Mn1.5O4 has cubic spinel structure with space group of Fdˉ3 m, high crystallinity, moderate and uniform particle size. The electrochemical experiment results show that the LiNi0.5Mn1.5O4 has excellent performances. It has only one discharge plateau at around 4.7 V. 0.1 C discharge capacity is up to 133 mAh/g and retains above 128 mAh/g after 50 cycles, 1 C and 3 C discharge capacities after 30 cycles also retain above 122 mAh/g and 101 mAh/g, respectively
5 V cathode material LiNi0.5Mn1.5O4 was synthesized via an oxalate co-precipitation process. The synthesized product was characterized by XRD, SEM, charge/discharge test and cyclic voltammetry. XRD and SEM results indicate that the synthesized product LiNi0.5Mn1.5O4 has cubic spinel structure with space group of Fdˉ3 m, high crystallinity, moderate and uniform particle size. The electrochemical experiment results show that the LiNi0.5Mn1.5O4 has excellent performances. It has only one discharge plateau at around 4.7 V. 0.1 C discharge capacity is up to 133 mAh/g and retains above 128 mAh/g after 50 cycles, 1 C and 3 C discharge capacities after 30 cycles also retain above 122 mAh/g and 101 mAh/g, respectively
2010, 39(10):1719-1722.
Abstract:
Based on the experimental dataset, the support vector regression (SVR) combined with particle swarm optimization (PSO) for parameter optimization, is proposed to establish a model for estimating the porosities of NiTi alloys synthesized by self-propagation high-temperature synthesis (SHS) approach under different process parameters, including temperature, particle size and green density. The prediction results indicate that the mean absolute percentage error (MAPE) achieved by SVR is smaller and more accurate than that of back-propagation neural network (BPNN) for identical training and test samples, reflecting the prediction ability of SVR is superior to that of BPNN; MAPE predicted by leave-one-out test of SVR (SVR-LOOCV) is also slightly better than that of BPNN, and the correlation coefficient (R2) reaches 0.999. Therefore it is demonstrated that SVR is a promising and practical technique to estimate the porosity of porous NiTi alloy synthesized under different SHS process parameters, and can provide a reasonable guidance for the SHS of porous NiTi theoretically
Based on the experimental dataset, the support vector regression (SVR) combined with particle swarm optimization (PSO) for parameter optimization, is proposed to establish a model for estimating the porosities of NiTi alloys synthesized by self-propagation high-temperature synthesis (SHS) approach under different process parameters, including temperature, particle size and green density. The prediction results indicate that the mean absolute percentage error (MAPE) achieved by SVR is smaller and more accurate than that of back-propagation neural network (BPNN) for identical training and test samples, reflecting the prediction ability of SVR is superior to that of BPNN; MAPE predicted by leave-one-out test of SVR (SVR-LOOCV) is also slightly better than that of BPNN, and the correlation coefficient (R2) reaches 0.999. Therefore it is demonstrated that SVR is a promising and practical technique to estimate the porosity of porous NiTi alloy synthesized under different SHS process parameters, and can provide a reasonable guidance for the SHS of porous NiTi theoretically
2010, 39(10):1723-1726.
Abstract:
The intrinsic mechanism of effects of Ti and F ions codoping on the dehydrogenating properties of the NaMgH3 hydrides was investigated by means of a plane-wave pseudopotential (PW-PP) method based on the density functional theory (DFT). The doped F ion replace some of hydrogen in the hydride to increase the hydrogen desorption properties of the system and subsequently Ti ions substitute for some of Na in Na4Mg4H11F. The electronic structure analysis shows that the strong interactions between H and metals (especially H-1s and Ti-3d) result in a split of the hydrogen energy level near the Fermi energy (EF) level. One part shifts to the left apart from the EF level while the other part shifts to the right over the EF level. The stability of hydrogen in the doped hydride is decreased compared with that in the NaMgH3 hydride without doping, thus improving the hydrogen desorption performance of the hydride
The intrinsic mechanism of effects of Ti and F ions codoping on the dehydrogenating properties of the NaMgH3 hydrides was investigated by means of a plane-wave pseudopotential (PW-PP) method based on the density functional theory (DFT). The doped F ion replace some of hydrogen in the hydride to increase the hydrogen desorption properties of the system and subsequently Ti ions substitute for some of Na in Na4Mg4H11F. The electronic structure analysis shows that the strong interactions between H and metals (especially H-1s and Ti-3d) result in a split of the hydrogen energy level near the Fermi energy (EF) level. One part shifts to the left apart from the EF level while the other part shifts to the right over the EF level. The stability of hydrogen in the doped hydride is decreased compared with that in the NaMgH3 hydride without doping, thus improving the hydrogen desorption performance of the hydride
2010, 39(10):1727-1731.
Abstract:
The high-temperature oxidation resistance behavior of Pt-Al coatings prepared by the electroplating of platinum with the following pack cementation of aluminum on nickel-based superalloys GH586 was studied by SEM, XRD and EDS. The results show that high temperature oxidation resistance of the Pt-Al coatings is excellent. The addition of platinum can prevent the diffusion of the alloy elements in the superalloys outwards to surface layer, and thus increase the high temperature oxidation resistance of coatings. The operation mechanisms of platinum on oxidation behavior were also discussed
The high-temperature oxidation resistance behavior of Pt-Al coatings prepared by the electroplating of platinum with the following pack cementation of aluminum on nickel-based superalloys GH586 was studied by SEM, XRD and EDS. The results show that high temperature oxidation resistance of the Pt-Al coatings is excellent. The addition of platinum can prevent the diffusion of the alloy elements in the superalloys outwards to surface layer, and thus increase the high temperature oxidation resistance of coatings. The operation mechanisms of platinum on oxidation behavior were also discussed
2010, 39(10):1732-1736.
Abstract:
Effects of silicon element on the load-displacement curves and the mechanical properties of Mg60Cu30Y10 amorphous alloys were investigated using nano indenter II. Results show that the load-displacement curves of Mg60Cu30-xY10Six amorphous alloys exhibit discontinuous serrations during nanoindentation, which corresponds to the formation and propagation of individual shear bands. And the loading curves become smoother and smoother until the serrations disappear with increasing of the silicon content. And the serrations of Mg60Cu30-xY10Six bulk amorphous alloys disappear gradually with the increasing of loading rates and strain rates. However, the mechanical properties of Mg60Cu30-xY10Six bulk amorphous alloys are not improved determinately with increasing of the component content and quantity
Effects of silicon element on the load-displacement curves and the mechanical properties of Mg60Cu30Y10 amorphous alloys were investigated using nano indenter II. Results show that the load-displacement curves of Mg60Cu30-xY10Six amorphous alloys exhibit discontinuous serrations during nanoindentation, which corresponds to the formation and propagation of individual shear bands. And the loading curves become smoother and smoother until the serrations disappear with increasing of the silicon content. And the serrations of Mg60Cu30-xY10Six bulk amorphous alloys disappear gradually with the increasing of loading rates and strain rates. However, the mechanical properties of Mg60Cu30-xY10Six bulk amorphous alloys are not improved determinately with increasing of the component content and quantity
11 Mechanism of Intermetallic Compound Growth in Eutectic SnBi Solder Matrix with High Current Density
2010, 39(10):1737-1740.
