Search2019 Vol. 26, No. 11
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2019, vol. 26, no. 11, pp.
1337-1350.
https://doi.org/10.1007/s12613-019-1826-5
Abstract:
Compared with the traditional pyrometallurgical process, copper bioleaching has distinctive advantages of high efficiency and lower cost, enabling efficiently extracts of valuable metal resources from copper sulfides. Moreover, during long-term industrial applications of bioleaching, many regulatory enhancements and technological methods are used to accelerate the interfacial reactions. With advances in microbial genetic and sequencing technologies, bacterial communities and their mechanisms in bioleaching systems have been revealed gradually. The bacterial proliferation and dissolution of sulfide ores by a bacterial community depends on the pH, temperature, oxygen, reaction product regulation, additives, and passivation substances, among other factors. The internal relationship among the influencing factors and the succession of microorganism diversity are discussed and reviewed in this paper. This paper is intended to provide a good reference for studies related to enhanced bioleaching.
Compared with the traditional pyrometallurgical process, copper bioleaching has distinctive advantages of high efficiency and lower cost, enabling efficiently extracts of valuable metal resources from copper sulfides. Moreover, during long-term industrial applications of bioleaching, many regulatory enhancements and technological methods are used to accelerate the interfacial reactions. With advances in microbial genetic and sequencing technologies, bacterial communities and their mechanisms in bioleaching systems have been revealed gradually. The bacterial proliferation and dissolution of sulfide ores by a bacterial community depends on the pH, temperature, oxygen, reaction product regulation, additives, and passivation substances, among other factors. The internal relationship among the influencing factors and the succession of microorganism diversity are discussed and reviewed in this paper. This paper is intended to provide a good reference for studies related to enhanced bioleaching.
2019, vol. 26, no. 11, pp.
1351-1363.
https://doi.org/10.1007/s12613-019-1879-5
Abstract:
For a long time, coalbed gas has brought about various problems to the safety of coal mine production. In addition, the mining of gas and coalbed methane (CBM) has attracted much attention. The occurrence and migration of CBM are believed to be closely related to the micro-surface properties of coal. To further explore the characteristics of CBM occurrence and migration, in this study, the micro-surface topography, adhesion, and elastic modulus of five metamorphic coals were measured by atomic force microscopy (AFM). The results show that the microtopography of coal fluctuates around 40 nm, reaching a maximum of 66.5 nm and the roughness of the surface decreases with the increase of metamorphism. The elastic modulus of coal micro-surface varies from 95.40 to 9626.41 MPa, while the adhesion varies from 15.08 to 436.22 nN, and they both exhibit a trend of "M" shape with the increase of metamorphism. Furthermore, a high correlation exists between adhesion and microtopography fluctuation. In most cases, the adhesion is larger in the concavity area and smaller in the convexity area. The research results may provide a new method for revealing the occurrence and migration of CBM and ensure efficient and safe CBM exploitation.
For a long time, coalbed gas has brought about various problems to the safety of coal mine production. In addition, the mining of gas and coalbed methane (CBM) has attracted much attention. The occurrence and migration of CBM are believed to be closely related to the micro-surface properties of coal. To further explore the characteristics of CBM occurrence and migration, in this study, the micro-surface topography, adhesion, and elastic modulus of five metamorphic coals were measured by atomic force microscopy (AFM). The results show that the microtopography of coal fluctuates around 40 nm, reaching a maximum of 66.5 nm and the roughness of the surface decreases with the increase of metamorphism. The elastic modulus of coal micro-surface varies from 95.40 to 9626.41 MPa, while the adhesion varies from 15.08 to 436.22 nN, and they both exhibit a trend of "M" shape with the increase of metamorphism. Furthermore, a high correlation exists between adhesion and microtopography fluctuation. In most cases, the adhesion is larger in the concavity area and smaller in the convexity area. The research results may provide a new method for revealing the occurrence and migration of CBM and ensure efficient and safe CBM exploitation.
2019, vol. 26, no. 11, pp.
