Volume 39,Issue 2,2010 Table of Contents
2010, 39(2):189-193.
Abstract:
Physical properties of Ni46Mn35Ga19 single crystal with transition temperatures above room temperature were investigated by various measuring methods. The measuring results of the resistance and ac susceptibility indicate that the magnetic transition and martensitic transformation can occur simultaneously in this alloy. The measurements of the isothermal magnetization show that the increasing rate of magnetic entropy change in this alloy is 9.0 J / kg·K·T. A large magnetic entropy change of 13.8 J/kg·K is obtained under the field of 1.6 T in the single crystal. Furthermore, the strain measurement shows that accompanying with magnetic entropy change, the alloy exhibits a large spontaneous transition strain of –0.89% and a large magnetic-field-enhanced strain of –1.90%.
Physical properties of Ni46Mn35Ga19 single crystal with transition temperatures above room temperature were investigated by various measuring methods. The measuring results of the resistance and ac susceptibility indicate that the magnetic transition and martensitic transformation can occur simultaneously in this alloy. The measurements of the isothermal magnetization show that the increasing rate of magnetic entropy change in this alloy is 9.0 J / kg·K·T. A large magnetic entropy change of 13.8 J/kg·K is obtained under the field of 1.6 T in the single crystal. Furthermore, the strain measurement shows that accompanying with magnetic entropy change, the alloy exhibits a large spontaneous transition strain of –0.89% and a large magnetic-field-enhanced strain of –1.90%.
2010, 39(2):194-198.
Abstract:
Superplasticity and deformation mechanism of Mg-7.0Al-0.2Zn（AZ70）alloys without typical fine-grained structure was investigated. It is indicated that the AZ70 alloy exhibits superior superplasticity and the maximum elongation of 191.5% was obtained at 380 ℃ and 1×10-3 s-1. It is worth mentioned that high-strain-rate (＝1×10-2 s-1) superplasticity with elongation of 161.5% was achieved at 380 ℃. The mean grain sizes increase with temperature increasing and strain rate decreasing. The grain boundary sliding (GBS) is the dominant deformation mode of the superplasticity, which is verified by grains remaining equiaxial during deformation. Cavities form and grow up along grain boundary. And then the growth and connection of cavities results in the final failure. SEM morphology of the failure surface shows typical tenacity failure characteristics with quantities of uniform dimples.
Superplasticity and deformation mechanism of Mg-7.0Al-0.2Zn（AZ70）alloys without typical fine-grained structure was investigated. It is indicated that the AZ70 alloy exhibits superior superplasticity and the maximum elongation of 191.5% was obtained at 380 ℃ and 1×10-3 s-1. It is worth mentioned that high-strain-rate (＝1×10-2 s-1) superplasticity with elongation of 161.5% was achieved at 380 ℃. The mean grain sizes increase with temperature increasing and strain rate decreasing. The grain boundary sliding (GBS) is the dominant deformation mode of the superplasticity, which is verified by grains remaining equiaxial during deformation. Cavities form and grow up along grain boundary. And then the growth and connection of cavities results in the final failure. SEM morphology of the failure surface shows typical tenacity failure characteristics with quantities of uniform dimples.
2010, 39(2):199-203.
Abstract:
Ag-10Cu in situ filamentary composite was prepared by hot extrusion and cold wire drawing. The as-cast and as-extruded Ag-10Cu alloys consist of Ag matrix, (Ag+Cu) eutectic and Cu precipitates which will become a structure of Ag matrix and Cu filaments after heavy deformation. The size of Cu filaments, transformed from coarse Cu precipitates, changes with drawing strain, and their relationship can be expressed as d=doexp(–0.144η). Two-stage strengthening characteristics were obtained and the strengthening mechanism of this composite was discussed. A combination of ultimate tensile strength approaching 1 GPa and electrical conductivity exceeding 60% IACS can be achieved for this composite. The effect of intermediate heat treatment was also discussed
Ag-10Cu in situ filamentary composite was prepared by hot extrusion and cold wire drawing. The as-cast and as-extruded Ag-10Cu alloys consist of Ag matrix, (Ag+Cu) eutectic and Cu precipitates which will become a structure of Ag matrix and Cu filaments after heavy deformation. The size of Cu filaments, transformed from coarse Cu precipitates, changes with drawing strain, and their relationship can be expressed as d=doexp(–0.144η). Two-stage strengthening characteristics were obtained and the strengthening mechanism of this composite was discussed. A combination of ultimate tensile strength approaching 1 GPa and electrical conductivity exceeding 60% IACS can be achieved for this composite. The effect of intermediate heat treatment was also discussed
2010, 39(2):204-208.
Abstract:
Based on ab-initio principle and pseudo-potential plain wave function combined with density function theory, crystal lattice dynamical characteristics and thermodynamical functions of V, VH2, VD2 and VT2 were calculated. The thermodynamical isotope effect was analyzed based on those calculated data. Calculation results show that both difference of vibration frequency of atoms in VQ2 (Q=H, D and T) and difference of oscillation frequency of hydrogen isotopes are mainly responsible for the hydrogen isotope effect. The standard Gibbs free energy change of the absorption reaction rises from –50 kJ/mol to 140 kJ/mol with the temperature increasing from 10 K to 1000 K. The equilibrium pressure climbs drastically when temperature is higher than room temperature. Within the whole temperature range, only inverse hydrogen isotope effect is found
Based on ab-initio principle and pseudo-potential plain wave function combined with density function theory, crystal lattice dynamical characteristics and thermodynamical functions of V, VH2, VD2 and VT2 were calculated. The thermodynamical isotope effect was analyzed based on those calculated data. Calculation results show that both difference of vibration frequency of atoms in VQ2 (Q=H, D and T) and difference of oscillation frequency of hydrogen isotopes are mainly responsible for the hydrogen isotope effect. The standard Gibbs free energy change of the absorption reaction rises from –50 kJ/mol to 140 kJ/mol with the temperature increasing from 10 K to 1000 K. The equilibrium pressure climbs drastically when temperature is higher than room temperature. Within the whole temperature range, only inverse hydrogen isotope effect is found
2010, 39(2):214-218.
Abstract:
Structures and electrochemical properties of TiMn2-5x(V4Fe)x(x＝0.30，0.35)alloys were investigated. The results of XRD analysis show that the alloys are mainly composed of body centered cubic (bcc) phase, whose lattice parameters are enhanced with the increase of V and Fe content. The SEM images of the alloys show that there are some colonies in the matrix phase. The proportion of colony to the matrix decreases with increasing of V and Fe content. The electrochemical measurements show that TiMn0.25(V4Fe)0.35 alloy has unfavorable activation performance until temperature reaches 327 K, while TiMn0.50(V4Fe)0.30 alloy shows better activation performance, but passivation phenomenon was found in the process of charging at low temperature, which can be eliminated by heating to high temperature. The PCT curves of alloys show that the TiMn0.50(V4Fe)0..30 alloy has a good comprehensive performance, with a favorable plateau pressure at room temperature and wide plateau. The enthalpy and entropy in hydrogen desorption of TiMn0.50(V4Fe)0..30 alloy were also calculated and they are –36.1 kJ/mol, –126.9 J/(mol·K), respectively
Structures and electrochemical properties of TiMn2-5x(V4Fe)x(x＝0.30，0.35)alloys were investigated. The results of XRD analysis show that the alloys are mainly composed of body centered cubic (bcc) phase, whose lattice parameters are enhanced with the increase of V and Fe content. The SEM images of the alloys show that there are some colonies in the matrix phase. The proportion of colony to the matrix decreases with increasing of V and Fe content. The electrochemical measurements show that TiMn0.25(V4Fe)0.35 alloy has unfavorable activation performance until temperature reaches 327 K, while TiMn0.50(V4Fe)0.30 alloy shows better activation performance, but passivation phenomenon was found in the process of charging at low temperature, which can be eliminated by heating to high temperature. The PCT curves of alloys show that the TiMn0.50(V4Fe)0..30 alloy has a good comprehensive performance, with a favorable plateau pressure at room temperature and wide plateau. The enthalpy and entropy in hydrogen desorption of TiMn0.50(V4Fe)0..30 alloy were also calculated and they are –36.1 kJ/mol, –126.9 J/(mol·K), respectively
2010, 39(2):219-223.