Abstract:
The morphology evolution of intermetallic compounds (IMC) in Cu/SnBi/Cu solder joint after current stressing at the current density of 8×103, 1×104 and 1.2×104 A/cm2 for 80 h was investigated. Results indicate that when the current density was 8×103 A/cm2, a lot of irregular-shaped IMCs were observed at the anode interface; however, there was no obvious IMC formation at the cathode interface. When the current density was 1×104 A/cm2, scallop-shaped IMC layer was formed at the cathode interface, and some of them had spalled from the interface; while at the anode interface, the lamellar IMC was formed, and it was thinner than that at the cathode interface. When the current density was 1.2×104 A/cm2, the thickness of the IMC layer at the anode interface increased. Nevertheless, the IMC at the cathode interface had diffused and migrated towards the solder matrix, which made the cathode interface uneven. It should be noted that, with the current density increasing, the thickness of Bi layer forming at the anode side increased greatly
The morphology evolution of intermetallic compounds (IMC) in Cu/SnBi/Cu solder joint after current stressing at the current density of 8×103, 1×104 and 1.2×104 A/cm2 for 80 h was investigated. Results indicate that when the current density was 8×103 A/cm2, a lot of irregular-shaped IMCs were observed at the anode interface; however, there was no obvious IMC formation at the cathode interface. When the current density was 1×104 A/cm2, scallop-shaped IMC layer was formed at the cathode interface, and some of them had spalled from the interface; while at the anode interface, the lamellar IMC was formed, and it was thinner than that at the cathode interface. When the current density was 1.2×104 A/cm2, the thickness of the IMC layer at the anode interface increased. Nevertheless, the IMC at the cathode interface had diffused and migrated towards the solder matrix, which made the cathode interface uneven. It should be noted that, with the current density increasing, the thickness of Bi layer forming at the anode side increased greatly
2010, 39(10):1741-1744.
Abstract:
The phase transition, Curie temperature and degree of order of the Fe60.5-xPt39.5Ndx (x≤1.5) alloys were investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and superconducting quantum interference device (SQUID). The addition of Nd favors the structural stability of FCC phase. Both the degree of order of the Fe60.5-xPt39.5Ndx (x≤1.5) alloys and Curie temperature of the order FCT phase decrease with increasing of the Nd content
The phase transition, Curie temperature and degree of order of the Fe60.5-xPt39.5Ndx (x≤1.5) alloys were investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and superconducting quantum interference device (SQUID). The addition of Nd favors the structural stability of FCC phase. Both the degree of order of the Fe60.5-xPt39.5Ndx (x≤1.5) alloys and Curie temperature of the order FCT phase decrease with increasing of the Nd content
2010, 39(10):1745-1748.
Abstract:
Severely deformational Ag/Ni20 fiber composite contacts were used as experimental samples and the scanning electron microscopy as the analytical manner. According to the deformation and distribution of fiber structure in contacts, the plastic problems of severely deformational metal fiber composite contacts during the preparation process were investigated by the creation of five area stress-strain models. The results indicate that both compressive deformation and tensile deformation exist during the preparation of contacts. Stress-strain is most intense in the third area which locates in the head and the corner of contact and the first area which locates in the surface of contact. Both areas suffer tensile deformation with average strain of 80%, and cracks would occur in these areas with the maximum probabilities. Contacts with high qualities could be produced if materials satisfy plastic tensile deformation in these two areas.
Severely deformational Ag/Ni20 fiber composite contacts were used as experimental samples and the scanning electron microscopy as the analytical manner. According to the deformation and distribution of fiber structure in contacts, the plastic problems of severely deformational metal fiber composite contacts during the preparation process were investigated by the creation of five area stress-strain models. The results indicate that both compressive deformation and tensile deformation exist during the preparation of contacts. Stress-strain is most intense in the third area which locates in the head and the corner of contact and the first area which locates in the surface of contact. Both areas suffer tensile deformation with average strain of 80%, and cracks would occur in these areas with the maximum probabilities. Contacts with high qualities could be produced if materials satisfy plastic tensile deformation in these two areas.
2010, 39(10):1749-1753.
Abstract:
The effects of Nd on the tensile properties of Mg-6Al as-cast alloy were studied. Results show that the yielding strengths of Mg-6Al-xNd (x=0, 2, 4, 6; mass fraction) alloys at room temperature and 175 oC increased with the Nd content increasing and reached the maximum value at the content of 6.0%Nd. The ultimate tensile strengths and elongations of these alloys at room temperature and 175 oC reached their maximum values at the content of 4.0%Nd. Both the ultimate strength and the elongation decreased slightly when the content of Nd increased from 4.0% to 6.0%, which is mainly due to the increase in the brittle phase of Al2Nd. The microstructure analysis indicates that Nd exists in the Mg-6Al alloy in the form of needle-like Al11Nd3 phase and polygonal Al2Nd phase and the amount of Al11Nd3 is much more than that of Al2Nd. The Al11Nd3 phase precipitates at the dendritic and grain boundaries resulting in the obvious refinement of the interdendritic space and grains. The improvement in tensile properties of Mg-6Al-xNd (x=2, 4, 6) alloys is mainly attributed to the grain refinement strengthening and the second phase strengthening caused by the Al11Nd3 phase, which is concluded from the mechanics analysis of the tensile process by hard-soft section model and the tensile fracture observation
The effects of Nd on the tensile properties of Mg-6Al as-cast alloy were studied. Results show that the yielding strengths of Mg-6Al-xNd (x=0, 2, 4, 6; mass fraction) alloys at room temperature and 175 oC increased with the Nd content increasing and reached the maximum value at the content of 6.0%Nd. The ultimate tensile strengths and elongations of these alloys at room temperature and 175 oC reached their maximum values at the content of 4.0%Nd. Both the ultimate strength and the elongation decreased slightly when the content of Nd increased from 4.0% to 6.0%, which is mainly due to the increase in the brittle phase of Al2Nd. The microstructure analysis indicates that Nd exists in the Mg-6Al alloy in the form of needle-like Al11Nd3 phase and polygonal Al2Nd phase and the amount of Al11Nd3 is much more than that of Al2Nd. The Al11Nd3 phase precipitates at the dendritic and grain boundaries resulting in the obvious refinement of the interdendritic space and grains. The improvement in tensile properties of Mg-6Al-xNd (x=2, 4, 6) alloys is mainly attributed to the grain refinement strengthening and the second phase strengthening caused by the Al11Nd3 phase, which is concluded from the mechanics analysis of the tensile process by hard-soft section model and the tensile fracture observation
2010, 39(10):1754-1758.
