Volume 44,Issue 5,2015 Table of Contents
2015, 44(5):1041-1045.
Abstract:
Impulse pressuring diffusion bonding of commercially pure titanium to 1Cr18Ni9 stainless steel was carried out using a copper interlayer in an attempt to reduce the bonding time and alleviate the detrimental effect of interfacial reaction products on bonding strength. Successful bonding has been achieved at 850 °C under a pulsed pressure of 8~20 MPa within a duration of only 120~180 s, which is notably shortened in comparison with conventional diffusion bonding. Microstructure characterization revealed that a sequence of Ti-Cu intermetallic compounds were formed at the Ti/Cu interface and the Cu/stainless steel interface was characterized by the presence of solid solution of Cu in γ Fe without any interfacial reaction products. Maximum bonding strength of 346 MPa was obtained when the joint was bonded for 120 s. Upon tensile loading, the joints fractured along the Ti/Cu interfacial reaction layer in a brittle cleavage manner, indicating that the impulse pressuring diffusion bonding can alleviate the harmful influence of interfacial intermetallic compounds on joint performances to a certain extent, but it is infeasible in completely eliminating the negative effect of the brittle intermetallic compounds.
Impulse pressuring diffusion bonding of commercially pure titanium to 1Cr18Ni9 stainless steel was carried out using a copper interlayer in an attempt to reduce the bonding time and alleviate the detrimental effect of interfacial reaction products on bonding strength. Successful bonding has been achieved at 850 °C under a pulsed pressure of 8~20 MPa within a duration of only 120~180 s, which is notably shortened in comparison with conventional diffusion bonding. Microstructure characterization revealed that a sequence of Ti-Cu intermetallic compounds were formed at the Ti/Cu interface and the Cu/stainless steel interface was characterized by the presence of solid solution of Cu in γ Fe without any interfacial reaction products. Maximum bonding strength of 346 MPa was obtained when the joint was bonded for 120 s. Upon tensile loading, the joints fractured along the Ti/Cu interfacial reaction layer in a brittle cleavage manner, indicating that the impulse pressuring diffusion bonding can alleviate the harmful influence of interfacial intermetallic compounds on joint performances to a certain extent, but it is infeasible in completely eliminating the negative effect of the brittle intermetallic compounds.
2015, 44(5):1046-1051.
Abstract:
Stress relaxation is a significant characteristic of titanium alloys at elevated temperature and load, which is the theoretical foundation of hot sizing and heat treatment. The tensile stress relaxation behaviors of a Ti-6Al-4V sheet over the medium temperature range from 923 K to 1023 K and at several strain levels were investigated. Comprehensive analysis results indicate that the stress relaxation rate increases with the increase of temperature. The residual stress in Ti-6Al-4V alloy reaches the relaxation limit gradually after a period of relaxation. In addition, the stress relaxation limits reach the same value for the different initial stresses at the same temperature. Furthermore, an explicit constitutive equation with a cubic delay function was established and its prediction precision is as high as 97% and this has laid the foundation of process design and theoretical analysis. Finally, the implicit creep-type constitutive equation was developed to describe the stress relaxation behavior of Ti-6Al-4V alloy, and identified material parameters were input into ABAQUS to simulate a stress relaxation process of Ti-6Al-4V alloy due to the creep forming. Comparison results show that the stress change simulated is in agreement with the stress relaxation curve. It is proved that the creep-type constitutive equation is valid for the simulation of stress relaxation.
Stress relaxation is a significant characteristic of titanium alloys at elevated temperature and load, which is the theoretical foundation of hot sizing and heat treatment. The tensile stress relaxation behaviors of a Ti-6Al-4V sheet over the medium temperature range from 923 K to 1023 K and at several strain levels were investigated. Comprehensive analysis results indicate that the stress relaxation rate increases with the increase of temperature. The residual stress in Ti-6Al-4V alloy reaches the relaxation limit gradually after a period of relaxation. In addition, the stress relaxation limits reach the same value for the different initial stresses at the same temperature. Furthermore, an explicit constitutive equation with a cubic delay function was established and its prediction precision is as high as 97% and this has laid the foundation of process design and theoretical analysis. Finally, the implicit creep-type constitutive equation was developed to describe the stress relaxation behavior of Ti-6Al-4V alloy, and identified material parameters were input into ABAQUS to simulate a stress relaxation process of Ti-6Al-4V alloy due to the creep forming. Comparison results show that the stress change simulated is in agreement with the stress relaxation curve. It is proved that the creep-type constitutive equation is valid for the simulation of stress relaxation.
2015, 44(5):1052-1056.
Abstract:
To improve the charge-discharge cycle stability of V-based hydrogen storage alloys, the different contents of oxygen (O) element were introduced into the V2Ti0.5Cr0.5Ni alloy, and the structures and electrochemical properties of the V2-xTi0.5Cr0.5NiOx (x =0~0.35) alloys were investigated. The structural investigations show that the alloys with lower O content mainly consist of a V-based solid solution phase with a bcc structure and a TiNi-based secondary phase, while a new phase Ti4Ni2O is observed for the alloys with higher O content. With increasing of O content, the maximum discharge capacity for the V2-xTi0.5Cr0.5NiOx (x =0~0.35) alloy electrodes decreases from 366.8 mAh/g (x=0) to 225.3 mAh/g (x=0.35), while the cycle stability of the alloy electrodes first increases from 69.9% (x=0) to 83.7% (x=0.2) and then decreases to 76.9% (x=0.35). Moreover, the high rate discharge ability, the exchange current density and the hydrogen diffusion coefficient of the alloys first increase and then decrease with increasing of O content.
To improve the charge-discharge cycle stability of V-based hydrogen storage alloys, the different contents of oxygen (O) element were introduced into the V2Ti0.5Cr0.5Ni alloy, and the structures and electrochemical properties of the V2-xTi0.5Cr0.5NiOx (x =0~0.35) alloys were investigated. The structural investigations show that the alloys with lower O content mainly consist of a V-based solid solution phase with a bcc structure and a TiNi-based secondary phase, while a new phase Ti4Ni2O is observed for the alloys with higher O content. With increasing of O content, the maximum discharge capacity for the V2-xTi0.5Cr0.5NiOx (x =0~0.35) alloy electrodes decreases from 366.8 mAh/g (x=0) to 225.3 mAh/g (x=0.35), while the cycle stability of the alloy electrodes first increases from 69.9% (x=0) to 83.7% (x=0.2) and then decreases to 76.9% (x=0.35). Moreover, the high rate discharge ability, the exchange current density and the hydrogen diffusion coefficient of the alloys first increase and then decrease with increasing of O content.
2015, 44(5):1057-1061.
Abstract:
SiCp/Al composites of 55%~70% (volume fraction) were prepared by pressureless infiltration to investigate the reaction mechanism, morphology and the thermo-physical properties of the prepared composites. X-ray diffraction (XRD) and thermodynamic analyses show that the main interface reaction may be SiO2(s)+Al(l)+MgO(s)→MgAl2O4(s)+Si(s) in the preparation process of the composites. The enhancing of Si activity can obviously suppresses the formation of harmful interface reaction product Al4C3. Metallographic observation shows that the microstructures of the composites are homogenous and dense, infiltration defects are liable to occur in the preparation process. The thermo-physical tests show that the best thermal conductivity (TC) and the coefficient of thermal expansion (CTE) for the prepared SiCp/Al composites with less infiltration defects and dense structure are 170.2 W/(m·K) and 6.64×10-6 K-1, respectively.
