Pub Date : 2023-12-05DOI: 10.3365/kjmm.2023.61.12.951
Byung Hak Choe, Kwang Soo Choi, S. Han, D. Kim, Jong-Kee Ahn, Dong Su Kang, Seong-Moon Seo
This study analyzed a recrystallization phenomenon that occurred simultaneously with hightemperature oxidation on the surface of a directionally solidified CM247LC creep specimen, using optical and scanning electron microscopy. After heat treatment, the surface of the specimen subjected to the creep test at 982oC was oxidized by exposure to high temperature and underwent microstructural changes due to high temperature stress. The outermost layer of the oxidized surface pits was found to consist of an oxide of the Cr/Co component, and the lower layer contained an oxide of the Al component. The area adjacent to the surface oxide layer is a precipitated free zone (PFZ) depleted of the y’ precipitated phase. The PFZ is caused by the diffusion of the Al component from this area to the surface oxide layer, resulting in the depletion of y'-Ni3Al as the main Al component. The area adjacent to the PFZ is a y' coarsening layer, which is the result of increasing y' phase fraction and coarsening as the Cr/Co component of this region diffuses into the PFZ of the y phase composition. This y' coarsening and y' rafting occurs in the direction perpendicular to the creep stress. In the EBSD analysis, the PFZ and y' coarsened layer were observed to be recrystallized regions, with the recrystallization composed of a single grain including the PFZ and y' coarsened layer. It is presumed that this recrystallization is caused by the residual stress of one-way solidification or the residual stress of the specimen surface processing. Accordingly, high-temperature oxidation in DS CM247LC creep gauge caused surface pits associated with recrystallization.
{"title":"Effect of High Temperature Oxidation on Surface Pit and Recrystallization of Directionally Solidified CM247LC Superalloy in Creep Gauge","authors":"Byung Hak Choe, Kwang Soo Choi, S. Han, D. Kim, Jong-Kee Ahn, Dong Su Kang, Seong-Moon Seo","doi":"10.3365/kjmm.2023.61.12.951","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.12.951","url":null,"abstract":"This study analyzed a recrystallization phenomenon that occurred simultaneously with hightemperature oxidation on the surface of a directionally solidified CM247LC creep specimen, using optical and scanning electron microscopy. After heat treatment, the surface of the specimen subjected to the creep test at 982oC was oxidized by exposure to high temperature and underwent microstructural changes due to high temperature stress. The outermost layer of the oxidized surface pits was found to consist of an oxide of the Cr/Co component, and the lower layer contained an oxide of the Al component. The area adjacent to the surface oxide layer is a precipitated free zone (PFZ) depleted of the y’ precipitated phase. The PFZ is caused by the diffusion of the Al component from this area to the surface oxide layer, resulting in the depletion of y'-Ni3Al as the main Al component. The area adjacent to the PFZ is a y' coarsening layer, which is the result of increasing y' phase fraction and coarsening as the Cr/Co component of this region diffuses into the PFZ of the y phase composition. This y' coarsening and y' rafting occurs in the direction perpendicular to the creep stress. In the EBSD analysis, the PFZ and y' coarsened layer were observed to be recrystallized regions, with the recrystallization composed of a single grain including the PFZ and y' coarsened layer. It is presumed that this recrystallization is caused by the residual stress of one-way solidification or the residual stress of the specimen surface processing. Accordingly, high-temperature oxidation in DS CM247LC creep gauge caused surface pits associated with recrystallization.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2023-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138598427","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 : 2023-12-05DOI: 10.3365/kjmm.2023.61.12.958
Tae O Park, Youn Woo Shin, Seung Hwan Lee, Pius Jwa, Y. Kwon, Suman Timilsina, Seong Min Jang, Chul Woo Jo, Ji Sik Kim
The phenomenon of mechanoluminescence (ML) refers to the emission of light induced by mechanical stimulation applied to mechano-optical materials for example SrAl2O3:Eu,Dy (SAO). Numerous technologies on the basis of ML have been presented to visualize the stress or strain in various structures for the applications including structural health monitoring. As a result, extensive attention has been devoted to the design, synthesis, characteristics, optimizations, and applications of ML materials. However, challenges still remain in the standardization of ML measurement and evaluation, thereby commercially viable ML applications are currently unavailable. To overcome these difficulties, present study proposes ML measurement and evaluation techniques employing the ML fracture mechanics, finite element method, and dual deep learnings. For the effective normalization of visualized ML images under fixed initial ML intensity condition, continuous UV irradiation above the critical ML power density has been subjected to tensile and compact tension (CT) specimens. Therefore, Plastic Stress Intensity Factor (SIF) as well as crack tip stress field have been extracted successfully from normalized ML images based on ML fracture mechanics. To complement and verify the ML analysis, numerical FEM simulation and analytical ASTM calculation have been also provided. Finally, a double deep learning consists of Generative Adversarial Networks (GAN) and Convolutional Neural Networks (CNN) has been trained and tested for the standard evaluation of in-situ ML images.
