Volume 44,Issue 7,2015 Table of Contents
2015, 44(7):1568-1574.
Abstract:
The crystal structures, electronic structures and optical properties of pure and nonmetal (B, C, N, F, P, S and Cl) doping anatase TiO2 were calculated by the first-principles based on the density functional theory with the plane-wave ultrasoft pesudopotentials method. The calculated results show that the octahedral dipole moments of TiO2 are increased by nonmetal doping owing to the changes of lattice parameters, bond length and charges on atoms, which is very effective for the separation of photoexcited electron-hole pairs. Because the impurity energy levels are formed by hybridizing with dopants’ p states, O 2p states and Ti 3d states, most dopants could narrow the band gap, resulting in its fundamental absorption edge red-shift to visible-light region. According to the calculated results, the effects of nonmetal doping on electronic structure and optical properties of anatase TiO2 were analyzed and compared, and the roles of nonmetal atoms in TiO2 photocatalyst under visible-light irradiation were clarified. The calculated results could explain the reasons that some nonmetal-doped TiO2 have higher photocatalytic activity under visible-light irradiation.
The crystal structures, electronic structures and optical properties of pure and nonmetal (B, C, N, F, P, S and Cl) doping anatase TiO2 were calculated by the first-principles based on the density functional theory with the plane-wave ultrasoft pesudopotentials method. The calculated results show that the octahedral dipole moments of TiO2 are increased by nonmetal doping owing to the changes of lattice parameters, bond length and charges on atoms, which is very effective for the separation of photoexcited electron-hole pairs. Because the impurity energy levels are formed by hybridizing with dopants’ p states, O 2p states and Ti 3d states, most dopants could narrow the band gap, resulting in its fundamental absorption edge red-shift to visible-light region. According to the calculated results, the effects of nonmetal doping on electronic structure and optical properties of anatase TiO2 were analyzed and compared, and the roles of nonmetal atoms in TiO2 photocatalyst under visible-light irradiation were clarified. The calculated results could explain the reasons that some nonmetal-doped TiO2 have higher photocatalytic activity under visible-light irradiation.
2015, 44(7):1581-1586.
Abstract:
Ti-Zr-Ni-based icosahedral quasicrystals (IQCs) are a type of hydrogen storage materials with promising application in the fields of hydrogen energy and nuclear fusion energy. In the present paper, the preparation of Ti39Zr38Ni17Pd6 IQC and its deuterium storage properties were investigated by XRD, TEM, XPS analysis and a gas-solid reaction system. Results show that the saturation concentration of absorbing deuterium for the alloy at room temperature reaches near 11 mmol·D2/g·M (D2 means deuterium molecular and M the metal), exceeding those of Zr2Fe and ZrCo alloys. After a few absorption/desorption cycles, no phase transformation is observed, but the quasilattice displays a remarkable expansion of 6.37% after full D intake. The binding energy rise of 0.2 eV for Ti and 0.6 eV for Zr, caused by the introduction of saturated deuterium atoms, provides the evidence of the preferential location of deuterium near Zr and Ti in quasicrystals of this kind. The possible existence of a lower D desorption equilibrium pressure with <1 kPa at about 350 °C reflects higher thermodynamic stability of deuterium in the IQC than in ZrCo alloy. The advantages in hydrogen volume, thermal and structural stabilities suggest that the quasicrystals of this type could be a candidate to replace Zr2Fe and ZrCo in nuclear fusion field.
Ti-Zr-Ni-based icosahedral quasicrystals (IQCs) are a type of hydrogen storage materials with promising application in the fields of hydrogen energy and nuclear fusion energy. In the present paper, the preparation of Ti39Zr38Ni17Pd6 IQC and its deuterium storage properties were investigated by XRD, TEM, XPS analysis and a gas-solid reaction system. Results show that the saturation concentration of absorbing deuterium for the alloy at room temperature reaches near 11 mmol·D2/g·M (D2 means deuterium molecular and M the metal), exceeding those of Zr2Fe and ZrCo alloys. After a few absorption/desorption cycles, no phase transformation is observed, but the quasilattice displays a remarkable expansion of 6.37% after full D intake. The binding energy rise of 0.2 eV for Ti and 0.6 eV for Zr, caused by the introduction of saturated deuterium atoms, provides the evidence of the preferential location of deuterium near Zr and Ti in quasicrystals of this kind. The possible existence of a lower D desorption equilibrium pressure with <1 kPa at about 350 °C reflects higher thermodynamic stability of deuterium in the IQC than in ZrCo alloy. The advantages in hydrogen volume, thermal and structural stabilities suggest that the quasicrystals of this type could be a candidate to replace Zr2Fe and ZrCo in nuclear fusion field.
3 Mechanical Properties of WC-8Co Wear- Resistant Coating on Pump Impellers Surface by Electro- Spark
2015, 44(7):1587-1590.
