Search2018 Vol. 25, No. 9
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2018, vol. 25, no. 9, pp.
981-989.
https://doi.org/10.1007/s12613-018-1648-x
Abstract:
Comprehensive utilization of pyrite cinders is increasingly important because of their huge annual outputs and potential valuable metals recovery to cope with the gradual depletion of high-grade mineral resources. In this work, a new process, i.e., a high-temperature chlorination-magnetizing roasting-magnetic separation process, was proposed for recovering Fe and removing Zn, Pb from a low-grade pyrite cinder containing 49.90wt% Fe, 1.23wt% Zn, and 0.29wt% Pb. Various parameters, including the chlorinating conditions (dosage of CaCl2, temperature, and time) and the magnetization roasting conditions (amount of coal, temperature, and time) were investigated. The results indicate that the proposed process is effective for Fe recovery and Zn, Pb removal from the pyrite cinder. Through this process, 97.06% Zn, 96.82% Pb, and approximately 90% S can be removed, and 89.74% Fe is recovered as magnetite into the final product under optimal conditions. A purified magnetite concentrate containing 63.07wt% Fe, 0.16wt% P, 0.26wt% S, and trace amounts of nonferrous metals (0.005wt% Cu, 0.013wt% Pb, and 0.051wt% Zn) was obtained. The concentrate can be potentially used as a high-quality feed material for producing oxidized pellets by blending with other high-grade iron ore concentrates.
Comprehensive utilization of pyrite cinders is increasingly important because of their huge annual outputs and potential valuable metals recovery to cope with the gradual depletion of high-grade mineral resources. In this work, a new process, i.e., a high-temperature chlorination-magnetizing roasting-magnetic separation process, was proposed for recovering Fe and removing Zn, Pb from a low-grade pyrite cinder containing 49.90wt% Fe, 1.23wt% Zn, and 0.29wt% Pb. Various parameters, including the chlorinating conditions (dosage of CaCl2, temperature, and time) and the magnetization roasting conditions (amount of coal, temperature, and time) were investigated. The results indicate that the proposed process is effective for Fe recovery and Zn, Pb removal from the pyrite cinder. Through this process, 97.06% Zn, 96.82% Pb, and approximately 90% S can be removed, and 89.74% Fe is recovered as magnetite into the final product under optimal conditions. A purified magnetite concentrate containing 63.07wt% Fe, 0.16wt% P, 0.26wt% S, and trace amounts of nonferrous metals (0.005wt% Cu, 0.013wt% Pb, and 0.051wt% Zn) was obtained. The concentrate can be potentially used as a high-quality feed material for producing oxidized pellets by blending with other high-grade iron ore concentrates.
2018, vol. 25, no. 9, pp.
990-999.
https://doi.org/10.1007/s12613-018-1649-9
Abstract:
The hydrometallurgical strategy of extracting Mn from low-grade Mn ores has attracted attention for the production of electrolytic manganese metal (EMM). In this work, the reductive dissolution of low-grade MnO2 ores using toxic nitrocellulose acidic wastewater (NAW) as a reductant was investigated for the first time. Under the optimized conditions of an MnO2 ore dosage of 100 g·L-1, an ore particle size of -200 mesh, concentrated H2SO4-to-NAW volume ratio of 0.12, reaction temperature of 90℃, stirring speed at 160 r·min-1, and a contact time of 120 min, the reductive leaching efficiency of Mn and the total organic carbon (TOC) removal efficiency of NAW reached 97.4% and 98.5%, respectively. The residual TOC of 31.6 mg·L-1 did not adversely affect the preparation of EMM. The current process offers a feasible route for the concurrent realization of the reductive leaching of Mn and the treatment of toxic wastewater via a simple one-step process.
The hydrometallurgical strategy of extracting Mn from low-grade Mn ores has attracted attention for the production of electrolytic manganese metal (EMM). In this work, the reductive dissolution of low-grade MnO2 ores using toxic nitrocellulose acidic wastewater (NAW) as a reductant was investigated for the first time. Under the optimized conditions of an MnO2 ore dosage of 100 g·L-1, an ore particle size of -200 mesh, concentrated H2SO4-to-NAW volume ratio of 0.12, reaction temperature of 90℃, stirring speed at 160 r·min-1, and a contact time of 120 min, the reductive leaching efficiency of Mn and the total organic carbon (TOC) removal efficiency of NAW reached 97.4% and 98.5%, respectively. The residual TOC of 31.6 mg·L-1 did not adversely affect the preparation of EMM. The current process offers a feasible route for the concurrent realization of the reductive leaching of Mn and the treatment of toxic wastewater via a simple one-step process.