{"title":"Diagnosis of Mechanoluminescent Crack Based on Double Deep Learning in Al 7075","authors":"Tae O Park, Youn Woo Shin, Seung Hwan Lee, Pius Jwa, Y. Kwon, Suman Timilsina, Seong Min Jang, Chul Woo Jo, Ji Sik Kim","doi":"10.3365/kjmm.2023.61.12.958","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.12.958","url":null,"abstract":"The phenomenon of mechanoluminescence (ML) refers to the emission of light induced by mechanical stimulation applied to mechano-optical materials for example SrAl2O3:Eu,Dy (SAO). Numerous technologies on the basis of ML have been presented to visualize the stress or strain in various structures for the applications including structural health monitoring. As a result, extensive attention has been devoted to the design, synthesis, characteristics, optimizations, and applications of ML materials. However, challenges still remain in the standardization of ML measurement and evaluation, thereby commercially viable ML applications are currently unavailable. To overcome these difficulties, present study proposes ML measurement and evaluation techniques employing the ML fracture mechanics, finite element method, and dual deep learnings. For the effective normalization of visualized ML images under fixed initial ML intensity condition, continuous UV irradiation above the critical ML power density has been subjected to tensile and compact tension (CT) specimens. Therefore, Plastic Stress Intensity Factor (SIF) as well as crack tip stress field have been extracted successfully from normalized ML images based on ML fracture mechanics. To complement and verify the ML analysis, numerical FEM simulation and analytical ASTM calculation have been also provided. Finally, a double deep learning consists of Generative Adversarial Networks (GAN) and Convolutional Neural Networks (CNN) has been trained and tested for the standard evaluation of in-situ ML images.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2023-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138600543","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 : 2023-12-05DOI: 10.3365/kjmm.2023.61.12.896
Duck Bin Yun, Hye Rin Bang, Wan Keun Kim, Sung Jin Kim
This study examined the effects of minor alloying elements (Cr and Mo) on the corrosion behaviors of API grade steel in CO2-saturated near-neutral aqueous solutions. Various experimental and analytical methods were applied to gain insights into the underlying CO2 corrosion mechanism of the steels. The findings revealed that steel with a minute quantity of Mo (0.1 ~ 0.15 wt%) exhibited the lowest corrosion current density and the highest polarization resistance. This outcome can be primarily attributed to the formation of a thin layer of Mo-based oxides/hydroxide, covered with a fine FeCO3 scale, consequently enhancing corrosion resistance in CO2 environments. On the other hand, the addition of Cr (0.4 ~ 0.5 wt%) in combination with Mo resulted in degraded corrosion resistance due to the competitive precipitation of amorphous Cr(OH)3 and crystalline FeCO3. This led to an uneven interface and the growth of FeCO3 particles, consequently reducing polarization resistance and increasing the corrosion rate. Based on the obtained results, it is recommended that cost-effective steels for CO2 transportation can be developed by adding a small amount of Mo along with a higher quantity of Cr. This optimized combination of alloying elements is expected to significantly improve the anti-corrosion performance of the steel in near-neutral brine environments with CO2.