Abstract:
Ti6Al4V alloy was treated by ultrasound-aided deep rolling (UADR) for surface mechanical strengthening. The microstructure evolution of the UADR treated specimen was characterized by scanning electron microscopy (SEM), hardness test, X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that obvious grain refinement is found after UADR treatment and a nano-structured surface layer is formed with an average grain size less than 20 nm in the immediate surface. Grain boundaries at about 150 μm away from the surface become distinguishable. In this area, although grain boundary structure keeps unchanged, there is an increase of dislocation density in those grains. The effect of grain refinement on fatigue performance was also discussed
Ti6Al4V alloy was treated by ultrasound-aided deep rolling (UADR) for surface mechanical strengthening. The microstructure evolution of the UADR treated specimen was characterized by scanning electron microscopy (SEM), hardness test, X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that obvious grain refinement is found after UADR treatment and a nano-structured surface layer is formed with an average grain size less than 20 nm in the immediate surface. Grain boundaries at about 150 μm away from the surface become distinguishable. In this area, although grain boundary structure keeps unchanged, there is an increase of dislocation density in those grains. The effect of grain refinement on fatigue performance was also discussed
2010, 39(10):1759-1763.
Abstract:
Effects of trace Ni, P or Ce element additions on the microstructure and the properties of the Sn3.0Ag0.5Cu solder alloy were investigated. Results show that single adding of Ni, P or Ce has little influence on the melting temperature of the Sn3.0Ag0.5Cu solder alloy. P addition can improve the wettability of the solder, i.e. the wetting force of the solder is increased, and the wetting time is decreased. Single adding of Ni or Ce has no significant effect on the wettability of the soldered alloy and the shear strength of the as-reflowed soldered joint, but can remarkably suppress the decrease of the shear strength of the solder joints due to the high-temperature aging. Besides, P addition significantly increases the oxidation resistance of the soldered alloy, but rare earth Ce addition deteriorates it. The property change of the Sn3.0Ag0.5 solder are attributed to the change of the microstructure caused by trace Ni, P, or rare earth Ce additions
Effects of trace Ni, P or Ce element additions on the microstructure and the properties of the Sn3.0Ag0.5Cu solder alloy were investigated. Results show that single adding of Ni, P or Ce has little influence on the melting temperature of the Sn3.0Ag0.5Cu solder alloy. P addition can improve the wettability of the solder, i.e. the wetting force of the solder is increased, and the wetting time is decreased. Single adding of Ni or Ce has no significant effect on the wettability of the soldered alloy and the shear strength of the as-reflowed soldered joint, but can remarkably suppress the decrease of the shear strength of the solder joints due to the high-temperature aging. Besides, P addition significantly increases the oxidation resistance of the soldered alloy, but rare earth Ce addition deteriorates it. The property change of the Sn3.0Ag0.5 solder are attributed to the change of the microstructure caused by trace Ni, P, or rare earth Ce additions
2010, 39(10):1764-1768.
Abstract:
Ni50-xMn29+xGa21(x=0-4) polycrystalline alloys were prepared by the technique of directional solidification and the effect of the component on the martensitic transformation temperature and magnetic properties of the alloys was analyzed. The results show that the martensitic transformation temperatures (Ms) increase and the martensitic transformation hysteresis (ΔT) decrease with increasing of x when x≤3. When x=3, Ms is increased to 309.6 K and the Curie temperature Tc is 360 K. But with x increasing continuously to 4, Ms decreases to 283.2 K and Tc is 362 K. The Ni47Mn32Ga21 alloy exhibits a large saturated magnetic-induced strain of –700×10-6 without stress at room temperature, whose corresponding magnetization intensity is 4.5×105 A/m
Ni50-xMn29+xGa21(x=0-4) polycrystalline alloys were prepared by the technique of directional solidification and the effect of the component on the martensitic transformation temperature and magnetic properties of the alloys was analyzed. The results show that the martensitic transformation temperatures (Ms) increase and the martensitic transformation hysteresis (ΔT) decrease with increasing of x when x≤3. When x=3, Ms is increased to 309.6 K and the Curie temperature Tc is 360 K. But with x increasing continuously to 4, Ms decreases to 283.2 K and Tc is 362 K. The Ni47Mn32Ga21 alloy exhibits a large saturated magnetic-induced strain of –700×10-6 without stress at room temperature, whose corresponding magnetization intensity is 4.5×105 A/m
2010, 39(10):1769-1772.
Abstract:
Au nanoparticles prepared in ultrasonic field, were electrostatically assembled onto mica substrates treated with MnCl2 solution of certain concentration. Au nanoparticles were characterized by means of scan electron microscope (SEM), scan probe microscope (SPM) and X-ray diffraction (XRD). The results indicate that ultrasonic field distribution and power significantly influence the morphology of Au nanoparticles. Spindle Au nanoparticles were prepared in the standing wave field. The average aspect ratio decreases of the spindle Au nanoparticles with the ultrasonic power increasing. Monodispersed spherical Au nanoparticles were synthesized in the diffusion wave field. SEM and XRD results show that the average particle size is 25 nm. Au nanoparticals can self-assemble onto the mica surface with or without treatment, but they cover large areas on the treated mica
Au nanoparticles prepared in ultrasonic field, were electrostatically assembled onto mica substrates treated with MnCl2 solution of certain concentration. Au nanoparticles were characterized by means of scan electron microscope (SEM), scan probe microscope (SPM) and X-ray diffraction (XRD). The results indicate that ultrasonic field distribution and power significantly influence the morphology of Au nanoparticles. Spindle Au nanoparticles were prepared in the standing wave field. The average aspect ratio decreases of the spindle Au nanoparticles with the ultrasonic power increasing. Monodispersed spherical Au nanoparticles were synthesized in the diffusion wave field. SEM and XRD results show that the average particle size is 25 nm. Au nanoparticals can self-assemble onto the mica surface with or without treatment, but they cover large areas on the treated mica
19 Effects of Alloying Elements on Growth and Morphology of TiC in Arc-Melted TiC/Ti-6Al-4V Composites
2010, 39(10):1773-1776.
Abstract:
10vol%TiC/Ti-6Al-4V composites with various alloying elements were prepared by arc-melting. The effects of different trace alloying elements on the morphology of TiC in the composites were investigated. The results indicate that coarse and developed dendritic is the primary form of TiC in as-cast 10vol%TiC/Ti-6Al-4V composites. However, as 0.3% Sn (mass fraction, similarly hereinafter) is added in the composites, the growth of TiC is restrained and TiC become fine and dispersed particles. The addition of 0.3% Ni element increases the crystallization interval of TiC and promotes the growth of dendritic TiC. In contrast to Ni element, 0.3% Nb addition to the composites decreases the crystallization interval of TiC, so the amount of dendritic TiC is reduced and the formation of eutectic TiC is promoted
10vol%TiC/Ti-6Al-4V composites with various alloying elements were prepared by arc-melting. The effects of different trace alloying elements on the morphology of TiC in the composites were investigated. The results indicate that coarse and developed dendritic is the primary form of TiC in as-cast 10vol%TiC/Ti-6Al-4V composites. However, as 0.3% Sn (mass fraction, similarly hereinafter) is added in the composites, the growth of TiC is restrained and TiC become fine and dispersed particles. The addition of 0.3% Ni element increases the crystallization interval of TiC and promotes the growth of dendritic TiC. In contrast to Ni element, 0.3% Nb addition to the composites decreases the crystallization interval of TiC, so the amount of dendritic TiC is reduced and the formation of eutectic TiC is promoted
2010, 39(10):1777-1780.
