Pub Date : 2023-12-05DOI: 10.3365/kjmm.2023.61.12.943
Hee-sup Shin, Yool-koo Kim, Sang-mok Lee
The friction properties of brake friction materials are investigated utilizing the different car cleaners. Water, wheel cleaner and tire dressing were used to designate driving conditions in the field. The friction materials were soaked in each solution before friction test. The Coefficient of friction (COF) was similar in the case of water and tire dressing due to a same menstruum. And, the effect of surfactants within wheel cleaner caused lowest the COF. Surface morphologies were measured using confocal microscope and wheel cleaners, showing significant effects on the formation of thick and even friction film. The hardness of friction film was measured through micro-Vickers test, and the specimen with wheel cleaner showed highest hardness due to the thick film. On the other hand, the specimens with water and tire dressing showed a lower hardness even though the film was thicker than specimen with dry condition. The components of wheel cleaners also affected the hydrophobicity of friction films for both disc and pad. Therefore, the contact angle was critically low compared to other specimens. The reduction of hydrophobicity caused by the solution effects increasing of rust occurring on the surface of the brake disc. This result suggests that the formation of friction film under different environments was deeply related to friction and corrosive properties of brake system.
{"title":"Effect of Corrosive Environment on Friction Characteristics of Brake Friction Materials","authors":"Hee-sup Shin, Yool-koo Kim, Sang-mok Lee","doi":"10.3365/kjmm.2023.61.12.943","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.12.943","url":null,"abstract":"The friction properties of brake friction materials are investigated utilizing the different car cleaners. Water, wheel cleaner and tire dressing were used to designate driving conditions in the field. The friction materials were soaked in each solution before friction test. The Coefficient of friction (COF) was similar in the case of water and tire dressing due to a same menstruum. And, the effect of surfactants within wheel cleaner caused lowest the COF. Surface morphologies were measured using confocal microscope and wheel cleaners, showing significant effects on the formation of thick and even friction film. The hardness of friction film was measured through micro-Vickers test, and the specimen with wheel cleaner showed highest hardness due to the thick film. On the other hand, the specimens with water and tire dressing showed a lower hardness even though the film was thicker than specimen with dry condition. The components of wheel cleaners also affected the hydrophobicity of friction films for both disc and pad. Therefore, the contact angle was critically low compared to other specimens. The reduction of hydrophobicity caused by the solution effects increasing of rust occurring on the surface of the brake disc. This result suggests that the formation of friction film under different environments was deeply related to friction and corrosive properties of brake system.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":"127 16","pages":""},"PeriodicalIF":1.2,"publicationDate":"2023-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138599121","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.2023.61.12.883
Seung Woo Jin, Jin Sung Park, Duck Bin Yun, Sang Chul Lee, Jong Kyo Choi, Min-Suk Oh, Sung Jin Kim
The corrosion and erosion-corrosion behaviors in the weld heat-affected zone (HAZ) of Hadfield steels with varying Cr contents (1, 2, and 3 wt%) were examined. Various experimental methods, including electrochemical polarization, impedance, and weight loss measurements, were utilized. Two types of isothermal heat treatments were conducted in a box furnace to simulate the intercritical HAZ, known to be the most vulnerable region in terms of mechanical properties and environmental stabilities, and large-scale samples for the erosion-corrosion experiment were fabricated. The results showed that increasing the Cr content improved the resistance to corrosion and erosion-corrosion, but there was an inflection point where adding more Cr had the opposite effect. Up to 2 wt%, a higher resistance was exhibited owing to the formation of a thin and protective oxide scale enriched with Cr that adhered to the steel surface. On the other hand, adding 3 wt% of Cr resulted in decreased resistance. This was due to the formation of coarse M7C3 (M: Cr) precipitated along the grain boundary, which caused the development of a thick and unstable oxide scale that detached locally. Based on these findings, it is essential to optimize the Cr content to ensure a high resistance to corrosion and erosion-corrosion in the HAZ of Hadfield steel.
