GaN 기판 제작을 위한 Al2O3(S) 기판의 습식 식각 기술

김도형 선문대학교 대학원 2011 국내석사

To make a GaN substrate, we used GaN/Al2O3(S) substrate grown by HVPE method, and etched to selectively etch Al2O3(S) substrate. We observed etching rate of Al2O3(S) substrate with respect to temperature of etchant, and made SiO2/Ti/Pt, Ti/Pt metal layers to protect GaN layer from etchant. Etching rate of Al2O3(S) substrate was exponentially increased with respect to temperature and the activation energy was 31.9 Kcal/mol. We also observed higher H2SO4 and H3PO4 concentrations at the etchant temperature of 320℃. In order to apply for breaking process of LED chip, we did wet scribing experiment. Scribing line of V-groove shape, and LED chip shape in size of 350 μm × 350 μm were fabricated on Al2O3(S) substrate. We researched an-isotropic characteristic of Al2O3(S) substrate. GaN기판을 제작하기 위하여, HVPE (Hydride Vapor Phase Epitaxy)법으로 제작된 GaN/Al2O3(S) 기판을, H2SO4와 H3PO4의 부피비가 3 : 1 인 혼합 용액을 사용하여 Al2O3(S) 기판을 선택 식각하였다. 식각 온도에 따른 Al2O3(S) 기판의 식각률 변화를 관찰하였으며, 산 혼합용액의 식각 보호막으로 SiO2, Pt 및 Pt/Ti을 사용하여 Al2O3(S) 기판의 선택식각 실험을 하였다. Al2O3(S) 기판의 식각률은 온도 증가에 따라 지수적으로 증가하였고, 식각 활성화 에너지(Ea)는 31.9 Kcal/mol 이었다. 또 산 혼합용액의 PO43-, SO42- 이온기의 농도는 320 ℃에서 가장 높게 나타났다. 발광다이오드(LED) 칩 분리제작에 응용하기 위하여, 습식 스크라이빙 실험을 하였다. Al2O3(S) 기판 위에 V-groove 형태의 스크라이빙 선을 형성하여, 350 μm × 350 μm 크기의 LED 칩 형상을 제작하였고, 이방성 식각 특성을 조사하였다.

Al-Fe 합금 도금 HPF강의 용접성

윤상만 포항공과대학교 철강에너지소재대학원 2023 국내박사

Al-Cu-Li-X(In,Be) 合金의 組織과 機械的性質의 相互關係

이승호 全北大學校 大學院 1995 국내석사

The purpose of this study was to examine the effects of In and Be additions on the aging behaviors and mechanical properties in the Al-Cu-Li alloy. This study was performed by the differential scanning calorimetry(DSC), the transmission electron microscope(TEM), the scanning electron microscope(SEM), hardness and tensile strength measurement. The results obtained were as follows; Firstly, the addition of In the Al-Cu-Li alloy retards the formation of GP zone and δ' phases, whereas it promotes the formation of T₁and θ' phases. However, the formation of T₁and θ' phases as well as the formation of GP zone and δ are promoted by the addition of In and Be in Al-Cu-Li alloy. Secondly, In addition or In and Be addition in the Al-Cu-Li alloy, the aging is promoted and resulted in double peak on the aging hardness curves. It is considered that secondary peak is due to the fine secondary T₁phases. Thirdly, by the addition of In the Al-Cu-Li alloy the strength is inceased but the elongation and toughness are decreased. And the addition of In and Be into the Al-Cu-Li alloy decreases a little strength than In addition alloy but increases elogation and toughness remarkably. Fourthly, slip band fracture mechanism by the planar slip in the Al-Cu-Li alloy was changed to dimpled fracture mechanism by the addition of In and Be. Therefore, the toughness of the Al-Cu-Li alloy was well developed by the addition of In and Be.