Abstract:
A WC-8Co cladding coating was prepared on the surface of 1Cr18Ni9Ti stainless steel by electro-spark cladding technique combined with an original spiral reciprocating processing method, to improve the capacity of anti-cavitation, anti-abrasion on the surface of flow parts of the pumps. The morphology, the microstructure, the microhardness and the wear resistance of the cladding coating were investigated by means of scanning electron microscopy (SEM), microhardness test and friction and wear test. The results indicate that the cladding coating is uniform, continuous, compact, with no obvious cracks and holes, and there is no clear dividing line and a metallurgical bonding is presented between cladding coating and substrate material. The highest microhardness HV0.3 is 18 920 MPa and the average hardness HV0.3 of the cladding coating is 17 950 MPa, which is about 6 times higher than that of the substrate (2600 MPa). The wear resistance of the cladding coating is 3.75 times of the substrate and the main wear mechanism is adhesive and abrasive wear.
A WC-8Co cladding coating was prepared on the surface of 1Cr18Ni9Ti stainless steel by electro-spark cladding technique combined with an original spiral reciprocating processing method, to improve the capacity of anti-cavitation, anti-abrasion on the surface of flow parts of the pumps. The morphology, the microstructure, the microhardness and the wear resistance of the cladding coating were investigated by means of scanning electron microscopy (SEM), microhardness test and friction and wear test. The results indicate that the cladding coating is uniform, continuous, compact, with no obvious cracks and holes, and there is no clear dividing line and a metallurgical bonding is presented between cladding coating and substrate material. The highest microhardness HV0.3 is 18 920 MPa and the average hardness HV0.3 of the cladding coating is 17 950 MPa, which is about 6 times higher than that of the substrate (2600 MPa). The wear resistance of the cladding coating is 3.75 times of the substrate and the main wear mechanism is adhesive and abrasive wear.
2015, 44(7):1601-1606.
Abstract:
The microstructural evolution and formation mechanism of nanograins in Ti-2Al-2.5Zr α-titanium alloys and Ti-10V-2Fe-3Al metastable β-titanium alloys subjected to multi-impact process at ambient temperature were investigated using optical microscopy, X-ray diffraction and transmission electron microscopy. The results show that deformation twinning, dislocation activities and shear banding successively dominate plastic deformation in Ti-2Al-2.5Zr alloy. In contrast, deformation-induced martensitic phase transformation becomes prevalent in Ti-10V-2Fe-3Al alloy. Martensitic subdivision, shear banding and reverse martensitic transformation contribute to grain refinement. Moreover, nanograins are finally achieved in both titanium alloys at a strain of 1.2, but grain refining efficiency is more significant in Ti-10V-2Fe-3Al alloy. The accelerated grain refinement could be attributed to the assistance of martensitic phase transformation.
The microstructural evolution and formation mechanism of nanograins in Ti-2Al-2.5Zr α-titanium alloys and Ti-10V-2Fe-3Al metastable β-titanium alloys subjected to multi-impact process at ambient temperature were investigated using optical microscopy, X-ray diffraction and transmission electron microscopy. The results show that deformation twinning, dislocation activities and shear banding successively dominate plastic deformation in Ti-2Al-2.5Zr alloy. In contrast, deformation-induced martensitic phase transformation becomes prevalent in Ti-10V-2Fe-3Al alloy. Martensitic subdivision, shear banding and reverse martensitic transformation contribute to grain refinement. Moreover, nanograins are finally achieved in both titanium alloys at a strain of 1.2, but grain refining efficiency is more significant in Ti-10V-2Fe-3Al alloy. The accelerated grain refinement could be attributed to the assistance of martensitic phase transformation.
2015, 44(7):1612-1616.
Abstract:
Fe/Beta zeolite selective catalytic reduction (SCR) catalysts supported on honeycomb ceramic were prepared by a standard water ion exchange method and evaluated in NOx conversion process. The zeolite material characters and effects of Ce-doping on the zeolite were investigated by Inductively Coupled Plasma Atomic Emission Spectrum (ICP-AES), low temperature N2 adsorption, X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), NH3 Temperature-Programmed Desorption (NH3-TPD) and H2 Temperature-Programmed Reduction (H2-TPR). The results show that the Fe-Beta zeolite SCR catalysts with better zeolite structure and Ce-doping exhibit a more excellent catalytic ability on the NOx conversion temperature window, no matter for the fresh one or the one treated under hydrothermal or sulfur aged condition. It is deduced that the larger BET surface area, more uniform and smaller particles and more regular framework of zeolite as well as the unsaturated Ce4+ on zeolite have a great effect on the promotion of NH3-SCR performance.
Fe/Beta zeolite selective catalytic reduction (SCR) catalysts supported on honeycomb ceramic were prepared by a standard water ion exchange method and evaluated in NOx conversion process. The zeolite material characters and effects of Ce-doping on the zeolite were investigated by Inductively Coupled Plasma Atomic Emission Spectrum (ICP-AES), low temperature N2 adsorption, X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), NH3 Temperature-Programmed Desorption (NH3-TPD) and H2 Temperature-Programmed Reduction (H2-TPR). The results show that the Fe-Beta zeolite SCR catalysts with better zeolite structure and Ce-doping exhibit a more excellent catalytic ability on the NOx conversion temperature window, no matter for the fresh one or the one treated under hydrothermal or sulfur aged condition. It is deduced that the larger BET surface area, more uniform and smaller particles and more regular framework of zeolite as well as the unsaturated Ce4+ on zeolite have a great effect on the promotion of NH3-SCR performance.
2015, 44(7):1617-1622.
