Microstructure and Tensile Properties in Low Pressure Cast Al-Si Alloy through Cooling Rate Control

Suh, Jun-Young,Park, Sung Jin,Lee, Hee-Kwon,Chang, Si Young Materials Research Society of Korea 2020 한국재료학회지 Vol.30 No.2

In this study, three kinds of metal chills such as SS400, AC4CH and brass, with different thicknesses of 40 ~ 80 mm, were applied for low pressure casting of Al-Si alloy to control cooling rate. The microstructural characteristics with increasing cooling rate were represented using factors including D₁, D₂, size of primary α phases and shape factor and size of eutectic Si. The tensile properties were investigated and additionally analyzed based on the microstructural characteristics. As the cooling rate increased, D₁, D₂, and sizes of primary α phases and eutectic Si apparently decreased and the shape factor of eutectic Si increased to over 0.8. The ultimate tensile strength (UTS) and yield strength (YS) increased with decreasing D₁, D₂, and size of primary α phases, while elongation increased with decreasing size of eutectic Si and concurrently increasing shape factor of eutectic Si. This indicated that the primary α phases and eutectic Si in Al-Si alloy were refined with increasing cooling rate, resulting in improvement of UTS and YS without sacrificing elongation. After the tensile test, preferential deformation of primary α phases was observed in the Al-Si alloy produced at higher cooling rates of more than 0.1 K/s.

LiF:Mg,Cu,Na,Si TL 소자의 선량계적 특성

남영미,김장렬,장시영 대한방사선 방어학회 2001 방사선방어학회지 Vol.26 No.1

최근 개발된 방사선량 측정용 LiF:Mg,Cu,Na,Si TL 소자의 글로우 곡선, 방출스펙트럼, 광자에 대한 선량의존성, 에너지의존성 및 페이딩 등과 같은 물리적 및 선량계적 특성들을 연구하였다. LiF:Mg,Cu,Na,Si TL 소자는 LiF:Mg,Cu,Na,Si TL 분말에 압력을 가한 후 소결하는 방법으로 제조되었다. 방사선에 대한 특성을 알아보기 위하여 광자선 조사는 한국원자력연구소의 X선 발생 장치 및 137Cs γ선 원격조사장치를 이용하였으며, 사용된 광자선 에너지 범위는 20-662keV, 선량 범위는 10-6-102 Gy이었다. 글로우 곡선은 수동형의 TLD 판독장치 (System 310, Teledyne)로 질소를 흘리면서 선형적인 가열률로 측정하였으며, TL 강도는 글로우 곡선을 전체 적분한 면적으로 평가하였다. 5℃·s-1의 선형적인 가열률로 측정한 글로우 곡선은 5개의 피그들로 분리되었으며, 234℃에 나타나는 주피크의 활성화에너지는 2.34 eV, 진동수인자는 1.00×1023이고, 방출스펙트럼은 410nm를 중심으로한 단일한 분포로 나타났다. 선량의존성은 100Gy 이상까지 선형성을 나타내었으며, 137Cs에 대한 저에너지 광자의 상대적인 에너지 반응값은 20% 범위 이내였다. 또한 실온에서 1년간 보관하였을 때, 시간경과에 따른 TL 감도의 감소가 거의 없는 좋은 페이딩 특성을 보였다. Sintered LiF:Mg,Cu,Na,Si thermoluminescence (TL) pellets were developed for application in radiation dosimetry. In the present study, the TL dosimetric properties of LiF:Mg,Cu,Na,Si TL pellets have been investigated for emission spectrum, dose response, energy response, and fading characteristics. LiF:Mg,Cu,Na,Si TL pellets were made by using a sintering process, that is, pressing and heat treatment from TL powders. Photon irradiations for the experiments were carried out using X-ray beams and a 137Cs gamma source at the Korea Atomic Energy Research Institute(KAERI). The average energies and the dose were in the range of 20-662 keV and 10-6- 102 Gy, respectively. The glow curves were measured with a manual type TLD reader(System 310, Teledyne) at a constant nitrogen flux and a linear heating rate. For a constant heating rate of 5℃·s-1, the main dosimetric peak of glow curve appeared at 234℃, the activation energy was 2.34eV and frequency factor was 1.00×1023. TL emission spectrum is appeared at the blue region centered at 410 nm. A linearity of photon dose response was maintained up to 100 Gy. The photon energy responses relative to 137Cs response were within ±20% at overall photon energy region. The fading of TL sensitivity of the pellets stored at the room temperature was not found for one year.