Al-Li계 合金에서 Nano structure를 갖는 複合析出相의 析出擧動에 관한 연구

이영호 충남대학교 대학원 2002 국내박사

In the last two decades, several types of Al-Li based alloys have been developed and some have been used as new light, weight, materials for next generation applications. Most of the investigations were concentrated on Al Cu-Li, Al-Cu-Mg-Li, and Al-Mg-Li alloys. Positive results for 2000-Li and Weldalite alloys have led to registration and commercial production. For the commercial application, these alloys requires high strength and good fracture toughness associated with the nano structure that develops during aging process. Numerous dispersed phases nucleate and grow at the grain boundaries and within the matrix when the alloys arc aged and the variety appearing in a particular alloy depends on its chemistry. The precipitates in the matrix are invariably some combination of the β',δ', G.P.zone, θ', T₁, and S' phases. The present work has been involved in the behavior of multiple precipitation during aging process of an 2090 Al-Li alloy and a Weldalite 049 alloy using high resolution electron microscope and in-situ aging process at high temperatures. In the 2090 alloy quenched from 530℃, the Ll₂-type microdomains and regions having lattice modulation parallel to{100} planes are observed in an atomic resolution. The δ '/G.P.zone multiple precipitate is formed by the epitaxial growth of the δ' phase on both faces of the G.P.I zone during the aging at 190℃. The G.P.I zone consisted of three layers containing a single layer of Cu between layers of two pure Al. An out of phase or antiphase correlation occurs between the δ' phase on opposite faces of the G.P.zone because of the attraction between Cu and Li atoms in the G.P. zone and δ' phase. Weldalite 049 alloy has higher micro-vickers hardness values than that of 2090 alloy. In the β'/δ' multiple precipitates and a lattice misfit of about 10nm width is partially observed in the interface boundary. Nucleation sites of S' phases are observed to be not only δ'/matrix interface and δ'/G.P.zone/matrix interface boundary, but the region with Cu and Mg clusters. The result of in situ experimental process shows that T₁phase is firstly precipitated from subgrain boundary and with increasing aging, is homogenously precipitated within the matrix. As a result of this study, it is suggested that it is necessary to know the micro structures of alloys and particularly the local structures such as the interface, lattice defects and lattice mismatch to understand and control the alloy properties. The high resolution electron microscope technique has a great, advantage in characterizing the local structure on the atomic-scale.

Al-Mg-Si 합금 볼트 성형공정의 최적화에 관한 연구

이기선 국민대학교 대학원 2010 국내석사

Al-Mg-Si 합금은 경량 재료로서, 비강도가 우수하여 내 식성이 요구되는 구조 부품에 폭넓게 적용되고 있다. 그 중에서 Al합금의 체결용 볼트 성형은 여러 단계의 냉간 성형 과정으로 이루어지는 것이 일반적이다. Al합금은 냉간 성형이 어려운 소재이나, 볼트 성형 공정을 최적화 하여 성형성 을 향상시킬 수 있다면 공정의 단축을 통해 생산성을 높일 수 있다. 본 논문에서는 유한 요소법 을 이용하여 Al-Mg-Si 합금의 육각 플랜지(flange) 볼트의 냉간 성형 공정을 설계하고, 열처리 효과를 포함한 다양한 설계변수가 볼트 성형에 주는 영향을 분석하였다. Al-Mg-Si 합금의 냉간 성형 성을 향상시키기 위해 풀림 처리를 실시하였다. 풀림 처리 전•후 소재의 상온 단축 압축시험을 통해 기계적 성질 변화를 관찰하였다. 풀림 처리 이후 소재는 강도는 낮아졌지만 성형 성이 향상 되었다. 기존 난 성형 성 소재의 육각 플랜지 볼트의 3~4단계 공정을 전방압출과 육각머리 업셋팅(upsetting)의 2단계 공정으로 단순화 하였다. 상용 유한요소 해석 프로그램을 이용하여 성형 성을 예측 하였으나, 육각머리 측면에서 과도한 변형에 의한 결함이 예측되었고 이는 볼트 성형 실험 결과와 일치하였다. 이러한 결함은 육각머리 형상에 의한 비대칭 변형과 연관된 것으로 사료된다. 육각머리의 형상을 변경하여 측면결함을 보완하였고, 예비 성형체 의 형상변화에 따라 플랜지의 결육(underfill) 정도가 향상되었다. 본 논문에서 제시된 열처리 효과와 육각머리 형상 및 예비성형 체 형상변화에 따른 성형 성을 예측하였다. 이를 기반으로 공정을 설계하는 기법은 난 성형 성 고강도 소재의 체결용 볼트의 성형 공정 설계와 생산에 응용할 수 있을 것으로 사료된다. The Al-Mg-Si alloys are light weight materials and are widely used for structural parts requiring high corrosion resistance because of their outstanding specific strength. Forming of Aluminum alloy bolts among them consists of several cold forging processes. Although forging of aluminum alloy at room temperature is difficult, its forgeability could be improved by optimizing bolt forming processes. This paper deals with a design of Al-Mg-Si alloy’s hexagonal flange bolt with FE simulation and examine the effects of variable parameters such as heat treatment, shape of perform. In order to improve the Al-Mg-Si cold formability, annealing is considered. In general, the material after annealing has lower strength and better formability than before heat treatment. The previous bolt forming process with hardly formable materials, which consisted of four steps, is simplified with two steps; forward extrusion and upsetting. The defects are detected at the side of bolt’s head, which are It is also predicted by FE simulation conducted before the experiments. These results reveal that the asymmetry shapes of bolt head result in those defects. By modifying the shapes of bolt head and preform, such defects can removed. Finally it is concluded that the optimized bolt forming process with hardly formable materials such as Al-Mg-Si alloy could be obtained by using finite elements method.

