Pub Date : 2023-11-05DOI: 10.3365/kjmm.2023.61.11.849
Su Hwan Jeong, Hyeon-jun Choi, Sang Jun Lee, Dong Park Lee, Suyoon Eum, San Moon, Jong Hyuk Yun, Joo-Hyung Kim
With the rapid development of portable devices and Energy Storage Systems (ESS), secondary batteries with high energy density and high capacity are in great demand. Among various candidates, Lithium-sulfur (Li-S) batteries have been considered for next-generation energy devices given their high theoretical capacity (1675 mAh g-1) and energy density (2500 Wh kg-1). However, the commercialization of Li-S batteries faces challenges due to sulfur’s low electrical conductivity and the shuttle effect, caused by the dissolution of lithium polysulfide intermediates in the electrolyte during the charge-discharge process. Herein, to resolve these problems, we report the fabrication of a vanadium dioxide (VO2) composite via a simple hydrothermal method and optimize the structure of VO2 for constructing an effective Multi-Walled Carbon Nano Tube (MWCNT) and 3D flower-shaped VO2 (MWCNT@VO2) binary sulfur host by a simple melt diffusion method. In particular, the polar VO2 composite not only physically absorbs the soluble lithium polysulfides but also has strong chemical bonds with a higher affinity for lithium polysulfides, which act as a catalyst, enhancing electrochemical reversibility. Additionally, MWCNT improves sulfur’s poor electrical conductivity and buffers volume expansion during cycling. The designed S-MWCNT@VO2 electrode also exhibits better capacity retention and cycling performance than a bare S-MWCNT electrode as a lithium polysulfide reservoir.
随着便携式设备和储能系统(ESS)的快速发展，对高能量密度、高容量的二次电池的需求越来越大。在各种候选电池中，锂硫(Li-S)电池由于其高理论容量(1675 mAh g<sup>-1</sup>)和能量密度(2500 Wh kg<sup>-1</sup>)而被考虑用于下一代能源设备。然而，锂硫电池的商业化面临挑战，因为硫的低导电性和穿梭效应，在充放电过程中，多硫化锂中间体溶解在电解质中。为了解决这些问题，我们报道了用简单的水热法制备二氧化钒(VO<sub>2</sub>)复合材料，并优化了VO<sub>2</sub>构建有效的多壁碳纳米管(MWCNT)和三维花形碳纳米管<sub>2</sub>(MWCNT@VO<sub>2</sub>)二元硫宿主的简单熔体扩散法。特别是极性的VO<sub>2</sub>复合材料不仅物理吸附可溶的多硫化锂，而且对多硫化锂具有较高亲和力的强化学键，起到催化剂的作用，增强了电化学可逆性。此外，MWCNT改善了硫的导电性差，并缓冲了循环过程中的体积膨胀。设计的S-MWCNT@VO<sub>2</sub>作为锂多硫化物储层，电极也表现出比裸S-MWCNT电极更好的容量保持和循环性能。
{"title":"Alleviating the Polysulfide Shuttle Effect by Optimization of 3D Flower-Shaped Vanadium Dioxide for Lithium-Sulfur Batteries","authors":"Su Hwan Jeong, Hyeon-jun Choi, Sang Jun Lee, Dong Park Lee, Suyoon Eum, San Moon, Jong Hyuk Yun, Joo-Hyung Kim","doi":"10.3365/kjmm.2023.61.11.849","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.11.849","url":null,"abstract":"With the rapid development of portable devices and Energy Storage Systems (ESS), secondary batteries with high energy density and high capacity are in great demand. Among various candidates, Lithium-sulfur (Li-S) batteries have been considered for next-generation energy devices given their high theoretical capacity (1675 mAh g<sup>-1</sup>) and energy density (2500 Wh kg<sup>-1</sup>). However, the commercialization of Li-S batteries faces challenges due to sulfur’s low electrical conductivity and the shuttle effect, caused by the dissolution of lithium polysulfide intermediates in the electrolyte during the charge-discharge process. Herein, to resolve these problems, we report the fabrication of a vanadium dioxide (VO<sub>2</sub>) composite via a simple hydrothermal method and optimize the structure of VO<sub>2</sub> for constructing an effective Multi-Walled Carbon Nano Tube (MWCNT) and 3D flower-shaped VO<sub>2</sub> (MWCNT@VO<sub>2</sub>) binary sulfur host by a simple melt diffusion method. In particular, the polar VO<sub>2</sub> composite not only physically absorbs the soluble lithium polysulfides but also has strong chemical bonds with a higher affinity for lithium polysulfides, which act as a catalyst, enhancing electrochemical reversibility. Additionally, MWCNT improves sulfur’s poor electrical conductivity and buffers volume expansion during cycling. The designed S-MWCNT@VO<sub>2</sub> electrode also exhibits better capacity retention and cycling performance than a bare S-MWCNT electrode as a lithium polysulfide reservoir.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":"15 3","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135723592","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-11-05DOI: 10.3365/kjmm.2023.61.11.857