Dynamic Young's Modulus and Internal Friction in Polycrystalline Copper

Kang, Chang-Seog,Chang, Si-Young,Hong, Sung-Kil 대한금속재료학회 2003 METALS AND MATERIALS International Vol.9 No.5

An attempt has been made to measure the temperature dependence of dynamic Young's modulus together with the related variation of internal friction in polycrystalline copper. A mechanical spectroscopy study was employed using a standard servo hydraulic fatigue testing machine equipped with a scanning laser extensometer. Dynamic Young's modulus and internal friction were measured over a temperature range of 298 to 873 K at very low frequencies of 0.1, 0.05, and 0.01 Hz. One internal friction peak was observed over the ranges 450 to 700 K, together with marked decreases in the dynamic Young's modulus in the same temperature range. From a quantitative analysis of the experimental data with the relaxation strength, relaxation time, and activation energy, it is concluded that the peak phenomenon is due to grain-boundary sliding relaxation.

Marked Decreases of Foxp3 and CTLA-4 Are Associated with Strong Antiviral Effects of Tenofovir in Patients with Chronic Hepatitis B

( Ji Young Kim ),( Chang Wook Kim ),( Yun Hui Kim ),( Seok Cheon Yeom ),( Su Gyeong Lee ),( Hee Yeon Kim ),( Si Hyun Bae ),( Jong Young Choi ),( Seung Kew Yoon ) 대한간학회 2016 춘·추계 학술대회 (KASL) Vol.2016 No.1

Aims: Immune regulatory molecules such as forkhead box P3 (Foxp3) on CD4+ T cell and cytotoxic T lymphocyte-associated antigen 4 CTLA-4) on CD8+ T cell are associated with antiviral effector T cell dysfunction, which influences on T cell exhaustion and persistent viral infection in patients with chronic hepatitis B. These Foxp3 and CTLA-4 are up-regulated in chronic hepatitis B. During antiviral therapy with tenofovir, the expressions of Foxp3 and CTLA-4 could be changed. We investigated the relationship between antiviral effects of tenofovir and the expression of Foxp3 and CTLA-4 during tenofovir treatment in chronic hepatitis B. Methods: Eight patients with chronic hepatitis B under tenofovir treatment were enrolled for detection of Foxp3 on CD4+ T cell and CTLA-4 on CD8+ T cell. Peripheral blood mononuclear cells were isolated from these subjects before tenofovir treatment (T0), 3 month (T3) and 6 month (T6) during tenofovir treatment. For antiviral effect analysis, serum HBV DNA levels were checked at same time. The expressions of Foxp3 and CTLA-4 on T cells were monitored by flow cytometry. Results: Three patients (3 of 8) showed marked decreases of Foxp3 and CTLA-4 during tenofovir therapy (group 1). Five patients (5 of 8) showed minimal changes of Foxp3 or CTLA-4 during tenofovir therapy (group 2). Group 1 showed complete virologic response within 6 month therapy regardless of baseline HBV DNA level but, group 2 showed complete virologic response within 6 month therapy only in patients with low baseline HBV DNA level (< 7log HBV DNA). Conclusions: Among the patients with chronic hepatitis B, the patients who showed marked decrease of Foxp3 and CTLA-4 during tenofovir therapy are associated with strong antiviral effects of tenofovir regardless of baseline HBV DNA level. This finding suggests that restoration of HBV-specific T cell strengthens the antiviral effects of tenofovir.

냉기치료후 슬관절강내의 온도변화

백승석,최기섭,박시복,이상건,김영호,양길태,장윤희 大韓再活醫學會 1998 Annals of Rehabilitation Medicine Vol.22 No.2

냉기 치료에 따른 둔근에서의 피부 및 근육내 온도 변화

정우성,김미정,박시복,이상건,김영호,양길태,장윤희 大韓再活醫學會 1998 Annals of Rehabilitation Medicine Vol.22 No.2

중증 고혈압증의 임상적 관찰

육동민(Dong Min Yook),곽시영(Si Young Kwak),김성식(Seong Sik Kim),이성숙(Seong Sook Lee),홍관표(Kwan Pyo Hong),최창필(Chang Pil Choi),이재우(Jae Woo Lee),이시래(Si Rhae Lee) 대한내과학회 1987 대한내과학회지 Vol.33 No.2