1364-1371.
https://doi.org/10.1007/s12613-019-1857-y
Abstract:
The kinetics and mechanism of natural wolframite interactions with sodium carbonate during air heating were studied. X-ray phase and X-ray microanalysis were used to establish that the initial monocrystalline wolframite consists of Fe0.5Mn0.5WO4 and Fe0.3Mn0.7WO4. Differential thermal analysis showed that the interaction of wolframite with sodium carbonate begins above 450℃ with the formation of tungstate, sodium ferrite, iron oxides, and manganese. Model experiments on sintering with the subsequent removal of water-soluble compounds (leaching) tracked the change in the structure of wolframite. The atomic ratio of Fe/Mn in wolframite does not change up to 600℃, and subsequently decreases to 0.2 during heating, which allows the mechanism of the process to be identified and indicates the greater reactivity of wolframites with an increased proportion of iron. Thermal analysis with data processing using non-isothermal kinetics established that the interaction of wolframite with sodium carbonate in an air stream proceeds via a two-stage mechanism, wherein the first stage is limited by diffusion (activation energy, E=243 kJ/mol) and the second stage is limited by autocatalysis (activation energy, E=212 kJ/mol) due to the formation of a Na2WO4-Na2CO3 eutectic.
The kinetics and mechanism of natural wolframite interactions with sodium carbonate during air heating were studied. X-ray phase and X-ray microanalysis were used to establish that the initial monocrystalline wolframite consists of Fe0.5Mn0.5WO4 and Fe0.3Mn0.7WO4. Differential thermal analysis showed that the interaction of wolframite with sodium carbonate begins above 450℃ with the formation of tungstate, sodium ferrite, iron oxides, and manganese. Model experiments on sintering with the subsequent removal of water-soluble compounds (leaching) tracked the change in the structure of wolframite. The atomic ratio of Fe/Mn in wolframite does not change up to 600℃, and subsequently decreases to 0.2 during heating, which allows the mechanism of the process to be identified and indicates the greater reactivity of wolframites with an increased proportion of iron. Thermal analysis with data processing using non-isothermal kinetics established that the interaction of wolframite with sodium carbonate in an air stream proceeds via a two-stage mechanism, wherein the first stage is limited by diffusion (activation energy, E=243 kJ/mol) and the second stage is limited by autocatalysis (activation energy, E=212 kJ/mol) due to the formation of a Na2WO4-Na2CO3 eutectic.
2019, vol. 26, no. 11, pp.
1372-1384.
https://doi.org/10.1007/s12613-019-1871-0
Abstract:
In order to improve the strength and toughness of Q690E steel sheets, the effect of rare earth element Ce on the strength and toughness of Q690E steel was studied by means of transmission electron microscopy, scanning electron microscopy, and metallographic microscope. The results showed that the addition of Ce in steel limited the combination of S with Mn and Ca, transformed Al2O3 inclusion into spherical CeAlO3 inclusion, and modified the precipitate form of some composite inclusions of TiN and sulfide oxides into TiN precipitation alone. The inclusions were spheroidizing. The size of inclusions was decreased from 3-5 μm to 1-2 μm, and the distribution was dispersed. Ce played a role in purifying molten steel through desulphurization and deoxidization. Meanwhile, the addition of Ce in steel effectively increased the nucleation particles in the liquid phase, improved the nucleation rate, enlarged the equiaxed grain refinement area, and limited the development of columnar crystals. The average grain size of slab decreased from 45.76 to 35.25 μm, and the proportion of large grain size (> 50 μm) decreased from 40.41% to 23.74%. The macrostructural examination of slab was improved from B0.5 to C2.0, which realized the refinement of the solidified structure and reduced the banded structure of hot rolled plate. In addition, due to the inheritance of refined structure in the upstream, the recrystallization of deformed austenite and the growth of grain after recrystallization were restrained, and a refined tempered sorbite structure was obtained. When rare earth element Ce was added, the width of the martensite lath bundle was narrowed from about 500 nm to about 200 nm, which realized a remarkable grain refinement strengthening and toughening effect. Mechanical properties such as tensile, yield, and low-temperature impact toughness were significantly improved.