SiCp/Al composites of 55%~70% (volume fraction) were prepared by pressureless infiltration to investigate the reaction mechanism, morphology and the thermo-physical properties of the prepared composites. X-ray diffraction (XRD) and thermodynamic analyses show that the main interface reaction may be SiO2(s)+Al(l)+MgO(s)→MgAl2O4(s)+Si(s) in the preparation process of the composites. The enhancing of Si activity can obviously suppresses the formation of harmful interface reaction product Al4C3. Metallographic observation shows that the microstructures of the composites are homogenous and dense, infiltration defects are liable to occur in the preparation process. The thermo-physical tests show that the best thermal conductivity (TC) and the coefficient of thermal expansion (CTE) for the prepared SiCp/Al composites with less infiltration defects and dense structure are 170.2 W/(m·K) and 6.64×10-6 K-1, respectively.
2015, 44(5):1067-1070.
Abstract:
Anatase TiO2 nanoparticles with the size of about 20 nm were synthesized using Ti(SO4)2 as titanium source and stronger ammonia water as precipitant at 240 °C for 48 h with pH=9 by a hydrothermal hydrolysis method. The samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and ultraviolet-visible absorption spectroscopy (UV-VIS). XRD analysis shows that the phase of the sample is anatase TiO2. SEM and TEM analysis confirms that with the increase of the reaction time, the size of TiO2 nanoparticles prepared without stronger ammonia water can reach nanometer grade, but its change is not obvious. With the addition of stronger ammonia water, the size of TiO2 nanoparticles becomes small noticeabley. With the further increase of pH value, its influence on the TiO2 nanoparticles size is not obvious. And UV-VIS analysis shows that the reduction in the size of anatase TiO2 nanoparticles is beneficial to the blue shift of their absorption peak.
Anatase TiO2 nanoparticles with the size of about 20 nm were synthesized using Ti(SO4)2 as titanium source and stronger ammonia water as precipitant at 240 °C for 48 h with pH=9 by a hydrothermal hydrolysis method. The samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and ultraviolet-visible absorption spectroscopy (UV-VIS). XRD analysis shows that the phase of the sample is anatase TiO2. SEM and TEM analysis confirms that with the increase of the reaction time, the size of TiO2 nanoparticles prepared without stronger ammonia water can reach nanometer grade, but its change is not obvious. With the addition of stronger ammonia water, the size of TiO2 nanoparticles becomes small noticeabley. With the further increase of pH value, its influence on the TiO2 nanoparticles size is not obvious. And UV-VIS analysis shows that the reduction in the size of anatase TiO2 nanoparticles is beneficial to the blue shift of their absorption peak.
2015, 44(5):1082-1087.
Abstract:
In order to investigate the optimal workpiece geometry of pure Ti extruded by equal channel angular pressing (ECAP) at room temperature, deformation behaviors of Ti billets were studied by means of three-dimensional (3D) finite element simulation. The optimal dimensions of pure Ti billets have been obtained by analyzing the influences of workpiece shapes and sizes on damage factor, pressing force, and strain rate distribution at the shearing band. The analytical results show that the square billet exhibits a much larger damage factor than the round billet, and also than the critical damage value of pure Ti materials, which suggests that the square billet is hard to make deformation and prone to trigger surface cracks. The 3D model reveals that the round billet with a diameter of 15 mm is optimal due to the smallest damage factor, proper pressing load and relatively homogeneous strain distribution. Under the optimal workpiece geometry according to numerical simulation results, ECAP experiment of the pure Ti round billet with a diameter of 15 mm can be successfully processed at room temperature. Additionally, hardness distribution of the as-ECAPed Ti rod is homogeneous at cross-section, which is consistent with the prediction of uniform strain distribution by 3D simulation.
In order to investigate the optimal workpiece geometry of pure Ti extruded by equal channel angular pressing (ECAP) at room temperature, deformation behaviors of Ti billets were studied by means of three-dimensional (3D) finite element simulation. The optimal dimensions of pure Ti billets have been obtained by analyzing the influences of workpiece shapes and sizes on damage factor, pressing force, and strain rate distribution at the shearing band. The analytical results show that the square billet exhibits a much larger damage factor than the round billet, and also than the critical damage value of pure Ti materials, which suggests that the square billet is hard to make deformation and prone to trigger surface cracks. The 3D model reveals that the round billet with a diameter of 15 mm is optimal due to the smallest damage factor, proper pressing load and relatively homogeneous strain distribution. Under the optimal workpiece geometry according to numerical simulation results, ECAP experiment of the pure Ti round billet with a diameter of 15 mm can be successfully processed at room temperature. Additionally, hardness distribution of the as-ECAPed Ti rod is homogeneous at cross-section, which is consistent with the prediction of uniform strain distribution by 3D simulation.
2015, 44(5):1094-1098.
Abstract:
The in situ X-ray diffraction (XRD) was used during uniaxial tensile loading to study the lattice response and deformation behavior of a2 U-5.8 wt% Nb (U5.8Nb) alloy. Diffraction patterns were recorded at incremental macroscopic strains until fracture of the sample, and the XRD data were analyzed by Rietveld method and single-peak fitting. The changes regulation of lattice parameter, diffraction peak intensity and interplanar spacing with applied stress during deformation were analyzed. It is found that the elastic deformation and the twinning deformation (reorientation) coexist in the initial stage of the first yield platform. The lattice response suggests that the remarkable anisotropy of elastic limit in various directions should be the genesis of double yield curve.
The in situ X-ray diffraction (XRD) was used during uniaxial tensile loading to study the lattice response and deformation behavior of a2 U-5.8 wt% Nb (U5.8Nb) alloy. Diffraction patterns were recorded at incremental macroscopic strains until fracture of the sample, and the XRD data were analyzed by Rietveld method and single-peak fitting. The changes regulation of lattice parameter, diffraction peak intensity and interplanar spacing with applied stress during deformation were analyzed. It is found that the elastic deformation and the twinning deformation (reorientation) coexist in the initial stage of the first yield platform. The lattice response suggests that the remarkable anisotropy of elastic limit in various directions should be the genesis of double yield curve.
2015, 44(5):1099-1103.
Abstract:
Oxygen vacancies with different charge states in cubic LaAlO3 were investigated using first-principles calculation based on the density functional theory and generalized gradient approximation. In the presence of oxygen vacancy, extra level appears in the energy band gap. From the formation energies, it is found that oxygen vacancy is thermodynamically favorable under O-poor condition. Oxygen vacancies of and are the most stable charge states with the changes of the Fermi level position. Moreover, the oxygen vacancy in LaAlO3 has a negative U behavior and it is energetically favorable for the oxygen vacancy to trap two holes when the holes are injected into the oxide. Therefore, oxygen vacancy is a main source of charge traps in LaAlO3 high-k dielectric.
Oxygen vacancies with different charge states in cubic LaAlO3 were investigated using first-principles calculation based on the density functional theory and generalized gradient approximation. In the presence of oxygen vacancy, extra level appears in the energy band gap. From the formation energies, it is found that oxygen vacancy is thermodynamically favorable under O-poor condition. Oxygen vacancies of and are the most stable charge states with the changes of the Fermi level position. Moreover, the oxygen vacancy in LaAlO3 has a negative U behavior and it is energetically favorable for the oxygen vacancy to trap two holes when the holes are injected into the oxide. Therefore, oxygen vacancy is a main source of charge traps in LaAlO3 high-k dielectric.
