Search2019 Vol. 26, No. 2
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2019, vol. 26, no. 2, pp.
143-151.
https://doi.org/10.1007/s12613-019-1718-8
Abstract:
The aim of this study was to determine the structural, compositional, and mineralogical composition of carbonatitic copper sulfide concentrator plant streams. Three samples, each from a different stream (run of mine (ROM), concentrate, and tailings) of a copper concentrator were characterized using various techniques, including stereomicroscopy, X-ray fluorescence, X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) in conjunction with energy-dispersive X-ray spectroscopy (EDS), and optical microscopy. The results reveal that each stream possesses its own unique compositional features. Carbonate minerals associated with calcite and dolomite, followed by quartz, remain the major minerals in both the ROM and tails streams. In the ROM stream, chalcopyrite appears to occur as veins within the carbonatite-hosting ore body. Mineral phase mutation was discovered in the tails stream because magnetite formerly identified in the ROM as the primary iron oxide had evolved into hematite. This metamorphosis was likely promoted by the concentration process. The concentration process was effective, upgrading the chalcopyrite content from 2wt% in the ROM stream to 58wt% in the concentrate stream; it was accompanied by bornite (4wt%), anilite (3wt%), and digenite (2.5wt%). In addition, the concentrate stream exhibited properties distinctive from those of the other streams. The FTIR analysis showed the existence of a sulfide group related to the chalcopyrite mineral. Free chalcopyrite grains were observed in the concentrate by SEM analysis, and their mineral presence was supported by the EDS analysis results. All characterization techniques corresponded well with each other regarding the structure, chemistry, and composition of the samples.
The aim of this study was to determine the structural, compositional, and mineralogical composition of carbonatitic copper sulfide concentrator plant streams. Three samples, each from a different stream (run of mine (ROM), concentrate, and tailings) of a copper concentrator were characterized using various techniques, including stereomicroscopy, X-ray fluorescence, X-ray diffraction, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) in conjunction with energy-dispersive X-ray spectroscopy (EDS), and optical microscopy. The results reveal that each stream possesses its own unique compositional features. Carbonate minerals associated with calcite and dolomite, followed by quartz, remain the major minerals in both the ROM and tails streams. In the ROM stream, chalcopyrite appears to occur as veins within the carbonatite-hosting ore body. Mineral phase mutation was discovered in the tails stream because magnetite formerly identified in the ROM as the primary iron oxide had evolved into hematite. This metamorphosis was likely promoted by the concentration process. The concentration process was effective, upgrading the chalcopyrite content from 2wt% in the ROM stream to 58wt% in the concentrate stream; it was accompanied by bornite (4wt%), anilite (3wt%), and digenite (2.5wt%). In addition, the concentrate stream exhibited properties distinctive from those of the other streams. The FTIR analysis showed the existence of a sulfide group related to the chalcopyrite mineral. Free chalcopyrite grains were observed in the concentrate by SEM analysis, and their mineral presence was supported by the EDS analysis results. All characterization techniques corresponded well with each other regarding the structure, chemistry, and composition of the samples.
2019, vol. 26, no. 2, pp.
152-159.
https://doi.org/10.1007/s12613-019-1719-7
Abstract:
Iron and titanium were recovered from beach titanomagnetite (TTM) concentrate by embedding direct reduction and magnetic separation. The reduction products and the effects of the reductant type and reduction temperature on the reduction behavior were investigated. The results showed that the reduction of TTM concentrate was strongly related to the gasification reactivity of the reductant. Bitumite presented a better product index than wheat-straw biochar and coke, mainly because the gasification reactivity of bitumite was better than that of the other reductants. In addition, high temperatures were not beneficial to embedding direct reduction because of the emergence of a molten phase and iron-joined crystals, which in turn reduced the diffusion rate of the reducing gas and impeded the reduction reaction in the central area of the roasted briquette. The use of bitumite as the reductant at a C/Fe molar ratio of 1.4 and a reduction temperature of 1200℃ for 120 min resulted in direct-reduction iron powder assaying 90.28wt% TFe and 0.91wt% TiO2 with an iron recovery of 91.83% and titanium concentrate assaying 46.01wt% TiO2 with a TiO2 recovery of 91.19%. Titanium existed mainly in the form of anosovite and ilmenite in the titanium concentrate.
