서지주요정보
질화규소에서 입계상이 접촉손상에 미치는 영향 = Effect of grain boundary phase on the contact damage behavior in $Si_3N_4$
서명 / 저자 질화규소에서 입계상이 접촉손상에 미치는 영향 = Effect of grain boundary phase on the contact damage behavior in $Si_3N_4$ / 이철승.
저자명 이철승 ; Lee, Chul-Seung
발행사항 [대전 : 한국과학기술원, 1999].
Online Access 원문보기 원문인쇄

소장정보

등록번호

8009379

소장위치/청구기호

학술문화관(문화관) 보존서고

MMS 99038

SMS전송

도서상태

이용가능

대출가능

반납예정일

초록정보

The role of grain boundary phase on contact damage behavior in silicon nitride ceramics was investigated using Hertzian indentation test. In order to consider only grain boundary effect, all of the microstructure effects except grain boundary must be fixed. The facts that could affect the contact damage behavior in silicon nitride ceramics are grain size, aspect ratio of grain, phase fraction, and interphase. In the prior study the effects of grain size, aspect ratio and phase fraction on contact damage behavior were considered simultaneously. But in those study they omitted the role of grain boundary effect because of the different sintering temperature of specimens. Especially because high toughness of silicon nitride are related with the crack deflection and bridging mechanism due to weak interphase boundary, we could expect that grain boundary phase could be a another factor for affecting the damage mode of Hertzian indentation. Grain boundary effects were treated as two parts. One was grain boundary phase effect, the other was grain boundary composition effect. In part I, grain boundary phase was changed by additional heat treatment. The sintering additives were 2wt% $Al_2O_3$, 5wt% $Y_2O_3$, and 1wt% MgO. From x-ray diffraction pattern new crystalline phases were made after heat treatment. The microstructures of two samples were regarded as similar size and shape as a result of image analysis, and phase fraction of β was also almost same as x-ray diffraction. And more hardness and toughness were not so different. So the grain boundary of G named specimen could be thought to have a glassy grain boundary phase and that of C named specimen to have a crystallized grain boundary phase. For these two samples damage mode were compared by Hertzian indentation as a like top view, side view by bonded specimen method, and strength degradation. As a result crystallized C sample made ring crack at lower load than that of G and showed longer cone crack and narrower damage zone. The reason they showed the different damage behavior was from the difference of grain boundary strength. After crystallization of grain boundary it has strong interface so that its grain boundaries can't slide easily. From that reason, C sample could show brittle fracture and less damage tolerance. In part Ⅱ, grain boundary composition effect was considered. The sintering additives of AY sample was 2wt% $Al_2O_3$ and 6wt% $Y_2O_3$, and that of M sample was 6.24wt% MgO. They were sintered at different temperatures so that they had similar microstructures when they were analyzed by x-ray diffractometer and image analysis. Hardness and toughness are also similar from the result of Vickers indentation. When Hertzian indentation test is conducted AY sample made ring crack at higher load than M sample and showed more wide damage zone. So we could think that AY sample was more damage tolerant than M sample. To distinguish the source of different damage behavior, glasses of grain boundary phase were made referring to phase diagrams of Y-Si-Al-O-N and Mg-Si-O-N. Then thermal expansion coefficients of each glass were measured and from this data residual stresses which were induced between grain and grain boundary could be calculated. Both sample had residual compressive stresses at grain and residual tensile stressed at grain boundary. But for residual stresses of AY sample was larger than M, we could think these different residual stresses could be the source of different damage behavior. At finally a conclusion could be made that grain boundary phase could be another factor for damage behavior as well as grain morphology.

서지기타정보

서지기타정보
청구기호 {MMS 99038
형태사항 v, 84 p. : 삽도 ; 26 cm
언어 한국어
일반주기 저자명의 영문표기 : Chul-Seung Lee
지도교수의 한글표기 : 배병수
지도교수의 영문표기 : Byung-Soo Bae
학위논문 학위논문(석사) - 한국과학기술원 : 재료공학과,
서지주기 참고문헌 : p. 77-84
주제 질화규소
구형압자압흔법
접촉손상
입계
Silicon nitride
Hertzian indentation
Contact damage
Grain boundary
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