Pub Date : 2024-06-05DOI: 10.3365/kjmm.2024.62.6.429
Ki-Seong Park, Lalit Kaushik, Hyo-Sang Yoo, Jae-Yeol Jeon, Shi-Hoon Choi
In this study, we investigated the influence of cold rolling reduction on microstructural evolution and slip behavior in Ta-10W alloy fabricated by vacuum arc melting (VAM). As the reduction increased, both single and multiple slips were observed within some grain interiors. At reductions of 20% and 40%, deformation bands, primarily consisting of γ-fiber components, formed within the grain interiors. The fraction of deformation bands (DBs) increased with higher reduction. Conversely, at 60% reduction, in addition to DBs, experimentally observed shear bands (SBs) with a herringbone pattern were formed. Both DBs and SBs predominantly formed in regions of concentrated strain (areas with high kernel average misorientation (KAM) and geometrically necessary dislocations (GND)). As the reduction increased, the misorientation angle between the matrix and the DBs or SBs gradually increased, while the width of the DBs decreased. To investigate the violation of Schmid’s law in Ta-10W alloy, slip trace and resolved shear stress (RSS) analyses were performed on observed slip lines within deformed grains. Contrary to conventional slips, where slip typically occurs on the plane with the highest RSS, slips in the Ta-10W alloy were confirmed to occur even on planes with lower RSS in certain grains. Hence, this study provides experimental evidence of Schmid’s law violation in Ta-10W alloy.
{"title":"The Effect of Rolling Reduction on the Microstructure Evolution and Slip Behavior of Ta-10W Alloy during Cold Rolling Process","authors":"Ki-Seong Park, Lalit Kaushik, Hyo-Sang Yoo, Jae-Yeol Jeon, Shi-Hoon Choi","doi":"10.3365/kjmm.2024.62.6.429","DOIUrl":"https://doi.org/10.3365/kjmm.2024.62.6.429","url":null,"abstract":"In this study, we investigated the influence of cold rolling reduction on microstructural evolution and slip behavior in Ta-10W alloy fabricated by vacuum arc melting (VAM). As the reduction increased, both single and multiple slips were observed within some grain interiors. At reductions of 20% and 40%, deformation bands, primarily consisting of γ-fiber components, formed within the grain interiors. The fraction of deformation bands (DBs) increased with higher reduction. Conversely, at 60% reduction, in addition to DBs, experimentally observed shear bands (SBs) with a herringbone pattern were formed. Both DBs and SBs predominantly formed in regions of concentrated strain (areas with high kernel average misorientation (KAM) and geometrically necessary dislocations (GND)). As the reduction increased, the misorientation angle between the matrix and the DBs or SBs gradually increased, while the width of the DBs decreased. To investigate the violation of Schmid’s law in Ta-10W alloy, slip trace and resolved shear stress (RSS) analyses were performed on observed slip lines within deformed grains. Contrary to conventional slips, where slip typically occurs on the plane with the highest RSS, slips in the Ta-10W alloy were confirmed to occur even on planes with lower RSS in certain grains. Hence, this study provides experimental evidence of Schmid’s law violation in Ta-10W alloy.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2024-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141265649","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 : 2024-06-05DOI: 10.3365/kjmm.2024.62.6.419
Jae Gyeong Kim, Chung-Soo Kim, Suk-Hee Park, Jeonghong Ha
Focused ion beam (FIB) technology is one of the most widely used methods for fabricating crosssectional analysis specimens because of its high precision and characteristics that minimize the occurrence of defects. Demand for large cross-sectional area analysis is increasing to improve product reliability in various industries, but is limited by the low milling speed of FIB. Other potential techniques such as Ar ion milling and plasma FIB have been adopted, but low milling speed for large areas still remains a problem. A promising solution to this issue involves laser machining prior to FIB milling. In laser machining a laser beam is irradiated to remove materials from the target. This technique can provide several orders of magnitude higher material removal rate than FIB, however, tapering of the machined surface and laser induced damage can occur. Removing these defects leads to increased FIB milling time. In this study, the laser parameters including angle of incident (AOI) were optimized to achieve a vertical like sidewall and minimize laser induced defects. Before applying AOI, laser machining parameters were optimized to reduce the angle of the machined sidewall. The taper angle of 2.5° was fabricated using the optimized parameters and application of AOI. Raman spectroscopy, SEM, and EDS analysis were used to measure not only the geometry of the laser machined sidewalls, but laser induced residual stress and defects. These results were then used to calculate the volume of FIB milling required to remove the laser induced damages and achieve vertical sidewalls. The application of AOI can significantly reduce the processing time in the FIB milling compared to the processing time when AOI is not applied.