In order to improve the strength and toughness of Q690E steel sheets, the effect of rare earth element Ce on the strength and toughness of Q690E steel was studied by means of transmission electron microscopy, scanning electron microscopy, and metallographic microscope. The results showed that the addition of Ce in steel limited the combination of S with Mn and Ca, transformed Al2O3 inclusion into spherical CeAlO3 inclusion, and modified the precipitate form of some composite inclusions of TiN and sulfide oxides into TiN precipitation alone. The inclusions were spheroidizing. The size of inclusions was decreased from 3-5 μm to 1-2 μm, and the distribution was dispersed. Ce played a role in purifying molten steel through desulphurization and deoxidization. Meanwhile, the addition of Ce in steel effectively increased the nucleation particles in the liquid phase, improved the nucleation rate, enlarged the equiaxed grain refinement area, and limited the development of columnar crystals. The average grain size of slab decreased from 45.76 to 35.25 μm, and the proportion of large grain size (> 50 μm) decreased from 40.41% to 23.74%. The macrostructural examination of slab was improved from B0.5 to C2.0, which realized the refinement of the solidified structure and reduced the banded structure of hot rolled plate. In addition, due to the inheritance of refined structure in the upstream, the recrystallization of deformed austenite and the growth of grain after recrystallization were restrained, and a refined tempered sorbite structure was obtained. When rare earth element Ce was added, the width of the martensite lath bundle was narrowed from about 500 nm to about 200 nm, which realized a remarkable grain refinement strengthening and toughening effect. Mechanical properties such as tensile, yield, and low-temperature impact toughness were significantly improved.
2019, vol. 26, no. 11, pp.
1385-1395.
https://doi.org/10.1007/s12613-019-1845-2
Abstract:
The formation mechanism of acicular ferrite and its microstructural characteristics in 430 ferrite stainless steel with TiC additions were studied by theory and experiment. Using an "edge-to-edge matching" model, a 5.25 mismatch between TiC (FCC structure) and ferritic stainless steel (BCC structure) was identified, which met the mismatch requirement for the heterogeneous nucleation of 430 ferritic stainless steel. TiC was found to be an effective nucleation site for the formation of acicular ferrite in a smelting experiment, as analyzed by metallographic examination, Image-Pro Plus 6.0 analysis software, and SEM-EDS. Furthermore, small inclusions in the size of 2-4 μm increased the probability of acicular ferrite nucleation, and the secondary acicular ferrite would grow sympathetically from the initial acicular ferrite to produce multi-dimensional acicular ferrites. Moreover, the addition of TiC can increase the average microstrain and dislocation density of 430 ferrite stainless steel, as calculated by Williamson-Hall (WH) method, which could play some role in strengthening the dislocation.
The formation mechanism of acicular ferrite and its microstructural characteristics in 430 ferrite stainless steel with TiC additions were studied by theory and experiment. Using an "edge-to-edge matching" model, a 5.25 mismatch between TiC (FCC structure) and ferritic stainless steel (BCC structure) was identified, which met the mismatch requirement for the heterogeneous nucleation of 430 ferritic stainless steel. TiC was found to be an effective nucleation site for the formation of acicular ferrite in a smelting experiment, as analyzed by metallographic examination, Image-Pro Plus 6.0 analysis software, and SEM-EDS. Furthermore, small inclusions in the size of 2-4 μm increased the probability of acicular ferrite nucleation, and the secondary acicular ferrite would grow sympathetically from the initial acicular ferrite to produce multi-dimensional acicular ferrites. Moreover, the addition of TiC can increase the average microstrain and dislocation density of 430 ferrite stainless steel, as calculated by Williamson-Hall (WH) method, which could play some role in strengthening the dislocation.
2019, vol. 26, no. 11, pp.
1396-1404.
https://doi.org/10.1007/s12613-019-1837-2
Abstract:
This study is conducted to develop an innovative and attractive selective laser melting (SLM) method to produce 316L stainless steel materials with excellent mechanical performance and complex part shape. In this work, the subregional manufacturing strategy, which separates the special parts from the components using an optimized process, was proposed. The results showed that produced 316L materials exhibited superior strength of~755 MPa and good ductility. In the as-built parts, austenite with preferred orientation of the (220) plane, δ-ferrite, and a small amount of CrO phases were present. In addition, the crystal size was fine, which contributed to the enhancement of the parts' mechanical properties. The structural anisotropy mechanism of the materials was also investigated for a group of half-sized samples with variable inclination directions. This technique was used to fabricate a set of impellers with helical bevels and high-precision planetary gears, demonstrating its strong potential for use in practical applications.
