Microstructure and toughness of nitrogen-doped TiAl alloys질소가 첨가된 TiAl 합금의 미세조직과 파괴인성

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The γ-based TiAl alloy has been studied extensively as a prominent substitute of conventional superalloys because of its low density, high specific strength and good high temperature properties. Depending on the heat treatment scheme, various microstructures can be obtained in TiAl alloys. Among them, fully lamellar TiAl alloy exhibits good creep resistance and fracture toughness but it still lacks room temperature ductility. Recently, it was reported that an addition of 0.3 ~ 1.0 at.% nitrogen or carbon to the lamellar TiAl alloys improved the yield strength and creep resistance without a concomitant loss in room temperature ductility. Microstructurally, the addition of nitrogen and/or carbon was instrumental in producing a significant refinement in colony size; two kinds of nitrides, $Ti_2AlN$ and $Ti_3AlN$, were observed in some of these alloys. Improvements in intermediate temperature ductility and creep rupture stress by the addition of 0.3 wt.% C to TiAl alloys with a fine duplex structure were already reported before. Other compressive and tensile studies of C or N-containing TiAl have confirmed enhancements in fracture stress and tensile elongation. However, the effect of these changes in microstructure as a consequence of nitrogen (or carbon) addition on crack growth resistance has not been reported thus far. Additionally, as one of important microstructural parameters that can affect various mechanical properties of fully lamellar TiAl alloys, lamellar spacing is being considered. It was reported that the yield strength of TiAl alloys had strong dependence on the lamellar spacing and the lamellar spacing refinement improved creep resistance both by decreasing the mobility of dislocation in soft oriented colonies and by increasing the difficulty for shear in hard oriented colonies. But no report has been addressed about the lamellar thickness variation with respect to the amount of interstitial element addition although the lamellar thickness is one o...
Advisors
Wee, Dang-Moonresearcher위당문researcher
Description
한국과학기술원 : 재료공학과,
Publisher
한국과학기술원
Issue Date
2001
Identifier
169426/325007 / 000993811
Language
eng
Description

학위논문(석사) - 한국과학기술원 : 재료공학과, 2001.8, [ ix, 77 p. ]

Keywords

fracture toughness; nitrogen; TiAl; microstructure; 미세조직; 파괴인성; 질소첨가; TiAl

URI
http://hdl.handle.net/10203/50841
Link
http://library.kaist.ac.kr/search/detail/view.do?bibCtrlNo=169426&flag=dissertation
Appears in Collection
MS-Theses_Master(석사논문)
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