Iron and titanium were recovered from beach titanomagnetite (TTM) concentrate by embedding direct reduction and magnetic separation. The reduction products and the effects of the reductant type and reduction temperature on the reduction behavior were investigated. The results showed that the reduction of TTM concentrate was strongly related to the gasification reactivity of the reductant. Bitumite presented a better product index than wheat-straw biochar and coke, mainly because the gasification reactivity of bitumite was better than that of the other reductants. In addition, high temperatures were not beneficial to embedding direct reduction because of the emergence of a molten phase and iron-joined crystals, which in turn reduced the diffusion rate of the reducing gas and impeded the reduction reaction in the central area of the roasted briquette. The use of bitumite as the reductant at a C/Fe molar ratio of 1.4 and a reduction temperature of 1200℃ for 120 min resulted in direct-reduction iron powder assaying 90.28wt% TFe and 0.91wt% TiO2 with an iron recovery of 91.83% and titanium concentrate assaying 46.01wt% TiO2 with a TiO2 recovery of 91.19%. Titanium existed mainly in the form of anosovite and ilmenite in the titanium concentrate.
2019, vol. 26, no. 2, pp.
160-167.
https://doi.org/10.1007/s12613-019-1720-1
Abstract:
The effect of microwave treatment on the grinding and dissociation characteristics of vanadium titano-magnetite (VTM) ore were investigated using scanning electron microscopy (SEM), nitrogen absorption measurements, particle size distribution measurements, X-ray diffraction (XRD) analysis, Fourier transform infrared (FT-IR) spectroscopic analysis, and magnetic separation. SEM analysis showed that microfractures appeared in the microwave-treated VTM, which is attributed to the microwaves' selective heating characteristic and the differential expansion between minerals and gangues. Nitrogen absorption showed that the microfractures were more pronounced when the microwave heating time was increased. Particle size distribution analysis showed that microwave treatment could improve the grindability of the VTM, thus increasing the weight percent of the fine-ground product. The increase in grindability was more significant with prolonged heating time. Moreover, the particle size distribution of the fine-ground product changed only slightly after the microwave treatment. XRD analysis showed that the crystallinity of the microwave-treated VTM increased with increasing microwave heating time. The magnetic separation tests revealed that the separation efficiency increased as a result of the intergranular fractures generated by microwave treatment. The Fe grade of the magnetic fraction of microwave-treated VTM was 1.72% higher than that of the raw ore. We concluded that the microwave treatment was beneficial, especially for the mineral processing characteristics.
The effect of microwave treatment on the grinding and dissociation characteristics of vanadium titano-magnetite (VTM) ore were investigated using scanning electron microscopy (SEM), nitrogen absorption measurements, particle size distribution measurements, X-ray diffraction (XRD) analysis, Fourier transform infrared (FT-IR) spectroscopic analysis, and magnetic separation. SEM analysis showed that microfractures appeared in the microwave-treated VTM, which is attributed to the microwaves' selective heating characteristic and the differential expansion between minerals and gangues. Nitrogen absorption showed that the microfractures were more pronounced when the microwave heating time was increased. Particle size distribution analysis showed that microwave treatment could improve the grindability of the VTM, thus increasing the weight percent of the fine-ground product. The increase in grindability was more significant with prolonged heating time. Moreover, the particle size distribution of the fine-ground product changed only slightly after the microwave treatment. XRD analysis showed that the crystallinity of the microwave-treated VTM increased with increasing microwave heating time. The magnetic separation tests revealed that the separation efficiency increased as a result of the intergranular fractures generated by microwave treatment. The Fe grade of the magnetic fraction of microwave-treated VTM was 1.72% higher than that of the raw ore. We concluded that the microwave treatment was beneficial, especially for the mineral processing characteristics.
2019, vol. 26, no. 2, pp.