JunSu Kim, Seong-Mee Hwang, Hyunjin Park, Yinglu Tang, Won-Seon Seo, Chae Woo Ryu, Heesun Yang, Weon Ho Shin, Hyun-Sik Kim
SnSe is a promising thermoelectric material due to its low toxicity, low thermal conductivity, and multiple valence band structures, which are ideal for high electronic transport properties. The multiple valence band structure has attracted many attempts to engineer the carrier concentration of the SnSe via doping, to place its fermi level at a position where the maximum number of valence bands can participate in the electronic transport. Up until now, ~5 × 1019 cm-3 was the highest carrier concentration achieved in SnSe via doping. Recently, introducing SnSe2 into SnSe was found to effectively increase the carrier concentration as high as ~6.5 × 1019 cm-3 (at 300 K) due to the generated Sn vacancies. This high carrier concentration at 300 K, combined with the reduction in lattice thermal conductivity due to SnSe2 micro-domains formed within the SnSe lattice, improved the thermoelectric performance (zT) of SnSe – xSnSe2 as high as ~2.2 at 773 K. Here, we analyzed the changes in the electronic band parameters of SnSe as a function of temperature with varying SnSe2 content using the Single Parabolic Band (SPB) model. According to the SPB model, the calculated density-of-states effective mass and the fermi level are changed with temperature in such a way that the Hall carrier concentration (nH) of the SnSe – xSnSe2 samples at 773 K coincides with the optimum nH where the theoretically maximum zT is predicted. To optimize the nH at high temperatures for the highest zT, it is essential to tune the 300 K nH and the rate of nH change with increasing temperature via doping.
{"title":"The Mechanism Behind the High zT of SnSe<sub>2</sub> Added SnSe at High Temperatures","authors":"JunSu Kim, Seong-Mee Hwang, Hyunjin Park, Yinglu Tang, Won-Seon Seo, Chae Woo Ryu, Heesun Yang, Weon Ho Shin, Hyun-Sik Kim","doi":"10.3365/kjmm.2023.61.11.857","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.11.857","url":null,"abstract":"SnSe is a promising thermoelectric material due to its low toxicity, low thermal conductivity, and multiple valence band structures, which are ideal for high electronic transport properties. The multiple valence band structure has attracted many attempts to engineer the carrier concentration of the SnSe via doping, to place its fermi level at a position where the maximum number of valence bands can participate in the electronic transport. Up until now, ~5 × 10<sup>19</sup> cm<sup>-3</sup> was the highest carrier concentration achieved in SnSe via doping. Recently, introducing SnSe<sub>2</sub> into SnSe was found to effectively increase the carrier concentration as high as ~6.5 × 10<sup>19</sup> cm<sup>-3</sup> (at 300 K) due to the generated Sn vacancies. This high carrier concentration at 300 K, combined with the reduction in lattice thermal conductivity due to SnSe<sub>2</sub> micro-domains formed within the SnSe lattice, improved the thermoelectric performance (<i>zT</i>) of SnSe – <i>x</i>SnSe<sub>2</sub> as high as ~2.2 at 773 K. Here, we analyzed the changes in the electronic band parameters of SnSe as a function of temperature with varying SnSe<sub>2</sub> content using the Single Parabolic Band (SPB) model. According to the SPB model, the calculated density-of-states effective mass and the fermi level are changed with temperature in such a way that the Hall carrier concentration (<i>nH</i>) of the SnSe – xSnSe2 samples at 773 K coincides with the optimum <i>nH</i> where the theoretically maximum <i>zT</i> is predicted. To optimize the <i>nH</i> at high temperatures for the highest <i>zT</i>, it is essential to tune the 300 K <i>nH</i> and the rate of <i>nH</i> change with increasing temperature via doping.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":"14 4","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135723597","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-11-05DOI: 10.3365/kjmm.2023.61.11.867
Sang-Hyeon Jo, Seong-Hee Lee
