Pub Date : 2023-08-05DOI: 10.3365/kjmm.2023.61.8.594
Cheol Min Kim, Kwi‐Il Park
Thermoelectric energy harvesting has attracted a lot of attention for powering self-powered devices because of the potential to generate energy anywhere with a temperature difference. In particular, a stretchable thermoelectric generator (S-TEG) can be applied to the repetitively moving parts of a machine and even a human body. Herein, we suggested a S-TEG using thermoelectric composite films made by dispersing n-type Bi2Te2.7Se0.3 powders into the polyvinylidene fluoride elastomer. The prepared n-type thermoelectric composite film with 75 wt% of Bi2Te2.7Se0.3 powders showed a power factor of 1.81 mW m−1 K−2 at room temperature. Next, we fabricated S-TEG by encapsulating thermoelectric powders-based composite films, and Ag-coated textile electrodes with an Eco-flex matrix. The fabricated stretchable energy harvester generated a maximum output power of 2.35 nW at a temperature difference (ΔT) of 25 K. By repeatedly introducing ΔT=5K, our S-TEG converted the output voltage of 3.4 mV and current signals of 0.25 mA. Moreover, a finite element analysis with multiphysics COMSOL simulation software was conducted to compare the experimental and theoretical thermoelectric output performance of the fabricated S-TEG. Finally, we demonstrated energy harvesting by converting human body heat into electrical energy for potential utilization of our energy harvester. This study led to the development of a S-TEG design using thermoelectric film with a simple and low-cost fabrication procedure, providing a potential approach for use as a next-generation wearable device power source.
{"title":"Stretchable Energy Harvesting Device based on Thermoelectric Composite Films","authors":"Cheol Min Kim, Kwi‐Il Park","doi":"10.3365/kjmm.2023.61.8.594","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.8.594","url":null,"abstract":"Thermoelectric energy harvesting has attracted a lot of attention for powering self-powered devices because of the potential to generate energy anywhere with a temperature difference. In particular, a stretchable thermoelectric generator (S-TEG) can be applied to the repetitively moving parts of a machine and even a human body. Herein, we suggested a S-TEG using thermoelectric composite films made by dispersing n-type Bi2Te2.7Se0.3 powders into the polyvinylidene fluoride elastomer. The prepared n-type thermoelectric composite film with 75 wt% of Bi2Te2.7Se0.3 powders showed a power factor of 1.81 mW m−1 K−2 at room temperature. Next, we fabricated S-TEG by encapsulating thermoelectric powders-based composite films, and Ag-coated textile electrodes with an Eco-flex matrix. The fabricated stretchable energy harvester generated a maximum output power of 2.35 nW at a temperature difference (ΔT) of 25 K. By repeatedly introducing ΔT=5K, our S-TEG converted the output voltage of 3.4 mV and current signals of 0.25 mA. Moreover, a finite element analysis with multiphysics COMSOL simulation software was conducted to compare the experimental and theoretical thermoelectric output performance of the fabricated S-TEG. Finally, we demonstrated energy harvesting by converting human body heat into electrical energy for potential utilization of our energy harvester. This study led to the development of a S-TEG design using thermoelectric film with a simple and low-cost fabrication procedure, providing a potential approach for use as a next-generation wearable device power source.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2023-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42069138","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 : 2023-08-05DOI: 10.3365/kjmm.2023.61.8.589
Woon-Seop Choi, Young Jik Lee, Yong Jae Kim
Oxide thin-film transistors (TFTs) are important semiconductor materials for display backplanes. To fabricate flexible displays, not only display modes but also TFTs are important. Flexible TFTs are especially needed for flexible displays, and related processes need to be developed. Printing is a good choice for the new fabrication of oxide TFTs. Electrohydrodynamic (EHD) jet printing is an excellent alternative for making flexible TFTs. To improve the electrical properties of oxide TFTs using EHD jet printing, propylene monomethyl ether acetate (PGMEA) was added to a zinc-tin oxide (ZTO) formulation. EHD jet printing was performed by Taylor cone jet mode with parameters of 2.4 kV and 0.064 µL/s to obtain uniform thin films at a substrate temperature of 50oC. Much improved TFT properties were obtained, including a mobility of 7.11 cm2/V s, on-to-off current ratio of 2.8 × 106 and subthreshold slope of 1.44 V/dec-1 for ZTO TFT with 5 wt% of PGMEA, and a mobility of 1.43 cm2/V s, on-to-off current ratio of 2.7 × 105 and subthreshold slope of 1.32 V/dec-1 for the ZTO TFT. Almost no hysteresis behavior was observed in the oxide TFTs with added PGMEA. We report a new way to improve the electrical properties of oxide TFTs, by the simple addition of PGMEA.