Abstract:
AlN nanopowders were added into Nd28Dy2.4FebalB0.98Al0.1Ga0.1Nb0.1 sintered magnets as grain boundary modifiers with the aim of improving the corrosion resistance and magnetic properties of the magnets. It is found that the appropriate intergranular addition of AlN nanopowders can improve the corrosion resistance. Optimum corrosion resistance can be obtained when 0.1% (mass fraction) AlN is added. In addition, the intrinsic coercivity (Hcj) is improved greatly by the AlN addition. Microstructure observation indicates that as AlN nanopowders are added to the intergranular phase, the grains are refined effectively. As a result, both the intrinsic coercivity and corrosion resistance are increased simultaneously
AlN nanopowders were added into Nd28Dy2.4FebalB0.98Al0.1Ga0.1Nb0.1 sintered magnets as grain boundary modifiers with the aim of improving the corrosion resistance and magnetic properties of the magnets. It is found that the appropriate intergranular addition of AlN nanopowders can improve the corrosion resistance. Optimum corrosion resistance can be obtained when 0.1% (mass fraction) AlN is added. In addition, the intrinsic coercivity (Hcj) is improved greatly by the AlN addition. Microstructure observation indicates that as AlN nanopowders are added to the intergranular phase, the grains are refined effectively. As a result, both the intrinsic coercivity and corrosion resistance are increased simultaneously
2010, 39(10):1781-1784.
Abstract:
Top-seeded melt growth is an effective method to fabricate REBaCuO large single domain superconducting bulks. It is a key factor to choose a right seed for preparing single domain SmBaCuO bulks which has a higher melting point. Six kinds of polydomain Nd-Ba-Cu-Mg-O bulk samples doped with MgO powders of 0.2%, 0.5%, 1%, 2%, 5% and 10% (mass fraction) were prepared through spontaneous nucleation with NdBaCuO as the substrate, and then near single domain SmBaCuO bulks were successfully prepared using the NdBaCuO with 1% and 10% MgO as seeds. The effect of MgO doping content on the melting temperature of NdBaCuO precursor powders, the saturation doping content of MgO powders in NdBaCuO substrate and characteristics of Nd-Ba-Cu-Mg-O seeds were investigated by DTA, XRD and OM. Results show that MgO powder doped in NdBaCuO can significantly increase the melting temperature of NdBaCuO precursor powder. The saturation value of MgO powders doping in NdBCO is about 1%. MgO-doping between 1% and 10% does not change the basic crystal structure of Nd-123 phase
Top-seeded melt growth is an effective method to fabricate REBaCuO large single domain superconducting bulks. It is a key factor to choose a right seed for preparing single domain SmBaCuO bulks which has a higher melting point. Six kinds of polydomain Nd-Ba-Cu-Mg-O bulk samples doped with MgO powders of 0.2%, 0.5%, 1%, 2%, 5% and 10% (mass fraction) were prepared through spontaneous nucleation with NdBaCuO as the substrate, and then near single domain SmBaCuO bulks were successfully prepared using the NdBaCuO with 1% and 10% MgO as seeds. The effect of MgO doping content on the melting temperature of NdBaCuO precursor powders, the saturation doping content of MgO powders in NdBaCuO substrate and characteristics of Nd-Ba-Cu-Mg-O seeds were investigated by DTA, XRD and OM. Results show that MgO powder doped in NdBaCuO can significantly increase the melting temperature of NdBaCuO precursor powder. The saturation value of MgO powders doping in NdBCO is about 1%. MgO-doping between 1% and 10% does not change the basic crystal structure of Nd-123 phase
2010, 39(10):1785-1789.
Abstract:
The effect of the Ti content on polycrystalline microstructure, phase transformation behavior, mechanical behavior and magnetic properties of the Ni53Mn23.5Ga23.5-xTix (x = 0, 0.5, 2, 3.5, 8, 15, at%) ferromagnetic shape memory alloy was studied by means of OM, DSC, room temperature compression tests and ac susceptibility measurements. The results show that the solubility limit of Ti element in the alloys is below 15%. The transformation temperature, the fracture strength and the fracture strain increase at first and then decrease with increasing of the Ti content. Furthermore, it is concluded that Ti addition can change the fracture type of Ni53Mn23.5Ga23.5-xTix alloys from the intergranular fracture to the transgranular to the intergranular again. In addition, the Curie temperature decreases gradually with the increase of Ti content in Ni53Mn23.5Ga23.5-xTix alloys
The effect of the Ti content on polycrystalline microstructure, phase transformation behavior, mechanical behavior and magnetic properties of the Ni53Mn23.5Ga23.5-xTix (x = 0, 0.5, 2, 3.5, 8, 15, at%) ferromagnetic shape memory alloy was studied by means of OM, DSC, room temperature compression tests and ac susceptibility measurements. The results show that the solubility limit of Ti element in the alloys is below 15%. The transformation temperature, the fracture strength and the fracture strain increase at first and then decrease with increasing of the Ti content. Furthermore, it is concluded that Ti addition can change the fracture type of Ni53Mn23.5Ga23.5-xTix alloys from the intergranular fracture to the transgranular to the intergranular again. In addition, the Curie temperature decreases gradually with the increase of Ti content in Ni53Mn23.5Ga23.5-xTix alloys
2010, 39(10):1790-1794.
Abstract:
The samples of Pr1.85Ce0.15CuO4-x and Pr2CuO4-x were prepared by a solid reaction method. X-ray diffraction patterns reveal that single-phase Pr1.85Ce0.15CuO4-x and Pr2CuO4-x have been obtained with a small amount of impurity phases. For the samples of Pr1.85Ce0.15CuO4-x, superconductivity transitions are observed in the range of 0.05≤x≤0.20, and Tconset is 24.5 K. The samples of Pr2CuO4-x can not achieve superconductivity only by adjusting the oxygen content. By the comparison of different effects of the oxygen content on structure and magnetic properties, it is found that in Pr1.85Ce0.15CuO4-x samples the reason of superconductivity realization by adjusting oxygen content is free carrier introduction, while for Pr2CuO4-x the reason why the superconductivity does not realize is that oxygen vacancies do not appear in the same oxygen position. The relative mechanism was discussed
The samples of Pr1.85Ce0.15CuO4-x and Pr2CuO4-x were prepared by a solid reaction method. X-ray diffraction patterns reveal that single-phase Pr1.85Ce0.15CuO4-x and Pr2CuO4-x have been obtained with a small amount of impurity phases. For the samples of Pr1.85Ce0.15CuO4-x, superconductivity transitions are observed in the range of 0.05≤x≤0.20, and Tconset is 24.5 K. The samples of Pr2CuO4-x can not achieve superconductivity only by adjusting the oxygen content. By the comparison of different effects of the oxygen content on structure and magnetic properties, it is found that in Pr1.85Ce0.15CuO4-x samples the reason of superconductivity realization by adjusting oxygen content is free carrier introduction, while for Pr2CuO4-x the reason why the superconductivity does not realize is that oxygen vacancies do not appear in the same oxygen position. The relative mechanism was discussed
2010, 39(10):1795-1801.
