Volume 43,Issue 5,2014 Table of Contents
2014, 43(5):1031-1036.
Abstract:
The effect of Mn addition in aluminum anode foils for high voltage electrolytic capacitors on the pitting behavior as well as the properties of the etched foils was studied. The Mn distribution in the aluminum foils which are processed with the same rolling and annealing condition was characterized by secondary ion mass spectrometer (SIMS). The results show that the distribution of Mn along the depth of the foil varies with the addition of Mn, while the volume fraction of the cube texture keeps stable. The SIMS results also show that the segregation tendency of Mn onto the foil surface becomes stronger with the increasing of Mn content. The square corrosion pits on the foils with higher Mn content after etching on the same condition are denser and more homogeneous. Also, the specific capacitance of the etched foils after forming at 520 V increases with the increase of Mn content in the range from 2.3 μg/g to 14.7 μg/g
The effect of Mn addition in aluminum anode foils for high voltage electrolytic capacitors on the pitting behavior as well as the properties of the etched foils was studied. The Mn distribution in the aluminum foils which are processed with the same rolling and annealing condition was characterized by secondary ion mass spectrometer (SIMS). The results show that the distribution of Mn along the depth of the foil varies with the addition of Mn, while the volume fraction of the cube texture keeps stable. The SIMS results also show that the segregation tendency of Mn onto the foil surface becomes stronger with the increasing of Mn content. The square corrosion pits on the foils with higher Mn content after etching on the same condition are denser and more homogeneous. Also, the specific capacitance of the etched foils after forming at 520 V increases with the increase of Mn content in the range from 2.3 μg/g to 14.7 μg/g
2014, 43(5):1037-1040.
Abstract:
The influence of high-temperature oxidation on soft magnetic properties of Fe78Si9B13 amorphous alloy was investigated using various analysis methods. The results reveal that a 10 mm thick iron oxide layer with high resistivity can be obtained on the surface of Fe78Si9B13 amorphous ribbons by high temperature oxidation treatment. It is found that the amorphous alloy magnetization becomes harder and the saturation induction density changes after the high-temperature oxidation. The saturation induction density value changes from Bs=1.42~1.46 T without chemical oxidation, to Bs=1.29~1.38 T after high-temperature oxidation. The factors which have a great effect on the magnetization difficulties of the amorphous ribbons were discussed
The influence of high-temperature oxidation on soft magnetic properties of Fe78Si9B13 amorphous alloy was investigated using various analysis methods. The results reveal that a 10 mm thick iron oxide layer with high resistivity can be obtained on the surface of Fe78Si9B13 amorphous ribbons by high temperature oxidation treatment. It is found that the amorphous alloy magnetization becomes harder and the saturation induction density changes after the high-temperature oxidation. The saturation induction density value changes from Bs=1.42~1.46 T without chemical oxidation, to Bs=1.29~1.38 T after high-temperature oxidation. The factors which have a great effect on the magnetization difficulties of the amorphous ribbons were discussed
2014, 43(5):1041-1046.
Abstract:
The cobalt-based composite coating reinforced with in-situ synthesized multiple particles was fabricated on TA15 titanium alloy surface by transverse flow CO2 laser adopting the optimizing laser cladding process parameters to improve wear resistance and hardness in surface. X-ray diffraction (XRD), metallurgical microscope, scanning electron microscope (SEM), hardness tester and wear testing machine were used to analyze the coating. The results show that the microstructures of the coating are mainly composed of γ-Co, α-Ti solid solution and in-situ synthesized TiB2, Cr5Si3, TiC, WB, SiC, Co3Ti and NiC particles. And these multiple granular reinforced phases are dispersively distributed among the fine dendritic structures in the cladding layer. The microhardness of the cladding layer compared with that of the substrate, has been improved a lot, HV reaching about 10000 MPa which is around three times higher than that of the substrate. Compared to titanium alloy, the wear resistance of the cladding layer has been distinctly improved, and the wear rate of the cladding layer is about 1/12 of the titanium alloy. The wear mechanism of the cladding layer is a mixed type of adhesion and abrasion
The cobalt-based composite coating reinforced with in-situ synthesized multiple particles was fabricated on TA15 titanium alloy surface by transverse flow CO2 laser adopting the optimizing laser cladding process parameters to improve wear resistance and hardness in surface. X-ray diffraction (XRD), metallurgical microscope, scanning electron microscope (SEM), hardness tester and wear testing machine were used to analyze the coating. The results show that the microstructures of the coating are mainly composed of γ-Co, α-Ti solid solution and in-situ synthesized TiB2, Cr5Si3, TiC, WB, SiC, Co3Ti and NiC particles. And these multiple granular reinforced phases are dispersively distributed among the fine dendritic structures in the cladding layer. The microhardness of the cladding layer compared with that of the substrate, has been improved a lot, HV reaching about 10000 MPa which is around three times higher than that of the substrate. Compared to titanium alloy, the wear resistance of the cladding layer has been distinctly improved, and the wear rate of the cladding layer is about 1/12 of the titanium alloy. The wear mechanism of the cladding layer is a mixed type of adhesion and abrasion
2014, 43(5):1051-1055.
Abstract:
The nanostructured W-Cu powder was prepared by high-energy ball-milling. The W-Cu alloy as liner materials was fabricated by the dynamic consolidation technique. The density of the consolidated sample was 99.6% T.D. The sample was determined by EPMA, and the results show that the composition and the distribution of the elements were uniform. The sample was analyzed by XRD, and the W crystalline sizes were measured as 26 nm. The sample was machined into W-Cu alloy liners, showing good properties of machinability. The armor-piercing experiment of the W-Cu alloy liner of shaped charge without an insulating board indicates that the armor-piercing capability increases by more than 30% in comparison with the copper liner
The nanostructured W-Cu powder was prepared by high-energy ball-milling. The W-Cu alloy as liner materials was fabricated by the dynamic consolidation technique. The density of the consolidated sample was 99.6% T.D. The sample was determined by EPMA, and the results show that the composition and the distribution of the elements were uniform. The sample was analyzed by XRD, and the W crystalline sizes were measured as 26 nm. The sample was machined into W-Cu alloy liners, showing good properties of machinability. The armor-piercing experiment of the W-Cu alloy liner of shaped charge without an insulating board indicates that the armor-piercing capability increases by more than 30% in comparison with the copper liner
2014, 43(5):1073-1078.
