Korean Journal of Metals and Materials最新文献

{"title":"Effect of Process Parameter and Scanning Strategy on the Microstructure and Mechanical Properties of Inconel 625 Superalloy Manufactured by Laser Direct Energy Deposition","authors":"Hyunji Nam, Qing-Ye Jin, Jiyoung Park, Wookjin Lee","doi":"10.3365/kjmm.2023.61.10.772","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.10.772","url":null,"abstract":"This study aimed to investigate the effect of process parameters on the microstructure and mechanical properties of Inconel 625 alloy manufactured by direct energy deposition process. The Inconel 625 samples were produced by varying the laser scanning speeds from 720 - 960 mm/min while maintaining the same the laser energy volume density. The microstructure and mechanical properties of the produced samples were evaluated, and their dimensional accuracy and mechanical properties were also analyzed in terms of the laser scanning strategy. Microstructural observations at the same energy density revealed a dendrite substructure near the laser melt pool boundaries, indicating that the dendritic microstructure was primarily formed at the beginning of the solidification of each laser bead. When the solidification further progressed into the melt pool, solidification cell substructures became dominant regardless of the laser scanning speed. The size of the solidification cell and the dendrite structure were nearly unchanged as laser scanning speed increased. This suggests that changing the laser scanning speed while maintaining the volumetric energy density does not significantly alter the solidification rates of the Inconel 625. As a consequence of the similar cell sizes, the samples produced with different laser scanning speed led to similar mechanical properties. When samples produced with two different scanning strategies, of unidirectional and 90o rotation, were compared, a better dimensional accuracy was obtained with the 90o rotation strategy, compared to that obtained with the unidirectional approach. Comparisons of mechanical properties obtained along different directions with the different laser scanning strategies revealed that the Inconel 625 produced by the laser direct energy deposition had pronounced anisotropic mechanical properties, and was the highest in strength but the lowest in maximum elongation along the laser scanning direction.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":"1 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134947446","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}

{"title":"Piezoresistive Characteristics of Carbon Nanotube Polymer Composites with Different Filler Content and Aspect Ratio for Pressure Sensors","authors":"Jongchan Yoo, Dong-Young Kim, Dong-Kwan Lee, Kunwoo Nam, Sung-Hoon Park","doi":"10.3365/kjmm.2023.61.10.793","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.10.793","url":null,"abstract":"Polymer composites enriched with conductive fillers hold immense potential for flexible pressure sensors, because of the remarkable piezoresistive effect they possess. Research on polymer composite pressure sensors has been actively ongoing because of their flexibility and high electrical resistance performance. This paper presents a comprehensive comparison of the piezoresistive characteristics of conductive composites for pressure sensors, focusing on the influence of carbon nanotube (CNT) content and aspect ratio. Polymer composites with conductive fillers, specifically CNTs, have demonstrated significant potential for pressure sensing applications based on the piezoresistive effect. By systematically varying the CNT concentration and aspect ratio, we investigated the impact of these parameters on the piezoresistive behavior of the composites. A pressure in the range of 0-200 kPa was applied to the conductive composite, and resistance change due to pressing was measured. The best performing samples were evaluated in 150 cycle tests to verify repeatability and durability. Experimental analysis and characterization revealed the intricate relationship between CNT content, aspect ratio, and the resulting piezoresistive properties. Through this study, we aim to enhance understanding of how CNT concentration and aspect ratio influence the performance of CNT/PDMS composites as pressure sensors, thereby facilitating the development of optimized sensing materials for various pressure sensing applications.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":"64 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134947444","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}