AL5083 초소성합금의 마이크로 단조 성형 특성에 관한 연구

박진석 울산대학교 대학원 2010 국내석사

Various electronic devices are miniaturized due to the rapid development in high-tech IT industry and medical field and sensors. By the miniaturization, the micro-parts for same functions at the same time the mechanical strength and magnetic features are required. Plastic forming have a high productivity and less loss of material, excellent mechanical properties, excellent dimensional control, etc, but the production of actual micro-(micro) components has not been significantly applied. The reason is that plastic processing technology of macro unit is not applied in micro unit, and then lack of understanding about material and material behavior of the micro-structure. Currently, micro-Plastic forming process has been applied in only a small area such as Blanking, Banding, Drawing. But, Almost no cases of micro parts in using bulk deformation process. Therefore, Superplastic alloy with excellent forming precision and mechanical strength is proposed. In this paper, micro-forming plastic formability were studied by using the Al5083 Superplastic alloy. It has a fine grain. Using a each size micro die with Pyramid shape, V-grooved shape, the forming experiments under the self-manufactured micro forming system were conducted. The best temperature for micro forming was 530℃ to 550℃for the Al5083 superplastic alloy. The bigger the forming laod and the longer the forming time, the better the micro formability was achieved. But, Formability was dropped when forming was more progress. Because, size effect is increased between the die and material dimension. Micro forming experiments under static load satus showed that distortion by slip or spin of the grain system and inside the grain was observed in the Al5083 superplastic alloy. Forming height was decreased when surface per volume ratio was increased. The difference in height of the forming between the open die and close die caused by Air Static Pressure Bearing effects. Air Static Pressure Bearing effects was decreased when die size was decreased. Therefore, the difference in height of the forming between the open die and close die, and difference in height per maximum height in die is decreased. Forability was increased when vibration load was increased. Vibration reduced the friction and sticking phenomenon and Air Static Pressure Bearing effects between the material and die. transmit efficiency of mean punching force per vibration load is increase when vibration load increased. transmit efficiency of mean punching force have direct influence on material forming. Power of the working distance is increased while Vibration load is increased. Vibration loss is occur when vibration load input. Because, It has a gap between the punch plane and material plane. Working distance is increase when vibration load is increase. Therefore, gap influence per working distance is decrease, and transmit efficiency of mean punching force is increase. The number of punching times is increase when increase the vibration frequency. And then impact force to material is increase. However, vibrations is amplify or offset, causing by that punching vibration and minor vibration from plastic material is interfering with each other. Therefore, formability is increased or decreased when vibration has increase. In lower frequency region, difference of height is reduced according to the Cavity array location. In higher frequency region, uniformity of forming height becomes worse causing by Amplify and offset. 첨단 IT 산업과 의료분야 및 센서의 급속한 발전으로 인하여 각종 전자기기가 소형화(miniaturization) 되고 있다. 이러한 소형화에 경향에 따라 미세 부품(micro-parts)들도 기능에 맞는 기계적 강도와 전자기적 기능을 동시에 요구되고 있다. 소성 가공은 높은 생산성과 재료의 손실이 적고, 우수한 기계적 특성을 가지고, 성형 치수제어 등이 우수하지만, 실제 마이크로(micro) 부품생산에 크게 적용되지 않고 있다. 그 이유로는 매크로(macro) 단위에서의 소성가공 기술이 마이크로 단위에서 적용이 될 수 없고, 마이크로 성형에 적합한 재료 및 재료의 미세 거동에 대한 이해가 부족하기 때문이다. 지금까지 마이크로 소성가공은 블랭킹(Blanking), 밴딩(banding), 드로잉(drawing) 등 극히 일부에 해당하는 기술들만 적용되고 있고, 부피 성형기술을 이용한 미세부품 사례는 미미하다. 그러므로 우수한 성형 정밀도와 기계적 강도를 가지는 초소성 합금(superplastic alloy)의 적용이 제안된다. 따라서 본 논문에서는 마이크로 소성가공에 적합한 미세 결정립을 가지는 Al5083 초소성 합금 재료를 이용하여 마이크로 소성가공 성형성에 대한 연구를 수행하였다. 초소성 합금에 대해서 각각 치수가 다른 Pyramid와 V-grooved 형상 마이크로 금형을 이용하여 자체 제작한 마이크로 단조 시스템에서 성형 실험을 수행하였다. Al5083 초소성 합금은 최적 성형 온도가 530˚C에서 550˚C 사이임을 알 수 있었다. 또한 성형시간이 길수록, 성형하중이 클수록 성형성이 좋아지지만, 성형성이 높아질수록 성형이 진행되는 금형과 재료 사이의 치수효과의 영향이 증가하기 때문에 성형성이 떨어졌다. 사하중(dead weight) 상태에서 결정립계의 미끄럼 및 회전에 의한 변형을 확인 할 수 있었다. 금형의 부피당 면적비가 클수록 치수효과의 영향에 의해 성형 높이는 낮아지는 것을 알 수 있었다. 같은 크기의 개방형 금형과 밀폐형 금형 사이의 높이 차이는 공기 정압 베어링 효과에 의해 발생하며, 금형의 크기가 작아질수록 공기정압 베어링 효과가 줄어들어 개방형과 밀폐형 금형 사이 높이 차이는 줄어들고 최대 금형 높이 대비 높이차이도 줄어든다. 인가 진동하중이 증가 할수록 성형성이 증가한다는 것을 알 수 있었다. 진동은 소재와 금형 사이 마찰력과 응착현상을 감소시키고 공기정압 베어링 효과도 감소 시켜주는 역할을 하기 때문이다. 인가 진동 하중을 증가 시키면 인가 진동 하중 대비 재료 성형에 영향을 미치는 평균 펀치력 전달 효율이 증가 하였다. 인가 진동 하중이 증가할수록 작동 힘이 증가함과 동시에 작동 거리도 증가하게 된다. 펀치부와 재료 사이의 간극이 존재 하므로 인가 진동하중 인가 시 에너지 손실이 발생하게 된다. 하지만, 인가 진동하중이 증가 할수록 작동 거리가 증가 되므로 총 작동 거리 대비 간극의 영향이 줄어들게 되고, 평균 펀치력 전달 효율이 높아지게 된다. 인가 진동수가 증가하면 시간당 펀칭수가 많아지므로, 충격력이 증가하게 되고 전달되는 에너지가 증가하게 된다. 하지만 성형부에 전달되는 진동과 재료부에서 반사된 진동이 서로 간섭을 일으켜 진동이 증폭 또는 상쇄를 일으킨다. 그러므로 진동수가 증가할수록 성형성은 증가 또는 감소하였다. 진동수가 낮은 영역에서는 Cavity array 위치에 따른 높이 차이를 감소시키는 효과를 얻을 수 있었다. 높은 진동수 영역에서는 진동의 발생부와 성형부에서 반사된 진동파에 의해 국부적으로 진동이 증폭 또는 감소를 일으켜 성형 균일성이 나빠짐을 알 수 있었다.