Abstract:
A high reversible capacity Si/C composite was synthesized by a thermal pyrolysis of citric acid embedded with fine graphite and silicon powders. The silicon was produced via an in-situ redox reaction between Mg and SiO. The structure, the morphology and the electrochemical performance of the materials were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), electrochemical tests, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Compared with the pristine silicon, the as-prepared composite exhibits much better electrochemical properties, which has a high reversible capacity of 780 mAh·g-1 at the 40th cycle with a retention up to 88.6%. The improved performance is mainly attributed to the uniform distribution of Si nanoparticles within the carbon matrix with buffering effect and excellent electric conductivity.
A high reversible capacity Si/C composite was synthesized by a thermal pyrolysis of citric acid embedded with fine graphite and silicon powders. The silicon was produced via an in-situ redox reaction between Mg and SiO. The structure, the morphology and the electrochemical performance of the materials were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), electrochemical tests, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Compared with the pristine silicon, the as-prepared composite exhibits much better electrochemical properties, which has a high reversible capacity of 780 mAh·g-1 at the 40th cycle with a retention up to 88.6%. The improved performance is mainly attributed to the uniform distribution of Si nanoparticles within the carbon matrix with buffering effect and excellent electric conductivity.
2014, 43(5):1079-1083.
Abstract:
The formation energy, the geometric structure, the electronic structure and the optical properties of pure and Si-doped orthorhombic SrHfO3 with Si substituting Hf were studied by the first-principles method using plane-wave ultra-soft pseudo-potential calculation based on density functional theory. The negative formation energy results show the reactions from single elements to Si-doped SrHfO3 are energetically favorable and that Si prefers entering the Hf sites rather than the Sr sites. The calculated equilibrium lattice constants of pure SrHfO3 are in good agreement with previous experimental and theoretical results, and the substitution of Si for Hf results in a decrease in the lattice constants. The band structure indicates the band gap decreases after introduction of Si to Hf site. The Mulliken analysis and charge densities suggest that the Hf-O bond is mainly covalent, and the Sr-O bond is mainly ionic in Si-doped SrHfO3. The dielectric functions, the reflectivity, the absorption coefficient, the refractive index, and the energy-loss spectrum were also calculated to get a better understanding of optical properties of Si-doped SrHfO3
The formation energy, the geometric structure, the electronic structure and the optical properties of pure and Si-doped orthorhombic SrHfO3 with Si substituting Hf were studied by the first-principles method using plane-wave ultra-soft pseudo-potential calculation based on density functional theory. The negative formation energy results show the reactions from single elements to Si-doped SrHfO3 are energetically favorable and that Si prefers entering the Hf sites rather than the Sr sites. The calculated equilibrium lattice constants of pure SrHfO3 are in good agreement with previous experimental and theoretical results, and the substitution of Si for Hf results in a decrease in the lattice constants. The band structure indicates the band gap decreases after introduction of Si to Hf site. The Mulliken analysis and charge densities suggest that the Hf-O bond is mainly covalent, and the Sr-O bond is mainly ionic in Si-doped SrHfO3. The dielectric functions, the reflectivity, the absorption coefficient, the refractive index, and the energy-loss spectrum were also calculated to get a better understanding of optical properties of Si-doped SrHfO3
2014, 43(5):1088-1091.
Abstract:
Three kinds of titanium alloying methods including low-titanium aluminum alloy addition, aluminum-titanium master alloy addition and villiaumite addition were chosen. The influences of titanium alloying methods on the microstructure and the mechanical property of Zn-Al alloy were studied. The test results show that it is effective for grain refining of Zn-Al alloy by adding titanium to the melt before casting. The low-titanium alloys addition is the most effective for grain refining of the Zn-Al alloy. The reason might be attributed to that the titanium atoms evenly spread to the whole melt rapidly under stirring action of electromagnetic field and, the better capacity of the heterogeneous nucleation of in-situ precipitating heterogeneous nucleation sites. The finer grain size increases the grain boundary areas and it causes that the grain boundary has better ability to prohibit dislocation passing through. Thus, the binding ability of the base is strengthened. The test alloy added by low-titanium aluminum alloy shows the highest tensile properties and wear resistance
Three kinds of titanium alloying methods including low-titanium aluminum alloy addition, aluminum-titanium master alloy addition and villiaumite addition were chosen. The influences of titanium alloying methods on the microstructure and the mechanical property of Zn-Al alloy were studied. The test results show that it is effective for grain refining of Zn-Al alloy by adding titanium to the melt before casting. The low-titanium alloys addition is the most effective for grain refining of the Zn-Al alloy. The reason might be attributed to that the titanium atoms evenly spread to the whole melt rapidly under stirring action of electromagnetic field and, the better capacity of the heterogeneous nucleation of in-situ precipitating heterogeneous nucleation sites. The finer grain size increases the grain boundary areas and it causes that the grain boundary has better ability to prohibit dislocation passing through. Thus, the binding ability of the base is strengthened. The test alloy added by low-titanium aluminum alloy shows the highest tensile properties and wear resistance
8 Fracture Mechanism of a Nickel-Based Single Crystal Superalloy during Creep at Moderate Temperature
2014, 43(5):1092-1098.
