Volume 45,Issue 7,2016 Table of Contents
2016, 45(7):1641-1646.
Abstract:
Mechanochemical effect which is the interaction of mechanical and chemical can accelerate the stress corrosion cracking (SCC) in nickel-based used in nuclear power plants. The mechanical properties heterogeneity in weld joints will influence the mechanochemical effect indirectly. The effects of yield strength and hardening exponent of alloy 600 on the mechanochemical effect of crack tip surface in high temperature water environment were studied by adopting one inch compact tension specimen and finite element method. The effects of elastic and plastic deformation on the change of mechanochemical effect were discussed. The results indicate that the mechanochemical effect is affected by the yield strength. In contrary, the hardening exponent change of alloy 600 has insignificantly influence on mechanochemical effect.
Mechanochemical effect which is the interaction of mechanical and chemical can accelerate the stress corrosion cracking (SCC) in nickel-based used in nuclear power plants. The mechanical properties heterogeneity in weld joints will influence the mechanochemical effect indirectly. The effects of yield strength and hardening exponent of alloy 600 on the mechanochemical effect of crack tip surface in high temperature water environment were studied by adopting one inch compact tension specimen and finite element method. The effects of elastic and plastic deformation on the change of mechanochemical effect were discussed. The results indicate that the mechanochemical effect is affected by the yield strength. In contrary, the hardening exponent change of alloy 600 has insignificantly influence on mechanochemical effect.
2016, 45(7):1647-1653.
Abstract:
The incompatibility of plastic deformation in a near β titanium alloy with (α β) two phases microstructure was analyzed based on the crystal plasticity finite element (CPFE) model. The bicrystal simulation results show that the plastic deformation in the microstructure with (α β) two phases is incompatible, wherein the deformation behavior of α phase is significantly affected by the crystal orientation and loading direction. In addition, by coupling with three-dimensional (3D) Voronoi tessellation (VT) geometric model, the effect of globular primary α phase in the β matrix on the macroscopic mechanical response was discussed. Based on the CPFE-VT model, it is found that the incompatibility of plastic deformation between the α and β phases results in a linear reduction of the macroscopic strength with the proportional increasing of volume fraction of α phase which has a lower critical resolved shear stress. Furthermore, the distribution of primary α phase also has a significant effect on the stress-strain response. The proposed model for near β titanium alloy with dual phase microstructure yields important information for the microstructure controlling and the performance prediction.
The incompatibility of plastic deformation in a near β titanium alloy with (α β) two phases microstructure was analyzed based on the crystal plasticity finite element (CPFE) model. The bicrystal simulation results show that the plastic deformation in the microstructure with (α β) two phases is incompatible, wherein the deformation behavior of α phase is significantly affected by the crystal orientation and loading direction. In addition, by coupling with three-dimensional (3D) Voronoi tessellation (VT) geometric model, the effect of globular primary α phase in the β matrix on the macroscopic mechanical response was discussed. Based on the CPFE-VT model, it is found that the incompatibility of plastic deformation between the α and β phases results in a linear reduction of the macroscopic strength with the proportional increasing of volume fraction of α phase which has a lower critical resolved shear stress. Furthermore, the distribution of primary α phase also has a significant effect on the stress-strain response. The proposed model for near β titanium alloy with dual phase microstructure yields important information for the microstructure controlling and the performance prediction.
2016, 45(7):1654-1658.
Abstract:
To investigate mechanical behaviors and deformation mechanisms of nanocrystalline materials, bulk nanocrystalline Ni samples were prepared by plasma evaporation method combined with hot pressure sintering in this paper. The compressive mechanical properties of the bulk samples were tested under different quasi-static strain rates at room temperature and the evolution of microstructure of bulk sample before and after compression was studied. The bulk samples show a good combination of strength and ductility during the compressive testing. Meanwhile, grain size of the compressed sample decreases compared with that of sintered sample, while the microstrain of the grain increases after compression. Based on experimental results, it is can be inferred that both grain boundary dislocation glide and grain boundary sliding mechanism are main operating deformation mechanisms for the bulk NC Ni samples.
To investigate mechanical behaviors and deformation mechanisms of nanocrystalline materials, bulk nanocrystalline Ni samples were prepared by plasma evaporation method combined with hot pressure sintering in this paper. The compressive mechanical properties of the bulk samples were tested under different quasi-static strain rates at room temperature and the evolution of microstructure of bulk sample before and after compression was studied. The bulk samples show a good combination of strength and ductility during the compressive testing. Meanwhile, grain size of the compressed sample decreases compared with that of sintered sample, while the microstrain of the grain increases after compression. Based on experimental results, it is can be inferred that both grain boundary dislocation glide and grain boundary sliding mechanism are main operating deformation mechanisms for the bulk NC Ni samples.
2016, 45(7):1659-1663.
Abstract:
Cr-doped ammonium aluminum carbonate hydroxide nanorods were successfully prepared by hydrothermal method, using Al(NO3)3?9H2O, Cr(NO3)3?9H2O, and urea as raw materials and PEG-20000 as surfactant. In-situ Cr-doped alumina nanorods powder can be obtained through calcinations at 1200 ℃. The crystal composition, structure and morphology of the as-prepared products were characterized by XRD, SEM and FTIR. Besides, the color performances of the products were analyzed by UV/Vis/NIR spectrometer and automatic color measurement. Results showed that the precursors of Cr-doped alumina nanorods powder prepared by the hydrothermal method were composed of uniform nanorods. After calcinations at 1200 ℃, the in-situ doping of Cr in the alumina substrate was achieved. In Cr-doped alumina nanorods powder, a continuous solid solution of Cr2O3 and Al2O3 was formed, which had a corundum crystal structure. With increasing Cr content, Cr-doped ammonium aluminum carbonate hydroxide nanorods gradually became short, and the melting phenomenon occurred in calcined products. UV-Vis spectroscopy analysis showed that Cr-doped alumina nanorods powder had three strong absorption bands at 562 nm, 406 nm and 372 nm, respectively, thus leading to a pink color for samples in agreement with chromatic data. In the study, Cr-doped alumina nanorods powder prepared by the hydrothermal method can reduce the formation temperature of corundum crystal structures and resolve the problem of mixing homogeneity of Al2O3 and Cr2O3, which will contribute to preparation and application of alumina-chrome refractory, pink corundum abrasive and ceramic pigment.
Cr-doped ammonium aluminum carbonate hydroxide nanorods were successfully prepared by hydrothermal method, using Al(NO3)3?9H2O, Cr(NO3)3?9H2O, and urea as raw materials and PEG-20000 as surfactant. In-situ Cr-doped alumina nanorods powder can be obtained through calcinations at 1200 ℃. The crystal composition, structure and morphology of the as-prepared products were characterized by XRD, SEM and FTIR. Besides, the color performances of the products were analyzed by UV/Vis/NIR spectrometer and automatic color measurement. Results showed that the precursors of Cr-doped alumina nanorods powder prepared by the hydrothermal method were composed of uniform nanorods. After calcinations at 1200 ℃, the in-situ doping of Cr in the alumina substrate was achieved. In Cr-doped alumina nanorods powder, a continuous solid solution of Cr2O3 and Al2O3 was formed, which had a corundum crystal structure. With increasing Cr content, Cr-doped ammonium aluminum carbonate hydroxide nanorods gradually became short, and the melting phenomenon occurred in calcined products. UV-Vis spectroscopy analysis showed that Cr-doped alumina nanorods powder had three strong absorption bands at 562 nm, 406 nm and 372 nm, respectively, thus leading to a pink color for samples in agreement with chromatic data. In the study, Cr-doped alumina nanorods powder prepared by the hydrothermal method can reduce the formation temperature of corundum crystal structures and resolve the problem of mixing homogeneity of Al2O3 and Cr2O3, which will contribute to preparation and application of alumina-chrome refractory, pink corundum abrasive and ceramic pigment.
2016, 45(7):1664-1668.
Abstract:
La2Sn2O7/SnO2 composite powder was firstly synthesized by a low-cost co-precipitation, and Ag-La2Sn2O7/SnO2 electrical contact material was prepared by powder metallurgy method. Anti-arc erosion properties, mass loss and Vickers hardness of Ag-La2Sn2O7/SnO2 were investigated, and anti-arc erosion mechanism was discussed. Results show that the welding force of Ag-La2Sn2O7/SnO2 composite is much better than that of Ag-SnO2, which is because the new phase La2Sn2O7 can increase the viscosity of melt poor and improve wettability between silver and tin oxide to some extent. Meanwhile, Flatter arcing area and “beads-like” particles embedded scatteredly in the surface could decentralized arc energy by “Pinning Effect”, which can decrease temperature rise and lower welding force. Ag-La2Sn2O7/SnO2 composite could be a leading candidate material for electrical contacts in the future.
La2Sn2O7/SnO2 composite powder was firstly synthesized by a low-cost co-precipitation, and Ag-La2Sn2O7/SnO2 electrical contact material was prepared by powder metallurgy method. Anti-arc erosion properties, mass loss and Vickers hardness of Ag-La2Sn2O7/SnO2 were investigated, and anti-arc erosion mechanism was discussed. Results show that the welding force of Ag-La2Sn2O7/SnO2 composite is much better than that of Ag-SnO2, which is because the new phase La2Sn2O7 can increase the viscosity of melt poor and improve wettability between silver and tin oxide to some extent. Meanwhile, Flatter arcing area and “beads-like” particles embedded scatteredly in the surface could decentralized arc energy by “Pinning Effect”, which can decrease temperature rise and lower welding force. Ag-La2Sn2O7/SnO2 composite could be a leading candidate material for electrical contacts in the future.
2016, 45(7):1669-1673.
Abstract:
The reduced graphene oxide wrapped Fe3O4 hollow nanospheres have been successfully synthesized by a simple self-assembly process driven by electrostatic interaction. The structure, chemical component and morphology were characterized by XRD, SEM, TEM, FTIR, and Raman spectroscopy. The fabricated nanocomposites exhibited superparamagnetic property with the saturation magnetization of 70.2 Am2 kg-1 at room temperature and allowed rapid separation under an external magnetic field. The high magnetism and excellent water dispersibility make these nanocomposites ideal candidates for various important applications such as magnetic resonance imaging, biosensors, communication, and microwave absorption.
The reduced graphene oxide wrapped Fe3O4 hollow nanospheres have been successfully synthesized by a simple self-assembly process driven by electrostatic interaction. The structure, chemical component and morphology were characterized by XRD, SEM, TEM, FTIR, and Raman spectroscopy. The fabricated nanocomposites exhibited superparamagnetic property with the saturation magnetization of 70.2 Am2 kg-1 at room temperature and allowed rapid separation under an external magnetic field. The high magnetism and excellent water dispersibility make these nanocomposites ideal candidates for various important applications such as magnetic resonance imaging, biosensors, communication, and microwave absorption.
2016, 45(7):1674-1677.