{"title":"Improving the Electrical Properties of Zinc-Tin Oxide Thin-Film Transistors by Additive using Electrohydrodynamic Jet Technology","authors":"Woon-Seop Choi, Young Jik Lee, Yong Jae Kim","doi":"10.3365/kjmm.2023.61.8.589","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.8.589","url":null,"abstract":"Oxide thin-film transistors (TFTs) are important semiconductor materials for display backplanes. To fabricate flexible displays, not only display modes but also TFTs are important. Flexible TFTs are especially needed for flexible displays, and related processes need to be developed. Printing is a good choice for the new fabrication of oxide TFTs. Electrohydrodynamic (EHD) jet printing is an excellent alternative for making flexible TFTs. To improve the electrical properties of oxide TFTs using EHD jet printing, propylene monomethyl ether acetate (PGMEA) was added to a zinc-tin oxide (ZTO) formulation. EHD jet printing was performed by Taylor cone jet mode with parameters of 2.4 kV and 0.064 µL/s to obtain uniform thin films at a substrate temperature of 50oC. Much improved TFT properties were obtained, including a mobility of 7.11 cm2/V s, on-to-off current ratio of 2.8 × 106 and subthreshold slope of 1.44 V/dec-1 for ZTO TFT with 5 wt% of PGMEA, and a mobility of 1.43 cm2/V s, on-to-off current ratio of 2.7 × 105 and subthreshold slope of 1.32 V/dec-1 for the ZTO TFT. Almost no hysteresis behavior was observed in the oxide TFTs with added PGMEA. We report a new way to improve the electrical properties of oxide TFTs, by the simple addition of PGMEA.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2023-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47441263","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 : 2023-07-05DOI: 10.3365/kjmm.2023.61.7.472
H. Son, Tae-Min Koo, Young-Hee Cho, Jung-Moo Lee
The effects of Mg content and cooling rate on the T5 treatment of Al-Si-Mg alloys have been investigated using Avrami kinetics and transmission electron microscopy. The alloys were super-heated at 800 oC for 1 hr followed by degassing treatment at 720 oC for 15 min, and poured into a metallic mold preheated to 250 oC. The as-cast alloys were then T5-treated at a temperature of 190 oC. As the Mg content and/or cooling rate increased, the strength of the T5-treated alloys increased while the elongation decreased over the entire aging time. However, some T5 treatment conditions were effective to at enhancinge elongation as well as strength. The alloy with low Mg content showed excellent elongation in the early stage of aging. B, but as the aging time increased, h. However, the elongation decreased rapidly so that there was showed no significant difference from with the alloy with high Mg content in the over-aging stage. This was due to a coarse and agglomerated precipitate structure, which were likely to be formed by the rapid precipitation and agglomeration of the β′ phase. The alloy with a high cooling rate exhibited superior strength with similar elongation over the entire aging time compared to the slowly cooled alloy. The reason for the decrease in strength for in the slowly cooled alloy was attributed to the coarsening of precipitates and suppression of the formation of fine precipitates during cooling.