Abstract:
By means of creep properties measurement, microstructure and fracture morphology observation, the damage and fracture mechanism of a nickel-based single crystal superalloy was investigated during creep at moderate temperature. The results show that the deformation mechanism of the alloy in the latter stage of creep is that the primary-secondary slipping systems are alternatively activated, and the initiation of the micro-crack may be generated on the interface of the cubical γ′/γ phases in the intersection regions of two slip systems. As creep goes on, the micro-crack may be propagated along the γ′/γ phase interface which is perpendicular to stress axis, to form the square cleavage plane parallel to <110> directions. Thereinto, when the propagation of the cracks on (001) plane is intersected with {111} cleavage plane which is secondary activated, it may terminate the propagation of the crack. This results in the (001) cleavage plane possessing the square-like feature. Due to that the multi-cracks may propagate on different cross-section of the alloy during creep, and the tearing edge or secondary cleavage plane form along the bigger shearing stress direction at the crack tip, the multi-cracks are connected each other until the occurrence of creep fracture. It is thought to be the main reason of the uneven and multi-level cleavage characteristics.
By means of creep properties measurement, microstructure and fracture morphology observation, the damage and fracture mechanism of a nickel-based single crystal superalloy was investigated during creep at moderate temperature. The results show that the deformation mechanism of the alloy in the latter stage of creep is that the primary-secondary slipping systems are alternatively activated, and the initiation of the micro-crack may be generated on the interface of the cubical γ′/γ phases in the intersection regions of two slip systems. As creep goes on, the micro-crack may be propagated along the γ′/γ phase interface which is perpendicular to stress axis, to form the square cleavage plane parallel to <110> directions. Thereinto, when the propagation of the cracks on (001) plane is intersected with {111} cleavage plane which is secondary activated, it may terminate the propagation of the crack. This results in the (001) cleavage plane possessing the square-like feature. Due to that the multi-cracks may propagate on different cross-section of the alloy during creep, and the tearing edge or secondary cleavage plane form along the bigger shearing stress direction at the crack tip, the multi-cracks are connected each other until the occurrence of creep fracture. It is thought to be the main reason of the uneven and multi-level cleavage characteristics.
2014, 43(5):1105-1110.
Abstract:
The high temperature oxidation of Ti-Nb alloy layer prepared by a double-glow technique was investigated. The oxidation behavior of treated TA2 was analyzed at 700, 800 and 900 oC for 100 h in air by mean of XRD, SEM and EDS. The results show that the oxidation behavior of TA2 at 700~900 oC for 100 h is improved after niobium alloying process and the effect is more pronounced at 900 oC. Cross-section morphology and composition of the treated TA2 after subjecting to oxidation for 20, 40 and 100 h at 900 oC were characterized using SEM and EDS. The upper layer is composed of the mixed oxides (Nb2O5/TiO2), which are formed by the oxidation product of high concentration niobium alloyed layer; TiO2/TiO/Nb2O5 exist in a compact intermediate layer, and the inner layer are distributed with white stripe phase rich in niobium
The high temperature oxidation of Ti-Nb alloy layer prepared by a double-glow technique was investigated. The oxidation behavior of treated TA2 was analyzed at 700, 800 and 900 oC for 100 h in air by mean of XRD, SEM and EDS. The results show that the oxidation behavior of TA2 at 700~900 oC for 100 h is improved after niobium alloying process and the effect is more pronounced at 900 oC. Cross-section morphology and composition of the treated TA2 after subjecting to oxidation for 20, 40 and 100 h at 900 oC were characterized using SEM and EDS. The upper layer is composed of the mixed oxides (Nb2O5/TiO2), which are formed by the oxidation product of high concentration niobium alloyed layer; TiO2/TiO/Nb2O5 exist in a compact intermediate layer, and the inner layer are distributed with white stripe phase rich in niobium
2014, 43(5):1143-1147.
Abstract:
TC4 titanium alloy plate was jointed by friction stir welding in air and forced cooling condition separately, and microstructure transformation characteristics in different zones of the joint were investigated by OM and TEM. The result shows that the joint consists of stir zone, thermo-mechanically affected zone and base material, and they have different microstructure characteristics as a result of different thermal cycle and plastic deformation in different zones. Base material annealed after heat rolling is characterized by primary α and β phase. Stir zone is fully lamellar α+β structure, which is mainly controlled by phase transformation from β monophase to lamellar α+β phase in air. Thermo-mechanically affected zone exhibits bimodal microstructure of equiaxed α grain and α+β lamellar microstructure. Its transformation characteristic is dynamic recrystallization and phase transformation. Stir zone is characterized by acicular martensite in forced cooling condition, which is mainly controlled by martensite transformation
TC4 titanium alloy plate was jointed by friction stir welding in air and forced cooling condition separately, and microstructure transformation characteristics in different zones of the joint were investigated by OM and TEM. The result shows that the joint consists of stir zone, thermo-mechanically affected zone and base material, and they have different microstructure characteristics as a result of different thermal cycle and plastic deformation in different zones. Base material annealed after heat rolling is characterized by primary α and β phase. Stir zone is fully lamellar α+β structure, which is mainly controlled by phase transformation from β monophase to lamellar α+β phase in air. Thermo-mechanically affected zone exhibits bimodal microstructure of equiaxed α grain and α+β lamellar microstructure. Its transformation characteristic is dynamic recrystallization and phase transformation. Stir zone is characterized by acicular martensite in forced cooling condition, which is mainly controlled by martensite transformation
2014, 43(5):1153-1156.