Abstract:
Micro-thermal contraction phenomenon of atom clusters in metal melts was discussed based on the X-ray diffraction experimental results of many pure metals and alloys, theoretical analysis and the free volume theory. The essentials and the mechanism of micro-thermal contraction were revealed. The micro-thermal contraction is the result of the expansion of free volume which is stronger than the expansion of melt volume. The structural change of clusters is the fundamental cause of thermal contraction.
Micro-thermal contraction phenomenon of atom clusters in metal melts was discussed based on the X-ray diffraction experimental results of many pure metals and alloys, theoretical analysis and the free volume theory. The essentials and the mechanism of micro-thermal contraction were revealed. The micro-thermal contraction is the result of the expansion of free volume which is stronger than the expansion of melt volume. The structural change of clusters is the fundamental cause of thermal contraction.
2010, 39(2):224-228.
Abstract:
The creep experiment of Ti40 alloy after annealing treatment at 600 ℃ for 4 h was carried on in a temperature range from 500 ℃ to 550 ℃ with various stresses. The experimental results indicate that the creep behavior can be analyzed in two temperature intervals in this creep temperature range. The first temperature interval is ranging from 500 ℃ to 520 ℃; the second one is ranging from 535 ℃ to 550 ℃. In different temperature intervals, the alloy has different creep constitutive equations. Judging by the analysis, it is deduced that the stress has obvious effect on dislocations glide and climbing controlled by heat activation when the temperature interval was at lower temperatures (500-520 ℃). With increasing temperature, the diffusion has more and more effect on the creep deformation. In higher temperature range (535-550 ℃), the creep deformation may be determined by self-diffusion or alloying element diffusion
The creep experiment of Ti40 alloy after annealing treatment at 600 ℃ for 4 h was carried on in a temperature range from 500 ℃ to 550 ℃ with various stresses. The experimental results indicate that the creep behavior can be analyzed in two temperature intervals in this creep temperature range. The first temperature interval is ranging from 500 ℃ to 520 ℃; the second one is ranging from 535 ℃ to 550 ℃. In different temperature intervals, the alloy has different creep constitutive equations. Judging by the analysis, it is deduced that the stress has obvious effect on dislocations glide and climbing controlled by heat activation when the temperature interval was at lower temperatures (500-520 ℃). With increasing temperature, the diffusion has more and more effect on the creep deformation. In higher temperature range (535-550 ℃), the creep deformation may be determined by self-diffusion or alloying element diffusion
2010, 39(2):229-233.
Abstract:
Using the first-principles pseudopotential plane-wave methods based on the density functional theory, the elastic constants of B2-(Ni1-xFex)Al (x=0-3.0 at%) supercells with or without Ni vacancy or Ni anti-site defect were calculated in the framework of Virtual Crystal Approximation. Several parameters, such as elastic constant C44, Cauchy pressure (C12-C44), Young modulus E, the shear modulus G and their ratio G/B0, have been adopted to characterize and assess the effect of Fe alloying concentration on the ductility and hardness of NiAl intermetallic compounds. It is found that Fe addition with x < 0.6 at% is proved to be efficient to enforce the strength or hardness of NiAl intermetallic compounds either for perfect crystals or for defect crystals. No improvement of the ductility of perfect B2-NiAl crystals can be demonstrated as Fe is added in the range from 0 to 3.0 at%. The Ni vacancy or Ni anti-site defects make the intrinsic ductility of perfect B2-NiAl crystals without Fe addition to be weakened. However, an obvious decrease in the degree of the embrittlement of B2-(Ni1-xFex)Al crystals with Ni vacancies can be seen as Fe alloying concentration x is lower than 0.5 at%, and the optimum additions locate in the range from 0.2 at% to 0.4 at%. From these calculations, a deduction therefore is conduced. That is for the distinct increase in the elongation rate of a B2-NiAl single crystal with Fe addition of 0.20-0.25 at% in the experiments could originate from the correlative and cooperative effects between vacancies and Fe addition in the B2-NiAl crystal
Using the first-principles pseudopotential plane-wave methods based on the density functional theory, the elastic constants of B2-(Ni1-xFex)Al (x=0-3.0 at%) supercells with or without Ni vacancy or Ni anti-site defect were calculated in the framework of Virtual Crystal Approximation. Several parameters, such as elastic constant C44, Cauchy pressure (C12-C44), Young modulus E, the shear modulus G and their ratio G/B0, have been adopted to characterize and assess the effect of Fe alloying concentration on the ductility and hardness of NiAl intermetallic compounds. It is found that Fe addition with x < 0.6 at% is proved to be efficient to enforce the strength or hardness of NiAl intermetallic compounds either for perfect crystals or for defect crystals. No improvement of the ductility of perfect B2-NiAl crystals can be demonstrated as Fe is added in the range from 0 to 3.0 at%. The Ni vacancy or Ni anti-site defects make the intrinsic ductility of perfect B2-NiAl crystals without Fe addition to be weakened. However, an obvious decrease in the degree of the embrittlement of B2-(Ni1-xFex)Al crystals with Ni vacancies can be seen as Fe alloying concentration x is lower than 0.5 at%, and the optimum additions locate in the range from 0.2 at% to 0.4 at%. From these calculations, a deduction therefore is conduced. That is for the distinct increase in the elongation rate of a B2-NiAl single crystal with Fe addition of 0.20-0.25 at% in the experiments could originate from the correlative and cooperative effects between vacancies and Fe addition in the B2-NiAl crystal
2010, 39(2):234-237.
Abstract:
FeMnCr/Cr3C2 cored wire was developed for building up the erosion-resistant coatings of super-critical boiler pipes by means of High-Velocity Arc Spraying. The high-temperature erosion behaviors at different impact angles of FeMnCr/Cr3C2 coatings were studied and compared with those of FeCrNi/Cr3C2 coatings and 20 steel by optical microscopy, scanning electron microscopy and energy dispersion spectrum analysis. Results show that FeMnCr/Cr3C2 coatings have the maximum erosive rate when the impact angle is about 60° due to the semi-brittleness erosion mechanism for FeMnCr/Cr3C2 coatings. The erosion resistance of FeMnCr/Cr3C2 coatings is closed to that of FeCrNi/Cr3C2 coatings, and obviously better than that of 20 steel.
FeMnCr/Cr3C2 cored wire was developed for building up the erosion-resistant coatings of super-critical boiler pipes by means of High-Velocity Arc Spraying. The high-temperature erosion behaviors at different impact angles of FeMnCr/Cr3C2 coatings were studied and compared with those of FeCrNi/Cr3C2 coatings and 20 steel by optical microscopy, scanning electron microscopy and energy dispersion spectrum analysis. Results show that FeMnCr/Cr3C2 coatings have the maximum erosive rate when the impact angle is about 60° due to the semi-brittleness erosion mechanism for FeMnCr/Cr3C2 coatings. The erosion resistance of FeMnCr/Cr3C2 coatings is closed to that of FeCrNi/Cr3C2 coatings, and obviously better than that of 20 steel.
2010, 39(2):238-242.
