Pub Date : 2024-01-05DOI: 10.3365/kjmm.2024.62.1.22
Kyeong-Min Kim, Yejin Jeong, D.V. Kiran, Suk-Hwan Kwon, Seong-Moon Seo, Eun-Joon Chun
Single-crystal superalloys have been popularly employed in high-temperature parts of gas turbines, such as blades. However, the welds of such alloys are highly susceptible to solidification cracking, which limits their applicability to high-temperature turbine blades. In this study, the effects of characteristics of weld solidification on solidification cracking susceptibilities (solidification brittle temperature range, BTR) were fundamentally investigated for the CMSX-4 single-crystal superalloy. We applied a transverse-Varestraint test procedure for both the linear and oscillated arc welds by changing the weld solidification characteristics, such as the degree of single crystal growth and formation of solidification grain boundaries. The BTR for the CMSX-4 alloy is 336 K for linear welding condition, whereas the values are 434 K and 342 K for 0.6 and 1.5 Hz oscillated welds. Interestingly, the BTR continuously increases with the weld oscillation frequency. By contrast, almost no changes in the weld mushy-zone temperature range are theoretically calculated for each welding condition via the diffusion-controlled Scheil model. The mechanism underlying the increase in BTR under oscillation welding is clarified based on the relationship between the achievement ratio of the weld single crystal growth and fraction of high-angle (>15o) solidification boundaries, which affect severe dendrite coalescence undercooling. The lower fraction of the high-angle weld solidification grain boundaries attributed to the superior achievement ratio of weld single crystal growth, which reduces the dendrite coalescence undercooling and BTR. Consequently, it enhances the solidification crack propagation resistance.
{"title":"Effect of Single Crystal Growth and Solidification Grain Boundaries on Weld Solidification Cracking Behavior of CMSX-4 Superalloy","authors":"Kyeong-Min Kim, Yejin Jeong, D.V. Kiran, Suk-Hwan Kwon, Seong-Moon Seo, Eun-Joon Chun","doi":"10.3365/kjmm.2024.62.1.22","DOIUrl":"https://doi.org/10.3365/kjmm.2024.62.1.22","url":null,"abstract":"Single-crystal superalloys have been popularly employed in high-temperature parts of gas turbines, such as blades. However, the welds of such alloys are highly susceptible to solidification cracking, which limits their applicability to high-temperature turbine blades. In this study, the effects of characteristics of weld solidification on solidification cracking susceptibilities (solidification brittle temperature range, BTR) were fundamentally investigated for the CMSX-4 single-crystal superalloy. We applied a transverse-Varestraint test procedure for both the linear and oscillated arc welds by changing the weld solidification characteristics, such as the degree of single crystal growth and formation of solidification grain boundaries. The BTR for the CMSX-4 alloy is 336 K for linear welding condition, whereas the values are 434 K and 342 K for 0.6 and 1.5 Hz oscillated welds. Interestingly, the BTR continuously increases with the weld oscillation frequency. By contrast, almost no changes in the weld mushy-zone temperature range are theoretically calculated for each welding condition via the diffusion-controlled Scheil model. The mechanism underlying the increase in BTR under oscillation welding is clarified based on the relationship between the achievement ratio of the weld single crystal growth and fraction of high-angle (>15o) solidification boundaries, which affect severe dendrite coalescence undercooling. The lower fraction of the high-angle weld solidification grain boundaries attributed to the superior achievement ratio of weld single crystal growth, which reduces the dendrite coalescence undercooling and BTR. Consequently, it enhances the solidification crack propagation resistance.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2024-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139381277","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-05DOI: 10.3365/kjmm.2024.62.1.12
Byeong Jo Han, Sang Ho Cho, Kang Rok Jeon, Jong-Hyun Lee