Commercial AA1070 alloy for electrical wire is severely deformed by the drawing process when a rod with a diameter of 2 mm is greatly reduced to 0.4 mm by multi-pass. Changes in the microstructure, mechanical properties, and electrical properties of the Al alloy during the wire-drawing process were investigated in detail. The as-drawn Al wires showed a deformation structure in which the grains are greatly elongated in the drawing direction, even though recovery and/or partial recrystallization occurred more actively in the specimens which had more than 84% in reduction of cross-sectional area (RA). In addition, the fraction of high angle grain boundaries tended to increase with the increase of RA. For all drawn specimens, the fiber texture of the {110}<111> and {112}<111> components was mainly developed, and their maximum intensity tended to increase with increasing RA. Recrystallization texture of (001)[100] and (110)[001] began to appear at an RA higher than 84%. The hardness tended to increase with increasing RA due to work hardening. In particular, increasing RA to 84% resulted in a great rise in hardness, accompanied by a distinct non-uniformity in hardness in the thickness direction. However, the average hardness hardly changed at RA above 84%, even when RA was increased to 96%. The strength also tended to increase stepwise as RA increased, very similar to the change in hardness. The specimen with an RA of 93% showed the highest tensile strength of 192 MPa, 2.8 times higher than that of the specimen before drawing. The electric conductivity did not decrease significantly, even with extreme increases in RA, and remained at an average value of 61.6 %IACS.
{"title":"Changes in Microstructure, Mechanical and Electrical Properties with Progress of Cold Wire-Drawing for AA1070","authors":"Sang-Hyeon Jo, Seong-Hee Lee","doi":"10.3365/kjmm.2023.61.11.867","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.11.867","url":null,"abstract":"Commercial AA1070 alloy for electrical wire is severely deformed by the drawing process when a rod with a diameter of 2 mm is greatly reduced to 0.4 mm by multi-pass. Changes in the microstructure, mechanical properties, and electrical properties of the Al alloy during the wire-drawing process were investigated in detail. The as-drawn Al wires showed a deformation structure in which the grains are greatly elongated in the drawing direction, even though recovery and/or partial recrystallization occurred more actively in the specimens which had more than 84% in reduction of cross-sectional area (<i>R<sub>A</sub></i>). In addition, the fraction of high angle grain boundaries tended to increase with the increase of <i>R<sub>A</sub></i>. For all drawn specimens, the fiber texture of the {110}<111> and {112}<111> components was mainly developed, and their maximum intensity tended to increase with increasing <i>R<sub>A</sub></i>. Recrystallization texture of (001)[100] and (110)[001] began to appear at an <i>R<sub>A</sub></i> higher than 84%. The hardness tended to increase with increasing <i>R<sub>A</sub></i> due to work hardening. In particular, increasing <i>R<sub>A</sub></i> to 84% resulted in a great rise in hardness, accompanied by a distinct non-uniformity in hardness in the thickness direction. However, the average hardness hardly changed at <i>R<sub>A</sub></i> above 84%, even when <i>R<sub>A</sub></i> was increased to 96%. The strength also tended to increase stepwise as <i>R<sub>A</sub></i> increased, very similar to the change in hardness. The specimen with an <i>R<sub>A</sub></i> of 93% showed the highest tensile strength of 192 MPa, 2.8 times higher than that of the specimen before drawing. The electric conductivity did not decrease significantly, even with extreme increases in <i>R<sub>A</sub></i>, and remained at an average value of 61.6 %IACS.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":"14 5","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135723596","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-11-05DOI: 10.3365/kjmm.2023.61.11.815
Hyojoo Lee, Sam Yaw Anaman, Nam-Su Rho, Si-Hyun Sung, Hyun-Min Sung, Sang-Yeob Lee, Hoon-Hwe Cho