Abstract:
Wetting behaviors of NdFeB magnet by molten Sn-Zn-Bi alloy systems at different temperatures were investigated by the sessile drop technique under vacuum and N2 atmosphere. The results show that the wettabilities of NdFeB magnet with liquid pure Sn or pure Bi elements are poor, and their contact angles are higher. While the wettability of NdFeB magnet with liquid pure Zn element is perfect, and the contact angle is near zero. The Sn-Zn-Bi alloys with certain composition were prepared and their melting points were measured in order to obtain good wettability of NdFeB magnet with molten Sn-Zn-Bi alloy and lower melting point. The wetting angles between Sn-Zn-Bi alloys and NdFeB magnet decrease dramatically with increasing the Bi contents from 1.0% to 7.0% (mass fraction) because the surface tension of the alloys is decreased by the addition of Bi, which were confirmed by calculation and experimental results. The melting point of Sn-8.5Zn-7Bi alloy is 194.3 oC, and the contact angle between the molten Sn-8.5Zn-7Bi alloy and NdFeB magnet is 53.2°.
Wetting behaviors of NdFeB magnet by molten Sn-Zn-Bi alloy systems at different temperatures were investigated by the sessile drop technique under vacuum and N2 atmosphere. The results show that the wettabilities of NdFeB magnet with liquid pure Sn or pure Bi elements are poor, and their contact angles are higher. While the wettability of NdFeB magnet with liquid pure Zn element is perfect, and the contact angle is near zero. The Sn-Zn-Bi alloys with certain composition were prepared and their melting points were measured in order to obtain good wettability of NdFeB magnet with molten Sn-Zn-Bi alloy and lower melting point. The wetting angles between Sn-Zn-Bi alloys and NdFeB magnet decrease dramatically with increasing the Bi contents from 1.0% to 7.0% (mass fraction) because the surface tension of the alloys is decreased by the addition of Bi, which were confirmed by calculation and experimental results. The melting point of Sn-8.5Zn-7Bi alloy is 194.3 oC, and the contact angle between the molten Sn-8.5Zn-7Bi alloy and NdFeB magnet is 53.2°.
2010, 39(2):243-248.
Abstract:
The effects of 3%-5% rhenium addition (mass fraction, similarly hereinafter) on the high-temperature corrosion resistance of CoNiCrAlY alloys were evaluated at 1000 ℃ by means of XRD, SEM and EDS. It is shown that there is an internal oxidation whether the rhenium is added to the alloy or not. The addition of rhenium can reduce the thickness of Al-depletion zone, stabilize the α-Cr(Re) phase and benefit the formation of Cr2O3 oxide scale which separates the base material from the molten salt and prevents from high-temperature corrosion
The effects of 3%-5% rhenium addition (mass fraction, similarly hereinafter) on the high-temperature corrosion resistance of CoNiCrAlY alloys were evaluated at 1000 ℃ by means of XRD, SEM and EDS. It is shown that there is an internal oxidation whether the rhenium is added to the alloy or not. The addition of rhenium can reduce the thickness of Al-depletion zone, stabilize the α-Cr(Re) phase and benefit the formation of Cr2O3 oxide scale which separates the base material from the molten salt and prevents from high-temperature corrosion
2010, 39(2):249-253.
Abstract:
Internal temperature field of solid-solution treated BT22 titanium alloy during cooling was simulated using ANSYS finite element software and the temperature isopleth map of workpieces was plotted during this procedure. Inhomogeneity of temperature distribution during cooling was analyzed from two points of view, i.e. the temperature-time curve and position-temperature curve of workpiece interior. By comparison the relative error of actual curve and simulation curve is 2%-5%. The actual cooling curve was divided into three phases: fast cooling phase, gentle cooling phase and slow cooling phase. The reason of phase formation was also analyzed.
Internal temperature field of solid-solution treated BT22 titanium alloy during cooling was simulated using ANSYS finite element software and the temperature isopleth map of workpieces was plotted during this procedure. Inhomogeneity of temperature distribution during cooling was analyzed from two points of view, i.e. the temperature-time curve and position-temperature curve of workpiece interior. By comparison the relative error of actual curve and simulation curve is 2%-5%. The actual cooling curve was divided into three phases: fast cooling phase, gentle cooling phase and slow cooling phase. The reason of phase formation was also analyzed.
2010, 39(2):254-257.
Abstract:
The polarity of electromigration at the interface between solder joints and finishes was studied with the interconnects structure of Ni(P)/Au finishes-SnPb solder joint-Ni(P)/Au finishes. The mechanism of microstructural evaluation of interconnects was investigated in terms of directional diffusion of atoms under electrical and chemical potential. The IMC layers on the interface between Ni(P)/Au finishes and solder joints have only a little change in thickness after the annealing of 120 ℃ for 100 h because the velocity of wetting reaction is faster than the solid state reaction. But under the condition of electromigration, the directional diffusion of Sn atoms along the electron flow direction induces the abnormal growth of IMC on the anode interface, and the restraint at cathode. The cathode contact is on the upside, where the electron current enters the solder bump, and locates at the triple point. The solder would melt at this point by Joule heating, resulting in the reaction between the Cu wire and solder.
The polarity of electromigration at the interface between solder joints and finishes was studied with the interconnects structure of Ni(P)/Au finishes-SnPb solder joint-Ni(P)/Au finishes. The mechanism of microstructural evaluation of interconnects was investigated in terms of directional diffusion of atoms under electrical and chemical potential. The IMC layers on the interface between Ni(P)/Au finishes and solder joints have only a little change in thickness after the annealing of 120 ℃ for 100 h because the velocity of wetting reaction is faster than the solid state reaction. But under the condition of electromigration, the directional diffusion of Sn atoms along the electron flow direction induces the abnormal growth of IMC on the anode interface, and the restraint at cathode. The cathode contact is on the upside, where the electron current enters the solder bump, and locates at the triple point. The solder would melt at this point by Joule heating, resulting in the reaction between the Cu wire and solder.
2010, 39(2):258-263.
Abstract:
The effects of heavy rare earth oxide additives on the high temperature performance of nickel electrodes were investigated. It is found that the 1 C charge acceptance ability of the spherical Ni(OH)2 electrode with heavy rare earth oxide additive is improved; however, the heavy rare earth oxide as additive has negative effect on the high rate discharge performance at room temperature. The cyclic voltammetry (CV) results indicate that the heavy rare earth oxide as additive can increase the overpotential of oxygen evolution at high temperatures. The oxygen evolution reaction is effectively depressed and leads to the increase of charge efficiency of Ni(OH)2 electrode at high temperatures. Moreover, the reversibility of Ni(OH)2 electrode is also improved at high temperatures.
The effects of heavy rare earth oxide additives on the high temperature performance of nickel electrodes were investigated. It is found that the 1 C charge acceptance ability of the spherical Ni(OH)2 electrode with heavy rare earth oxide additive is improved; however, the heavy rare earth oxide as additive has negative effect on the high rate discharge performance at room temperature. The cyclic voltammetry (CV) results indicate that the heavy rare earth oxide as additive can increase the overpotential of oxygen evolution at high temperatures. The oxygen evolution reaction is effectively depressed and leads to the increase of charge efficiency of Ni(OH)2 electrode at high temperatures. Moreover, the reversibility of Ni(OH)2 electrode is also improved at high temperatures.
2010, 39(2):262-267.