168-177.
https://doi.org/10.1007/s12613-019-1721-0
Abstract:
Effective silver recovery is usually restricted by either environmental pollution or high recovery costs. To tackle the issues, this study introduces a novel method for the effective recovery of silver by utilizing the alkaline sodium thiosulfate-potassium ferricyanide leaching system. The reaction kinetics of silver dissolution in this system was investigated via the rotating disk electrode technology. The influences of important parameters, including the rotation speed, sodium thiosulfate concentration, potassium ferricyanide concentration, and temperature, on the silver dissolution rate were systematically investigated. The activation energy was measured to be 17.96 kJ·mol-1 when the silver dissolution was controlled by a diffusion process. When the silver dissolution was in the region of mixed control, the reaction orders of ferricyanide and thiosulfate were found to be 0.57 and 0.19, respectively, and the reaction orders of ferricyanide and thiosulfate were 0.55 and 0.22, respectively, when the silver dissolution was controlled by surface reaction. This study has great potential for the development of an environmentally friendly silver recovery process from end-of-life products.
Effective silver recovery is usually restricted by either environmental pollution or high recovery costs. To tackle the issues, this study introduces a novel method for the effective recovery of silver by utilizing the alkaline sodium thiosulfate-potassium ferricyanide leaching system. The reaction kinetics of silver dissolution in this system was investigated via the rotating disk electrode technology. The influences of important parameters, including the rotation speed, sodium thiosulfate concentration, potassium ferricyanide concentration, and temperature, on the silver dissolution rate were systematically investigated. The activation energy was measured to be 17.96 kJ·mol-1 when the silver dissolution was controlled by a diffusion process. When the silver dissolution was in the region of mixed control, the reaction orders of ferricyanide and thiosulfate were found to be 0.57 and 0.19, respectively, and the reaction orders of ferricyanide and thiosulfate were 0.55 and 0.22, respectively, when the silver dissolution was controlled by surface reaction. This study has great potential for the development of an environmentally friendly silver recovery process from end-of-life products.
2019, vol. 26, no. 2, pp.
178-185.
https://doi.org/10.1007/s12613-019-1722-z
Abstract:
Al2O3 and TiN inclusions in interstitial-free (IF) steel deteriorate the properties of the steel. To decrease the defects of cold-rolled sheet, it is important to clearly distinguish between the degrees of damage caused by these two inclusions on the surface quality of the steel. In this study, a nanoindenter was used to test the mechanical properties of the inclusions, and the distribution and size of the inclusions were obtained by scanning electron microscopy (SEM). It was found that when only mechanical properties are considered, TiN inclusions are more likely to cause defects than Al2O3 inclusions of the same size during the rolling process. However, Al2O3 inclusions are generally more inclined to cause defects in the rolling process than TiN inclusions because of their distribution characteristic in the thickness direction. The precipitation of Al2O3 and TiN was obtained through thermodynamical calculations. The growth laws of inclusions at different cooling rates were calculated by solidification and segregation models. The results show that the precipitation regularity is closely related to the distribution law of the inclusions in IF slabs along the thickness direction.
Al2O3 and TiN inclusions in interstitial-free (IF) steel deteriorate the properties of the steel. To decrease the defects of cold-rolled sheet, it is important to clearly distinguish between the degrees of damage caused by these two inclusions on the surface quality of the steel. In this study, a nanoindenter was used to test the mechanical properties of the inclusions, and the distribution and size of the inclusions were obtained by scanning electron microscopy (SEM). It was found that when only mechanical properties are considered, TiN inclusions are more likely to cause defects than Al2O3 inclusions of the same size during the rolling process. However, Al2O3 inclusions are generally more inclined to cause defects in the rolling process than TiN inclusions because of their distribution characteristic in the thickness direction. The precipitation of Al2O3 and TiN was obtained through thermodynamical calculations. The growth laws of inclusions at different cooling rates were calculated by solidification and segregation models. The results show that the precipitation regularity is closely related to the distribution law of the inclusions in IF slabs along the thickness direction.
2019, vol. 26, no. 2, pp.
186-193.
https://doi.org/10.1007/s12613-019-1723-y
Abstract:
For the control of surface defects in interstitial-free (IF) steel, quantitative metallographic analyses of near-surface inclusions and surface liquid flow detection via the nail-board tipping method were conducted. The results show that, at casting speeds of 0.8 and 1.0 m/min, a thin liquid mold flux layer forms and non-uniform floating of argon bubbles occurs, inducing the entrainment and subsequent entrapment of the liquid flux; fine inclusion particles of Al2O3 can also aggregate at the solidification front. At higher casting speeds of 1.4 and 1.6 m/min, the liquid mold flux can be entrained and carried deeper into the liquid steel pool because of strong level fluctuations of the liquid steel and the flux. The optimal casting speed is approximately 1.2 m/min, with the most favorable surface flow status and, correspondingly, the lowest number of inclusions near the slab surface.