{"title":"Effect of Angle of Incident on Taper Angle in Femtosecond Laser Machining for Fabrication of Cross Section Analysis Specimen","authors":"Jae Gyeong Kim, Chung-Soo Kim, Suk-Hee Park, Jeonghong Ha","doi":"10.3365/kjmm.2024.62.6.419","DOIUrl":"https://doi.org/10.3365/kjmm.2024.62.6.419","url":null,"abstract":"Focused ion beam (FIB) technology is one of the most widely used methods for fabricating crosssectional analysis specimens because of its high precision and characteristics that minimize the occurrence of defects. Demand for large cross-sectional area analysis is increasing to improve product reliability in various industries, but is limited by the low milling speed of FIB. Other potential techniques such as Ar ion milling and plasma FIB have been adopted, but low milling speed for large areas still remains a problem. A promising solution to this issue involves laser machining prior to FIB milling. In laser machining a laser beam is irradiated to remove materials from the target. This technique can provide several orders of magnitude higher material removal rate than FIB, however, tapering of the machined surface and laser induced damage can occur. Removing these defects leads to increased FIB milling time. In this study, the laser parameters including angle of incident (AOI) were optimized to achieve a vertical like sidewall and minimize laser induced defects. Before applying AOI, laser machining parameters were optimized to reduce the angle of the machined sidewall. The taper angle of 2.5° was fabricated using the optimized parameters and application of AOI. Raman spectroscopy, SEM, and EDS analysis were used to measure not only the geometry of the laser machined sidewalls, but laser induced residual stress and defects. These results were then used to calculate the volume of FIB milling required to remove the laser induced damages and achieve vertical sidewalls. The application of AOI can significantly reduce the processing time in the FIB milling compared to the processing time when AOI is not applied.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2024-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141384230","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 : 2024-06-05DOI: 10.3365/kjmm.2024.62.6.480
Dong Hwi Kim, Sang Yun, Il-Ho Kim
In this study, thermoelectric chalcostibite (CuSbS2) compounds were fabricated using mechanical alloying (MA) and hot pressing (HP), and phase identification, microstructural observation, and thermal analysis were conducted. The thermal properties were then measured and compared with those of other Cu–Sb–S ternary compounds synthesized by the same solid-state process, namely, skinnerite (Cu3SbS3), famatinite (Cu3SbS4), and tetrahedrite (Cu12Sb4S13). Both the MA powder and HP-sintered samples contained a single-phase chalcostibite with an orthorhombic structure, and relative densities of 94.6–99.7% were obtained based on HP temperature. The full width at half maximum of the X-ray diffraction peak was significantly reduced for the HP specimens compared to that of the MA powder due to stress relaxation and grain growth during HP at elevated temperatures. However, practically no changes were observed in the lattice constants based on HP temperature. Differential scanning calorimetric analysis revealed that one endothermic reaction occurred at 814–815 K for the MA powder and at 818–821 K for the HP specimen, which were interpreted as the melting points of chalcostibite. Densely sintered compacts with densities close to the theoretical density were obtained using HP at temperatures of 623 K or higher. The constituent elements of the chalcostibites were uniformly distributed. As the HP temperature increased, thermal diffusivity and conductivity increased, but they decreased significantly as the measurement temperature increased. For the chalcostibite specimen hot-pressed at 623 K, the thermal diffusivity and conductivity were (0.75–0.36) × 10-2 cm2 s-1 and 1.47–0.72 W m-1 K-1 at 323–623 K, respectively. Compared with other Cu–Sb–S ternary compounds, the thermal diffusivity was higher at low temperatures but similar at high temperatures, and the thermal conductivity above 500 K was lower than 1 W m-1 K-1.