{"title":"Effect of Mg Content and Cooling Rate After Solidification on the Mechanical Properties of T5-treated Al-Si-Mg Alloy","authors":"H. Son, Tae-Min Koo, Young-Hee Cho, Jung-Moo Lee","doi":"10.3365/kjmm.2023.61.7.472","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.7.472","url":null,"abstract":"The effects of Mg content and cooling rate on the T5 treatment of Al-Si-Mg alloys have been investigated using Avrami kinetics and transmission electron microscopy. The alloys were super-heated at 800 oC for 1 hr followed by degassing treatment at 720 oC for 15 min, and poured into a metallic mold preheated to 250 oC. The as-cast alloys were then T5-treated at a temperature of 190 oC. As the Mg content and/or cooling rate increased, the strength of the T5-treated alloys increased while the elongation decreased over the entire aging time. However, some T5 treatment conditions were effective to at enhancinge elongation as well as strength. The alloy with low Mg content showed excellent elongation in the early stage of aging. B, but as the aging time increased, h. However, the elongation decreased rapidly so that there was showed no significant difference from with the alloy with high Mg content in the over-aging stage. This was due to a coarse and agglomerated precipitate structure, which were likely to be formed by the rapid precipitation and agglomeration of the β′ phase. The alloy with a high cooling rate exhibited superior strength with similar elongation over the entire aging time compared to the slowly cooled alloy. The reason for the decrease in strength for in the slowly cooled alloy was attributed to the coarsening of precipitates and suppression of the formation of fine precipitates during cooling.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2023-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42428756","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 : 2023-07-05DOI: 10.3365/kjmm.2023.61.7.514
Ji-A Lee, Chang-Su Ha, J. Han
Employing post-combustion technology in the converter, using the sensible heat of the hot metal and the oxidation reaction heat as a heat source, is known to compensate for insufficient heat in the converter process. However, most studies on post-combustion have been conducted using subsonic nozzles, whereas actual converter processes use supersonic nozzles. Therefore, research on the combustion behavior of supersonic jets is needed. In this study, experiments and analyses were conducted using a converter simulator and a supersonic nozzle to investigate the effect of nozzle height on the post-combustion behavior. The reaction was set to complete combustion, with an O2gas flow rate of 150 L/min blown through the upper lance and a CO gas flow rate of 300 L/min blown at the bottom of the simulator to represent the surface of the molten metal. The combustion reaction of CO gas was calculated to be rate-controlled by reactant mixing. The nozzle heights were set to 250, 380, and 530 mm from the surface of the molten metal. Post-combustion analysis showed that the lowest gas velocity was observed under the condition of the highest nozzle height of 530 mm, and the high temperature and reaction zones were widely distributed in the lower region. Therefore, to facilitate heat compensation to the molten metal, it is necessary to control the gas velocity of the molten steelgas interface slowly.