N/A Clinical studies were carried out in the 110 cases of severe hypertension who had been admitted from January 1979 to August 1985 and the following results were obtained: 1) Underlying diseases of severe hypertension were essential hypertension in 67 cases, renal parenchymal hypertension in 36 cases, and renovascular hypertension in 7 cases. 2) Plasma renin activity was the highest in the group of renovascular hypertension which was 22.07±9.20 ng/ ml/hr, and as a whole, the higher diastolic blood pressure, the higher plasma renin activity was. Plasma renin activity in the group of K-W grade IV retinopathy was higher than those of the other groups. 3) The incidence of ventricular hypertrophy fullfilling voltage criteria and with accompanying ST-T changes on electrocardiolgram was 81.5% in the group of essential hypertension and there was no difference in relation to the level of pressure or fundoscopic changes. 4) The serum creatinine level was the highest in the group of renal parenchymal hypertension (7.93±2.98 mg/dl), and in the group of K-W grade IV retinopathy (6.86±3.50mg/dl), but there was no significant difference in relation to the level of diastolic blood pressure, 5) There were no significant difference in cardiothoracic ratio on chest X-ray in relation to underlying diseases, diastolic blood pressure or fundoscopic changes. 6) The major complications were congestive heart failure (49.1%), hypertensive encephalopathy (17.3%), and cerebrovascular accident (8.2%). 7) In the group of essential hypertension blood pressure was controlled by conservative treatment in 81.0% but in 35.7% in the group of renal hypertension. The patients of chronic renal failure who were treated with dialysis blood pressure was controlled in 87.0%. In all 6 cases with renal transplantation, nephrectomy or renal angioplasty blood pressure was well controlled. 8) In cases refractory to triple antihypertensive regimen blood pressure was controlled by minoxidil in 66.7% and by captopril in 75.0%. 9) In 45 cases who were followed up for more than 6 months diastolic blood pressure was controlled under 100mmHg in 77.8% and there were improvement of renal function, fundoscopic findings and electrocardiographic findings in 20.0%, 33.3% and 16.7%, respectively.

주조마그네슘합금의 미세조직과 기계적 성질에 미치는 ECAP가공의 영향

장시영 한국항공대학교 항공우주산업기술연구소 2002 航空宇宙産業技術硏究所 硏究誌 Vol.12 No.-

주조 Mg 합금은 여러 온도에서 ECAP가공되었다. 순 Mg은 573 K보다 낮은 온도에서는 시료표면에 전단 방향으로 표면크랙이 발생하였으나 온도가 증가함에 따라 segemented 한 flow는 일정하게 변하여 표면 크랙은 사라져, 573 K에서는 반복 ECAP 가공후에도 깨끗한 표면의 시료를 얻을 수 있었다. 상용 AZ계 합금도 같은 결과를 나타내었고, 특히 573 K이상의 온도에서도 심한 표면크랙이 발생하였다. 그러나, ECAP가공전에 압연을 함으로서 ECAP가공온도는 낮아졌다. 또한 AI의 농도가 감소할수록 가공온도는 낮아져, AZ31합금의 경우 493 K에서 반복 ECAP가공이 가능하였다. 573 K에서 4번의 반복 ECAP 가공 후에 순 Mg의 결정립은 400 ㎛에서 80 ㎛로 감소하였으며, 493 K에서 ECAP가공한 AZ31 합금은 약 1 ㎛에서 10 ㎛정도의 크기를 갖는 동적재결정립의 미세조직을 나타내었다. 이와 같이, 높은 가공온도에 의한 동적 재결정 및 결정립 성장에도 불구하고, 순 Mg 및 주조 AZ계 합금의 경도는 향상되었다. ECAP가공 중의 변형은 전위 조직의 관찰로부터 설명되었다. The difficult-to-work Mg alloys was subjected to equal channel angular pressing(ECAP) under a condition of various pressing temperatures. Pure Mg was susceptible to shear localization during ECAP; surface cracking occurred along to the direction of shear localization at lower temperatures than 573 K. Uniform flow occurred at 573 K, resulting in the successful 4 repetitive ECAPs. The ECAP of Mg alloys containing AI (AZ series alloys) was unsuccessful even at higher temperature than 573 K. However, the ECAP temperature of AZ series alloys hot-rolled before ECAP became lowered, and the temperature for successful ECAP decreased with decreasing AI content. In particular, the hot-rolled AZ 31 alloy could be ECAPed at 493 K. The grain size of pure Mg was decreased from approximately 400 ㎛ to 80 ㎛ after the 4 repetitive ECAP. In addition, the ECAPed AZ 31 alloy revealed the microstructure of dynamically recrystallized grains with a grain size in range of 1 ㎛ to 10 ㎛. Despite the dynamic recrystallization during ECAP at higher temperatures ( > 1/2 Tm), the microhardness of AZ series alloys was considerably increased by a single ECAP. The deformation during ECAP was explained by dislocation characteristics.