Abstract:
AZ31 Mg alloy sheets were processed by pre-stretched (PRS) at the angles of 0o, 30o, 45o, 60o and 90o between the tensile direction and the extrusion direction at room temperature. Twinning was thus introduced and gradually increased. The corrosion performance of the twinned Mg alloy sheets was sensitive to the area fraction of twins. Meanwhile, the sheet processing most area fraction of twins (～52%) exhibited the best corrosion resistance. This was attributed to the subdivision of grains by introducing extension twin boundaries. Twinning brought about more grain boundaries that acted as a corrosion barrier and thus improved the corrosion resistance. The microstructure evolutions and corrosion behavior were examined and compared.
AZ31 Mg alloy sheets were processed by pre-stretched (PRS) at the angles of 0o, 30o, 45o, 60o and 90o between the tensile direction and the extrusion direction at room temperature. Twinning was thus introduced and gradually increased. The corrosion performance of the twinned Mg alloy sheets was sensitive to the area fraction of twins. Meanwhile, the sheet processing most area fraction of twins (～52%) exhibited the best corrosion resistance. This was attributed to the subdivision of grains by introducing extension twin boundaries. Twinning brought about more grain boundaries that acted as a corrosion barrier and thus improved the corrosion resistance. The microstructure evolutions and corrosion behavior were examined and compared.
2016, 45(7):1678-1682.
Abstract:
Nb-Si based alloys show great promise to surpass current advanced Ni-base superalloys due to their low densities and high melting points. Both Ti and Al are beneficial alloying elements for Nb-Si based alloys. In the literature, small amount (≤ 3 at. % ) of Al have frequently examined, and Nb aluminides are usually not formed in this case. Since Nb3Al and Nb2Al have good strength and creep properties, NbAl3 is also a candidate hot-section material, and the study of Nb-Si alloys with these possible Nb alumininides is lacking, so we focus our efforts on primarily whether Nb aluminide is formed or not by adding more Al in the as-cast Nb-Ti-Si alloys. This work studied the microstructures and mechanical properties of two Nb-Ti-Si-Al alloys (A2: Nb-18Ti-14Si-9Al, A4: Nb-21Ti-14Si-9Al) with higher Al content, and the A4 alloy was designed to examine the alloying effect of more Ti. The A2 alloy consists of (Nb), Nb5Si3 and Nb3Al, while the A4 alloy is composed of (Nb) and Nb5Si3. The comparable fracture toughness of the A2 alloy and the A4 alloy is 11.1 MPa.m1/2 and 10.9 MPa.m1/2, respectively. Moreover, the indention experiments are employed to characterize the micro scale mechanical properties of these Nb-Ti-Si-Al alloys.
Nb-Si based alloys show great promise to surpass current advanced Ni-base superalloys due to their low densities and high melting points. Both Ti and Al are beneficial alloying elements for Nb-Si based alloys. In the literature, small amount (≤ 3 at. % ) of Al have frequently examined, and Nb aluminides are usually not formed in this case. Since Nb3Al and Nb2Al have good strength and creep properties, NbAl3 is also a candidate hot-section material, and the study of Nb-Si alloys with these possible Nb alumininides is lacking, so we focus our efforts on primarily whether Nb aluminide is formed or not by adding more Al in the as-cast Nb-Ti-Si alloys. This work studied the microstructures and mechanical properties of two Nb-Ti-Si-Al alloys (A2: Nb-18Ti-14Si-9Al, A4: Nb-21Ti-14Si-9Al) with higher Al content, and the A4 alloy was designed to examine the alloying effect of more Ti. The A2 alloy consists of (Nb), Nb5Si3 and Nb3Al, while the A4 alloy is composed of (Nb) and Nb5Si3. The comparable fracture toughness of the A2 alloy and the A4 alloy is 11.1 MPa.m1/2 and 10.9 MPa.m1/2, respectively. Moreover, the indention experiments are employed to characterize the micro scale mechanical properties of these Nb-Ti-Si-Al alloys.
2016, 45(7):1683-1686.
Abstract:
Microstructures of as-fabricated and post heat treated Ti-47Al-2Nb-2Cr (at.%)alloy produced by selective electron beam melting (SEBM) were examined, solidification path and phase transformation of Ti-47Al-2Nb-2Cr alloy during SEBM process were also analyzed .Results show that microstructure with fine fully lamellar (FL) consisted of γ-TiAl and α2-Ti3Al was formed in the as-fabricated TiAl sample. Due to the rapid cooling and the cyclic heat treatment during the SEBM process, solidification took place solely through the β phase, phase transformation path was L → L β → β → β α → α → α γ and the lamellar colonies and lamellae all coarser from the top to the bottom of the specimen. Different post heat treatment were carried out to got a homogeneous microstructure .A fine and homogeneous microstructure was achieved after oil quenching from 1250℃ and holding at 1200℃ for 2h.
Microstructures of as-fabricated and post heat treated Ti-47Al-2Nb-2Cr (at.%)alloy produced by selective electron beam melting (SEBM) were examined, solidification path and phase transformation of Ti-47Al-2Nb-2Cr alloy during SEBM process were also analyzed .Results show that microstructure with fine fully lamellar (FL) consisted of γ-TiAl and α2-Ti3Al was formed in the as-fabricated TiAl sample. Due to the rapid cooling and the cyclic heat treatment during the SEBM process, solidification took place solely through the β phase, phase transformation path was L → L β → β → β α → α → α γ and the lamellar colonies and lamellae all coarser from the top to the bottom of the specimen. Different post heat treatment were carried out to got a homogeneous microstructure .A fine and homogeneous microstructure was achieved after oil quenching from 1250℃ and holding at 1200℃ for 2h.
2016, 45(7):1687-1694.
Abstract:
The present work aims to clarify the formation of the ?1(Al8Cu4Ce) phase and its formation mechanism in the high Cu content alloy with Ce addition. The microstructure evolution during the two-step homogenization annealing process was investigated in the novel high Cu/Li Al–Cu–Li–Ce alloy. The formation of the coarse Ag Mg enriched TB (Al7Cu4Li) phase and the primary AlCuCe phase was found to occur under solidification. Two types of the minor ?1 phases were found to form after homogenization. It is concluded that the ?1 phase nucleation mechanism could involve either nucleation on an existing TB phase by Ce diffusion from the Al matrix or the transformation of the primary AlCuCe phase into the ?1 phase by Ce diffusion through the coarse primary AlCuCe phase shrink. It also can be deduced that the grain refinement is mainly the result of the primary AlCuCe promoting ? (Al) nucleation and further prohibiting the grain growth for the experimental alloy.
The present work aims to clarify the formation of the ?1(Al8Cu4Ce) phase and its formation mechanism in the high Cu content alloy with Ce addition. The microstructure evolution during the two-step homogenization annealing process was investigated in the novel high Cu/Li Al–Cu–Li–Ce alloy. The formation of the coarse Ag Mg enriched TB (Al7Cu4Li) phase and the primary AlCuCe phase was found to occur under solidification. Two types of the minor ?1 phases were found to form after homogenization. It is concluded that the ?1 phase nucleation mechanism could involve either nucleation on an existing TB phase by Ce diffusion from the Al matrix or the transformation of the primary AlCuCe phase into the ?1 phase by Ce diffusion through the coarse primary AlCuCe phase shrink. It also can be deduced that the grain refinement is mainly the result of the primary AlCuCe promoting ? (Al) nucleation and further prohibiting the grain growth for the experimental alloy.
2016, 45(7):1695-1699.
Abstract:
The oxidation behavior of a full-lamellar Ti-42.5Al-8Nb-0.2W-0.2B-0.1Y alloys with different colony sizes was investigated by using thermogravimetric method at 900℃ for 100 hours in air. The microstructure and composition of the alloy as well as the oxide scales were analyzed by OM, SEM, EDS and XRD. It was found that the oxidation kinetic of the present TiAl alloys accorded with the parabolic law, and the alloy with larger lamellar colony have a better oxidation resistance than that of the one with smaller lamellar colony. The weight gain after 100 h oxidation was 7.62 g/m2 and 6.45 g/cm2, respectively for these two alloys, and correspondingly the thickness of oxide scale was about 7μm and 5μm, respectively. Base on the analysis of oxidation kinetic and microstructure characterization, we concluded that lamellar colony size has a significant effect on the oxidation behavior of TiAl alloys.
The oxidation behavior of a full-lamellar Ti-42.5Al-8Nb-0.2W-0.2B-0.1Y alloys with different colony sizes was investigated by using thermogravimetric method at 900℃ for 100 hours in air. The microstructure and composition of the alloy as well as the oxide scales were analyzed by OM, SEM, EDS and XRD. It was found that the oxidation kinetic of the present TiAl alloys accorded with the parabolic law, and the alloy with larger lamellar colony have a better oxidation resistance than that of the one with smaller lamellar colony. The weight gain after 100 h oxidation was 7.62 g/m2 and 6.45 g/cm2, respectively for these two alloys, and correspondingly the thickness of oxide scale was about 7μm and 5μm, respectively. Base on the analysis of oxidation kinetic and microstructure characterization, we concluded that lamellar colony size has a significant effect on the oxidation behavior of TiAl alloys.
2016, 45(7):1700-1704.
Abstract:
Cubic Co9S8 fracture structure nanoshells and cubic Co3S4 nanocrystallines were prepared by ultrasonic spray pyrolysis process using cobalt chloride (CoCl2?6H2O) and thiourea (CH4N2S) as the starting materials. The as-prepared Co9S8 nanoshells and Co3S4 nanocrystallines were characterized by X-ray diffraction (XRD), Scanning electron microscope (SEM) with energy-disperse X-ray spectroscopy (EDX) attachment and Fourier-transform infrared (FTIR) spectrometer respectively. It was found that the phase transition could be controlled by adjusting the reaction temperature, while morphologies of final products could be influenced by the molar ratio and reaction time of precursor. Meanwhile, possible mechanism for the formation of hollow and solid crystalline structures of the product was proposed.
Cubic Co9S8 fracture structure nanoshells and cubic Co3S4 nanocrystallines were prepared by ultrasonic spray pyrolysis process using cobalt chloride (CoCl2?6H2O) and thiourea (CH4N2S) as the starting materials. The as-prepared Co9S8 nanoshells and Co3S4 nanocrystallines were characterized by X-ray diffraction (XRD), Scanning electron microscope (SEM) with energy-disperse X-ray spectroscopy (EDX) attachment and Fourier-transform infrared (FTIR) spectrometer respectively. It was found that the phase transition could be controlled by adjusting the reaction temperature, while morphologies of final products could be influenced by the molar ratio and reaction time of precursor. Meanwhile, possible mechanism for the formation of hollow and solid crystalline structures of the product was proposed.
2016, 45(7):1705-1708.
