서지주요정보
탄소를 함유한 Mn-Al 합금의 구조 및 상변태에 관한 연구 = Crystal structure and phase transformation of C-doped Mn-Al alloys
서명 / 저자 탄소를 함유한 Mn-Al 합금의 구조 및 상변태에 관한 연구 = Crystal structure and phase transformation of C-doped Mn-Al alloys / 이종탁.
저자명 이종탁 ; Lee, Chong-Tak
발행사항 [대전 : 한국과학기술원, 1992].
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소장정보

등록번호

8003140

소장위치/청구기호

학술문화관(문화관) 보존서고

DMS 92028

SMS전송

도서상태

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초록정보

This study has been undertaken to investigate the site occupancy of carbon atoms in the ordered b.c.t. τ phase of Mn-Al alloys. The phase transformation mechanism induced by the presence of carbon atoms in ε phase lattice leading to τ phase has also been investigated. The phase constitution and the lattice parameter relationships in the rapidly solidified and heat-treated $(Mn_0.53Al_0.47)_{100-x}C_x$ pseudobinary alloys (x=0~5.36) have been investigated by means of X-ray diffraction and transmission electron microscopy. The melt-spun alloy was in single ε phase (c.p.h.) in the 0.63 ~ 4.0 at.% C composition range. Below the lower carbon composition limit traces of $γ_2$ were found while $Al_4C_3$ carbide was found beyond the upper limit. Heat treatment of the melt-spun alloys at 823 K produced single τ phase (ordered b.c.t., Cuau type I, $Ll_0$) in the $0.63~3.6 at.% C range. The lattice parameters (a and c) of ε phase were observed to incease with the carbon content. In contrast, c parameter increased markedly with the carbon content while a decreased slightly in τ phase, thereby a large value of the c/a ratio resulted. The lattice parameter data for both the ε and τ phases clearly indicated an increase of the unit cell volume with the carbon content, which supports a notion that carbon atoms in the τ lattice occupy interstitial site. In order to investigate the site occupancy of carbon atoms in the ordered body-centered structure fo τ phase in carbon doped Mn-Al alloys, a series of structure analyses by x-ray diffraction has been carried out. Four different carbon atom occupancy models were presented, i.e, a substitutional (aluminum) site (1/2,1/2,1/2,), octahedral interstitial site (1/2,1/2,0), (0,0,1/2) site and intersititial random occupation. The structure factor for each model is formulated by introducing a disorder parameter that is defined by the number of aluminum atoms at the manganese site, (0,0,0), therefore, the semi-empirical integrated intensities are calculated for $(Mn_0.53Al_0.47)_100-x C_x (x=0~3.15) τ phase using an experimentally determined disorder parameter of carbon free alloy and employing an assumption that it would not be significantly influenced by the carbon addition. The semi-empirical intensity ratio $I_{200}/I_{100}$ calculated for each model was compared with the observed intensity ratio as a function of the carbon content, from which it becomes evident that carbon atoms preferentially occupy the octahedral interstitial site (1/2,1/2,0). Further discussions relevant to this conclusion are also presented. The phase transformation of τ phase and orientation relationship between the τ phase and the matrix in the rapidly solidified $(Mn_0.53Al_0.47)_96.86C_3.14$ alloy have been investigated by the transmission electron microscopy. After heat treatment of the melt-spun alloy at 723K, single ε phase transformed to ordered ε phase and τ phase. Nucleation of τ phase took place at the grain boundaries as well as subgrain boundaries of the initial ε phase. But two types of τ phase nucleation occurred simulataneously at the grain boundaries. In the first case, an orientation relationship between nuclei of τ phase and the adjacent grain is established. In this case, the nuclei of τ phase is in the platelike shape and they grow to the direction of plate. It is seen that nuclei plates are parallel with the $(0002)_ε$ habit plane of the adjacent grain. Nucleation takes place via the diffusion controlled process which may be interpreted as a discontinuous precipitation reaction. In the second case, another orientation relationship between τ phase and matrix is established. In this case, streaks in the SAD pattern of τ phase appears and the tip of τ phase front shows the sharp martensitic character. Thus, it is assumed that this mechanism proceeds via martensitic transformation.

서지기타정보

서지기타정보
청구기호 {DMS 92028
형태사항 v, 113 p. : 삽도 ; 26 cm
언어 한국어
일반주기 부록 수록
저자명의 영문표기 : Chong-Tak Lee
지도교수의 한글표기 : 주웅길
지도교수의 영문표기 : Woong-Gil Choo
학위논문 학위논문(박사) - 한국과학기술원 : 재료공학과,
서지주기 참고문헌 : p. 111-112
주제 Crystallography.
Precipitation (Chemistry)
Oriantation.
Aluminum-Mangnese alloys.
상변태. --과학기술용어시소러스
미세 구조. --과학기술용어시소러스
망간 함유 합금. --과학기술용어시소러스
석출. --과학기술용어시소러스
결정 방위. --과학기술용어시소러스
Phase transformations (Statistical physics)
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