실시간 관찰을 통한 응력부식균열의 개시 및 성장거동 평가 연구

Title
실시간 관찰을 통한 응력부식균열의 개시 및 성장거동 평가 연구
Author
송단비
Advisor(s)
이창희
Issue Date
2018-08
Publisher
한양대학교
Degree
Master
Abstract
본 연구는 In-situ 광학 현미경 및 전자 후방산란 회절(EBSD) 장치를 이용하여 예민화 열처리된 니켈 합금의 입계부식균열(IGSCC)의 initiation 및 coalescence의 메커니즘에 관한 내용이다. C-ring 시편에 항복응력을 가하기 전후를 EBSD를 이용하여 촬영하여 결정립계의 변화에 대한 정보를 얻었다. 0.1M의 sodium tetrathionate 용액에서 부식시험을 수행하면서 C-ring 시편의 옆면에 생성되는 균열성장 거동을 실시간으로 관찰하였다. 광학현미경을 통해 실시간으로 결정립계를 따라 성장하는 균열의 전파를 local misorientation, Schmid factor, Schmid factor mismatch와 grain boundary character와 같은 EBSD로 부터 유도된 인자와 비교하였다. 균열이 발생한 결정립계와 발생하지 않은 결정립계에서의 각 균열 단계에서 주요 요인을 EBSD를 이용하여 얻은 local strain, normal/residual stress 그리고 grain boundary character 측면에서 논의하였다.
The present work is concerned with a mechanism of IGSCC initiation and coalescence of thermally sensitized Ni alloy using in-situ optical microscopy and electron back scatter diffraction (EBSD). The in-situ observation was performed on the side surface of C-ring specimen during the corrosion test in a sodium tetrathionate solution at room temperature. The geometric and microstructural factors at grain boundary characters were measured on the observation area from EBSD before and after deformation of the C-ring specimen. The cracking behavior of grain boundary monitored from the in-situ observation along the cracking path was compared with the EBSD-derived parameters such as local misorientation, Schmid factor, Schmid factor mismatch and grain boundary character. From the analysis of the distribution of EBSD-derived parameters of the cracked and the intact GBs, dominant factors playing an important role in each cracking step are discussed in terms of local strain, normal/residual stress, and grain boundary character. The residual strain at GB is not a dominant factor for IGSCC but possibly enhance crack initiation in a random manner. Among those factors, the GB character is the most crucial to determine cracking possibility. The normal stress applied to GB becomes dominant when GB characters are the same.
URI
http://dcollection.hanyang.ac.kr/common/orgView/000000107147http://repository.hanyang.ac.kr/handle/20.500.11754/75724
Appears in Collections:
GRADUATE SCHOOL[S](대학원) > MATERIALS SCIENCE & ENGINEERING(신소재공학과) > Theses (Master)
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