박판주조법으로 제조한 Al-8Zn-2.5Mg-xCu 합금의 미세조직 및 기계적 특성에 미치는 Cu의 영향

김동국 경상국립대학교 대학원 2022 국내석사

The effect of Cu content on the microstructure and mechanical properties of Al-8.0Zn-2.5Mg-xCu (x: 0, 1, 2, 3) aluminum alloys manufactured by the twin-roll casting process was investigated. The Al-8.0Zn-2.5Mg-xCu alloy showed an increase in surface defects with increasing of Cu content. This is because the amount of residual liquid in the final solidification region increased from 9.6 wt.% to 18.3 wt.% as the Cu content increased from 0Cu to 3 Cu alloy. In the case of 3Cu alloy, as the amount of residual liquid in the final solidification region exceeded the critical point, a large number of surface defects and internal shrinkage defect were observed. The main secondary phases of the four alloys are the T(Mg32(Al, Zn)49) and η(MgZn2) phase, and their fraction increases with Cu content. These secondary phases were mainly existed in the center segregation band, and a fine η(MgZn2) phase of 141nm was additionally observed. In the case of mechanical properties, as the Cu content increased, the hardness of center matrix, secondary phase, and overall hardness increased respectively. Although the yield strength increased, the tensile strength and elongation decreased because the center segregation band was widened from 684 μm to 790 μm with increasing of Cu content. 박판주조공정으로 제조된 Al-8.0Zn-2.5Mg-xCu(x: 0, 1, 2, 3) 알루미늄 합금의 미세구조 및 기계적 특성에 대한 Cu 함량의 영향을 조사하였다. Al-8.0Zn-2.5Mg-xCu 합금은 Cu 함량이 증가함에 따라 표면 결함이 증가하는 것으로 나타났다. 이는 Cu 함량이 0Cu에서 3 Cu 합금으로 증가함에 따라 최종응고영역에서 잔류 액상량이 9.6 에서 18.3 wt.%로 증가했기 때문이다. 3Cu 합금의 경우 최종응고영역의 잔류 액상량이 임계점을 초과함에 따라 표면결함 및 내부 수축결함이 다수 관찰되었다. 4 가지 합금의 주요 2차상은 T(Mg32(Al, Zn)49) 및 η(MgZn2) 상이며 이들의 분율은 Cu 함량에 따라 증가합니다. 이러한 2차상은 중심편석대에 주로 존재하며, 추가적으로 141nm의 미세한 η(MgZn2)상이 관찰되었다. 기계적 물성의 경우 Cu 함량이 증가할수록 중심기지의 경도, 2차상의 경도, 전체 경도가 각각 증가하였다. 항복강도는 증가하였으나 Cu 함량이 증가함에 따라 중심 편석대가 684에서 790 μm로 넓어지기 때문에 인장강도와 신율은 감소하였다.