{"title":"Effect of Supersonic Oxygen Lance on Post-Combustion in Converter Steelmaking Process – Experiment and Analysis with Converter Simulator","authors":"Ji-A Lee, Chang-Su Ha, J. Han","doi":"10.3365/kjmm.2023.61.7.514","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.7.514","url":null,"abstract":"Employing post-combustion technology in the converter, using the sensible heat of the hot metal and the oxidation reaction heat as a heat source, is known to compensate for insufficient heat in the converter process. However, most studies on post-combustion have been conducted using subsonic nozzles, whereas actual converter processes use supersonic nozzles. Therefore, research on the combustion behavior of supersonic jets is needed. In this study, experiments and analyses were conducted using a converter simulator and a supersonic nozzle to investigate the effect of nozzle height on the post-combustion behavior. The reaction was set to complete combustion, with an O2gas flow rate of 150 L/min blown through the upper lance and a CO gas flow rate of 300 L/min blown at the bottom of the simulator to represent the surface of the molten metal. The combustion reaction of CO gas was calculated to be rate-controlled by reactant mixing. The nozzle heights were set to 250, 380, and 530 mm from the surface of the molten metal. Post-combustion analysis showed that the lowest gas velocity was observed under the condition of the highest nozzle height of 530 mm, and the high temperature and reaction zones were widely distributed in the lower region. Therefore, to facilitate heat compensation to the molten metal, it is necessary to control the gas velocity of the molten steelgas interface slowly.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2023-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44053747","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 : 2023-07-05DOI: 10.3365/kjmm.2023.61.7.480
H. Kim, Dooho Choi
In this study, we fabricated transparent heaters composed of an ultrathin Cu-layer heating element sandwiched between a ZnO underlayer and an Al2O3 overlayer. With the Cu layer thickness fixed at 8.5 nm, the thicknesses of the ZnO and Al2O3 layers were independently varied to reach the optimum antireflecting condition (maximum transmittance of 88.3% and average visible light transmittance of 79.8% were achieved). The sheet resistances for the ZnO/Cu/Al2O3 heaters can be varied by simply modulating the Cu layer thicknesses. In order to assess the flexibility of the transparent heaters, we constructed a ZnO/Cu/Al2O3 structure on flexible polyimide substrates, and the thermal, electrical, optical and mechanical characteristics were evaluated. Because of the planar heating element of the Cu layer, the thermal response was found to be extremely high, i.e., less than 10 s were required to reach 90% of the target temperatures. Once the target temperatures were reached, the heater temperatures were highly stable with no degradation of electrical and optical properties. Furthermore, the heating capability was maintained under severe mechanical deformation, e.g., at a bending radius of 4 mm. The structure also exhibited highly sustainable optoelectronic properties under repetitive mechanical deformation, confirming the potential for commercialization. Finally, we demonstrated that ZnO/Cu/Al2O3 rolled around a human finger exhibited highly uniform heating characteristics, rendering the heaters suitable for wearable, healthcare electronics.
{"title":"Flexible Transparent Planar Heater Comprising ZnO/Cu/Al2O3","authors":"H. Kim, Dooho Choi","doi":"10.3365/kjmm.2023.61.7.480","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.7.480","url":null,"abstract":"In this study, we fabricated transparent heaters composed of an ultrathin Cu-layer heating element sandwiched between a ZnO underlayer and an Al2O3 overlayer. With the Cu layer thickness fixed at 8.5 nm, the thicknesses of the ZnO and Al2O3 layers were independently varied to reach the optimum antireflecting condition (maximum transmittance of 88.3% and average visible light transmittance of 79.8% were achieved). The sheet resistances for the ZnO/Cu/Al2O3 heaters can be varied by simply modulating the Cu layer thicknesses. In order to assess the flexibility of the transparent heaters, we constructed a ZnO/Cu/Al2O3 structure on flexible polyimide substrates, and the thermal, electrical, optical and mechanical characteristics were evaluated. Because of the planar heating element of the Cu layer, the thermal response was found to be extremely high, i.e., less than 10 s were required to reach 90% of the target temperatures. Once the target temperatures were reached, the heater temperatures were highly stable with no degradation of electrical and optical properties. Furthermore, the heating capability was maintained under severe mechanical deformation, e.g., at a bending radius of 4 mm. The structure also exhibited highly sustainable optoelectronic properties under repetitive mechanical deformation, confirming the potential for commercialization. Finally, we demonstrated that ZnO/Cu/Al2O3 rolled around a human finger exhibited highly uniform heating characteristics, rendering the heaters suitable for wearable, healthcare electronics.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2023-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45299830","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 : 2023-07-05DOI: 10.3365/kjmm.2023.61.7.459
Y. Jo, Hui Ju Lee, S. Yi, B. Jang
The degree to which parameters affect the spheroidization heat treatment of steel was calculated by setting the spheroidization heat treatment conditions of Cr-Mo steel and using data analysis such as S/N ratio and ANOVA. After analyzing the transformation temperatures of the steel, Ac1 and Ac3 , using a DSC, the conditions were set accordingly. The surface hardness was measured for the conditions and used as an evaluation index. The correlation was analyzed by comparing the spheroidized volume fraction and the surface hardness, and the Pearson correlation coefficient was -0.88, proving that a correlation existed between the two values. Using S/N ratio and ANOVA, the degree to which each control parameter affects the decrease in the surface hardness was analyzed, qualitatively and quantitatively. For the S/N ratio, priority affecting the surface hardness for each control parameter was analyzed. The 1st heating temperature was found to have a more preferential effect on the surface hardness than the 1st heating time and the 2nd heating temperature. Using ANOVA, the 1st heating temperature was determined to be a very significant factor with the greatest influence, contributing 73.2% to the surface hardness. Intercritical annealing is a suitable spheroidization heat treatment condition, so if the surface hardness of the steel needs to be reduced using Intercritical annealing, the 1st heating temperature and time should be designed as the priority.