Abstract:
Dynamic compression properties and adiabatic shear behavior of TiB2/Al composites (55%-65%, volume fraction) were investigated by split Hopkinson pressure bar (SHPB). The instantaneous failure of the composite was ascribed to the formation of adiabatic shear band when compressed. It is found that the composites tend to adiabatic shear failure as the reinforcement content increases. The flow stress and strain rate sensitivity exhibit rise/fall tendency with the increasing of strain rates. Additionally, the plastic deformation ability of the composites at high strain rates is highly improved. All the composites were failed in brittle fracture, which is controlled by the breaking of reinforcement particles and splitting of TiB2-Al interfaces
Dynamic compression properties and adiabatic shear behavior of TiB2/Al composites (55%-65%, volume fraction) were investigated by split Hopkinson pressure bar (SHPB). The instantaneous failure of the composite was ascribed to the formation of adiabatic shear band when compressed. It is found that the composites tend to adiabatic shear failure as the reinforcement content increases. The flow stress and strain rate sensitivity exhibit rise/fall tendency with the increasing of strain rates. Additionally, the plastic deformation ability of the composites at high strain rates is highly improved. All the composites were failed in brittle fracture, which is controlled by the breaking of reinforcement particles and splitting of TiB2-Al interfaces
2010, 39(2):268-272.
Abstract:
By means of X-ray diffraction analysis at different temperatures and microstructure observation, an investigation has been made on the influence of element Re and temperatures on the lattice parameter and the misfit of single-crystal nickel based superalloys. Results show that the bigger lattice parameter and misfit are displayed in as-cast superalloy. After fully heat treatment, the cubic g ￠ phase is coherently embedded in the g matrix phase, and the lattice parameters and misfit of g ￠ and g phases are slightly reduced. After aged for long time, the coarsening of g ￠ phase in the alloy occurs, and the interfacial dislocations appear between g ￠ and g phases, which increases the parameters and the absolute misfit of g ￠ and g phases. The lattice parameters of g ￠ and g phases in the alloys at room temperature increase with the element Re increasing, and the absolute values of the misfit decrease. Compared with the g ￠ phase, the g matrix phase displays a bigger dilation coefficient; therefore, the lattice parameters and the absolute misfit value of g ' and g phases in the alloy increase with the temperature increasing
By means of X-ray diffraction analysis at different temperatures and microstructure observation, an investigation has been made on the influence of element Re and temperatures on the lattice parameter and the misfit of single-crystal nickel based superalloys. Results show that the bigger lattice parameter and misfit are displayed in as-cast superalloy. After fully heat treatment, the cubic g ￠ phase is coherently embedded in the g matrix phase, and the lattice parameters and misfit of g ￠ and g phases are slightly reduced. After aged for long time, the coarsening of g ￠ phase in the alloy occurs, and the interfacial dislocations appear between g ￠ and g phases, which increases the parameters and the absolute misfit of g ￠ and g phases. The lattice parameters of g ￠ and g phases in the alloys at room temperature increase with the element Re increasing, and the absolute values of the misfit decrease. Compared with the g ￠ phase, the g matrix phase displays a bigger dilation coefficient; therefore, the lattice parameters and the absolute misfit value of g ' and g phases in the alloy increase with the temperature increasing
2010, 39(2):273-276.
Abstract:
Effects of trace element Sr on the as-cast microstructure and mechanical properties of magnesium alloy AM60B were studied by optical microscope (OM), field emission scanning electron microscopy (FESEM), electronic universal testing machine, digital display Rockwell hardness tester and microhardness tester. The results show that the addition of trace element Sr can refine grains without change of dendrite morphology of matrix α-Mg phase, but can change the morphology and size of γ-Mg17A112 phase from continuous/discontinuous netlike or strip form to cobble or particulate form. The effect of Sr on the tensile strength and elongation of AM60B magnesium alloy has the similar tendency, i.e. with the increase of Sr content, the tensile strength and elongation of AM60B magnesium alloy are first increased and then decreased. With addition of 0.05% Sr, the tensile strength and elongation reach the maximum 191.82 MPa and 4.63%, respectively, while the Rockwell hardness and microhardness are increased with the increase of Sr content. The fracture mechanism of AM60B magnesium alloy is changed from cleavage fracture to quasi-cleavage fracture to cleavage fracture
Effects of trace element Sr on the as-cast microstructure and mechanical properties of magnesium alloy AM60B were studied by optical microscope (OM), field emission scanning electron microscopy (FESEM), electronic universal testing machine, digital display Rockwell hardness tester and microhardness tester. The results show that the addition of trace element Sr can refine grains without change of dendrite morphology of matrix α-Mg phase, but can change the morphology and size of γ-Mg17A112 phase from continuous/discontinuous netlike or strip form to cobble or particulate form. The effect of Sr on the tensile strength and elongation of AM60B magnesium alloy has the similar tendency, i.e. with the increase of Sr content, the tensile strength and elongation of AM60B magnesium alloy are first increased and then decreased. With addition of 0.05% Sr, the tensile strength and elongation reach the maximum 191.82 MPa and 4.63%, respectively, while the Rockwell hardness and microhardness are increased with the increase of Sr content. The fracture mechanism of AM60B magnesium alloy is changed from cleavage fracture to quasi-cleavage fracture to cleavage fracture
2010, 39(2):277-280.
Abstract:
Superplastic deformation mechanical behavior of laser welded joints of TC4 alloys was investigated by hot tensile tests. Non-uniform deformation coefficient K was introduced to characterize the non-uniform deformation between welded joints and base metal during superplastic deformation. Results show that the laser welded joints of TC4 alloys can bear high-temperature superplastic deformation without damage. When the initial strain rate was below 10-2 s-1, the flow stress was below 60 MPa. Both the deformation rate of joints and K value of specimens were first increased and then decreased with increase of the deformation temperature and strain rate. At 900 oC and 10-2 s-1, superplastic deformation rate of joints and K value reach their maximum of 46% and 0.18, respectively at the same time. It reveals that the welded joints have better superplastic deformability, and sensitive index of strain rate m is bigger than 1.5
Superplastic deformation mechanical behavior of laser welded joints of TC4 alloys was investigated by hot tensile tests. Non-uniform deformation coefficient K was introduced to characterize the non-uniform deformation between welded joints and base metal during superplastic deformation. Results show that the laser welded joints of TC4 alloys can bear high-temperature superplastic deformation without damage. When the initial strain rate was below 10-2 s-1, the flow stress was below 60 MPa. Both the deformation rate of joints and K value of specimens were first increased and then decreased with increase of the deformation temperature and strain rate. At 900 oC and 10-2 s-1, superplastic deformation rate of joints and K value reach their maximum of 46% and 0.18, respectively at the same time. It reveals that the welded joints have better superplastic deformability, and sensitive index of strain rate m is bigger than 1.5
2010, 39(2):281-287.
