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":" ","pages":""},"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":" ","pages":""},"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":" ","pages":""},"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}
Pub Date : 2023-07-05DOI: 10.3365/kjmm.2023.61.7.509
Geun-Hyoung Lee
MgO nanowires were grown by a thermal evaporation method at different N2/O2 gas ratios in order to investigate the effect of oxygen concentration on the growth and luminescence properties of the MgO nanowires. A thermal evaporation process was conducted at 1000oC and under a pressure of 500Torr. No nanowires were grown in a pure N2 gas atmosphere. Nanowires were formed at oxygen concentrations above 25% in a mixture of N2 and O2 gases. X-ray diffraction analysis showed that the MgO nanowires had a cubic crystal structure. Compared to the nanowires formed at high oxygen concentration, the nanowires grown at low oxygen concentration had larger diameters and rougher side surfaces. Nanowires with very smooth side surfaces were formed at high oxygen concentrations. The difference in surface roughness was supposed to be due to the change in the growth habit of nuclei. Two visible emissions were observed in the cathodoluminescence spectra of the MgO nanowires. One was an emission peak centered near 400 nm and the other was an emission peak with a central wavelength of 500 nm. As the oxygen concentration increased, the emission intensity of the 400 nm band decreased and the emission intensity of the 500 nm band increased. The maximum emission at 500 nm was observed from the nanowires formed in a pure O2 atmosphere. The full width at half maximum of the emission peak at 500 nm was narrower than that of the emission peak at 400 nm.
{"title":"Effect of Oxygen Concentration on the Growth and Cathodoluminescence Properties of MgO Nanowires","authors":"Geun-Hyoung Lee","doi":"10.3365/kjmm.2023.61.7.509","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.7.509","url":null,"abstract":"MgO nanowires were grown by a thermal evaporation method at different N2/O2 gas ratios in order to investigate the effect of oxygen concentration on the growth and luminescence properties of the MgO nanowires. A thermal evaporation process was conducted at 1000oC and under a pressure of 500Torr. No nanowires were grown in a pure N2 gas atmosphere. Nanowires were formed at oxygen concentrations above 25% in a mixture of N2 and O2 gases. X-ray diffraction analysis showed that the MgO nanowires had a cubic crystal structure. Compared to the nanowires formed at high oxygen concentration, the nanowires grown at low oxygen concentration had larger diameters and rougher side surfaces. Nanowires with very smooth side surfaces were formed at high oxygen concentrations. The difference in surface roughness was supposed to be due to the change in the growth habit of nuclei. Two visible emissions were observed in the cathodoluminescence spectra of the MgO nanowires. One was an emission peak centered near 400 nm and the other was an emission peak with a central wavelength of 500 nm. As the oxygen concentration increased, the emission intensity of the 400 nm band decreased and the emission intensity of the 500 nm band increased. The maximum emission at 500 nm was observed from the nanowires formed in a pure O2 atmosphere. The full width at half maximum of the emission peak at 500 nm was narrower than that of the emission peak at 400 nm.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":" ","pages":""},"PeriodicalIF":1.2,"publicationDate":"2023-07-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44272134","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 : 2023-06-05DOI: 10.3365/kjmm.2023.61.6.414
C. Jin, Sangwoo Kim, Dong Eung Kim, A. Mirzaei, J. Roh, Sun-Woo Choi, Myung Sik Choi
Dihydrogen sulfide (H2S) gas has a flammable nature and is one of the most toxic and dangerous gases. Even small concentrations can be fatal to humans. Herein, we investigated the H2S gas-sensing features of commercial pristine cerium oxide (CeO2 ) and gadolinium (Gd)-doped CeO2 (GDC) nanoparticles. First, the sensing materials were well-characterized using various methods including X-ray photoelectron spectroscopy, transmission electron microscopy and X-ray diffraction to gain insight into their chemical composition, morphology, phases, and crystallinity, respectively. In the next step, gas sensors were fabricated using a top electrode (Au/Ti) configuration. Preliminary H2S-gas-sensing studies revealed that GDC gas sensor had a superior gas response to H2S gas than the pristine CeO2 gas sensor at 350°C. The responses of the pristine CeO2 gas sensor to 20 ppm H2S gas was 1.542, while the response of the GDC gas sensor to the aforementioned H2S concentration was 3.489. In addition, the GDC sensor exhibited good selectivity to H2S gas among C2H5OH, C7H8 and NH3 gases. Also, we investigated the response of the sensor in up to 60% relative humidity. The enhanced response of the GDC gas sensor to H2S gas was mainly related to the formation of oxygen defects as a result of Gd-doping in CeO2 . Also, good selectivity to H2S was related to the sensing temperature, the higher reactivity of H2S relative to other gases and the small bond energy of H-SH. This study demonstrates the promising ability of Gd-doping to enhance the H2S gas-sensing characteristics of CeO2 , which can be applied to other similar systems based on semiconducting metal oxides.