{"title":"Effects of Intercritical Heat Treatment on the Temper Embrittlement of SA508 Gr.4N Ni-Cr-Mo High Strength Low Alloy Steels for Reactor Pressure Vessels","authors":"Seokmin Hong, Cho-Long Lee, Bong-Sang Lee, Hong-Deok Kim, Min-Chul Kim","doi":"10.3365/kjmm.2023.61.10.729","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.10.729","url":null,"abstract":"To analyze the effects of intercritical heat treatment on the temper embrittlement of SA508 Gr.4N steels, two model alloys with different phosphorus (P) contents were fabricated. Each sample was heat treated by applying a conventional heat treatment process (quenching-tempering) with/without an intercritical heat treatment process (IHT) and a step-cooling heat treatment for temper embrittlement. Then their microstructure and mechanical properties were evaluated. The microstructure of the SA508 Gr.4N model alloy was composed of tempered lower bainite and martensite, and nano-sized precipitates formed both inside and at boundaries. The grain size was reduced when IHT was applied. There was a small difference in tensile properties according to the heat-treatment conditions and P contents, but the difference in Charpy impact properties was large. The heat treatment for temper embrittlement (TE) increased the impact transition temperature, and a very significant increase was observed in steels with a high P content. The increase in transition temperature owing to TE was reduced when IHT was applied. The fractograph analysis of Charpy fractured specimens at transition temperatures showed that an increase in intergranular fracture was main reason for the TE, and that IHT reduced the formation of intergranular fracture. The AES results showed that P-Ni was segregated at grain boundaries, and the level of segregation was reduced by applying IHT. This occurred because the formation of prior austenite grain boundaries by IHT dispersed the P at grain boundaries, and reduced the amount of P segregation.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":"53 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134947448","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}

{"title":"Optimization of Sintering Temperature for the Synthesis of n-type Mg&lt;sub&gt;3&lt;/sub&gt;SbBi&lt;sub&gt;0.99&lt;/sub&gt;Te&lt;sub&gt;0.01&lt;/sub&gt; Thermoelectric Materials","authors":"Sung-Jae Joo, Ji-Hee Son, JeongIn Jang, Bong-Seo Kim, Bok-Ki Min","doi":"10.3365/kjmm.2023.61.10.785","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.10.785","url":null,"abstract":"Mg3Sb2-based materials are promising candidates to replace n-type Bi2Te3 for cooling and power generation at low temperatures. Generally, the thermoelectric performance of a material is sensitively affected by synthesis process parameters, and among them, sintering temperature (<i>Ts</i>) is a critical one. In this study, n-type Mg3SbBi0.99Te0.01 polycrystalline samples were fabricated by mechanical alloying and spark plasma sintering (SPS), and the effects of varying <i>Ts</i> (923 – 1073 K) on the thermoelectric properties were investigated. Sintering Mg3SbBi0.99Te0.01 at an elevated temperature of 1073 K resulted in a notable increase in electrical conductivity at low temperatures below about 423 K. This is ascribed to a sharp reduction in carrier scattering by ionized impurities. For the same reason, the carrier mobility increased sharply at a <i>Ts</i> of 1073 K, which is a critical temperature for sintering in this study. Moreover, the Seebeck coefficient increased and thermal conductivity decreased simultaneously by raising <i>Ts</i>, resulting in the maximum power factor (<i>PFmax</i>) of 2.2 × 10-3 W m-1K-2 and the maximum dimensionless figure of merit (<i>zTmax</i>) of 1.20 in the sample sintered at 1073 K. Therefore, when <i>Ts</i> was raised from 923 K to 1073 K, the <i>PFmax</i> and <i>zTmax</i> increased by 29 % and 64 %, respectively. This improvement in performance is attributed to the annihilation of defects generated during the mechanical alloying process, which was confirmed by microstructure analysis by transmission electron microscopy (TEM).","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":"300 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134947445","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}

{"title":"Analysis of Precipitation Phase of Alloy1.4957 Heat-Resistant Steel for Gasoline Turbocharger","authors":"Jong-Kwan Lee, Byeong-Joo Lee, Eon-Sik Lee","doi":"10.3365/kjmm.2023.61.10.721","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.10.721","url":null,"abstract":"Recently, strengthened environmental regulations have required the downsizing of gasoline engines, and as a result, demand for gasoline turbochargers has rapidly increased. The vane of a turbocharger controls the flow of gases toward the turbine, and it is manufactured by powder metallurgy due to its complex shape. Gasoline engines have a high exhaust gas temperature (~1000oC), and thus, Alloy1.4957 (GX15CrNiCo21-20-20) containing large amounts of Cr, Ni, and Co is used. In this study, Alloy1.4957 powders were sintered by hot isostatic pressing (HIP), and then homogenized and thermally exposed to exhaust gas temperatures. Then, a microstructural analysis was conducted to observe the changes that occurred for each process. M6X carbonitride containing Si, called Cr3Ni2SiX, was observed to be the main precipitate phase in this alloy. In general, it is known that Cr3Ni2SiX is only rarely observed in heat-resistant steel. However, in Alloy1.4957, a large amount of Cr3Ni2SiX was precipitated or dissolved depending on the process, and this is probably due to the high Si and N content of Alloy1.4957. In addition to Cr3Ni2SiX, Cr23C6 and NbX were observed. Cr23C6 was dissolved during the homogenization process, but NbX, which has high thermal stability, retained a fine size during the homogenization process and provided a nucleation site for Cr3Ni2SiX during thermal exposure.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":"65 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134947449","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}