백금과 코발트를 담지한 알루미나 촉매상에서 수소를 이용한 NO의 선택적 촉매 환원

최윤정 공주대학교 대학원 2015 국내석사

Al2O3에 Pt와 Co를 공침하여 제조한 촉매들에 대하여 XRD, XPS, TEM, TPR 등을 이용하여 특성분석하고 이들 촉매상에서 H2-SCR을 행하였다. Co/Al2O3와 Pt-Co/Al2O3 촉매에 담지된 Co 입자는 Co3O4 상태로 존재하였고, Co3O4 입자의 평균 크기는 Co 담지량에 관계없이 각각 13 nm와 8 nm였다. 이러한 결과는 Co와 공침한 Pt가 일종의 분산제로서 작용함을 보여준다. Pt-Co/Al2O3 촉매는 Co/Al2O3 촉매와 비교하여 Co3O4 입자의 환원성이 크게 증가하였다. 이러한 결과는 PtO2와 Co3O4가 높은 상호 분산으로 상호 작용이 크게 발현되었기 때문으로 판단된다. 당량비 3에서 Pt/Al2O3 촉매의 경우 담지량에 관계없이 150oC에서 50% 이상의 NOx 전환율을 보였고, 450oC에서는 20% 이상의 전환율을 보였다. Co/Al2O3 촉매의 경우 담지량에 관계없이 200oC에서는 매우 낮은 활성을 보였고, 350oC에서 35% 정도의 NOx 전환율을 보였다. 0.25Pt-Co/Al2O3 촉매의 경우 150oC에서 20-25%의 NOx 전환율을 보였고, 350oC에서 40% 정도의 전환율을 보였다. 이러한 결과는 저온 영역의 활성은 Pt에 기인하며, 고온 영역의 활성은 Co3O4 입자의 환원성 증가에 기인한다고 판단된다. Pt/Al2O3, Co/Al2O3, 0.25Pt-Co/Al2O3 시료 모두 담지량과 당량비에 무관하게 온도가 증가함에 따라 N2O로의 선택성은 감소하고 N2로의 선택성은 증가하였다. 0.25Pt-7Co/Al2O3 촉매에서 당량비에 따라 저온 영역의 활성은 증가하고, 고온 영역의 활성은 거의 일정한 경향을 보였다. 이러한 결과는 수소 농도가 높아지면 Pt와 Co 입자 표면의 환원 상태가 더 안정하지만 고온에서는 촉매 활성을 저해하는 물의 생성이 증가하는 것과 관련 있다고 판단된다. 0.25Pt-Co/Al2O3 촉매에서 당량비 3일 때 저온 영역의 활성은 Co 담지량 7% 시료가 가장 높은 활성을 보였고, 고온 영역의 활성은 담지량에 관계없이 비슷하였다. 0.25Pt-7Co/Al2O3 촉매에서 산소가 없으면 반응온도에 관계없이 100%에 가까운 NOx 전환율을 보였으며, 산소 농도가 증가함에 따라 활성이 약간 감소하는 경향을 보였다. The catalytic characteristics of Al2O3-supported platinum and cobalt catalysts which were prepared by co-impregnation method were studied by XRD, XPS, TEM, and TPR. The SCR of NO with H2 has been investigated over these catalysts with various platinum and cobalt content in a continuous flow reactor. It was found that loaded cobalt in Co/Al2O3 and Pt-Co/Al2O3 existed as Co3O4 on the surface of particles of the catalyst. The average particle sizes of Co3O4 in Co/Al2O3 and Pt-Co/Al2O3 were about 13 nm and 8 nm, respectively. This result indicates that platinum played a role as a dispersant in co-impregnation of Pt and Co. The reducibility of Co3O4 in Pt-Co/Al2O3 made a favorable comparison with that in Co/Al2O3. This result was due to the enhanced interaction between particles of PtO2 and Co3O4 by a good dispersion of loaded platinum and cobalt. Pt/Al2O3 catalysts exhibited above 50% conversion of NOx at 150oC and above 20% conversion at 450oC regardless of platinum content at NSR =3. Co/Al2O3 exhibited a very low activity at 200oC and about 35% conversion of NOx at 350oC regardless of cobalt content. 0.25Pt-Co/Al2O3 catalysts exhibited 20-25% conversion of NOx at 150oC and about 40% conversion at 350oC regardless of platinum content under the same condition. These results suggest that the activity at low temperature of 0.25Pt-Co/Al2O3 was due to platinum and that the activity at high temperature was due to the enhanced reducibility of Co3O4. Selectivity to N2O of Pt/Al2O3, Co/Al2O3 and 0.25Pt-Co/Al2O3 decreased with temperature regardless of loading amount and NSR, whereas selectivity to N2 increased. The activity at low temperature of 0.25Pt-7Co/Al2O3 increased with NSR, while the activity at low temperature showed nearly no difference. This result may be related to increase of H2O to impede the catalytic activity at high temperature, although the reduced state of particle surfaces of Pt and Co was more stable with hydrogen concentration. 0.25Pt-Co/Al2O3 with 7% of cobalt exhibited the maximum activity at low temperature, whereas the catalysts showed similar activities at high temperature regardless of loading amount at NSR = 3. NOx conversion of almost 100% was observed over 0.25Pt-7Co/Al2O3 in oxygen free feed and the catalytic activity slightly decreased with oxygen concentration.

