In this study, we report the microstructure and characteristics of Ag-SnO2-Bi2O3 contact materials using a controlled milling process with a subsequent compaction process. Using magnetic pulsed compaction (MPC), the milled Ag-SnO2-Bi2O3 powders have been consolidated into bulk samples. The effects of the compaction conditions on the microstructure and characteristics have been investigated in detail. The nanoscale SnO2 phase and microscale Bi2O3 phase are well-distributed homogeneously in the Ag matrix after the consolidation process. The successful consolidation of Ag-SnO2-Bi2O3 contact materials was achieved by an MPC process with subsequent atmospheric sintering, after which the hardness and electrical conductivity of the Ag-SnO2-Bi2O3 contact materials were found to be 62–75 HV and 52–63% IACS, respectively, which is related to the interfacial stability between the Ag matrix, the SnO2 phase, and the Bi2O3 phase.

In the powder bed fusion (PBF) process, a 3D shape is formed by the continuous stacking of very fine powder layers using computer-aided design (CAD) modeling data, following which laser irradiation can be used to fuse the layers forming the desired product. In this method, the main process parameters for manufacturing the desired 3D products are laser power, laser speed, powder form, powder size, laminated thickness, and laser diameter. Stainless steel (STS) 316L exhibits excellent strength at high temperatures, and is also corrosion resistant. Due to this, it is widely used in various additive manufacturing processes, and in the production of corrosion-resistant components with complicated shapes. In this study, rectangular specimens have been manufactured using STS 316L powder via the PBF process. Further, the effect of heat treatment at 800 °C on the microstructure and hardness has been investigated.

In this study, Ti-Mo-EB composites are prepared by ball milling and spark plasma sintering (SPS) to obtain a low elastic modulus and high strength and to evaluate the microstructure and mechanical properties as a function of the process conditions. As the milling time and sintering temperature increased, Mo, as a β-Ti stabilizing element, diffused, and the microstructure of β-Ti increased. In addition, the size of the observed phase was small, so the modulus and hardness of α-Ti and β-Ti were measured using nanoindentation equipment. In both phases, as the milling time and sintering temperature increased, the modulus of elasticity decreased, and the hardness increased. After 12 h of milling, the specimen sintered at 1000oC showed the lowest values of modulus of elasticity of 117.52 and 101.46 GPa for α-Ti and β-Ti, respectively, confirming that the values are lower compared to the that in previously reported studies.

Oxide dispersion-strengthened (ODS) steel has excellent high-temperature properties, corrosion resistance, and oxidation resistance, and is expected to be applicable in various fields. Recently, various studies on mechanical alloying (MA) have been conducted for the dispersion of oxide particles in ODS steel with a high number density. In this study, ODS steel is manufactured by introducing a complex milling process in which planetary ball milling, cryogenic ball milling, and drum ball milling are sequentially performed, and the microstructure and high-temperature mechanical properties of the ODS steel are investigated. The microstructure observation revealed that the structure is stretched in the extrusion direction, even after the heat treatment. In addition, transmission electron microscopy (TEM) analysis confirmed the presence of oxide particles in the range of 5 to 10 nm. As a result of the room-temperature and high-temperature compression tests, the yield strengths were measured as 1430, 1388, 418, and 163 MPa at 25, 500, 700, and 900oC, respectively. Based on these results, the correlation between the microstructure and mechanical properties of ODS steel manufactured using the composite milling process is also discussed.

In this study, we investigate the effect of the duration of mechanical alloying on the microstructures and mechanical properties of ODS ferritic/martensitic steel. The Fe(bal.)-10Cr-1Mo pre-alloyed powder and Y2O3 powder are mechanically alloyed for the different mechanical alloying duration (0 to 40 h) and then constantly fabricated using a uniaxial hot pressing process. Upon increasing the mechanical alloying time, the average powder diameter and crystallite size increased dramatically. In the initial stages within 5 h of mechanical alloying, inhomogeneous grain morphology is observed along with coarsened carbide and oxide distributions; thus, precipitate phases are temporarily observed between the two powders because of insufficient collision energy to get fragmented. After 40 h of the MA process, however, fine martensitic grains and uniformly distributed oxide particles are observed. This led to a favorable tensile strength and elongation at room temperature and 650oC.