Abstract:
Crystal structure of annealed alloy La0.67Mg0.33Ni2.5Co0.5 and (La0.67Mg0.33Ni2.5Co0.5)D4.0 deuterides were studied by X-ray diffraction, neutron diffraction and Rietveld refinement. It is found that the alloys are mainly composed of (La,Mg)Ni3 phase with rhombohedra PuNi3 type (space group: R3m) structure, and the second phases are LaMgNi4 phase (MgCu4Sn type) and La2Ni7 phase (Ce2Ni7 type). In the (La,Mg)Ni3 phase, the Mg atoms only occupy at 6c sites in the RM2 unit, while the Co atoms mainly occupy at 18 h in the RM5 unit and 6c positions in the boundary between the RM5 and RM2 blocks. The full deuteride of the main phase (La0.67Mg0.33Ni2.5Co0.5)D4.0 has a rhombohedral structure. For the (La0.67Mg0.33Ni2.5Co0.5)D4.0 deuteride, the significant occupancy of deuterium atoms are mainly six sites: 6c1, 18h3 and 18h1 within the RM2 units and 36i2, 18h5, 6c4 within the RM5 units. At the same time, it is found that the 6.5(1)D/f.u. is located within the RM5 units whereas the 3.2(2) )D/f.u. belongs to the RM2 units. For the PuNi3 type structure of (La0.67Mg0.33Ni2.5Co0.5)D4.0, the total isotropic lattice expansions of the a-axis and c-axis are δa/a＝7.1% and δc/c=9.1%, respectively. A significant anisotropic volume expansion (δc/c=15.8%, δV/VRM2=32.8%) is found inside the RM2 unit, but inside the RM5 unit, the volumetric expansions are 2.4% (δc/c) and 17.5% (δV/VRM5)
Crystal structure of annealed alloy La0.67Mg0.33Ni2.5Co0.5 and (La0.67Mg0.33Ni2.5Co0.5)D4.0 deuterides were studied by X-ray diffraction, neutron diffraction and Rietveld refinement. It is found that the alloys are mainly composed of (La,Mg)Ni3 phase with rhombohedra PuNi3 type (space group: R3m) structure, and the second phases are LaMgNi4 phase (MgCu4Sn type) and La2Ni7 phase (Ce2Ni7 type). In the (La,Mg)Ni3 phase, the Mg atoms only occupy at 6c sites in the RM2 unit, while the Co atoms mainly occupy at 18 h in the RM5 unit and 6c positions in the boundary between the RM5 and RM2 blocks. The full deuteride of the main phase (La0.67Mg0.33Ni2.5Co0.5)D4.0 has a rhombohedral structure. For the (La0.67Mg0.33Ni2.5Co0.5)D4.0 deuteride, the significant occupancy of deuterium atoms are mainly six sites: 6c1, 18h3 and 18h1 within the RM2 units and 36i2, 18h5, 6c4 within the RM5 units. At the same time, it is found that the 6.5(1)D/f.u. is located within the RM5 units whereas the 3.2(2) )D/f.u. belongs to the RM2 units. For the PuNi3 type structure of (La0.67Mg0.33Ni2.5Co0.5)D4.0, the total isotropic lattice expansions of the a-axis and c-axis are δa/a＝7.1% and δc/c=9.1%, respectively. A significant anisotropic volume expansion (δc/c=15.8%, δV/VRM2=32.8%) is found inside the RM2 unit, but inside the RM5 unit, the volumetric expansions are 2.4% (δc/c) and 17.5% (δV/VRM5)
2010, 39(2):288-291.
Abstract:
Deformation behavior in high-frequency fatigue failure of laser melting deposited Ti-6Al-2Zr-Mo-V alloys was investigated. The deformation modes and mechanisms were also discussed. The results indicate that the deformation behavior during fatigue crack nucleation and propagation are closely related to the dislocation motion and slip behavior. The fatigue cracks by slip deformation propagate along two slip planes. A lot of secondary cracks were observed on the crack propagation subsurface. Formation mechanism and effect of two types of secondary cracks were explained. Grain boundary deformation of coarse-columnar crystal was also discussed.
Deformation behavior in high-frequency fatigue failure of laser melting deposited Ti-6Al-2Zr-Mo-V alloys was investigated. The deformation modes and mechanisms were also discussed. The results indicate that the deformation behavior during fatigue crack nucleation and propagation are closely related to the dislocation motion and slip behavior. The fatigue cracks by slip deformation propagate along two slip planes. A lot of secondary cracks were observed on the crack propagation subsurface. Formation mechanism and effect of two types of secondary cracks were explained. Grain boundary deformation of coarse-columnar crystal was also discussed.
2010, 39(2):292-295.
Abstract:
In order to improve the electrocatalytic activity of Pt based formic acid oxidation, the PMo12 and Na2MoO4 modified Pt electrodes were prepared and their electrocatalytic effects on the formic acid oxidation were studied. The electrocatalytic activities for the formic acid oxidation were evaluated with the electrochemical techniques of CV. The result shows that the PMo12 and Na2MoO4 modified Pt electrode can increase the activity of formic acid. In addition when adding NiSO4 solution，the PMo12 modified Pt electrodes can increase the activity of formic acid oxidation.
In order to improve the electrocatalytic activity of Pt based formic acid oxidation, the PMo12 and Na2MoO4 modified Pt electrodes were prepared and their electrocatalytic effects on the formic acid oxidation were studied. The electrocatalytic activities for the formic acid oxidation were evaluated with the electrochemical techniques of CV. The result shows that the PMo12 and Na2MoO4 modified Pt electrode can increase the activity of formic acid. In addition when adding NiSO4 solution，the PMo12 modified Pt electrodes can increase the activity of formic acid oxidation.
2010, 39(2):296-299.
Abstract:
The 4N-Mg alloys with and without modification and the TC4 alloy were embedded in the thigh bones of rabbits. The slices were tested by X-ray method and the concentrations of Mg2+ ion in blood were measured for the died rabbits after operation for 2, 6, and 12 w, respectively. The specimens were analyzed by SEM and EDS, and tissue slices were observed by optical microscope. The vivo results show that the magnesium concentrations in the blood of two groups of animal subjects were in the normal scale. The Mg-based materials have good bone inducement and show the better capability of bonding with bone. The new bone mineralizes obviously on the interface. And on the new bone, the osteoclast cells array orderly. The untreated magnesium-based materials are corroded faster than the treated magnesium-based materials. All results indicate that the Mg-based materials show better biocompatibility and capacity to induce new bone, and the surface modification has an effect to control the corrosion rate of Mg-based biomaterials
The 4N-Mg alloys with and without modification and the TC4 alloy were embedded in the thigh bones of rabbits. The slices were tested by X-ray method and the concentrations of Mg2+ ion in blood were measured for the died rabbits after operation for 2, 6, and 12 w, respectively. The specimens were analyzed by SEM and EDS, and tissue slices were observed by optical microscope. The vivo results show that the magnesium concentrations in the blood of two groups of animal subjects were in the normal scale. The Mg-based materials have good bone inducement and show the better capability of bonding with bone. The new bone mineralizes obviously on the interface. And on the new bone, the osteoclast cells array orderly. The untreated magnesium-based materials are corroded faster than the treated magnesium-based materials. All results indicate that the Mg-based materials show better biocompatibility and capacity to induce new bone, and the surface modification has an effect to control the corrosion rate of Mg-based biomaterials
2010, 39(2):300-303.
Abstract:
以Ba(NO3)2，Mg(NO3)2·6H2O，Al(NO3)3·9H2O，Eu2O3和适量表面活性剂为原料，以NH4HCO3为沉淀剂，采用化学共沉淀法一次煅烧工艺，在1200 ℃下合成单相BaMgA110O17:Eu2+蓝色荧光粉。结果表明，化学共沉淀法的煅烧温度比传统的高温固相法降低了400 ℃左右，合成的荧光粉体色白、发光强度高、结构松散且无烧结现象，粒度主要分布在190~295 nm之间。在254 nm的紫外光激发下，BaMgA110O17:Eu2+的发射光谱最强峰在450 nm左右；当Eu2+掺杂浓度为14%时，发光强度最大
以Ba(NO3)2，Mg(NO3)2·6H2O，Al(NO3)3·9H2O，Eu2O3和适量表面活性剂为原料，以NH4HCO3为沉淀剂，采用化学共沉淀法一次煅烧工艺，在1200 ℃下合成单相BaMgA110O17:Eu2+蓝色荧光粉。结果表明，化学共沉淀法的煅烧温度比传统的高温固相法降低了400 ℃左右，合成的荧光粉体色白、发光强度高、结构松散且无烧结现象，粒度主要分布在190~295 nm之间。在254 nm的紫外光激发下，BaMgA110O17:Eu2+的发射光谱最强峰在450 nm左右；当Eu2+掺杂浓度为14%时，发光强度最大
2010, 39(2):304-308.