{"title":"Effects of Cr additions on Corrosion and Erosion-Corrosion Behaviors in the Weld Heat-Affected Zone of Hadfield Steel in Brine Environments","authors":"Seung Woo Jin, Jin Sung Park, Duck Bin Yun, Sang Chul Lee, Jong Kyo Choi, Min-Suk Oh, Sung Jin Kim","doi":"10.3365/kjmm.2023.61.12.883","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.12.883","url":null,"abstract":"The corrosion and erosion-corrosion behaviors in the weld heat-affected zone (HAZ) of Hadfield steels with varying Cr contents (1, 2, and 3 wt%) were examined. Various experimental methods, including electrochemical polarization, impedance, and weight loss measurements, were utilized. Two types of isothermal heat treatments were conducted in a box furnace to simulate the intercritical HAZ, known to be the most vulnerable region in terms of mechanical properties and environmental stabilities, and large-scale samples for the erosion-corrosion experiment were fabricated. The results showed that increasing the Cr content improved the resistance to corrosion and erosion-corrosion, but there was an inflection point where adding more Cr had the opposite effect. Up to 2 wt%, a higher resistance was exhibited owing to the formation of a thin and protective oxide scale enriched with Cr that adhered to the steel surface. On the other hand, adding 3 wt% of Cr resulted in decreased resistance. This was due to the formation of coarse M7C3 (M: Cr) precipitated along the grain boundary, which caused the development of a thick and unstable oxide scale that detached locally. Based on these findings, it is essential to optimize the Cr content to ensure a high resistance to corrosion and erosion-corrosion in the HAZ of Hadfield steel.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":"115 23","pages":""},"PeriodicalIF":1.2,"publicationDate":"2023-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138599539","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.2023.61.12.933
Gue Serb Cho, Kyung Il Kim, W. Noh
WC-Co cemented carbide has excellent mechanical properties and is widely used in many industrial applications including cold forging dies and cutting tools. The tensile and fatigue properties of WC-20wt%Co cemented carbides with microstructural variations were investigated. Microstructure parameters such as Co binder content, WC particle size, binder mean free path, and contiguity were obtained by linear intercept method using BSE microstructure images. Standard specimens of WC-20wt%Co cemented carbides were prepared for tensile and fatigue testing. Uniaxial tensile stress-strain curves and tensile-compression fatigue S-N curves were obtained. The 22Co-Cr alloy with higher Co content showed the largest binder mean free path and the lowest continuity. The 20Co-dwc alloy with fine WC grains of submicron size showed the lowest binder mean free path due to fine WC grain distribution. The 20Co-dwc alloy with fine WC grains showed the highest tensile strength and fatigue strength, compared to other alloys. The 22Co-Cr alloy with a higher FCC Co phase content, which has excellent plastic deformability, showed higher fatigue properties. The fatigue life of the 22Co-Cr alloy increased with increasing compressive mean stress level. Based on the axial tensile and fatigue properties, a reasonable fatigue life prediction of WC-20wt%Co cemented carbide dies for cold forging can be estimated.
{"title":"Tensile and Fatigue Properties of WC-20 wt%Co Cemented Carbides under Microstructural Variations","authors":"Gue Serb Cho, Kyung Il Kim, W. Noh","doi":"10.3365/kjmm.2023.61.12.933","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.12.933","url":null,"abstract":"WC-Co cemented carbide has excellent mechanical properties and is widely used in many industrial applications including cold forging dies and cutting tools. The tensile and fatigue properties of WC-20wt%Co cemented carbides with microstructural variations were investigated. Microstructure parameters such as Co binder content, WC particle size, binder mean free path, and contiguity were obtained by linear intercept method using BSE microstructure images. Standard specimens of WC-20wt%Co cemented carbides were prepared for tensile and fatigue testing. Uniaxial tensile stress-strain curves and tensile-compression fatigue S-N curves were obtained. The 22Co-Cr alloy with higher Co content showed the largest binder mean free path and the lowest continuity. The 20Co-dwc alloy with fine WC grains of submicron size showed the lowest binder mean free path due to fine WC grain distribution. The 20Co-dwc alloy with fine WC grains showed the highest tensile strength and fatigue strength, compared to other alloys. The 22Co-Cr alloy with a higher FCC Co phase content, which has excellent plastic deformability, showed higher fatigue properties. The fatigue life of the 22Co-Cr alloy increased with increasing compressive mean stress level. Based on the axial tensile and fatigue properties, a reasonable fatigue life prediction of WC-20wt%Co cemented carbide dies for cold forging can be estimated.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":"63 2","pages":""},"PeriodicalIF":1.2,"publicationDate":"2023-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138598526","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.2023.61.12.951
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":"11 2","pages":""},"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":"60 6","pages":""},"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":"86 7","pages":""},"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":"64 5","pages":""},"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":"15 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":"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":"15 1","pages":"0"},"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":"15 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":"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}
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