{"title":"Gadolinium-Doped CeO2 Gas Sensor for H2S Sensing","authors":"C. Jin, Sangwoo Kim, Dong Eung Kim, A. Mirzaei, J. Roh, Sun-Woo Choi, Myung Sik Choi","doi":"10.3365/kjmm.2023.61.6.414","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.6.414","url":null,"abstract":"Dihydrogen sulfide (H<sub>2</sub>S) gas has a flammable nature and is one of the most toxic and dangerous gases. Even small concentrations can be fatal to humans. Herein, we investigated the H<sub>2</sub>S gas-sensing features of commercial pristine cerium oxide (CeO<sub>2</sub> ) and gadolinium (Gd)-doped CeO<sub>2</sub> (GDC) nanoparticles. First, the sensing materials were well-characterized using various methods including X-ray photoelectron spectroscopy, transmission electron microscopy and X-ray diffraction to gain insight into their chemical composition, morphology, phases, and crystallinity, respectively. In the next step, gas sensors were fabricated using a top electrode (Au/Ti) configuration. Preliminary H<sub>2</sub>S-gas-sensing studies revealed that GDC gas sensor had a superior gas response to H<sub>2</sub>S gas than the pristine CeO<sub>2</sub> gas sensor at 350°C. The responses of the pristine CeO<sub>2</sub> gas sensor to 20 ppm H<sub>2</sub>S gas was 1.542, while the response of the GDC gas sensor to the aforementioned H<sub>2</sub>S concentration was 3.489. In addition, the GDC sensor exhibited good selectivity to H<sub>2</sub>S gas among C<sub>2</sub>H<sub>5</sub>OH, C<sub>7</sub>H<sub>8</sub> and NH<sub>3</sub> gases. Also, we investigated the response of the sensor in up to 60% relative humidity. The enhanced response of the GDC gas sensor to H<sub>2</sub>S gas was mainly related to the formation of oxygen defects as a result of Gd-doping in CeO<sub>2</sub> . Also, good selectivity to H<sub>2</sub>S was related to the sensing temperature, the higher reactivity of H<sub>2</sub>S relative to other gases and the small bond energy of H-SH. This study demonstrates the promising ability of Gd-doping to enhance the H<sub>2</sub>S gas-sensing characteristics of CeO<sub>2</sub> , which can be applied to other similar systems based on semiconducting metal oxides.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":" ","pages":""},"PeriodicalIF":1.2,"publicationDate":"2023-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47200656","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 : 2023-06-05DOI: 10.3365/kjmm.2023.61.6.444
Geun-Hyoung Lee
MgO nanowires with a branched structure were fabricated using a thermal evaporation method in air at atmospheric pressure. The branched MgO nanowire was made up of two parts: a primary central nanowire trunk and lots of secondary nanowire branches. The branched MgO nanowires had a 4-fold symmetrical structure. The secondary nanowire branches grew perpendicular on the four side facets of the central nanowire trunks with square cross-sections. The nanowire branches also grew in a single row and were vertically well aligned in the same direction with each other. The scanning electron microscopy images of the branched nanowires grown at 1000oC showed that the diameter of branches gradually decreased along the growth direction and no catalyst particle was found at the tips of the branches, indicating that the branches were grown by a vapor-solid process. For the branched nanowires grown at 1150oC, spherical particles which were shown to be catalysts were observed at the tips of the branches. The chemical analysis by energy dispersive spectroscopy showed that the spherical particles were composed of Mg and O elements. These results suggest that the branches’ growth resulted from a self-catalyzed vapor-liquid-solid process. The structural characterization by X-ray diffraction confirmed that the branched MgO nanowires had a cubic lattice structure. The room temperature cathodoluminescence spectra of the branched MgO nanowires exhibited a very strong visible emission which was associated with oxygen vacancies.