마그네슘과 복합재료로 구성된 bi-material의 인장특성

장시영 한국 항공대학교 항공산업기술연구소 2001 航空宇宙産業技術硏究所 硏究誌 Vol.11 No.-

용탕단조법을 이용하여 마그네슘과 복합재료의 사이에 macro-interface를 갖는 bi-material을 제조하여 미크로조직과 인장특성을 조사하였다. 또한, 열사이클처리가 bi-material의 인장특성에 미치는 영향을 조사하였다. Macro-interface은 강화재의 체적율이 낮은 영역으로 약 7∼10 ㎛의 두께로 형성되었으며, 반응생성물이 macro-interface 주위에 형성되었다. 실온에서 bi-material의 인장강도는 미강화 마그네슘과 복합재료보다 낮았고, 온도가 증가함에 따라 423 K까지는 변함이 없었다. 그보다 높은 온도에서는 온도증가에 따라 감소하여 미강화 마그네슘의 인장강도와 같아졌다. 한편, 연신율은 온도에 따라 증가하였으나, 미장화 마그네슘보다는 낮고, 복합재료보다는 높았다 또한, 열사이클처리는 bi-material의 인장강도에 영향을 미쳐, 사이클 수와 △T의 증가에 따라 인장강도는 감소하였다. 파단 거동은 macro-interface에서 파단한 bi-material의 양쪽 파면을 관찰하여 평가하였다. Microstructural and mechanical characteristics of hi-materials with the macro-interface between unreinforced magnesium and composite manufactured by squeeze casting were determined. The effect of thermal cycling on the tensile properties of the hi-materials with the macro-interface, which is a potential site of cyclic stress formation, was also investigated. The macro-interface has diffuse interface characteristics; its thickness is about 7~10 ㎛. A reaction product formed near the macro-interface. It has been found that the tensile strength of bi-materials at R.T. is lower than that of its corresponding pure magnesium and the composites, and remains unchanged until 423 K. Above 423 K, the tensile strength decreases with increasing temperature and becomes the same as that of magnesium. The elongation is in between the pure magnesium and the composite at R.T. and elevated temperatures. In addition, the tensile strength of the bi-materials decreases with thermal cycling as a function of both the number of thermal cycles and △T. The fracture behavior was evaluated by the study of fracture surfaces on both sides of the bi-materials fractured at the macro-interface.

비감속 252Cf중성자선원에 대한 비등방성교정인자 및 선량당량환산인자

장시영,정덕연,윤석철,김종수 대한방사선 방어학회 1993 방사선방어학회지 Vol.18 No.2

중성자 측정장비 교정을 위한 표준중성자장을 제작하기 위하여 순수멕스월분포(kt=1.42MeV)로부터 ??Cf 자발핵분열 중성자선원의 밀봉이 교정인자에 미치는 영향을 고찰하였다. SR-Cf-100과 SR-Cf-1273 밀봉모형을 실제 제작조건으로 하여 MCNP 코드를 사용하여 몬테카를로 모의를 수행하여, 비등방성교정인자와 선속밀도-대-선량당량 환산인자를 산정하였고, 다른 연구결과와 비교하였다. 결과로서, Fi(θ=90˚)는 1.061(통계오차 : ±0.2%), H/??는 333.9[pSv·㎠] (통계오차 : ±0.5%)인 것으로 산정되었다. 이 환산인자(H/??)의 값은 ISO 8529의 권고보다 1.8%가 작은 것인데, 이것은 한국원자력연구소의 비감속 ??Cf중성자선원의 스펙트럼이 ISO의 것보다 약간 더 연화하다는 물리적 의미를 갖는다. Form the pure Maxwellian distribution(kT= 1.42MeV), the effects upon calibration factors of encapsulating a Cf spontaneous fission neutron source were invdwtigated to establish a standark neutron field in the Secondary Standark Kosimetry laboratory at Korea Atomic Inergy Research Institute(KAERI). A Monte Carlo code MCNP was used in simulating the encapsulation SR-Cf-100 and SR-Cf-1273 to be real conditions. The anisotropy(FI) and fluence-to-dose equivalents conversion factors(H/Φ) were evaluated and compared with other results. As the results, the FI was determined to be 1.061 atθ=90˚ with ±0.2% statistical error and the (H/Φ) was evaluated to be 333.9 [pSv·㎠] with ±0.5% statistical error, which is lower by 1.8% than that recommended by the ISO 8529. This means physically that the neutron spectrum of the unmoderated Cf source in KAERI is a little more softened than that by the ISO.