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Laser weldability of cast and rolled high-entropy alloys for cryogenic applications
Nam, Hyunbin,Park, Chulho,Moon, Jongun,Na, Youngsang,Kim, Hyoungseop,Kang, Namhyun Elsevier 2019 Materials science & engineering. properties, micro Vol.742 No.-
<P><B>Abstract</B></P> <P>Laser similar welding of cast and rolled high-entropy alloys (HEAs) was performed using the cantor system (Co<SUB>0.2</SUB>Cr<SUB>0.2</SUB>Fe<SUB>0.2</SUB>Mn<SUB>0.2</SUB>Ni<SUB>0.2</SUB>). As the welding velocity was increased from 6 to 10 m min<SUP>−1</SUP>, the shrinkage voids, primary dendrite arm spacing, and dendrite packet size decreased, thus improving the mechanical properties of the cast and rolled HEA welds. The cast HEA welds showed tensile properties comparable to those of the base metal (BM). In all the specimens fracture occurred near the heat-affected zone and BM at 298 K. However, the rolled HEA welds showed lower tensile strength than the BM, and fracture occurred in the weld metal (WM). This can be attributed to the larger dendrite packet size of the WM than the grain size of the BM. In addition, the tensile properties of the specimens at the cryogenic temperature were superior to those observed at 298 K, regardless of the cast and rolled HEA welds. This is because the formation of deformation twins and dislocations was predominant at 77 K. Therefore, the laser similar welds of cast and rolled HEAs are suitable for cryogenic applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Laser similar welds of the cast and rolled HEAs were obtained with no defects. </LI> <LI> The cast HEA welds and BM showed similar tensile properties. </LI> <LI> The tensile strength of the rolled HEA welds was ~ 90% of that of the BM. </LI> <LI> The tensile properties of all the specimens at 77 K were superior to those at 298 K. </LI> <LI> The formation of deformation twins and dislocations was predominant at 77 K. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
( Nam-hee Kim ),( Hye Sun Choi ),( Moon Young Lee ),( Hyunbin Seong ),( Nam Soo Han ),( Hae-jin Hu ),( Yong Sung Kim ),( Jung Ho Park ) 대한소화기기능성질환·운동학회 2024 Journal of Neurogastroenterology and Motility (JNM Vol.30 No.2
Background/Aims This study aims to investigate the effect of a fermented rice drink with Lactiplantibacillus plantarum JSA22 on symptoms, blood tests, microbiomes, and fecal metabolites in patients with irritable bowel syndrome (IBS) who were overweight. Methods Sixty overweight (body mass index ≥ 23 kg/m2) patients aged between 20 and 65 with IBS were enrolled. Patients were divided into 2 groups and administered either a fermented rice drink or an nonfermented rice drink for a month. The symptom questionnaire, blood samples, and stool samples for microbiome and metabolite were collected before and after the month of rice drink administration. The primary efficacy variable was the subject’s global assessment of IBS symptoms. Results In both groups, global IBS symptoms, including abdominal pain, bowel habit, urgency, and abdominal distension, improved significantly (P < 0.01). The abdominal bloating was more significantly improved in the fermented rice drink group than in the nonfermented rice drink group (P < 0.05). Significant changes were not observed in metabolic syndrome-related blood tests or fecal metabolites in either group. However, microbiome analysis showed significant differences in genus levels before and after consuming fermented rice drink, such as in Blautia in stool (P = 0.020) and Prevotella (P = 0.017) and Oribacterium (P = 0.018) in saliva. Conclusions The fermented rice drink with L. plantarum JSA22 showed a beneficial effect in reducing abdominal distension in IBS patients. Bacteria that reduce visceral fat accumulation increased in the stool and saliva of patients who consumed fermented rice drinks. (J Neurogastroenterol Motil 2024;30:194-207)
CuCrFeMnNi 용접재료를 적용한 rolled high-entropy alloys의 GTA 용접성 평가
남현빈(Hyunbin Nam),박상현(Sanghyun Park),심상훈(Sang Hoon Shim),나영상(Youngsang Na),송상우(Sangwoo Song),홍순익(Sun Ig Hong),강남현(Namhyun Kang) 대한용접·접합학회 2021 대한용접학회 특별강연 및 학술발표대회 개요집 Vol.2021 No.11
최근 고엔트로피합금은 구조용 강재를 대체할 수 있는 재료로 각광받고 있다. 신재료인 고엔트로피합금의 강도 및 극저온/고온특성을 향상시키기 위하여 많은 연구가 진행되고 있으나, 상용화를 위하여 필수적으로 수행되어야 하는 용접성 평가과 관련된 연구는 현저하게 부족한 실정이다. 고엔트로피합금의 용접성과 관련된 연구는 LBW 및 FSW 등의 저입열 용접에서 주로 수행되었으나, 최근에는 고입열 용접인 GTAW를 통한 연구도 발표되고 있다. 특히, CoCrFeMnNi 고엔트로피합금에서는 용접열에 의한 상변태가 발생되지 않으므로 용접부의 각 영역별(BM/HAZ/WM) 결정립도가 용접성을 결정한다. 용접 시, 용접열에 의해 WM의 결정립도가 모재보다 조대화되어 인장파단이 WM에서 발생되므로 용접부의 강화를 위하여 WM의 결정립도를 미세화시킬 필요가 있다. 따라서 본 연구에서는 용접부의 결정립 미세화를 위하여 Cu가 대체된 고인트로피합금 용접재료를 개발하여 용접성을 평가하였다. Cu-rich phases의 생성으로 인하여 CuCrFeMnNi 용접부의 결정립도 보다 CoCrFeMnNi 용접부의 결정립도가 더 미세한 것으로 확인되었으며, 이로 인하여 기계적 특성 또한 CuCrFeMnNi 용접부가 더 우수한 결과를 보였다.