Abstract:
The mechanical properties of lead-free solder (Sn3.0Ag0.5Cu, Sn0.7Cu and Sn3.5Ag) joints and its inner intermetallic compounds (IMC) were measured by nanoindentation. The samples were prepared according to actual reflow soldering condition and service. Using the continuous stiffness measurement (CSM) technique, the values of hardness and elastic modulus for lead-free solder joints and IMC were measured. The creep stress exponents were obtained according to nanoindentation. The result indicates that the elastic modulus and creep stress exponents of IMC of Sn0.7Cu are 2.03 and 6.73 times of lead-free solders. It is reasonable to consider the influence of the IMC layer when evaluating the lead-free solder joints reliability
The mechanical properties of lead-free solder (Sn3.0Ag0.5Cu, Sn0.7Cu and Sn3.5Ag) joints and its inner intermetallic compounds (IMC) were measured by nanoindentation. The samples were prepared according to actual reflow soldering condition and service. Using the continuous stiffness measurement (CSM) technique, the values of hardness and elastic modulus for lead-free solder joints and IMC were measured. The creep stress exponents were obtained according to nanoindentation. The result indicates that the elastic modulus and creep stress exponents of IMC of Sn0.7Cu are 2.03 and 6.73 times of lead-free solders. It is reasonable to consider the influence of the IMC layer when evaluating the lead-free solder joints reliability
2014, 43(5):1169-1172.
Abstract:
The crystal structure of (Sm0.6Y0.4)2Zr2O7 ceramic has been investigated by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) coupled with selected area electron diffraction (SAED) and Raman spectroscopy. XRD result shows that (Sm0.6Y0.4)2Zr2O7 ceramic exhibits a single defect fluorite-type structure. However, HRTEM and SAED observation reveals that additional weak diffuse reflections belonging to the pyrochlore-type structure appear in the electron diffraction patterns expect for the characteristic reflections of the defect fluorite-type lattice, which suggests short-range ordering in the bulk defect fluorite lattice. Raman spectroscopy also confirms the short-range order phenomenon at the micro- or nano-scaled regions
The crystal structure of (Sm0.6Y0.4)2Zr2O7 ceramic has been investigated by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) coupled with selected area electron diffraction (SAED) and Raman spectroscopy. XRD result shows that (Sm0.6Y0.4)2Zr2O7 ceramic exhibits a single defect fluorite-type structure. However, HRTEM and SAED observation reveals that additional weak diffuse reflections belonging to the pyrochlore-type structure appear in the electron diffraction patterns expect for the characteristic reflections of the defect fluorite-type lattice, which suggests short-range ordering in the bulk defect fluorite lattice. Raman spectroscopy also confirms the short-range order phenomenon at the micro- or nano-scaled regions
2014, 43(5):1173-1176.
Abstract:
Knowing the correct corrosion mechanism of Alloy 690 is valuable for corrosion protection of equipment. Considering the semiconductor characteristics of metal oxide film on the corrosion surface, a new corrosion dynamics mechanism was proposed based on the quantum mechanics. At first, the nature and characteristics of currents were analyzed in different applied potentials by the band structures of metal. Then the relationship between corrosion potential and current was developed and the kinetic mechanism of corrosion was explained from microscopic view. The results show that the corrosion process is controlled by four kinds of electron transfer named generation-compound, diffusion, tunneling and avalanche in the interface of solution, oxidation film and metal. It is reasonable to interpret the polarization curve of Alloy 690 by quantum mechanics because this relationship has very good consistency with that of experiments
Knowing the correct corrosion mechanism of Alloy 690 is valuable for corrosion protection of equipment. Considering the semiconductor characteristics of metal oxide film on the corrosion surface, a new corrosion dynamics mechanism was proposed based on the quantum mechanics. At first, the nature and characteristics of currents were analyzed in different applied potentials by the band structures of metal. Then the relationship between corrosion potential and current was developed and the kinetic mechanism of corrosion was explained from microscopic view. The results show that the corrosion process is controlled by four kinds of electron transfer named generation-compound, diffusion, tunneling and avalanche in the interface of solution, oxidation film and metal. It is reasonable to interpret the polarization curve of Alloy 690 by quantum mechanics because this relationship has very good consistency with that of experiments
2014, 43(5):1181-1186.
Abstract:
The laser lap welding experiment with Cu, Pb metal sandwich addition was carried out based on the DC56D+ZF galvanized steel of 1.2 mm thickness and the 6016 aluminum alloy of 1.15 mm thickness. Using optical microscopy, scanning electron microscopy, X-ray diffraction and tensile test, the forming of welding, microstructure, element distribution, fracture morphology and the main phase of the welded joint region and mechanical properties of joints were studied. The results show that when Cu and Pb sandwich is added in steel/aluminum, the average tensile strength and elongation of the steel/aluminum laser welding joints is 49.44 MPa and 1.63% as well as 73.51 MPa and 2.37%, respectively. Compared with that without Cu or Pb sandwich addition, the strength and elongation are improved, and Pb is considered as the best metal sandwich based on improved mechanical properties of joints. Steel and aluminum joint specimen fracture shows a brittle fracture characteristic without metal sandwich, the brittle characteristic is not obvious with Cu metal sandwich, while the ductile characteristic is found with Pb sandwich. When Pb sandwich is added, Fe, Al, Zn, Mg and Pb elements change a lot and the mixing zone width is larger in the transition region of steel/aluminum joints. In addition, a new Mg2Pb intermetallic compound is produced with the better stability, FeAl brittle intermetallic compounds are inhibited, and the mechanical properties of weld metal is improved significantly with Pb sandwich addition
The laser lap welding experiment with Cu, Pb metal sandwich addition was carried out based on the DC56D+ZF galvanized steel of 1.2 mm thickness and the 6016 aluminum alloy of 1.15 mm thickness. Using optical microscopy, scanning electron microscopy, X-ray diffraction and tensile test, the forming of welding, microstructure, element distribution, fracture morphology and the main phase of the welded joint region and mechanical properties of joints were studied. The results show that when Cu and Pb sandwich is added in steel/aluminum, the average tensile strength and elongation of the steel/aluminum laser welding joints is 49.44 MPa and 1.63% as well as 73.51 MPa and 2.37%, respectively. Compared with that without Cu or Pb sandwich addition, the strength and elongation are improved, and Pb is considered as the best metal sandwich based on improved mechanical properties of joints. Steel and aluminum joint specimen fracture shows a brittle fracture characteristic without metal sandwich, the brittle characteristic is not obvious with Cu metal sandwich, while the ductile characteristic is found with Pb sandwich. When Pb sandwich is added, Fe, Al, Zn, Mg and Pb elements change a lot and the mixing zone width is larger in the transition region of steel/aluminum joints. In addition, a new Mg2Pb intermetallic compound is produced with the better stability, FeAl brittle intermetallic compounds are inhibited, and the mechanical properties of weld metal is improved significantly with Pb sandwich addition
2014, 43(5):1193-1198.