Abstract:
Functionally graded cemented carbides (FGCCs) have an excellent combination of high hardness and high toughness. But the appearance of residual stresses, resulting from cobalt gradient and mismatch between mechanical properties and material constituents, is an influence on the lifetime of FGCCs. To get the thermal stress field distribution, a constitutive equation for WC-Co FGCCs is developed by redefinition of elastic constraint factor and introduction of plastic constraint factor. The constitutive model is applied to thermal stress analysis of WC-Co composites. The distribution of thermal stresses in WC-Co specimen is obtained by means of finite element numerical method. Simultaneously, the surface compressive stress of FGCCs alloy is measured by X-ray diffraction method. Numerical results show the thermal stresses of WC-Co composites mainly concentrate in the cobalt gradient zone and the maximum value of principal compressive stress is 380MPa in the surface zone. This results is good agreement with X-ray diffraction measurement.
Functionally graded cemented carbides (FGCCs) have an excellent combination of high hardness and high toughness. But the appearance of residual stresses, resulting from cobalt gradient and mismatch between mechanical properties and material constituents, is an influence on the lifetime of FGCCs. To get the thermal stress field distribution, a constitutive equation for WC-Co FGCCs is developed by redefinition of elastic constraint factor and introduction of plastic constraint factor. The constitutive model is applied to thermal stress analysis of WC-Co composites. The distribution of thermal stresses in WC-Co specimen is obtained by means of finite element numerical method. Simultaneously, the surface compressive stress of FGCCs alloy is measured by X-ray diffraction method. Numerical results show the thermal stresses of WC-Co composites mainly concentrate in the cobalt gradient zone and the maximum value of principal compressive stress is 380MPa in the surface zone. This results is good agreement with X-ray diffraction measurement.
2016, 45(7):1709-1713.
Abstract:
An environment-friendly surface etching and activation technics for ABS surface metallization were investigated as a replacement for conventional chromic acid etching bath and palladium catalyst. After etching by H2SO4-MnO2 colloid, the ABS surfaces become roughness; meanwhile the carboxyl and hydroxyl groups were formed on the surface. With absorption and a reduction by a sodium borohydride solution, copper particles were deposited on the ABS surface, which serves as a catalyst replacement for SnCl2/PdCl2 colloid. The effects of CuSO4 concentration, NaBH4 concentration, reduction temperature and reduction time on the adhesion strength between the ABS surface and the electroless copper film were investigated. The average adhesion strengths reached 0.87 KN m-1.
An environment-friendly surface etching and activation technics for ABS surface metallization were investigated as a replacement for conventional chromic acid etching bath and palladium catalyst. After etching by H2SO4-MnO2 colloid, the ABS surfaces become roughness; meanwhile the carboxyl and hydroxyl groups were formed on the surface. With absorption and a reduction by a sodium borohydride solution, copper particles were deposited on the ABS surface, which serves as a catalyst replacement for SnCl2/PdCl2 colloid. The effects of CuSO4 concentration, NaBH4 concentration, reduction temperature and reduction time on the adhesion strength between the ABS surface and the electroless copper film were investigated. The average adhesion strengths reached 0.87 KN m-1.
2016, 45(7):1714-1718.
Abstract:
The Al2O3-ZrB2 nanocomposite ceramics were prepared and the mechanical properties of the process parameters’ effect were studied. The results showed that: Among the various values of sintering temperatures applied, a maximum Vickers hardness of 1897HV and high reliability were attained at 1500 癈 and at atmosphere sintering. In addition, the sample was not well densified under the sintering temperature. Scanning electron microscopy (SEM) showed that fine ZrB2 particles dispersed and pinning at grain boundaries to inhibit grain boundary movement effectively. While larger ZrB2 particles distributed between A12O3 particles uniformly and occupy A12O3 particles grow space to hinder the matrix grains, which greatly promoted the densification of the ceramic, improving the microstructure. Fracture morphology indicates that trans-granular fracture was occurred, the ceramic material having high toughness.
The Al2O3-ZrB2 nanocomposite ceramics were prepared and the mechanical properties of the process parameters’ effect were studied. The results showed that: Among the various values of sintering temperatures applied, a maximum Vickers hardness of 1897HV and high reliability were attained at 1500 癈 and at atmosphere sintering. In addition, the sample was not well densified under the sintering temperature. Scanning electron microscopy (SEM) showed that fine ZrB2 particles dispersed and pinning at grain boundaries to inhibit grain boundary movement effectively. While larger ZrB2 particles distributed between A12O3 particles uniformly and occupy A12O3 particles grow space to hinder the matrix grains, which greatly promoted the densification of the ceramic, improving the microstructure. Fracture morphology indicates that trans-granular fracture was occurred, the ceramic material having high toughness.
2016, 45(7):1719-1725.
Abstract:
Abstract: The influence of Ru element on the creep properties under 1120 ℃/140 MPa of high Re Ni-based single crystal superalloys with two levels of Ru (0, 2wt.%) additions was investigated. The γ/γ′ phase, partitioning ratio of alloying elements, deformation microstructures and the morphology of dislocations were studied by SEM, STEM/TEM and EDS. The results indicate that Ru addition results in decreasing the size of γ′ phase, width of γ channel and elemental partitioning ratio of Re，Mo and Cr which are important for the precipitation of TCP phase. Ru addition decreased the size of γ′ phase and width of γ channel, decreased the spacing of γ/γ′ interfacial dislocation networks and inhibited the precipitation of TCP phase in the process of creep loading, finally improving the creep properties of the investigatived alloy significantly. This study would be helpful for the understanding of ruthenium’s role of strengthening mechanism in high temperature creep of Ni-base single crystal superalloys. Key words: single crystal superalloys; Ru; micrstructures; partitioning of elements in γ/γ′ phase; creep properties
Abstract: The influence of Ru element on the creep properties under 1120 ℃/140 MPa of high Re Ni-based single crystal superalloys with two levels of Ru (0, 2wt.%) additions was investigated. The γ/γ′ phase, partitioning ratio of alloying elements, deformation microstructures and the morphology of dislocations were studied by SEM, STEM/TEM and EDS. The results indicate that Ru addition results in decreasing the size of γ′ phase, width of γ channel and elemental partitioning ratio of Re，Mo and Cr which are important for the precipitation of TCP phase. Ru addition decreased the size of γ′ phase and width of γ channel, decreased the spacing of γ/γ′ interfacial dislocation networks and inhibited the precipitation of TCP phase in the process of creep loading, finally improving the creep properties of the investigatived alloy significantly. This study would be helpful for the understanding of ruthenium’s role of strengthening mechanism in high temperature creep of Ni-base single crystal superalloys. Key words: single crystal superalloys; Ru; micrstructures; partitioning of elements in γ/γ′ phase; creep properties
2016, 45(7):1726-1731.
Abstract:
Influence of low temperature aging on phase transformation behavior and mechanical properties of Ti-10V-2F2-3Al alloy has been investigated. Results show that isothermal ω particles and α″ martensitic plates are continuously formed in the β matrix with increasing aging time. When the aging time is more than 4h, ω particles gradually disappear and lots of isothermal martensites are still produced. Tensile testing shows that, the 0.5h-aged specimen has the highest plasticity and lower yield strength than the rest specimens. With increasing aging time, plasticity is decreased sharply and strength is increased rapidly. However, plasticity is recovered slowly and strength is increased continuously once the aging time is more than 4h. Comprehensive analysis indicates that good plasticity in the 0.5h-aged specimen is attributed to transformation-induced plasticity effect (TRIP) during tensile process; Embrittlement induced by ω particles and consumption of β matrix due to isothermal martensitic transformation result in reduction of plasticity and increasement of strength.. On the contrary, when the aging time is longer than 4h, disappearance of ω particles and formation of plenty of isothermal martensites are beneficial for the increasement of both strength and plasticity.
Influence of low temperature aging on phase transformation behavior and mechanical properties of Ti-10V-2F2-3Al alloy has been investigated. Results show that isothermal ω particles and α″ martensitic plates are continuously formed in the β matrix with increasing aging time. When the aging time is more than 4h, ω particles gradually disappear and lots of isothermal martensites are still produced. Tensile testing shows that, the 0.5h-aged specimen has the highest plasticity and lower yield strength than the rest specimens. With increasing aging time, plasticity is decreased sharply and strength is increased rapidly. However, plasticity is recovered slowly and strength is increased continuously once the aging time is more than 4h. Comprehensive analysis indicates that good plasticity in the 0.5h-aged specimen is attributed to transformation-induced plasticity effect (TRIP) during tensile process; Embrittlement induced by ω particles and consumption of β matrix due to isothermal martensitic transformation result in reduction of plasticity and increasement of strength.. On the contrary, when the aging time is longer than 4h, disappearance of ω particles and formation of plenty of isothermal martensites are beneficial for the increasement of both strength and plasticity.
2016, 45(7):1732-1735.
Abstract:
Hot compression tests of Ti-5553 titanium alloy were conducted at deformation temperature of 800-860℃and strain rates of 0.1～10s-1.The relationship curve of work hardening rate θ and critical strain ε was obtained according to true stress—true strain curves. The critica1 conditions of dynamic recrvstallization of Ti-5553 alloy were studied with the inflection point criterion of curves. The critical condition of dynamic recrystallization was obtained using mode of Sellarsn.
Hot compression tests of Ti-5553 titanium alloy were conducted at deformation temperature of 800-860℃and strain rates of 0.1～10s-1.The relationship curve of work hardening rate θ and critical strain ε was obtained according to true stress—true strain curves. The critica1 conditions of dynamic recrvstallization of Ti-5553 alloy were studied with the inflection point criterion of curves. The critical condition of dynamic recrystallization was obtained using mode of Sellarsn.
2016, 45(7):1736-1739.
Abstract:
The ingot of Ti-6Al-4V alloy was prepared by investment casting. Microstructure and formation mechanism of alpha-case in the surface layer of the ingot were investigated by optical microscope (OM), electron probe micro-analyzer (EPMA) and Vickers hardness. The results show that the alpha-case covers the whole surface of the sample, and the microstructure of the alpha-case features in a coarse plate-shaped structure which ranked as-basketweave. The formation mechanism of alpha-case is associated with the diffusion of interstitial oxygen and carbon atoms in the shell material toward matrix alloy. Depth of alpha-case obtained from micro-hardness testing is slightly deeper than that observed by OM. More reliable results come from the micro-hardness testing for removing the alpha-case completely.
The ingot of Ti-6Al-4V alloy was prepared by investment casting. Microstructure and formation mechanism of alpha-case in the surface layer of the ingot were investigated by optical microscope (OM), electron probe micro-analyzer (EPMA) and Vickers hardness. The results show that the alpha-case covers the whole surface of the sample, and the microstructure of the alpha-case features in a coarse plate-shaped structure which ranked as-basketweave. The formation mechanism of alpha-case is associated with the diffusion of interstitial oxygen and carbon atoms in the shell material toward matrix alloy. Depth of alpha-case obtained from micro-hardness testing is slightly deeper than that observed by OM. More reliable results come from the micro-hardness testing for removing the alpha-case completely.
2016, 45(7):1740-1744.