2018, vol. 25, no. 9, pp.
1000-1009.
https://doi.org/10.1007/s12613-018-1650-3
Abstract:
Ludwigite is a kind of complex iron ore containing boron, iron, and magnesium, and it is the most promising boron resource in China. Selective reduction of iron oxide is the key step for the comprehensive utilization of ludwigite. In the present work, the reduction mechanism of ludwigite was investigated. The thermogravimetry and differential scanning calorimetry analysis and isothermal reduction of ludwigite/coal composite pellet were performed. Ludwigite yielded a lower reduction starting temperature and a higher final reduction degree compared with the traditional iron concentrates. Higher specific surface area and more fine cracks might be the main reasons for the better reducibility of ludwigite. Reducing temperature highly affected the reaction fraction and microstructure of the reduced pellets, which are closely related to the separation degree of boron and iron. Increasing reducing temperature benefited the boron and iron magnetic separation. Optimum magnetic separation results could be obtained when the pellet was reduced at 1300℃. The separated boron-rich non-magnetic concentrate presented poor crystalline structure, and its extraction efficiency for boron reached 64.3%. The obtained experimental results can provide reference for the determination of the comprehensive utilization flow sheet of ludwigite.
Ludwigite is a kind of complex iron ore containing boron, iron, and magnesium, and it is the most promising boron resource in China. Selective reduction of iron oxide is the key step for the comprehensive utilization of ludwigite. In the present work, the reduction mechanism of ludwigite was investigated. The thermogravimetry and differential scanning calorimetry analysis and isothermal reduction of ludwigite/coal composite pellet were performed. Ludwigite yielded a lower reduction starting temperature and a higher final reduction degree compared with the traditional iron concentrates. Higher specific surface area and more fine cracks might be the main reasons for the better reducibility of ludwigite. Reducing temperature highly affected the reaction fraction and microstructure of the reduced pellets, which are closely related to the separation degree of boron and iron. Increasing reducing temperature benefited the boron and iron magnetic separation. Optimum magnetic separation results could be obtained when the pellet was reduced at 1300℃. The separated boron-rich non-magnetic concentrate presented poor crystalline structure, and its extraction efficiency for boron reached 64.3%. The obtained experimental results can provide reference for the determination of the comprehensive utilization flow sheet of ludwigite.
2018, vol. 25, no. 9, pp.
1010-1017.
https://doi.org/10.1007/s12613-018-1651-2
Abstract:
A method for preparing novel ceramics was developed in this study. Different ratios red muds were added to steel slags to optimize the preparation of novel ceramics by a traditional ceramic preparation process. The sintering mechanism, microstructure, and performance were studied by X-ray diffraction techniques, scanning electron microscopy, and combined experiments of linear shrinkage, water absorption, and flexural strength. The results confirmed that red mud can reduce the volumetric instabilities through the complementarity of red mud and ferroalloy slag. The crystal phases in the ceramics are all pyroxene group minerals, including diopside ferrian, augite, and diopside. The flexural strength of the ceramic that contains 40wt% red mud and was prepared at the optimal sintering temperature (1140℃) is greater than 93 MPa; its corresponding water absorption is less than 0.05%.
A method for preparing novel ceramics was developed in this study. Different ratios red muds were added to steel slags to optimize the preparation of novel ceramics by a traditional ceramic preparation process. The sintering mechanism, microstructure, and performance were studied by X-ray diffraction techniques, scanning electron microscopy, and combined experiments of linear shrinkage, water absorption, and flexural strength. The results confirmed that red mud can reduce the volumetric instabilities through the complementarity of red mud and ferroalloy slag. The crystal phases in the ceramics are all pyroxene group minerals, including diopside ferrian, augite, and diopside. The flexural strength of the ceramic that contains 40wt% red mud and was prepared at the optimal sintering temperature (1140℃) is greater than 93 MPa; its corresponding water absorption is less than 0.05%.