제주지역 알아넌(Al-Anon) 참여자들의 치유과정 연구

박후남 제주대학교 2020 국내석사

This study sought to categorize the healing process of alcohol-related disabled spouses attending in "Jeju City Al-Anon" through the grounded theory. In particular, the company wanted to establish a substantial theory on the healing process of alcohol-impaired spouses attending in Jeju Al -Anon by exploring the special nature of Jeju Island. A key research issue to this end is ‘How is the healing process of Al-Anon attenders?’, ‘What is the specificity and context of Jeju Al-Anon’ and ‘How can typify the healing process of Jeju Al-Anon attenders?’ For the purpose of this study, the target was presented in theory to eight alcohol-impaired spouses who participated in ‘Jeju City Al-Anon.’ The research method was qualitatively analyzed through in-depth interviews with study attenders by applying the evidence theory research method presented by Strauss and Corbin (1998/2001). The analysis result produced 132 concepts with open coding, and abstracted the concept to obtain 41 subcategories, and the final 16 categories were derived. The main contents of the analysis are as follows. First, causative conditions were found to be "deteriorating spouse’s drinking," "compressed by pain," "family crisis" and "interference and control." The central phenomenon was ‘I want to live my life happily In the midst of pain and difficulty.’ - 98 - The contextual condition was ‘awareness of addiction’. Also, the Jeju area’s contextual characteristics results showed that ‘visit the church to consult’ and ‘It is difficult to participate because of the Gwendang culture.’ The arbitration terms were first ‘internal resource utilization’ and ‘assistance to the operation of Al-Anon’. Next, Jeju’s ‘intermediated characteristics’ were ‘the same faith group,’ ‘regular education and programs,’ and ‘continuous counseling.’ Action and interaction strategies were found to be ‘focusing on one’s own changes, ‘efficiency in response’ and ‘positive changes presented’. As a result of these action and interaction strategies, ‘living as a healthy entity’, ‘relationship recovery.’ And ‘speciality of Jeju results’ was found to be ‘the formation of a new Gwendang called Al-Anon-specific application of anonymity’ and ‘the inner strength by faith.’ Second, considering the specificity of Jeju area and the change over time, the healing process for attenders in Jeju Al-Anon was derived in five stages. Stage 1 is ‘the phase of reaching the limit’. It is a phase in which attenders face their limits in despair over their spouse's drinking situation. Stage 2 is the ‘Step of Conflict between Gwendang Culture and the Al-Anon.’ Participants of Al-Anon become aware that disability is a disease and feel they need help. However, it is in the process of wandering in the Jeju area, which is composed of "Gwendang," unable to come to Al-Anon. Stage 3 is the ‘Step of application of the principles of faith and Al-Anon’. This is the stage in which participants will attend Al-Anon thanks to the encouragement of the priest and the counselor sister. At this stage, changes take place as participants apply Al-Anon's principles to life. The following are steps 4, which are ‘the same faith group and the steps to form a new Gwendang’. Participants will participate in long-term meetings recognized by the same faith-based trust. Around this stage, a new ‘Gwendang’ is formed. In the fifth phase of ‘the quality of life change