{"title":"Effects of Minor Alloying Elements (Cr and Mo) on the Corrosion Behaviors of API Grade Steel in CO2-Saturated Brine Environments","authors":"Duck Bin Yun, Hye Rin Bang, Wan Keun Kim, Sung Jin Kim","doi":"10.3365/kjmm.2023.61.12.896","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.12.896","url":null,"abstract":"This study examined the effects of minor alloying elements (Cr and Mo) on the corrosion behaviors of API grade steel in CO2-saturated near-neutral aqueous solutions. Various experimental and analytical methods were applied to gain insights into the underlying CO2 corrosion mechanism of the steels. The findings revealed that steel with a minute quantity of Mo (0.1 ~ 0.15 wt%) exhibited the lowest corrosion current density and the highest polarization resistance. This outcome can be primarily attributed to the formation of a thin layer of Mo-based oxides/hydroxide, covered with a fine FeCO3 scale, consequently enhancing corrosion resistance in CO2 environments. On the other hand, the addition of Cr (0.4 ~ 0.5 wt%) in combination with Mo resulted in degraded corrosion resistance due to the competitive precipitation of amorphous Cr(OH)3 and crystalline FeCO3. This led to an uneven interface and the growth of FeCO3 particles, consequently reducing polarization resistance and increasing the corrosion rate. Based on the obtained results, it is recommended that cost-effective steels for CO2 transportation can be developed by adding a small amount of Mo along with a higher quantity of Cr. This optimized combination of alloying elements is expected to significantly improve the anti-corrosion performance of the steel in near-neutral brine environments with CO2.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2023-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138600251","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 : 2023-12-05DOI: 10.3365/kjmm.2023.61.12.915
Joonha Lee, H. Park, Jeong-Yeon Kim, Won-Seon Seo, Heesun Yang, Umut Aydemir, Se Yun Kim, W. Shin, Hyun-Sik Kim
SnTe has drawn much attention due to its Pb-free composition along with tunable electronic and lattice structures. However, its intrinsically high defect concentration and high lattice thermal conductivity (κ1) have hindered its application in devices. Recently, Bi doping at Sn-sites in Sn1-xBixTe (x = 0.0 – 0.08) has been demonstrated to be effective in improving the thermoelectric performance (zT) of SnTe. Bi doping was particularly effective in improving the Seebeck coefficient in a wide range of temperature while suppressing its κ1. However, the effect of Bi doping on electronic band structure of SnTe has not been studied. Here, we applied the Single Parabolic Band (SPB) model to the room temperature electronic transport properties measurements (Seebeck coefficient, electrical conductivity, Hall carrier concentration) and analyzed how electronic band parameters like the density-of-states effective mass (md *), non-degenerate mobility (μ0), weighted mobility (μw), and B-factor changes with a changing Bi doping content (x). As the x increases, the md * increases while μ0 decreases. As the μw depends both on md * and μ0, it peaks at x = 0.02. Lastly, the B-factor is related to the ratio of μw to κ1, due to significantly decreasing κ1 at high x, the B-factor also becomes the highest at x = 0.08. Based on the B-factor of x = 0.08 sample, the highest theoretical zT of 0.31 is predicted using the SPB model. This is approximately 2.2 times higher than the experimental zT (~0.139) reported in literature at 300 K. The SPB model also guides us that the highest theoretical zT of 0.31 can be achieved if its Hall carrier concentration is tuned to 9.06 × 1018 cm-3.