2018, vol. 25, no. 9, pp.
1018-1026.
https://doi.org/10.1007/s12613-018-1652-1
Abstract:
The effects of high pressure rheo-squeeze casting (HPRC) on the Fe-rich phases (FRPs) and mechanical properties of Al-17Si-(1,1.5)Fe alloys were investigated. The alloy melts were first treated by ultrasonic vibration (UV) and then formed by high-pressure squeeze casting (HPSC). The FRPs in the as-cast HPSC Al-17Si-1Fe alloys only contained a long, needle-shaped β-Al5FeSi phase at 0 MPa. In addition to the β-Al5FeSi phase, the HPSC Al-17Si-1.5Fe alloy also contained the plate-shaped δ-Al4FeSi2 phase. A fine, block-shaped δ-Al4FeSi2 phase was formed in the Al-17Si-1Fe alloy treated by UV. The size of FRPs decreased with increasing pressure. After UV treatment, solidification under pressure led to further refinement of the FRPs. Considering alloy samples of the same composition, the ultimate tensile strength (UTS) of the HPRC samples was higher than that of the HPSC samples, and the UTS increased with increasing pressure. The UTS of the Al-17Si-1Fe alloy formed by HPSC exceeded that of the Al-17Si-1.5Fe alloy formed in the same manner under the same pressure. Conversely, the UTS of the Al-17Si-1Fe alloy formed by HPRC decreased to a value lower than that of the Al-17Si-1.5Fe alloy formed in the same manner.
The effects of high pressure rheo-squeeze casting (HPRC) on the Fe-rich phases (FRPs) and mechanical properties of Al-17Si-(1,1.5)Fe alloys were investigated. The alloy melts were first treated by ultrasonic vibration (UV) and then formed by high-pressure squeeze casting (HPSC). The FRPs in the as-cast HPSC Al-17Si-1Fe alloys only contained a long, needle-shaped β-Al5FeSi phase at 0 MPa. In addition to the β-Al5FeSi phase, the HPSC Al-17Si-1.5Fe alloy also contained the plate-shaped δ-Al4FeSi2 phase. A fine, block-shaped δ-Al4FeSi2 phase was formed in the Al-17Si-1Fe alloy treated by UV. The size of FRPs decreased with increasing pressure. After UV treatment, solidification under pressure led to further refinement of the FRPs. Considering alloy samples of the same composition, the ultimate tensile strength (UTS) of the HPRC samples was higher than that of the HPSC samples, and the UTS increased with increasing pressure. The UTS of the Al-17Si-1Fe alloy formed by HPSC exceeded that of the Al-17Si-1.5Fe alloy formed in the same manner under the same pressure. Conversely, the UTS of the Al-17Si-1Fe alloy formed by HPRC decreased to a value lower than that of the Al-17Si-1.5Fe alloy formed in the same manner.
2018, vol. 25, no. 9, pp.
1027-1034.
https://doi.org/10.1007/s12613-018-1653-0
Abstract:
SnCo alloy nanowires were successfully electrodeposited from SnCl2-CoCl2-1-ethyl-3-methylimidazolium chloride (EMIC) ionic liquid without a template. The nanowires were obtained from the molar ratio of 5:40:60 for SnCl2:CoCl2:EMIC at -0.55 V and showed a minimum diameter of about 50 nm and lengths of over 20 μm. The as-fabricated SnCo nanowires were about 70 nm in diameter and featured a Sn/Co weight ratio of 3.85:1, when used as an anode for a Li-ion battery, they presented respective specific capacities of 687 and 678 mAh·g-1 after the first charge and discharge cycle and maintained capacities of about 654 mAh·g-1 after 60 cycles and 539 mAh·g-1 after 80 cycles at a current density of 300 mA·g-1. Both the nanowire structure and presence of elemental Co helped buffer large volume changes in the Sn anode during charging and discharging to a certain extent, thereby improving the cycling performance of the Sn anode.
