서지주요정보
탄소 및 질소가 첨가된 TiAl 금속간화합물의 미세조직과 기계적 성질 = Microstructure and deformation of TiAl intermetallic compound added with carbon and nitrogen
서명 / 저자 탄소 및 질소가 첨가된 TiAl 금속간화합물의 미세조직과 기계적 성질 = Microstructure and deformation of TiAl intermetallic compound added with carbon and nitrogen / 윤주환.
저자명 윤주환 ; Yun, Ju-Hwan
발행사항 [대전 : 한국과학기술원, 2000].
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8011480

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학술문화관(문화관) 보존서고

DMS 00035

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초록정보

Gamma-based TiAl alloy has been known to be one of the most promising candidates for high-temperature structural applications. However, two typical microstructures of the TiAl alloy, such as the fully lamellar microstructure and the duplex microstructure, have shown a so-called inverse relationship between room-temperature ductility and fracture toughness/creep resistance. The fully lamellar TiAl have excellent creep resistance and fracture toughness, even though poor room temperature ductility. In contrast, the duplex TiAl alloys have considerable room temperature ductility but low levels of creep properties. Therefore, it is necessary to develop a TiAl alloy system with balanced mechanical properties. This thesis deals with the microstructural control of the fully lamellar and the duplex microstructure of carbon and nitrogen doped alloys Chapter 3 and their tensile properties in Chapter 4 and their creep properties in Chapter 5 and their fracture toughness in Chapter 6. In chapter 3, Effects of nitrogen addition on the microstructure and the mechanical properties of two-phase TiAl intermeetallic compounds were investigated. 1.0at.% nitrogen addition leads to remarkable grain refinement in the fully lamellar microstructure but had little effect on the duplex microstructure. These facts are caused by $Ti_2AlN$ precipitates which observed in only 1.0at.% nitrogen-doped alloys. The carbon and nitrogen atoms may delayed the diffusion in the lattice. Therefore, heat treatment time of the duplex alloys were required over 24 hours. In Chapter 4, We examined tensile properties of the alloys of Chapter 3 at room temperature and elavated temperature. Though 0.3at.% nitrogen-doped alloy had much lower elongation than the mother alloy, 1.0at.% nitrogen addition had little effect on room temperature elongation and increased room temperature yield strength by two times in the fully lamellar microstructure. High temperature yield strength of the nitrogen-doped alloys increased due to solute hardening and precipitation hardening of $Ti_3AlN$. In Chapter 5, we investigated the creep properties of carbon and nitrogen doped alloys seclected in Chapter 3 and 4. Nitrogen addition led to remarkable improvement of creep resistance in the duplex microstructure as well as in the fully lamellar microstructure. In particular, the primary creep deformation of the 1.0at.% nitrogen-doped alloy with the duplex microstructure decreased definitely to a similar or superior level of the fully lamellar alloy. We consider that precipitate hardening of $Ti_3AlN$ precipitates and solute hardening of nitrogen atoms may be responsible for such remarkable creep resistance of the nitrogen-doped alloys. At last, in Chapter 6, we evaluated the fracture toughness of fully lamellar nitrogen-doped alloys. Effect of nitrogen addition on the fracture toughness of the lamellay alloys is similar to the case of the elongation of the lamellar alloy at the room temperature. Though the lamellar alloy which added with 0.3at.% nitrogen shows the lower $K_Q$ value than the mother alloy, $K_Q$ value of 1.0at.% nitrogen alloy was similar to that value of the mother alloy. These may be caused by $Ti_2AlN$ precipitates. From these results, we reach a conclusion that the carbon and nitrogen doped alloys had balanced-mechanical properties, in particular creep resistance. Therefore, I have expected to progrees further study as structural intermetallic compounds for high temperature.

서지기타정보

서지기타정보
청구기호 {DMS 00035
형태사항 ix, 114 p. : 삽도 ; 26 cm
언어 한국어
일반주기 저자명의 영문표기 : Ju-Hwan Yun
지도교수의 한글표기 : 위당문
지도교수의 영문표기 : Dang-Moon Wee
수록잡지명 : "Microalloying effects in TiAl+Mo alloys". Materials science and enginnering, A, A239-240, pp.702-708(1997)
수록잡지명 : "Nitrogen-doped tial alloys-part I microstructure control". Journal of materials science, in press, (2000)
학위논문 학위논문(박사) - 한국과학기술원 : 재료공학과,
서지주기 참고문헌 : p. 103-108
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