{"title":"Spheroidization Heat Treatment Conditions with Data Analysis in Medium Carbon Cr-Mo Steel for Ultra High Strength Cold Heading","authors":"Y. Jo, Hui Ju Lee, S. Yi, B. Jang","doi":"10.3365/kjmm.2023.61.7.459","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.7.459","url":null,"abstract":"The degree to which parameters affect the spheroidization heat treatment of steel was calculated by setting the spheroidization heat treatment conditions of Cr-Mo steel and using data analysis such as S/N ratio and ANOVA. After analyzing the transformation temperatures of the steel, Ac1 and Ac3 , using a DSC, the conditions were set accordingly. The surface hardness was measured for the conditions and used as an evaluation index. The correlation was analyzed by comparing the spheroidized volume fraction and the surface hardness, and the Pearson correlation coefficient was -0.88, proving that a correlation existed between the two values. Using S/N ratio and ANOVA, the degree to which each control parameter affects the decrease in the surface hardness was analyzed, qualitatively and quantitatively. For the S/N ratio, priority affecting the surface hardness for each control parameter was analyzed. The 1st heating temperature was found to have a more preferential effect on the surface hardness than the 1st heating time and the 2nd heating temperature. Using ANOVA, the 1st heating temperature was determined to be a very significant factor with the greatest influence, contributing 73.2% to the surface hardness. Intercritical annealing is a suitable spheroidization heat treatment condition, so if the surface hardness of the steel needs to be reduced using Intercritical annealing, the 1st heating temperature and time should be designed as the priority.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2023-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45637176","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 : 2023-07-05DOI: 10.3365/kjmm.2023.61.7.524
Wontak Shin, Yoon-Jun Kim
A356 cast aluminum alloy contains 7 at.% Si and 0.3 at.% Mg, producing an approximately 50% eutectic microstructure. This high Si content and various casting conditions play a significant role in strengthening A356 alloy, by controlling the eutectic morphology and precipitates of other intermetallic compounds. Understanding how Si-related precipitates and clusters are soluble in the α-matrix is necessary to provide high strength and fatigue resistance to A356 alloys. The aging heat-treatment temperature in the A356 alloy most likely promotes the formation of these precipitates and clusters. The A356 samples were differently aged at temperatures of 110 oC and 130 oC for 2 h, and were labeled 110A, and 130A, respectively. 110A was found to have improved mechanical properties, such as high strength and elongation, compared to 130A, which may be attributed to the formation of secondary phases in the α-phase matrix. Scanning and transmission electron microscopy and atom probe tomography analyses demonstrated Ti2Si precipitation and various-sized cluster formations in 110A. In contrast, 130A had fewer clusters than 110A. Therefore, different aging heat-treatment temperatures relate to a change in the behavior of atoms, affecting the mechanical properties.