Abstract:
The influencing rule of alloy elements (Mo, Zr, Nb), processing and heat treatment on the microstructure and mechanical properties of a near β type biomedical titanium alloy TiZrMoNb (TLE) were investigated systematically; the influential factors on biomechanical compatibility matching of the TLE alloy and how to keep it were discussed. The results show that increasing the contents of Zr and Mo can strengthen the alloy, whereas increasing the contents of Mo and Nb and larger hot working rate are helpful to decrease the elastic modulus. The hot-rolled alloy after solid solution treatment possesses lower strength and elastic modulus; while for the above-mentioned alloy with another aging treatment, the strength and elastic modulus are increased, due to dispersive strengthening and fine grain strengthening. The prepared alloy possesses better cold and hot wrought properties without obvious anisotropy, and higher strength, lower elastic modulus and good comprehensive matching of ductility and toughness and fatigue resistance can be obtained after adequate heat treatment
The influencing rule of alloy elements (Mo, Zr, Nb), processing and heat treatment on the microstructure and mechanical properties of a near β type biomedical titanium alloy TiZrMoNb (TLE) were investigated systematically; the influential factors on biomechanical compatibility matching of the TLE alloy and how to keep it were discussed. The results show that increasing the contents of Zr and Mo can strengthen the alloy, whereas increasing the contents of Mo and Nb and larger hot working rate are helpful to decrease the elastic modulus. The hot-rolled alloy after solid solution treatment possesses lower strength and elastic modulus; while for the above-mentioned alloy with another aging treatment, the strength and elastic modulus are increased, due to dispersive strengthening and fine grain strengthening. The prepared alloy possesses better cold and hot wrought properties without obvious anisotropy, and higher strength, lower elastic modulus and good comprehensive matching of ductility and toughness and fatigue resistance can be obtained after adequate heat treatment
2010, 39(10):1802-1806.
Abstract:
In order to discuss the influence of grain refinement on the oxidation behavior of binary two-phase alloys, Cr-25Nb alloys with different grain sizes were prepared by arc-casting and mechanical alloying, and their oxidation behaviors at 950 and 1200 oC in air were investigated. The results show that in both alloys a single and continuous Cr2O3 film did not form, but a complex oxidation films occurred which contained an outer layer of Cr2O3 plus an inner layer of NbCrO4. The oxidation resistance of mechanically alloyed Cr-25Nb was higher than that of the cast alloy. In particular, the mass gain of the cast alloy is twice as much as that of mechanically alloyed alloy when they were oxidized at 1200 oC for 100 h. The differences observed above are attributed to that fine grains can accelerate the relaxation of the oxide scale stress and increase the adhesion of the oxide layer on the matrix
In order to discuss the influence of grain refinement on the oxidation behavior of binary two-phase alloys, Cr-25Nb alloys with different grain sizes were prepared by arc-casting and mechanical alloying, and their oxidation behaviors at 950 and 1200 oC in air were investigated. The results show that in both alloys a single and continuous Cr2O3 film did not form, but a complex oxidation films occurred which contained an outer layer of Cr2O3 plus an inner layer of NbCrO4. The oxidation resistance of mechanically alloyed Cr-25Nb was higher than that of the cast alloy. In particular, the mass gain of the cast alloy is twice as much as that of mechanically alloyed alloy when they were oxidized at 1200 oC for 100 h. The differences observed above are attributed to that fine grains can accelerate the relaxation of the oxide scale stress and increase the adhesion of the oxide layer on the matrix
2010, 39(10):1807-1810.
Abstract:
The effects of the spark plasma sintering temperature on microstructure and dynamic mechanical properties of the tungsten heavy alloy with nano-crystalline 93W-4.9Ni-2.1Fe alloy powder as raw material were investigated. Results show that ultra-fine tungsten alloy with uniform microstructure can be prepared by the spark plasma sintering technology. In the sintering temperature range between 950 oC and 1400 oC, the average particle size of the tungsten heavy alloy increases from 2 μm to 10 μm with the sintering temperature elevation while the dynamic compressive strength decreases accordingly. During the process of dynamic compression the plasticity of samples sintered at the temperature between 1000 oC and 1200 oC is good. However, dynamic plasticity of samples sintered at the temperature between 1300 oC and 1400 oC is almost zero, showing typical brittle failure
The effects of the spark plasma sintering temperature on microstructure and dynamic mechanical properties of the tungsten heavy alloy with nano-crystalline 93W-4.9Ni-2.1Fe alloy powder as raw material were investigated. Results show that ultra-fine tungsten alloy with uniform microstructure can be prepared by the spark plasma sintering technology. In the sintering temperature range between 950 oC and 1400 oC, the average particle size of the tungsten heavy alloy increases from 2 μm to 10 μm with the sintering temperature elevation while the dynamic compressive strength decreases accordingly. During the process of dynamic compression the plasticity of samples sintered at the temperature between 1000 oC and 1200 oC is good. However, dynamic plasticity of samples sintered at the temperature between 1300 oC and 1400 oC is almost zero, showing typical brittle failure
2010, 39(10):1811-1814.
Abstract:
With TLM titanium alloy as the anodization substrate, the preparation parameters for TiO2 nanoporous films were determined by changing anodization potential and phase structure of titanium alloys. Through the condition experiment, it is found that the TiO2 nanoporous film with alloy element doping can be prepared on the surface of the TLM alloy with aging treatment
With TLM titanium alloy as the anodization substrate, the preparation parameters for TiO2 nanoporous films were determined by changing anodization potential and phase structure of titanium alloys. Through the condition experiment, it is found that the TiO2 nanoporous film with alloy element doping can be prepared on the surface of the TLM alloy with aging treatment
2010, 39(10):1815-1819.
Abstract:
A cold spinning-annealing technique was used to refine grains of U-6.5Nb alloy. The effects of reduction ratio, annealing temperature and holding time on the recrystallized microstructures were studied. The results show that grains become coarse when the annealing temperature was increased from 700 oC to 800 oC, and then to 900 oC, while the reduction ratio has no obvious effects on the recrystallized microstructure. The grain growth indexes at 700 oC, 800 oC and 900 oC are 0.47, 0.31 and 0.34, respectively, and the activation energy for grain growth is 100.4 kJ/mol, indicating that the grain growth of U-6.5Nb alloy is a Nb diffusion-controlled process
A cold spinning-annealing technique was used to refine grains of U-6.5Nb alloy. The effects of reduction ratio, annealing temperature and holding time on the recrystallized microstructures were studied. The results show that grains become coarse when the annealing temperature was increased from 700 oC to 800 oC, and then to 900 oC, while the reduction ratio has no obvious effects on the recrystallized microstructure. The grain growth indexes at 700 oC, 800 oC and 900 oC are 0.47, 0.31 and 0.34, respectively, and the activation energy for grain growth is 100.4 kJ/mol, indicating that the grain growth of U-6.5Nb alloy is a Nb diffusion-controlled process
2010, 39(10):1820-1824.
