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오스테나이트계 Fe-Ni based 합금강의 열화 시간에 의한 탄화물 거동과 기계적 물성 변화에 대한 연구
김기근(Keekeun Kim),박수(Soo Park),석창성(Chang-Sung Seok),최재구(Jae Gu Choi),김가연(Gayeon Kim) 대한기계학회 2018 大韓機械學會論文集A Vol.42 No.11
Fe-Ni-Cr 오스테나이트계 합금강 중 NCF3015 소재는 Ni 원소의 함량을 증가시켜 고온 기계적 물성을 우수하게 만든 소재이다. 고온 기계적 물성은 미세조직의 형상과 밀접한 관계가 있으며 미세조직의 형상은 고온노출 온도와 시간에 따라 변할 수 있기 때문에, 재료의 고온 미세조직 변화와 기계적 물성변화에 대한 연구가 필요하다. 본 연구에서는 950℃에서 NCF3015 소재의 열화 시간에 따른 미세조직 및 탄화물 변화와 기계적 물성과의 관계를 분석하기 위해 Thermo-calc 프로그램을 통한 평형 상태도 해석으로 NCF3015 소재의 고온 미세조직 변화를 예측하였으며, 실험적으로 열화된 시편의 미세조직 분석을 통해 해석결과와 비교하였다. 또한 인장시험과 비커스 경도를 측정함으로써 열화 시간에 따른 기계적 물성변화를 분석하였으며 이를 탄화물 거동변화와 관련 지어 두 변화의 상관관계를 도출하였다. NCF3015 is a Fe-Ni-Cr austenitic alloy steel that increases the content of Ni elements and which results in excellent high-temperature mechanical properties. High-temperature mechanical properties are closely related to the microstructure, and the shape of the microstructure can be changed by the exposure temperature and time. Therefore, it is necessary to study the changes in the high-temperature microstructure and mechanical properties of materials. In this research, to analyze the relationship between microstructural and carbide changes, as well as the mechanical properties of NCF3015 at 950℃, an equilibrium-state analysis is performed using the Thermo-calc program to determine the microstructural changes. The results are compared with the experimental results obtained. In addition, the tensile test and the Vicker"s hardness test are conducted to determine the variation in the mechanical properties with degradation time, which was correlated with the changes of microstructural and carbide behavior.
High-temperature delamination mechanism of superalloy and ceramic composites
Keekeun Kim(김기근),Kibum Park(박기범),Damhyun Kim(김담현),Namgyu Jun(전남규),Chang-Sung Seok(석창성) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11
Composite materials are considered as a new alternative for high performance in extreme environments owing to the advantage of being able to utilize the properties of different materials at the same time. Accordingly, the issue of bonding and life-span management of composite is attracting attention, and in order to solve these issues, a basic understanding of the failure mechanism at the interface is required. In this study, a study was conducted on a composite material composed of a superalloy used in an ultra-high temperature gas turbine environment and a ceramic to protect it, and the failure mechanism at high temperature was investigated. The delamination of the composite interface was dominantly affected by the oxide growth and the resulting stress distribution, and the fracture surface was different due to the change in the stress distribution accelerated as the temperature increased.