Abstract:
The influence of Nb contents on the high temperature strength and ambient ductility of cast high Al containing TiAl alloys are investigated with Nb content varying from 2at%-9at%. It shows that the tensile strength increases firstly then decreases with increasing Nb conternt. Alloy with 7at%Nb has the highest tensile strength at 900 ℃, about 587 MPa。These high strengths arise from high Nb solute in the γ-TiAl matrix leads to a high critical resolved shear stress(CRSS) of dislocation, reduction of the stacking fault energy and reduction of diffusivity. Al/Ti antisite defects, the hard orientation of the lamellar and tensile direction and the twinning may provide a substantial hardening of high Al containing cast TiAl alloys. While B2 increases with increasing the Nb content, may be the reason that ambient ductility decreases with increasing Nb content.
The influence of Nb contents on the high temperature strength and ambient ductility of cast high Al containing TiAl alloys are investigated with Nb content varying from 2at%-9at%. It shows that the tensile strength increases firstly then decreases with increasing Nb conternt. Alloy with 7at%Nb has the highest tensile strength at 900 ℃, about 587 MPa。These high strengths arise from high Nb solute in the γ-TiAl matrix leads to a high critical resolved shear stress(CRSS) of dislocation, reduction of the stacking fault energy and reduction of diffusivity. Al/Ti antisite defects, the hard orientation of the lamellar and tensile direction and the twinning may provide a substantial hardening of high Al containing cast TiAl alloys. While B2 increases with increasing the Nb content, may be the reason that ambient ductility decreases with increasing Nb content.
2016, 45(7):1745-1748.
Abstract:
In this work the effect of cooling rates on microstructure of Ti-48Al-4Cr(at.%) alloy rapidly solidified at different wheel speeds were experimentally investigated by using the single roller melt-spinning technique. The results indicate that after rapid solidification at the wheel speed of 10m/s and 20m/s, the microstructures mainly consist of equiaxed γ phase, few volume fraction of α2, B2 phase particles and lamellar structures exists in the γ phase matrix. At the wheel speed of 30m/s, the matrix changes to α2 phase and the lamellar structures disappear. The nanohardness increases with the cooling rate increasing. It enhances from 4.98±0.10GPa under normal pressure to 7.48±0.16GPa under 4GPa. The nanohardness increases from 5.04±0.09GPa of conventional cast Ti-48Al alloy to 10.48±0.13GPa of rapidly solidified Ti-48Al-4Cr alloy with the wheel speed of 30m/s. This research has provided the basis of further studying on the microstructures, reducing the segregation and enhancing the mechanical properites of TiAl alloy.
In this work the effect of cooling rates on microstructure of Ti-48Al-4Cr(at.%) alloy rapidly solidified at different wheel speeds were experimentally investigated by using the single roller melt-spinning technique. The results indicate that after rapid solidification at the wheel speed of 10m/s and 20m/s, the microstructures mainly consist of equiaxed γ phase, few volume fraction of α2, B2 phase particles and lamellar structures exists in the γ phase matrix. At the wheel speed of 30m/s, the matrix changes to α2 phase and the lamellar structures disappear. The nanohardness increases with the cooling rate increasing. It enhances from 4.98±0.10GPa under normal pressure to 7.48±0.16GPa under 4GPa. The nanohardness increases from 5.04±0.09GPa of conventional cast Ti-48Al alloy to 10.48±0.13GPa of rapidly solidified Ti-48Al-4Cr alloy with the wheel speed of 30m/s. This research has provided the basis of further studying on the microstructures, reducing the segregation and enhancing the mechanical properites of TiAl alloy.
2016, 45(7):1749-1754.
Abstract:
In the process of heat treatment, the electric field has a certain effect on the migration of ions inside materials, thus affecting the organization and performance of the material. In this paper, diffusion bonding SiC to Ti was carried out by applying voltage. Study shows that, when the metal and ceramic connect the positive and negative of the electric field respectively, the electric field will promote the increase of the thickness of interface diffusion layer, but reversed connection can weaken the promotion of interface diffusion layer thickening significantly. In the process of SiC/Ti interface diffusion reaction, new phase Ti5Si3 and TiC generate at the interface, and the interface structure from SiC to Ti is SiC/TiC/(Ti5Si3 TiC)/Ti. Mechanical properties testing results show that the shear strength of the joint at 1000℃/2h/7.5MPa is 66.4MPa, but the shear strength of the joint at 950℃/1.5h/7.5MPa/400V is 69.6MPa, so applying voltage during the bonding process can keep the shear strength and, as the same time, improve the efficiency of the bonding.
In the process of heat treatment, the electric field has a certain effect on the migration of ions inside materials, thus affecting the organization and performance of the material. In this paper, diffusion bonding SiC to Ti was carried out by applying voltage. Study shows that, when the metal and ceramic connect the positive and negative of the electric field respectively, the electric field will promote the increase of the thickness of interface diffusion layer, but reversed connection can weaken the promotion of interface diffusion layer thickening significantly. In the process of SiC/Ti interface diffusion reaction, new phase Ti5Si3 and TiC generate at the interface, and the interface structure from SiC to Ti is SiC/TiC/(Ti5Si3 TiC)/Ti. Mechanical properties testing results show that the shear strength of the joint at 1000℃/2h/7.5MPa is 66.4MPa, but the shear strength of the joint at 950℃/1.5h/7.5MPa/400V is 69.6MPa, so applying voltage during the bonding process can keep the shear strength and, as the same time, improve the efficiency of the bonding.
2016, 45(7):1755-1759.
Abstract:
Spinel LiNi0.5Mn1.5O4 and Fe-doped compound LiNi0.45Fe0.1Mn1.45O4 were synthesized by a wet chemical method combining a solid state reaction process. The comparison from the aspects of crystal structure, surface morphology, charge-discharge characteristics and rate capability of spinel LiNi0.5Mn1.5O4 and LiNi0.45Fe0.1Mn1.45O4 was made. The mechanism of doped Fe was deduced based on the measured oxygen deficiency amount from the TGA experiment. The doped Fe can maintain some oxygen deficiency which makes spinel LiNi0.5Mn1.5O4 contain some Mn3 , improving the rate capability.
Spinel LiNi0.5Mn1.5O4 and Fe-doped compound LiNi0.45Fe0.1Mn1.45O4 were synthesized by a wet chemical method combining a solid state reaction process. The comparison from the aspects of crystal structure, surface morphology, charge-discharge characteristics and rate capability of spinel LiNi0.5Mn1.5O4 and LiNi0.45Fe0.1Mn1.45O4 was made. The mechanism of doped Fe was deduced based on the measured oxygen deficiency amount from the TGA experiment. The doped Fe can maintain some oxygen deficiency which makes spinel LiNi0.5Mn1.5O4 contain some Mn3 , improving the rate capability.
2016, 45(7):1760-1764.
Abstract:
The Dss2205/X65 bimerallic plate were welded by the fiber laser，the means of OM were used to observe the microstructure of welding joint. The distribution of the Cr element in the welded joint were studied to infer the fluidity of molten pool. The potentiodynamic scanning method was carried out to measure the anodic polarization curves of DSS2205base metal and the welded joint. The experimental results show that the microstrucure of the welded joint exhabits a typical hierarchical characteristic along thickness direction of welded joint.The Cr distribution in the welded joint shows that the fluidity of molten pool possess the characteristics of Marangoni convection,the Molten metal in Molten pool tend to spread upward flow, and less affected by gravity.Polarization curves show that the corrosion potential between the composite layer of joint and the DSS2205 base metal is same, but the pitting potential of welded joint are lower than that of the base metal DSS2205. Polarization curvesn also show that the joint welded by laser beam with a small focusing spot size shows a better point corrosion resistant ability compared with the joint welded by laser beam with a big focusing spot size.
The Dss2205/X65 bimerallic plate were welded by the fiber laser，the means of OM were used to observe the microstructure of welding joint. The distribution of the Cr element in the welded joint were studied to infer the fluidity of molten pool. The potentiodynamic scanning method was carried out to measure the anodic polarization curves of DSS2205base metal and the welded joint. The experimental results show that the microstrucure of the welded joint exhabits a typical hierarchical characteristic along thickness direction of welded joint.The Cr distribution in the welded joint shows that the fluidity of molten pool possess the characteristics of Marangoni convection,the Molten metal in Molten pool tend to spread upward flow, and less affected by gravity.Polarization curves show that the corrosion potential between the composite layer of joint and the DSS2205 base metal is same, but the pitting potential of welded joint are lower than that of the base metal DSS2205. Polarization curvesn also show that the joint welded by laser beam with a small focusing spot size shows a better point corrosion resistant ability compared with the joint welded by laser beam with a big focusing spot size.
2016, 45(7):1765-1770.
Abstract:
Tungsten (W) coating plasma facing material (PFM) was fabricated on the copper (Cu) substrate by means of plasma spraying technolgoy, and it was analysed that the coating porosity, the theoretical density, the bonding strength between tungsten coating and copper substract, the thermal conductivity, the Vickers micro-hardness distribution of tungsten coating. And it was discussed in detail that the damage evolution of tungsten coatings with both of the direct and in-direct cooling condition. The results indicated that the failure reason of W PFM with the direct cooling was the delamination between the lamellar layers, not the surface damage. The damage evolution of W PFM was as follows: the columnar crystals growing up, micro-cracks between the lamellar layers, then the lamellar layer delamination and W PFM failure. But under the indirect cooling, the heat flux performance of W PFM was limited to 7.5MW/m2, not the 10MW/m2 of the direct cooling W coating, and the main failure behaviors were W coating detachment from Cu substrate, which was induced by Cu melting.
Tungsten (W) coating plasma facing material (PFM) was fabricated on the copper (Cu) substrate by means of plasma spraying technolgoy, and it was analysed that the coating porosity, the theoretical density, the bonding strength between tungsten coating and copper substract, the thermal conductivity, the Vickers micro-hardness distribution of tungsten coating. And it was discussed in detail that the damage evolution of tungsten coatings with both of the direct and in-direct cooling condition. The results indicated that the failure reason of W PFM with the direct cooling was the delamination between the lamellar layers, not the surface damage. The damage evolution of W PFM was as follows: the columnar crystals growing up, micro-cracks between the lamellar layers, then the lamellar layer delamination and W PFM failure. But under the indirect cooling, the heat flux performance of W PFM was limited to 7.5MW/m2, not the 10MW/m2 of the direct cooling W coating, and the main failure behaviors were W coating detachment from Cu substrate, which was induced by Cu melting.
2016, 45(7):1771-1776.