{"title":"Estimation of the Highest Thermoelectric Performance of the Bi-Doped SnTe at Room Temperature","authors":"Joonha Lee, H. Park, Jeong-Yeon Kim, Won-Seon Seo, Heesun Yang, Umut Aydemir, Se Yun Kim, W. Shin, Hyun-Sik Kim","doi":"10.3365/kjmm.2023.61.12.915","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.12.915","url":null,"abstract":"SnTe has drawn much attention due to its Pb-free composition along with tunable electronic and lattice structures. However, its intrinsically high defect concentration and high lattice thermal conductivity (<i>κ<sub>1</sub></i>) have hindered its application in devices. Recently, Bi doping at Sn-sites in Sn<sub>1-<i>x</i></sub>Bi<sub><i>x</i></sub>Te (<i>x</i> = 0.0 – 0.08) has been demonstrated to be effective in improving the thermoelectric performance (<i>zT</i>) of SnTe. Bi doping was particularly effective in improving the Seebeck coefficient in a wide range of temperature while suppressing its <i>κ<sub>1</sub></i>. However, the effect of Bi doping on electronic band structure of SnTe has not been studied. Here, we applied the Single Parabolic Band (SPB) model to the room temperature electronic transport properties measurements (Seebeck coefficient, electrical conductivity, Hall carrier concentration) and analyzed how electronic band parameters like the density-of-states effective mass (<i>m<sub>d</sub></i> *), non-degenerate mobility (<i>μ<sub>0</sub></i>), weighted mobility (<i>μ<sub>w</sub></i>), and <i>B</i>-factor changes with a changing Bi doping content (<i>x</i>). As the <i>x</i> increases, the <i>m<sub>d</sub></i> * increases while <i>μ<sub>0</sub></i> decreases. As the <i>μ<sub>w</sub></i> depends both on <i>m<sub>d</sub></i> * and <i>μ<sub>0</sub></i>, it peaks at <i>x</i> = 0.02. Lastly, the <i>B</i>-factor is related to the ratio of <i>μ<sub>w</sub></i> to <i>κ<sub>1</sub></i>, due to significantly decreasing <i>κ<sub>1</sub></i> at high <i>x</i>, the <i>B</i>-factor also becomes the highest at <i>x</i> = 0.08. Based on the <i>B</i>-factor of <i>x</i> = 0.08 sample, the highest theoretical <i>zT</i> of 0.31 is predicted using the SPB model. This is approximately 2.2 times higher than the experimental <i>zT</i> (~0.139) reported in literature at 300 K. The SPB model also guides us that the highest theoretical <i>zT</i> of 0.31 can be achieved if its Hall carrier concentration is tuned to 9.06 × 10<sup>18</sup> cm<sup>-3</sup>.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2023-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138598514","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.2023.61.11.842
Seung Min Kang, Jong Wook Rho, Hyungyu Cho, Sanghyun Park, Joontae Park, Sang-il Kim
SnSe2 alloys have been investigated in recent times as potential n-type thermoelectric materials. In this study, the thermoelectric transport properties of a series of Sb-doped SnSe2, Sn(Se1-xSbx)2 (x = 0, 0.015, 0.03, 0.045, 0.06) alloys are investigated. The electrical conductivity was generally enhanced with Sb doping owing to a large increase in electron concentration. However, the Seebeck coefficient largely decreased with doping. Consequently, the power factor was significantly lower at a low doping of x = 0.015, and then began rising as the doping was increased beyond x = 0.015. It was found that the density-of-states effective mass and weighted mobility decreased with Sb doping, implying that the electrical transport properties of SnSe2 were degraded by Sb doping. The total and lattice thermal conductivities gradually decreased due to additional point defect scattering. Thus, the thermoelectric figure of merit declined significantly, from 0.30 of the pristine sample with a low doping of Sb (x = 0.015) at 750 K, to 0.18, and then for x = 0.06 it gradually recovered to the value of the undoped sample. The thermoelectric quality factor decreased as the Sb doping was increased, implying that Sb doping did not enhance the thermoelectric transport properties, despite the large increase in electron concentration.