SnCo alloy nanowires were successfully electrodeposited from SnCl2-CoCl2-1-ethyl-3-methylimidazolium chloride (EMIC) ionic liquid without a template. The nanowires were obtained from the molar ratio of 5:40:60 for SnCl2:CoCl2:EMIC at -0.55 V and showed a minimum diameter of about 50 nm and lengths of over 20 μm. The as-fabricated SnCo nanowires were about 70 nm in diameter and featured a Sn/Co weight ratio of 3.85:1, when used as an anode for a Li-ion battery, they presented respective specific capacities of 687 and 678 mAh·g-1 after the first charge and discharge cycle and maintained capacities of about 654 mAh·g-1 after 60 cycles and 539 mAh·g-1 after 80 cycles at a current density of 300 mA·g-1. Both the nanowire structure and presence of elemental Co helped buffer large volume changes in the Sn anode during charging and discharging to a certain extent, thereby improving the cycling performance of the Sn anode.
2018, vol. 25, no. 9, pp.
1035-1041.
https://doi.org/10.1007/s12613-018-1654-z
Abstract:
The effects of vacuum induction melting (VIM) and vacuum arc remelting (VAR) processes on the microstructure and stress rupture properties of Ni-based GTD-111 superalloy were investigated. Samples of GTD-111 master alloy were melted in VIM and VAR furnaces and then poured into a preheated ceramic mold for VIM melt or into a water-cooled copper mold for VAR melt. The as-cast samples were examined radiographically to ensure that no casting defects were present in the final castings; the samples were then heat-treated using a standard heat-treatment cycle. The microstructure of the samples was investigated using optical microscopy and scanning electron microscopy in conjunction with energy-dispersive X-ray spectroscopy for microanalysis. On the basis of standard ASTM-E139, stress rupture tests were carried out at 1000℃ under a stress of 300 MPa. The results showed that a γ matrix, fine γ' precipitates, a γ-γ' eutectic structure, carbide particles, and some harmful phases such as σ and η phases were present in the as-cast samples. The γ' precipitates with cubic morphology appeared in the matrix after the standard heat-treatment process. The extent of segregation and the amount of γ-γ' eutectic structure formed in the VAR-prepared sample were less than in the VIM-prepared sample. The results of stress rupture tests showed that the rupture time for the VAR sample was 43% longer than that for the VIM sample.
The effects of vacuum induction melting (VIM) and vacuum arc remelting (VAR) processes on the microstructure and stress rupture properties of Ni-based GTD-111 superalloy were investigated. Samples of GTD-111 master alloy were melted in VIM and VAR furnaces and then poured into a preheated ceramic mold for VIM melt or into a water-cooled copper mold for VAR melt. The as-cast samples were examined radiographically to ensure that no casting defects were present in the final castings; the samples were then heat-treated using a standard heat-treatment cycle. The microstructure of the samples was investigated using optical microscopy and scanning electron microscopy in conjunction with energy-dispersive X-ray spectroscopy for microanalysis. On the basis of standard ASTM-E139, stress rupture tests were carried out at 1000℃ under a stress of 300 MPa. The results showed that a γ matrix, fine γ' precipitates, a γ-γ' eutectic structure, carbide particles, and some harmful phases such as σ and η phases were present in the as-cast samples. The γ' precipitates with cubic morphology appeared in the matrix after the standard heat-treatment process. The extent of segregation and the amount of γ-γ' eutectic structure formed in the VAR-prepared sample were less than in the VIM-prepared sample. The results of stress rupture tests showed that the rupture time for the VAR sample was 43% longer than that for the VIM sample.
2018, vol. 25, no. 9, pp.
1042-1054.
https://doi.org/10.1007/s12613-018-1655-y
Abstract:
In this work, network former SiO2 and network intermediate Al2O3 were introduced into typical low-melting binary compositions CaO·B2O3, CaO·2B2O3, and BaO·B2O3 via an aqueous solid-state suspension milling route. Accordingly, multiple-phase aluminosilicate glass-ceramics were directly obtained via liquid-phase sintering at temperatures below 950℃. On the basis of liquid-phase sintering theory, mineral-phase evolutions and glass-phase formations were systematically investigated in a wide MO-SiO2-Al2O3-B2O3 (M=Ca, Ba) composition range. The results indicate that major mineral phases of the aluminosilicate glass-ceramics are Al20B4O36, CaAl2Si2O8, and BaAl2Si2O8 and that the glass-ceramic materials are characterized by dense microstructures and excellent dielectric properties.