Abstract:
Stress corrosion cracking(SCC) of reactor components welded 304L stainless steel in deoxygenized solution with different concentration chloride ions was studied using slow strain rate testing (SSRT), the basic water chemistry is simulated in pressure water reactor(PWR) primary loop, high temperature and high pressure water containing boric and lithium ion. Results shown the mechanical properties of welded 304L in 1mg/L chloride solution is equal those of welded 304L in inert nitrogen atmosphere, which implied welded 304L is immune to SCC in deoxygenized solution with low concentration chloride. The tendency of SCC susceptibility of welded 304L increased with increasing chloride ion concentration at range of 1mg/L to 50mg/L. There is not obvious crack on the side of fracture, the lower the chloride concentration, the more obvious the necking-down phenomenon, which implied the fracture mechanics is mainly mechanical fracture. There appeared microcracks source at angular parts, which is relative the stress gathering at these parts. The fracture position all lay in the weld and heat affected zone. There occurred huge deformation in the weld and heat affected zone, the near the fracture, the serious the deformation. The welded parts are weaknesses in the reactor components, which should be key monitoring sites for SCC susceptibility and other properties.
Stress corrosion cracking(SCC) of reactor components welded 304L stainless steel in deoxygenized solution with different concentration chloride ions was studied using slow strain rate testing (SSRT), the basic water chemistry is simulated in pressure water reactor(PWR) primary loop, high temperature and high pressure water containing boric and lithium ion. Results shown the mechanical properties of welded 304L in 1mg/L chloride solution is equal those of welded 304L in inert nitrogen atmosphere, which implied welded 304L is immune to SCC in deoxygenized solution with low concentration chloride. The tendency of SCC susceptibility of welded 304L increased with increasing chloride ion concentration at range of 1mg/L to 50mg/L. There is not obvious crack on the side of fracture, the lower the chloride concentration, the more obvious the necking-down phenomenon, which implied the fracture mechanics is mainly mechanical fracture. There appeared microcracks source at angular parts, which is relative the stress gathering at these parts. The fracture position all lay in the weld and heat affected zone. There occurred huge deformation in the weld and heat affected zone, the near the fracture, the serious the deformation. The welded parts are weaknesses in the reactor components, which should be key monitoring sites for SCC susceptibility and other properties.
2016, 45(7):1777-1781.
Abstract:
In order to improve magnetostrictive properties of the polycrystalline Fe-Ga alloys, the rare earth elements Ce, Tb and Dy were doped into Fe-Ga alloys. The microstructures and magnetostrictions of Fe83Ga17 and Fe83Ga17R0.6 ( R=Ce, Tb and Dy ) alloys were studied. The results indicated that Fe83Ga17 alloy consists of a single Fe(Ga) solid solution phase with bcc structure. However, the Fe83Ga17R0.6 ( R=Ce, Tb and Dy ) alloys are composed of the Fe(Ga) solid solution phase and a small amount of R2Fe17 secondary phase. The magnetostriction coefficients of the Fe83Ga17R0.6 ( R=Ce, Tb and Dy ) alloys are significantly larger than that of the Fe83Ga17 alloy. The improvement degree of magnetostrictive properties of Fe-Ga alloy varies with different rare earth elements doping into the alloy. The magnetostriction coefficient of Fe83Ga17Ce0.6 alloy (206×10-6) is larger than that of the Fe83Ga17Tb0.6 (165×10-6) and Fe83Ga17Dy0.6 (161×10-6) at the magnetic field of 557 kA/m.
In order to improve magnetostrictive properties of the polycrystalline Fe-Ga alloys, the rare earth elements Ce, Tb and Dy were doped into Fe-Ga alloys. The microstructures and magnetostrictions of Fe83Ga17 and Fe83Ga17R0.6 ( R=Ce, Tb and Dy ) alloys were studied. The results indicated that Fe83Ga17 alloy consists of a single Fe(Ga) solid solution phase with bcc structure. However, the Fe83Ga17R0.6 ( R=Ce, Tb and Dy ) alloys are composed of the Fe(Ga) solid solution phase and a small amount of R2Fe17 secondary phase. The magnetostriction coefficients of the Fe83Ga17R0.6 ( R=Ce, Tb and Dy ) alloys are significantly larger than that of the Fe83Ga17 alloy. The improvement degree of magnetostrictive properties of Fe-Ga alloy varies with different rare earth elements doping into the alloy. The magnetostriction coefficient of Fe83Ga17Ce0.6 alloy (206×10-6) is larger than that of the Fe83Ga17Tb0.6 (165×10-6) and Fe83Ga17Dy0.6 (161×10-6) at the magnetic field of 557 kA/m.
2016, 45(7):1782-1787.
Abstract:
In order to investigate high temperature mechanical properties and fracture behaviors of Mone1-400 alloy and cladding metal tensile tests were conducted at different temperatures on a Gleeble-1500D thermal simulation machine. The results show that strength of base metal and cladding metal are declining from 700℃ to 1100℃. The plasticity of base metal increases with increasing temperature, while plasticity of the cladding metal declines. At 700℃, the dispersed second phase particles has played a significant role in strengthening the yield strength and tensile strength on the cladding metal, while plasticity of which is seriously deteriorated. At the range of 700 - 1100℃, the fracture pattern of base metal is ductile fracture, while fracture pattern of cladding metal from ductile fracture gradually become brittle fracture. In the actual thermal processing and application, it is crucial to avoid cladding metal large deformation to prevent thermal cracking, and the base metal should not be used above 700℃.
In order to investigate high temperature mechanical properties and fracture behaviors of Mone1-400 alloy and cladding metal tensile tests were conducted at different temperatures on a Gleeble-1500D thermal simulation machine. The results show that strength of base metal and cladding metal are declining from 700℃ to 1100℃. The plasticity of base metal increases with increasing temperature, while plasticity of the cladding metal declines. At 700℃, the dispersed second phase particles has played a significant role in strengthening the yield strength and tensile strength on the cladding metal, while plasticity of which is seriously deteriorated. At the range of 700 - 1100℃, the fracture pattern of base metal is ductile fracture, while fracture pattern of cladding metal from ductile fracture gradually become brittle fracture. In the actual thermal processing and application, it is crucial to avoid cladding metal large deformation to prevent thermal cracking, and the base metal should not be used above 700℃.
2016, 45(7):1788-1792.
Abstract:
Tungsten helix is a component of transfer wave tube (TWT), its high frequency loss and heat dissipation become serious with power level and working frequency of TWT increasing. To solve the problems, gold thin films were deposited on the surface of helix in our previous. How is the thermal reliability of gold thin films when helix operates at higher temperature? In this paper, the binding force between gold film and substrate was tested by using nanoscratch. The film binding forces of samples pre-plated copper respectively for 5s,10s,15s,20s and then gold-plated for 1.5h before and after heat treatment were analyzed.The results indicate that the films adhesion of samples after heat treatment show no obvious decrease compared with those of as-deposited samples. Especially, the binding force of the sample pre-plated copper for 10s after heat increases . The thermal reliability of gold films is good.
Tungsten helix is a component of transfer wave tube (TWT), its high frequency loss and heat dissipation become serious with power level and working frequency of TWT increasing. To solve the problems, gold thin films were deposited on the surface of helix in our previous. How is the thermal reliability of gold thin films when helix operates at higher temperature? In this paper, the binding force between gold film and substrate was tested by using nanoscratch. The film binding forces of samples pre-plated copper respectively for 5s,10s,15s,20s and then gold-plated for 1.5h before and after heat treatment were analyzed.The results indicate that the films adhesion of samples after heat treatment show no obvious decrease compared with those of as-deposited samples. Especially, the binding force of the sample pre-plated copper for 10s after heat increases . The thermal reliability of gold films is good.
2016, 45(7):1793-1797.
Abstract:
Atomic ratio of 1:1 TiNi alloy powder was prepared by high energy ball milling process, then sintered by plasma in vacuum. The TiNi alloy powder and TiNi sintered sample were used to characterize the composition and microstructure by XRD, EDS and SEM, the hardness of the sintered sample was tested. The experimental results show that the TiNi powder was amorphous form after 22h high energy ball milling, the solid state reactions obviously take place and the new phases,such as TiNi, ,Ti3Ni4 ,appear after 30h high energy ball milling. phases of the sintered sample phase are TiNi, Ni4Ti3,Ni3Ti and Ti2Ni, its microstructure is mainly composed of fine grain with size of less 2 micron, its average Vickers hardness is up to 900Hv, after one year natural aging, its average Vickers hardness is down to 680Hv. The hardness of TiNi alloy prepared by plasma sintering is 2 ~ 5 times of that prepared by arc melting method.
Atomic ratio of 1:1 TiNi alloy powder was prepared by high energy ball milling process, then sintered by plasma in vacuum. The TiNi alloy powder and TiNi sintered sample were used to characterize the composition and microstructure by XRD, EDS and SEM, the hardness of the sintered sample was tested. The experimental results show that the TiNi powder was amorphous form after 22h high energy ball milling, the solid state reactions obviously take place and the new phases,such as TiNi, ,Ti3Ni4 ,appear after 30h high energy ball milling. phases of the sintered sample phase are TiNi, Ni4Ti3,Ni3Ti and Ti2Ni, its microstructure is mainly composed of fine grain with size of less 2 micron, its average Vickers hardness is up to 900Hv, after one year natural aging, its average Vickers hardness is down to 680Hv. The hardness of TiNi alloy prepared by plasma sintering is 2 ~ 5 times of that prepared by arc melting method.
2016, 45(7):1798-1803.
Abstract:
The alloys with Ti, Zr separate and combined micro-alloying were prepared by ingot metallurgy method. The effect of Ti, Zr separate and combined addition on the grain refinement and anti-fading performance of grain refinement was investigated and compared by metallographic microscope (OM), scanning electron microscopy (SEM), energy spectrum (EDS) and X-ray diffraction (XRD) and other means. The results show that Ti, Zr composite added possesses more excellent grain refining effect and more significant anti-fading performance of grain refinement than that of Ti, Zr added alone. When holding time up to 110minute, the Al-0.15Zr-0.15Ti alloy still keeps effective grain refinement effect.
The alloys with Ti, Zr separate and combined micro-alloying were prepared by ingot metallurgy method. The effect of Ti, Zr separate and combined addition on the grain refinement and anti-fading performance of grain refinement was investigated and compared by metallographic microscope (OM), scanning electron microscopy (SEM), energy spectrum (EDS) and X-ray diffraction (XRD) and other means. The results show that Ti, Zr composite added possesses more excellent grain refining effect and more significant anti-fading performance of grain refinement than that of Ti, Zr added alone. When holding time up to 110minute, the Al-0.15Zr-0.15Ti alloy still keeps effective grain refinement effect.
2016, 45(7):1804-1810.
Abstract:
The magnetic field intensity of central electromagnetic stirring equipment and the melt pool’s electromagnetic force were simulated, and the influence of rotating magnetic field on melt pool electromagnetic force,the flow field and temperature distribution of the meltpool was analyzed by finite element method.The results showed that the electricity magnetic in melt pool decreased slowly at first when increasing the current frequency, and the power loss increased rapidly at the same time,when frequency continued to rise, the electromagnetic force increased gradually and the power loss became stable at this time.And the magnetic field strength of electromagnetic stirrer changed periodically in one exciting current cycle.Under the condition of rotating magnetic field,the temperature and the temperature gradient of melt pooldecreased, and circulation in melt pool circumferential direction formed and its velocity distribution was uniform.