Abstract:
Mg92Zn4Y4 and Mg92Zn4Y3Gd1 alloys with long period stacking ordered (LPSO) structure phases were prepared by conventional solidification process. By OM, SEM, EDS, XRD and TEM analysis the phases and 14H-LPSO structures of the two alloys were characterized. The results show that as-cast Mg-alloy with the atomic ratio of Zn/RE = 1 will lead to LPSO phase; adding of Gd element to Mg92Zn4Y4 alloy can facilitate the formation of LPSO phase, and its volume fraction increases from 12.1% to 30.4%; Mg dendrites are split and refined during the precipitation of LPSO phase formed at high temperature, resulting in that the average grain size of a-Mg decreases from 50 μm to 10 μm; the solidification microstructure of as-cast Mg92Zn4Y4 alloy is a-Mg solid solution + Mg12ZnY + Mg3Zn3Y2 + Mg-Y; In Mg92Zn4Y3Gd1 alloy, the as-cast microstructure is confirmed to be composed mainly of a-Mg solid solution, Mg12Zn(Y, Gd) and Mg3Zn3(Y, Gd)2; at room temperature, the compression ratio and the thermal conductivity of Mg92Zn4Y4 and Mg92Zn4Y3Gd1 alloys are 12.4% and 15.5%, and 99.233 W·(m·K)-1 and 88.639 W·(m·K)-1, respectively.
Mg92Zn4Y4 and Mg92Zn4Y3Gd1 alloys with long period stacking ordered (LPSO) structure phases were prepared by conventional solidification process. By OM, SEM, EDS, XRD and TEM analysis the phases and 14H-LPSO structures of the two alloys were characterized. The results show that as-cast Mg-alloy with the atomic ratio of Zn/RE = 1 will lead to LPSO phase; adding of Gd element to Mg92Zn4Y4 alloy can facilitate the formation of LPSO phase, and its volume fraction increases from 12.1% to 30.4%; Mg dendrites are split and refined during the precipitation of LPSO phase formed at high temperature, resulting in that the average grain size of a-Mg decreases from 50 μm to 10 μm; the solidification microstructure of as-cast Mg92Zn4Y4 alloy is a-Mg solid solution + Mg12ZnY + Mg3Zn3Y2 + Mg-Y; In Mg92Zn4Y3Gd1 alloy, the as-cast microstructure is confirmed to be composed mainly of a-Mg solid solution, Mg12Zn(Y, Gd) and Mg3Zn3(Y, Gd)2; at room temperature, the compression ratio and the thermal conductivity of Mg92Zn4Y4 and Mg92Zn4Y3Gd1 alloys are 12.4% and 15.5%, and 99.233 W·(m·K)-1 and 88.639 W·(m·K)-1, respectively.
2015, 44(7):1633-1638.
Abstract:
Fe-Cu-TiC composites were synthesized and consolidated simultaneously at an ignition temperature of 759 °C by electric field-assisted combustion synthesis (EFACS). This electric field was generated by a Gleeble thermal simulation instrument. The combustion synthesis process of 15(Ti+C)-65Fe-20Cu (wt%) system, where the molar ratio of Ti to C was 1:1, was studied according to quenching at different temperatures. A four-step model was proposed to describe the combustion synthesis process of Fe-Cu-TiC composites under an electric field. It is suggested that EFACS consists of preheating (I), solid diffusion (II), combustion (III), and post-combustion (IV) stages. The solid diffusion of reactant atoms increases with temperature increasing from the stage I to the stage II. From the stage II to the stage III, carbon atoms gradually diffuse towards titanium atoms until their close contact is performed. During the initial stage III, Ti starts to react with C, i.e. Ti(s) +C(s) =TiC(s) at their interfaces and TiC surrounds the raw Ti atom. Moreover, liquid Cu is formed at the same time. In the following stage III, C atoms diffuse further through the reactant TiC layer, and full reaction between C and Ti is accomplished. The nucleation and growth of TiC takes place in the stage IV. As can be seen from the SEM photographs, TiC exhibits spherical particle.
Fe-Cu-TiC composites were synthesized and consolidated simultaneously at an ignition temperature of 759 °C by electric field-assisted combustion synthesis (EFACS). This electric field was generated by a Gleeble thermal simulation instrument. The combustion synthesis process of 15(Ti+C)-65Fe-20Cu (wt%) system, where the molar ratio of Ti to C was 1:1, was studied according to quenching at different temperatures. A four-step model was proposed to describe the combustion synthesis process of Fe-Cu-TiC composites under an electric field. It is suggested that EFACS consists of preheating (I), solid diffusion (II), combustion (III), and post-combustion (IV) stages. The solid diffusion of reactant atoms increases with temperature increasing from the stage I to the stage II. From the stage II to the stage III, carbon atoms gradually diffuse towards titanium atoms until their close contact is performed. During the initial stage III, Ti starts to react with C, i.e. Ti(s) +C(s) =TiC(s) at their interfaces and TiC surrounds the raw Ti atom. Moreover, liquid Cu is formed at the same time. In the following stage III, C atoms diffuse further through the reactant TiC layer, and full reaction between C and Ti is accomplished. The nucleation and growth of TiC takes place in the stage IV. As can be seen from the SEM photographs, TiC exhibits spherical particle.
2015, 44(7):1648-16542014-7-20.