To ensure the high-temperature stability of a bondline under next-generation power devices such as SiC semiconductors, a die bonding test was performed by transient liquid-phase (TLP) sinter-bonding using a Sn-coated Cu (Cu@Sn) particle-based preform. Compared to the existing 20 min-bonding result using a 30 μm Cu@Sn particle-based preform, a 5 μm Cu@Sn particle-based preform was used to significantly reduce the bonding time to 5 min, and the optimal levels of the amount of Sn in the Cu@Sn particles, the thicknesses of Sn surface finish layers on the chip and substrate, and compression pressure during the bonding were investigated. The Sn content in the Cu@Sn particles significantly changed the microstructure, including the porosity of the prepared preform. The preform porosity of 0.01% was confirmed after the formation of sufficient Sn shells with an average thickness of about 602 nm at Sn 30 wt%. In addition, in the preform with Sn 30 wt% content, the Sn phase was almost depleted after 3 min after annealing at 250 °C. The Sn finish layer was evaluated in the thickness range of 0.63−4.12 µm, and it was observed that the shear strength of the formed bondline tended to increase with increasing pressure for all Sn layer thicknesses. In particular, when the bonding was carried out at a pressure of 2 MPa using a dummy Cu chip and substrate coated with a 1.53 μm thick Sn layer, the best shear strength value of 36.89 MPa was achieved. In this case, all the Sn phases transformed into intermetallic compound phases of Cu6Sn5 and Cu3Sn, and all the phases formed within the bondline, including Cu, exhibited high melting-point characteristics. Therefore, it was determined that there would be no remelting of the bondline or a drastic decrease in mechanical properties in a high-temperature environment below 300 oC, as initially intended. By increasing the content of the Sn shell up to 30 wt%, it was possible to achieve a nearly full density (porosity: 0.3%) bondline structure, due to the rearrangement behavior of particles, by maintaining liquid Sn for a long time during the bonding process. In conclusion, the optimal Sn finish thickness was determined to be at the level of 1.5 µm, and the optimal pressure was at the level of 2 MPa. The short bonding time of 5 min represents a significant advance in TLP bonding processes, and it is expected to contribute to a substantial improvement in the die bonding of future SiC power devices.
{"title":"Transient Liquid-Phase Sinter-Bonding Characteristics of a 5 um Cu@Sn Particle-Based Preform for High-Speed Die Bonding of Power Devices","authors":"Byeong Jo Han, Sang Ho Cho, Kang Rok Jeon, Jong-Hyun Lee","doi":"10.3365/kjmm.2024.62.1.12","DOIUrl":"https://doi.org/10.3365/kjmm.2024.62.1.12","url":null,"abstract":"To ensure the high-temperature stability of a bondline under next-generation power devices such as SiC semiconductors, a die bonding test was performed by transient liquid-phase (TLP) sinter-bonding using a Sn-coated Cu (Cu@Sn) particle-based preform. Compared to the existing 20 min-bonding result using a 30 μm Cu@Sn particle-based preform, a 5 μm Cu@Sn particle-based preform was used to significantly reduce the bonding time to 5 min, and the optimal levels of the amount of Sn in the Cu@Sn particles, the thicknesses of Sn surface finish layers on the chip and substrate, and compression pressure during the bonding were investigated. The Sn content in the Cu@Sn particles significantly changed the microstructure, including the porosity of the prepared preform. The preform porosity of 0.01% was confirmed after the formation of sufficient Sn shells with an average thickness of about 602 nm at Sn 30 wt%. In addition, in the preform with Sn 30 wt% content, the Sn phase was almost depleted after 3 min after annealing at 250 °C. The Sn finish layer was evaluated in the thickness range of 0.63−4.12 µm, and it was observed that the shear strength of the formed bondline tended to increase with increasing pressure for all Sn layer thicknesses. In particular, when the bonding was carried out at a pressure of 2 MPa using a dummy Cu chip and substrate coated with a 1.53 μm thick Sn layer, the best shear strength value of 36.89 MPa was achieved. In this case, all the Sn phases transformed into intermetallic compound phases of Cu6Sn5 and Cu3Sn, and all the phases formed within the bondline, including Cu, exhibited high melting-point characteristics. Therefore, it was determined that there would be no remelting of the bondline or a drastic decrease in mechanical properties in a high-temperature environment below 300 oC, as initially intended. By increasing the content of the Sn shell up to 30 wt%, it was possible to achieve a nearly full density (porosity: 0.3%) bondline structure, due to the rearrangement behavior of particles, by maintaining liquid Sn for a long time during the bonding process. In conclusion, the optimal Sn finish thickness was determined to be at the level of 1.5 µm, and the optimal pressure was at the level of 2 MPa. The short bonding time of 5 min represents a significant advance in TLP bonding processes, and it is expected to contribute to a substantial improvement in the die bonding of future SiC power devices.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2024-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139381796","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-05DOI: 10.3365/kjmm.2024.62.1.1