9 Neural Network Prediction of Conversion Rate of TbFe2 Alloy Prepared by Reduction-Diffusion Process
2015, 44(5):1104-1107.
Abstract:
A BP neural network was established based on the following main experiment parameters of producing TbFe2 alloy by reduction-diffusion process: reaction temperature, holding time, quantity of Ca and particle size of Fe. A simulation was conducted, and the rate of conversion of TbFe2 alloy was predicted. The neural network was simulated and tested by 44 groups of experimental data. It can be concluded that the neural network has good performance to predict the rate of conversion of TbFe2 alloy. The design and the application of this neural network can help to shorten the periodic time of experiments, lower the experimental cost, and optimize the preparation processes.
A BP neural network was established based on the following main experiment parameters of producing TbFe2 alloy by reduction-diffusion process: reaction temperature, holding time, quantity of Ca and particle size of Fe. A simulation was conducted, and the rate of conversion of TbFe2 alloy was predicted. The neural network was simulated and tested by 44 groups of experimental data. It can be concluded that the neural network has good performance to predict the rate of conversion of TbFe2 alloy. The design and the application of this neural network can help to shorten the periodic time of experiments, lower the experimental cost, and optimize the preparation processes.
2015, 44(5):1108-1111.
Abstract:
Adopting a gradient temperature method, hexagonal-cubic mixed boron nitride films were synthesized by MW-ECR radio frequency (RF) magnetron sputtering. The binding structure, the chemical composition, and the mechanical property of the films were investigated. The results show that there is a temperature threshold of the appearance of cubic BN film, and the hardness of the film increases with the increase of deposition temperature. Compared to the conventional methods the gradient temperature method is more efficient.
Adopting a gradient temperature method, hexagonal-cubic mixed boron nitride films were synthesized by MW-ECR radio frequency (RF) magnetron sputtering. The binding structure, the chemical composition, and the mechanical property of the films were investigated. The results show that there is a temperature threshold of the appearance of cubic BN film, and the hardness of the film increases with the increase of deposition temperature. Compared to the conventional methods the gradient temperature method is more efficient.
2015, 44(5):1112-1115.
Abstract:
The hot corrosion behaviors of pure Ni, Ni-10Cr alloy and Ni-10Cr-5Al alloy (mass fractions, %, similarly hereinafter) coated with salt film of 75%Na2SO4+25%NaCl (mass fraction) were investigated at 900 °C in air. Results show that the corrosion kinetic curve of Ni-10Cr approximately follows the parabolic rate law while the corrosion kinetic curves of Ni and Ni-10Cr-5Al alloy follow the parabolic rate low by stages. The corrosion mass gain of Ni-10Cr is minimum, the one of Ni-10Cr-5Al comes next and that of pure Ni is maximum. The corrosion products of Ni-10Cr-5Al can be divided into three layers, of which the outermost layer is mainly composed of NiO, the intermediate layer consists of Cr2O3 and Al2O3 , and the internal corrosion zone contains a small amount of Cr2S3 and Al2S3. For Ni-10Cr alloy, the corrosion products consist of three layers, the outermost layer of NiO, the intermediate layer of noncontinuous Cr2O3 and the internal corrosion zone with a small amount of Cr2S3. The corrosion scales of Ni-10Cr-5Al and Ni-10Cr are both loose and porous due to the existence of NaCl.
The hot corrosion behaviors of pure Ni, Ni-10Cr alloy and Ni-10Cr-5Al alloy (mass fractions, %, similarly hereinafter) coated with salt film of 75%Na2SO4+25%NaCl (mass fraction) were investigated at 900 °C in air. Results show that the corrosion kinetic curve of Ni-10Cr approximately follows the parabolic rate law while the corrosion kinetic curves of Ni and Ni-10Cr-5Al alloy follow the parabolic rate low by stages. The corrosion mass gain of Ni-10Cr is minimum, the one of Ni-10Cr-5Al comes next and that of pure Ni is maximum. The corrosion products of Ni-10Cr-5Al can be divided into three layers, of which the outermost layer is mainly composed of NiO, the intermediate layer consists of Cr2O3 and Al2O3 , and the internal corrosion zone contains a small amount of Cr2S3 and Al2S3. For Ni-10Cr alloy, the corrosion products consist of three layers, the outermost layer of NiO, the intermediate layer of noncontinuous Cr2O3 and the internal corrosion zone with a small amount of Cr2S3. The corrosion scales of Ni-10Cr-5Al and Ni-10Cr are both loose and porous due to the existence of NaCl.
2015, 44(5):1116-1118.
Abstract:
6061-O and 6061-T4 aluminum alloy sheets with 0.04 inch (1.02 mm) nominal thickness are widely used in the aviation industry. After argon arc welding, the sheets were subjected to a solution heat treatment followed by a quenching and tempering treatment (T62 treatment), afterwards fabricated to specimens. The fatigue tests were carried out at 60 Hz, stress ratio of 0.1 both in atmosphere and water at room temperature, and loading direction was perpendicular to welding bead. The fracture morphologies were examined by scanning electron microscopy (SEM). The results show that the fatigue life in water is considerably decreased, and fatigue striation is not so clear compared with that in atmosphere, which might be attributed to the fact that the oxygen content on the fracture surface tested in water after dry treatment is much higher than that in atmosphere.
6061-O and 6061-T4 aluminum alloy sheets with 0.04 inch (1.02 mm) nominal thickness are widely used in the aviation industry. After argon arc welding, the sheets were subjected to a solution heat treatment followed by a quenching and tempering treatment (T62 treatment), afterwards fabricated to specimens. The fatigue tests were carried out at 60 Hz, stress ratio of 0.1 both in atmosphere and water at room temperature, and loading direction was perpendicular to welding bead. The fracture morphologies were examined by scanning electron microscopy (SEM). The results show that the fatigue life in water is considerably decreased, and fatigue striation is not so clear compared with that in atmosphere, which might be attributed to the fact that the oxygen content on the fracture surface tested in water after dry treatment is much higher than that in atmosphere.
2015, 44(5):1129-1133.
Abstract:
To better understand the effect of tin on the corrosion behavior of Zr-Sn-Nb-Fe alloy, Zr-XSn-1Nb-0.3Fe (X=0 wt%~1.5 wt%) sheets were prepared and corroded by a static autoclave in 360 oC/18.6 MPa pure water, 360 oC/18.6 MPa/0.01 mol·L-1 LiOH aqueous solution and 400 oC/10.3 MPa superheated steam. The characteristics of the precipitates were analyzed by TEM, the crystal structure transformation of the oxide film during corrosion and its effect on the corrosion resistance of alloys were characterized by laser-Raman spectrometry. Results show that the corrosion mass gain decreases when tin content decreases from 1.5 wt% to 0.6 wt%. As tin content decreases from 0.6 wt% to 0, the corrosion mass gain hardly changes in pure water and steam. However, it is found that the corrosion mass gain increases in LiOH aqueous solution. The microstructural characteristic indicates that the crystal structure and mean size of the precipitates in all tested alloys are almost the same even though the tin considerably changes, but the area fraction of precipitates in the alloy decreases with the tin content increasing when all of the samples are heat-treated in the same condition. It is observed that the oxide film of alloys consists mostly of m-ZrO2 and t-ZrO2 when alloys are corroded in a short time. With the prolongation of corrosion time, the t-ZrO2 transforms to m-ZrO2. The higher the transformation rate, the lower the t-ZrO2 content in the oxide film and the higher the corrosion rate of alloy specimens.