Abstract:
In order to study the interdiffusion between Pd and Ti at high temperatures in a short time, the Pd coating was prepared on the surface of C.P.Ti by the magnetron sputtering technique. The Pd/Ti samples were heat-treated at 500, 550, 600 and 700 °C for 5 h. The phase composition, microstructure and element distribution of alloy layers were studied by XRD, SEM and EDS. The result shows that after the Pd/Ti sample is heat-treated at 500 °C for 5 h, a very slight interdiffusion occurs between Pd and Ti. When the temperature rises to 550 °C, a continuous diffusion layer appears between Pd coating and the substrate. As the temperature increases further, the interdiffusion becomes more and more obvious. When the temperature rises to 700 °C, TiPd3, TiPd2, Ti2Pd3, TiPd and Ti2Pd compound phases are observed on the alloyed surface layer. This paper also analyzed the Pd/Ti interface diffusion and reaction kinetics. The results indicate that increase of diffusion layer thickness experiences a process from interface reaction control to diffusion control.
In order to study the interdiffusion between Pd and Ti at high temperatures in a short time, the Pd coating was prepared on the surface of C.P.Ti by the magnetron sputtering technique. The Pd/Ti samples were heat-treated at 500, 550, 600 and 700 °C for 5 h. The phase composition, microstructure and element distribution of alloy layers were studied by XRD, SEM and EDS. The result shows that after the Pd/Ti sample is heat-treated at 500 °C for 5 h, a very slight interdiffusion occurs between Pd and Ti. When the temperature rises to 550 °C, a continuous diffusion layer appears between Pd coating and the substrate. As the temperature increases further, the interdiffusion becomes more and more obvious. When the temperature rises to 700 °C, TiPd3, TiPd2, Ti2Pd3, TiPd and Ti2Pd compound phases are observed on the alloyed surface layer. This paper also analyzed the Pd/Ti interface diffusion and reaction kinetics. The results indicate that increase of diffusion layer thickness experiences a process from interface reaction control to diffusion control.
2015, 44(7):1661-1667.
Abstract:
Near-β deformation combined with subsequent heat treatment process provides a possible way to obtain the tri-modal microstructure for TA15 Ti-alloy. As an important component of tri-modal microstructure, the evolution of lamellar α, which determines damage tolerance properties, is complex and difficult to control in the process of near β deformation and subsequent heat treatment. At the same time, the tri-modal microstructure has strict requirements on the composition and morphology of final microstructure, especially on lamellar α. In this paper the microstructure evolution behavior of TA15 Ti-alloy after deformation and 950 °C, 100 min, WQ+800 °C, 8 h, AC under different deformation conditions (deformation temperature, deformation degree and strain rate) were investigated via the thermal simulation test and metallographic test. The evolution mechanism of lamellar α in tri-modal microstructure was revealed. Based on the obtained results, taking high damage tolerance as target, the reasonable range of near β deformation condition were determined to obtain lamellar α possessing excellent fracture toughness and microstructure meeting requirement of tri-modal microstructure. Experimental and theoretical analyses show that for TA15 Ti-alloy the tri-modal microstructure of excellent performance could be obtained within the deformation condition range. The results can provide a guide for obtaining the tri-modal microstructure and excellent lamellar α via near-β deformation processing.
Near-β deformation combined with subsequent heat treatment process provides a possible way to obtain the tri-modal microstructure for TA15 Ti-alloy. As an important component of tri-modal microstructure, the evolution of lamellar α, which determines damage tolerance properties, is complex and difficult to control in the process of near β deformation and subsequent heat treatment. At the same time, the tri-modal microstructure has strict requirements on the composition and morphology of final microstructure, especially on lamellar α. In this paper the microstructure evolution behavior of TA15 Ti-alloy after deformation and 950 °C, 100 min, WQ+800 °C, 8 h, AC under different deformation conditions (deformation temperature, deformation degree and strain rate) were investigated via the thermal simulation test and metallographic test. The evolution mechanism of lamellar α in tri-modal microstructure was revealed. Based on the obtained results, taking high damage tolerance as target, the reasonable range of near β deformation condition were determined to obtain lamellar α possessing excellent fracture toughness and microstructure meeting requirement of tri-modal microstructure. Experimental and theoretical analyses show that for TA15 Ti-alloy the tri-modal microstructure of excellent performance could be obtained within the deformation condition range. The results can provide a guide for obtaining the tri-modal microstructure and excellent lamellar α via near-β deformation processing.
2015, 44(7):1668-1673.
Abstract:
The effects of 2 wt% Sn on the microstructures and the mechanical properties of the die-cast Mg-7Al alloy and the solution-treated alloy were studied by optical microscope (OM), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and tensile tests. The results show that after 2 wt% Sn is added into the Mg-7Al alloys, the grains are refined, the growth of Mg17Al12 phase is suppressed and a few dispersed Mg2Sn particles with granular morphology are formed. After solution treatment the second phases of Mg-7Al alloys drastically decrease while fine granular Mg2Sn phases are still on the AT72 alloy matrix. AT72 alloy exhibits better tensile properties at both room and elevated temperature than Mg-7Al alloys due to the refinement of grains, increase of second phases, optimum morphology of Mg17Al12 and precipitation of Mg2Sn with better thermodynamic properties. The mechanical properties are improved after solid-solution treatment, which is attributed to solid-solution strengthening and dispersion strengthening. In addition, from the view of microscopic theory, the effect of Sn on the improvement of the mechanical properties of Mg-7Al alloy at elevated temperatures was discussed by first-principle calculation.