The magnetic field intensity of central electromagnetic stirring equipment and the melt pool’s electromagnetic force were simulated, and the influence of rotating magnetic field on melt pool electromagnetic force,the flow field and temperature distribution of the meltpool was analyzed by finite element method.The results showed that the electricity magnetic in melt pool decreased slowly at first when increasing the current frequency, and the power loss increased rapidly at the same time,when frequency continued to rise, the electromagnetic force increased gradually and the power loss became stable at this time.And the magnetic field strength of electromagnetic stirrer changed periodically in one exciting current cycle.Under the condition of rotating magnetic field,the temperature and the temperature gradient of melt pooldecreased, and circulation in melt pool circumferential direction formed and its velocity distribution was uniform.
2016, 45(7):1811-1815.
Abstract:
Bulk intermetallic-ceramic composite Al2O3/Ti4AlN3 was fabricated by in-situ hot isostatic pressing of Al3Ti/TiN nanopowders under 1280 ℃/150 MPa/1 h conditions . The microstructure of composite were investigated by X-ray diffraction, SEM(Scanning Electron Microscope) and TEM(Transmission Electron Microscope). It is revealed that matrix Ti4AlN3 grains are strip-like and Al2O3 particles disperse in matrix uniformly with irregular shape. The averagegrain size of Ti4AlN3 is 7 μm. The size of Al2O3 particles are in the range of 1-3 μm, and volume fraction is about 40%. The Vickers hardness of Al2O3/Ti4AlN3 composite is 6.7GPa, maximal compressed strength is 1 800 MPa. Maximum compressive strain increased from 4% to 6.2%.Compared with the micro-hardness and compressed strength，Al2O3/Ti4AlN3 composite is higher than single Ti4AlN3 phase. The strengthening mechanisms of composite are fine grain strengthening and second phase strengthening.
Bulk intermetallic-ceramic composite Al2O3/Ti4AlN3 was fabricated by in-situ hot isostatic pressing of Al3Ti/TiN nanopowders under 1280 ℃/150 MPa/1 h conditions . The microstructure of composite were investigated by X-ray diffraction, SEM(Scanning Electron Microscope) and TEM(Transmission Electron Microscope). It is revealed that matrix Ti4AlN3 grains are strip-like and Al2O3 particles disperse in matrix uniformly with irregular shape. The averagegrain size of Ti4AlN3 is 7 μm. The size of Al2O3 particles are in the range of 1-3 μm, and volume fraction is about 40%. The Vickers hardness of Al2O3/Ti4AlN3 composite is 6.7GPa, maximal compressed strength is 1 800 MPa. Maximum compressive strain increased from 4% to 6.2%.Compared with the micro-hardness and compressed strength，Al2O3/Ti4AlN3 composite is higher than single Ti4AlN3 phase. The strengthening mechanisms of composite are fine grain strengthening and second phase strengthening.
2016, 45(7):1816-1820.
Abstract:
In this paper, a novel method Micro-fields activated sintering technology was applied to the preparation of NiTi alloy. Cylindrical specimens with the diameter of 4mm and a height of 4mm were prepared successfully in a short time (about 8mins). The effect of heating rate on the preparation of NiTi alloy was discussed. The research result shows that the axial reduction in rapid heating stage was the biggest among the four sintering stages of Micro-FAST, which directly influenced the quality of sintering samples. In the experimental range of 25℃/s to 125℃/s, the relative densities of NiTi alloy sintered by Micro-FAST was decreased with the increasing heating rates. The higher the heating rate, the bigger the electric current is. Under electric current, atomic diffusion was promoted. As a result, NiTi2 and Ni3Ti were easier to be formed, and the effect of Kirkendall was aggravated. Meanwhile, local liquid-phase was produced by local high temperature under electric current, which promoted the fusions of particles and pores.
In this paper, a novel method Micro-fields activated sintering technology was applied to the preparation of NiTi alloy. Cylindrical specimens with the diameter of 4mm and a height of 4mm were prepared successfully in a short time (about 8mins). The effect of heating rate on the preparation of NiTi alloy was discussed. The research result shows that the axial reduction in rapid heating stage was the biggest among the four sintering stages of Micro-FAST, which directly influenced the quality of sintering samples. In the experimental range of 25℃/s to 125℃/s, the relative densities of NiTi alloy sintered by Micro-FAST was decreased with the increasing heating rates. The higher the heating rate, the bigger the electric current is. Under electric current, atomic diffusion was promoted. As a result, NiTi2 and Ni3Ti were easier to be formed, and the effect of Kirkendall was aggravated. Meanwhile, local liquid-phase was produced by local high temperature under electric current, which promoted the fusions of particles and pores.
2016, 45(7):1821-1825.
Abstract:
The influence of cathodic arc plasma titanizing on the structure and tribological performance of 316L stainless steels was studied by scanning electron microscope, X-ray diffractometer, micro-hardness tester, 3D profile-meter, and reciprocating tribometer in the paper. It was found that the closely adherent titanized layer with a peak titanium content of 66 wt.% can be obtained by cathodic arc plasma titanizing. The titanized layer is composed of Fe2Ti and NiTi; the surface hardness of the titanized layer with a depth of 150μm is increased to 400 HV from 200 HV of original substrate. Under dry friction, the friction coefficient of the titanized layer is obviously lower than that of the original substrate, and the cathodic arc plasma titanizing improves the wear resistance of 316L stainless steels by 6 times. The wear mechanism of the original substrate is abrasive wear, oxidation wear and adhesive wear, while the wear mechanism of the titanized samples is mass loss caused by flaking of the particles in the titanized layer.
The influence of cathodic arc plasma titanizing on the structure and tribological performance of 316L stainless steels was studied by scanning electron microscope, X-ray diffractometer, micro-hardness tester, 3D profile-meter, and reciprocating tribometer in the paper. It was found that the closely adherent titanized layer with a peak titanium content of 66 wt.% can be obtained by cathodic arc plasma titanizing. The titanized layer is composed of Fe2Ti and NiTi; the surface hardness of the titanized layer with a depth of 150μm is increased to 400 HV from 200 HV of original substrate. Under dry friction, the friction coefficient of the titanized layer is obviously lower than that of the original substrate, and the cathodic arc plasma titanizing improves the wear resistance of 316L stainless steels by 6 times. The wear mechanism of the original substrate is abrasive wear, oxidation wear and adhesive wear, while the wear mechanism of the titanized samples is mass loss caused by flaking of the particles in the titanized layer.
2016, 45(7):1826-1831.
Abstract:
In order to further improve the oxidation resistance of the open-cell Ni-Cr-Fe alloy foam, the Y-Cr and Ce-Cr coatings were deposited onto the Ni-Cr-Fe alloy foam by a pack cementation process, respectively. The oxidation resistance of Y-Cr and Ce-Cr coatings were also studied under static oxidation conditions for 120 h at 900℃ and 1000℃. The phase composition, the morphology and microstructure of the Y–Cr coating and the Ce–Cr coating before and after oxidation were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The results show that the Ce–Cr coating is continuous and compact, and surface grain refinement in Ce–Cr coating can be achieved by comparison of experimental results in Y–Cr coating. The interface between coating and substrate is combined closely. Simultaneously, the Ce–Cr coated foam has better high-temperature oxidation resistance than the Y–Cr coated foams, and the oxidation kinetics curve of Ce-Cr coated foam follows a parabolic law. This is because that a uniform and dense Cr2O3 layer is formed on the surface of the Ce–Cr coating. At the same time, interfacial transition layer consisting of Ni-Cr-Fe and [Fe,Ni] is formed around the interface of Ce–Cr coating and substrate to facilitate metallurgical bonding, resulting in enhanced interfacial bonding between the coating and substrate.
In order to further improve the oxidation resistance of the open-cell Ni-Cr-Fe alloy foam, the Y-Cr and Ce-Cr coatings were deposited onto the Ni-Cr-Fe alloy foam by a pack cementation process, respectively. The oxidation resistance of Y-Cr and Ce-Cr coatings were also studied under static oxidation conditions for 120 h at 900℃ and 1000℃. The phase composition, the morphology and microstructure of the Y–Cr coating and the Ce–Cr coating before and after oxidation were studied by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The results show that the Ce–Cr coating is continuous and compact, and surface grain refinement in Ce–Cr coating can be achieved by comparison of experimental results in Y–Cr coating. The interface between coating and substrate is combined closely. Simultaneously, the Ce–Cr coated foam has better high-temperature oxidation resistance than the Y–Cr coated foams, and the oxidation kinetics curve of Ce-Cr coated foam follows a parabolic law. This is because that a uniform and dense Cr2O3 layer is formed on the surface of the Ce–Cr coating. At the same time, interfacial transition layer consisting of Ni-Cr-Fe and [Fe,Ni] is formed around the interface of Ce–Cr coating and substrate to facilitate metallurgical bonding, resulting in enhanced interfacial bonding between the coating and substrate.
2016, 45(7):1832-1835.
Abstract:
Coated conductors become the significant materials that provide the potential to support high current for electric utility and high magnetic field applications at 77 K. In RABiTS/CSD routs with low-cost, the epitaxial growth of buffer layer on textured metallic substrate is an essential precondition for the biaxial texture growth of superconducting layer and its high current carrying capacity. Therefore, the study of the epitaxial growth behavior of buffer layer becomes important. In this paper, we have explored the influence of the thermal decomposition behavior of LTO-gels and the heat-treatment process route on the texture and morphology evolution of buffer layer. LTO buffer layer with good c-axis texture and smooth surface could be obtained by choosing the suitable LTO precursor solution and adjusting a rapid elevated temperature processing methods.
Coated conductors become the significant materials that provide the potential to support high current for electric utility and high magnetic field applications at 77 K. In RABiTS/CSD routs with low-cost, the epitaxial growth of buffer layer on textured metallic substrate is an essential precondition for the biaxial texture growth of superconducting layer and its high current carrying capacity. Therefore, the study of the epitaxial growth behavior of buffer layer becomes important. In this paper, we have explored the influence of the thermal decomposition behavior of LTO-gels and the heat-treatment process route on the texture and morphology evolution of buffer layer. LTO buffer layer with good c-axis texture and smooth surface could be obtained by choosing the suitable LTO precursor solution and adjusting a rapid elevated temperature processing methods.
2016, 45(7):1836-1841.