To better understand the effect of tin on the corrosion behavior of Zr-Sn-Nb-Fe alloy, Zr-XSn-1Nb-0.3Fe (X=0 wt%~1.5 wt%) sheets were prepared and corroded by a static autoclave in 360 oC/18.6 MPa pure water, 360 oC/18.6 MPa/0.01 mol·L-1 LiOH aqueous solution and 400 oC/10.3 MPa superheated steam. The characteristics of the precipitates were analyzed by TEM, the crystal structure transformation of the oxide film during corrosion and its effect on the corrosion resistance of alloys were characterized by laser-Raman spectrometry. Results show that the corrosion mass gain decreases when tin content decreases from 1.5 wt% to 0.6 wt%. As tin content decreases from 0.6 wt% to 0, the corrosion mass gain hardly changes in pure water and steam. However, it is found that the corrosion mass gain increases in LiOH aqueous solution. The microstructural characteristic indicates that the crystal structure and mean size of the precipitates in all tested alloys are almost the same even though the tin considerably changes, but the area fraction of precipitates in the alloy decreases with the tin content increasing when all of the samples are heat-treated in the same condition. It is observed that the oxide film of alloys consists mostly of m-ZrO2 and t-ZrO2 when alloys are corroded in a short time. With the prolongation of corrosion time, the t-ZrO2 transforms to m-ZrO2. The higher the transformation rate, the lower the t-ZrO2 content in the oxide film and the higher the corrosion rate of alloy specimens.
2015, 44(5):1139-1143.
Abstract:
Based on the empirical electron theory of solids and molecules(EET), the valence electron structures(VESs) of TiB and TiB2 were calculated, and then the relationship between their VESs and boronizing layer hardening of TC4 alloy was analyzed. The B-B bonds of TiB and TiB2 on boronizing layer are the strongest, and they are far bigger than that of the strongest bond of the substrate. The strongest bond of TiB2 (=0.555 4) is stronger than that of TiB (=0.404 2), so the strengthening effect of TiB2 on substrate is stronger. From the number of atom state group of phases σN, we can know that the stability of TiB2 is far bigger than that of TiB. The space distribution of the covalence bonds decides that it is easy for TiB to grow along the [010] direction and form short threadiness, while for TiB2 it is easy to form high symmetry granulous or globular shape, therefore TiB2 is better than TiB at substrate hardening and the improvement of wear-resisting. From the forming-bond ability of phases F, we can know that the amount of TiB is more than that of TiB2 on the boronizing layer.
Based on the empirical electron theory of solids and molecules(EET), the valence electron structures(VESs) of TiB and TiB2 were calculated, and then the relationship between their VESs and boronizing layer hardening of TC4 alloy was analyzed. The B-B bonds of TiB and TiB2 on boronizing layer are the strongest, and they are far bigger than that of the strongest bond of the substrate. The strongest bond of TiB2 (=0.555 4) is stronger than that of TiB (=0.404 2), so the strengthening effect of TiB2 on substrate is stronger. From the number of atom state group of phases σN, we can know that the stability of TiB2 is far bigger than that of TiB. The space distribution of the covalence bonds decides that it is easy for TiB to grow along the [010] direction and form short threadiness, while for TiB2 it is easy to form high symmetry granulous or globular shape, therefore TiB2 is better than TiB at substrate hardening and the improvement of wear-resisting. From the forming-bond ability of phases F, we can know that the amount of TiB is more than that of TiB2 on the boronizing layer.
2015, 44(5):1149-1153.
Abstract:
High temperature tensile creep behavior of N36 zirconium alloy cladding tubes in the temperature range from 593 K to 723 K and the stress range from 60 MPa to 160 MPa was investigated. The results show that there are three distinct rate-controlled creep mechanisms for N36 zirconium alloy cladding tubes. In the temperature range from 593 K to 673 K the stress exponent n is ~3 and creep activation Q≈150 kJ·mol-1 is found in the low applied stress region, which means the dominant process is viscous-glide-controlled. But in the high applied stress region the stress exponent n is 5~6 and the creep activation Q≈170 kJ·mol-1 is found, which obeys the typical five power law creep mechanism controlled by the climb of edge dislocations. At 723 K and with high applied stress the power law breakdown appears and the exact mechanism is not clear by now. In the test condition N36 zirconium alloy cladding tubes exhibit a type of creep behavior similar to that noted in class-I(A) alloys, which is very different from zircaloy.
High temperature tensile creep behavior of N36 zirconium alloy cladding tubes in the temperature range from 593 K to 723 K and the stress range from 60 MPa to 160 MPa was investigated. The results show that there are three distinct rate-controlled creep mechanisms for N36 zirconium alloy cladding tubes. In the temperature range from 593 K to 673 K the stress exponent n is ~3 and creep activation Q≈150 kJ·mol-1 is found in the low applied stress region, which means the dominant process is viscous-glide-controlled. But in the high applied stress region the stress exponent n is 5~6 and the creep activation Q≈170 kJ·mol-1 is found, which obeys the typical five power law creep mechanism controlled by the climb of edge dislocations. At 723 K and with high applied stress the power law breakdown appears and the exact mechanism is not clear by now. In the test condition N36 zirconium alloy cladding tubes exhibit a type of creep behavior similar to that noted in class-I(A) alloys, which is very different from zircaloy.
2015, 44(5):1154-1158.
Abstract:
The parameter characterizing and estimating for room temperature creep crack tip stress-strain field of commercially pure titanium TA2 were studied by testing, theoretical analysis and finite element (FE) simulation. Testing results indicate that for commercially pure titanium TA2, the primary creep will occur at room temperature. Theoretical analysis and FE simulation demonstrate that the stress-strain field at the crack tip under loading hold period is HRR field. Thus, the time dependent J-integral was proposed to characterize this HRR field, and an estimation method for the J-integral was provided. Then the FE simulation was used to obtain the time dependent J-integral of TA2 CT specimen under the condition of room temperature creep, which shows that J-integral may appropriately characterize the crack tip stress-stain field. At last, the J-integral obtained by FE simulation and the estimation method were compared, which proves the effectiveness and accuracy of the estimation method.
The parameter characterizing and estimating for room temperature creep crack tip stress-strain field of commercially pure titanium TA2 were studied by testing, theoretical analysis and finite element (FE) simulation. Testing results indicate that for commercially pure titanium TA2, the primary creep will occur at room temperature. Theoretical analysis and FE simulation demonstrate that the stress-strain field at the crack tip under loading hold period is HRR field. Thus, the time dependent J-integral was proposed to characterize this HRR field, and an estimation method for the J-integral was provided. Then the FE simulation was used to obtain the time dependent J-integral of TA2 CT specimen under the condition of room temperature creep, which shows that J-integral may appropriately characterize the crack tip stress-stain field. At last, the J-integral obtained by FE simulation and the estimation method were compared, which proves the effectiveness and accuracy of the estimation method.