本研究采用机械合金化（MA）和热压（HP）工艺制备了热电霞石（CuSbS2）化合物，并进行了相鉴定、微观结构观察和热分析。然后测量了这些化合物的热性能，并与采用相同固态工艺合成的其他铜-锑-锑三元化合物（即矽卡岩（Cu3SbS3）、法曼石（Cu3SbS4）和四面体（Cu12Sb4S13））的热性能进行了比较。MA粉末和HP烧结样品中都含有具有正方体结构的单相菱锰矿，根据HP温度可获得94.6-99.7%的相对密度。与 MA 粉末相比，HP 试样的 X 射线衍射峰的半最大全宽明显减小，这是由于在高温下进行 HP 时发生了应力松弛和晶粒生长。然而，根据 HP 温度，晶格常数几乎没有变化。差示扫描量热分析表明，MA粉末在814-815 K和HP试样在818-821 K发生了一个内热反应，这两个温度点被解释为钙钛矿的熔点。使用 HP 在 623 K 或更高温度下获得了密度接近理论密度的致密烧结压实物。钙钛矿的组成元素分布均匀。随着 HP 温度的升高，热扩散率和电导率也随之升高，但随着测量温度的升高，热扩散率和电导率显著降低。对于在 623 K 下热压的霞石试样，在 323-623 K 下的热扩散率和电导率分别为 (0.75-0.36) × 10-2 cm2 s-1 和 1.47-0.72 W m-1 K-1。与其他铜-锑-锑三元化合物相比，低温下的热扩散率较高，但高温下的热扩散率相近，500 K 以上的热导率低于 1 W m-1 K-1。
{"title":"Thermoelectric Chalcostibite: Solid-State Synthesis and Thermal Properties","authors":"Dong Hwi Kim, Sang Yun, Il-Ho Kim","doi":"10.3365/kjmm.2024.62.6.480","DOIUrl":"https://doi.org/10.3365/kjmm.2024.62.6.480","url":null,"abstract":"In this study, thermoelectric chalcostibite (CuSbS2) compounds were fabricated using mechanical alloying (MA) and hot pressing (HP), and phase identification, microstructural observation, and thermal analysis were conducted. The thermal properties were then measured and compared with those of other Cu–Sb–S ternary compounds synthesized by the same solid-state process, namely, skinnerite (Cu3SbS3), famatinite (Cu3SbS4), and tetrahedrite (Cu12Sb4S13). Both the MA powder and HP-sintered samples contained a single-phase chalcostibite with an orthorhombic structure, and relative densities of 94.6–99.7% were obtained based on HP temperature. The full width at half maximum of the X-ray diffraction peak was significantly reduced for the HP specimens compared to that of the MA powder due to stress relaxation and grain growth during HP at elevated temperatures. However, practically no changes were observed in the lattice constants based on HP temperature. Differential scanning calorimetric analysis revealed that one endothermic reaction occurred at 814–815 K for the MA powder and at 818–821 K for the HP specimen, which were interpreted as the melting points of chalcostibite. Densely sintered compacts with densities close to the theoretical density were obtained using HP at temperatures of 623 K or higher. The constituent elements of the chalcostibites were uniformly distributed. As the HP temperature increased, thermal diffusivity and conductivity increased, but they decreased significantly as the measurement temperature increased. For the chalcostibite specimen hot-pressed at 623 K, the thermal diffusivity and conductivity were (0.75–0.36) × 10-2 cm2 s-1 and 1.47–0.72 W m-1 K-1 at 323–623 K, respectively. Compared with other Cu–Sb–S ternary compounds, the thermal diffusivity was higher at low temperatures but similar at high temperatures, and the thermal conductivity above 500 K was lower than 1 W m-1 K-1.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2024-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141265506","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 : 2024-06-05DOI: 10.3365/kjmm.2024.62.6.487
Minkyu Lee, Seong-Mee Hwang, Se Jun Kim, Won-Seon Seo, Sang-Il Kim, Hyun-Sik Kim
Cu3SbSe4 is considered a promising thermoelectric material because of its large effective mass and low thermal conductivity, originating from its unique lattice structure. However, Cu3SbSe4 has intrinsically low carrier concentration and relatively high electric resistance which limit performance. Recently, a zT improvement in Cu3SbSe4 was reported where doping/precipitation is controlled by changing the content of the starting materials. However, the effect of these changes in starting content on electronic band structures has not been studied. Here, we investigate how the change in starting materials content (x varying from 6 to 20) affects band parameters like density-of-states effective mass (md *), non-degenerate mobility (μ0), weighted mobility (μW), and B-factor using the Single Parabolic Band (SPB) model. For x greater than 8, precipitation of the secondary phase (CuSe) was observed, and the band parameters changed differently for x greater than 8. The md * increases up to x = 8 and then rapidly decreases for x > 8. For μ0, an overall decrease is observed for increasing x, but the rate of decrease is suppressed for x > 8. The μW reaches the maximum at x = 8. As x increases, the experimental lattice thermal conductivity also increases, especially for x > 8. Therefore, the B-factor, which is directly related to the theoretical maximum zT, becomes maximum at = 8. Hence the SPB model predicts a maximum zT of 0.0484 for x = 8 at 300 K, which is 15.5% higher than the experimental zT of 0.0419, which can be achieved by tuning the Hall carrier concentration to 4.44 × 1019 cm-3.