{"title":"Thermoelectric Transport Properties of Sb-doped SnSe<sub>2</sub> Polycrystalline Alloys","authors":"Seung Min Kang, Jong Wook Rho, Hyungyu Cho, Sanghyun Park, Joontae Park, Sang-il Kim","doi":"10.3365/kjmm.2023.61.11.842","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.11.842","url":null,"abstract":"SnSe<sub>2</sub> alloys have been investigated in recent times as potential <i>n</i>-type thermoelectric materials. In this study, the thermoelectric transport properties of a series of Sb-doped SnSe<sub>2</sub>, Sn(Se<sub>1-x</sub>Sb<sub>x</sub>)<sub>2</sub> (<i>x</i> = 0, 0.015, 0.03, 0.045, 0.06) alloys are investigated. The electrical conductivity was generally enhanced with Sb doping owing to a large increase in electron concentration. However, the Seebeck coefficient largely decreased with doping. Consequently, the power factor was significantly lower at a low doping of <i>x</i> = 0.015, and then began rising as the doping was increased beyond <i>x</i> = 0.015. It was found that the density-of-states effective mass and weighted mobility decreased with Sb doping, implying that the electrical transport properties of SnSe<sub>2</sub> were degraded by Sb doping. The total and lattice thermal conductivities gradually decreased due to additional point defect scattering. Thus, the thermoelectric figure of merit declined significantly, from 0.30 of the pristine sample with a low doping of Sb (<i>x</i> = 0.015) at 750 K, to 0.18, and then for <i>x</i> = 0.06 it gradually recovered to the value of the undoped sample. The thermoelectric quality factor decreased as the Sb doping was increased, implying that Sb doping did not enhance the thermoelectric transport properties, despite the large increase in electron concentration.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135723589","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.2023.61.11.807
Sang-Gyu Kim, Jae-Yun Kim, Hyun-Joo Seo, Hwan-Gyo Jung, Jaeyoung Park, Un-Bong Baek, Byoungchul Hwang
The effect of hydrogen charging methods on the hydrogen embrittlement characteristics of tempered martensitic steels were discussed in terms of hydrogen diffusion behavior. Two tempered martensitic steels with different Si content were fabricated by quenching and tempering. The steel with high Si content had a lower cementite fraction because the addition of Si changed the morphology of cementite from a long film-like shape to a short-rod shape by suppressing the precipitation and growth of the cementite. To evaluate the hydrogen embrittlement resistance of the two tempered martensitic steels with different Si content, slow strain-rate tensile testing was employed after introducing hydrogen using three types of hydrogen charging methods (ex-situ electrochemical hydrogen charging, in-situ electrochemical hydrogen charging, and in-situ high-pressure gaseous hydrogen environment). For the hydrogen pre-charged tensile specimens using the ex-situ electrochemical charging method, the steel with high Si content had a better hydrogen embrittlement resistance, with a higher relative reduction in area. On the other hand, there was no significant difference in the relative notch tensile strength of the two tempered martensitic steels with different Si content, regardless of the hydrogen charging methods. In addition, the ex-situ hydrogen charging method exhibited higher relative notch tensile strength compared to the in-situ hydrogen charging method due to the release of hydrogen during the tensile test, after exsitu hydrogen charging. This implies that hydrogen embrittlement resistance can be differently estimated depending on the kind of hydrogen charging methods.