2015, 44(5):1169-1172.
Abstract:
The isothermal oxidation behavior of packed aluminide coatings of Ni-Cr-W superalloy at 1100 oC was investigated. Results from scanning electron microscopy and X-ray diffraction indicate that the oxidation dynamics curve of packed aluminide coatings can be divided into two stages: initial rapidly stage and metaphase slowly stage. Oxides on packed aluminide coatings surface have a transformation process as following: crystal θ-A12O3→equalaxial α-A12O3→α-A12O3→particle α-A12O3→particle unite α-A12O3 during the whole oxidation. During the initial stage of oxidation, carbides can be able to holdback coating degeneration caused by interdiffusion between Ni element and Al element.
The isothermal oxidation behavior of packed aluminide coatings of Ni-Cr-W superalloy at 1100 oC was investigated. Results from scanning electron microscopy and X-ray diffraction indicate that the oxidation dynamics curve of packed aluminide coatings can be divided into two stages: initial rapidly stage and metaphase slowly stage. Oxides on packed aluminide coatings surface have a transformation process as following: crystal θ-A12O3→equalaxial α-A12O3→α-A12O3→particle α-A12O3→particle unite α-A12O3 during the whole oxidation. During the initial stage of oxidation, carbides can be able to holdback coating degeneration caused by interdiffusion between Ni element and Al element.
2015, 44(5):1173-1176.
Abstract:
The flat plate specimens of nickel-base single crystal superalloy DD6 with different numbers of laser-processed cooling film holes were used to study the low cycle fatigue properties at 900 oC. The test data and SEM fracture images were analyzed. The results show that the life of single-hole specimens is ten times of that of the close-spaced holes specimens in the same experimental condition. A number of microcracks are found around the cooling film hole and the destruction of the specimens with cooling film holes is a typical multi-source rupture. The cracks propagate along the {001} planes for single-hole specimens and the middle holes of the close-spaced holes specimens, but the cracks extend along a plurality of slip plane for up and bottom holes of the specimens with close-spaced holes.
The flat plate specimens of nickel-base single crystal superalloy DD6 with different numbers of laser-processed cooling film holes were used to study the low cycle fatigue properties at 900 oC. The test data and SEM fracture images were analyzed. The results show that the life of single-hole specimens is ten times of that of the close-spaced holes specimens in the same experimental condition. A number of microcracks are found around the cooling film hole and the destruction of the specimens with cooling film holes is a typical multi-source rupture. The cracks propagate along the {001} planes for single-hole specimens and the middle holes of the close-spaced holes specimens, but the cracks extend along a plurality of slip plane for up and bottom holes of the specimens with close-spaced holes.
2015, 44(5):1177-1180.
Abstract:
A novel Cu based composite was fabricated by powder metallurgy, which was reinforced by Ti2AlN and La2O3. The study was focused on the Ti2AlN-Cu interfacial reaction and its effect on the properties of Ti2AlN-La2O3/Cu composite. The results indicate that Ti2AlN particles with a copper coating is effective for interfacial bonding, and a transition zone of 20 nm width forms between Ti2AlN and Cu matrix. In the range of sintering temperature from 880 oC to 940 oC, a reaction happens between Ti2AlN and plated copper layer. New substances, Cu(Al) and TiNx form, which is beneficial to the increasing of tensile strength, but harmful to electrical conductivity. In addition, La2O3 nanoparticles disperse in the Cu matrix which also strengthens the composite.
A novel Cu based composite was fabricated by powder metallurgy, which was reinforced by Ti2AlN and La2O3. The study was focused on the Ti2AlN-Cu interfacial reaction and its effect on the properties of Ti2AlN-La2O3/Cu composite. The results indicate that Ti2AlN particles with a copper coating is effective for interfacial bonding, and a transition zone of 20 nm width forms between Ti2AlN and Cu matrix. In the range of sintering temperature from 880 oC to 940 oC, a reaction happens between Ti2AlN and plated copper layer. New substances, Cu(Al) and TiNx form, which is beneficial to the increasing of tensile strength, but harmful to electrical conductivity. In addition, La2O3 nanoparticles disperse in the Cu matrix which also strengthens the composite.
2015, 44(5):1181-1184.
Abstract:
In order to have a deep understanding of the relationship between adiabatic shear bands and cracks in magnesium alloys, the split Hopkinson pressure bar (SHPB) was used to study the deformation localization of the hat-shaped AZ31 magnesium alloy specimen under high strain rate impacting. The microstructure and the cracking formed within the adiabatic shear band were observed by OM and SEM, and the microhardness within and around the adiabatic shear band were tested. The results demonstrate that the adiabatic shear band is formed along the maximum shear stress direction. With the increasing of the impact loading, the micro holes form along the adiabatic shear band. When the micro holes are coarsened and connect with each other the crack forms and then the specimen is broken. The micro hardness of the microstructure in the core of the adiabatic shear band is higher than that of the microstructure around the adiabatic shear band.
In order to have a deep understanding of the relationship between adiabatic shear bands and cracks in magnesium alloys, the split Hopkinson pressure bar (SHPB) was used to study the deformation localization of the hat-shaped AZ31 magnesium alloy specimen under high strain rate impacting. The microstructure and the cracking formed within the adiabatic shear band were observed by OM and SEM, and the microhardness within and around the adiabatic shear band were tested. The results demonstrate that the adiabatic shear band is formed along the maximum shear stress direction. With the increasing of the impact loading, the micro holes form along the adiabatic shear band. When the micro holes are coarsened and connect with each other the crack forms and then the specimen is broken. The micro hardness of the microstructure in the core of the adiabatic shear band is higher than that of the microstructure around the adiabatic shear band.
2015, 44(5):1191-1196.
Abstract:
In order to research the Na2MoO4 modifying mechanism of micro-arc oxidation (MAO) coating on ZL108 aluminum alloy, the alloy was treated by MAO in an electrolyte with Na2MoO4 addition of 5 kinds of concentration. Surface morphologies, Mo and O elements content on cross-section of MAO coating, valence state of Mo and O element, phase composition and corrosion resistance of MAO coating were analyzed by SEM, EDS, XPS, XRD and polarization curve, respectively. The results show that the oxidation voltage declines with the Na2MoO4 concentration increasing. The MoO42- begins to transform to MoO2 when the temperature of micro-arc discharges area is above 1823.84 K, and MoO2 strains the formation of porous coating on the surface of MAO coating. Therefore, the compactness, thickness and corrosion resistance of MAO coating are improved. In addition, the effect of Na2MoO4 concentration on the phase composition of MAO coating is not obvious.
In order to research the Na2MoO4 modifying mechanism of micro-arc oxidation (MAO) coating on ZL108 aluminum alloy, the alloy was treated by MAO in an electrolyte with Na2MoO4 addition of 5 kinds of concentration. Surface morphologies, Mo and O elements content on cross-section of MAO coating, valence state of Mo and O element, phase composition and corrosion resistance of MAO coating were analyzed by SEM, EDS, XPS, XRD and polarization curve, respectively. The results show that the oxidation voltage declines with the Na2MoO4 concentration increasing. The MoO42- begins to transform to MoO2 when the temperature of micro-arc discharges area is above 1823.84 K, and MoO2 strains the formation of porous coating on the surface of MAO coating. Therefore, the compactness, thickness and corrosion resistance of MAO coating are improved. In addition, the effect of Na2MoO4 concentration on the phase composition of MAO coating is not obvious.