Cu3SbSe4 因其独特的晶格结构而具有较大的有效质量和较低的热导率，因此被认为是一种前景广阔的热电材料。然而，Cu3SbSe4 固有的低载流子浓度和相对较高的电阻限制了其性能。最近有报道称，通过改变起始材料的含量来控制掺杂/沉淀，Cu3SbSe4 的 zT 得到了改善。然而，这些起始材料含量的变化对电子能带结构的影响尚未得到研究。在此，我们利用单抛物线带（SPB）模型研究了起始材料含量的变化（x 从 6 到 20 不等）如何影响带参数，如态密度有效质量（md *）、非退化迁移率（μ0）、加权迁移率（μW）和 B 因子。当 x 大于 8 时，观察到第二相（CuSe）析出，并且当 x 大于 8 时，带参数发生了不同的变化。 md * 在 x = 8 之前增加，然后在 x > 8 时迅速减小。就 μ0 而言，随着 x 的增大，观察到整体下降，但当 x > 8 时，下降速度被抑制。随着 x 的增大，实验晶格热导率也随之增大，尤其是 x > 8 时。因此，SPB 模型预测 x = 8 在 300 K 时的最大 zT 为 0.0484，比实验 zT 0.0419 高出 15.5%。
{"title":"Estimation of Maximum zT in Cu3SbSe4 for Different Starting Materials Content","authors":"Minkyu Lee, Seong-Mee Hwang, Se Jun Kim, Won-Seon Seo, Sang-Il Kim, Hyun-Sik Kim","doi":"10.3365/kjmm.2024.62.6.487","DOIUrl":"https://doi.org/10.3365/kjmm.2024.62.6.487","url":null,"abstract":"Cu3SbSe4 is considered a promising thermoelectric material because of its large effective mass and low thermal conductivity, originating from its unique lattice structure. However, Cu3SbSe4 has intrinsically low carrier concentration and relatively high electric resistance which limit performance. Recently, a zT improvement in Cu3SbSe4 was reported where doping/precipitation is controlled by changing the content of the starting materials. However, the effect of these changes in starting content on electronic band structures has not been studied. Here, we investigate how the change in starting materials content (x varying from 6 to 20) affects band parameters like density-of-states effective mass (md *), non-degenerate mobility (μ0), weighted mobility (μW), and B-factor using the Single Parabolic Band (SPB) model. For x greater than 8, precipitation of the secondary phase (CuSe) was observed, and the band parameters changed differently for x greater than 8. The md * increases up to x = 8 and then rapidly decreases for x > 8. For μ0, an overall decrease is observed for increasing x, but the rate of decrease is suppressed for x > 8. The μW reaches the maximum at x = 8. As x increases, the experimental lattice thermal conductivity also increases, especially for x > 8. Therefore, the B-factor, which is directly related to the theoretical maximum zT, becomes maximum at = 8. Hence the SPB model predicts a maximum zT of 0.0484 for x = 8 at 300 K, which is 15.5% higher than the experimental zT of 0.0419, which can be achieved by tuning the Hall carrier concentration to 4.44 × 1019 cm-3.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2024-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141265329","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 : 2024-06-05DOI: 10.3365/kjmm.2024.62.6.411
Min-hyeok Yang, Bum-Soon Park, H. Moon, Jae-Cheol Park, Hyun-kuk Park
The use of heat dissipation materials in various field such as power semiconductor device, LED and microelectronic system. Therefore, there is a need for heat dissipation materials using copper (Cu) and graphite (Gr). These materials have high thermal conductivity. In particular, graphite has high thermal stability with a low coefficient of thermal expansion. This study was conducted to enhance the thermal properties of Cu for use in heat dissipation materials, using a spark plasma sintering method. Cu-Gr powders were mixed by a shaking mixer and fabricated with volume fractions of 7:3, 6:4, 5:5, 4:6 and 3:7. The spark plasma sintering method is a uniaxial pressurization process, which can control the direction of Gr. The Cu-Gr powders were sintered at a temperature of 850 oC at a heating rate of 30 oC/min and a sintering pressure of 40MPa. Consequently, as the Gr contents were increased, the relative densities of the Cu-Gr composites decreased from 99.25 to 94.85%. Gr has high resistance to high-temperature deformation, which contributed to a decrease in shrinkage and relative density. The highest thermal conductivity was measured at 539.7 W/ m·K for a Cu-Gr volume ratio of 5:5. The thermal conductivity of the directionally controlled Gr was measured to be about 20-30 W/m·K higher than the uncontrolled sample. Furthermore, the TDP (Thermal distortion parameter), for which a lower value indicates better thermal stability, was systematically investigated.