For the control of surface defects in interstitial-free (IF) steel, quantitative metallographic analyses of near-surface inclusions and surface liquid flow detection via the nail-board tipping method were conducted. The results show that, at casting speeds of 0.8 and 1.0 m/min, a thin liquid mold flux layer forms and non-uniform floating of argon bubbles occurs, inducing the entrainment and subsequent entrapment of the liquid flux; fine inclusion particles of Al2O3 can also aggregate at the solidification front. At higher casting speeds of 1.4 and 1.6 m/min, the liquid mold flux can be entrained and carried deeper into the liquid steel pool because of strong level fluctuations of the liquid steel and the flux. The optimal casting speed is approximately 1.2 m/min, with the most favorable surface flow status and, correspondingly, the lowest number of inclusions near the slab surface.
2019, vol. 26, no. 2, pp.
194-201.
https://doi.org/10.1007/s12613-019-1724-x
Abstract:
High-velocity compaction is an advanced compaction technique to obtain high-density compacts at a compaction velocity of ≤ 10 m/s. It was applied to various metallic powders and was verified to achieve a density greater than 7.5 g/cm3 for the Fe-based powders. The ability to rapidly and accurately predict the green density of compacts is important, especially as an alternative to costly and time-consuming materials design by trial and error. In this paper, we propose a machine-learning approach based on materials informatics to predict the green density of compacts using relevant material descriptors, including chemical composition, powder properties, and compaction energy. We investigated four models using an experimental dataset for appropriate model selection and found the multilayer perceptron model worked well, providing distinguished prediction performance, with a high correlation coefficient and low error values. Applying this model, we predicted the green density of nine materials on the basis of specific processing parameters. The predicted green density agreed very well with the experimental results for each material, with an inaccuracy less than 2%. The prediction accuracy of the developed method was thus confirmed by comparison with experimental results.
High-velocity compaction is an advanced compaction technique to obtain high-density compacts at a compaction velocity of ≤ 10 m/s. It was applied to various metallic powders and was verified to achieve a density greater than 7.5 g/cm3 for the Fe-based powders. The ability to rapidly and accurately predict the green density of compacts is important, especially as an alternative to costly and time-consuming materials design by trial and error. In this paper, we propose a machine-learning approach based on materials informatics to predict the green density of compacts using relevant material descriptors, including chemical composition, powder properties, and compaction energy. We investigated four models using an experimental dataset for appropriate model selection and found the multilayer perceptron model worked well, providing distinguished prediction performance, with a high correlation coefficient and low error values. Applying this model, we predicted the green density of nine materials on the basis of specific processing parameters. The predicted green density agreed very well with the experimental results for each material, with an inaccuracy less than 2%. The prediction accuracy of the developed method was thus confirmed by comparison with experimental results.
2019, vol. 26, no. 2, pp.
202-209.
https://doi.org/10.1007/s12613-019-1725-9
Abstract:
Low-carbon steel plates were successfully subjected to normal friction stir processing (NFSP) in air and submerged friction stir processing (SFSP) under water, and the microstructure, mechanical properties, and corrosion behavior of the NFSP and SFSP samples were investigated. Phase transformation and dynamic recrystallization resulted in fine-grained ferrite and martensite in the processed zone. The SFSP samples had smaller ferrites (5.1 μm), finer martensite laths (557 nm), and more uniform distribution of martensite compared to the NFSP samples. Compared to the base material (BM), the microhardness of the NFSP and SFSP samples increased by 19.8% and 27.1%, respectively because of the combined strengthening effects of grain refinement, phase transformation, and dislocation. The ultimate tensile strengths (UTSs) of the NFSP and SFSP samples increased by 27.1% and 38.7%, respectively. Grain refinement and martensite transformation also improved the electrochemical corrosion properties of the low-carbon steel. Overall, the SFSP samples had better mechanical properties and electrochemical corrosion resistance than the NFSP samples.