phase’, participants will embrace their spouses, children and themselves. Thank you for everything and try to find God's will in his painful life. Participants will live a life of service. In addition, as a result of the study, a core category of ‘sublimation of pain’ was introduced. The meaning of the core category is that the participants have found the outcome of a healing process in which they live in pursuit of their own and family happiness beyond their own limits, recognizing that they are ill and leaving their own suffering to God, even though they have been suffering from alcohol-related assaults and family crises. It is meaningful that by developing a theory of substance in the special context of ‘Jeju City Al-Anon ’ in this study, Al-Anon may be applied to different regions in a unified structure. Because use-disorder is repetitive and persistent, spouses have psychological challenges that cannot be solved. A strong support system is formed within the special context of ‘the same faith group’ and ‘Gwendang’. It is also worth the research to reveal that this structure is providing an effective stage for the treatment of unsolved challenges. The significance of this study is that it has uncovered actual and concrete grounds data for counseling interventions of alcohol use disorder spouses. 이 연구는 ‘제주시 알아넌’에 참여하는 알코올사용장애 배우자의 치유과정을 근거이론을 통해 유형화하고자 했다. 특히 제주지역의 특수성에 대해 심층 탐색 하여 ‘제주시 알아넌’에 참여하는 알코올사용장애 배우자의 치유과정에 대한 실 체이론을 구축하고자 했다. 이를 위한 핵심 연구 문제는 ‘알아넌 참여자들의 치 유과정은 어떠한가?’와 ‘제주시 알아넌의 특수성과 그 맥락은 무엇인가?’, 그리고 ‘제주시 알아넌 참여자의 치유과정을 어떻게 유형화 할 수 있는가?’이다. 이 연구를 위하여 대상은 ‘제주시 알아넌’에 참여하고 있는 알코올사용장애 배우자 8명을 대상으로 이론 표출하였다. 연구방법은 Strauss와 Corbin(1998/2001)이 제시한 근거이론 연구방법을 적용하여 연구 참여자들과의 심층 면담을 통해 수집한 자료를 질적 분석하였다. 분석 결과 개방코딩으로 132 개의 개념을 생성하였고, 개념을 추상화하여 41개의 하위범주를 얻었으며 최종 16개의 범주를 도출하였다. 주요 내용은 다음과 같다. 첫째, 인과적 조건은 ‘배우자의 음주 악화’, ‘고통에 짓눌림’, ‘가족의 위기’, ‘간 섭과 통제’로 나타났다. 중심현상은 ‘고통과 난관 속에서도 삶을 행복하게 살아내 고 싶다.’라고 나타났다. 맥락적 조건은 ‘사용장애에 대한 인식’이 있었다. 그리고 제주지역의 맥락적 특성으로 ‘교회를 찾아가서 상담을 함’과 ‘괸당 문화로 인해 알아넌 참여가 어려움’으로 나타났다. 중재적 조건은 우선 ‘내적 자원 활용’과 ‘알 아넌 운영의 도움’이 있었다. 다음으로 ‘제주지역 중재적 특성’으로 ‘동일한 신앙 그룹’, ‘정기적인 교육 및 프로그램’, ‘지속적 상담’으로 나타났다. 작용․상호작용 전략은 ‘자신의 변화에 집중’, ‘효율적인 대처’, ‘긍정적인 변화 나타남’으로 나타났 다. 이러한 작용․상호작용 전략의 결과로 ‘건강한 개체로 살아가기’, ‘관계 회복’ 으로 나왔다. 그리고 ‘제주지역 결과의 특수성’으로 ‘알아넌이라는 새로운 괸당 형성-익명성의 특수한 적용’, ‘신앙으로 내면이 강해짐’으로 나타났다. 둘째, 제주지역의 특수성과 시간의 흐름에 따른 변화를 감안했을 때 ‘제주시 알아넌’에 참여하는 참여자들의 치유과정은 5단계로 도출되었다. 1단계는 ‘한계 상황 도달 단계’이다. 참여자들이 배우자의 음주 상황에 절망적인 상태에서 자신 - v 의 한계에 부딪히게 되는 단계이다. 2단계는 ‘괸당 문화와 알아넌의 충돌 단계’이 다. 참여자들이 알코사용장애가 병임을 인식하고 도움이 필요함을 느끼게 된다. 그러나 ‘괸당’으로 엮여 있는 제주지역 안에서 알아넌에 오지 못하고 방황하는 단계이다. 3단계는 ‘신앙과 알아넌의 원리 적용 단계’이다. 참여자들이 신부님과 상담 수녀님의 격려에 힘입어 알아넌에 참석하게 되는 단계이다. 이 단계에서 참 여자들은 알아넌의 원리를 삶에 적용하면서 변화가 일어나게 된다. 다음은 ‘동일 한 신앙그룹 및 새로운 괸당 형성의 단계’인 4단계이다. 참여자들은 동일한 신앙 에 의한 신뢰감으로 알아넌 모임에 장기적으로 참여하게 된다. 이 단계 즈음에 새로운 ‘괸당’이 형성된다. 5단계인 ‘삶의 질의 변화 단계’에서는 참여자들이 배우 자와 자녀 및 자신을 수용하게 된다. 모든 상황에 감사하며 자신의 고통스러운 삶 안에서 신의 뜻을 찾으려 한다. 참여자들은 봉사의 삶을 살아가게 된다. 또한, 연구의 결과로 ‘고통의 승화’라는 핵심범주가 상정되었다. 핵심범주의 의미는 참여자들이 음주로 인한 배우자의 폭행과 가정의 위기 속에서 고통스럽 게 살았으나 사용장애가 병임을 인식하고 신께 자신의 고통을 맡기면서 자신의 한계를 넘어서 자신과 가족의 행복을 추구하며 살게 되는 치유 과정의 결과를 찾아냈다는 것이다. 이 연구에서 ‘제주시 알아넌’의 특수한 맥락의 실체이론을 개발함으로써 알아 넌이 통일된 구조 안에서 지역마다 특색적으로 적용될 수도 있다는 점을 밝힌 것은 의미가 있다. 사용장애가 반복적이고 지속적인 것이므로 해결되지 못한 심 리적 과제들을 배우자들은 갖게 된다. ‘제주시 알아넌’은 ‘동일한 신앙 집단’이라 는 것과 ‘괸당’이라는 특수한 맥락 안에서 강력한 지지체계가 형성된다. 이 구조 가 미해결과제의 치료에 대해서 효과적인 장을 마련하고 있다는 것을 밝힌 것도 연구의 가치라고 보겠다. 이 연구의 의의는 알코올사용장애 배우자의 상담개입을 위한 실제적이며 구체적인 근거자료를 밝혀냈다는 것이다.