This study is conducted to develop an innovative and attractive selective laser melting (SLM) method to produce 316L stainless steel materials with excellent mechanical performance and complex part shape. In this work, the subregional manufacturing strategy, which separates the special parts from the components using an optimized process, was proposed. The results showed that produced 316L materials exhibited superior strength of~755 MPa and good ductility. In the as-built parts, austenite with preferred orientation of the (220) plane, δ-ferrite, and a small amount of CrO phases were present. In addition, the crystal size was fine, which contributed to the enhancement of the parts' mechanical properties. The structural anisotropy mechanism of the materials was also investigated for a group of half-sized samples with variable inclination directions. This technique was used to fabricate a set of impellers with helical bevels and high-precision planetary gears, demonstrating its strong potential for use in practical applications.
2019, vol. 26, no. 11, pp.
1405-1414.
https://doi.org/10.1007/s12613-019-1861-2
Abstract:
The cathodic reaction mechanisms in CO2 corrosion of low-Cr steels were investigated by potentiodynamic polarization and galvanostatic measurements. Distinct but different dominant cathodic reactions were observed at different pH levels. At the higher pH level (pH >~5), H2CO3 reduction was the dominant cathodic reaction. The reaction was under activation control. At the lower pH level (pH <~3.5), H+ reduction became the dominant one and the reaction was under diffusion control. In the intermediate area, there was a transition region leading from one cathodic reaction to another. The measured electrochemical impedance spectrum corresponded to the proposed cathodic reaction mechanisms.
The cathodic reaction mechanisms in CO2 corrosion of low-Cr steels were investigated by potentiodynamic polarization and galvanostatic measurements. Distinct but different dominant cathodic reactions were observed at different pH levels. At the higher pH level (pH >~5), H2CO3 reduction was the dominant cathodic reaction. The reaction was under activation control. At the lower pH level (pH <~3.5), H+ reduction became the dominant one and the reaction was under diffusion control. In the intermediate area, there was a transition region leading from one cathodic reaction to another. The measured electrochemical impedance spectrum corresponded to the proposed cathodic reaction mechanisms.
2019, vol. 26, no. 11, pp.
1415-1426.
https://doi.org/10.1007/s12613-019-1825-6
Abstract:
Polarization curves and mass losses of SAF3207 hyper-duplex stainless steel under various conditions were measured. The damaged surfaces after erosion-corrosion tests were characterized by scanning electron microscopy. The results showed that an increase in flow velocity could enhance the electrochemical corrosion and consequently decrease the passivation properties of the steel. The erosion-corrosion damage of the samples increased substantially when the flow velocity exceeded the critical value of 4 m·s-1. The mass loss rate increased as the sand content increased, reaching a maximum at 7wt% sand content, corresponding to the most severe electrochemical corrosion damage. When the sand content was increased further, however, the mass loss rate decreased and then tended stable. The mass loss was divided into incubation, sustained, and stationary periods, with a maximum mass loss rate of 12.97 g·h-1·m-2 after an erosion period of 2.5 h. The erosion-corrosion mechanism was investigated in detail.
Polarization curves and mass losses of SAF3207 hyper-duplex stainless steel under various conditions were measured. The damaged surfaces after erosion-corrosion tests were characterized by scanning electron microscopy. The results showed that an increase in flow velocity could enhance the electrochemical corrosion and consequently decrease the passivation properties of the steel. The erosion-corrosion damage of the samples increased substantially when the flow velocity exceeded the critical value of 4 m·s-1. The mass loss rate increased as the sand content increased, reaching a maximum at 7wt% sand content, corresponding to the most severe electrochemical corrosion damage. When the sand content was increased further, however, the mass loss rate decreased and then tended stable. The mass loss was divided into incubation, sustained, and stationary periods, with a maximum mass loss rate of 12.97 g·h-1·m-2 after an erosion period of 2.5 h. The erosion-corrosion mechanism was investigated in detail.
2019, vol. 26, no. 11, pp.
1427-1435.
https://doi.org/10.1007/s12613-019-1798-5
Abstract:
Two kinds of experimental methods were tried in the present work:(i) the powder metallurgy method combined with differential thermal analysis (DTA) to determine the metastable liquidus miscibility gap for a Fe-Cu binary system and (ii) the high-temperature melting method combined with isothermal treatment to determine the stable liquidus miscibility gap for a Fe-Sn binary system. The experimental method was adopted according to the characteristics of the liquidus miscibility gap of the specific system. Using the powder metallurgy method, a uniform microstructure morphology and chemical composition was obtained in the DTA specimen, and the phase-separation temperature of the supercooled metastable liquid was measured. The isothermal treatment was applied for the samples inside the stable liquidus miscibility gap; here, equilibrated compositions were reached, and a layered morphology was formed after rapid cooling. The liquid miscibility gaps of the Fe-Cu and Fe-Sn binary systems were measured, and the peak temperatures of the corresponding miscibility gaps were determined to be about 1417℃ at x(Cu)=0.465at% and 1350℃ at x(Sn)=0.487at%, respectively. On the basis of the experimental results, both the Fe-Cu and the Fe-Sn binary systems were thermodynamically assessed.