Abstract:
Two precursors, Tungstic acid/DWCNTs and pure tungstic acid, prepared by liquid phase method, were calcinated at 700 ℃for 2h at nitrogen atmosphere. Therefore, WO3/DWCNTs and WO3 powder were obtained respectively. The structure and morphology of as-synthesized products were characterized by powder X-ray diffraction (XRD) and Scanning electron microscope (SEM). The photocatalytic activity of the samples was evaluated by photocatalytic degradation of the methylene blue under visible light (11W) irridation. The clear upper layer solution was analyzed by a Milton Roy Spectronic 3000 Array spectrophotometer (New York, USA).The photocatalytic degradation rate of the samples were calculated according to the lambert beer''s law. The degradation rate of WO3/DWCNTs and pure WO3 is 87.50% and 25.39% respectively under photocatalytic degradation for 30 min. Results show that as the size of particles decreases, the specific surface area increases, and the adsorption capability of WO3/DWCNTs is improved; all these effects are ascribed to the addition of DWCNTs.Therefore, the WO3/DWCNTs composite photocatalyst exhibits much higher photocatalytic activity than that of pure WO3.
Two precursors, Tungstic acid/DWCNTs and pure tungstic acid, prepared by liquid phase method, were calcinated at 700 ℃for 2h at nitrogen atmosphere. Therefore, WO3/DWCNTs and WO3 powder were obtained respectively. The structure and morphology of as-synthesized products were characterized by powder X-ray diffraction (XRD) and Scanning electron microscope (SEM). The photocatalytic activity of the samples was evaluated by photocatalytic degradation of the methylene blue under visible light (11W) irridation. The clear upper layer solution was analyzed by a Milton Roy Spectronic 3000 Array spectrophotometer (New York, USA).The photocatalytic degradation rate of the samples were calculated according to the lambert beer''s law. The degradation rate of WO3/DWCNTs and pure WO3 is 87.50% and 25.39% respectively under photocatalytic degradation for 30 min. Results show that as the size of particles decreases, the specific surface area increases, and the adsorption capability of WO3/DWCNTs is improved; all these effects are ascribed to the addition of DWCNTs.Therefore, the WO3/DWCNTs composite photocatalyst exhibits much higher photocatalytic activity than that of pure WO3.
2016, 45(7):1842-1847.
Abstract:
B4C/6061Al neutron absorber materials with four volume fractions(0vol%，20vol.%,30vol.% and 40vol.%) were successfully fabricated by vacuum hot pressing and following hot rolling(VHPR) in atmospheric environments. Microstructure and interface behavior were studied. Besides，the tensile strength, fracture behavior and strengthening mechanism of neutron absorber materials were also investigated. The results showed that the space network of matrix was constructed by 6061Al.Besides, the interface reached metallurgical bonding state and the thickness of the diffusion layer was about 5um. With the increase of the volume fraction of B4C, some small B4C particles agglomerated locally, and the tensile strength first increased and then decreased.The main fracture behaviors were interface fracture and the cleavage fracture of B4C particles. After multi-pass hot cross rolling, the grains of the matrix materials were refined and the distribution of B4C particles was also improved; besides, internal defects were reduced and plastic deformation zones around B4C particles also formed after hot cross rolling.
B4C/6061Al neutron absorber materials with four volume fractions(0vol%，20vol.%,30vol.% and 40vol.%) were successfully fabricated by vacuum hot pressing and following hot rolling(VHPR) in atmospheric environments. Microstructure and interface behavior were studied. Besides，the tensile strength, fracture behavior and strengthening mechanism of neutron absorber materials were also investigated. The results showed that the space network of matrix was constructed by 6061Al.Besides, the interface reached metallurgical bonding state and the thickness of the diffusion layer was about 5um. With the increase of the volume fraction of B4C, some small B4C particles agglomerated locally, and the tensile strength first increased and then decreased.The main fracture behaviors were interface fracture and the cleavage fracture of B4C particles. After multi-pass hot cross rolling, the grains of the matrix materials were refined and the distribution of B4C particles was also improved; besides, internal defects were reduced and plastic deformation zones around B4C particles also formed after hot cross rolling.
2016, 45(7):1848-1854.
Abstract:
The effect of Er content on microstructure of Al-Zn-In alloy anodes were studied by using scanning electron microscopy(SEM), energy spectrum analysis and X-ray diffraction analysis. The polarization curves and EIS of Al-Zn-In alloy with different Er content were tested in the 3.5wt% NaCl solution. The results show that with the increase of Er content, the dendrite was refined, the amount of inter-dendritic precipitates increased, the corrosion potential became more positive, the radius of electrochemical impedance spectroscopy enlarged and corrosion rate also decreased. Al-5Zn-0.03In-1Er alloy has refined dendrites and proper amount of precipitates, with the corrision morphologies of independent pitting, corrosion in uniformity, which is an ideal choice for using as sacrifical alloy.
The effect of Er content on microstructure of Al-Zn-In alloy anodes were studied by using scanning electron microscopy(SEM), energy spectrum analysis and X-ray diffraction analysis. The polarization curves and EIS of Al-Zn-In alloy with different Er content were tested in the 3.5wt% NaCl solution. The results show that with the increase of Er content, the dendrite was refined, the amount of inter-dendritic precipitates increased, the corrosion potential became more positive, the radius of electrochemical impedance spectroscopy enlarged and corrosion rate also decreased. Al-5Zn-0.03In-1Er alloy has refined dendrites and proper amount of precipitates, with the corrision morphologies of independent pitting, corrosion in uniformity, which is an ideal choice for using as sacrifical alloy.
2016, 45(7):1855-1860.
Abstract:
Using friction stir processing to produce fine-grained microstructure in AZ31 magnesium alloy. The superplasticity of base metal and fine-grained AZ31 magnesium alloy with different grain sizes were compared. The results show that microstructure of the AZ31 hot-rolled plate with an average grain size of 7.67μm is refined to 0.94μm~3.21μm. The maximum elongation of the BM is 630% at 450℃ and 5×10-4/s-1, The maximum elongation of the FSP AZ31 alloy is 405% in the same situation. Grain size have no linear relationship with superplastic performance. Superplastic deformation mechanism is mainly based on grain boundary sliding. Twin crystal also affects the deformation. The failure mechanism is cavity generation, growth and coalescence.
Using friction stir processing to produce fine-grained microstructure in AZ31 magnesium alloy. The superplasticity of base metal and fine-grained AZ31 magnesium alloy with different grain sizes were compared. The results show that microstructure of the AZ31 hot-rolled plate with an average grain size of 7.67μm is refined to 0.94μm~3.21μm. The maximum elongation of the BM is 630% at 450℃ and 5×10-4/s-1, The maximum elongation of the FSP AZ31 alloy is 405% in the same situation. Grain size have no linear relationship with superplastic performance. Superplastic deformation mechanism is mainly based on grain boundary sliding. Twin crystal also affects the deformation. The failure mechanism is cavity generation, growth and coalescence.
2016, 45(7):1861-1865.
Abstract:
The joining of arc-sprayed aluminum coatings to AZ91D substrates was achieved by solid-liquid bonding method, and the microstructures, elements and phases of the interface were analyzed. The results show that hole-defect is usually occurred in the interface after the coatings were cleaned by surface treatment. Metallurgical bonding is formed between the untreated aluminum coating and AZ91D substrate, and intermetallic compound layers are found in the interface. As the pouring temperatures rise, the diffusion regions become larger, and the coatings are gradually transformed into Al12Mg17 and Al3Mg2. The heat treatment on the composite can lead to a uniform structure and a larger diffusion region.
The joining of arc-sprayed aluminum coatings to AZ91D substrates was achieved by solid-liquid bonding method, and the microstructures, elements and phases of the interface were analyzed. The results show that hole-defect is usually occurred in the interface after the coatings were cleaned by surface treatment. Metallurgical bonding is formed between the untreated aluminum coating and AZ91D substrate, and intermetallic compound layers are found in the interface. As the pouring temperatures rise, the diffusion regions become larger, and the coatings are gradually transformed into Al12Mg17 and Al3Mg2. The heat treatment on the composite can lead to a uniform structure and a larger diffusion region.
2016, 45(7):1866-1870.
Abstract:
Hastelloy C-276 was solution-treated at 1150℃ for 30min, after that, the samples were subjected to cold rolling with different reductions and annealing at high temperature. The grain boundary character distribution(GBCD) and the grain boundary plane distribution were characterized by electron backscatter diffraction (EBSD) technique. The results shown the fraction of Σ1 boundary was decreasing during annealing process. Meanwhile, the fraction of Σ9 boundary and Σ27 boundary was increasing. This is due to the stored energy was exposed to the migration of grain boundaries and promoting the interaction of grain boundaries. While grain size grew up abnormally during heat treatment, that led to the formation of special boundary. The special boundaries disrupted the connectivity of high angle boundaries. After the low-strains higher temperature annealing process, Σ3 boundaries with the {111} plane were twist boundaries and Σ9 boundaries with the [110] zone were tilt boundaries. Under different deformation conditions, the distribution of Σ3 grain boundary plane was different from Σ9 grain boundary plane, due to the proportion of Σ3 grain boundaries was different and the interactions of special boundaries were occurred.
Hastelloy C-276 was solution-treated at 1150℃ for 30min, after that, the samples were subjected to cold rolling with different reductions and annealing at high temperature. The grain boundary character distribution(GBCD) and the grain boundary plane distribution were characterized by electron backscatter diffraction (EBSD) technique. The results shown the fraction of Σ1 boundary was decreasing during annealing process. Meanwhile, the fraction of Σ9 boundary and Σ27 boundary was increasing. This is due to the stored energy was exposed to the migration of grain boundaries and promoting the interaction of grain boundaries. While grain size grew up abnormally during heat treatment, that led to the formation of special boundary. The special boundaries disrupted the connectivity of high angle boundaries. After the low-strains higher temperature annealing process, Σ3 boundaries with the {111} plane were twist boundaries and Σ9 boundaries with the [110] zone were tilt boundaries. Under different deformation conditions, the distribution of Σ3 grain boundary plane was different from Σ9 grain boundary plane, due to the proportion of Σ3 grain boundaries was different and the interactions of special boundaries were occurred.
2016, 45(7):1871-1875.
Abstract:
Tungsten-rhenium mixed powders were prepared by spray drying followed by two-step hydrogen reduction method. With these powders, W-Re mixed metal matrix cathodes were prepared by processes of die pressing, sintering and impregnation. Thermal electron emission properties of the cathodes were tested using the self-prepared pulsed power testing system. SEM, XRD and AES were adopted to analyze the surface morphology, phase structure and surface chemical elements of the cathodes respectively. It revealed that the phase of the cathodes depends on the content of rhenium in the matrixs. The W-75Re cathode (containing 75at% Re) is composed of Re3W singular phase. The emission testing results show that the W-75Re cathode impregnated with 411 salt has the lowest work function of 1.902 eV and the highest zero field emission current density of 14.03A cm-2 at 1000℃b among the prepared cathodes. It is possibly due to the high concentration of Re in the matrix, which results in fine grains in the matrix and is favourable to the formation of active Ba element and its diffusion on the cathode surface.