Low-carbon steel plates were successfully subjected to normal friction stir processing (NFSP) in air and submerged friction stir processing (SFSP) under water, and the microstructure, mechanical properties, and corrosion behavior of the NFSP and SFSP samples were investigated. Phase transformation and dynamic recrystallization resulted in fine-grained ferrite and martensite in the processed zone. The SFSP samples had smaller ferrites (5.1 μm), finer martensite laths (557 nm), and more uniform distribution of martensite compared to the NFSP samples. Compared to the base material (BM), the microhardness of the NFSP and SFSP samples increased by 19.8% and 27.1%, respectively because of the combined strengthening effects of grain refinement, phase transformation, and dislocation. The ultimate tensile strengths (UTSs) of the NFSP and SFSP samples increased by 27.1% and 38.7%, respectively. Grain refinement and martensite transformation also improved the electrochemical corrosion properties of the low-carbon steel. Overall, the SFSP samples had better mechanical properties and electrochemical corrosion resistance than the NFSP samples.
2019, vol. 26, no. 2, pp.
210-221.
https://doi.org/10.1007/s12613-019-1726-8
Abstract:
Weldments were produced using gas tungsten arc welding (GTAW) and pulsed current gas tungsten arc welding (PCGTAW) techniques with ERNiCr-3 filler wire. Macro examination revealed that the resultant weldments were free from defects. A refined microstructure was observed in the weldment fabricated through PCGTAW. Scanning electron microscopy (SEM) analysis revealed secondary phases in the grain boundaries. Energy-dispersive X-ray spectroscopy (EDS) analysis revealed that microsegregation of Cr carbide precipitates was completely eradicated through PCGTAW. The microsegregation of Nb precipitates was observed in the GTA and PCGTA weldments. X-ray diffraction (XRD) analysis revealed the existence of M23C6 Cr-rich carbide and Ni8Nb phases in the GTA weldments. By contrast, in the PCGTA weldments, the Ni8Nb phase was observed. The Cr2Ti phase was observed in both the GTA and the PCGTA weldments. Tensile tests showed that the strength and ductility of the PCGTA weldments were slightly higher than those of the GTA weldments.
Weldments were produced using gas tungsten arc welding (GTAW) and pulsed current gas tungsten arc welding (PCGTAW) techniques with ERNiCr-3 filler wire. Macro examination revealed that the resultant weldments were free from defects. A refined microstructure was observed in the weldment fabricated through PCGTAW. Scanning electron microscopy (SEM) analysis revealed secondary phases in the grain boundaries. Energy-dispersive X-ray spectroscopy (EDS) analysis revealed that microsegregation of Cr carbide precipitates was completely eradicated through PCGTAW. The microsegregation of Nb precipitates was observed in the GTA and PCGTA weldments. X-ray diffraction (XRD) analysis revealed the existence of M23C6 Cr-rich carbide and Ni8Nb phases in the GTA weldments. By contrast, in the PCGTA weldments, the Ni8Nb phase was observed. The Cr2Ti phase was observed in both the GTA and the PCGTA weldments. Tensile tests showed that the strength and ductility of the PCGTA weldments were slightly higher than those of the GTA weldments.
2019, vol. 26, no. 2, pp.
222-233.
https://doi.org/10.1007/s12613-019-1727-7
Abstract:
The aim of the present study was to investigate the effect of element segregation on the microstructure and γ' phase in a γ/γ' cobalt-based superalloy. Several samples were prepared from a cast alloy and homogenized at 1300℃ for different times, with a maximum of 24 h. A microstructural study of the cast alloy using wavelength-dispersive spectroscopic analysis revealed that elements such as Al, Ti, and Ni segregated mostly within interdendritic regions, whereas W atoms were segregated within dendrite cores. With an increase in homogenization time, segregation decreased and the initial dendritic structure was eliminated. Field-emission scanning electron microscopy micrographs showed that the γ' phases in the cores and interdendritic regions of the as-cast alloy were 392 and 124 nm, respectively. The size difference of γ' was found to be due to the different segregation behaviors of constituent elements during solidification. After homogenization, particularly after 16 h, segregation decreased; thus, the size, chemical composition, and hardness of the precipitated γ' phase was mostly uniform throughout the samples.