In this work, network former SiO2 and network intermediate Al2O3 were introduced into typical low-melting binary compositions CaO·B2O3, CaO·2B2O3, and BaO·B2O3 via an aqueous solid-state suspension milling route. Accordingly, multiple-phase aluminosilicate glass-ceramics were directly obtained via liquid-phase sintering at temperatures below 950℃. On the basis of liquid-phase sintering theory, mineral-phase evolutions and glass-phase formations were systematically investigated in a wide MO-SiO2-Al2O3-B2O3 (M=Ca, Ba) composition range. The results indicate that major mineral phases of the aluminosilicate glass-ceramics are Al20B4O36, CaAl2Si2O8, and BaAl2Si2O8 and that the glass-ceramic materials are characterized by dense microstructures and excellent dielectric properties.
2018, vol. 25, no. 9, pp.
1055-1059.
https://doi.org/10.1007/s12613-018-1656-x
Abstract:
In this study, the mechanical properties of tungsten-rhenium wires with nanofibrous microstructure were investigated at both room temperature (RT) and 800℃. The strengthening mechanism associated to the nanofibrous microstructure was discussed. The results showed that the tungsten-rhenium wires with nanofibrous grains exhibited a very high tensile strength reaching values of 3.5 GPa and 4.4 GPa for the coarse (grains diameter of 240 nm) and fine (grains diameter of 80 nm) wires, respectively. With increasing the temperature from RT to 800℃, the tensile strength decreased slightly but still held high values (1.8 GPa and 3.8 GPa). All the fracture surfaces exhibited apparent necking and characteristics of spear-edge shaped fracture surface, indicating excellent ductility of the wires. A model of the strengthening mechanism of these tungsten-rhenium wires was proposed.
In this study, the mechanical properties of tungsten-rhenium wires with nanofibrous microstructure were investigated at both room temperature (RT) and 800℃. The strengthening mechanism associated to the nanofibrous microstructure was discussed. The results showed that the tungsten-rhenium wires with nanofibrous grains exhibited a very high tensile strength reaching values of 3.5 GPa and 4.4 GPa for the coarse (grains diameter of 240 nm) and fine (grains diameter of 80 nm) wires, respectively. With increasing the temperature from RT to 800℃, the tensile strength decreased slightly but still held high values (1.8 GPa and 3.8 GPa). All the fracture surfaces exhibited apparent necking and characteristics of spear-edge shaped fracture surface, indicating excellent ductility of the wires. A model of the strengthening mechanism of these tungsten-rhenium wires was proposed.
2018, vol. 25, no. 9, pp.
1060-1069.
https://doi.org/10.1007/s12613-018-1657-9
Abstract:
A quenching and partitioning (Q&P) process was applied to vanadium carbide particle (VCp)-reinforced Fe-matrix composites (VC-Fe-MCs) to obtain a multiphase microstructure comprising VC, V8C7, M3C, α-Fe, and γ-Fe. The effects of the austenitizing temperature and the quenching temperature on the microstructure, mechanical properties, and wear resistance of the VC-Fe-MCs were studied. The results show that the size of the carbide became coarse and that the shape of some particles began to transform from diffused graininess into a chrysanthemum-shaped structure with increasing austenitizing temperature. The microhardness decreased with increasing austenitizing temperature but substantially increased after wear testing compared with the microhardness before wear testing; the microhardness values improved by 20.0% ±2.5%. Retained austenite enhanced the impact toughness and promoted the transformation-induced plasticity (TRIP) effect to improve wear resistance under certain load conditions.
A quenching and partitioning (Q&P) process was applied to vanadium carbide particle (VCp)-reinforced Fe-matrix composites (VC-Fe-MCs) to obtain a multiphase microstructure comprising VC, V8C7, M3C, α-Fe, and γ-Fe. The effects of the austenitizing temperature and the quenching temperature on the microstructure, mechanical properties, and wear resistance of the VC-Fe-MCs were studied. The results show that the size of the carbide became coarse and that the shape of some particles began to transform from diffused graininess into a chrysanthemum-shaped structure with increasing austenitizing temperature. The microhardness decreased with increasing austenitizing temperature but substantially increased after wear testing compared with the microhardness before wear testing; the microhardness values improved by 20.0% ±2.5%. Retained austenite enhanced the impact toughness and promoted the transformation-induced plasticity (TRIP) effect to improve wear resistance under certain load conditions.