{"title":"Hydrogen Embrittlement Characteristics of Tempered Martensitic Steels under Electrochemical and High-Pressure Hydrogen Environments","authors":"Sang-Gyu Kim, Jae-Yun Kim, Hyun-Joo Seo, Hwan-Gyo Jung, Jaeyoung Park, Un-Bong Baek, Byoungchul Hwang","doi":"10.3365/kjmm.2023.61.11.807","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.11.807","url":null,"abstract":"The effect of hydrogen charging methods on the hydrogen embrittlement characteristics of tempered martensitic steels were discussed in terms of hydrogen diffusion behavior. Two tempered martensitic steels with different Si content were fabricated by quenching and tempering. The steel with high Si content had a lower cementite fraction because the addition of Si changed the morphology of cementite from a long film-like shape to a short-rod shape by suppressing the precipitation and growth of the cementite. To evaluate the hydrogen embrittlement resistance of the two tempered martensitic steels with different Si content, slow strain-rate tensile testing was employed after introducing hydrogen using three types of hydrogen charging methods (ex-situ electrochemical hydrogen charging, in-situ electrochemical hydrogen charging, and in-situ high-pressure gaseous hydrogen environment). For the hydrogen pre-charged tensile specimens using the ex-situ electrochemical charging method, the steel with high Si content had a better hydrogen embrittlement resistance, with a higher relative reduction in area. On the other hand, there was no significant difference in the relative notch tensile strength of the two tempered martensitic steels with different Si content, regardless of the hydrogen charging methods. In addition, the ex-situ hydrogen charging method exhibited higher relative notch tensile strength compared to the in-situ hydrogen charging method due to the release of hydrogen during the tensile test, after exsitu hydrogen charging. This implies that hydrogen embrittlement resistance can be differently estimated depending on the kind of hydrogen charging methods.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135723594","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.2023.61.11.874
Jiwon Park, Su-Hyeon Kim, Jisu Kim, Byung-joo Kim, Hyun-seok Cheon, Chang-Seok Oh
In this study, the Vickers hardness of precipitation-strengthened Al-Sc-X (X = Zr, Si, and Fe) alloys were predicted using machine learning models, depending on the alloys’ compositions, solid-solution treatment and aging conditions. The data used for machine learning were collected from the literature. Among the models, tree-based ensemble models such as extreme gradient boosting and random forest performed well. Then the feature impact on the model output was analyzed with SHarpely Additive eXplanation (SHAP). Based on the SHAP analysis and prior domain knowledge, the process conditions were restricted to narrow down the inverse design search space. Candidate alloys suggested by the optimization using a genetic algorithm showed improved hardness values. The hardness prediction model and the inverse designsuggested candidates were then experimentally validated. The accuracy of the hardness prediction model was 0.994, when the predicted hardness was 85.4 Hv, and the experimentally measured hardness was 84.9 Hv. A specimen whose composition was close to the inverse-designed alloy was cast and heat treated according to the suggested conditions. The inverse design showed an accuracy of 0.965. Exploring the entire combination of possible feature space requires vast effort and time. An efficient search for materials with improved properties can be achieved using an appropriate configuration of well-performing machine learning models and explainable AI techniques guided by domain knowledge.
{"title":"Predicting the Hardness of Al-Sc-X Alloys with Machine Learning Models, Explainable Artificial Intelligence Analysis and Inverse Design","authors":"Jiwon Park, Su-Hyeon Kim, Jisu Kim, Byung-joo Kim, Hyun-seok Cheon, Chang-Seok Oh","doi":"10.3365/kjmm.2023.61.11.874","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.11.874","url":null,"abstract":"In this study, the Vickers hardness of precipitation-strengthened Al-Sc-X (X = Zr, Si, and Fe) alloys were predicted using machine learning models, depending on the alloys’ compositions, solid-solution treatment and aging conditions. The data used for machine learning were collected from the literature. Among the models, tree-based ensemble models such as extreme gradient boosting and random forest performed well. Then the feature impact on the model output was analyzed with SHarpely Additive eXplanation (SHAP). Based on the SHAP analysis and prior domain knowledge, the process conditions were restricted to narrow down the inverse design search space. Candidate alloys suggested by the optimization using a genetic algorithm showed improved hardness values. The hardness prediction model and the inverse designsuggested candidates were then experimentally validated. The accuracy of the hardness prediction model was 0.994, when the predicted hardness was 85.4 Hv, and the experimentally measured hardness was 84.9 Hv. A specimen whose composition was close to the inverse-designed alloy was cast and heat treated according to the suggested conditions. The inverse design showed an accuracy of 0.965. Exploring the entire combination of possible feature space requires vast effort and time. An efficient search for materials with improved properties can be achieved using an appropriate configuration of well-performing machine learning models and explainable AI techniques guided by domain knowledge.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-11-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135723590","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.2023.61.11.849
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":null,"pages":null},"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":null,"pages":null},"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":null,"pages":null},"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}
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