The microstructure, tensile and fatigue properties of a martensitic stainless steel (MSS) plate with a thickness of 0.152 mm are investigated in this study. The microstructural properties were initially studied using electron backscatter diffraction microscopy. High dislocation densities were observed in the microstructure, along with the rolling texture revealed by the pole figure, following an initial cold rolling process of the as-received MSS plate. Tensile tests were conducted in both the rolling and transverse directions to compare the strength of the material in both directions. The results showed that the tensile strength was relatively low in the rolling direction. This can be attributed to the microstructure and crystallographic orientation of the material along that direction. Additional tensile tests were performed at various temperatures within the operating temperature range in the rolling direction. The results indicate that the highest tensile strength and elastic modulus are observed at room temperature. A high-cycle fatigue test was performed to determine the fatigue limit of the MSS plate. Furthermore, the microstructure was analyzed by controlling the fatigue cycles within the same stress range. The results revealed a proportional relationship between the accumulated deformation within the grains and the fatigue cycles. This can be helpful in understanding the fatigue damage mechanisms of the MSS plate.
{"title":"A Study on the Microstructure, Tensile and Fatigue Properties of Martensitic Stainless Steel Plate","authors":"Hyojoo Lee, Sam Yaw Anaman, Nam-Su Rho, Si-Hyun Sung, Hyun-Min Sung, Sang-Yeob Lee, Hoon-Hwe Cho","doi":"10.3365/kjmm.2023.61.11.815","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.11.815","url":null,"abstract":"The microstructure, tensile and fatigue properties of a martensitic stainless steel (MSS) plate with a thickness of 0.152 mm are investigated in this study. The microstructural properties were initially studied using electron backscatter diffraction microscopy. High dislocation densities were observed in the microstructure, along with the rolling texture revealed by the pole figure, following an initial cold rolling process of the as-received MSS plate. Tensile tests were conducted in both the rolling and transverse directions to compare the strength of the material in both directions. The results showed that the tensile strength was relatively low in the rolling direction. This can be attributed to the microstructure and crystallographic orientation of the material along that direction. Additional tensile tests were performed at various temperatures within the operating temperature range in the rolling direction. The results indicate that the highest tensile strength and elastic modulus are observed at room temperature. A high-cycle fatigue test was performed to determine the fatigue limit of the MSS plate. Furthermore, the microstructure was analyzed by controlling the fatigue cycles within the same stress range. The results revealed a proportional relationship between the accumulated deformation within the grains and the fatigue cycles. This can be helpful in understanding the fatigue damage mechanisms of the MSS plate.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":"15 4","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135723591","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-11-05DOI: 10.3365/kjmm.2023.61.11.824
Young-Hwan Choi, Joo-Youl Huh, Young-Joon Baik
Cubic boron nitride (cBN) thin films were deposited using DC magnetron sputtering, and the effect of the ion flux on the deposition behavior and residual stress of the cBN thin films was investigated. To increase the ion flux, the magnetic force ratio of the central/peripheral permanent magnets inserted in the magnetron sputtering source was reduced. Due to the complementary relationship between ion flux and energy for cBN deposition, the critical bias voltage required for cBN nucleation decreased as the ion flux increased. The cBN content of the films was relatively higher under the deposition condition of the increased ion flux. This was interpreted to indicate the thinning of the intervening hexagonal boron nitride (hBN) layer formed prior to cBN nucleation. Comparing the compressive residual stress of the cBN films, the residual stress was relieved as the bias voltage decreased regardless of the ion flux. The increase in ion flux made it possible to deposit the cBN films at a low bias voltage, thereby depositing cBN films with lower residual stress. The results showed that reducing ion energy by increasing ion flux for cBN deposition is a promising method for depositing low-stress cBN thin film having thin intervening hBN layer.