The effects of 2 wt% Sn on the microstructures and the mechanical properties of the die-cast Mg-7Al alloy and the solution-treated alloy were studied by optical microscope (OM), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and tensile tests. The results show that after 2 wt% Sn is added into the Mg-7Al alloys, the grains are refined, the growth of Mg17Al12 phase is suppressed and a few dispersed Mg2Sn particles with granular morphology are formed. After solution treatment the second phases of Mg-7Al alloys drastically decrease while fine granular Mg2Sn phases are still on the AT72 alloy matrix. AT72 alloy exhibits better tensile properties at both room and elevated temperature than Mg-7Al alloys due to the refinement of grains, increase of second phases, optimum morphology of Mg17Al12 and precipitation of Mg2Sn with better thermodynamic properties. The mechanical properties are improved after solid-solution treatment, which is attributed to solid-solution strengthening and dispersion strengthening. In addition, from the view of microscopic theory, the effect of Sn on the improvement of the mechanical properties of Mg-7Al alloy at elevated temperatures was discussed by first-principle calculation.
2015, 44(7):1679-1684.
Abstract:
Porous ceramic layers were prepared on AZ31B magnesium alloy by Micro-arc Oxidation (MAO), and then electrophoretic coat (E-coat) was deposited on MAO coated Mg alloy. The surface roughness, surface and cross section morphologies, electrochemical properties and scribed corrosion properties of the MAO layer and MAO composite electrophoretic (MAOE) coating were studied. The results indicate that the discharge channels on surface of MAO layer are completely covered by E-coat and the surface of MAOE coating is very smooth; as a result, the surface roughness decreases obviously. The corrosion current density of MAOE coating is two and four orders of magnitudes lower than that of MAO layer and bare Mg alloy, respectively, and the polarization resistance is two and four orders of magnitudes higher, respectively, suggesting that the corrosion trend decreases. The EIS resistance of MAOE coating is four orders higher than that of MAO layer while the EIS capacitance is four orders lower, and thus the corrosion resistance is improved uncommonly. Due to the mechanical interlock between the MAO layer and E-coat, the substrate is corroded seriously during scribed corrosion test, and the coating delaminating at the interface of MAO layer and substrate also occur. However the interface of MAOE composite coating is still compact.
Porous ceramic layers were prepared on AZ31B magnesium alloy by Micro-arc Oxidation (MAO), and then electrophoretic coat (E-coat) was deposited on MAO coated Mg alloy. The surface roughness, surface and cross section morphologies, electrochemical properties and scribed corrosion properties of the MAO layer and MAO composite electrophoretic (MAOE) coating were studied. The results indicate that the discharge channels on surface of MAO layer are completely covered by E-coat and the surface of MAOE coating is very smooth; as a result, the surface roughness decreases obviously. The corrosion current density of MAOE coating is two and four orders of magnitudes lower than that of MAO layer and bare Mg alloy, respectively, and the polarization resistance is two and four orders of magnitudes higher, respectively, suggesting that the corrosion trend decreases. The EIS resistance of MAOE coating is four orders higher than that of MAO layer while the EIS capacitance is four orders lower, and thus the corrosion resistance is improved uncommonly. Due to the mechanical interlock between the MAO layer and E-coat, the substrate is corroded seriously during scribed corrosion test, and the coating delaminating at the interface of MAO layer and substrate also occur. However the interface of MAOE composite coating is still compact.
2015, 44(7):1696-1701.
Abstract:
Mechanical strength and electrical conductivity of Cu-Nb microcomposite wires with Cu core were investigated by tensile tests and resistivity measurements. Microstructure and fracture were examined by scanning electron microscopy. The results show that the fracture mode changes from normal fracture to shear fracture from the fracture core to the edge. The additional Cu core optimizes the conductivity and strength. The strength of deformed wires increases greatly with the decreasing of Nb filament spacing by a power law. Obvious size effect shows up when the spacing is below 100 nm. At the same time, the strength increases faster at 77 K than that at RT with decrease of spacing. When the spacing is above 300 nm, the size effect is slight for the strength.
Mechanical strength and electrical conductivity of Cu-Nb microcomposite wires with Cu core were investigated by tensile tests and resistivity measurements. Microstructure and fracture were examined by scanning electron microscopy. The results show that the fracture mode changes from normal fracture to shear fracture from the fracture core to the edge. The additional Cu core optimizes the conductivity and strength. The strength of deformed wires increases greatly with the decreasing of Nb filament spacing by a power law. Obvious size effect shows up when the spacing is below 100 nm. At the same time, the strength increases faster at 77 K than that at RT with decrease of spacing. When the spacing is above 300 nm, the size effect is slight for the strength.
2015, 44(7):1702-1705.