2018, vol. 25, no. 9, pp.
1070-1079.
https://doi.org/10.1007/s12613-018-1658-8
Abstract:
In this study, the processing and mechanical properties of porous metal matrix composites (MMCs) composed of spheroidal cast iron chips (GGG40) and bronze chips (CuSn10) and formed by hot isostatic pressing were investigated. Bronze chips (CuSn10) were used as a matrix component, and spheroidal cast iron (GGG40) chips were used as a reinforcement component. The MMCs were produced with different CuSn10 contents (90wt%, 80wt%, 70wt%, and 60wt%). The hot isostatic pressing process was performed under three different pressures and temperatures. The produced MMCs were characterized using density tests, Brinell hardness tests, and compression tests. In addition, the consolidation mechanism was investigated by X-ray diffraction (XRD) analysis and scanning electron microscopy. The test results were compared with those for bulk CuSn10 and bulk GGG40. Mechanical tests results revealed that the metallic chips can be recycled by using hot pressing and that the mechanical properties of the produced MMCs were similar to those of bulk CuSn10. XRD and microscopy studies showed that no intermetallic compounds formed between the metallic chips. The results showed that the CuSn10 and GGG40 chips were consolidated by mechanical interlocking.
In this study, the processing and mechanical properties of porous metal matrix composites (MMCs) composed of spheroidal cast iron chips (GGG40) and bronze chips (CuSn10) and formed by hot isostatic pressing were investigated. Bronze chips (CuSn10) were used as a matrix component, and spheroidal cast iron (GGG40) chips were used as a reinforcement component. The MMCs were produced with different CuSn10 contents (90wt%, 80wt%, 70wt%, and 60wt%). The hot isostatic pressing process was performed under three different pressures and temperatures. The produced MMCs were characterized using density tests, Brinell hardness tests, and compression tests. In addition, the consolidation mechanism was investigated by X-ray diffraction (XRD) analysis and scanning electron microscopy. The test results were compared with those for bulk CuSn10 and bulk GGG40. Mechanical tests results revealed that the metallic chips can be recycled by using hot pressing and that the mechanical properties of the produced MMCs were similar to those of bulk CuSn10. XRD and microscopy studies showed that no intermetallic compounds formed between the metallic chips. The results showed that the CuSn10 and GGG40 chips were consolidated by mechanical interlocking.
2018, vol. 25, no. 9, pp.
1080-1089.
https://doi.org/10.1007/s12613-018-1659-7
Abstract:
The effect of high-speed direct-chill (DC) casting on the microstructure and mechanical properties of Al-Mg2Si in situ composites and AA6061 alloy was investigated. The microstructural evolution of the Al-Mg2Si composites and AA6061 alloy was examined by optical microscopy, field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The results revealed that an increase of the casting speed substantially refined the primary Mg2Si particles (from 28 to 12 μm), the spacing of eutectic Mg2Si (from 3 to 0.5 μm), and the grains of AA6061 alloy (from 102 to 22 μm). The morphology of the eutectic Mg2Si transformed from lamellar to rod-like and fibrous with increasing casting speed. The tensile tests showed that the yield strength, tensile strength, and elongation improved at higher casting speeds because of refinement of the Mg2Si phase and the grains in the Al-Mg2Si composites and the AA6061 alloy. High-speed DC casting is demonstrated to be an effective method to improve the mechanical properties of Al-Mg2Si composites and AA6061 alloy billets.