{"title":"Sintering Behavior and Thermal Properties of Cu-Graphite Materials by a Spark Plasma Sintering Method","authors":"Min-hyeok Yang, Bum-Soon Park, H. Moon, Jae-Cheol Park, Hyun-kuk Park","doi":"10.3365/kjmm.2024.62.6.411","DOIUrl":"https://doi.org/10.3365/kjmm.2024.62.6.411","url":null,"abstract":"The use of heat dissipation materials in various field such as power semiconductor device, LED and microelectronic system. Therefore, there is a need for heat dissipation materials using copper (Cu) and graphite (Gr). These materials have high thermal conductivity. In particular, graphite has high thermal stability with a low coefficient of thermal expansion. This study was conducted to enhance the thermal properties of Cu for use in heat dissipation materials, using a spark plasma sintering method. Cu-Gr powders were mixed by a shaking mixer and fabricated with volume fractions of 7:3, 6:4, 5:5, 4:6 and 3:7. The spark plasma sintering method is a uniaxial pressurization process, which can control the direction of Gr. The Cu-Gr powders were sintered at a temperature of 850 oC at a heating rate of 30 oC/min and a sintering pressure of 40MPa. Consequently, as the Gr contents were increased, the relative densities of the Cu-Gr composites decreased from 99.25 to 94.85%. Gr has high resistance to high-temperature deformation, which contributed to a decrease in shrinkage and relative density. The highest thermal conductivity was measured at 539.7 W/ m·K for a Cu-Gr volume ratio of 5:5. The thermal conductivity of the directionally controlled Gr was measured to be about 20-30 W/m·K higher than the uncontrolled sample. Furthermore, the TDP (Thermal distortion parameter), for which a lower value indicates better thermal stability, was systematically investigated.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2024-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141265623","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 : 2024-06-05DOI: 10.3365/kjmm.2024.62.6.464
Seung-Taek Jo, Jin Wook Shin, Walter Commerell, Dae-Hwang Yoo, Hyesun Yoo, Jinyoung Hwang, Hyun-Sik Kim, Sang-Il Kim, Jong-Wook Roh
It is well-known that optical transparence and electric resistance have a trade-off relationship in transparent electrodes. For this reason, developing methods to predict this relation have been important in various fields of academic research as well as for industrial applications. Herein, we suggest a simple method which reveals the relationship between optical transparence and electric resistance using MATLAB, based on the geometric characteristics of a random metal network. Ag metal-mesh transparent electrodes were fabricated with various conditions using colloidal silica cracked-templates and a Radio Frequency (RF) sputtering system. MATLAB software was used to analyze structural images of the Ag mesh network, automatically quantifying the density and width of the Ag meshes. From these data, the transparency and sheet resistance values of the Ag mesh electrodes were predicted and compared with measured values. Regarding transparency, the introduction of fitting parameters revealed minimal differences between the experimental and predicted values obtained from the structure images. Although the predicted sheet resistance was slightly different than the real measured values due to atomic defects or imperfections in the crystals of the Ag-mesh network, it was possible to observe a similar trend between the measured and predicted sheet resistances with changes in the fractional coverage area of the Ag-mesh network.
{"title":"Characterization of Transparent Electrodes with Ag Metal-mesh using MATLAB","authors":"Seung-Taek Jo, Jin Wook Shin, Walter Commerell, Dae-Hwang Yoo, Hyesun Yoo, Jinyoung Hwang, Hyun-Sik Kim, Sang-Il Kim, Jong-Wook Roh","doi":"10.3365/kjmm.2024.62.6.464","DOIUrl":"https://doi.org/10.3365/kjmm.2024.62.6.464","url":null,"abstract":"It is well-known that optical transparence and electric resistance have a trade-off relationship in transparent electrodes. For this reason, developing methods to predict this relation have been important in various fields of academic research as well as for industrial applications. Herein, we suggest a simple method which reveals the relationship between optical transparence and electric resistance using MATLAB, based on the geometric characteristics of a random metal network. Ag metal-mesh transparent electrodes were fabricated with various conditions using colloidal silica cracked-templates and a Radio Frequency (RF) sputtering system. MATLAB software was used to analyze structural images of the Ag mesh network, automatically quantifying the density and width of the Ag meshes. From these data, the transparency and sheet resistance values of the Ag mesh electrodes were predicted and compared with measured values. Regarding transparency, the introduction of fitting parameters revealed minimal differences between the experimental and predicted values obtained from the structure images. Although the predicted sheet resistance was slightly different than the real measured values due to atomic defects or imperfections in the crystals of the Ag-mesh network, it was possible to observe a similar trend between the measured and predicted sheet resistances with changes in the fractional coverage area of the Ag-mesh network.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2024-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141265353","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 : 2024-06-05DOI: 10.3365/kjmm.2024.62.6.445
Byung-Hoon Kim, Byeong-Ook Kong, Yun-Kon Joo, Young-Kyu Ju, Hyun-Uk Hong, Je-Hyun Lee
The strength of Ni-base superalloys mainly depends on the γ' precipitates that improve the strength of the materials at high temperatures. The presence of γ' particles within the matrix restricts dislocation movement, and optimized heat treatments can tailor the size, shape, and volume fraction of γ'. In this study the effects of solidification rate and solution temperature on the tensile properties of IN738LC superalloy were investigated. The secondary dendritic arm spacing of casting materials with different diameters was measured and the solidification rate of the casting materials was derived by comparing the results of the solidification microstructure obtained from a directional solidification experiment. The D17 material, which had a faster solidification rate, showed higher values of tensile strength and yield strength than the D60 material, which had a slower solidification rate. The study also concluded that the monomodal γ' precipitates in the S80 material have higher tensile strength and yield strength at room temperature and 760℃ than the bimodal γ' precipitates in the S20 material. As for the deformation behavior at 760℃, an isolated stacking fault was observed in the S20 material only within the large γ’ precipitates. In the S80 material, the high dislocation density increased the yield strength due to the strong interaction between dislocations and fine γ’ precipitates.