Abstract:
Millisecond laser and picosecond laser were used to drill in Ni-based single crystal alloy with thermal barrier coatings for processing film cooling holes. The morphology of the thermal barrier coating and the metal substrate processed by long pulse laser and ultrashort pulse laser has been studied. Results show that when the energy density generated by millisecond laser of λ=1064 nm is 2866 J/cm2, the process from the top coatings requires long time for melting and heat accumulation will be conducted to the alloy, and thus the heat affected zone appears in the form of molten pool. However, millisecond laser drilling from the metal surface avoids obvious heat affection, because there is enough time to accumulate heat to melt the ceramic coating but not affect the alloy. When the energy density of millisecond laser has been increased to 6369 J/cm2, the accumulation of heat in the coating is very rapid, the ceramic material is molten rapidly, so heat transmitted to the metal substrate is avoided, while there is ceramic chip is attached to the hole wall when the molten ceramic pass through the hole. The picosecond laser requires only energy density of 32 J/cm2 for ceramic coating processing. The process of picosecond laser trepanning drilling is that the material on the circumference of the hole is ablated until the hole is opened up, and the rest material of the hole falls out from the hole. The microcracks in the coating are generated by plasma impact force caused by picosecond laser processing. The preparation methods of TBCs cause the different directions of microcracks. The TBCs prepared by plasma spraying is a layered structure and the microcracks grow up along the direction parallel to the deposited layers. However, the EB-PVD coatings is columnar crystal structure, therefore microcracks appear in the gap of columnar crystals.
Millisecond laser and picosecond laser were used to drill in Ni-based single crystal alloy with thermal barrier coatings for processing film cooling holes. The morphology of the thermal barrier coating and the metal substrate processed by long pulse laser and ultrashort pulse laser has been studied. Results show that when the energy density generated by millisecond laser of λ=1064 nm is 2866 J/cm2, the process from the top coatings requires long time for melting and heat accumulation will be conducted to the alloy, and thus the heat affected zone appears in the form of molten pool. However, millisecond laser drilling from the metal surface avoids obvious heat affection, because there is enough time to accumulate heat to melt the ceramic coating but not affect the alloy. When the energy density of millisecond laser has been increased to 6369 J/cm2, the accumulation of heat in the coating is very rapid, the ceramic material is molten rapidly, so heat transmitted to the metal substrate is avoided, while there is ceramic chip is attached to the hole wall when the molten ceramic pass through the hole. The picosecond laser requires only energy density of 32 J/cm2 for ceramic coating processing. The process of picosecond laser trepanning drilling is that the material on the circumference of the hole is ablated until the hole is opened up, and the rest material of the hole falls out from the hole. The microcracks in the coating are generated by plasma impact force caused by picosecond laser processing. The preparation methods of TBCs cause the different directions of microcracks. The TBCs prepared by plasma spraying is a layered structure and the microcracks grow up along the direction parallel to the deposited layers. However, the EB-PVD coatings is columnar crystal structure, therefore microcracks appear in the gap of columnar crystals.
2014, 43(5):1219-1223.
Abstract:
Mo-C-N-Si coating on Mo substrates was prepared. The oxidation property of the coating at 1600 oC in air was investigated. Microstructures and phase composition of the coatings were analyzed by means of SEM and XRD, respectively. Results show that Mo-C-N-Si coating consists of the MoSi2, SiC and Si3N4 phases. The middle layer of Mo2C+MoxN can be observed in the coating. Mo-C-N-Si coating becomes four layer structures, i.e. SiO2 oxidation layer, MoSi2 body layer, Mo5Si3 layer and Mo2C+MoxN layer at the initial stage of oxidation duet to the diffusion and oxidation. However, Mo-C-N-Si coating fails in the later stage, probably because it changes to double-layer structures of Mo2C+MoxN layer and Mo3Si+ Mo5Si3 layer. In addition, the thermal shock resistance of the coating is improved by the addition of the C and N elements.
Mo-C-N-Si coating on Mo substrates was prepared. The oxidation property of the coating at 1600 oC in air was investigated. Microstructures and phase composition of the coatings were analyzed by means of SEM and XRD, respectively. Results show that Mo-C-N-Si coating consists of the MoSi2, SiC and Si3N4 phases. The middle layer of Mo2C+MoxN can be observed in the coating. Mo-C-N-Si coating becomes four layer structures, i.e. SiO2 oxidation layer, MoSi2 body layer, Mo5Si3 layer and Mo2C+MoxN layer at the initial stage of oxidation duet to the diffusion and oxidation. However, Mo-C-N-Si coating fails in the later stage, probably because it changes to double-layer structures of Mo2C+MoxN layer and Mo3Si+ Mo5Si3 layer. In addition, the thermal shock resistance of the coating is improved by the addition of the C and N elements.
2014, 43(5):1224-1228.