{"title":"Effect of Ion Flux Variation in DC Magnetron Sputtering on the Deposition of Cubic Boron Nitride Film","authors":"Young-Hwan Choi, Joo-Youl Huh, Young-Joon Baik","doi":"10.3365/kjmm.2023.61.11.824","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.11.824","url":null,"abstract":"Cubic boron nitride (cBN) thin films were deposited using DC magnetron sputtering, and the effect of the ion flux on the deposition behavior and residual stress of the cBN thin films was investigated. To increase the ion flux, the magnetic force ratio of the central/peripheral permanent magnets inserted in the magnetron sputtering source was reduced. Due to the complementary relationship between ion flux and energy for cBN deposition, the critical bias voltage required for cBN nucleation decreased as the ion flux increased. The cBN content of the films was relatively higher under the deposition condition of the increased ion flux. This was interpreted to indicate the thinning of the intervening hexagonal boron nitride (hBN) layer formed prior to cBN nucleation. Comparing the compressive residual stress of the cBN films, the residual stress was relieved as the bias voltage decreased regardless of the ion flux. The increase in ion flux made it possible to deposit the cBN films at a low bias voltage, thereby depositing cBN films with lower residual stress. The results showed that reducing ion energy by increasing ion flux for cBN deposition is a promising method for depositing low-stress cBN thin film having thin intervening hBN layer.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":"15 2","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135723593","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-11-05DOI: 10.3365/kjmm.2023.61.11.830
Yu Sung Jang, Jin Sung Park, Seung Gab Hong, Sung Jin Kim
This study examined the effects of sulfuric acid concentrations on the corrosion behaviors of three types of commercial steels, conventional carbon steel (SA192), sulfuric acid dew resistant steel (S-TEN), and duplex stainless steel (S32205), considered to be potential materials for the heat recovery steam generator (HRSG) in combined cycle power plants. Based on the results of electrochemical polarization, immersion and wet-dry cycle tests, when exposed to a high sulfuric acid concentration (50%), SA192 and S-TEN exhibited higher corrosion resistance than S32205, which was due to the formation of a stable FeSO4 scale on the carbon steel materials. With prolonged exposure, S-TEN with slightly higher concentrations of Cu and Sb showed lower weight loss than SA192. Conversely, when subjected to low sulfuric acid concentrations (5 and 10%), S32205 exhibited passivation behavior, and showed significantly superior corrosion resistance (i.e., much smaller weight loss) than the other two steel samples. The examination of localized corrosion damages through cross-section observation using a scanning electron microscope revealed also that S32205 suffered less damages from the wet-dry cycling. The long-term superior corrosion resistance of duplex stainless steel in low sulfuric acid concentrations, compared to carbon steel and sulfuric acid due resistant steel, make it a promising candidate material for the HRSG in combined cycle power plants.