{"title":"Microstructure and Tensile Properties of Ni-Base Superalloy IN738LC according to Solidification Rate and Heat Treatment","authors":"Byung-Hoon Kim, Byeong-Ook Kong, Yun-Kon Joo, Young-Kyu Ju, Hyun-Uk Hong, Je-Hyun Lee","doi":"10.3365/kjmm.2024.62.6.445","DOIUrl":"https://doi.org/10.3365/kjmm.2024.62.6.445","url":null,"abstract":"The strength of Ni-base superalloys mainly depends on the γ' precipitates that improve the strength of the materials at high temperatures. The presence of γ' particles within the matrix restricts dislocation movement, and optimized heat treatments can tailor the size, shape, and volume fraction of γ'. In this study the effects of solidification rate and solution temperature on the tensile properties of IN738LC superalloy were investigated. The secondary dendritic arm spacing of casting materials with different diameters was measured and the solidification rate of the casting materials was derived by comparing the results of the solidification microstructure obtained from a directional solidification experiment. The D17 material, which had a faster solidification rate, showed higher values of tensile strength and yield strength than the D60 material, which had a slower solidification rate. The study also concluded that the monomodal γ' precipitates in the S80 material have higher tensile strength and yield strength at room temperature and 760℃ than the bimodal γ' precipitates in the S20 material. As for the deformation behavior at 760℃, an isolated stacking fault was observed in the S20 material only within the large γ’ precipitates. In the S80 material, the high dislocation density increased the yield strength due to the strong interaction between dislocations and fine γ’ precipitates.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2024-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141265517","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 : 2024-06-05DOI: 10.3365/kjmm.2024.62.6.472
Shin-Woo Myeong, Song Jin, Chi-Kwan Kim, Jooyoung Lee, Yangdo Kim, Mook Choi
To achieve net zero emissions, green hydrogen should be produced via water electrolysis with renewable energy. To develop efficient anion exchange membrane water electrolyzers (AEMWE), the development of efficient and stable non-precious metal electrocatalysts for the oxygen evolution reaction (OER) is essential. In this study, a high-performance ternary NiFeCo-layer double hydroxide (LDH) electrocatalyst for AEMWE was easily developed by the co-precipitation method. The introduction of Co has been shown to have an effect on the electronic structure of Ni and Fe, improving their intrinsic OER properties. In addition, the three-dimensional flower-like nanosheet morphology improved mass transfer and achieved excellent current density at high voltages. The ternary NiFeCo-LDH electrocatalyst requires low overpotentials (253 mV at 10 mA cm-2) and Tafel slope (45 mV dec-1) in 1 M KOH. AEMWE using the ternary NiFeCo-LDH electrocatalyst showed excellent electrolysis performance with a high current density of 2.27 A cm-2 at 1.8 V cell. Moreover, an energy conversion efficiency of 86.73 % was achieved during the durability test for 100 hours at a current density of 0.5 A cm-2. The performance of the AEMWE electrolyzer utilizing the ternary NiFeCo-LDH electrocatalyst surpassed that of previously reported AEMWE electrolyzers. This work reports a highly active OER electrocatalyst that could open numerous opportunities for the development of ternary LDH electrocatalysts in AEMWE.