본 연구는 정맥의 서식지 관리 및 보전을 위한 기초자료를 제공하고자 수행하였다. 18개의 중점조사지역에서 지형, 서식지 환경을 고려하여 각 지점별로 개발지, 계곡부, 임도 및 능선 3가지 서식지유형으로 총 54개의 고정조사구를 선정하였다. 조사는 2016년부터 2018년까지 겨울철을 제외한 계절별(5월,8월, 10월)로 수행하였다. 서식지 유형별로 관찰된 조류를 자기조직화지도(SOM)를 활용하여 분포 패턴을 분석한 결과, 총 4개의 그룹으로 분류되었다(MRPP, A=0.12, p <0.005). 자기조직화지도 그룹별 종수와 개체수, 종다양도 지수를 비교분석한 결과 종수와 개체수, 종다양도 지수 모두 Ⅲ번 그룹에 가장 높게 나타났다(Kruskal-Wallis, 종수: x2 = 13.436, P <0.005; 개체수: x2 = 8.229, P <0.05; 종다양도: x2 = 17.115, P <0.005). 또한 그룹별 지표종 분석과, 서식지 환경 특성을 파악하기 위해 토지피복도를 랜덤 포레스트 모델에 적용하여 분석한 결과, 4개 그룹간의 서식지환경이 구성하는 비율과 지표종에 차이를 보였다. 지표종 분석은 Ⅱ번 그룹을 제외한 3그룹에서 총 18종의 조류가 지표종으로 확인되었다. 본 연구에서 자기조직화지도 를 활용하여 4개 그룹으로 분류된 결과를 기초로 랜덤 포레스트 모델과 지표종 분석을 적용하였을 때 그룹별 지표종 구성과 그룹별 서식지 특성과 상호 연관성을 보였다. 또한 그룹별 우점하는 서식환경에 따라 관찰된 종의 분포패턴과 밀도가 뚜렷하게 구분이 되었다. 자기조직화지도와 지표종분석, 랜덤 포레스트 모델을 함께 적용한 분석은 서식지 환경에 따라 조류 서식 특징파악에 유용한 결과를 도출할 수 있을 것으로 판단된다.

The effects of different spray angles (90°, 85°, 80°) on the microstructure and mechanical properties of a Y2O3 coating layer prepared using the atmospheric plasma spray (APS) process were studied. The powders employed in this study had a spherical shape and included a cubic Y2O3 phase. The APS coating layer exhibited the same phase as the powders. Thickness values of the coating layers were 90°: 203.7 ± 8.5 μm, 85°: 196.4 ± 9.6 μm, and 80°: 208.8 ± 10.2 μm, and it was confirmed that the effect of the spray angle on the thickness was insignificant. The porosities were measured as 90°: 3.9 ± 0.85%, 85°: 11.4 ± 2.3%, and 80°: 12.7 ± 0.5%, and the surface roughness values were 90°: 5.9 ± 0.3 μm, 85°: 8.5 ± 1.1 μm, and 80°: 8.5 ± 0.4 μm. As the spray angle decreased, the porosity increased, but the surface roughness did not show a significant difference. Vickers hardness measurements revealed values of 90°: 369.2 ± 22.3, 85°: 315.8 ± 31.4, and 80°: 267.1 ± 45.1 HV. It was found that under the condition of a 90° angle with the lowest porosity exhibited the best hardness value. Based on the aforementioned results, an improved method for the APS Y2O3 coating layer was also discussed.

알루미늄합금 6061-T6 판재에 대하여 마찰교반용접과 텅스텐 이너트 가스 용접의 교차 용접부의 미세조직과 기계적 특성에 있어서 용접 순서의 영향을 분석하기 위한 시험편을 성공적으로 제작하였다. FSW-ED 시험편이 다른 조합들보다 가장 좋은 기계적 특성을 나타내었다. 흥미롭게도, TIG-FSW ED 시험편이 FSW-TIG ED 시험편보다 높은 인장강도를 나타내었다. 용접부 경도의 경우, FSW 시편이 TIG-FSW 및 FSW-TIG 시험편보다 높은 값을 나타내었고, TIG-FSW 시험편이 FSW-TIG 시험편보다 높은 값을 나타내었다. FE-SEM을 이용한 인장 파면에 대한 관찰을 통하여, 모든 시험편에서 연성파괴를 나타내는 다양한 크기의 딤플들이 관찰되었다. FSW-TIG 시험편의 파면에서는 용융지(熔融池) 표면 영역에서 기공들이 관찰되는 반면, TIG-FSW 시험편에서는 기공의 형성은 관찰되지 않았다. 경도와 미세조직의 결과를 통해 TIG-FSW 공정이 FSW-TIG 공정보다 높은 인장강도를 확보할 수 있는 공정임을 확인하였다.