Abstract:
Amorphous ribbons (Fe1-xCox)86Hf7B6Cu1 (x=0.4~0.6) were prepared using the single-roller melt-spinning technique. M?ssbauer Spectroscopy, transmission electron microscope (TEM) and vibrating sample magnetometer (VSM) were used to characterize microstructures and soft magnetic properties. The result confirms the fully amorphous state of the as-quenched alloy. The valence electron structures and the magnetic moment of the amorphous alloys were calculated using the method of Bond Length Difference (BLD) of the Empirical Electron Theory of solids and molecules (EET). The error of the computed value in theory and experimental value of the magnetic moment is less than 10%, which satisfies the demand of first approximation, indicating that magnetic moment calculation of amorphous alloy could be realized on the valence electron level.
Amorphous ribbons (Fe1-xCox)86Hf7B6Cu1 (x=0.4~0.6) were prepared using the single-roller melt-spinning technique. M?ssbauer Spectroscopy, transmission electron microscope (TEM) and vibrating sample magnetometer (VSM) were used to characterize microstructures and soft magnetic properties. The result confirms the fully amorphous state of the as-quenched alloy. The valence electron structures and the magnetic moment of the amorphous alloys were calculated using the method of Bond Length Difference (BLD) of the Empirical Electron Theory of solids and molecules (EET). The error of the computed value in theory and experimental value of the magnetic moment is less than 10%, which satisfies the demand of first approximation, indicating that magnetic moment calculation of amorphous alloy could be realized on the valence electron level.
14 Microstructure and Mechanical Properties of Titanium Foams Prepared with Carbamide as Space Holder
2015, 44(7):1724-1729.
Abstract:
Production of Ti foams using acicular carbamide as space holder in the case of spacer content between 60%~80% has been investigated. Ti foams having porosities in the range of 50.2%~71.4% have been manufactured. The SEM microstructure shows that the connectivity degree of macrospores grows with higher spacer content, and Ti foams with open-cell structure are formed when the spacer content is beyond 70%. The compressive tests indicate that the mechanical properties of Ti foams decrease with increasing porosity. The resultant yield strength, compressive strength and Young’s modulus vary in the range of 34.4~146.8 MPa, 40.6~193.2 MPa and 0.5~3.3 GPa, respectively. Ti foams with porosity 50.2% and 71.4% may theoretically serve as potential substituted materials for cortical and cancellous bone, respectively.
Production of Ti foams using acicular carbamide as space holder in the case of spacer content between 60%~80% has been investigated. Ti foams having porosities in the range of 50.2%~71.4% have been manufactured. The SEM microstructure shows that the connectivity degree of macrospores grows with higher spacer content, and Ti foams with open-cell structure are formed when the spacer content is beyond 70%. The compressive tests indicate that the mechanical properties of Ti foams decrease with increasing porosity. The resultant yield strength, compressive strength and Young’s modulus vary in the range of 34.4~146.8 MPa, 40.6~193.2 MPa and 0.5~3.3 GPa, respectively. Ti foams with porosity 50.2% and 71.4% may theoretically serve as potential substituted materials for cortical and cancellous bone, respectively.
2015, 44(7):1740-1745.
Abstract:
In order to inhibit the metal catalytic coking, a TiN coating was deposited on the inner surface of stainless steel oil duct with the internal diameter of 2 mm and the length of 700 mm by chemical vapor deposition (CVD), in the process of which the deposition temperature was set as 800 °C for 2 h. Furthermore, the TiN coating turned into TiO2 coating in oxidizing atmosphere at 700 °C. The coating’s morphological features and textures were characterized by SEM, EDS and XRD. As shown in SEM, the surface of the TiN and TiO2 coating prepared by CVD, is continuous, close-packed and homogeneous. According to the observation of EDS, both of them are stoichiometric. The results from XRD indicate that the TiN in the coating has cub phase and the TiO2 has rutile phase. A supercritical cracking system was set up for preliminary evaluating of the coking inhibition characteristic of two kinds of inhibitors and with some hydrocarbon fuel A as feedstock. The results show that compared with the 304 blank tube, the duration time of fuel cracking at high temperature is enhanced obviously in TiN and TiO2 coating tubes, and the anti-coking performance of TiN is more significant.
In order to inhibit the metal catalytic coking, a TiN coating was deposited on the inner surface of stainless steel oil duct with the internal diameter of 2 mm and the length of 700 mm by chemical vapor deposition (CVD), in the process of which the deposition temperature was set as 800 °C for 2 h. Furthermore, the TiN coating turned into TiO2 coating in oxidizing atmosphere at 700 °C. The coating’s morphological features and textures were characterized by SEM, EDS and XRD. As shown in SEM, the surface of the TiN and TiO2 coating prepared by CVD, is continuous, close-packed and homogeneous. According to the observation of EDS, both of them are stoichiometric. The results from XRD indicate that the TiN in the coating has cub phase and the TiO2 has rutile phase. A supercritical cracking system was set up for preliminary evaluating of the coking inhibition characteristic of two kinds of inhibitors and with some hydrocarbon fuel A as feedstock. The results show that compared with the 304 blank tube, the duration time of fuel cracking at high temperature is enhanced obviously in TiN and TiO2 coating tubes, and the anti-coking performance of TiN is more significant.
2015, 44(7):1746-1749.