Two kinds of experimental methods were tried in the present work:(i) the powder metallurgy method combined with differential thermal analysis (DTA) to determine the metastable liquidus miscibility gap for a Fe-Cu binary system and (ii) the high-temperature melting method combined with isothermal treatment to determine the stable liquidus miscibility gap for a Fe-Sn binary system. The experimental method was adopted according to the characteristics of the liquidus miscibility gap of the specific system. Using the powder metallurgy method, a uniform microstructure morphology and chemical composition was obtained in the DTA specimen, and the phase-separation temperature of the supercooled metastable liquid was measured. The isothermal treatment was applied for the samples inside the stable liquidus miscibility gap; here, equilibrated compositions were reached, and a layered morphology was formed after rapid cooling. The liquid miscibility gaps of the Fe-Cu and Fe-Sn binary systems were measured, and the peak temperatures of the corresponding miscibility gaps were determined to be about 1417℃ at x(Cu)=0.465at% and 1350℃ at x(Sn)=0.487at%, respectively. On the basis of the experimental results, both the Fe-Cu and the Fe-Sn binary systems were thermodynamically assessed.
2019, vol. 26, no. 11, pp.
1436-1449.
https://doi.org/10.1007/s12613-019-1886-6
Abstract:
Cu-Zn-Sn shape memory alloys (SMAs) with an average composition of 56.0at%, 36.1at%, and 7.9at% for Cu, Zn, and Sn, respectively, were successfully fabricated via an electrodeposition-annealing route. The produced SMAs were assessed for shape memory response in terms of percent displacement (martensite phase recovery) by subjecting the ternary alloys to flame tests and subsequently characterizing them via differential scanning calorimetry (DSC), optical microscopy, scanning electron microscopy in conjunction with energy-dispersive spectroscopy (SEM-EDS), and X-ray diffraction (XRD) analysis. The flame tests showed that the highest displacement was ca. 93%, with average austenite and martensitic start transformation temperature of 225℃ and 222℃, respectively. XRD analysis revealed that the intermetallic phases responsible for the observed shape memory properties have substitutional Zn in the lattice occupied by Cu and Sn, leading to the formation of Cu(Zn,Sn) and Cu6(Zn,Sn)5 variants. The formation of these variants was attributed to the faster interdiffusion of Cu into Sn, driven by an activation energy of 34.82 kJ·mol-1. Five cycles of repeated torching-annealing revealed an essentially constant shape memory response, suggesting that the fabricated SMAs were consistent and sufficiently reliable for their intended service application.
Cu-Zn-Sn shape memory alloys (SMAs) with an average composition of 56.0at%, 36.1at%, and 7.9at% for Cu, Zn, and Sn, respectively, were successfully fabricated via an electrodeposition-annealing route. The produced SMAs were assessed for shape memory response in terms of percent displacement (martensite phase recovery) by subjecting the ternary alloys to flame tests and subsequently characterizing them via differential scanning calorimetry (DSC), optical microscopy, scanning electron microscopy in conjunction with energy-dispersive spectroscopy (SEM-EDS), and X-ray diffraction (XRD) analysis. The flame tests showed that the highest displacement was ca. 93%, with average austenite and martensitic start transformation temperature of 225℃ and 222℃, respectively. XRD analysis revealed that the intermetallic phases responsible for the observed shape memory properties have substitutional Zn in the lattice occupied by Cu and Sn, leading to the formation of Cu(Zn,Sn) and Cu6(Zn,Sn)5 variants. The formation of these variants was attributed to the faster interdiffusion of Cu into Sn, driven by an activation energy of 34.82 kJ·mol-1. Five cycles of repeated torching-annealing revealed an essentially constant shape memory response, suggesting that the fabricated SMAs were consistent and sufficiently reliable for their intended service application.