{"title":"Comparative Study on the Corrosion Behavior of Materials in Heat Recovery Steam Generators for Combined Cycle Power Plant, Based on Sulfuric Acid Concentrations: Carbon Steels vs. Duplex Stainless Steel (UNS S32205)","authors":"Yu Sung Jang, Jin Sung Park, Seung Gab Hong, Sung Jin Kim","doi":"10.3365/kjmm.2023.61.11.830","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.11.830","url":null,"abstract":"This study examined the effects of sulfuric acid concentrations on the corrosion behaviors of three types of commercial steels, conventional carbon steel (SA192), sulfuric acid dew resistant steel (S-TEN), and duplex stainless steel (S32205), considered to be potential materials for the heat recovery steam generator (HRSG) in combined cycle power plants. Based on the results of electrochemical polarization, immersion and wet-dry cycle tests, when exposed to a high sulfuric acid concentration (50%), SA192 and S-TEN exhibited higher corrosion resistance than S32205, which was due to the formation of a stable FeSO4 scale on the carbon steel materials. With prolonged exposure, S-TEN with slightly higher concentrations of Cu and Sb showed lower weight loss than SA192. Conversely, when subjected to low sulfuric acid concentrations (5 and 10%), S32205 exhibited passivation behavior, and showed significantly superior corrosion resistance (i.e., much smaller weight loss) than the other two steel samples. The examination of localized corrosion damages through cross-section observation using a scanning electron microscope revealed also that S32205 suffered less damages from the wet-dry cycling. The long-term superior corrosion resistance of duplex stainless steel in low sulfuric acid concentrations, compared to carbon steel and sulfuric acid due resistant steel, make it a promising candidate material for the HRSG in combined cycle power plants.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":"14 6","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135723595","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-10-05DOI: 10.3365/kjmm.2023.61.10.760
Jiyoung Park, Hyunji Nam, Qing-Ye Jin, Wookjin Lee
In this study, AISI 316L stainless steels were manufactured by the L-DED process with various laser scanning speeds and laser powers, in order to analyze how volumetric energy density (VED) can affect their final shape, microstructure and mechanical properties. Under various VED conditions, it was found that a higher VED decreases the formation of lack of fusion when the powder feed rate is adequate, and the ratio of VED and powder feed rate affect the dimensional accuracy. Furthermore, the microstructure and mechanical properties of the L-DED processed AISI 316L were not significantly influenced by the laser scanning speed when the same VED was used, indicating that the solidification rate and solidification cell size are mainly determined by the VED.
{"title":"Effects of Process Parameters on the Dimensions and Mechanical Properties of L-DED AISI 316L Stainless Steel","authors":"Jiyoung Park, Hyunji Nam, Qing-Ye Jin, Wookjin Lee","doi":"10.3365/kjmm.2023.61.10.760","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.10.760","url":null,"abstract":"In this study, AISI 316L stainless steels were manufactured by the L-DED process with various laser scanning speeds and laser powers, in order to analyze how volumetric energy density (VED) can affect their final shape, microstructure and mechanical properties. Under various VED conditions, it was found that a higher VED decreases the formation of lack of fusion when the powder feed rate is adequate, and the ratio of VED and powder feed rate affect the dimensional accuracy. Furthermore, the microstructure and mechanical properties of the L-DED processed AISI 316L were not significantly influenced by the laser scanning speed when the same VED was used, indicating that the solidification rate and solidification cell size are mainly determined by the VED.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":"95 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134947450","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-10-05DOI: 10.3365/kjmm.2023.61.10.772
Hyunji Nam, Qing-Ye Jin, Jiyoung Park, Wookjin Lee
This study aimed to investigate the effect of process parameters on the microstructure and mechanical properties of Inconel 625 alloy manufactured by direct energy deposition process. The Inconel 625 samples were produced by varying the laser scanning speeds from 720 - 960 mm/min while maintaining the same the laser energy volume density. The microstructure and mechanical properties of the produced samples were evaluated, and their dimensional accuracy and mechanical properties were also analyzed in terms of the laser scanning strategy. Microstructural observations at the same energy density revealed a dendrite substructure near the laser melt pool boundaries, indicating that the dendritic microstructure was primarily formed at the beginning of the solidification of each laser bead. When the solidification further progressed into the melt pool, solidification cell substructures became dominant regardless of the laser scanning speed. The size of the solidification cell and the dendrite structure were nearly unchanged as laser scanning speed increased. This suggests that changing the laser scanning speed while maintaining the volumetric energy density does not significantly alter the solidification rates of the Inconel 625. As a consequence of the similar cell sizes, the samples produced with different laser scanning speed led to similar mechanical properties. When samples produced with two different scanning strategies, of unidirectional and 90o rotation, were compared, a better dimensional accuracy was obtained with the 90o rotation strategy, compared to that obtained with the unidirectional approach. Comparisons of mechanical properties obtained along different directions with the different laser scanning strategies revealed that the Inconel 625 produced by the laser direct energy deposition had pronounced anisotropic mechanical properties, and was the highest in strength but the lowest in maximum elongation along the laser scanning direction.