Abstract:
The in-situ synthesis of AlMgB14-TiB2 composite and its simultaneous diffusion bonding to Nb and Mo were achieved by FAPAS sintering process. XRD, SEM and EDS were used to analyze the phase composition, microstructure and elements distribution characteristics in the joint interface; the formation mechanism of diffusion layer and the process of diffusion bonding under multi-physics coupling condition (electric field, temperature field and pressure field) were discussed. Results indicate that the simultaneous synthesis and diffusion bonding of AlMgB14-30 wt%TiB2 composites to Nb and Mo could be realized, forming uniform and dense diffusion layers with an average width of about 170~180 μm; TiB2 particles gather in the joint interface during the sintering process and react with the metal to form intermetallic compounds; the continuous diffusion of boron element driven by concentration gradient and the formation of intermetallic compounds are the main mechanisms in diffusion bonding.
The in-situ synthesis of AlMgB14-TiB2 composite and its simultaneous diffusion bonding to Nb and Mo were achieved by FAPAS sintering process. XRD, SEM and EDS were used to analyze the phase composition, microstructure and elements distribution characteristics in the joint interface; the formation mechanism of diffusion layer and the process of diffusion bonding under multi-physics coupling condition (electric field, temperature field and pressure field) were discussed. Results indicate that the simultaneous synthesis and diffusion bonding of AlMgB14-30 wt%TiB2 composites to Nb and Mo could be realized, forming uniform and dense diffusion layers with an average width of about 170~180 μm; TiB2 particles gather in the joint interface during the sintering process and react with the metal to form intermetallic compounds; the continuous diffusion of boron element driven by concentration gradient and the formation of intermetallic compounds are the main mechanisms in diffusion bonding.
2015, 44(7):1758-1762.
Abstract:
Electroforming nickel was prepared from a purified sulfamate system. The effects of cathode-current density, temperature and pH of the solution on the microstructure, internal stress and mechanical properties (tensile strength and elongation) of electroforming nickel layer were investigated by metallographic microscope, cathode bending method and tensile test. The results show that the properties of electroforming nickel layer are influenced by microstructure, while the microstructure is influenced by electroforming parameters; the grain size of electroforming nickel decreases with the decrease of cathode-current density or the increase of temperature; when the pH is 4.0, the grain diminishes too; with the decrease of the grain size, the tensile strength of electroforming nickel layer increases while internal stress and elongation decrease. By optimizing technology parameters, the electroforming nickel layer with excellent properties are prepared, including the tensile strength of 673 MPa, elongation of 23.2% and internal stress of 48 MPa.
Electroforming nickel was prepared from a purified sulfamate system. The effects of cathode-current density, temperature and pH of the solution on the microstructure, internal stress and mechanical properties (tensile strength and elongation) of electroforming nickel layer were investigated by metallographic microscope, cathode bending method and tensile test. The results show that the properties of electroforming nickel layer are influenced by microstructure, while the microstructure is influenced by electroforming parameters; the grain size of electroforming nickel decreases with the decrease of cathode-current density or the increase of temperature; when the pH is 4.0, the grain diminishes too; with the decrease of the grain size, the tensile strength of electroforming nickel layer increases while internal stress and elongation decrease. By optimizing technology parameters, the electroforming nickel layer with excellent properties are prepared, including the tensile strength of 673 MPa, elongation of 23.2% and internal stress of 48 MPa.
2015, 44(7):1763-1767.
Abstract:
Ni(400)/Al, Ni(1500)/Al and Ni(6500)/Al composite materials were fabricated by adding 30~40 μm, 8~10 μm and 2~3 μm Ni powder to the Al substrate in the friction stir processing (FSP) period. The microstructures of the surface composites were analyzed by SEM and EDS, while the phase composition was examined by XRD. Results show that Ni powder particle size has a great influence on morphological characteristics of their products. As the powder size increases, the aggregation effect becomes weaker while the crushing effect is enhanced. And Ni aggregation in Ni(6500)/Al, Ni(1500)/Al and Ni(400)/Al present an unique laminated structure, a nearly elliptic structure and a nearly circular structure, respectively. The increase of powder size is more conducive to the intermetallic compound reaction. Moreover, compared with the matrix, the tensile strength of Ni (6500)/Al, Ni(1500)/Al and Ni(400)/Al is increased greatly by 50%, 59% and 71.9%, respectively.
Ni(400)/Al, Ni(1500)/Al and Ni(6500)/Al composite materials were fabricated by adding 30~40 μm, 8~10 μm and 2~3 μm Ni powder to the Al substrate in the friction stir processing (FSP) period. The microstructures of the surface composites were analyzed by SEM and EDS, while the phase composition was examined by XRD. Results show that Ni powder particle size has a great influence on morphological characteristics of their products. As the powder size increases, the aggregation effect becomes weaker while the crushing effect is enhanced. And Ni aggregation in Ni(6500)/Al, Ni(1500)/Al and Ni(400)/Al present an unique laminated structure, a nearly elliptic structure and a nearly circular structure, respectively. The increase of powder size is more conducive to the intermetallic compound reaction. Moreover, compared with the matrix, the tensile strength of Ni (6500)/Al, Ni(1500)/Al and Ni(400)/Al is increased greatly by 50%, 59% and 71.9%, respectively.
2015, 44(7):1777-1781.