2019, vol. 26, no. 11, pp.
1450-1456.
https://doi.org/10.1007/s12613-019-1839-0
Abstract:
To explore the specimen size effect of mechanical behavior of ultrafine-grained (UFG) materials with different structures, UFG Al sheets processed by equal channel angular pressing (ECAP) were selected as target materials and the dependency of tensile behavior on sheet thickness (t) was systematically investigated. The strength and ductility of ECAPed UFG Al sheets were improved synchronously as t increased from 0.2 to 0.7 mm, and then no apparent change occurred when t reached to 0.7 and 1.0 mm. The corresponding microstructure evolved from dislocation networks in equiaxed grains into the walls and subgrains and finally into the dominated cells in elongated grains or subgrains. Meanwhile, dense shear lines (SLs) and shear bands (SBs) were clearly observed and microvoids and cracks were initiated along SBs with the increase of t. These observations indicated that the plastic deformation of UFG Al sheets was jointly controlled by shear banding, dislocation sliding, and grain-boundary sliding. Furthermore, the propagation of SBs became difficult as t increased. Finally, the obtained results were discussed and compared with those of annealed UFG Al and UFG Cu.
To explore the specimen size effect of mechanical behavior of ultrafine-grained (UFG) materials with different structures, UFG Al sheets processed by equal channel angular pressing (ECAP) were selected as target materials and the dependency of tensile behavior on sheet thickness (t) was systematically investigated. The strength and ductility of ECAPed UFG Al sheets were improved synchronously as t increased from 0.2 to 0.7 mm, and then no apparent change occurred when t reached to 0.7 and 1.0 mm. The corresponding microstructure evolved from dislocation networks in equiaxed grains into the walls and subgrains and finally into the dominated cells in elongated grains or subgrains. Meanwhile, dense shear lines (SLs) and shear bands (SBs) were clearly observed and microvoids and cracks were initiated along SBs with the increase of t. These observations indicated that the plastic deformation of UFG Al sheets was jointly controlled by shear banding, dislocation sliding, and grain-boundary sliding. Furthermore, the propagation of SBs became difficult as t increased. Finally, the obtained results were discussed and compared with those of annealed UFG Al and UFG Cu.
2019, vol. 26, no. 11, pp.
1457-1466.
https://doi.org/10.1007/s12613-019-1838-1
Abstract:
The effect of Ca addition on the elemental composition, microstructure, Brinell hardness and tensile properties of Al-7Si-0.3Mg alloy were investigated. The residual content of Ca in the alloy linearly increased with the amount of Ca added to the melt. The optimal microstructure and properties were obtained by adding 0.06wt% Ca to Al-7Si-0.3Mg alloy. The secondary dendrite arm spacing (SDAS) of the primary α phase decreased from 44.41 μm to 19.4 μm, and the eutectic Si changed from coarse plates to fine coral. The length of the Fe-rich phase (β-Al5FeSi) decreased from 30.2 μm to 3.8 μm, and the Brinell hardness can reach to 66.9. The ultimate tensile strength, yield strength, and elongation of the resulting alloy increased from 159.5 MPa, 79 MPa, and 2.5% to 212 MPa, 86.5 MPa, and 4.5%, respectively. The addition of Ca can effectively refine the primary α phase and modify the eutectic Si phase, likely because Ca enrichment at the front of the solid-liquid interface led to undercooling of the alloy, reduced the growth rate of the primary α phase, and refined the grain size. Also, it could increase the latent heat of crystallization, undercooling, and the nucleation rate of eutectic Si, which was beneficial to the improvement of the morphology of eutectic Si.
The effect of Ca addition on the elemental composition, microstructure, Brinell hardness and tensile properties of Al-7Si-0.3Mg alloy were investigated. The residual content of Ca in the alloy linearly increased with the amount of Ca added to the melt. The optimal microstructure and properties were obtained by adding 0.06wt% Ca to Al-7Si-0.3Mg alloy. The secondary dendrite arm spacing (SDAS) of the primary α phase decreased from 44.41 μm to 19.4 μm, and the eutectic Si changed from coarse plates to fine coral. The length of the Fe-rich phase (β-Al5FeSi) decreased from 30.2 μm to 3.8 μm, and the Brinell hardness can reach to 66.9. The ultimate tensile strength, yield strength, and elongation of the resulting alloy increased from 159.5 MPa, 79 MPa, and 2.5% to 212 MPa, 86.5 MPa, and 4.5%, respectively. The addition of Ca can effectively refine the primary α phase and modify the eutectic Si phase, likely because Ca enrichment at the front of the solid-liquid interface led to undercooling of the alloy, reduced the growth rate of the primary α phase, and refined the grain size. Also, it could increase the latent heat of crystallization, undercooling, and the nucleation rate of eutectic Si, which was beneficial to the improvement of the morphology of eutectic Si.