为实现净零排放，应利用可再生能源通过电解水生产绿色氢气。要开发高效的阴离子交换膜水电解槽（AEMWE），开发高效稳定的非贵金属氧进化反应（OER）电催化剂至关重要。在本研究中，通过共沉淀法轻松开发出了用于 AEMWE 的高性能三元镍铁钴层双氢氧化物（LDH）电催化剂。研究表明，Co 的引入会对 Ni 和 Fe 的电子结构产生影响，从而改善它们的内在 OER 性能。此外，三维花朵状纳米片形态改善了传质，并在高电压下实现了出色的电流密度。三元 NiFeCo-LDH 电催化剂在 1 M KOH 中需要较低的过电位（10 mA cm-2 时为 253 mV）和 Tafel 斜坡（45 mV dec-1）。使用三元镍铁合金-LDH 电催化剂的 AEMWE 显示出卓越的电解性能，在 1.8 V 的电池中电流密度高达 2.27 A cm-2。此外，在电流密度为 0.5 A cm-2 的条件下，经过 100 小时的耐久性测试，能量转换效率达到了 86.73%。利用三元 NiFeCo-LDH 电催化剂的 AEMWE 电解槽的性能超过了之前报道的 AEMWE 电解槽。这项工作报告了一种高活性 OER 电催化剂，它为在 AEMWE 中开发三元 LDH 电催化剂提供了许多机会。
{"title":"Development of Ternary Layered Double Hydroxide Oxygen Evolution Reaction Electrocatalyst for Anion Exchange Membrane Water Electrolysis","authors":"Shin-Woo Myeong, Song Jin, Chi-Kwan Kim, Jooyoung Lee, Yangdo Kim, Mook Choi","doi":"10.3365/kjmm.2024.62.6.472","DOIUrl":"https://doi.org/10.3365/kjmm.2024.62.6.472","url":null,"abstract":"To achieve net zero emissions, green hydrogen should be produced via water electrolysis with renewable energy. To develop efficient anion exchange membrane water electrolyzers (AEMWE), the development of efficient and stable non-precious metal electrocatalysts for the oxygen evolution reaction (OER) is essential. In this study, a high-performance ternary NiFeCo-layer double hydroxide (LDH) electrocatalyst for AEMWE was easily developed by the co-precipitation method. The introduction of Co has been shown to have an effect on the electronic structure of Ni and Fe, improving their intrinsic OER properties. In addition, the three-dimensional flower-like nanosheet morphology improved mass transfer and achieved excellent current density at high voltages. The ternary NiFeCo-LDH electrocatalyst requires low overpotentials (253 mV at 10 mA cm-2) and Tafel slope (45 mV dec-1) in 1 M KOH. AEMWE using the ternary NiFeCo-LDH electrocatalyst showed excellent electrolysis performance with a high current density of 2.27 A cm-2 at 1.8 V cell. Moreover, an energy conversion efficiency of 86.73 % was achieved during the durability test for 100 hours at a current density of 0.5 A cm-2. The performance of the AEMWE electrolyzer utilizing the ternary NiFeCo-LDH electrocatalyst surpassed that of previously reported AEMWE electrolyzers. This work reports a highly active OER electrocatalyst that could open numerous opportunities for the development of ternary LDH electrocatalysts in AEMWE.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2024-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141265619","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 : 2024-05-05DOI: 10.3365/kjmm.2024.62.5.334
Youn-Ji Heo, Eui Seon Lee, Ji Won Choi, Jongmin Byun, Sung-Tag oH
The effect of powder processing on the microstructure and sinterability of the heavy alloy W-Ni-Cu was investigated. The heavy alloy powders were prepared by the ball milling and hydrogen reduction of metal oxide powders. As the milling time increased, the size of the powder mixture decreased and at 5 h of milling was found to be about 2.5 μm. Microstructural analysis revealed that the powder mixture was changed to W and NiCu alloys with an average particle size of about 200 nm after hydrogen reduction at 800°C for 2 h. The reduction kinetics of the oxide powder mixture was evaluated by the amount of peak shift with heating rates using TGA in a N2-10% H2 atmosphere. The activation energy of the reduction reaction, calculated from the slope of the Kissinger plot, was measured to be 42.8 kJ/mol for CuO, 57.9 kJ/mol for NiO, and 50.1~112.6 for kJ/mol WO3. The relative densities of the heavy alloy sintered at 1100oC and 1200oC using oxide powder were 81.4% and 96.0%, while the specimen using metal powder as a raw material showed a relatively low value of 67% and an inhomogeneous microstructure. It was explained that the changes in sintered microstructure with different powder synthesis methods are mainly due to the powder characteristics, such as the size of the particles of the initial mixed powder.