High-entropy alloys have excellent mechanical properties under extreme environments, rendering them promising candidates for next-generation structural materials. It is desirable to develop non-equiatomic high-entropy alloys that do not require many expensive or heavy elements, contrary to the requirements of typical high-entropy alloys. In this study, a non-equiatomic high-entropy alloy powder Fe49.5Mn30Co10Cr10C0.5 (at.%) is prepared by high energy ball milling and fabricated by spark plasma sintering. By combining different ball milling times and ball-topowder ratios, we attempt to find a proper mechanical alloying condition to achieve improved mechanical properties. The milled powder and sintered specimens are examined using X-ray diffraction to investigate the progress of mechanical alloying and microstructural changes. A miniature tensile specimen after sintering is used to investigate the mechanical properties. Furthermore, quantitative analysis of the microstructure is performed using electron backscatter diffraction.

Cr-Si based alloys are not only excellent in corrosion resistance at high temperatures, but also have good wear resistance due to the formation of Cr3Si phase, therefore they are promising as metallic coating materials. Aluminum is often added to Cr-Si alloys to improve the oxidation resistance through which stable alumina surface film is formed. On the other hand, due to the addition of aluminum, various Al-containing phases may be formed and may negatively affect the heat resistance of the Cr-Si-Al alloys, so detailed investigation is required. In this study, two Cr-Si-Al alloys (high-Si & high-Al) were prepared in the form of cast ingots through a vacuum arc melting process and the microstructural changes after high temperature heating process were investigated. In the case of the cast high-Si alloy, a considerable amount of Cr3Si phase was formed, and its hardness was significantly higher than that of the cast high-Al alloy. Also, Al-rich phases (with the high Al/ Cr ratio) were not found much compared to the high-Al alloy. Meanwhile, it was observed that the amount of the Al-rich phases reduced by the annealing heat treatment for both alloys. In the case of the high temperature heating at 1,400 oC, no significant microstructural change was observed in the high Si alloy, but a little more coarse and segregated AlCr phases were found in the high Al alloy compared to the cast state.

This study compared and analyzed the quality characteristics and antioxidant activity of the commercial stick-type jelly of pomegranate (P1-P3), green apple (G1-G3), and red ginseng (R1-R3). The pomegranate group's pH showed a relatively low range (3.38-3.61), and the red ginseng group showed a relatively high range (4.14-4.96). The total acidity of commercial stick-type jelly was in the range of 0.31-4.60, and this value satisfied the total acidity standard of candy prescribed in the Ministry of Food and Drug Safety. Water content in the commercial stick-type jelly was lowest in P1 (45.99%) and highest in R3 (83.16%). The pomegranate group was significantly higher than the other samples for sugar content and turbidity (p<0.05). Fracturability was measured only in G2 and G3 with significantly lower hardness values (p<0.05), while the pomegranate group showed significantly higher values for hardness, adhesiveness, cohesiveness, gumminess, and chewiness compared to other samples (p<0.05). In DPPH free radical scavenging activity and total phenolic content results, the pomegranate group tended to have a high value, especially P3, which showed significantly the highest DPPH free radical scavenging activity (p<0.05). These results show that various commercial stick-type jelly products have different characteristics according to such factors like raw material and manufacturer.

Martensitic stainless steel is commonly used in the medical implant instrument. The alloy has drawbacks in terms of strength and wear properties when applied to instruments with sharp parts. 440C STS alloy, with improved durability, is an alternative to replace 420 J2 STS. In the present study, the carbide precipitation, and mechanical and corrosion properties of STS 440C alloy are studied as a function of different heat treatments. The STS 440C alloy is first austenitized at different temperatures; this is immediately followed by oil quenching and sub-zero treatment. After sub-zero treatment, the alloy is tempered at low temperatures. The microstructures of the heat treated STS 440C alloy consist of martensite and retained austenite and carbides. Using EDX and SADP with a TEM, the precipitated carbides are identified as a Cr23C6 carbide with a size of 1 to 2 μm. The hardness of STS 440C alloy is improved by austenitization at 1,100 oC with sub-zero treatment and tempering at 200 oC. The values of Ecorr and Icorr for STS 440C increase with austenitization temperature. Results can be explained by the dissolution of Cr-carbide and the increase in the retained austenite. Sub-zero treatment followed by tempering shows a little difference in the properties of potentiodynamic polarizations.