2015, 44(5):1214-1218.
Abstract:
Using titanium hydride powder and magnesium powder as starting materials, pure titanium was prepared by the press-sintering process. Magnesium was used as the addition and its effect on the sintering densification behavior of titanium hydride were studied. The results show that a bit of magnesium could accelerate the densification process, while excessive magnesium decreases the relative density. The optimal amount of magnesium is 0.5 wt% and the relative density is improved from 96.5% to 98.7%. By investigating the sintering kinetics, thermodynamics and kinetics of titanium dioxide reduction by magnesium and EDS element mapping analysis of the sintered sample, the densification mechanism was clarified. In the sintering process, magnesium volatilizes from the green body and the magnesium vapor reduces the oxidation film of the powder particles, thus improving the sintering activity and enhancing the sintered density.
Using titanium hydride powder and magnesium powder as starting materials, pure titanium was prepared by the press-sintering process. Magnesium was used as the addition and its effect on the sintering densification behavior of titanium hydride were studied. The results show that a bit of magnesium could accelerate the densification process, while excessive magnesium decreases the relative density. The optimal amount of magnesium is 0.5 wt% and the relative density is improved from 96.5% to 98.7%. By investigating the sintering kinetics, thermodynamics and kinetics of titanium dioxide reduction by magnesium and EDS element mapping analysis of the sintered sample, the densification mechanism was clarified. In the sintering process, magnesium volatilizes from the green body and the magnesium vapor reduces the oxidation film of the powder particles, thus improving the sintering activity and enhancing the sintered density.
2015, 44(5):1219-1223.
Abstract:
Silver copper oxide composites were prepared by the in-situ synthesized method. The relationship between the number of tests and the contact resistance under different conditions of DC arc were studied by a contact resistance parameter tester. The sample surface morphology changes were analyzed by scanning electron microscopy (SEM). The results show that the contact resistance of AgCuO electrical contact material presents an elevated trend in the early time, then decreases at a certain number of test times and reaches a saturation value at last. In the experiment, the contact resistance of AgCuO electrical contact material decreases as the test current increases. When the current reaches 25 A, the contact resistance of AgCuO electrical contact materials exhibits the lowest value, and with the increase in the number of tests, the contact resistance changes a little, the material exhibits excellent stability in contact resistance. By analyzing the contact morphology features after arc erosion, it is found that there are obvious differences between the anode and the cathode contact surface morphology, the surface of the anode showing a concave convex shape with some cracks and pores and the cathode contact surface showing paste peak.
Silver copper oxide composites were prepared by the in-situ synthesized method. The relationship between the number of tests and the contact resistance under different conditions of DC arc were studied by a contact resistance parameter tester. The sample surface morphology changes were analyzed by scanning electron microscopy (SEM). The results show that the contact resistance of AgCuO electrical contact material presents an elevated trend in the early time, then decreases at a certain number of test times and reaches a saturation value at last. In the experiment, the contact resistance of AgCuO electrical contact material decreases as the test current increases. When the current reaches 25 A, the contact resistance of AgCuO electrical contact materials exhibits the lowest value, and with the increase in the number of tests, the contact resistance changes a little, the material exhibits excellent stability in contact resistance. By analyzing the contact morphology features after arc erosion, it is found that there are obvious differences between the anode and the cathode contact surface morphology, the surface of the anode showing a concave convex shape with some cracks and pores and the cathode contact surface showing paste peak.
2015, 44(5):1229-1233.
Abstract:
Ni60A cladding layers with different contents of rare earth CeO2 were prepared on the surface of 6063 aluminum alloys using a laser cladding technique. Then the microstructure and hardness of CeO2+Ni60A cladding layers were analyzed. The optimal content of rare earth was selected, and the wear resistance of CeO2+Ni60A cladding layers was analyzed. The results show that Ni60A cladding layers with less than 2% CeO2 are prone to pores, but more than 2% are prone to cracks. When 2% CeO2 is added, the cladding layer has better quality and least microstructure deficiencies, and also higher surface hardness. Rare earth content should not be more than 4%, and an excess of CeO2 has little effect on improving the hardness of the cladding layers; when the CeO2 content ranges from 0% to 2%, the hardness increases significantly with the increases of content. In the same abrasive wear conditions, the wear resistance of 2% CeO2 + Ni60A cladding layer is 7.1 times as that of aluminum alloy substrate, and 1.6 times of that of Ni60A cladding layer. The surface friction coefficient can be greatly reduced by laser cladding Ni60A layer, and adding Ce can improve the stability of the cladding layer friction coefficient, thereby improving the wear resistance.
Ni60A cladding layers with different contents of rare earth CeO2 were prepared on the surface of 6063 aluminum alloys using a laser cladding technique. Then the microstructure and hardness of CeO2+Ni60A cladding layers were analyzed. The optimal content of rare earth was selected, and the wear resistance of CeO2+Ni60A cladding layers was analyzed. The results show that Ni60A cladding layers with less than 2% CeO2 are prone to pores, but more than 2% are prone to cracks. When 2% CeO2 is added, the cladding layer has better quality and least microstructure deficiencies, and also higher surface hardness. Rare earth content should not be more than 4%, and an excess of CeO2 has little effect on improving the hardness of the cladding layers; when the CeO2 content ranges from 0% to 2%, the hardness increases significantly with the increases of content. In the same abrasive wear conditions, the wear resistance of 2% CeO2 + Ni60A cladding layer is 7.1 times as that of aluminum alloy substrate, and 1.6 times of that of Ni60A cladding layer. The surface friction coefficient can be greatly reduced by laser cladding Ni60A layer, and adding Ce can improve the stability of the cladding layer friction coefficient, thereby improving the wear resistance.
2015, 44(5):1239-1243.
Abstract:
LiFePO4/C composite cathode material was prepared with polyacrylic acid as carbon source by a method combining a low temperature reduction-inserted lithium and polymer pyrolysis, in which FePO4 was reduced with lithium insertion and a simultaneous chemical coating occurred with carbon-containing polymer. The technique simplifies the preparation process and reduces the production cost. The phase structures, lattice parameters, morphologies and electrochemical properties of LiFePO4/C samples synthesized at different calcination temperatures were characterized by XRD, SEM and galvanostatic charge-discharge test. The results show that the maximum discharge capacity and best cycling stability of present products are obtained when the calcination temperature is 600 oC at 0.1C rate. The initial discharge specific capacities of resulting LiFePO4/C composite material reaches 141.3 mAh/g with a coulombic efficiency of 98.0% at 0.1C rate, and the capacity retention rate is 108.3% after 100 cycles.
LiFePO4/C composite cathode material was prepared with polyacrylic acid as carbon source by a method combining a low temperature reduction-inserted lithium and polymer pyrolysis, in which FePO4 was reduced with lithium insertion and a simultaneous chemical coating occurred with carbon-containing polymer. The technique simplifies the preparation process and reduces the production cost. The phase structures, lattice parameters, morphologies and electrochemical properties of LiFePO4/C samples synthesized at different calcination temperatures were characterized by XRD, SEM and galvanostatic charge-discharge test. The results show that the maximum discharge capacity and best cycling stability of present products are obtained when the calcination temperature is 600 oC at 0.1C rate. The initial discharge specific capacities of resulting LiFePO4/C composite material reaches 141.3 mAh/g with a coulombic efficiency of 98.0% at 0.1C rate, and the capacity retention rate is 108.3% after 100 cycles.