{"title":"Branched MgO Nanowires Synthesized by Thermal Evaporation Method in Air at Atmospheric Pressure","authors":"Geun-Hyoung Lee","doi":"10.3365/kjmm.2023.61.6.444","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.6.444","url":null,"abstract":"MgO nanowires with a branched structure were fabricated using a thermal evaporation method in air at atmospheric pressure. The branched MgO nanowire was made up of two parts: a primary central nanowire trunk and lots of secondary nanowire branches. The branched MgO nanowires had a 4-fold symmetrical structure. The secondary nanowire branches grew perpendicular on the four side facets of the central nanowire trunks with square cross-sections. The nanowire branches also grew in a single row and were vertically well aligned in the same direction with each other. The scanning electron microscopy images of the branched nanowires grown at 1000oC showed that the diameter of branches gradually decreased along the growth direction and no catalyst particle was found at the tips of the branches, indicating that the branches were grown by a vapor-solid process. For the branched nanowires grown at 1150oC, spherical particles which were shown to be catalysts were observed at the tips of the branches. The chemical analysis by energy dispersive spectroscopy showed that the spherical particles were composed of Mg and O elements. These results suggest that the branches’ growth resulted from a self-catalyzed vapor-liquid-solid process. The structural characterization by X-ray diffraction confirmed that the branched MgO nanowires had a cubic lattice structure. The room temperature cathodoluminescence spectra of the branched MgO nanowires exhibited a very strong visible emission which was associated with oxygen vacancies.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":" ","pages":""},"PeriodicalIF":1.2,"publicationDate":"2023-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44021837","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 : 2023-06-05DOI: 10.3365/kjmm.2023.61.6.437
S. Joo, J. Son, Jeongin Jang, B. Min, Bong-Seo Kim
Mg3Sb2-based materials are very promising for thermoelectric applications at low temperatures, and are strong candidates to replace n-type Bi2Te3 for cooling and power generation. Substituting Sb atoms with chalcogen elements (S, Se, Te) is a typical method of n-type doping, while doping the Mg site with Group 3 elements (Y, Sc) and Lanthanides has also been studied. Unique advantages have been recently reported. In this study, a La-containing compound, LaSb, was used to fabricate n-type Mg3SbBi. The thermoelectric properties of polycrystalline Mg3LaxSbBi (0 ≤ x ≤ 0.02) were investigated after synthesis by sequential processes of arc melting, ball milling, and spark plasma sintering. Undoped Mg3SbBi is p-type with poor thermoelectric performance, and switched to n-type with La doping. The electron concentration of Mg3LaxSbBi increased linearly with La content x, reaching up to 9.4 × 1019 cm-3 at x = 0.02. The power factor and the figure of merit were also maximized in Mg3La0.02SbBi, reaching 1.8 mW m-1K-2 (573 K) and 0.89 (623 K), respectively. The lattice thermal conductivity decreased with increasing La content above ~500 K, and the minimum value of 0.73 W m-1K-1 was obtained in Mg3La0.02SbBi. This study shows that La doping using LaSb provides a reliable method for n-type doping of Mg3Sb2-based materials.