The aim of the present study was to investigate the effect of element segregation on the microstructure and γ' phase in a γ/γ' cobalt-based superalloy. Several samples were prepared from a cast alloy and homogenized at 1300℃ for different times, with a maximum of 24 h. A microstructural study of the cast alloy using wavelength-dispersive spectroscopic analysis revealed that elements such as Al, Ti, and Ni segregated mostly within interdendritic regions, whereas W atoms were segregated within dendrite cores. With an increase in homogenization time, segregation decreased and the initial dendritic structure was eliminated. Field-emission scanning electron microscopy micrographs showed that the γ' phases in the cores and interdendritic regions of the as-cast alloy were 392 and 124 nm, respectively. The size difference of γ' was found to be due to the different segregation behaviors of constituent elements during solidification. After homogenization, particularly after 16 h, segregation decreased; thus, the size, chemical composition, and hardness of the precipitated γ' phase was mostly uniform throughout the samples.
2019, vol. 26, no. 2, pp.
234-240.
https://doi.org/10.1007/s12613-019-1728-6
Abstract:
Monodispersed dihydrated zinc oxalate (ZnC2O4·2H2O) particles with characteristic morphology were synthesized by aging a mixed solution of zinc nitrate (Zn(NO3)2) and sodium oxalate (Na2C2O4) in the presence of a citrate ligand, with an average flat size of approximately 10-15 μm. The important parameters, including the solution pH values and the concentration of the zinc ions and citrate ligand, were investigated using a series of experiments. It is verified that the citrate ligand significantly affects the morphology of zinc oxalate particles, probably via its multiple roles of chelating, dispersing, and selective absorption. Thermodynamic equilibrium of the distribution of zinc species in an aqueous solution of Zn(Ⅱ)-citrate-oxalate-H2O was estimated to explain the experimental results and to clarify the size and morphological evolution mechanism of the precipitated particles.
Monodispersed dihydrated zinc oxalate (ZnC2O4·2H2O) particles with characteristic morphology were synthesized by aging a mixed solution of zinc nitrate (Zn(NO3)2) and sodium oxalate (Na2C2O4) in the presence of a citrate ligand, with an average flat size of approximately 10-15 μm. The important parameters, including the solution pH values and the concentration of the zinc ions and citrate ligand, were investigated using a series of experiments. It is verified that the citrate ligand significantly affects the morphology of zinc oxalate particles, probably via its multiple roles of chelating, dispersing, and selective absorption. Thermodynamic equilibrium of the distribution of zinc species in an aqueous solution of Zn(Ⅱ)-citrate-oxalate-H2O was estimated to explain the experimental results and to clarify the size and morphological evolution mechanism of the precipitated particles.
2019, vol. 26, no. 2, pp.
241-250.
https://doi.org/10.1007/s12613-019-1729-5
Abstract:
The independently designed and manufactured ultra-high-strength aluminum alloy Al-12.18Zn-3.31Mg-1.43Cu-0.20Zr-0.04Sr was investigated via scanning electron microscopy observations, X-ray diffraction analysis, hardness tests, electrical conductivity tests, tensile tests, intergranular corrosion tests, and exfoliation corrosion tests. The effect of pre-recovery on the microstructure and mechanical properties of this aluminum alloy was also studied. The results show that the pre-recovery heat treatment releases deformation energy, inhibits recrystallization, and decreases the dislocation density. Although the pre-recovery heat treatment has little effect on the hardness, electrical conductivity, and elongation of this aluminum alloy, it can dramatically improve the alloy's tensile strength (the maximum tensile strength increased from 785.0 MPa to 809.2 MPa). Moreover, the tensile properties of this aluminum alloy have a certain degree of isotropy, and the pre-recovery heat treatment does not affect this property. In addition, the rolled aluminum alloy exhibits good corrosion resistance, but the effect of the pre-recovery heat treatment on the alloy's resistance to intergranular and exfoliation corrosion is negligible.