Abstract:
Oxidation of EB-PVD thermal barrier coatings (TBC) deposited and undeposited on nickel base superalloy CMSX-4 with Pt content modified aluminide bond coating have been studied in air at 900, 1000 and 1100 ℃ in order to determine the influence factor of temperature, Pt content and TBC for TGO. It is found that some cracks growth due to the alumina phase transformation and aluminum oxide spallation happened on the surface of low αAl coating TGO. Some voids were formed on the interface between TGO and low aAl bond coating during the initial oxidation period. However, at 900 ℃ inner voids still exist after 300 h oxidation. Thermally grown oxide (TGO) stress trend of samples with TBC was also different compared with that without TBC. The TBC lifetime would be rapidly decreased if the operated oxidation temperature increases
Oxidation of EB-PVD thermal barrier coatings (TBC) deposited and undeposited on nickel base superalloy CMSX-4 with Pt content modified aluminide bond coating have been studied in air at 900, 1000 and 1100 ℃ in order to determine the influence factor of temperature, Pt content and TBC for TGO. It is found that some cracks growth due to the alumina phase transformation and aluminum oxide spallation happened on the surface of low αAl coating TGO. Some voids were formed on the interface between TGO and low aAl bond coating during the initial oxidation period. However, at 900 ℃ inner voids still exist after 300 h oxidation. Thermally grown oxide (TGO) stress trend of samples with TBC was also different compared with that without TBC. The TBC lifetime would be rapidly decreased if the operated oxidation temperature increases
2010, 39(2):309-313.
Abstract:
In order to enlarge the dimensions of titanium cladding steel plate, a new method of two main procedures was used, in which the DT4 thin slice was exploded firstly with titanium plate to assemble billet according to a symmetrical way. The effects of rolling and annealing temperatures on the shear strength of titanium cladding steel plate were investigated. The microstructures and interfacial diffusion of the cladding plates were observed or measured by optical microscope, scanning electric microscope and micro-hardness tester. The results show that the shear strength of the cladding plates is remarkably depended on the rolling and annealing temperatures, and the brittle compound amount in the interface of titanium/DT4 will increase evidently and the shear strength of titanium cladding steel plate will decrease sharply when the rolling temperature is above 882 ℃ (the α→β phase transformation temperature of titanium), or the annealing temperature is above 750 ℃. The micro-hardness peak value appears in titanium side when the annealing temperature is higher than 900 ℃ due to Fe element diffusion in titanium. Annealed within the range from 550 to 650 ℃, the shear strength will slightly increase.
In order to enlarge the dimensions of titanium cladding steel plate, a new method of two main procedures was used, in which the DT4 thin slice was exploded firstly with titanium plate to assemble billet according to a symmetrical way. The effects of rolling and annealing temperatures on the shear strength of titanium cladding steel plate were investigated. The microstructures and interfacial diffusion of the cladding plates were observed or measured by optical microscope, scanning electric microscope and micro-hardness tester. The results show that the shear strength of the cladding plates is remarkably depended on the rolling and annealing temperatures, and the brittle compound amount in the interface of titanium/DT4 will increase evidently and the shear strength of titanium cladding steel plate will decrease sharply when the rolling temperature is above 882 ℃ (the α→β phase transformation temperature of titanium), or the annealing temperature is above 750 ℃. The micro-hardness peak value appears in titanium side when the annealing temperature is higher than 900 ℃ due to Fe element diffusion in titanium. Annealed within the range from 550 to 650 ℃, the shear strength will slightly increase.
2010, 39(2):314-317.
Abstract:
Fine-grained 93W-4.9Ni-2.1Fe tungsten heavy alloy rods with diameter of 25 mm were fabricated by mechanical alloying (MA), trace Y2O3 adding, cold isostatic pressing and sintering. The tungsten grain size of the as-sintered alloy was 3-4 μm. The effects of MA, addition of trace Y2O3 and sintering process on the densification and microstructure of the alloy were studied. It is indicated that the tungsten grains were spheroidized during liquid phase sintering at 1480 oC, and at this temperature the sintering time greatly affects the control of tungsten grains growth. The grain size of the tungsten alloy sintered at 1480 ℃ for 30 min was 5-8 μm. The grain size of the tungsten alloy was 8-10 μm when the sintering time was 60 min at 1480 ℃. The addition of trace Y2O3 further prevents the tungsten grain growth, effectively refining the tungsten grain and inducing a homogeneous microstructure. The tungsten grain size of tungsten alloy sintered at 1480 ℃ for 60 min with addition of Y2O3 was 3-4 μm and more uniform
Fine-grained 93W-4.9Ni-2.1Fe tungsten heavy alloy rods with diameter of 25 mm were fabricated by mechanical alloying (MA), trace Y2O3 adding, cold isostatic pressing and sintering. The tungsten grain size of the as-sintered alloy was 3-4 μm. The effects of MA, addition of trace Y2O3 and sintering process on the densification and microstructure of the alloy were studied. It is indicated that the tungsten grains were spheroidized during liquid phase sintering at 1480 oC, and at this temperature the sintering time greatly affects the control of tungsten grains growth. The grain size of the tungsten alloy sintered at 1480 ℃ for 30 min was 5-8 μm. The grain size of the tungsten alloy was 8-10 μm when the sintering time was 60 min at 1480 ℃. The addition of trace Y2O3 further prevents the tungsten grain growth, effectively refining the tungsten grain and inducing a homogeneous microstructure. The tungsten grain size of tungsten alloy sintered at 1480 ℃ for 60 min with addition of Y2O3 was 3-4 μm and more uniform
2010, 39(2):325-328.
Abstract:
Diameters of titania nanotubes could be controlled through changing the oxidation voltages and anodization time. By anodization of one time, the nanotubes with the diameters of 50 nm and 100 nm were fabricated, even of 120 nm for the biggest diameter. By the two-step anodization, however, the diameter of the nanotubes was up to 280 nm, above the limit by one time anodization. It is demonstrated that the increase of voltage in a limited range could increase the diameter of the titana nanotubes, and the diameter of the nanotubes can hardly be expanded beyond 120 nm. In the two-step anodization, the diameter of the nanotubes could be enlarged to a larger range, in which the application of the nanotubes could also be widened.
Diameters of titania nanotubes could be controlled through changing the oxidation voltages and anodization time. By anodization of one time, the nanotubes with the diameters of 50 nm and 100 nm were fabricated, even of 120 nm for the biggest diameter. By the two-step anodization, however, the diameter of the nanotubes was up to 280 nm, above the limit by one time anodization. It is demonstrated that the increase of voltage in a limited range could increase the diameter of the titana nanotubes, and the diameter of the nanotubes can hardly be expanded beyond 120 nm. In the two-step anodization, the diameter of the nanotubes could be enlarged to a larger range, in which the application of the nanotubes could also be widened.
2010, 39(2):329-332.
Abstract:
Based on the easily-formed preform made of the mixture of TiB2 particles and aluminum powder, 20% TiB2P/6061Al composites (volume fraction) were fabricated by pressure infiltration method; subsequently, the composites were hot extruded with 10:1 extrusion ratio. The microstructures and mechanical properties of the composites before and after hot extrusion were studied with SEM, TEM and a tensile machine. Results show that the composites after hot extrusion exhibit better tensile strength, such as the tensile strength of 447.5 MPa, elastic modulus of 121.8 GPa and large elongation of 7.95 %. The high strength-plasticity for the composites is attributed to the interfacial bonding strength and grain refining strengthening and precipitation strengthening
Based on the easily-formed preform made of the mixture of TiB2 particles and aluminum powder, 20% TiB2P/6061Al composites (volume fraction) were fabricated by pressure infiltration method; subsequently, the composites were hot extruded with 10:1 extrusion ratio. The microstructures and mechanical properties of the composites before and after hot extrusion were studied with SEM, TEM and a tensile machine. Results show that the composites after hot extrusion exhibit better tensile strength, such as the tensile strength of 447.5 MPa, elastic modulus of 121.8 GPa and large elongation of 7.95 %. The high strength-plasticity for the composites is attributed to the interfacial bonding strength and grain refining strengthening and precipitation strengthening
2010, 39(2):333-337.