Hyun-Uk Jun, Jae-Hun Kim, Wonho Kim, Jooyong Cheon, Ki-Man Bae, Eun-Kyung Lee, Yeong-Do Park, Changwook Ji
This study was performed to compare the resistance spot weldability of Al 5052-H32 alloy and Al 6014-T4 alloy, and the cause of the differences in the weldability was investigated. In general, the surface of the aluminum alloy has an oxide film several nm thick, and local heat input is generated at the electrode-sheet interface and the sheet-sheet interface during resistance spot welding. XPS analysis proved that the Al 5052- H32 alloy has a relatively thick magnesium oxide film on the surface and contains a large amount of magnesium solute element. As a result, Al 5052-H32 has a higher resistance, in both the contact resistance of the electrodesheet interface and sheet-sheet interface, compared with the Al 6014-T4 alloy. Therefore, the Al 5052-H32 alloy has a larger nugget diameter at the same welding current as compared to the Al 6014-T4 alloy, but the surface contamination of the electrode is aggravated due to local heat input. The results indicated that a difference in oxide film type and thickness can significantly influence resistance heat generation and electrode cooling effects, as well as produce welds with different weld morphology and microstructure. In addition, the Al 5052-H32 alloy had more pores and shrinkage in the weld than Al 6014-T4 alloy, and longitudinal cracks were observed in the center of the nugget, but had relatively excellent mechanical properties.
本研究对 Al 5052-H32 合金和 Al 6014-T4 合金的电阻点焊性进行了比较，并探究了焊接性差异的原因。一般来说，铝合金表面有一层数 nm 厚的氧化膜，电阻点焊时在电极-薄板界面和薄板-薄板界面会产生局部热输入。XPS 分析证明，Al 5052- H32 合金表面有一层较厚的氧化镁膜，并含有大量的镁溶质元素。因此，与 Al 6014-T4 合金相比，Al 5052-H32 在电极板界面和板-板界面的接触电阻方面都具有更高的电阻。因此，与 Al 6014-T4 合金相比，在相同的焊接电流下，Al 5052-H32 合金的金块直径更大，但由于局部热输入，电极表面污染加剧。结果表明，氧化膜类型和厚度的不同会显著影响电阻发热和电极冷却效果，并产生不同焊接形态和微观结构的焊缝。此外，与 Al 6014-T4 合金相比，Al 5052-H32 合金在焊缝中具有更多的气孔和收缩，并在焊块中心观察到纵向裂纹，但具有相对优异的机械性能。
{"title":"Comparison of Weldability and Microstructure in Resistance Spot Welding of Aluminum 5052-H32 Alloy and Al 6014-T4 Alloy","authors":"Hyun-Uk Jun, Jae-Hun Kim, Wonho Kim, Jooyong Cheon, Ki-Man Bae, Eun-Kyung Lee, Yeong-Do Park, Changwook Ji","doi":"10.3365/kjmm.2024.62.1.1","DOIUrl":"https://doi.org/10.3365/kjmm.2024.62.1.1","url":null,"abstract":"This study was performed to compare the resistance spot weldability of Al 5052-H32 alloy and Al 6014-T4 alloy, and the cause of the differences in the weldability was investigated. In general, the surface of the aluminum alloy has an oxide film several nm thick, and local heat input is generated at the electrode-sheet interface and the sheet-sheet interface during resistance spot welding. XPS analysis proved that the Al 5052- H32 alloy has a relatively thick magnesium oxide film on the surface and contains a large amount of magnesium solute element. As a result, Al 5052-H32 has a higher resistance, in both the contact resistance of the electrodesheet interface and sheet-sheet interface, compared with the Al 6014-T4 alloy. Therefore, the Al 5052-H32 alloy has a larger nugget diameter at the same welding current as compared to the Al 6014-T4 alloy, but the surface contamination of the electrode is aggravated due to local heat input. The results indicated that a difference in oxide film type and thickness can significantly influence resistance heat generation and electrode cooling effects, as well as produce welds with different weld morphology and microstructure. In addition, the Al 5052-H32 alloy had more pores and shrinkage in the weld than Al 6014-T4 alloy, and longitudinal cracks were observed in the center of the nugget, but had relatively excellent mechanical properties.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2024-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139382434","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-05DOI: 10.3365/kjmm.2024.62.1.32
Jeonyoung Song, Jiho Gu, Won Hui Jo, Cho Hyeon Lee, Jae Bok Seol, Youngwha Ma