{"title":"Influence of Elevated Temperature on the Mechanical and Microstructural Properties of Glass Fiber-Reinforced Polymers","authors":"Se Woong Lee, Seulgi Han, Okmin Park, Sang-il Kim, Sungmo Choi","doi":"10.3365/kjmm.2023.61.10.800","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.10.800","url":null,"abstract":"Glass fiber-reinforced polymers (GFRPs) have attracted significant attention as structural materials because of their high fatigue resistance, corrosion resistance, strength, and stiffness. This study examined the effect of elevated temperatures (150, 250, 350, and 450oC) on the microstructural and mechanical properties of GFRP plates. The number of bubbles increased as the firing temperature increased, and the bubbles burst at 250oC or higher, forming pores on the surface. A tensile test was conducted, and the maximum stress of the GFRP plates fired at 150, 250, and 350oC was reduced from 54.2 to 52.2, 40.3, and 24.0 MPa, respectively, compared to that of the unfired GFRP plate. Meanwhile, the elastic moduli of the GFRP plates fired at 150, 250, and 350oC reduced from 19.1 to 18.3, 16.1, and 12.1 GPa, respectively, compared to that of the unfired GFRP plate. This reduction in the mechanical properties of the GFRP plates at elevated temperatures was attributed to the degradation of the mechanical properties of the resin matrix due to glass transition and decomposition, debonding, and an increase in surface defects. The maximum strain decreased gradually with increasing firing temperature, suggesting that the brittleness of the GFRP plates increased at elevated temperatures.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":"13 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134947447","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}

{"title":"Effects of Stacking Number on Microstructure and Mechanical Properties for Cold Roll Bonding Process of Dissimilar Aluminum Alloy Sheets","authors":"Seong-Hee Lee","doi":"10.3365/kjmm.2023.61.9.652","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.9.652","url":null,"abstract":"A cold roll-bonding (CRB) process is applied to study the effects of stacking number on the microstructure and mechanical properties of roll-bonded and age-treated Al sheets. Commercial AA1050 and AA6061 sheets with a thickness of 2 mm were stacked alternately on each other to two and four layers, and roll-bonded by multi-pass cold rolling. The roll-bonded Al sheets were then subjected to natural aging (T4) and artificial aging (T6) treatments. The as roll-bonded Al sheets showed a typical deformation structure, where the grains are elongated in the rolling direction regardless of the stacking number. However, after the T4 and T6 aging treatments, the Al sheets had a recrystallization structure consisting of coarse grains in both the AA5052 and AA6061 regions with different grain sizes in each. In addition, the sheets showed an inhomogeneous hardness distribution in the thickness direction, with higher hardness in AA6061 than in AA1050 after the T4 and T6 age treatments. The tensile strength of the T6-treated specimen was higher than that of the T4-treated one for both the 2 and 4-layer CRBs. In addition, both the tensile strength and elongation of the specimens processed by the 4-layer stack CRB were higher than those of the 2-layer stack CRB for all experimental conditions.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":" ","pages":""},"PeriodicalIF":1.2,"publicationDate":"2023-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42527679","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}

{"title":"Properties and Lightfastness of Natural and Artificial Azurite Used As Painting Pigment","authors":"Ju-Hyun Park, Myoung-Nam Kim, Se-Rin Park, Sun-Myung Lee","doi":"10.3365/kjmm.2023.61.9.704","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.9.704","url":null,"abstract":"Azurite is an inorganic pigment commonly used in traditional painting arts and even today. This pigment has two types: natural azurite and synthetic artificial azurite, called blue verditer or blue bice. Because they have the same structure and similar appearance they are difficult to distinguish. The purpose of this study is to compare these two types pigments, focusing on material properties and accelerated weathering behavior. Natural azurite consist of copper carbonate and mineral compounds like quartz, kaolinite. On the other hand, artificial azurites are synthesized using azurite and calcite. As a result of thermal analysis, unlike natural azurite, the calcite in artificial azurite resulted in weight loss at three temperatures, at approximately 350 ℃, 650 ℃, and 840 ℃. According to the microscope analysis results, natural azurites have clearly blue angular particles with sharp edges, produced by crushing. Artificial azurite showed spherules and aggregates with tiny rounded or fibrous particles. After accelerated weathering tests, the natural azurites had no change in color, particle shape or original components, but the artificial azurites noticeably changed color and shape. The color changes of artificial azurites occurred due to the growth of calcite crystallite, a slight new product formation, and change in particle shape. Even though natural azurites are more expensive pigments, they provide superior color durability and particle shape stability compared to artificial azurites.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":" ","pages":""},"PeriodicalIF":1.2,"publicationDate":"2023-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49247069","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}