Abstract:
Co-Al co-doped cathode material LiNi0.8Co0.2-xAlxO2 (0≤x≤0.15) was directly synthesized without artificial grinding and washing by a eutectic molten-salt mixture (0.38LiOH-0.62LiNO3) method. According to this method, the eutectic molten-salt mixture was self-mixed with high tap density precursor Ni0.8Co0.2-xAlx(OH)2 thoroughly at low temperature and then sintered at a certain temperature. The tap-density of LiNi0.8Co0.15Al0.05O2 obtained is 2.97 g·cm-3. According to XRD and SEM, these LiNi0.8Co0.2-x AlxO2 materials have an order α-NaFeO2 layer structure and regular morphology. The charge-discharge tests show that the LiNi0.8Co0.15Al0.05O2 has an initial discharge capacity as high as 167.5 mAh·g-1 and excellent capacity retention in the range from 3.0 V to 4.3 V at a specific current of 0.2 C.
Co-Al co-doped cathode material LiNi0.8Co0.2-xAlxO2 (0≤x≤0.15) was directly synthesized without artificial grinding and washing by a eutectic molten-salt mixture (0.38LiOH-0.62LiNO3) method. According to this method, the eutectic molten-salt mixture was self-mixed with high tap density precursor Ni0.8Co0.2-xAlx(OH)2 thoroughly at low temperature and then sintered at a certain temperature. The tap-density of LiNi0.8Co0.15Al0.05O2 obtained is 2.97 g·cm-3. According to XRD and SEM, these LiNi0.8Co0.2-x AlxO2 materials have an order α-NaFeO2 layer structure and regular morphology. The charge-discharge tests show that the LiNi0.8Co0.15Al0.05O2 has an initial discharge capacity as high as 167.5 mAh·g-1 and excellent capacity retention in the range from 3.0 V to 4.3 V at a specific current of 0.2 C.
2010, 39(2):338-342.
Abstract:
In order to reveal the effect of vacuum treatment and Ti content on the properties and microstructure of Mo-0.1Zr alloy, Mo-0.1Zr and Mo-0.1Zr-nTi (n=0.4, 0.55, 0.7 and 0.9) alloys were prepared via powder metallurgy processes and final vacuum treatment was adopted. The result shows that the mechanical properties of Mo-0.1Zr alloy were enhanced greatly by the vacuum treatment, especially the elongation of the alloy (25.6%), much higher than that of the forged Mo alloys. Simultaneously, obvious transgranular fracture was observed on the fracture surface after vacuum treatment instead of the intergranular fracture. It induces the generation of (Mo,Ti)xOy second-phase particles by adding element Ti into the Mo-0.1Zr alloy, which exists in the grain boundaries. With the increase of Ti content, the amount of second-phase particles increases and leads to the reduction of mechanical properties of the alloys
In order to reveal the effect of vacuum treatment and Ti content on the properties and microstructure of Mo-0.1Zr alloy, Mo-0.1Zr and Mo-0.1Zr-nTi (n=0.4, 0.55, 0.7 and 0.9) alloys were prepared via powder metallurgy processes and final vacuum treatment was adopted. The result shows that the mechanical properties of Mo-0.1Zr alloy were enhanced greatly by the vacuum treatment, especially the elongation of the alloy (25.6%), much higher than that of the forged Mo alloys. Simultaneously, obvious transgranular fracture was observed on the fracture surface after vacuum treatment instead of the intergranular fracture. It induces the generation of (Mo,Ti)xOy second-phase particles by adding element Ti into the Mo-0.1Zr alloy, which exists in the grain boundaries. With the increase of Ti content, the amount of second-phase particles increases and leads to the reduction of mechanical properties of the alloys
2010, 39(2):343-346.
Abstract:
La0.65Sr0.35MnO3 was prepared at different pH values by sol-gel method. The phase composition of the as-received powder was measured using X-ray diffraction. The particle size and morphology were observed by SEM. The results show that the samples called manganites have single perovskite structure and homogeneous particle size distribution when the pH value is controlled near 0.5 and 8.0 during the sol-gel process. The layer-shaped gel forms in the system when pH=0.5. However, the three-dimensional reticulate gel occurs when pH=8.0. The homogeneous distribution of La, Sr and Mn ions in the gel benefits avoiding the deviation of the chemical composition of manganites and the agglomeration of the powder in the following heat treatment.
La0.65Sr0.35MnO3 was prepared at different pH values by sol-gel method. The phase composition of the as-received powder was measured using X-ray diffraction. The particle size and morphology were observed by SEM. The results show that the samples called manganites have single perovskite structure and homogeneous particle size distribution when the pH value is controlled near 0.5 and 8.0 during the sol-gel process. The layer-shaped gel forms in the system when pH=0.5. However, the three-dimensional reticulate gel occurs when pH=8.0. The homogeneous distribution of La, Sr and Mn ions in the gel benefits avoiding the deviation of the chemical composition of manganites and the agglomeration of the powder in the following heat treatment.
2010, 39(2):347-351.
Abstract:
A three dimensional finite element mathematical model of electromagnetic field and temperature field was developed to investigate the effect of high frequency amplitude-modulated magnetic field on the billet surface temperature. The results show that the induction heat power of magnetic field amplitude-modulated with sine wave and square wave is unrelated to the frequency of modulating wave. The induction heat power of magnetic field modulated with square wave is between the induction heat powers of the two constant amplitude magnetic fields employed to modulate. If the induction heat powers of the two constant amplitude magnetic fields are determined, the induction heat power of magnetic fields modulated with square wave is determined by the relative scale of the acting time of the two constant amplitude magnetic fields. The induction heat power of magnetic field modulated with sine wave is about 62-64% of that of the high frequency magnetic field before modulation
A three dimensional finite element mathematical model of electromagnetic field and temperature field was developed to investigate the effect of high frequency amplitude-modulated magnetic field on the billet surface temperature. The results show that the induction heat power of magnetic field amplitude-modulated with sine wave and square wave is unrelated to the frequency of modulating wave. The induction heat power of magnetic field modulated with square wave is between the induction heat powers of the two constant amplitude magnetic fields employed to modulate. If the induction heat powers of the two constant amplitude magnetic fields are determined, the induction heat power of magnetic fields modulated with square wave is determined by the relative scale of the acting time of the two constant amplitude magnetic fields. The induction heat power of magnetic field modulated with sine wave is about 62-64% of that of the high frequency magnetic field before modulation
2010, 39(2):352-356.
Abstract:
The microstructure and mechanical properties of Al-Mg2Si alloys by equal channel angular pressing (ECAP) at 250 oC were studied. Vickers hardness and tensile testing show that the hardness, tensile strength and elongation of the alloys increase after ECAP for 4 passes. However, the hardness and tensile strength decrease after ECAP for 8 passes while the elongation increases further. SEM and TEM observations show that the original skelecton shape or the Chinese-script Mg2Si phase are obviously broken after ECAP. The more the extrusion passes, the more the fragmentated Mg2Si phase, and the more the alloys refining. The mechanism for the decrease in hardness and tensile strength of the specimen after ECAP for 8 passes compared with 4 passes was discussed.