Here, we investigated the influence of δ-precipitate (orthorhombic D0a Ni3Nb-ordered phase) on the room- and high-temperature tensile properties in wrought nickel-based Inconel 625 superalloys subjected to solution and aging heat treatment. Typically, solution heat-treatment temperatures in these alloys affect the solid-state precipitation of δ-phase, which governs high-temperature tensile properties. While precipitation of fine D0a δ-phase is known to have beneficial effects on the mechanical properties owing to the retardation of grain coarsening, Widmanstätten δ precipitation plays a deleterious influence on the fracture toughness, tensile ductility, and fatigue resistance. Therefore, to enhance the mechanical properties of this alloy series, it is key to generate a high number density of fine D0a δ precipitate by adjusting solid solution treatment temperatures. In this study, solution heat treatments were conducted above and below δ-phase solvus temperatures. By applying solution heat treatment at 900°C and 970°C, this alloy was confirmed to have a Widmanstätten δ phase and is composed similarly to the annealed microstructure. This Widmanstätten δ precipitate was densely distributed at both intergranular and intragranular grains. On the other hand, when solution treatment was applied at 1040 and 1100°C, more coarse particles (approximately 30 μm) with a significant reduction of Widmanstätten type δ phase were obtained. We found that grain size and Widmanstätten δ-phases have an important role in the high-temperature tensile properties of Inconel 625 superalloy series.
{"title":"Effect of Heat Treatment Temperature on Microstructure, Tensile Properties and δ-Precipitate Phase in Ni-based Superalloy","authors":"Jeonyoung Song, Jiho Gu, Won Hui Jo, Cho Hyeon Lee, Jae Bok Seol, Youngwha Ma","doi":"10.3365/kjmm.2024.62.1.32","DOIUrl":"https://doi.org/10.3365/kjmm.2024.62.1.32","url":null,"abstract":"Here, we investigated the influence of δ-precipitate (orthorhombic D0a Ni3Nb-ordered phase) on the room- and high-temperature tensile properties in wrought nickel-based Inconel 625 superalloys subjected to solution and aging heat treatment. Typically, solution heat-treatment temperatures in these alloys affect the solid-state precipitation of δ-phase, which governs high-temperature tensile properties. While precipitation of fine D0a δ-phase is known to have beneficial effects on the mechanical properties owing to the retardation of grain coarsening, Widmanstätten δ precipitation plays a deleterious influence on the fracture toughness, tensile ductility, and fatigue resistance. Therefore, to enhance the mechanical properties of this alloy series, it is key to generate a high number density of fine D0a δ precipitate by adjusting solid solution treatment temperatures. In this study, solution heat treatments were conducted above and below δ-phase solvus temperatures. By applying solution heat treatment at 900°C and 970°C, this alloy was confirmed to have a Widmanstätten δ phase and is composed similarly to the annealed microstructure. This Widmanstätten δ precipitate was densely distributed at both intergranular and intragranular grains. On the other hand, when solution treatment was applied at 1040 and 1100°C, more coarse particles (approximately 30 μm) with a significant reduction of Widmanstätten type δ phase were obtained. We found that grain size and Widmanstätten δ-phases have an important role in the high-temperature tensile properties of Inconel 625 superalloy series.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2024-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139383441","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-05DOI: 10.3365/kjmm.2024.62.1.65
Jaeho Choi
To select materials suitable for products, material perception, which is the feeling consumers have about materials, has been studied. Material perception data were obtained through surveys using digital logic for bipolar adjective pairs. The material perception data were analyzed through unsupervised learning of data mining. Prior to data analysis, to increase the reliability of the data, the homogeneity of the data between surveys was tested using clustering analysis, correlation analysis and chi-squared test. After checking the homogeneity of the data between surveys, the data were merged. The merged material perception data were analyzed using relative frequencies, hierarchical clustering, and association rules. The relative frequencies obtained from survey participants' selections were used to determine the prevailing perceptions of each material and as basic data for other analyses. In the hierarchical clustering analysis, hierarchy was identified using distances within clusters and distances between clusters. Through association rule analysis, the consumer's simultaneous perceptions of the material can be known, so not only the individual characteristics of the material but also the relational characteristics can be considered when selecting materials based on consumer's perception. The analyzed characteristics were designed into a material perception map, and this material perception map will be a powerful tool to help product designers make better choices that match consumers' perception and experience when selecting materials.