{"title":"Microstructural Evolutions and Strengthening Mechanism according to the Aging Temperatures of a High Si Cast Aluminum Alloy","authors":"Wontak Shin, Yoon-Jun Kim","doi":"10.3365/kjmm.2023.61.7.524","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.7.524","url":null,"abstract":"A356 cast aluminum alloy contains 7 at.% Si and 0.3 at.% Mg, producing an approximately 50% eutectic microstructure. This high Si content and various casting conditions play a significant role in strengthening A356 alloy, by controlling the eutectic morphology and precipitates of other intermetallic compounds. Understanding how Si-related precipitates and clusters are soluble in the α-matrix is necessary to provide high strength and fatigue resistance to A356 alloys. The aging heat-treatment temperature in the A356 alloy most likely promotes the formation of these precipitates and clusters. The A356 samples were differently aged at temperatures of 110 oC and 130 oC for 2 h, and were labeled 110A, and 130A, respectively. 110A was found to have improved mechanical properties, such as high strength and elongation, compared to 130A, which may be attributed to the formation of secondary phases in the α-phase matrix. Scanning and transmission electron microscopy and atom probe tomography analyses demonstrated Ti2Si precipitation and various-sized cluster formations in 110A. In contrast, 130A had fewer clusters than 110A. Therefore, different aging heat-treatment temperatures relate to a change in the behavior of atoms, affecting the mechanical properties.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2023-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43341348","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 : 2023-07-05DOI: 10.3365/kjmm.2023.61.7.500
Yuhwan Hwangbo, H. Nam, Sung‐Hoon Choa
Wearable strain sensors with high and broad sensitivity, high stretchability and excellent mechanical endurance will be widely useful in smart wearable electronics. In this work, we developed a stretchable strain sensor fabricated with a simple stencil printing technique. The stretchable strain sensor was fabricated using a multi-walled carbon nanotubes (MWCNTs)-Ecoflex composite paste on an Ecoflex substrate. In particular, using IPA solvent, CNT particles were uniformly dispersed in the Ecoflex binder. The effect of the amount of Ecoflex resin on the stretchability and sensitivity of the sensor were also investigated. It was found that as the amount of Ecoflex resin increased, the stretchability of the sensor increased. The fabricated stretchable strain sensor showed a maximum stretchability of 1,000% with a wide sensitivity range from 3 to 12,287. The hysteresis tests indicated that the hysteresis of the fabricated stretchable strain sensor was very small, the electrical resistances of the sensors quickly returned to original value after tests. The strain sensor showed excellent mechanical durability during cyclic repeated tensile tests of 400,000 cycles. The results of the cross-cut adhesion tests indicated that the adhesion strength between the sensor composite layer and Ecoflex substrate was excellent. We also demonstrated the potential application of the stretchable sensor in wearable electronics by bending tests on a human finger and wrist.
{"title":"Highly Stretchable Strain Sensor with a High and Broad Sensitivity Composed of Carbon Nanotube and Ecoflex Composite","authors":"Yuhwan Hwangbo, H. Nam, Sung‐Hoon Choa","doi":"10.3365/kjmm.2023.61.7.500","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.7.500","url":null,"abstract":"Wearable strain sensors with high and broad sensitivity, high stretchability and excellent mechanical endurance will be widely useful in smart wearable electronics. In this work, we developed a stretchable strain sensor fabricated with a simple stencil printing technique. The stretchable strain sensor was fabricated using a multi-walled carbon nanotubes (MWCNTs)-Ecoflex composite paste on an Ecoflex substrate. In particular, using IPA solvent, CNT particles were uniformly dispersed in the Ecoflex binder. The effect of the amount of Ecoflex resin on the stretchability and sensitivity of the sensor were also investigated. It was found that as the amount of Ecoflex resin increased, the stretchability of the sensor increased. The fabricated stretchable strain sensor showed a maximum stretchability of 1,000% with a wide sensitivity range from 3 to 12,287. The hysteresis tests indicated that the hysteresis of the fabricated stretchable strain sensor was very small, the electrical resistances of the sensors quickly returned to original value after tests. The strain sensor showed excellent mechanical durability during cyclic repeated tensile tests of 400,000 cycles. The results of the cross-cut adhesion tests indicated that the adhesion strength between the sensor composite layer and Ecoflex substrate was excellent. We also demonstrated the potential application of the stretchable sensor in wearable electronics by bending tests on a human finger and wrist.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2023-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45279937","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 : 2023-07-05DOI: 10.3365/kjmm.2023.61.7.534