Tungsten-rhenium mixed powders were prepared by spray drying followed by two-step hydrogen reduction method. With these powders, W-Re mixed metal matrix cathodes were prepared by processes of die pressing, sintering and impregnation. Thermal electron emission properties of the cathodes were tested using the self-prepared pulsed power testing system. SEM, XRD and AES were adopted to analyze the surface morphology, phase structure and surface chemical elements of the cathodes respectively. It revealed that the phase of the cathodes depends on the content of rhenium in the matrixs. The W-75Re cathode (containing 75at% Re) is composed of Re3W singular phase. The emission testing results show that the W-75Re cathode impregnated with 411 salt has the lowest work function of 1.902 eV and the highest zero field emission current density of 14.03A cm-2 at 1000℃b among the prepared cathodes. It is possibly due to the high concentration of Re in the matrix, which results in fine grains in the matrix and is favourable to the formation of active Ba element and its diffusion on the cathode surface.
2016, 45(7):1876-1880.
Abstract:
Ti4 was selected to modified PbZrO3, and sol-gel method was used to prepare PZ and PZT (95/5) dried gel powder. XRD results showed that the calcination temperature of PZ is 900℃ with single perovskite structure, while that for PZT (95/5) is 750℃. SEM results showed that PZ is sintered into ceramic when calcined at 900℃ and the grain boundary is obvious. However, the particle size of PZT(95/5) is about 150nm after calcined at 750℃. TEM and EDS results indicated that PZT (95/5) nano-powder with single perovskite structure is antiferroelectric material. The content of Ti4 was determined by ICP-OES.DSC-TGA results illustrated that a large number of Ti4 hydroxyl substances was formed because of the addition of Ti4 . And with the decomposition of Ti4 hydroxyl substances, a large amount of heat was released, which is conducive to the crystallization of PZT(95/5).
Ti4 was selected to modified PbZrO3, and sol-gel method was used to prepare PZ and PZT (95/5) dried gel powder. XRD results showed that the calcination temperature of PZ is 900℃ with single perovskite structure, while that for PZT (95/5) is 750℃. SEM results showed that PZ is sintered into ceramic when calcined at 900℃ and the grain boundary is obvious. However, the particle size of PZT(95/5) is about 150nm after calcined at 750℃. TEM and EDS results indicated that PZT (95/5) nano-powder with single perovskite structure is antiferroelectric material. The content of Ti4 was determined by ICP-OES.DSC-TGA results illustrated that a large number of Ti4 hydroxyl substances was formed because of the addition of Ti4 . And with the decomposition of Ti4 hydroxyl substances, a large amount of heat was released, which is conducive to the crystallization of PZT(95/5).
2016, 45(7):1881-1886.
Abstract:
In order to prepare spherical particles of cobalt powders and add Y2O3 into cobalt powders, the preparation thermodynamic of the precursor of Co-Y2O3 composite powders by coprecipitation was analyzed. The lg[M]T-pH diagram was obtained by analyzing the thermodynamics of Co2 -Y3 -NH3-C2O42--H2O precipitation system. It is shown that the complexation of Co2 ions is promoted by increasing the total concentration of oxalic acid root [C]T and ammonium root [N]T could. The precipitation rate of Y3 ion is only influenced by the total concentration of oxalic acid root [C]T and declines with its increase. The optimum pH values for the precipitation of Co2 and Y3 are 2~2.5 and 1.5~2.5, respectively. The precursor of Co-Y2O3 composite powders was prepared by coprecipitation with the pH value of 2.5. The shape of the precursor composite powders is cluster ball with good dispersion. The spherical Co-Y2O3 composite powders with uniform size distribution and the mean particle size of about 5 μm were obtained.
In order to prepare spherical particles of cobalt powders and add Y2O3 into cobalt powders, the preparation thermodynamic of the precursor of Co-Y2O3 composite powders by coprecipitation was analyzed. The lg[M]T-pH diagram was obtained by analyzing the thermodynamics of Co2 -Y3 -NH3-C2O42--H2O precipitation system. It is shown that the complexation of Co2 ions is promoted by increasing the total concentration of oxalic acid root [C]T and ammonium root [N]T could. The precipitation rate of Y3 ion is only influenced by the total concentration of oxalic acid root [C]T and declines with its increase. The optimum pH values for the precipitation of Co2 and Y3 are 2~2.5 and 1.5~2.5, respectively. The precursor of Co-Y2O3 composite powders was prepared by coprecipitation with the pH value of 2.5. The shape of the precursor composite powders is cluster ball with good dispersion. The spherical Co-Y2O3 composite powders with uniform size distribution and the mean particle size of about 5 μm were obtained.
47 Study on Preparation, Catalytic and Antibacterial Properties of Silver-deposited Fe3O4 Nanoparticles
2016, 45(7):1887-1892.
Abstract:
Silver-deposited magnetic nanoparticles (PDA-Fe3O4@Ag) were prepared though the seed-mediated method exploiting the adsorption of silver ions by the polydopamine (PDA) which was coated on the surface of Fe3O4. The preparation process was studied using UV-Vis spectra and the prepared nanoparticles were characterized with several analytical techniques including Fourier-transform infrared (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM). The catalytic action on the reduction of 4-nitrophenol and the antibacterial property of PDA-Fe3O4@Ag were studied. The result indicates that the existence of gold seeds is the key to prepare PDA-Fe3O4@Ag nanoparticles. The magnetic catalyst can be separated easily from the reaction system by applied magnetic field, and still has good catalytic performance after repeated recycling. In addition PDA-Fe3O4@Ag nanoparticles exhibit bactericidal properties, and still shows good bactericidal effect on S. aureus after recycling use for 5 times.
Silver-deposited magnetic nanoparticles (PDA-Fe3O4@Ag) were prepared though the seed-mediated method exploiting the adsorption of silver ions by the polydopamine (PDA) which was coated on the surface of Fe3O4. The preparation process was studied using UV-Vis spectra and the prepared nanoparticles were characterized with several analytical techniques including Fourier-transform infrared (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), and vibrating sample magnetometer (VSM). The catalytic action on the reduction of 4-nitrophenol and the antibacterial property of PDA-Fe3O4@Ag were studied. The result indicates that the existence of gold seeds is the key to prepare PDA-Fe3O4@Ag nanoparticles. The magnetic catalyst can be separated easily from the reaction system by applied magnetic field, and still has good catalytic performance after repeated recycling. In addition PDA-Fe3O4@Ag nanoparticles exhibit bactericidal properties, and still shows good bactericidal effect on S. aureus after recycling use for 5 times.
2016, 45(7):1893-1897.
Abstract:
Recycling coal fly ash provides the perfect opportunity to achieve the significant economic and environmental benefits because of the vast number of potential applications. A production procedure is reported for the recovery of gallium from production of alumina from high-alumina coal fly ash with predesilication and lime-soda sinter combination process. The present paper gives a comprehensive description of the whole process. The low concentration of gallium in the spent liquor, along with the high concentration of aluminum, prompted the use of chelating ion exchangers as an alternative separation process. Gallium extraction studies were carried out using chelating ion exchangers. The experimental data were simulated and analyzed by Boltzmann distribution function. The paper also deals with the pitting corrosion of carbon steel as well as the studies carried out on the glass flake mortar resistant to corrosion.
Recycling coal fly ash provides the perfect opportunity to achieve the significant economic and environmental benefits because of the vast number of potential applications. A production procedure is reported for the recovery of gallium from production of alumina from high-alumina coal fly ash with predesilication and lime-soda sinter combination process. The present paper gives a comprehensive description of the whole process. The low concentration of gallium in the spent liquor, along with the high concentration of aluminum, prompted the use of chelating ion exchangers as an alternative separation process. Gallium extraction studies were carried out using chelating ion exchangers. The experimental data were simulated and analyzed by Boltzmann distribution function. The paper also deals with the pitting corrosion of carbon steel as well as the studies carried out on the glass flake mortar resistant to corrosion.
2016, 45(7):1898-1902.
Abstract:
Diffusion bonding of micrometers thick U-Al sheets by hot pressing in vacuum was carried out under different temperatures, pressures and holding times. We have carried on the microscopic analysis, energy spectrum analysis and nanoindentation test to the bonding interface. The appropriate process parameters without diffusion layer were 350 ℃/ 63 MPa/ 1 h. Under the precondition of 1 h holding time, the process parameters for homogeneous diffusion layer were 400 ℃/ 80 MPa. The composition of homogeneous diffusion layer was mainly UAl2.
Diffusion bonding of micrometers thick U-Al sheets by hot pressing in vacuum was carried out under different temperatures, pressures and holding times. We have carried on the microscopic analysis, energy spectrum analysis and nanoindentation test to the bonding interface. The appropriate process parameters without diffusion layer were 350 ℃/ 63 MPa/ 1 h. Under the precondition of 1 h holding time, the process parameters for homogeneous diffusion layer were 400 ℃/ 80 MPa. The composition of homogeneous diffusion layer was mainly UAl2.
2016, 45(7):1903-1909.
Abstract:
High Nb containing TiAl based alloy has more excellent mechanical properties than tranditional TiAl based alloy, but ω phase which is a hard and brittle phase in as-cast, as-worked and thermal exposured high Nb containing TiAl based alloy in the range of service temperature is bad for the improvement of mechanical propeties and limits the further application of high Nb containing TiAl based alloy. The progress in research on ω phase in high Nb containing TiAl based alloy is summarized. Mechanism of ω phase formation, microstructure morphology, the effcte on menchanical properties and elimination of ω phase in high Nb containing based alloy are discussed.
High Nb containing TiAl based alloy has more excellent mechanical properties than tranditional TiAl based alloy, but ω phase which is a hard and brittle phase in as-cast, as-worked and thermal exposured high Nb containing TiAl based alloy in the range of service temperature is bad for the improvement of mechanical propeties and limits the further application of high Nb containing TiAl based alloy. The progress in research on ω phase in high Nb containing TiAl based alloy is summarized. Mechanism of ω phase formation, microstructure morphology, the effcte on menchanical properties and elimination of ω phase in high Nb containing based alloy are discussed.
2016, 45(7):1910-1916.
Abstract:
Among various Li-ion battery (LIB) anodes, the binary Mn-based transition metal oxides (AMn2O4, A = Zn, Co, Ni, etc.) have bee proven to be the ideal candidates for LIBs. This review mainly introduced their energy storage mechanism, synthetic methods and relationship between the structure and Li-storage properties, based on three kinds of anode materials of ZnMn2O4, CoMn2O4 and NiMn2O4. The existing problems of each material, and corresponding settlements were presented to facilitate its promotion in the LIB market.
Among various Li-ion battery (LIB) anodes, the binary Mn-based transition metal oxides (AMn2O4, A = Zn, Co, Ni, etc.) have bee proven to be the ideal candidates for LIBs. This review mainly introduced their energy storage mechanism, synthetic methods and relationship between the structure and Li-storage properties, based on three kinds of anode materials of ZnMn2O4, CoMn2O4 and NiMn2O4. The existing problems of each material, and corresponding settlements were presented to facilitate its promotion in the LIB market.