Abstract:
Sb2Se3 nanowires were synthesized by a hydrothermal method at 150 oC for 24 h using SbCl3 and different Se sources of SeO2 or Se powder as starting materials and N2H4·H2O as reductant. X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM) and high-resolution TEM (HRTEM) were applied to characterize the phase distributions, microstructures and grain sizes of the nanostructured product. Results show that the orthorhombic Sb2Se3 nanocrystals are formed during the hydrothermal synthesis process, with the microstructure of one-dimensional nanowires. The morphologies of the synthesized Sb2Se3 nanowires with SeO2 or Se powder as the precursors are similar; however, the growth processes are different due to the different reaction route. The Sb2Se3 nanowires using SeO2 as the precursors are narrower and thinner but more uniform than the products using Se powder as the precursor. The growth of the Sb2Se3 nanowires along the [001] direction is mainly related to the special crystal structure of Sb2Se3
Sb2Se3 nanowires were synthesized by a hydrothermal method at 150 oC for 24 h using SbCl3 and different Se sources of SeO2 or Se powder as starting materials and N2H4·H2O as reductant. X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM) and high-resolution TEM (HRTEM) were applied to characterize the phase distributions, microstructures and grain sizes of the nanostructured product. Results show that the orthorhombic Sb2Se3 nanocrystals are formed during the hydrothermal synthesis process, with the microstructure of one-dimensional nanowires. The morphologies of the synthesized Sb2Se3 nanowires with SeO2 or Se powder as the precursors are similar; however, the growth processes are different due to the different reaction route. The Sb2Se3 nanowires using SeO2 as the precursors are narrower and thinner but more uniform than the products using Se powder as the precursor. The growth of the Sb2Se3 nanowires along the [001] direction is mainly related to the special crystal structure of Sb2Se3
2010, 39(10):1825-1828.
Abstract:
Novel red phosphors SrMgSi2O6:Eu3+ were synthesized by a gel-combustion method, with Na2CO3 as the charge compensation agent. The as-synthesized phosphors were analyzed and characterized by XRD and fluorescence spectrophotometer. The results show that the SrMgSi2O6:Eu3+ phosphor possesses a tetragonal crystal structure which is similar to that of Sr2MgSi2O7. The excitation spectrum of the SrMgSi2O6:Eu3+ sample presents wide band absorption between 220 and 300 nm, which is ascribed to the charge transfer between Eu3+ and O2-. The sharp peaks appearing after 300 nm belong to f-f transition of Eu3+, and the strongest sharp peak is located at 400 nm. Therefore, samples can be efficiently excited by ultraviolet radiation from InGaN chip. The emission spectrum consists of two strong emission peaks at 592 nm and 618 nm, which are ascribed to 5D0→7F1 and 5D0→7F2 respectively. Moreover, it is found that co-doped Gd3+ or Ti4+ can sensitize the luminescence of Eu3+ in SrMgSi2O6:Eu3+, in other words, co-doped Gd3+ or Ti4+ can improve red light emission of samples efficiently. So SrMgSi2O6:Eu3+, M(M=Gd3+, Ti4+) shows good prospect for red phosphors of white LED
Novel red phosphors SrMgSi2O6:Eu3+ were synthesized by a gel-combustion method, with Na2CO3 as the charge compensation agent. The as-synthesized phosphors were analyzed and characterized by XRD and fluorescence spectrophotometer. The results show that the SrMgSi2O6:Eu3+ phosphor possesses a tetragonal crystal structure which is similar to that of Sr2MgSi2O7. The excitation spectrum of the SrMgSi2O6:Eu3+ sample presents wide band absorption between 220 and 300 nm, which is ascribed to the charge transfer between Eu3+ and O2-. The sharp peaks appearing after 300 nm belong to f-f transition of Eu3+, and the strongest sharp peak is located at 400 nm. Therefore, samples can be efficiently excited by ultraviolet radiation from InGaN chip. The emission spectrum consists of two strong emission peaks at 592 nm and 618 nm, which are ascribed to 5D0→7F1 and 5D0→7F2 respectively. Moreover, it is found that co-doped Gd3+ or Ti4+ can sensitize the luminescence of Eu3+ in SrMgSi2O6:Eu3+, in other words, co-doped Gd3+ or Ti4+ can improve red light emission of samples efficiently. So SrMgSi2O6:Eu3+, M(M=Gd3+, Ti4+) shows good prospect for red phosphors of white LED
2010, 39(10):1829-1834.
Abstract:
An extensive accurate finite element (FE) analysis of the impression creep test was performed for two material systems, i.e. a single phase half infinite system and a coating/substrate system. For each case, the FE analysis was carried out for different classes of punch sizes aimed to develop methods to separate creep properties of a coating from a coating/substrate system. The study emphasis was placed on understanding how the punch size influenced the impression creep exponent of a certain coating/substrate system. A weight expression was proposed to quantify the coating’s and the substrate’s contributions to the impression creep exponent of the coating/substrate system. The results of finite element analysis show that the value of the weight expression exhibits a good power-law dependence on the radius of the punch for a certain coating/substrate system. The weight function proposed allows developing an analytic approach to separate coating’s creep exponent from a coating/substrate system. Then a numerical approach including procedures of fitting the curve of n vs R/Tc and extrapolating to R=0 was put forward to determine the coating’s creep exponent. Both of the results obtained by the two methods agree reasonably well with the input FE model
An extensive accurate finite element (FE) analysis of the impression creep test was performed for two material systems, i.e. a single phase half infinite system and a coating/substrate system. For each case, the FE analysis was carried out for different classes of punch sizes aimed to develop methods to separate creep properties of a coating from a coating/substrate system. The study emphasis was placed on understanding how the punch size influenced the impression creep exponent of a certain coating/substrate system. A weight expression was proposed to quantify the coating’s and the substrate’s contributions to the impression creep exponent of the coating/substrate system. The results of finite element analysis show that the value of the weight expression exhibits a good power-law dependence on the radius of the punch for a certain coating/substrate system. The weight function proposed allows developing an analytic approach to separate coating’s creep exponent from a coating/substrate system. Then a numerical approach including procedures of fitting the curve of n vs R/Tc and extrapolating to R=0 was put forward to determine the coating’s creep exponent. Both of the results obtained by the two methods agree reasonably well with the input FE model
32 Preparation of HA/Ag Composite Coatings by Pulse Electrochemical Deposition on Titanium Substrate
2010, 39(10):1835-1839.