Abstract:
The effect of heat treatment temperature on the microstructure and precipitate at grain boundary of G3 alloy was investigated by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and transmission electron microscope (TEM). And then, the effects of the microstructure change and precipitate at grain boundary on the pitting resistance of G3 alloy were studied by immersion tests and electrochemical measurements. The results show that the pitting resistance of G3 alloy is mainly affected by the precipitates at grain boundary. The pitting resistance of G3 alloy is increased after annealing at low temperature (500 oC), due to fewer precipitates in G3 alloy and the improved microstructure uniformity. With the further increasing annealing temperature, there are a large number of precipitates formed at the grain boundary, which can increase the microstructure inhomogeneity of G3 alloy, and the stability of the passive film in poor Mo region becomes worse. It is prone to local active dissolution in poor Mo region, and the susceptibility to pitting of G3 alloy increases significantly.
The effect of heat treatment temperature on the microstructure and precipitate at grain boundary of G3 alloy was investigated by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and transmission electron microscope (TEM). And then, the effects of the microstructure change and precipitate at grain boundary on the pitting resistance of G3 alloy were studied by immersion tests and electrochemical measurements. The results show that the pitting resistance of G3 alloy is mainly affected by the precipitates at grain boundary. The pitting resistance of G3 alloy is increased after annealing at low temperature (500 oC), due to fewer precipitates in G3 alloy and the improved microstructure uniformity. With the further increasing annealing temperature, there are a large number of precipitates formed at the grain boundary, which can increase the microstructure inhomogeneity of G3 alloy, and the stability of the passive film in poor Mo region becomes worse. It is prone to local active dissolution in poor Mo region, and the susceptibility to pitting of G3 alloy increases significantly.
2015, 44(7):1786-1790.
Abstract:
Carbon nano-tubes (CNTs) reinforced 7075 aluminum alloy matrix composite was prepared by friction stir processing, and the microstructure and fatigue properties of the composite were investigated. The results show that the grain size of the composite is much finer and MWCNTs (multi-walled carbon nano-tubes) are uniformly distributed in matrix material. Along with the increase of volume fraction of MWCNTs, the dispersion becomes worse and the fatigue property of the composite is higher than that of the annealed 7075 aluminum alloy matrix. Meanwhile, the fatigue property increases with the increase of MWCNTs content, but the tensile strength decreases gradually. Defects of large size intermetallics, non-metallic inclusion and chip-like metal oxide are observed in the composite which could strongly reduce the fatigue of the composite.
Carbon nano-tubes (CNTs) reinforced 7075 aluminum alloy matrix composite was prepared by friction stir processing, and the microstructure and fatigue properties of the composite were investigated. The results show that the grain size of the composite is much finer and MWCNTs (multi-walled carbon nano-tubes) are uniformly distributed in matrix material. Along with the increase of volume fraction of MWCNTs, the dispersion becomes worse and the fatigue property of the composite is higher than that of the annealed 7075 aluminum alloy matrix. Meanwhile, the fatigue property increases with the increase of MWCNTs content, but the tensile strength decreases gradually. Defects of large size intermetallics, non-metallic inclusion and chip-like metal oxide are observed in the composite which could strongly reduce the fatigue of the composite.
2015, 44(7):1800-1804.
Abstract:
In this paper, the hard alloy Al-Si-B has been prepared through melting the precursor, which is obtained by sintering the powders of B, Al, Mg and SiO2 by electron beam. The structure and properties of the final obtained alloy has been studied by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). The results reveal that the alloy is amorphous. Nano indentor test shows that the average hardness of this alloy is 33.8 GPa. The electrical resistivity measured with a four probe instrument of the alloy is 6.8×10-5 Ω·cm showing a excellent electrical conductivity. Relative friction test shows that this boride has a extremely low friction coefficient of 0.06.
In this paper, the hard alloy Al-Si-B has been prepared through melting the precursor, which is obtained by sintering the powders of B, Al, Mg and SiO2 by electron beam. The structure and properties of the final obtained alloy has been studied by X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). The results reveal that the alloy is amorphous. Nano indentor test shows that the average hardness of this alloy is 33.8 GPa. The electrical resistivity measured with a four probe instrument of the alloy is 6.8×10-5 Ω·cm showing a excellent electrical conductivity. Relative friction test shows that this boride has a extremely low friction coefficient of 0.06.
2015, 44(7):1815-1820.
Abstract:
Iridium is one of the most important coating materials in high-temperature oxidation protective field, due to its excellent physical and chemical properties. On the basis of comparison and analysis of various preparation methods of iridium coatings, the preparation of iridium and iridium alloy coatings by electrodeposition in molten salt is reviewed in the present paper. The apparatus and pretreatment procedure of electrodeposition are introduced. The effects of processing parameters of electrodeposition on preparation of the coatings are discussed. The summary of properties and applications of iridium and iridium alloy coatings is presented. Several key issues which need to be studied hereafter are put forward.
Iridium is one of the most important coating materials in high-temperature oxidation protective field, due to its excellent physical and chemical properties. On the basis of comparison and analysis of various preparation methods of iridium coatings, the preparation of iridium and iridium alloy coatings by electrodeposition in molten salt is reviewed in the present paper. The apparatus and pretreatment procedure of electrodeposition are introduced. The effects of processing parameters of electrodeposition on preparation of the coatings are discussed. The summary of properties and applications of iridium and iridium alloy coatings is presented. Several key issues which need to be studied hereafter are put forward.