{"title":"Synthesis and Thermoelectric Properties of La-doped n-type Mg3SbBi Materials","authors":"S. Joo, J. Son, Jeongin Jang, B. Min, Bong-Seo Kim","doi":"10.3365/kjmm.2023.61.6.437","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.6.437","url":null,"abstract":"Mg<sub>3</sub>Sb<sub>2</sub>-based materials are very promising for thermoelectric applications at low temperatures, and are strong candidates to replace n-type Bi<sub>2</sub>Te<sub>3</sub> for cooling and power generation. Substituting Sb atoms with chalcogen elements (S, Se, Te) is a typical method of n-type doping, while doping the Mg site with Group 3 elements (Y, Sc) and Lanthanides has also been studied. Unique advantages have been recently reported. In this study, a La-containing compound, LaSb, was used to fabricate n-type Mg<sub>3</sub>SbBi. The thermoelectric properties of polycrystalline Mg<sub>3</sub>La<sub>x</sub>SbBi (0 ≤ <i>x</i> ≤ 0.02) were investigated after synthesis by sequential processes of arc melting, ball milling, and spark plasma sintering. Undoped Mg<sub>3</sub>SbBi is p-type with poor thermoelectric performance, and switched to n-type with La doping. The electron concentration of Mg<sub>3</sub>La<sub>x</sub>SbBi increased linearly with La content <i>x</i>, reaching up to 9.4 × 10<sup>19</sup> cm<sup>-3</sup> at <i>x</i> = 0.02. The power factor and the figure of merit were also maximized in Mg<sub>3</sub>La<sub>0.02</sub>SbBi, reaching 1.8 mW m<sup>-1</sup>K<sup>-2</sup> (573 K) and 0.89 (623 K), respectively. The lattice thermal conductivity decreased with increasing La content above ~500 K, and the minimum value of 0.73 W m<sup>-1</sup>K<sup>-1</sup> was obtained in Mg<sub>3</sub>La<sub>0.02</sub>SbBi. This study shows that La doping using LaSb provides a reliable method for n-type doping of Mg<sub>3</sub>Sb<sub>2</sub>-based materials.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":" ","pages":""},"PeriodicalIF":1.2,"publicationDate":"2023-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47149362","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 : 2023-06-05DOI: 10.3365/kjmm.2023.61.6.397
Seung-Ho Lee, J. Yoon, Du-rim Eo, S. Yeon, Kyun Choi
17-4 precipitation hardened stainless steel (17-4PH SS) has been reported to have excellent mechanical properties and excellent corrosion resistance, and is one of the materials used and studied with the powder bed fusion (PBF) method. Powder bed fusion (PBF) is a new manufacturing technology that has recently attracted attention in automotive, aerospace and other industries because of its ability to produce complex geometries for high-strength and lightweight applications. In the PBF process, each layer has a different laser scan length resulting from the application of laser rotation. The laser rotation could affect the laser scan length, which causes a difference in the peak temperature and cooling rate of the deposited layer, resulting in microstructure changes. This work aims to investigate how varying the laser scan pattern in the PBF process affects the microstructure and mechanical properties of 17-4PH SS. A decrease in cooling rate was observed after applying laser scan rotation, resulting in a higher austenite phase fraction. It was confirmed that a transformation induced plasticity (TRIP) phenomenon affects mechanical characteristics. These results could be suggested for fabricating thin wall shaped such as tire blow mold parts in the powder bed fusion process using the 17-4PH SS.