{"title":"Preparation of W-Ni-Cu Alloy Powder by Hydrogen Reduction of Metal Oxides","authors":"Youn-Ji Heo, Eui Seon Lee, Ji Won Choi, Jongmin Byun, Sung-Tag oH","doi":"10.3365/kjmm.2024.62.5.334","DOIUrl":"https://doi.org/10.3365/kjmm.2024.62.5.334","url":null,"abstract":"The effect of powder processing on the microstructure and sinterability of the heavy alloy W-Ni-Cu was investigated. The heavy alloy powders were prepared by the ball milling and hydrogen reduction of metal oxide powders. As the milling time increased, the size of the powder mixture decreased and at 5 h of milling was found to be about 2.5 μm. Microstructural analysis revealed that the powder mixture was changed to W and NiCu alloys with an average particle size of about 200 nm after hydrogen reduction at 800°C for 2 h. The reduction kinetics of the oxide powder mixture was evaluated by the amount of peak shift with heating rates using TGA in a N2-10% H2 atmosphere. The activation energy of the reduction reaction, calculated from the slope of the Kissinger plot, was measured to be 42.8 kJ/mol for CuO, 57.9 kJ/mol for NiO, and 50.1~112.6 for kJ/mol WO3. The relative densities of the heavy alloy sintered at 1100oC and 1200oC using oxide powder were 81.4% and 96.0%, while the specimen using metal powder as a raw material showed a relatively low value of 67% and an inhomogeneous microstructure. It was explained that the changes in sintered microstructure with different powder synthesis methods are mainly due to the powder characteristics, such as the size of the particles of the initial mixed powder.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2024-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141012203","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 : 2024-05-05DOI: 10.3365/kjmm.2024.62.5.393
So Jin Kim, Woo Rin Han, Young Do Kim
Archaeological excavations in Buyeo had revealed Bronze vessels interred within a hole in the building at the Gwanbuk-ri site. These bronze vessels are dated to the Unified silla period (9-10th centuries). To identify the bronze vessels’ manufacturing technology, metallurgical analyses were carried out using Optical Microscopy, SEM-EDS and EPMA. The results allowed a reconstruction of the manufacturing process of bronze vessels in the Unified silla. It proved that bronze vessels were manufactured with Cu-Sn alloy with varying tin contents, which may be related to the application of uncontrolled procedures in making the bronze alloys. Also a casting process was used to shape the bronze vessels and the strength and hardness of the container were improved through a quenching process. Twins were observed in one of the samples, so it was assumed that hot working had been attempted. Non-metallic inclusions in bronze vessels have circular or polygonal shapes, and Cu and S were detected. The presence of Cu-S inclusions showed the probable use of copper sulphide ores for metal production and smelting. Se and Te in the inclusions of the bronze vessels show that the copper ore is different. From the results of metallurgical analyses of bronze vessels excavated from other regions of the same era, casting and quenching treatments were confirmed, and the sequential relationship of the technological system was revealed.
在扶餘进行的考古发掘中，发现了埋藏在观北里遗址建筑孔洞中的青铜器。这些青铜器的年代为统一新罗时期（9-10 世纪）。为了确定青铜器的制造技术，使用光学显微镜、扫描电镜-电子显微镜和 EPMA 进行了冶金分析。分析结果有助于重建统一新罗时期青铜器的制造过程。结果表明，青铜器是用含锡量不同的铜锡合金制造的，这可能与制造青铜合金时采用了不受控的程序有关。此外，青铜器还采用了铸造工艺，并通过淬火工艺提高了容器的强度和硬度。在其中一个样品中观察到了孪晶，因此推测曾尝试过热加工。青铜容器中的非金属夹杂物呈圆形或多边形，并检测到铜和 S。Cu-S夹杂物的存在表明可能使用了硫化铜矿石进行金属生产和冶炼。青铜器夹杂物中的 Se 和 Te 表明铜矿石是不同的。从同一时代其他地区出土的青铜器的冶金分析结果来看，铸造和淬火处理得到了证实，并揭示了工艺系统的先后关系。
{"title":"An Examination of Bronze Vessel Technology in the Unified Silla Period: Case Study on the Bronzes Excavated from Gwanbuk-ri Site in Buyeo","authors":"So Jin Kim, Woo Rin Han, Young Do Kim","doi":"10.3365/kjmm.2024.62.5.393","DOIUrl":"https://doi.org/10.3365/kjmm.2024.62.5.393","url":null,"abstract":"Archaeological excavations in Buyeo had revealed Bronze vessels interred within a hole in the building at the Gwanbuk-ri site. These bronze vessels are dated to the Unified silla period (9-10th centuries). To identify the bronze vessels’ manufacturing technology, metallurgical analyses were carried out using Optical Microscopy, SEM-EDS and EPMA. The results allowed a reconstruction of the manufacturing process of bronze vessels in the Unified silla. It proved that bronze vessels were manufactured with Cu-Sn alloy with varying tin contents, which may be related to the application of uncontrolled procedures in making the bronze alloys. Also a casting process was used to shape the bronze vessels and the strength and hardness of the container were improved through a quenching process. Twins were observed in one of the samples, so it was assumed that hot working had been attempted. Non-metallic inclusions in bronze vessels have circular or polygonal shapes, and Cu and S were detected. The presence of Cu-S inclusions showed the probable use of copper sulphide ores for metal production and smelting. Se and Te in the inclusions of the bronze vessels show that the copper ore is different. From the results of metallurgical analyses of bronze vessels excavated from other regions of the same era, casting and quenching treatments were confirmed, and the sequential relationship of the technological system was revealed.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2024-05-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141011662","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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