{"title":"Effect of Oxygen Content on Microstructure and Mechanical Properties of Additive Manufactured Ti-6Al-4V","authors":"Tae Jin Kang, P. Narayana, S. Choi, Jae Hyuk Kim, J. Hong, Taekyung Lee","doi":"10.3365/kjmm.2023.61.9.714","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.9.714","url":null,"abstract":"Titanium alloys are used in many fields including military, aerospace, and biomedical because of their excellent specific strength, corrosion resistance, and biocompatibility. Recently, much research has been focused on addressing the disadvantages of conventional manufacturing methods, including reducing material and energy waste when manufacturing titanium alloy parts by additive manufacturing methods. However, due to rapid cooling, during the additive manufacturing process the material develops acicular and lamellar microstructures, and despite high strength, those features are detrimental to ductility and toughness, as compared with conventionally manufactured alloys. As a result, numerous studies have sought to obtain an equiaxed microstructure through heat treatment. However, the developed heat treatment processes are quite complex, and involve several heat treatment cycles, making such processes economically unfavorable. To overcome these limitations we suggest a different approach to obtaining an equiaxed structure in 3D-printed titanium alloy, by controlling the oxygen level. The present study analyzed the globularization behavior of Direct Energy Deposited (DED) Ti-6Al-4V alloy as a function of oxygen content and a simple heat treatment. The microstructure was globularized through oxygen level control and furnace cooling to compensate the disadvantages in the mechanical properties of additive manufactured alloys.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":" ","pages":""},"PeriodicalIF":1.2,"publicationDate":"2023-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43497069","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}

{"title":"A Study on the Relationship between Microstructure and Impact Toughness with Different Heat Inputs and Post-Seam Annealing Temperatures in API X70 Electric Resistance Welded Steel Pipe","authors":"Tae-Hun Kim, Chiwon Kim, Chan-Hee Lee, Jinseop Kwack, Donghyeon Jeon, Hyun-Uk Hong","doi":"10.3365/kjmm.2023.61.9.659","DOIUrl":"https://doi.org/10.3365/kjmm.2023.61.9.659","url":null,"abstract":"In this study, the influence of heat input and post-seam annealing (PSA) temperature on the microstructure and impact toughness of electric resistance welded (ERWed) API X70 steel pipe was investigated. The ERW seam welds of pipes were fabricated with low, moderate, and high heat inputs, and followed by the PSA process at 950 ℃. Regardless of heat input, the API X70 steel pipe exhibited good weldability, resulting in similar microstructure factors, i.e., metal flow angle (~70o), bondline width (~22 μm), and ferrite grain size (~4.4 μm). Although (Mn, Si)-rich oxide penetrators which are known to impair impact toughness were observed at the bondline, the area fraction was estimated to be as low as 0.011% in all the ERW seam welds. The impact toughness was not affected by these penetrators because of their minimal fraction, leading to ductile fracture at -20 ℃. However, different PSA temperatures (870, 950, and 1040 ℃) resulted in the different grain sizes of the seam welds. The ERW seam weld annealed at 1040 ℃ (PSA1040) exhibited the largest ferrite grain size near the bondline, whilst the smallest grain size was found in the ERW weld annealed at 870 ℃ (PSA870). In spite of having the smallest grain size, PSA870 exhibited the lowest impact toughness value, showing brittle fracture at –20 ℃. It was observed that the difference in residual stresses was not macroscopically detectable by the hole drilling method. The kernel average misorientation (KAM) maps indicated that the highest level of residual stress was observed near the bondline of PSA870, as evidenced by a high density of dislocations. This study provides instructive results, indicating that the impact toughness of ERW seam welds are significantly more affected by residual stresses than by the grain refinement effect.","PeriodicalId":17894,"journal":{"name":"Korean Journal of Metals and Materials","volume":" ","pages":""},"PeriodicalIF":1.2,"publicationDate":"2023-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45100683","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}