The microstructure and mechanical properties of Al-Mg2Si alloys by equal channel angular pressing (ECAP) at 250 oC were studied. Vickers hardness and tensile testing show that the hardness, tensile strength and elongation of the alloys increase after ECAP for 4 passes. However, the hardness and tensile strength decrease after ECAP for 8 passes while the elongation increases further. SEM and TEM observations show that the original skelecton shape or the Chinese-script Mg2Si phase are obviously broken after ECAP. The more the extrusion passes, the more the fragmentated Mg2Si phase, and the more the alloys refining. The mechanism for the decrease in hardness and tensile strength of the specimen after ECAP for 8 passes compared with 4 passes was discussed.
34 Comparison of Compressed Powders in Single and Double Tubes Designs Driven by Convergent Detonation
2010, 39(2):357-361.
Abstract:
According to the material compressed conditions and the hypothesis of detonation drive, and based on the conservation of mass and momentum, the motion differential equation of compressible powder was obtained. Combined with the planar Taylor wave and the equation of state of powder, the coupling relationship between the convergent flow filed and the shrinking of powders can be gained, and then the copper powder explosive consolidation was calculated. The results indicate that the velocity and average density history curves agree with the reported reference values. It was convincing that the displacement history curve is satisfied with physical fact because the displacement history curve is derived from the velocity. By comparison, it can be known that in double-tubes, the pressure is higher at the same ratio of explosive mass because the external tube is performed as shape charge, so the density is higher. Besides, the experiment results show that the equipment of double-tubes fits with central pole can avoid the Mach pores and enlarge the size of the sintered body. As a conclusion, the double-tubes design is better
According to the material compressed conditions and the hypothesis of detonation drive, and based on the conservation of mass and momentum, the motion differential equation of compressible powder was obtained. Combined with the planar Taylor wave and the equation of state of powder, the coupling relationship between the convergent flow filed and the shrinking of powders can be gained, and then the copper powder explosive consolidation was calculated. The results indicate that the velocity and average density history curves agree with the reported reference values. It was convincing that the displacement history curve is satisfied with physical fact because the displacement history curve is derived from the velocity. By comparison, it can be known that in double-tubes, the pressure is higher at the same ratio of explosive mass because the external tube is performed as shape charge, so the density is higher. Besides, the experiment results show that the equipment of double-tubes fits with central pole can avoid the Mach pores and enlarge the size of the sintered body. As a conclusion, the double-tubes design is better
2010, 39(2):362-366.
Abstract:
The Ti-24Al-15Nb-1.5Mo/TC11 dual alloy discs were joined by electron beam welding firstly, and then underwent near isothermal forging and gradient heat treatment. The welding interface state was investigated by OM, SEM, TEM and XRD. The results show that the elevated temperature properties of the dual alloy disc are better and the high temperature strength is larger than that of the TC11 alloy. However, the dispersion degree of tensile properties is larger at the room temperature. When the dual alloy disc is deformed by 50%, the α phase is distributed in the β phase grain boundary from welding seam to the heat-affected zone of TC11 alloy, which can not be eliminated by gradient heat treatment. The cluster α2 phase in the welding seam area is formed, which is ascribed to the diffusion of the Al and Nb elements from the α2 phase during near isothermal forging and gradient heat treatment.
The Ti-24Al-15Nb-1.5Mo/TC11 dual alloy discs were joined by electron beam welding firstly, and then underwent near isothermal forging and gradient heat treatment. The welding interface state was investigated by OM, SEM, TEM and XRD. The results show that the elevated temperature properties of the dual alloy disc are better and the high temperature strength is larger than that of the TC11 alloy. However, the dispersion degree of tensile properties is larger at the room temperature. When the dual alloy disc is deformed by 50%, the α phase is distributed in the β phase grain boundary from welding seam to the heat-affected zone of TC11 alloy, which can not be eliminated by gradient heat treatment. The cluster α2 phase in the welding seam area is formed, which is ascribed to the diffusion of the Al and Nb elements from the α2 phase during near isothermal forging and gradient heat treatment.
2010, 39(2):367-371.
Abstract:
Al2O3/ZrO2 coating was deposited on γ-TiAl based alloys with aluminum isopropoxide (Al(OC3H7)3) and zirconium oxychloride octahydrate (ZrOCl2?8H2O) as starting materials by sol-gel method. The coating synthesized using dip-coating process, was uniform and crack-free. Isothermal and cyclic oxidations of the coated and uncoated specimens at 1000 ℃ in static air were carried out to test the coating effect on the oxidation behavior of the alloy. The coating decreases the oxidation rate of the alloys and increases the cyclic oxidation resistance. The possible mechanism of the coating on the oxidation behavior of the alloy was discussed
Al2O3/ZrO2 coating was deposited on γ-TiAl based alloys with aluminum isopropoxide (Al(OC3H7)3) and zirconium oxychloride octahydrate (ZrOCl2?8H2O) as starting materials by sol-gel method. The coating synthesized using dip-coating process, was uniform and crack-free. Isothermal and cyclic oxidations of the coated and uncoated specimens at 1000 ℃ in static air were carried out to test the coating effect on the oxidation behavior of the alloy. The coating decreases the oxidation rate of the alloys and increases the cyclic oxidation resistance. The possible mechanism of the coating on the oxidation behavior of the alloy was discussed
2010, 39(2):372-376.
Abstract:
The detailed microstructure characteristics and the formation regulation of the duplex microstructure of Ti-23Al-17Nb (at%) alloys under different heat treatment conditions were studied. The effects of detailed microstructure characteristics on the mechanical properties of alloys were also investigated. The approaches to improve the both tensile and endurance properties at elevated temperature were discussed. The results indicate that for the alloys forged in (α2+B2) phase field, the duplex microstructure can be obtained either by treatment of solution in (α2+B2) field and oil quenching plus aging in (α2+B2+O) field. The volume fraction, size and distribution pattern of O phase laths can be controlled well. The relatively lower aging temperature is of benefit to form the finer and more random distribution of O phase laths. Increasing the volume fractions of O phase laths can improve the endurance properties at elevated temperature but decrease the room-temperature elongation in the case of similar sizes and same percent content (15%-20%) as equiaxed α2 particles, while the finer sizes of O phase laths can increase the tensile properties both at room and elevated temperatures, but decrease the endurance properties. The optimum matching of tensile strength, elongation and endurance properties of the alloys at elevated temperature can be obtained by the heat treatment of 1060 oC solution and oil quenching plus 850 oC aging
The detailed microstructure characteristics and the formation regulation of the duplex microstructure of Ti-23Al-17Nb (at%) alloys under different heat treatment conditions were studied. The effects of detailed microstructure characteristics on the mechanical properties of alloys were also investigated. The approaches to improve the both tensile and endurance properties at elevated temperature were discussed. The results indicate that for the alloys forged in (α2+B2) phase field, the duplex microstructure can be obtained either by treatment of solution in (α2+B2) field and oil quenching plus aging in (α2+B2+O) field. The volume fraction, size and distribution pattern of O phase laths can be controlled well. The relatively lower aging temperature is of benefit to form the finer and more random distribution of O phase laths. Increasing the volume fractions of O phase laths can improve the endurance properties at elevated temperature but decrease the room-temperature elongation in the case of similar sizes and same percent content (15%-20%) as equiaxed α2 particles, while the finer sizes of O phase laths can increase the tensile properties both at room and elevated temperatures, but decrease the endurance properties. The optimum matching of tensile strength, elongation and endurance properties of the alloys at elevated temperature can be obtained by the heat treatment of 1060 oC solution and oil quenching plus 850 oC aging
