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기계적 합금화법으로 제조된 과포정 Al-Ti합금에서 Al3Ti 형성에 관한 연구
김혜성,서동수,김긍호,금동화 ( Hye Sung Kim,Dong Soo Suhr,Gyeung Ho Kim,Dong Wha Kum ) 한국열처리공학회 1996 熱處理工學會誌 Vol.9 No.1
Mechanical alloying is an effective process to finely distribute inert dispersoids in an Al-TM(TM is a transition metal) system. It has been considered that high melting point aluminides are formed by precipitation from supersaturated Al(Ti) powder. This analysis is based on the fact that much higher content of TM than the solubioity can be dissolved in alpha aluminum during the high energy ball milling. Thus, decomposition behavior of Ti in the Al(Ti) was considered very important. But it is confirmed that the higher portion of Ti than Al(Ti) solid solution is existed as nano-sized Ti particles in the MA powders by high energy ball nilling from the XRD spectrum and TEM analysis in this study. Therefore, the role of undissolved TM particles affect the formation of aluminides should be suitably considered. In this study, we present experimental observation on the formation of Al₃Ti fron mechanical alloyed Al-Ti alloys in the hyperperitectic region. This study showed that, in the mechanically alloyed Al-20wt%Ti specimen, intermediate phase of cubic Al₃Ti and tetragonal Al_(24)Ti_8 formed at 300∼400℃ and 400∼500℃, respectively, before the MA state reaches to equilibrium at higher temperatures. The formation behavior of Ll₂-Al₃Ti is interpreted by interdiffusion of A1 and Ti in solid state based on the fact that large amount of nano-sized Ti particles exist in the milled powder. Present analysis indicated undissolved Ti particles of nanosize should have played an important role initiation the formation of Al₃Ti phase during annealing.
기계적 합금화법에 의해 제조된 Al+Al3Ti합금 및 Al+10wt.%Ti합금의 고용현상
김혜성,이정일,김긍호,금동화,서동수( Hye Sung Kim,Jung Ill Lee,Gyeung Ho Kim,Dong Wha Kum,Dong Soo Shur ) 한국열처리공학회 1996 熱處理工學會誌 Vol.9 No.2
The solubility of Ti in Al matrix was determined by X-ray diffraction method on two different mechanical alloying systems, i.e Al+Al₃Ti and Al+Ti alloys. Starting powder compositions of two systems were chosen for final volume fraction of Al₃Ti phase being 25%. The solubility of Ti in α-Al was estimated by the lattice parameter measurement of Al. For Al+Al₃Ti mixture, it appeared that some of Al₃Ti particles decomposed during milling and maximum solubility of Ti in A1 was about 0.99%. The majority of Al₃Ti particles were dispersed uniformly in Al matrix, having approximate size of 100∼200㎚. On the other hand, higher Ti solubility of 1.24 wt.% was found in Al+Ti system, with starting composition of Al+10 wt.%Ti. After 15 hours of milling, Ti phase was identified as 20㎚ sized particles embedded in Al matrix. The annealing of mechanically alloyed powders from Al+Al₃Ti and Al+10 wt.%Ti systems was followed in the temperature range of 200 to 600℃ to study thermal stability of supersaturated solution of Al(Ti). After annealing, the lattice parameter of A1 reverted back to that of pure Al, and the peak intensity ratio of Al₃Ti/Al was increased more than the original value before annealing. These results suggest that Ti dissolve into alpha-Al solutions during milling, and by annealing, Do_(22)-Al₃Ti phase forms from Al(Ti) solution.
유전체장벽방전에 의한 질소함유 활성종의 개발 및 저온 GaN 박막 성장
김주성,변동진,김진상,금동화,Kim, Joo-Sung,Byun, Dong-Jin,Kim, Jin-Sang,Kum, Dong-Wha 한국재료학회 1999 한국재료학회지 Vol.9 No.12
TMGa와 유전체 장벽방전에 기초한 질소함유 활성종을 이용하여 (0001) 사파이어 기판위에 GaN 박막을 저온에서 성장시켰다. III-V 질소화합물 반도체의 에피막 성장에 있어서 암모니아는 유기금속 화학증착법에서 지금까지 알려진 가장 보편적인 질소 공급원이며 충분한 질소공급을 위해 $1000^{\circ}C$ 이상의 고온 성장이 필수적이다. GaN 박막을 비교적 저온에서 성장시키기 위하여 질소 공급원으로 암모니아 대신 유전체 장벽방전을 이용하였다. 유전체 장벽방전은 전극사이에 유전체 장벽을 설치하여 arc를 조절하는 방전이며 수 기압의 높은 공정압력보다 훨씬 높으므로 기판표면까지 전달하는데도 이점이 있다. GaN 박막의 결정성과 표면형상은 성장온도, 완충층에 따라 변화하였으며, $700^{\circ}C$의 저온에서도 우수한 (0001) 배향성을 갖는 GaN 박막을 성장할 수 있었다. GaN films were deposited on sapphire [$Al_2O_3(0001)$] substrates at relatively low temperature by MOCVD using N-atom source based on a Dielectric Barrier Discharged method. Ammonia gas($NH_3$is commonly used as an N-source to grow GaN films in conventional MOCVD process, and heating to high temperature is required to provide sufficient dissociation of $NH_3$. We used a dielectric barrier discharge method instead of $NH_3$ to grow GaN film relatively low temperature. DBD is a type of discharge, which have at least one dielectric material as a barrier between electrode. DBD is a type of controlled microarc that can be operated at relatively high gas pressure. Crystallinity and surface morphology depend on growth temperature and buffer layer growth. With the DBD-MOCVD method, wurtzite GaN which is dominated by the (0001) reflection was successfully grown on sapphire substrate even at $700^{\circ}C$.