Abstract:
Uniform and dense nano-spherical HA/Ag composite coatings were prepared by a pulse electrochemical deposition method on biomedical titanium surfaces. The coatings were characterized by XRD and SEM. Escherichia coli and Staphylococcus albus were utilized to test the antibacterial ability of the coatings. The cytocompatibility of composite coatings was evaluated by culturing osteoblast MC3T3-E1 on the coatings. The results demonstrate that Ag uniformly distribute in the composite coatings without agglomeration. The coatings have good antibacterial effects on the two types of bacteria. However, they have a better antibacterial effect on Escherichia coli of 100% than on Staphylococcus albus of near 100%. The MC3T3-E1 cell culturing results indicate that the MC3T3-E1 osteoblast has good adhesion and spreading on HA/Ag composite coatings. It is concluded that HA/Ag composite coatings prepared by pulse electrochemical deposition have good antibacterial property and cytocompatibility
Uniform and dense nano-spherical HA/Ag composite coatings were prepared by a pulse electrochemical deposition method on biomedical titanium surfaces. The coatings were characterized by XRD and SEM. Escherichia coli and Staphylococcus albus were utilized to test the antibacterial ability of the coatings. The cytocompatibility of composite coatings was evaluated by culturing osteoblast MC3T3-E1 on the coatings. The results demonstrate that Ag uniformly distribute in the composite coatings without agglomeration. The coatings have good antibacterial effects on the two types of bacteria. However, they have a better antibacterial effect on Escherichia coli of 100% than on Staphylococcus albus of near 100%. The MC3T3-E1 cell culturing results indicate that the MC3T3-E1 osteoblast has good adhesion and spreading on HA/Ag composite coatings. It is concluded that HA/Ag composite coatings prepared by pulse electrochemical deposition have good antibacterial property and cytocompatibility
2010, 39(10):1840-1844.
Abstract:
Cr-W pre-alloyed powders with the atomic ratio of 4:1 were prepared by mechanical milling using chromium and tungsten powder as raw material. The prepared powders were analyzed by XRD, SEM and TEM. The influence of ball milling time on morphology, microstructure and grain size of Cr-W pre-alloyed powders as well as compactness and solid solubility of the sintered Cr-W alloy were discussed. The results show that nanoscale Cr-W pre-alloyed powder can be prepared by mechanical alloying. At the initial stage of ball milling, the change of grain size and microstrain is very distinct; but it becomes a steady sate after milling for 48 h and at the same time the Cr-W pre-alloyed powders with nanocrystalline size of about 30 nm are obtained. After ball milling for 72 h, there is solid solution formed in the chromium and tungsten pre-alloyed powders. Lattice constants change during the milling process. For longer milling time of the powders, the more uniform distribution of each phase and the higher solubility are obtained after sintering
Cr-W pre-alloyed powders with the atomic ratio of 4:1 were prepared by mechanical milling using chromium and tungsten powder as raw material. The prepared powders were analyzed by XRD, SEM and TEM. The influence of ball milling time on morphology, microstructure and grain size of Cr-W pre-alloyed powders as well as compactness and solid solubility of the sintered Cr-W alloy were discussed. The results show that nanoscale Cr-W pre-alloyed powder can be prepared by mechanical alloying. At the initial stage of ball milling, the change of grain size and microstrain is very distinct; but it becomes a steady sate after milling for 48 h and at the same time the Cr-W pre-alloyed powders with nanocrystalline size of about 30 nm are obtained. After ball milling for 72 h, there is solid solution formed in the chromium and tungsten pre-alloyed powders. Lattice constants change during the milling process. For longer milling time of the powders, the more uniform distribution of each phase and the higher solubility are obtained after sintering
2010, 39(10):1845-1848.
Abstract:
Nanocrystalline Ni with a mean grain size of 27.2 nm and a broad grain size distribution ranging from 10 nm to 120 nm (B-NC-Ni) was prepared by direct current electrodeposition. In tensile experiments of B-NC-Ni, there are two types of engineering stress-strain curves and macroscopic fracture. Results reveal that a complete tensile curve, i.e. an intrinsic curve, possesses a constant stress deformation stage, and macrofracture is shear; a incomplete tensile curve shows premature plastic instability before the appearance of the flat plastic region, mainly because in the process of nickel deposition, flaws including vacancies and porosity may form in the deposit due to the cathode hydrogen evolution, resulting in more serious crack formation at the grain boundary during deformation, and the fracture is vertical shear. In addition, the effect of S impurities (0.015 wt%) on tensile properties can be neglected in the present work
Nanocrystalline Ni with a mean grain size of 27.2 nm and a broad grain size distribution ranging from 10 nm to 120 nm (B-NC-Ni) was prepared by direct current electrodeposition. In tensile experiments of B-NC-Ni, there are two types of engineering stress-strain curves and macroscopic fracture. Results reveal that a complete tensile curve, i.e. an intrinsic curve, possesses a constant stress deformation stage, and macrofracture is shear; a incomplete tensile curve shows premature plastic instability before the appearance of the flat plastic region, mainly because in the process of nickel deposition, flaws including vacancies and porosity may form in the deposit due to the cathode hydrogen evolution, resulting in more serious crack formation at the grain boundary during deformation, and the fracture is vertical shear. In addition, the effect of S impurities (0.015 wt%) on tensile properties can be neglected in the present work
2010, 39(10):1849-1852.
Abstract:
The microstructure evolution and tensile properties of the isothermally forged TG6 alloy were studied with different heating time and different deformation degrees of each forging by means of different isothermal forging times and the same total deformation degree. The results indicate that with increasing of isothermal forging times, the content of primary α phases increases, the length of lamellar secondary α phases and the size of sub-β grains decrease at first and then increase, and the thickness of lamellar secondary α phases increases progressively. At room temperature and high temperature the tensile strength of the forging decreases firstly and then increases while the ductility changes on the contrary. For the one-time forging formation with high deformation degree, there are fewer primary α phases in the microstructure caused by temperature rise in the forging; meanwhile more secondary α phases which are long and thin increase the tensile strength of the forging. For the three-time forging formation, more α phases which are fine and equiaxed occur at the sub-β grain boundaries because of different recrystallization degree of every phase in the alloy, leading to the increased ductility of the forging. For five-time forging, the prolonged heating time of the forging results in the aggregation and growth of α phases in the microstructure. When the TG6 alloy is isothermally forged with multi-times formation, there is a critical range for each-forging deformation degree; in the range, partial recrystallization takes place for the forged alloy during air cooling to form fine equiaxed α phases, which restrict the transfer of sub-β grain boundaries, resulting in the small sub-β grain sizes and uneven equiaxed α phase sizes in the microstructure
The microstructure evolution and tensile properties of the isothermally forged TG6 alloy were studied with different heating time and different deformation degrees of each forging by means of different isothermal forging times and the same total deformation degree. The results indicate that with increasing of isothermal forging times, the content of primary α phases increases, the length of lamellar secondary α phases and the size of sub-β grains decrease at first and then increase, and the thickness of lamellar secondary α phases increases progressively. At room temperature and high temperature the tensile strength of the forging decreases firstly and then increases while the ductility changes on the contrary. For the one-time forging formation with high deformation degree, there are fewer primary α phases in the microstructure caused by temperature rise in the forging; meanwhile more secondary α phases which are long and thin increase the tensile strength of the forging. For the three-time forging formation, more α phases which are fine and equiaxed occur at the sub-β grain boundaries because of different recrystallization degree of every phase in the alloy, leading to the increased ductility of the forging. For five-time forging, the prolonged heating time of the forging results in the aggregation and growth of α phases in the microstructure. When the TG6 alloy is isothermally forged with multi-times formation, there is a critical range for each-forging deformation degree; in the range, partial recrystallization takes place for the forged alloy during air cooling to form fine equiaxed α phases, which restrict the transfer of sub-β grain boundaries, resulting in the small sub-β grain sizes and uneven equiaxed α phase sizes in the microstructure
2010, 39(10):1853-1857.