Direct water quenching technique can be used in hot stamping process to obtain higher cooling rate compared to that of the normal die cooling method. In the direct water quenching process, setting proper water flow rate in consideration of material thickness and the size of the area directly cooled in the component is important to ensure uniform microstructure and mechanical properties. In this study, to derive proper water flow rate conditions that can achieve uniform microstructure and mechanical properties, microstructure and hardness distribution in various water flow rate conditions are measured for 3.2 mm thick boron steel sheet. Hardness distribution is uniform under the flow condition of 1.5 L/min or higher. However, due to the lower cooling rate in that area, the lower flow conditions result in a drastic decrease in hardness in some areas in the hot-stamped part, resulting in low martensite fraction. From these results, it is found that the selection of proper water flow rate is an important factor in hot stamping with direct water quenching process to ensure uniform mechanical properties.

본 연구는 점오염원인 하수종말처리장으로부터 배출되는 물의 수질을 분석하고 배출수의 영향을 받는 어류 중 지점들에서 공통적으로 출현하는 어종인 피라미 (Z. platypus) 를 선택하여 조직학적 변화를 참조하천 지점의 수질과 어류 조직을 비교·분석하였다. 2019년 6월 27~28일 하수종 말처리장 4곳 (대전, 전주, 청주, 익산)의 채집 결과, 참조하 천에서 22종 450개체로 가장 많은 종수 및 개체수가 확인 되었다. 지점별로 5개체씩 2~3년생 피라미의 조직표본을 제작하여 아가미와 근육조직 (피부조직)을 관찰한 결과, 참조하천을 제외한 나머지 지점의 조직은 병리적인 양상을 나타내었다. 수질분석 결과, 각 WTP에서는 배출수질 기준을 준수 혹은 더 좋은 수질로 방류하고 있었다. 그러나 하수종말처리수 배출수 및 방류수계 수질에서 오염도지표를 나타내는 항목인 BOD, COD, TP, TN, SS 값이 참조하천에 비해 높은 것으로 나타났다. 빈약한 어류상과 바이오마커로 이용된 종의 조직병리학적 상태는 참조하천에 비해 낮은 수질에서 기인한 것으로 추측되며, 따라서 원인이 되는 하수종말처리장 배출수 수질개선이 이루어져야 할 것으로 사료된다.

Microstructural characteristics of directionally solidified René 80 superalloy are investigated with optical microscope and scanning electron microscope; solidification velocity is found to change from 25 to 200 μm/s under the condition of constant thermal gradient (G) and constant alloy composition (Co). Based on differential scanning calorimetry (DSC) measurement, γ phase (1,322 oC), MC carbide (1,278 oC), γ/γ' eutectic phase (1,202 oC), and γ' precipitate (1,136 oC) are formed sequentially during cooling process. The size of the MC carbide and γ/γ' eutectic phases gradually decrease with increasing solidification velocity, whereas the area fractions of MC carbide and γ/γ' eutectic phase are nearly constant as a function of solidification velocity. It is estimated that the area fractions of MC carbide and γ/γ' eutectic phase are determined not by the solidification velocity but by the alloy composition. Microstructural characteristics of René 80 superalloy after solid solution heat-treatment and primary aging heat-treatment are such that the size and the area fraction of γ' precipitate are nearly constant with solidification velocity and the area fraction of γ/γ' eutectic phase decreases from 1.7 % to 0.955 %, which is also constant regardless of the solidification velocity. However, the size of carbide solely decreases with increasing solidification velocity, which influences the tensile properties at room temperature.

The objective of this study was to determine chemical compositions affecting the physical and thermal properties of the textured vegetable protein (TVP). The 14 commercial TVPs were pulverized, followed by analyzing their morphology, chemical composition, water absorption index (WAI) and water solubility index (WSI) (for the pulverized and original TVPs), solubility, swelling power, melting property, and hardness. All TVPs showed the rough surface with irregular cracks and pores and the porous structure with varied pore sizes. WAI was positively correlated to moisture and crude protein contents and negatively correlated to the total carbohydrate content. WSI and solubility were directly and reversely influenced by the crude ash and total carbohydrate contents and the crude protein and total starch contents, respectively. The swelling power and melting temperature of TVPs did not significantly affect chemical compositions. Melting enthalpies increased with crude ash content, while decreased with the total starch content. The hardness of the rehydrated TVPs was enhanced with their crude ash and total carbohydrate contents, whereas reduced with their crude protein and total starch contents. Overall, the yield and texture of the rehydrated TVP could be modulated with the crude protein and ash contents of TVP.