{"title":"Effect of Process Parameter and Scanning Strategy on the Microstructure and Mechanical Properties of Inconel 625 Superalloy Manufactured by Laser Direct Energy Deposition","authors":"Hyunji Nam, Qing-Ye Jin, Jiyoung Park, Wookjin Lee","doi":"10.3365/kjmm.2023.61.10.772","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.10.772","url":null,"abstract":"This study aimed to investigate the effect of process parameters on the microstructure and mechanical properties of Inconel 625 alloy manufactured by direct energy deposition process. The Inconel 625 samples were produced by varying the laser scanning speeds from 720 - 960 mm/min while maintaining the same the laser energy volume density. The microstructure and mechanical properties of the produced samples were evaluated, and their dimensional accuracy and mechanical properties were also analyzed in terms of the laser scanning strategy. Microstructural observations at the same energy density revealed a dendrite substructure near the laser melt pool boundaries, indicating that the dendritic microstructure was primarily formed at the beginning of the solidification of each laser bead. When the solidification further progressed into the melt pool, solidification cell substructures became dominant regardless of the laser scanning speed. The size of the solidification cell and the dendrite structure were nearly unchanged as laser scanning speed increased. This suggests that changing the laser scanning speed while maintaining the volumetric energy density does not significantly alter the solidification rates of the Inconel 625. As a consequence of the similar cell sizes, the samples produced with different laser scanning speed led to similar mechanical properties. When samples produced with two different scanning strategies, of unidirectional and 90o rotation, were compared, a better dimensional accuracy was obtained with the 90o rotation strategy, compared to that obtained with the unidirectional approach. Comparisons of mechanical properties obtained along different directions with the different laser scanning strategies revealed that the Inconel 625 produced by the laser direct energy deposition had pronounced anisotropic mechanical properties, and was the highest in strength but the lowest in maximum elongation along the laser scanning direction.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134947446","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-10-05DOI: 10.3365/kjmm.2023.61.10.793
Jongchan Yoo, Dong-Young Kim, Dong-Kwan Lee, Kunwoo Nam, Sung-Hoon Park
Polymer composites enriched with conductive fillers hold immense potential for flexible pressure sensors, because of the remarkable piezoresistive effect they possess. Research on polymer composite pressure sensors has been actively ongoing because of their flexibility and high electrical resistance performance. This paper presents a comprehensive comparison of the piezoresistive characteristics of conductive composites for pressure sensors, focusing on the influence of carbon nanotube (CNT) content and aspect ratio. Polymer composites with conductive fillers, specifically CNTs, have demonstrated significant potential for pressure sensing applications based on the piezoresistive effect. By systematically varying the CNT concentration and aspect ratio, we investigated the impact of these parameters on the piezoresistive behavior of the composites. A pressure in the range of 0-200 kPa was applied to the conductive composite, and resistance change due to pressing was measured. The best performing samples were evaluated in 150 cycle tests to verify repeatability and durability. Experimental analysis and characterization revealed the intricate relationship between CNT content, aspect ratio, and the resulting piezoresistive properties. Through this study, we aim to enhance understanding of how CNT concentration and aspect ratio influence the performance of CNT/PDMS composites as pressure sensors, thereby facilitating the development of optimized sensing materials for various pressure sensing applications.