Abstract:
By means of the chronoamperometry method and SEM observation, the effects of sintering conditions on the properties of the Pt/YSZ electrodes were studied. The results indicate that with the sintering time increasing at 850 oC, the pore number of the electrode decreases, and the pore size increases; the steady current density of the electrodes after the anodic step potential polarization increases at first and then decreases. The electrode sintered for 10 h has the highest steady current density and the best activity. The effects of the sintering temperature on the electrode properties are similar to that of the sintering time. When the sintering time is kept at 1 h, increasing of the sintering temperature can cause the decrease of the pore number, increase of the pore size and first increase with following decrease of the steady current density of the electrodes after the anodic step potential polarization. The electrode sintered at 1100 oC possesses the largest steady current density and optimal properties
By means of the chronoamperometry method and SEM observation, the effects of sintering conditions on the properties of the Pt/YSZ electrodes were studied. The results indicate that with the sintering time increasing at 850 oC, the pore number of the electrode decreases, and the pore size increases; the steady current density of the electrodes after the anodic step potential polarization increases at first and then decreases. The electrode sintered for 10 h has the highest steady current density and the best activity. The effects of the sintering temperature on the electrode properties are similar to that of the sintering time. When the sintering time is kept at 1 h, increasing of the sintering temperature can cause the decrease of the pore number, increase of the pore size and first increase with following decrease of the steady current density of the electrodes after the anodic step potential polarization. The electrode sintered at 1100 oC possesses the largest steady current density and optimal properties
2010, 39(10):1858-1862.
Abstract:
Preparation of porous Ni bulk catalyst by spark plasma sintering (SPS) with spherical atomized Ni powder as the starting material was studied. The microstructure and phases of the prepared porous Ni bulks were characterized by SEM, the nitrogen adsorption test and XRD. In addition, the catalysis properties of the porous Ni bulk in the Partial Oxidation of Methane (POM) process with high flow rates were investigated. The results show that the clean porous Ni bulk catalyst with porosity larger than 70% can be prepared by the SPS process. The catalyst prepared at 850 oC and held for 120 s can be applied in the POM process with a flow rate up to 2.70 L/min. The conversion ratio of CH4 in the catalyzed POM process with the catalyst is higher than 80%.
Preparation of porous Ni bulk catalyst by spark plasma sintering (SPS) with spherical atomized Ni powder as the starting material was studied. The microstructure and phases of the prepared porous Ni bulks were characterized by SEM, the nitrogen adsorption test and XRD. In addition, the catalysis properties of the porous Ni bulk in the Partial Oxidation of Methane (POM) process with high flow rates were investigated. The results show that the clean porous Ni bulk catalyst with porosity larger than 70% can be prepared by the SPS process. The catalyst prepared at 850 oC and held for 120 s can be applied in the POM process with a flow rate up to 2.70 L/min. The conversion ratio of CH4 in the catalyzed POM process with the catalyst is higher than 80%.
2010, 39(10):1863-1867.
Abstract:
Recent progress in the research on bimetallic nanomaterial synthesis, such as polyol method, hydrothermal method, colloidal seed method, sol-gel method, replacement method, coprecipitation method, electrochemistry method, sonochemistry method, successive reduction method, micelle/reverse micelle method, microemulsion method and so on, were reviewed. The basic principle and characteristics of these methods were evaluated briefly
Recent progress in the research on bimetallic nanomaterial synthesis, such as polyol method, hydrothermal method, colloidal seed method, sol-gel method, replacement method, coprecipitation method, electrochemistry method, sonochemistry method, successive reduction method, micelle/reverse micelle method, microemulsion method and so on, were reviewed. The basic principle and characteristics of these methods were evaluated briefly
2010, 39(10):1868-1874.
Abstract:
The effects of the exchange-coupling between nano-grains on effective anisotropy and coercivity of Nd-Fe-B based nanocomposite permanent magnets were discussed, and the coercivity mechanism of the magnets was also analyzed. The exchange-coupling between hard grains promotes the movement of domain walls and the reversal of magnetic moment at the applied field, which decreases the coercivity of nanocomposite magnets. Therefore, nonmagnetic grain boundary phases with suitable thickness can weaken the exchange-coupling between nano-grains of hard magnetic phase to improve the coercivity of nanocomposite permanent magnets. Besides the nucleation field and self-pining, the pining effect of nonmagnetic precipitates distributed in grains may impede the movement of the domain walls to further increase the coercivity of nanocomposite magnets.
The effects of the exchange-coupling between nano-grains on effective anisotropy and coercivity of Nd-Fe-B based nanocomposite permanent magnets were discussed, and the coercivity mechanism of the magnets was also analyzed. The exchange-coupling between hard grains promotes the movement of domain walls and the reversal of magnetic moment at the applied field, which decreases the coercivity of nanocomposite magnets. Therefore, nonmagnetic grain boundary phases with suitable thickness can weaken the exchange-coupling between nano-grains of hard magnetic phase to improve the coercivity of nanocomposite permanent magnets. Besides the nucleation field and self-pining, the pining effect of nonmagnetic precipitates distributed in grains may impede the movement of the domain walls to further increase the coercivity of nanocomposite magnets.
2010, 39(10):1875-1880.
Abstract:
The status quo of the research on minor boron addition in γ-TiAl based alloy was summarized. The grain refinement mechanisms of boron addition in γ-TiAl based alloy were stated emphatically; moreover, the factors affecting the boride morphology and their effects on the microstructures and properties of γ-TiAl based alloy were analyzed. Some suggestions for the research on boron addition in γ-TiAl based alloys were proposed
The status quo of the research on minor boron addition in γ-TiAl based alloy was summarized. The grain refinement mechanisms of boron addition in γ-TiAl based alloy were stated emphatically; moreover, the factors affecting the boride morphology and their effects on the microstructures and properties of γ-TiAl based alloy were analyzed. Some suggestions for the research on boron addition in γ-TiAl based alloys were proposed