Sang-Cheol Park, Inyeong Kim, Young Il Kim, Dae-Kyeom Kim, S. Oh, Kee‐Ahn Lee, Bin Lee
The physical properties of metal-based structural materials, such as hardness, strength and toughness, are directly or indirectly affected by residual stress inside or on the surface of the given part. Repeated rapid heating and cooling during the additive manufacturing process causes thermal gradients and expansion and contraction in the material, which causes residual stress. Tensile residual stresses are known to exist on the surface of additive manufactured products and should be kept to a minimum as they affect the mechanical properties and lead to product deformation and product failure. Therefore, it is important to evaluate the residual stress after making the product and to control it under the desired conditions. There are limitations to using the destructive method commonly used for residual stress evaluation with additive manufacturing products, due to difficulties in repeated measurements, product size, and cost issues. Therefore, it is necessary to apply a non-destructive evaluation method and verify the validity of the method. In this study, A356.2 aluminum alloy powders were used for additive manufacturing using the powder bed fusion process, and the surface residual stress generated during the process was measured. X-ray diffraction (XRD) methods were used to observe the surface residual stress. After XRD measurement, analyses were performed using the Williamson-Hall plot, sin2ψ, and cosα methods. The residual stress measurement results of samples manufactured through the LPBF process and the characteristics and limitations of each method were discussed.
{"title":"Residual Stress Analysis of Additive Manufactured A356.2 Aluminum Alloys using X-Ray Diffraction Methods","authors":"Sang-Cheol Park, Inyeong Kim, Young Il Kim, Dae-Kyeom Kim, S. Oh, Kee‐Ahn Lee, Bin Lee","doi":"10.3365/kjmm.2023.61.7.534","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.7.534","url":null,"abstract":"The physical properties of metal-based structural materials, such as hardness, strength and toughness, are directly or indirectly affected by residual stress inside or on the surface of the given part. Repeated rapid heating and cooling during the additive manufacturing process causes thermal gradients and expansion and contraction in the material, which causes residual stress. Tensile residual stresses are known to exist on the surface of additive manufactured products and should be kept to a minimum as they affect the mechanical properties and lead to product deformation and product failure. Therefore, it is important to evaluate the residual stress after making the product and to control it under the desired conditions. There are limitations to using the destructive method commonly used for residual stress evaluation with additive manufacturing products, due to difficulties in repeated measurements, product size, and cost issues. Therefore, it is necessary to apply a non-destructive evaluation method and verify the validity of the method. In this study, A356.2 aluminum alloy powders were used for additive manufacturing using the powder bed fusion process, and the surface residual stress generated during the process was measured. X-ray diffraction (XRD) methods were used to observe the surface residual stress. After XRD measurement, analyses were performed using the Williamson-Hall plot, sin2ψ, and cosα methods. The residual stress measurement results of samples manufactured through the LPBF process and the characteristics and limitations of each method were discussed.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2023-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47348217","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 : 2023-07-05DOI: 10.3365/kjmm.2023.61.7.489
B. Hong, Il-Ho Kim