{"title":"Material Selection: Material Perception Data Analysis Using Clustering Analysis and Association Rule Analysis of Data Mining","authors":"Jaeho Choi","doi":"10.3365/kjmm.2024.62.1.65","DOIUrl":"https://doi.org/10.3365/kjmm.2024.62.1.65","url":null,"abstract":"To select materials suitable for products, material perception, which is the feeling consumers have about materials, has been studied. Material perception data were obtained through surveys using digital logic for bipolar adjective pairs. The material perception data were analyzed through unsupervised learning of data mining. Prior to data analysis, to increase the reliability of the data, the homogeneity of the data between surveys was tested using clustering analysis, correlation analysis and chi-squared test. After checking the homogeneity of the data between surveys, the data were merged. The merged material perception data were analyzed using relative frequencies, hierarchical clustering, and association rules. The relative frequencies obtained from survey participants' selections were used to determine the prevailing perceptions of each material and as basic data for other analyses. In the hierarchical clustering analysis, hierarchy was identified using distances within clusters and distances between clusters. Through association rule analysis, the consumer's simultaneous perceptions of the material can be known, so not only the individual characteristics of the material but also the relational characteristics can be considered when selecting materials based on consumer's perception. The analyzed characteristics were designed into a material perception map, and this material perception map will be a powerful tool to help product designers make better choices that match consumers' perception and experience when selecting materials.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2024-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139381337","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-01-05DOI: 10.3365/kjmm.2024.62.1.51
Yoon Hwan Moon, Jong Geun Park, Yong Jun Oh
Immiscible Au-Ni alloy thin films undergo phase separation and dewetting because of thermodynamic and morphological instability at elevated temperatures below the miscibility gap. We report the formation and assembly of bimetallic nanoparticles (BNPs) on topographic Si templates. An ordered array of inverted pyramidal pits were produced via solid-state and liquid-state dewetting of a 12-nm-thick Au-Ni thin film by respectively using thermal annealing and laser irradiation. Upon direct thermal annealing at 600 and 800 oC, the thin film on the templates self-assembled into an ordered array of BNPs composed of Au-rich and Ni-rich sub-clusters in pits. But the relative proportions of the two sub-clusters varied with annealing temperature due to the additional formation of smaller Ni-rich NPs that were scattered around the BNPs. Laser irradiation of the film, in contrast, formed an ordered array of fully mixed alloy NPs on the template and left no other residues on the surface. Subsequent thermal annealing induced the elements within the NPs to segregate, resulting in Au-rich and Ni-rich sub-clusters. In brief, the combination of solid-state and liquidstate dewetting processes on a topographic template not only enabled the 2-dimesional self-assembly of BNPs but also allowed control of the mixing of alloying elements within the BNPs. These results offer insights into the tailored fabrication of BNPs, which have potential applications in bio-functional catalysts, and plasmonic and chemical sensors.