{"title":"Piezoresistive Characteristics of Carbon Nanotube Polymer Composites with Different Filler Content and Aspect Ratio for Pressure Sensors","authors":"Jongchan Yoo, Dong-Young Kim, Dong-Kwan Lee, Kunwoo Nam, Sung-Hoon Park","doi":"10.3365/kjmm.2023.61.10.793","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.10.793","url":null,"abstract":"Polymer composites enriched with conductive fillers hold immense potential for flexible pressure sensors, because of the remarkable piezoresistive effect they possess. Research on polymer composite pressure sensors has been actively ongoing because of their flexibility and high electrical resistance performance. This paper presents a comprehensive comparison of the piezoresistive characteristics of conductive composites for pressure sensors, focusing on the influence of carbon nanotube (CNT) content and aspect ratio. Polymer composites with conductive fillers, specifically CNTs, have demonstrated significant potential for pressure sensing applications based on the piezoresistive effect. By systematically varying the CNT concentration and aspect ratio, we investigated the impact of these parameters on the piezoresistive behavior of the composites. A pressure in the range of 0-200 kPa was applied to the conductive composite, and resistance change due to pressing was measured. The best performing samples were evaluated in 150 cycle tests to verify repeatability and durability. Experimental analysis and characterization revealed the intricate relationship between CNT content, aspect ratio, and the resulting piezoresistive properties. Through this study, we aim to enhance understanding of how CNT concentration and aspect ratio influence the performance of CNT/PDMS composites as pressure sensors, thereby facilitating the development of optimized sensing materials for various pressure sensing applications.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":"64 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134947444","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-10-05DOI: 10.3365/kjmm.2023.61.10.729
Seokmin Hong, Cho-Long Lee, Bong-Sang Lee, Hong-Deok Kim, Min-Chul Kim
To analyze the effects of intercritical heat treatment on the temper embrittlement of SA508 Gr.4N steels, two model alloys with different phosphorus (P) contents were fabricated. Each sample was heat treated by applying a conventional heat treatment process (quenching-tempering) with/without an intercritical heat treatment process (IHT) and a step-cooling heat treatment for temper embrittlement. Then their microstructure and mechanical properties were evaluated. The microstructure of the SA508 Gr.4N model alloy was composed of tempered lower bainite and martensite, and nano-sized precipitates formed both inside and at boundaries. The grain size was reduced when IHT was applied. There was a small difference in tensile properties according to the heat-treatment conditions and P contents, but the difference in Charpy impact properties was large. The heat treatment for temper embrittlement (TE) increased the impact transition temperature, and a very significant increase was observed in steels with a high P content. The increase in transition temperature owing to TE was reduced when IHT was applied. The fractograph analysis of Charpy fractured specimens at transition temperatures showed that an increase in intergranular fracture was main reason for the TE, and that IHT reduced the formation of intergranular fracture. The AES results showed that P-Ni was segregated at grain boundaries, and the level of segregation was reduced by applying IHT. This occurred because the formation of prior austenite grain boundaries by IHT dispersed the P at grain boundaries, and reduced the amount of P segregation.
{"title":"Effects of Intercritical Heat Treatment on the Temper Embrittlement of SA508 Gr.4N Ni-Cr-Mo High Strength Low Alloy Steels for Reactor Pressure Vessels","authors":"Seokmin Hong, Cho-Long Lee, Bong-Sang Lee, Hong-Deok Kim, Min-Chul Kim","doi":"10.3365/kjmm.2023.61.10.729","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.10.729","url":null,"abstract":"To analyze the effects of intercritical heat treatment on the temper embrittlement of SA508 Gr.4N steels, two model alloys with different phosphorus (P) contents were fabricated. Each sample was heat treated by applying a conventional heat treatment process (quenching-tempering) with/without an intercritical heat treatment process (IHT) and a step-cooling heat treatment for temper embrittlement. Then their microstructure and mechanical properties were evaluated. The microstructure of the SA508 Gr.4N model alloy was composed of tempered lower bainite and martensite, and nano-sized precipitates formed both inside and at boundaries. The grain size was reduced when IHT was applied. There was a small difference in tensile properties according to the heat-treatment conditions and P contents, but the difference in Charpy impact properties was large. The heat treatment for temper embrittlement (TE) increased the impact transition temperature, and a very significant increase was observed in steels with a high P content. The increase in transition temperature owing to TE was reduced when IHT was applied. The fractograph analysis of Charpy fractured specimens at transition temperatures showed that an increase in intergranular fracture was main reason for the TE, and that IHT reduced the formation of intergranular fracture. The AES results showed that P-Ni was segregated at grain boundaries, and the level of segregation was reduced by applying IHT. This occurred because the formation of prior austenite grain boundaries by IHT dispersed the P at grain boundaries, and reduced the amount of P segregation.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":"53 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134947448","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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