2015, 44(5):1244-1248.
Abstract:
A series of green-emitting phosphors NaLa1-x(MoO4)2:Tb3+x (x=0.02, 0.1, 0.15) were prepared by a microwave-assisted sol-gel method. X-ray diffraction and fluorescence spectrophotometer were used to analyze the phase structure and luminescent properties of as-synthesized phosphors, respectively. The results show that NaLa(MoO4)2:Tb3+ phosphors possess a tetragonal crystal structure similar to that of NaLa(MoO4)2. The excitation spectrum of NaLa(MoO4)2:Tb3+ is a broad band between 250 nm and 350 nm, and the main peak is at 300 nm. The emission spectrum is composed of a series of sharp lines. The main emission peak is at 544 nm, which is ascribed to the transition of 5D4–7F5. The luminescent intensity of NaLa(MoO4)2:Tb3+ increases with the increase of Tb3+ content, and reaches the maximum when the content of Tb3+ is 10 mol%, and then decreases with the further increase of Tb3+ content. The concentration quenching is caused by the interaction of electric dipole-electric dipole of Tb3+ according to the Dexter theory. Moreover, the luminescent intensity of NaLa(MoO4)2:Tb3+ can be greatly enhanced with incorporation of SO42-.
A series of green-emitting phosphors NaLa1-x(MoO4)2:Tb3+x (x=0.02, 0.1, 0.15) were prepared by a microwave-assisted sol-gel method. X-ray diffraction and fluorescence spectrophotometer were used to analyze the phase structure and luminescent properties of as-synthesized phosphors, respectively. The results show that NaLa(MoO4)2:Tb3+ phosphors possess a tetragonal crystal structure similar to that of NaLa(MoO4)2. The excitation spectrum of NaLa(MoO4)2:Tb3+ is a broad band between 250 nm and 350 nm, and the main peak is at 300 nm. The emission spectrum is composed of a series of sharp lines. The main emission peak is at 544 nm, which is ascribed to the transition of 5D4–7F5. The luminescent intensity of NaLa(MoO4)2:Tb3+ increases with the increase of Tb3+ content, and reaches the maximum when the content of Tb3+ is 10 mol%, and then decreases with the further increase of Tb3+ content. The concentration quenching is caused by the interaction of electric dipole-electric dipole of Tb3+ according to the Dexter theory. Moreover, the luminescent intensity of NaLa(MoO4)2:Tb3+ can be greatly enhanced with incorporation of SO42-.
2015, 44(5):1249-1253.
Abstract:
With polymethyl methacrylate (PMMA) prepared by dispersion polymerization as sacrifice template, CeO2/PMMA composite microspheres were prepared by inorganic precursor homogeneous precipitation and self-assembly. The CeO2 hollow nanospheres were obtained after the polymer sphere template was removed through calcination at a suitable temperature. Scanning electron microscope, transmission electron microscope, fourier transform infrared spectroscopy, X-ray photoelectron spectrum, X-ray diffraction and thermogravimetry were employed to characterize the structure and morphology of the CeO2 hollow nanospheres. The results reveal that the face-centered cubic-phase CeO2 hollow nanospheres with a diameter of about 0.9 μm as well as the thin shell thickness about 40 nm are prepared. It indicates that adding CeO2 hollow nanospheres in butyl rubber as packing materials can obviously improve its low frequency damping capacity in different frequency (0~180 Hz).
With polymethyl methacrylate (PMMA) prepared by dispersion polymerization as sacrifice template, CeO2/PMMA composite microspheres were prepared by inorganic precursor homogeneous precipitation and self-assembly. The CeO2 hollow nanospheres were obtained after the polymer sphere template was removed through calcination at a suitable temperature. Scanning electron microscope, transmission electron microscope, fourier transform infrared spectroscopy, X-ray photoelectron spectrum, X-ray diffraction and thermogravimetry were employed to characterize the structure and morphology of the CeO2 hollow nanospheres. The results reveal that the face-centered cubic-phase CeO2 hollow nanospheres with a diameter of about 0.9 μm as well as the thin shell thickness about 40 nm are prepared. It indicates that adding CeO2 hollow nanospheres in butyl rubber as packing materials can obviously improve its low frequency damping capacity in different frequency (0~180 Hz).
2015, 44(5):1254-1258.
Abstract:
Based on TZM molybdenum alloy, La-TZM alloy sheets, with solid-solid doping of rare earth La2O3 or liquid-solid doping of La(NO3)3, were manufactured by sintering, hot rolling, warm rolling and cold rolling. The powder morphology, microstructures of sintering compact and fracture morphology of the alloy sheets were observed by SEM, and the alloy powder particle size and alloy composition were analyzed by particle size distribution and EDS, respectively. The results show that the distribution of the second phase in the La(NO3)3 doped TZM alloy sheets is more uniform than that in La2O3 doped TZM alloy sheets. The grain size of La(NO3)3 doped TZM alloy is finer. Besides, the tensile strength of La(NO3)3 doped TZM alloy is much higher than that of La2O3 doped alloy, which increases by 10.9%.
Based on TZM molybdenum alloy, La-TZM alloy sheets, with solid-solid doping of rare earth La2O3 or liquid-solid doping of La(NO3)3, were manufactured by sintering, hot rolling, warm rolling and cold rolling. The powder morphology, microstructures of sintering compact and fracture morphology of the alloy sheets were observed by SEM, and the alloy powder particle size and alloy composition were analyzed by particle size distribution and EDS, respectively. The results show that the distribution of the second phase in the La(NO3)3 doped TZM alloy sheets is more uniform than that in La2O3 doped TZM alloy sheets. The grain size of La(NO3)3 doped TZM alloy is finer. Besides, the tensile strength of La(NO3)3 doped TZM alloy is much higher than that of La2O3 doped alloy, which increases by 10.9%.
2015, 44(5):1259-1263.
Abstract:
Nano-Al2O3 is a promising reinforcing material of Cu based nano-composites due to its unique mechanical properties. However, the wetting property of Cu matrix and nano-Al2O3 is poor. The wetting property and the interfacial strength between nano-Al2O3 and Cu matrix would be improved through electroless plating a Cu film on nano-Al2O3 powders. Effects of key factors of complexing agent and reducing agent in bath, bath temperature and bath operating condition on the electroless plating process as well as the quality of the Cu film were studied by SEM, TEM, XRD and EDS. The plating process was then optimized, and the Cu coated nano-Al2O3 composite powders with uniform size and good dispersion were finally obtained. All these work will construct a steady base for the fabrication of A12O3/Cu nano-composites.
Nano-Al2O3 is a promising reinforcing material of Cu based nano-composites due to its unique mechanical properties. However, the wetting property of Cu matrix and nano-Al2O3 is poor. The wetting property and the interfacial strength between nano-Al2O3 and Cu matrix would be improved through electroless plating a Cu film on nano-Al2O3 powders. Effects of key factors of complexing agent and reducing agent in bath, bath temperature and bath operating condition on the electroless plating process as well as the quality of the Cu film were studied by SEM, TEM, XRD and EDS. The plating process was then optimized, and the Cu coated nano-Al2O3 composite powders with uniform size and good dispersion were finally obtained. All these work will construct a steady base for the fabrication of A12O3/Cu nano-composites.