The independently designed and manufactured ultra-high-strength aluminum alloy Al-12.18Zn-3.31Mg-1.43Cu-0.20Zr-0.04Sr was investigated via scanning electron microscopy observations, X-ray diffraction analysis, hardness tests, electrical conductivity tests, tensile tests, intergranular corrosion tests, and exfoliation corrosion tests. The effect of pre-recovery on the microstructure and mechanical properties of this aluminum alloy was also studied. The results show that the pre-recovery heat treatment releases deformation energy, inhibits recrystallization, and decreases the dislocation density. Although the pre-recovery heat treatment has little effect on the hardness, electrical conductivity, and elongation of this aluminum alloy, it can dramatically improve the alloy's tensile strength (the maximum tensile strength increased from 785.0 MPa to 809.2 MPa). Moreover, the tensile properties of this aluminum alloy have a certain degree of isotropy, and the pre-recovery heat treatment does not affect this property. In addition, the rolled aluminum alloy exhibits good corrosion resistance, but the effect of the pre-recovery heat treatment on the alloy's resistance to intergranular and exfoliation corrosion is negligible.
2019, vol. 26, no. 2, pp.
251-259.
https://doi.org/10.1007/s12613-019-1730-z
Abstract:
The weldability of the ZhS6U nickel-based superalloy, which is prone to solidification cracking during electron-beam welding (EBW) repair processes, was investigated. The effects of two different pre-weld heat-treatment cycles on the final microstructure before and after welding were examined. Welds were made on flat coupons using an EBW machine, and the two heat-treatment cycles were designed to reduce γ' liquation before welding. Microstructural features were also examined by optical and scanning electron microscopy. The results showed that the change in the morphology and size of the γ' precipitates in the pre-weld heat-treatment cycles changed the ability of the superalloy to release the tensile stresses caused by the matrix phase cooling after EBW. The high hardness in the welded coupons subjected to the first heat-treatment cycle resulted in greater resistance to stress release by the base alloy, and the concentration of stress in the base metal caused liquation cracks in the heat-affected zone and solidification cracks in the weld area.
The weldability of the ZhS6U nickel-based superalloy, which is prone to solidification cracking during electron-beam welding (EBW) repair processes, was investigated. The effects of two different pre-weld heat-treatment cycles on the final microstructure before and after welding were examined. Welds were made on flat coupons using an EBW machine, and the two heat-treatment cycles were designed to reduce γ' liquation before welding. Microstructural features were also examined by optical and scanning electron microscopy. The results showed that the change in the morphology and size of the γ' precipitates in the pre-weld heat-treatment cycles changed the ability of the superalloy to release the tensile stresses caused by the matrix phase cooling after EBW. The high hardness in the welded coupons subjected to the first heat-treatment cycle resulted in greater resistance to stress release by the base alloy, and the concentration of stress in the base metal caused liquation cracks in the heat-affected zone and solidification cracks in the weld area.
Preparation of rare-earth-modified medical stone powders and their application as conductive fillers
2019, vol. 26, no. 2, pp.
260-266.
https://doi.org/10.1007/s12613-019-1731-y
Abstract:
Traditional metal conductive fillers are expensive and prone to oxidation. Thus, the development of new conductive powders as fillers is urgently needed. A novel gaseous penetration technology was adopted to prepare La-doped medical stone powders (La-MSPs), which are inexpensive mesoporous materials, as a new kind of conductive filler material. The prepared La-MSPs attained a resistivity of 450 Ω·m and were used as a filler to prepare conductive coatings with epoxy resin as the resin matrix. The influence of the La-MSPs dosage on the resistance and hardness of the coatings was also determined. The resistance and the hardness both decreased with increasing filler dosage. Finally, the optimum recipe of the conductive coatings with the most suitable fillers dosage (55wt%) was obtained. The hardness and resistance of the coatings with 55wt% La-MSPs were HV 4 and 5.5×107 Ω, respectively.
Traditional metal conductive fillers are expensive and prone to oxidation. Thus, the development of new conductive powders as fillers is urgently needed. A novel gaseous penetration technology was adopted to prepare La-doped medical stone powders (La-MSPs), which are inexpensive mesoporous materials, as a new kind of conductive filler material. The prepared La-MSPs attained a resistivity of 450 Ω·m and were used as a filler to prepare conductive coatings with epoxy resin as the resin matrix. The influence of the La-MSPs dosage on the resistance and hardness of the coatings was also determined. The resistance and the hardness both decreased with increasing filler dosage. Finally, the optimum recipe of the conductive coatings with the most suitable fillers dosage (55wt%) was obtained. The hardness and resistance of the coatings with 55wt% La-MSPs were HV 4 and 5.5×107 Ω, respectively.
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