Abstract:
The in-situ reduction and carbonization reactions were used to synthesize the WC-Co composite powder with nanoscale particle sizes. The nanocrystalline WC-Co cemented carbides bulk material was prepared by spark plasma sintering (SPS). Results show that the particle size of the grain growth inhibitor VC has a significant effect on the microstructure, grain size and properties of the prepared nanocrystalline WC-Co bulk material. When the VC particle size is below 100 nm, the prepared nanocrystalline WC-Co bulk has a mean grain size of about 70 nm. It has a high density, pure phase constitution, homogeneous grain size distribution and excellent mechanical properties, with a Vickers hardness of 19.84 GPa and a fracture toughness of 12.10 MPa×m1/2
The in-situ reduction and carbonization reactions were used to synthesize the WC-Co composite powder with nanoscale particle sizes. The nanocrystalline WC-Co cemented carbides bulk material was prepared by spark plasma sintering (SPS). Results show that the particle size of the grain growth inhibitor VC has a significant effect on the microstructure, grain size and properties of the prepared nanocrystalline WC-Co bulk material. When the VC particle size is below 100 nm, the prepared nanocrystalline WC-Co bulk has a mean grain size of about 70 nm. It has a high density, pure phase constitution, homogeneous grain size distribution and excellent mechanical properties, with a Vickers hardness of 19.84 GPa and a fracture toughness of 12.10 MPa×m1/2
2014, 43(5):1229-1333.
Abstract:
The effect of the morphology structure of tungsten oxide powders on the homogeneity of nanometer W/WC powder was studied during a conventional hydrogen reduction process. The properties of tungsten carbide powder and sintered WC-Co composites were characterized. It is shown that homogenous nanometer tungsten and tungsten carbide powders with loose and porous morphology structure can be prepared from fine tungsten oxide with loose and porous morphology structure. The grain aggregation and abnormal coarse grain are mainly due to the burning binding of agglomeration particle of nano tungsten powder during carbonization process
The effect of the morphology structure of tungsten oxide powders on the homogeneity of nanometer W/WC powder was studied during a conventional hydrogen reduction process. The properties of tungsten carbide powder and sintered WC-Co composites were characterized. It is shown that homogenous nanometer tungsten and tungsten carbide powders with loose and porous morphology structure can be prepared from fine tungsten oxide with loose and porous morphology structure. The grain aggregation and abnormal coarse grain are mainly due to the burning binding of agglomeration particle of nano tungsten powder during carbonization process
2014, 43(5):1238-1241.
Abstract:
Ti-24Nb-4Zr-8Sn alloys (wt%) were prepared by spark plasma sintering (SPS). The effects of different sintering temperatures on the relative density, microstructure and mechanical properties of the alloys were investigated. The results show that in the sintering temperature range from 1000 oC to 1200 oC, the alloys present a high relative density and compressive strength levels. The alloys mainly contain the mixed matrix consisting of β-Ti phase and the Ti-Nb solid solution, and some α-Ti phase. With the sintering temperatures increasing from 1000 oC to 1200 oC, the alloys exhibit a increasing trend for the relative density and the compressive strength. In the meantime, the transformation from α-Ti to β-Ti phase appears, and the size and amount of the Ti-Nb solid solution decrease. The compressive elastic modulus of the alloys is in the range of 58~61 GPa, and it is little affected by the sintering temperatures
Ti-24Nb-4Zr-8Sn alloys (wt%) were prepared by spark plasma sintering (SPS). The effects of different sintering temperatures on the relative density, microstructure and mechanical properties of the alloys were investigated. The results show that in the sintering temperature range from 1000 oC to 1200 oC, the alloys present a high relative density and compressive strength levels. The alloys mainly contain the mixed matrix consisting of β-Ti phase and the Ti-Nb solid solution, and some α-Ti phase. With the sintering temperatures increasing from 1000 oC to 1200 oC, the alloys exhibit a increasing trend for the relative density and the compressive strength. In the meantime, the transformation from α-Ti to β-Ti phase appears, and the size and amount of the Ti-Nb solid solution decrease. The compressive elastic modulus of the alloys is in the range of 58~61 GPa, and it is little affected by the sintering temperatures
2014, 43(5):1250-1253.
Abstract:
Phase formation, thermal hysteresis and magnetocaloric effect in Mn1.25Fe0.75P1-xSix (x=0.50, 0.52, 0.54, 0.56, 0.58, 0.60) alloys have been investigated. X-ray diffraction analysis shows that the alloys crystallize in the Fe2P-type hexagonal structure (space group ) with second phase of FeSi or Fe3Si. By adjusting the content ratio of Si to P, Curie temperature increases linearly from 240 K to 313 K with the increasing of Si content, and the thermal hysteresis of the alloys decreases gradually. When the Si content is 0.58, the maximum value of the magnetic entropy change of the alloy is 8.6 J/kg·K for a field change from 0 to 1.5 T
Phase formation, thermal hysteresis and magnetocaloric effect in Mn1.25Fe0.75P1-xSix (x=0.50, 0.52, 0.54, 0.56, 0.58, 0.60) alloys have been investigated. X-ray diffraction analysis shows that the alloys crystallize in the Fe2P-type hexagonal structure (space group ) with second phase of FeSi or Fe3Si. By adjusting the content ratio of Si to P, Curie temperature increases linearly from 240 K to 313 K with the increasing of Si content, and the thermal hysteresis of the alloys decreases gradually. When the Si content is 0.58, the maximum value of the magnetic entropy change of the alloy is 8.6 J/kg·K for a field change from 0 to 1.5 T
Cai Hongzhong
,
Yi Jianhong
,
Hu Changyi
,
Chang Qiaowen
,
Wei Yan
,
Zheng Xu
,
Liu Weiping
,
Chen Li
2014, 43(5):1254-1257.