2015, 44(5):1264-1268.
Abstract:
In order to improve the wear resistance of surfacing layer of 4043 aluminum welding wires, Mg and Sr were added based on the chemical composition of traditional 4043 aluminum welding wires and the surfacing layer from obtained Al-Si-Mg-Sr welding wires were heat treated. The effects of Mg, Sr and heat treatment on the wear resistance of the surfacing layer were studied. The results show that the morphology of eutectic silicon particles could be changed by Sr and the strengthening phase Mg2Si appears with the addition of Mg. Meanwhile eutectic silicon particles are spheroidized and their binding ability with the matrix is intensified after the reasonable heat treatment. Therefore, Sr, Mg and heat treatment improve significantly the wear resistance of the surfacing layer together.
In order to improve the wear resistance of surfacing layer of 4043 aluminum welding wires, Mg and Sr were added based on the chemical composition of traditional 4043 aluminum welding wires and the surfacing layer from obtained Al-Si-Mg-Sr welding wires were heat treated. The effects of Mg, Sr and heat treatment on the wear resistance of the surfacing layer were studied. The results show that the morphology of eutectic silicon particles could be changed by Sr and the strengthening phase Mg2Si appears with the addition of Mg. Meanwhile eutectic silicon particles are spheroidized and their binding ability with the matrix is intensified after the reasonable heat treatment. Therefore, Sr, Mg and heat treatment improve significantly the wear resistance of the surfacing layer together.
2015, 44(5):1269-1272.
Abstract:
The nanoscale cerium (IV) oxide with oxygen-storage capacity was prepared by chemical precipitation. The influence of calcination temperature on phase structure was evaluated by X-ray diffraction. The mass change accompanied with the process of the precipitate converted to the oxide was analyzed by TG. In addition, the synthesized cerium (IV) oxide as oxygen-storage material was further characterized by OSC, H2-TPR and BET. The results suggest that the prepared cerium oxide is nano-scale mesoporous material with good tolerance of high temperature aging and good redox potential. Besides, oxygen storage and release capability loss is attributed to high calcination temperature. The synthesized material has large specific surface area and appropriate average pore size. The cubic fluorite structure and porous structure are kept perfectly even after calcination at 1000 oC.
The nanoscale cerium (IV) oxide with oxygen-storage capacity was prepared by chemical precipitation. The influence of calcination temperature on phase structure was evaluated by X-ray diffraction. The mass change accompanied with the process of the precipitate converted to the oxide was analyzed by TG. In addition, the synthesized cerium (IV) oxide as oxygen-storage material was further characterized by OSC, H2-TPR and BET. The results suggest that the prepared cerium oxide is nano-scale mesoporous material with good tolerance of high temperature aging and good redox potential. Besides, oxygen storage and release capability loss is attributed to high calcination temperature. The synthesized material has large specific surface area and appropriate average pore size. The cubic fluorite structure and porous structure are kept perfectly even after calcination at 1000 oC.
2015, 44(5):1277-1280.
Abstract:
To improve the laser deposition repair quality of BT20 titanium alloy, a magnetic field device was designed and introduced to the laser repair system. The effects of magnetic field intensity on the macro morphologies, microstructures and micro-hardness of the laser repaired zone were studied. The results show that there is a dense metallurgical bond between the repaired zone and the substrate under the magnetic field, and flat surface can be gained with few powders. And also, the repaired zone is composed of prior β grain with α/β lamellae in it. With the increasing of magnetic field, the α lamellae length declines and its thickness is 0.4~0.5 μm. The micro-hardness of the repaired zone improves with the increasing of magnetic field intensity, but it tends to be homogenization in certain parameters. It indicates that rotating magnetic field reduces enrichment of solute, and then decreases β→α phase transformation driving force. Hence, α lamellae precipitation needs high degree of supercooling, which lead to a higher nucleation rate, resulting in finer microstructures and improved mechanical property.
To improve the laser deposition repair quality of BT20 titanium alloy, a magnetic field device was designed and introduced to the laser repair system. The effects of magnetic field intensity on the macro morphologies, microstructures and micro-hardness of the laser repaired zone were studied. The results show that there is a dense metallurgical bond between the repaired zone and the substrate under the magnetic field, and flat surface can be gained with few powders. And also, the repaired zone is composed of prior β grain with α/β lamellae in it. With the increasing of magnetic field, the α lamellae length declines and its thickness is 0.4~0.5 μm. The micro-hardness of the repaired zone improves with the increasing of magnetic field intensity, but it tends to be homogenization in certain parameters. It indicates that rotating magnetic field reduces enrichment of solute, and then decreases β→α phase transformation driving force. Hence, α lamellae precipitation needs high degree of supercooling, which lead to a higher nucleation rate, resulting in finer microstructures and improved mechanical property.
2015, 44(5):1281-1284.
Abstract:
Experiments of vacuum annealing were carried out for nanoparticles of TiAl intermetallic compound prepared by the flow-levitation method. And the effect of annealing parameters on the phase transformation of TiAl alloy was investigated by X-ray diffraction analysis. The results show that more g-TiAl phase is transformed from a2-Ti3Al phase with the increasing of annealing temperature and time. And the grain size of two phases increases accordingly. This phase transformation is promoted after nanoparticles are compressed into a bulk by vacuum-pressing. The nanocrystalline alloy with pure g-TiAl phase is obtained after the bulk compressed from mixed phase nanoparticles is vacuum-annealed.
Experiments of vacuum annealing were carried out for nanoparticles of TiAl intermetallic compound prepared by the flow-levitation method. And the effect of annealing parameters on the phase transformation of TiAl alloy was investigated by X-ray diffraction analysis. The results show that more g-TiAl phase is transformed from a2-Ti3Al phase with the increasing of annealing temperature and time. And the grain size of two phases increases accordingly. This phase transformation is promoted after nanoparticles are compressed into a bulk by vacuum-pressing. The nanocrystalline alloy with pure g-TiAl phase is obtained after the bulk compressed from mixed phase nanoparticles is vacuum-annealed.
2015, 44(5):1289-1292.
Abstract:
A new method of directional processing for CdGeAs2 (CGA) crystal was presented. Based on the cleavage plans of CGA single crystals combined with standard pole figure and the X-ray diffraction pattern, the c axis of the single crystal can be quickly obtained by this new method. Using this method combined with directional cutting, grinding and polishing, the initial SHG devices of CGA crystals grown by an improved vertical Bridgman method through spontaneous nucleation have been fabricated. Its phase matched angle θm is 33.58o, azimuth angle φ is 0o, and the device size is 5 mm×5 mm×8 mm.
A new method of directional processing for CdGeAs2 (CGA) crystal was presented. Based on the cleavage plans of CGA single crystals combined with standard pole figure and the X-ray diffraction pattern, the c axis of the single crystal can be quickly obtained by this new method. Using this method combined with directional cutting, grinding and polishing, the initial SHG devices of CGA crystals grown by an improved vertical Bridgman method through spontaneous nucleation have been fabricated. Its phase matched angle θm is 33.58o, azimuth angle φ is 0o, and the device size is 5 mm×5 mm×8 mm.