{"title":"Changes in Microstructure and Mechanical Properties of 17-4PH Stainless Steel according to the Application of Laser Rotation in the Powder Bed Fusion(PBF) Process","authors":"Seung-Ho Lee, J. Yoon, Du-rim Eo, S. Yeon, Kyun Choi","doi":"10.3365/kjmm.2023.61.6.397","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.6.397","url":null,"abstract":"17-4 precipitation hardened stainless steel (17-4PH SS) has been reported to have excellent mechanical properties and excellent corrosion resistance, and is one of the materials used and studied with the powder bed fusion (PBF) method. Powder bed fusion (PBF) is a new manufacturing technology that has recently attracted attention in automotive, aerospace and other industries because of its ability to produce complex geometries for high-strength and lightweight applications. In the PBF process, each layer has a different laser scan length resulting from the application of laser rotation. The laser rotation could affect the laser scan length, which causes a difference in the peak temperature and cooling rate of the deposited layer, resulting in microstructure changes. This work aims to investigate how varying the laser scan pattern in the PBF process affects the microstructure and mechanical properties of 17-4PH SS. A decrease in cooling rate was observed after applying laser scan rotation, resulting in a higher austenite phase fraction. It was confirmed that a transformation induced plasticity (TRIP) phenomenon affects mechanical characteristics. These results could be suggested for fabricating thin wall shaped such as tire blow mold parts in the powder bed fusion process using the 17-4PH SS.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":" ","pages":""},"PeriodicalIF":1.2,"publicationDate":"2023-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42496539","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 : 2023-06-05DOI: 10.3365/kjmm.2023.61.6.431
H. Cho, Taewan Kim, Seung-Min Kang, Sang‐Yeup Park, Sang‐il Kim
The addition of Cu to layered Bi2Te3-based thermoelectric alloys has been studied as an effective way to enhance thermoelectric transport properties. In this study, the influence of adding Cu to Bi2Se3 alloys, which have the same rhombohedral crystal structure as Bi2Te3, was investigated by synthesizing a series of CuxBi2Se3 (x = 0, 0.004, 0.008, 0.012, and 0.016) alloys. The power factors of all the Cu-added samples were enhanced compared with that of the pristine Bi2Se3 sample, primarily because of the increase in electrical conductivity. The power factor for the Cu0.016Bi2Se3 sample (x = 0.016) was 0.80 mW/mK2, a 35% increase compared to 0.59 mW/mK2 for the pristine sample at 520 K. A decrease in the total and lattice thermal conductivity was observed for the Cu-added samples, caused by additional point defect scattering after doping. The lattice thermal conductivity of the Cu0.016Bi2Se3 sample (x = 0.016) was 0.56 W/mK, a 42% reduction. Consequently, the zT values of all the Cu-added samples were enhanced, and the maximum zT value was 0.38 for the Cu0.016Bi2Se3 sample (x = 0.016) at 520 K, a 48% increase compared to that of pristine Bi2Se3. The phenomenological transport parameters, including density of state, effective mass, weighted mobility, and thermoelectric quality factor, were calculated to analyze the enhanced electronic transport properties of the Cu-added Bi2Se3.
{"title":"Enhanced Thermoelectric Transport Properties in Cu-added Bi2Se3 Polycrystalline Alloys","authors":"H. Cho, Taewan Kim, Seung-Min Kang, Sang‐Yeup Park, Sang‐il Kim","doi":"10.3365/kjmm.2023.61.6.431","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.6.431","url":null,"abstract":"The addition of Cu to layered Bi<sub>2</sub>Te<sub>3</sub>-based thermoelectric alloys has been studied as an effective way to enhance thermoelectric transport properties. In this study, the influence of adding Cu to Bi<sub>2</sub>Se<sub>3</sub> alloys, which have the same rhombohedral crystal structure as Bi<sub>2</sub>Te<sub>3</sub>, was investigated by synthesizing a series of Cu<sub>x</sub>Bi<sub>2</sub>Se<sub>3</sub> (<i>x</i> = 0, 0.004, 0.008, 0.012, and 0.016) alloys. The power factors of all the Cu-added samples were enhanced compared with that of the pristine Bi<sub>2</sub>Se<sub>3</sub> sample, primarily because of the increase in electrical