2019, vol. 26, no. 11, pp.
1467-1476.
https://doi.org/10.1007/s12613-019-1863-0
Abstract:
In the last decade, extensive research has been carried out on the microstructural behavior of high-entropy alloys (HEA), for which the in-situ formation of nanoparticles has been reported. However, studies of the incorporation of nanoparticles in HEA have been rarely reported. In this work, the addition of zinc oxide nanoparticles (ZnO NP) as reinforcement in a CoCrFeMoNi high-entropy alloy matrix, as well as the morphological, structural, and microstructural evolution of composites synthesized via powder metallurgy, were studied. Scanning electron microscopy and X-ray diffraction analysis were performed in order to study the microstructural and phase characterization of the composites. After sintering, it was found that the ZnO NP addition (0.5wt%, 1wt% and 2wt%) had a significant influence on the microstructure and hardness of the CoCrFeMoNi high-entropy alloy. Stronger bonding among metal particles was promoted with the additions of ZnO NP. A reduction in porosity as a function of ZnO NP content was also observed. The microhardness results showed that the composite reached its highest reinforcement in bulk samples with 1wt% ZnO NP (HV 870), which represented a 20% improvement over the unreinforced HEA matrix.
In the last decade, extensive research has been carried out on the microstructural behavior of high-entropy alloys (HEA), for which the in-situ formation of nanoparticles has been reported. However, studies of the incorporation of nanoparticles in HEA have been rarely reported. In this work, the addition of zinc oxide nanoparticles (ZnO NP) as reinforcement in a CoCrFeMoNi high-entropy alloy matrix, as well as the morphological, structural, and microstructural evolution of composites synthesized via powder metallurgy, were studied. Scanning electron microscopy and X-ray diffraction analysis were performed in order to study the microstructural and phase characterization of the composites. After sintering, it was found that the ZnO NP addition (0.5wt%, 1wt% and 2wt%) had a significant influence on the microstructure and hardness of the CoCrFeMoNi high-entropy alloy. Stronger bonding among metal particles was promoted with the additions of ZnO NP. A reduction in porosity as a function of ZnO NP content was also observed. The microhardness results showed that the composite reached its highest reinforcement in bulk samples with 1wt% ZnO NP (HV 870), which represented a 20% improvement over the unreinforced HEA matrix.
2019, vol. 26, no. 11, pp.
1477-1484.
https://doi.org/10.1007/s12613-019-1889-3
Abstract:
Tungsten nanoparticle-strengthened Cu composites were prepared from nanopowder synthesized by a sol-gel method and in-situ hydrogen reduction. The tungsten particles in the Cu matrix were well-dispersed with an average size of approximately 100-200 nm. The addition of nanosized W particles remarkably improves the mechanical properties, while the electrical conductivity did not substantially decrease. The Cu-W composite with 6wt% W has the most comprehensive properties with an ultimate strength of 310 MPa, yield strength of 238 MPa, hardness of HV 108 and electrical conductivity of 90% IACS. The enhanced mechanical property and only a small loss of electrical conductivity demonstrate the potential of this new strategy to prepare W nanoparticle-strengthened Cu composites.
Tungsten nanoparticle-strengthened Cu composites were prepared from nanopowder synthesized by a sol-gel method and in-situ hydrogen reduction. The tungsten particles in the Cu matrix were well-dispersed with an average size of approximately 100-200 nm. The addition of nanosized W particles remarkably improves the mechanical properties, while the electrical conductivity did not substantially decrease. The Cu-W composite with 6wt% W has the most comprehensive properties with an ultimate strength of 310 MPa, yield strength of 238 MPa, hardness of HV 108 and electrical conductivity of 90% IACS. The enhanced mechanical property and only a small loss of electrical conductivity demonstrate the potential of this new strategy to prepare W nanoparticle-strengthened Cu composites.
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