Cu3Sb1–x–yGexInySe4 (0.02 ≤ x ≤ 0.12; 0.04 ≤ y ≤ 0.08) permingeatite compounds doped with Ge and In were prepared using solid-state synthesis. The phases and microstructures were analyzed, and the charge transport and thermoelectric properties were evaluated according to the Ge and In doping content. Most of the samples contained a single phase of permingeatite with a tetragonal structure; however, secondary phases (Cu0.875InSe2, In2Se3, and InSb) were detected in the samples with x = 0.12 and y = 0.08. Both the a-axis and c-axis lattice constants of permingeatite were increased by Ge and In doping, with a = 0.5651–0.5655 nm and c = 1.1249–1.1255 nm, but the change in lattice constant due to the change in doping amount was insignificant. The melting point of the sample double-doped with Ge and In was determined to be 736 K, which was lower than the melting point (741 K) of pure Cu3SbSe4. This lowering of the melting point was attributed to the formation of a solid solution. The electrical conductivity exhibited degenerate semiconductor behavior, decreasing with increasing temperature. As the Ge and In doping content increased, the carrier concentration and electrical conductivity increased; however, when x ≥ 0.12, the electrical conductivity did not increase further. The Seebeck coefficient exhibited positive values and p-type conduction characteristics. In addition, intrinsic transitions did not occur in the measurement temperature range, and the Seebeck coefficient increased as the doping level increased. The power factor exhibited a positive temperature dependence, and Cu3Sb0.86Ge0.08In0.06Se4 exhibited the highest value of 0.89 mWm–1K–2 at 623 K. As the temperature increased, the thermal conductivity tended to decrease because of the decreased lattice thermal conductivity and slightly increased electronic thermal conductivity. All the samples exhibited minimum thermal conductivities of 0.94–1.11 Wm–1K–1 at 523 K. At high temperatures, the double doping of Ge and In improved the thermoelectric performance; thus, the dimensionless figure of merit obtained at 623 K for Cu3Sb0.86Ge0.08In0.06Se4, was 0.47.
{"title":"Effects of Double Doping Germanium and Indium on the Thermoelectric Properties of Permingeatite","authors":"B. Hong, Il-Ho Kim","doi":"10.3365/kjmm.2023.61.7.489","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.7.489","url":null,"abstract":"Cu3Sb1–x–yGexInySe4 (0.02 ≤ x ≤ 0.12; 0.04 ≤ y ≤ 0.08) permingeatite compounds doped with Ge and In were prepared using solid-state synthesis. The phases and microstructures were analyzed, and the charge transport and thermoelectric properties were evaluated according to the Ge and In doping content. Most of the samples contained a single phase of permingeatite with a tetragonal structure; however, secondary phases (Cu0.875InSe2, In2Se3, and InSb) were detected in the samples with x = 0.12 and y = 0.08. Both the a-axis and c-axis lattice constants of permingeatite were increased by Ge and In doping, with a = 0.5651–0.5655 nm and c = 1.1249–1.1255 nm, but the change in lattice constant due to the change in doping amount was insignificant. The melting point of the sample double-doped with Ge and In was determined to be 736 K, which was lower than the melting point (741 K) of pure Cu3SbSe4. This lowering of the melting point was attributed to the formation of a solid solution. The electrical conductivity exhibited degenerate semiconductor behavior, decreasing with increasing temperature. As the Ge and In doping content increased, the carrier concentration and electrical conductivity increased; however, when x ≥ 0.12, the electrical conductivity did not increase further. The Seebeck coefficient exhibited positive values and p-type conduction characteristics. In addition, intrinsic transitions did not occur in the measurement temperature range, and the Seebeck coefficient increased as the doping level increased. The power factor exhibited a positive temperature dependence, and Cu3Sb0.86Ge0.08In0.06Se4 exhibited the highest value of 0.89 mWm–1K–2 at 623 K. As the temperature increased, the thermal conductivity tended to decrease because of the decreased lattice thermal conductivity and slightly increased electronic thermal conductivity. All the samples exhibited minimum thermal conductivities of 0.94–1.11 Wm–1K–1 at 523 K. At high temperatures, the double doping of Ge and In improved the thermoelectric performance; thus, the dimensionless figure of merit obtained at 623 K for Cu3Sb0.86Ge0.08In0.06Se4, was 0.47.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2023-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42210091","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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