The effect of high-speed direct-chill (DC) casting on the microstructure and mechanical properties of Al-Mg2Si in situ composites and AA6061 alloy was investigated. The microstructural evolution of the Al-Mg2Si composites and AA6061 alloy was examined by optical microscopy, field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The results revealed that an increase of the casting speed substantially refined the primary Mg2Si particles (from 28 to 12 μm), the spacing of eutectic Mg2Si (from 3 to 0.5 μm), and the grains of AA6061 alloy (from 102 to 22 μm). The morphology of the eutectic Mg2Si transformed from lamellar to rod-like and fibrous with increasing casting speed. The tensile tests showed that the yield strength, tensile strength, and elongation improved at higher casting speeds because of refinement of the Mg2Si phase and the grains in the Al-Mg2Si composites and the AA6061 alloy. High-speed DC casting is demonstrated to be an effective method to improve the mechanical properties of Al-Mg2Si composites and AA6061 alloy billets.
2018, vol. 25, no. 9, pp.
1090-1103.
https://doi.org/10.1007/s12613-018-1660-1
Abstract:
Coated Electrodes with small amounts of nickel were developed for welding ductile iron (DI) and conversion of the same into austempered ductile iron (ADI) after austempering. Among six electrodes, Trials 3 and 4 were selected for establishing crack-free weld deposits via preheating and post-weld heat treatment. Austenitization was performed at 900℃ for 2 h and austempering at 300 or 350℃ for three different holding times to observe the results of austempering with respect to the microstructure, hardness, and austempering kinetics of the samples. The microstructures of the weld deposits showed needle-like bainitic ferrite with small amounts of retained austenite when treated at 300℃ and feathery bainitic ferrite with large amounts of retainedaustenite when treated at 350℃. The electrode labeled with Trial 3 revealed greater austenite contents than that labeled with Trial 4 when treated with a 2 h holding time regardless of the austempering temperature applied. The transformation rate of the bainitic ferrite of Trial 3 was relatively higher than that of Trial 4 and showed a lower rate constant, leading to a higher diffusion rate of carbon in austenite.
Coated Electrodes with small amounts of nickel were developed for welding ductile iron (DI) and conversion of the same into austempered ductile iron (ADI) after austempering. Among six electrodes, Trials 3 and 4 were selected for establishing crack-free weld deposits via preheating and post-weld heat treatment. Austenitization was performed at 900℃ for 2 h and austempering at 300 or 350℃ for three different holding times to observe the results of austempering with respect to the microstructure, hardness, and austempering kinetics of the samples. The microstructures of the weld deposits showed needle-like bainitic ferrite with small amounts of retained austenite when treated at 300℃ and feathery bainitic ferrite with large amounts of retainedaustenite when treated at 350℃. The electrode labeled with Trial 3 revealed greater austenite contents than that labeled with Trial 4 when treated with a 2 h holding time regardless of the austempering temperature applied. The transformation rate of the bainitic ferrite of Trial 3 was relatively higher than that of Trial 4 and showed a lower rate constant, leading to a higher diffusion rate of carbon in austenite.
2018, vol. 25, no. 9, pp.
1104-1112.
https://doi.org/10.1007/s12613-018-1661-0
Abstract:
Wind power has attracted increasing attention as a renewable and clean energy. Gear fault frequently occurs under extreme environment and complex loads. The time-varying meshing stiffness is one of the main excitations. This study proposes a 5 degree-of-freedom torsional vibration model for the planetary gear system. The influence of some parameters (e.g., contact ratio and phase difference) is discussed under different conditions of a single teeth pair and double pairs of teeth. The impact load caused by the teeth face fault, ramped load induced by the complex wind conditions, and the harmonic excitation are investigated. The analysis of the time-varying meshing stiffness and the dynamic meshing force shows that the dynamic design under different loads can be made to avoid resonance, can provide the basis for the gear fault location of a wind turbine, and distinguish the fault characteristics from the vibration signals.
Wind power has attracted increasing attention as a renewable and clean energy. Gear fault frequently occurs under extreme environment and complex loads. The time-varying meshing stiffness is one of the main excitations. This study proposes a 5 degree-of-freedom torsional vibration model for the planetary gear system. The influence of some parameters (e.g., contact ratio and phase difference) is discussed under different conditions of a single teeth pair and double pairs of teeth. The impact load caused by the teeth face fault, ramped load induced by the complex wind conditions, and the harmonic excitation are investigated. The analysis of the time-varying meshing stiffness and the dynamic meshing force shows that the dynamic design under different loads can be made to avoid resonance, can provide the basis for the gear fault location of a wind turbine, and distinguish the fault characteristics from the vibration signals.
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