conductivity. The power factor for the Cu<sub>0.016</sub>Bi<sub>2</sub>Se<sub>3</sub> sample (<i>x</i> = 0.016) was 0.80 mW/mK<sup>2</sup>, a 35% increase compared to 0.59 mW/mK<sup>2</sup> for the pristine sample at 520 K. A decrease in the total and lattice thermal conductivity was observed for the Cu-added samples, caused by additional point defect scattering after doping. The lattice thermal conductivity of the Cu<sub>0.016</sub>Bi<sub>2</sub>Se<sub>3</sub> sample (<i>x</i> = 0.016) was 0.56 W/mK, a 42% reduction. Consequently, the zT values of all the Cu-added samples were enhanced, and the maximum zT value was 0.38 for the Cu<sub>0.016</sub>Bi<sub>2</sub>Se<sub>3</sub> sample (<i>x</i> = 0.016) at 520 K, a 48% increase compared to that of pristine Bi<sub>2</sub>Se<sub>3</sub>. The phenomenological transport parameters, including density of state, effective mass, weighted mobility, and thermoelectric quality factor, were calculated to analyze the enhanced electronic transport properties of the Cu-added Bi<sub>2</sub>Se<sub>3</sub>.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":" ","pages":""},"PeriodicalIF":1.2,"publicationDate":"2023-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42145036","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 : 2023-06-05DOI: 10.3365/kjmm.2023.61.6.389
Young-Kyun Kim, K. Lim, Y. Na
Materials with superior cryogenic strength and good ductility are increasingly in demand for resident friendly liquid-hydrogen (20K) storage tanks. Additionally, the space industry also requires materials that retain excellent mechanical properties at extremely low temperatures. However, mechanical testing at such low temperatures is highly limited due to the difficulties in achieving and maintaining such conditions, while also providing adequate thermal insulation to prevent heat transfer from the surrounding environment. In this study, we present a novel tensile testing technique for a Fe-15Mn-13Cr-3Si-3Ni-0.1C (wt.%) steel at the temperature of liquid helium. To minimize the use of expensive liquid helium, we adopted a method of injecting liquid helium vapor and set the temperature for tensile testing at 6 K. The present alloy has a single face-centered cubic (FCC) structure with a large amount of stacking faults after annealing treatment. The Fe-Mn-Cr steel exhibited a superior ultimate tensile strength of 1200 MPa and good ductility of 35% at 6K. Moreover, compared with room temperature tensile tests, discontinuous plastic flow, i.e. serrated flow, occurred at extremely low temperature.
{"title":"Tensile testing at the Extremely Low Temperature of 6K : Microstructure and Mechanical Properties of a Fe-Mn-Cr Steel","authors":"Young-Kyun Kim, K. Lim, Y. Na","doi":"10.3365/kjmm.2023.61.6.389","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.6.389","url":null,"abstract":"Materials with superior cryogenic strength and good ductility are increasingly in demand for resident friendly liquid-hydrogen (20K) storage tanks. Additionally, the space industry also requires materials that retain excellent mechanical properties at extremely low temperatures. However, mechanical testing at such low temperatures is highly limited due to the difficulties in achieving and maintaining such conditions, while also providing adequate thermal insulation to prevent heat transfer from the surrounding environment. In this study, we present a novel tensile testing technique for a Fe-15Mn-13Cr-3Si-3Ni-0.1C (wt.%) steel at the temperature of liquid helium. To minimize the use of expensive liquid helium, we adopted a method of injecting liquid helium vapor and set the temperature for tensile testing at 6 K. The present alloy has a single face-centered cubic (FCC) structure with a large amount of stacking faults after annealing treatment. The Fe-Mn-Cr steel exhibited a superior ultimate tensile strength of 1200 MPa and good ductility of 35% at 6K. Moreover, compared with room temperature tensile tests, discontinuous plastic flow, i.e. serrated flow, occurred at extremely low temperature.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":" ","pages":""},"PeriodicalIF":1.2,"publicationDate":"2023-06-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48800872","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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