Abstract:
A new precursor, bis(2,2,6,6-tetramethyl-3,5-heptanedionato)palladium was synthesized from PdCl2 and Hthd in methanol. The structure of bis(2,2,6,6-tetramethyl-3,5-heptanedionato)palladium was characterized by element analysis, infrared spectroscopy, 1HNMR spectroscopy and single crystal XRD analysis. Thermal decomposition properties were studied by thermogravimetric analysis under nitrogen atmosphere. The results show that bis(2,2,6,6-tetramethyl-3,5-heptanedionato)palladium is an ideal precursor for it is completely volatiled at 291 oC. The palladium films were prepared from the synthesized precursor by metal organic chemical vapor deposition (MOCVD) on quartz. The structure and morphology of palladium films were studied by XRD and AFM, respectively. The results indicate that the pure palladium films are successfully prepared and the surface of films is continuous and compact
A new precursor, bis(2,2,6,6-tetramethyl-3,5-heptanedionato)palladium was synthesized from PdCl2 and Hthd in methanol. The structure of bis(2,2,6,6-tetramethyl-3,5-heptanedionato)palladium was characterized by element analysis, infrared spectroscopy, 1HNMR spectroscopy and single crystal XRD analysis. Thermal decomposition properties were studied by thermogravimetric analysis under nitrogen atmosphere. The results show that bis(2,2,6,6-tetramethyl-3,5-heptanedionato)palladium is an ideal precursor for it is completely volatiled at 291 oC. The palladium films were prepared from the synthesized precursor by metal organic chemical vapor deposition (MOCVD) on quartz. The structure and morphology of palladium films were studied by XRD and AFM, respectively. The results indicate that the pure palladium films are successfully prepared and the surface of films is continuous and compact
2014, 43(5):1258-1261.
Abstract:
Ti-Al intermetallic compound porous material was prepared by the element mixture partial diffusion-reactive synthesis-sintering method. Its tensile deformation was studied experimentally. The effect of porosity on the tensile properties and its microscopic fracture mechanism in tension were revealed. Results show that the tensile stress-strain curve can be divided into four stages: elasticity, yielding, strengthening and failure without necking. Its mechanical properties (including elastic modulus, yield strength and ultimate strength) decrease with the increasing of the porosity and the elongation is much lower than 5%, indicating obvious brittleness at room temperature. The characteristic of the fracture surface is of brittle fracture in macroscopy and of transgranular and intergranular fracture existing simultaneously in microscopy, which is closely related to the microstructure of the dense Ti-Al intermetallic compound.
Ti-Al intermetallic compound porous material was prepared by the element mixture partial diffusion-reactive synthesis-sintering method. Its tensile deformation was studied experimentally. The effect of porosity on the tensile properties and its microscopic fracture mechanism in tension were revealed. Results show that the tensile stress-strain curve can be divided into four stages: elasticity, yielding, strengthening and failure without necking. Its mechanical properties (including elastic modulus, yield strength and ultimate strength) decrease with the increasing of the porosity and the elongation is much lower than 5%, indicating obvious brittleness at room temperature. The characteristic of the fracture surface is of brittle fracture in macroscopy and of transgranular and intergranular fracture existing simultaneously in microscopy, which is closely related to the microstructure of the dense Ti-Al intermetallic compound.
2014, 43(5):1262-1265.
Abstract:
The effect of phosphate passivation and different inorganic adhesives on properties of Fe-Si-Al powder core was investigated. When the Fe-Si-Al magnetic powder core is made from the powder passivated in 0.4 wt% phosphoric acid solution, coated with 0.9 wt% of low melting point glass powder, compacted under 1980 MPa and annealed at 700 oC for 1 h in N2 atmosphere, it presents the optimum magnetic properties. Its effective permeability is 125.98, the total core loss is 316.7 mW/cm3 (f=50 kHz, Bm=100 mT). Besides, tensile strength of the core is 261 N. Meanwhile, it improves the anti-aging ability of Fe-Si-Al powder core during using
The effect of phosphate passivation and different inorganic adhesives on properties of Fe-Si-Al powder core was investigated. When the Fe-Si-Al magnetic powder core is made from the powder passivated in 0.4 wt% phosphoric acid solution, coated with 0.9 wt% of low melting point glass powder, compacted under 1980 MPa and annealed at 700 oC for 1 h in N2 atmosphere, it presents the optimum magnetic properties. Its effective permeability is 125.98, the total core loss is 316.7 mW/cm3 (f=50 kHz, Bm=100 mT). Besides, tensile strength of the core is 261 N. Meanwhile, it improves the anti-aging ability of Fe-Si-Al powder core during using
2014, 43(5):1269-1271.
Abstract:
In order to prepare high purity tungsten silicide (W-Si) alloy powder, high purity W powder and Si powder as starting materials were pre-alloyed in high temperature and vacuum environment. The pre-alloying temperature was 800, 1000 and 1200 oC, and the optimized temperature was 1000 oC. Through the pre-alloying of 1000 oC, the W phase disappeared and the WSi2 phase formed in the powder. The powder particles present single peak distribution and the particle size of d50 is 21.037 μm, and d90 is 50.905 μm. And the powder purity could reach more than 99.995%. Using the pre-alloying tungsten silicide powder as material, the magnetron sputtering target was sintered with a uniform microstructure and alloy composition, which solve the problem of non-uniform microstructure and alloy composition of tungsten silicide target
In order to prepare high purity tungsten silicide (W-Si) alloy powder, high purity W powder and Si powder as starting materials were pre-alloyed in high temperature and vacuum environment. The pre-alloying temperature was 800, 1000 and 1200 oC, and the optimized temperature was 1000 oC. Through the pre-alloying of 1000 oC, the W phase disappeared and the WSi2 phase formed in the powder. The powder particles present single peak distribution and the particle size of d50 is 21.037 μm, and d90 is 50.905 μm. And the powder purity could reach more than 99.995%. Using the pre-alloying tungsten silicide powder as material, the magnetron sputtering target was sintered with a uniform microstructure and alloy composition, which solve the problem of non-uniform microstructure and alloy composition of tungsten silicide target
2014, 43(5):1272-1274.