본 연구는 동질성이 강조된 한국 사회·문화 맥락과 독특한 산업적 관행에 의한 다양성 특성이 이직의 도에 어떠한 영향 경로가 있는지 다양성 조직풍토 인식과 소속감 인식의 매개 및 조절효과를 중심으로 구조방정식 모형을 활용하여 검증하였다. 한국의 사회문화적 맥락에서 성별·결혼상태, 세대 및 학력을, 첨단기술산업 분야 인수합병기업의 독특성으로 근무지역, 근무부서 및 근속을 주요 다양성 특성으로 보았다. 연구결과, 첫째, 다양성 특성 중 성별·결혼상태, 세대, 근무부서, 근무지역이 임직원들의 소속감과 다양성 조직풍토 인식에 유의미한 영향을 미쳤다. 둘째, 이직의도와 직접적 영향이 없던 다양성 특성 중 성별·결혼상태에서 다양성 조직풍토 및 높은 소속감 인식을 모두 매개하여 이직의도가 낮았고, 세대에서 소속감 인식을 매개하여 이직의도가 낮아지는 간접경로가 발견되었다. 더불어, 이직의도와 직접 효과가 없던 근무지역과 근무부서에서도 두 인식을 매개하여 이직의도가 낮아졌다. 셋째, 다양성 조직풍토 인식 과 소속감 인식에서 조절효과가 나타나 긍정적인 다양성 조직풍토 인식에서 소속감 인식은 더 가파르게 이직의도를 낮추었다. 본 연구를 통해 한국 사회문화적 맥락 및 독특한 조직 배경에서의 소속감 및 다양 성 조직풍토 인식에 중요한 다양성 특성을 규명하였고, 그 다양성 특성에 적합한 맞춤형 다양성 관리제도 가 시급히 마련되어야 함은 물론, 특정 소수집단에 초점화된 다양성 관리를 넘어 모든 조직구성원의 여러 다양성이 가치 있게 포용 되는 다양성 조직문화적 접근이 매우 중요함을 제시하였다.

Effects of Sc addition on microstructure, electrical conductivity, thermal conductivity and mechanical properties of the as-cast and as-extruded Al-2Zn-1Cu-0.3Mg-xSc (x = 0, 0.25, 0.5 wt%) alloys are investigated. The average grain size of the as-cast Al-2Zn-1Cu-0.3Mg alloy is 2,334 μm; however, this value drops to 914 and 529 μm with addition of Sc element at 0.25 wt% and 0.5 wt%, respectively. This grain refinement is due to primary Al3Sc phase forming during solidification. The as-extruded Al-2Zn-1Cu-0.3Mg alloy has a recrystallization structure consisting of almost equiaxed grains. However, the asextruded Sc-containing alloys consist of grains that are extremely elongated in the extrusion direction. In addition, it is found that the proportion of low-angle grain boundaries below 15 degree is dominant. This is because the addition of Sc results in the formation of coherent and nano-scale Al3Sc phases during hot extrusion, inhibiting the process of recrystallization and improving the strength by pinning of dislocations and the formation of subgrain boundaries. The maximum values of the yield and tensile strength are 126 MPa and 215 MPa for the as-extruded Al-2Zn-1Cu-0.3Mg-0.25Sc alloy, respectively. The increase in strength is probably due to the existence of nano-scale Al3Sc precipitates and dense Al2Cu phases. Thermal conductivity of the as-cast Al-2Zn-1Cu-0.3Mg-xSc alloy is reduced to 204, 187 and 183 W/MK by additions of elemental Sc of 0, 0.25 and 0.5 wt%, respectively. On the other hand, the thermal conductivity of the as-extruded Al-2Zn-1Cu-0.3Mg-xSc alloy is about 200 W/Mk regardless of the content of Sc. This is because of the formation of coherent Al3Sc phase, which decreases Sc content and causes extremely high electrical resistivity.

In this study, we fabricate a thin- and dense-BCuP-5 coating layer, one of the switching device multilayers, through a plasma spray process. In addition, the microstructure and macroscopic properties of the coating layer, such as hardness and bond strength, are investigated. Both the initial powder feedstock and plasma-sprayed BCuP-5 coating layer show the main Cu phase, Cu-Ag-Cu3P ternary phases, and Ag phase. This means that microstructural degradation does not occur during plasma spraying. The Vickers hardness of the coating layer was measured as 117.0 HV, indicating that the fine distribution of the three phases enables the excellent mechanical properties of the plasma-sprayed BCuP-5 coating layer. The pull-off strength of the plasma-sprayed BCuP-5 coating layer is measured as 16.5 kg/cm2. Based on the above findings, the applicability of plasma spray for the fabrication process of low-cost multi-layered electronic contact materials is discussed and suggested.