{"title":"Control of Self-Assembly and Elemental Mixing of AuNi Bimetallic Nanoparticles via Solid-State and Liquid-State Dewetting of Metal Thin Films","authors":"Yoon Hwan Moon, Jong Geun Park, Yong Jun Oh","doi":"10.3365/kjmm.2024.62.1.51","DOIUrl":"https://doi.org/10.3365/kjmm.2024.62.1.51","url":null,"abstract":"Immiscible Au-Ni alloy thin films undergo phase separation and dewetting because of thermodynamic and morphological instability at elevated temperatures below the miscibility gap. We report the formation and assembly of bimetallic nanoparticles (BNPs) on topographic Si templates. An ordered array of inverted pyramidal pits were produced via solid-state and liquid-state dewetting of a 12-nm-thick Au-Ni thin film by respectively using thermal annealing and laser irradiation. Upon direct thermal annealing at 600 and 800 oC, the thin film on the templates self-assembled into an ordered array of BNPs composed of Au-rich and Ni-rich sub-clusters in pits. But the relative proportions of the two sub-clusters varied with annealing temperature due to the additional formation of smaller Ni-rich NPs that were scattered around the BNPs. Laser irradiation of the film, in contrast, formed an ordered array of fully mixed alloy NPs on the template and left no other residues on the surface. Subsequent thermal annealing induced the elements within the NPs to segregate, resulting in Au-rich and Ni-rich sub-clusters. In brief, the combination of solid-state and liquidstate dewetting processes on a topographic template not only enabled the 2-dimesional self-assembly of BNPs but also allowed control of the mixing of alloying elements within the BNPs. These results offer insights into the tailored fabrication of BNPs, which have potential applications in bio-functional catalysts, and plasmonic and chemical sensors.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2024-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139382601","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":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2023-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"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.2023.61.12.909
Yong-min Jeon, S. Ryu, Min Jun Kim, Seong Eui Lee
In this study, a composition-gradient thin film was applied for the formation of intermediate layer of Ti seed layer for an stable electrode stack Ag metal layer. Various composition of Ag-Ti hetero metal layer were simultaneously deposited by using the sputtering process with Ti and Ag target, respectively. An intermediate layer was deposited at a gradient composition ratio such as 5:5 and 7:3. In addition, the optimal deposition conditions were evaluated by confirming the plasma codition such as density of plasma ion, plasma potential with the Langmuir Probe (Hiden ESPion). Flow rate, power, and composition ratio were optimized as variables for thin film structures of compositional gradient thin films. In addition, thin film samples were heat treated at 200 ℃, 300 ℃, and 400 ℃ to relieve the residual stress between the interface of laminated thin films. Under these conditions, a composition-gradient thin film was evaluated by XRD (X-Ray Diffraction, SmartLab Rigaku 9kW), SEM (Scanning Electron Microscope, Nova NanoSEM 450), and EDS (energy dispersive X-ray spectroscopy). As a result of the measurement, it was confirmed that interfacial diffusion occurred due to the composition gradient thin film. When the composition gradient intermediate layer was applied to thin film stack, the residual stress increased more than that of single thin film stack. However, after stress relief annealing, residual stress was dramatically decreased compared to single stack.
{"title":"Study on Ag-Ti Thin Film Structure with Compositional Gradient Fabricated by Sputtering Process","authors":"Yong-min Jeon, S. Ryu, Min Jun Kim, Seong Eui Lee","doi":"10.3365/kjmm.2023.61.12.909","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.12.909","url":null,"abstract":"In this study, a composition-gradient thin film was applied for the formation of intermediate layer of Ti seed layer for an stable electrode stack Ag metal layer. Various composition of Ag-Ti hetero metal layer were simultaneously deposited by using the sputtering process with Ti and Ag target, respectively. An intermediate layer was deposited at a gradient composition ratio such as 5:5 and 7:3. In addition, the optimal deposition conditions were evaluated by confirming the plasma codition such as density of plasma ion, plasma potential with the Langmuir Probe (Hiden ESPion). Flow rate, power, and composition ratio were optimized as variables for thin film structures of compositional gradient thin films. In addition, thin film samples were heat treated at 200 ℃, 300 ℃, and 400 ℃ to relieve the residual stress between the interface of laminated thin films. Under these conditions, a composition-gradient thin film was evaluated by XRD (X-Ray Diffraction, SmartLab Rigaku 9kW), SEM (Scanning Electron Microscope, Nova NanoSEM 450), and EDS (energy dispersive X-ray spectroscopy). As a result of the measurement, it was confirmed that interfacial diffusion occurred due to the composition gradient thin film. When the composition gradient intermediate layer was applied to thin film stack, the residual stress increased more than that of single thin film stack. However, after stress relief annealing, residual stress was dramatically decreased compared to single stack.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2023-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138598577","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.2023.61.12.943
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":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2023-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"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":null,"pages":null},"PeriodicalIF":1.2,"publicationDate":"2023-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"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}
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