Abstract:
Dispersion strengthened copper-base composites Al2O3/Cu were fabricated by mechanical alloying and spark-plasma sintering. The effect of the content of rare earth La on the microstructure and properties of Al2O3/Cu composite powder and the sintered materials were studied. The results show that 0.05%La addition to the Al2O3/Cu composite powder accelerates grain refinement and alumina particle dispersion in the mechanical alloying process, so as to improve the microhardness and tensile strength of the composites. The conductivity of the composite increases and then decreases with the increase of the content of La, and the conductivity increases by 11.3%IACS when the La content is 0.10%.
Dispersion strengthened copper-base composites Al2O3/Cu were fabricated by mechanical alloying and spark-plasma sintering. The effect of the content of rare earth La on the microstructure and properties of Al2O3/Cu composite powder and the sintered materials were studied. The results show that 0.05%La addition to the Al2O3/Cu composite powder accelerates grain refinement and alumina particle dispersion in the mechanical alloying process, so as to improve the microhardness and tensile strength of the composites. The conductivity of the composite increases and then decreases with the increase of the content of La, and the conductivity increases by 11.3%IACS when the La content is 0.10%.
2014, 43(5):1275-1280.
Abstract:
Pr-containing giant magnetostrictive materials with MgCu2-type possess high magnetoelastic properties due to low-cost light rare earth Pr, which show a good practical prospect. Much attention has been focused on the synthesis and the study of the magnetostrictive properties for these materials. In this paper, we review the recent developments of the studies based on elements substituting and composition adjusting as well as the preparation technique. The growth methods of single-crystal and oriented polycrystal are also mentioned.
Pr-containing giant magnetostrictive materials with MgCu2-type possess high magnetoelastic properties due to low-cost light rare earth Pr, which show a good practical prospect. Much attention has been focused on the synthesis and the study of the magnetostrictive properties for these materials. In this paper, we review the recent developments of the studies based on elements substituting and composition adjusting as well as the preparation technique. The growth methods of single-crystal and oriented polycrystal are also mentioned.
2014, 43(5):1334-1337.
Abstract:
A kind of composite material, tungsten wire-CVD tungsten was fabricated by winding tungsten wire on the substrate periodically in the CVD process using the homemade CVD device. The density, composition and micro-hardness were tested and analyzed; the crushing strength was calculated according to crushing test; the tensile and bending curves were obtained according to tensile test and three-point bending test. The results show that the dense coating without holes can be obtained when the chemical reaction temperature is controlled at 550 oC and the flows of WF6 and H2 are controlled at 2 g/min and 1 L/min, respectively. Compared with the CVD tungsten samples without wound tungsten wire under the same process conditions, the tungsten wire-CVD tungsten composite materials still possesses high purity and density, the similar micro-hardness, but the crushing strength, the tensile strength and the bending strength are improved greatly
A kind of composite material, tungsten wire-CVD tungsten was fabricated by winding tungsten wire on the substrate periodically in the CVD process using the homemade CVD device. The density, composition and micro-hardness were tested and analyzed; the crushing strength was calculated according to crushing test; the tensile and bending curves were obtained according to tensile test and three-point bending test. The results show that the dense coating without holes can be obtained when the chemical reaction temperature is controlled at 550 oC and the flows of WF6 and H2 are controlled at 2 g/min and 1 L/min, respectively. Compared with the CVD tungsten samples without wound tungsten wire under the same process conditions, the tungsten wire-CVD tungsten composite materials still possesses high purity and density, the similar micro-hardness, but the crushing strength, the tensile strength and the bending strength are improved greatly
2014, 43(5):1056-1060.
Abstract:
The surface treatment technique of laser shock processing (LSP), also known as laser peening, was applied to treat the surface of Ti-6Al-4V titanium alloy, which was widely used in many fields including aeronautic industry. The high pressure shock wave (GPa level) and high strain rate (>106 s-1) for laser shocking make it possible to realize the grain refinement even nanocrystallization on the surface of Ti-6Al-4V alloy to improve the performance of material. However, the investigations of self-nanocrystallization of Ti-6Al-4V induced by LSP are seldom reported by now. The advantages of LSP technique is high peak value power, short duration (nano second level), easily realizing and repeated operating. The pressure model of plasma shock was carried out considering the left absorbing layer for the LSP, which is in accordance with the practical situation with more accurate calculation results than previous model. The self-nanocrystallization of titanium alloy surface can be realized using the method of laser shocking. The results enrich the theoretical basis, present a practice method of self-nanocrystallization of material surface and no other impurities are introduced and the performance of fretting wear resistance is improved simultaneously
The surface treatment technique of laser shock processing (LSP), also known as laser peening, was applied to treat the surface of Ti-6Al-4V titanium alloy, which was widely used in many fields including aeronautic industry. The high pressure shock wave (GPa level) and high strain rate (>106 s-1) for laser shocking make it possible to realize the grain refinement even nanocrystallization on the surface of Ti-6Al-4V alloy to improve the performance of material. However, the investigations of self-nanocrystallization of Ti-6Al-4V induced by LSP are seldom reported by now. The advantages of LSP technique is high peak value power, short duration (nano second level), easily realizing and repeated operating. The pressure model of plasma shock was carried out considering the left absorbing layer for the LSP, which is in accordance with the practical situation with more accurate calculation results than previous model. The self-nanocrystallization of titanium alloy surface can be realized using the method of laser shocking. The results enrich the theoretical basis, present a practice method of self-nanocrystallization of material surface and no other impurities are introduced and the performance of fretting wear resistance is improved simultaneously