Combined effects of ultrasonic melt treatment and Cu/Mg solute on strengthening and microstructural refinement for Al-Si-Cu-Mg alloys

김수배 Graduate School, Yonsei University 2020 국내박사

Hypo-eutectic Al-Si-Cu-Mg cast alloys are most widely used for automobile component among the various Al cast alloys due to their good castability, relatively high strength, high resistance to corrosion, good weldability and low coefficient of thermal expansion etc. The microstructure of these alloys consists of coarse dendritic α-Al, coarse needle-like eutectic Si and various intermetallic compounds (IMC) which are formed by addition of alloying elements, mainly Cu and Mg. Because the coarse dendritic α-Al and needle-like eutectic Si have detrimental to mechanical properties of the alloys, various microstructural refinement methods such as addition of refiner, rapid solidification and mechanical stirring are usually employed. Among mechanical stirring methods, ultrasonic melt treatment (UST) has been raised as the promising method due to its economic and environmental friendliness. Pioneer researchers have successfully obtained the microstructural refinement and improvement of the mechanical properties of hypoeutectic Al-Si-Cu-Mg alloys, by employing UST. Two most important phenomena of UST, cavitation and acoustic streaming, has been suggested to account for the microstructural refinement of α-Al grain and various primary phases formed in the initial stage of solidification. On the other hand, its effect on solute behavior at the final stage of solidification has been less understood. The strength of Al-Si-Cu-Mg alloys mainly depend on Cu/Mg solutes which induce solid solution strengthening and precipitation strengthening. In addition, Cu and Mg solutes form IMC at the final stage of solidification. Therefore, such a lack of understanding for the interactive effect of solute with UST could limit the exact interpretation of following important issues achieved through UST : 1) ultrasonically induced strengthening of the alloys and 2) alloying design using UST. Thus, the current study aims to investigate the effect of UST on Cu and Mg solute during solidification of hypoeutectic Al-Si-Cu-Mg alloys. Based on this, the author tried to achieve following purposes ; 1) interpretation of microstructural refinement and strengthening induced by UST, 2) investigation each roles of Cu and Mg which are main alloying elements for the alloy under UST. According to the purposes, in chapter 3, the role of UST on solute behavior during solidification of hypoeutectic Al-Si-Cu-Mg alloy was investigated. Furthermore, based on the solute effect under UST, strengthening by UST was tried to be interpreted. UST was applied to Al-7Si-2Cu-1Mg alloy at a temperature about 100 oC higher than liquidus of the alloys. UST did not refine grain, and instead decreased secondary dendrite arm spacing (SDAS). It was found that MgAl2O4 particles naturally present in the alloys are well wetted by UST and induces hyper-branching dendrite, leading to SDAS refinement. IMCs were more uniformly distributed by UST compared to absence of UST. Quantitative analysis on volume fraction of IMC confirmed that UST reduced micro-segregation, suppressing formation of IMC formed at the final stage of solidification, along with the decrease in SDAS. In addition, as the micro-segregation decreased, solubility of solute in α-Al matrix increased. The mathematical model of yield strength predicted that the strengthening by UST attributes to increment of solid solution strengthening due to increase in solute content in Al matrix. In chapter 4, each role of Cu and Mg under UST on the microstructure and tensile properties was investigated by varying Cu (0-4 wt.%) and Mg (0.35-1.00 wt.%) content. It was found that UST was ineffective in refining grain but reduced micro-segregation with SDAS refinement. However, with increasing Cu content, SDAS refinement efficiency decreased and IMC volume fraction of the alloy with UST becomes similar with that of the alloy without UST. On the other hand, as Mg content increases, SDAS of the alloy with UST decreased and the effect of decreasing IMC volume fraction by UST was also increased. This is due to the increase in numbers of MgAl2O4 particles finely dispersed by UST, which can somehow affect the SDAS refinement. With UST, Cu solute in refining grain size and SDAS diminished while, an increase in Mg led to structural refinement. A significant reduction in grain size through Mg addition combined with UST may be associated with the formation of finely dispersed MgAl2O4 particles with the increase in the number density. The most significant increase in yield strength was achieved for the Al-7Si-2Cu-1Mg alloy with UST where SDAS was well refined. In chapter 5, the effect of UST on primary α-Al grain refinement was investigated. In the previous chapters, UST did not induce the grain refinement. The absence of the grain refinement under UST is mainly explained by high temperature of melt and reduction in nucleation particles size. However these interpretations are still in controversial. Thus, Ultrasonic melt treatment (UST) was applied to Al-7Si-2Cu-1Mg melt at various temperatures of 620, 650, 700 and 785 oC. MgAl2O4 particles which were often found to be densely populated along oxide films, became effectively dispersed and well-wetted by UST. Transmission electron microscopy work combined with crystallography analysis clearly indicates that MgAl2O4 particles can act as α-Al nucleation site with the aid of UST. However, with UST, grain refinement occurred only at temperature of 620 oC and the grain size increased from 97 to 351 μm with increase of melt temperature to 785 oC for UST. In quantitative analysis of grain size and MgAl2O4 particle diameter, it was found that ultrasonic de-agglomeration decreased mean particle size of the MgAl2O4 particles, significantly reducing size from 1.2 to 0.4 μm when temperature increased from 620 to 785 oC. Such a size reduction with increased number of MgAl2O4 particles does not always guarantee grain refinement. Thus, in this work, detailed condition for achieving grain refinement by UST is discussed based on quantitative measurement. Furthermore, we tried to suggest the most valid grain refinement mechanism among the known mechanisms by investigation of the relationship between grain size and particle size with variation of melt temperature.