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Ti-43Al-3Si 일방향 응고 합금의 층상조직 제어
김승언,이용태,오명훈,박노진,산구정치 대한금속재료학회(대한금속학회) 2000 대한금속·재료학회지 Vol.38 No.6
Directional solidification process of Ti-43Al-3Si alloy has been studied. DS ingots having rotated columnar grains with respect to longitudinal axis as well as fully lamellar microstructure parallel to longitudinal axis were successfully obtained using a polycrystalline seed material. Successful seeding and growing require plane-front solidification condition during the entire DS process. (101)⊥ND texture by pole figure measurement was found to be dominant in the DS ingot grown at a velocity of 5 ㎜/hr. Fracture toughness of the DS alloys was superiors to that of the PST alloys, with a value of K_Q = 21.7∼31.7 ㎫(m)^½ for the crack arrest/divide orientation and K_Q = 7.4∼9.0 ㎫(m)^½ for the brittle orientation.
Seed를 이용한 일방향응고 Ti-46A1-1.5Mo-0.2C 합금의 크리프 특성
李鎬年,丁仁洙,吳明勳,山口正治,韋當文 대한금속재료학회 2002 대한금속·재료학회지 Vol.40 No.1
Creep properties of directionally solidified Ti-46A1-1.5Mo-0.2C alloys with well aligned lamellar microstructure have been dramatically improved. The ingots were manufactured by seeding technique directional solidification. Directionally solidified Ti-46A1-1.5Mo-0.2C alloys showed excellent creep properties. However, the creep resistance decreased as the angle between lamellar orientation and loading axis increased. It is found that the control of the lamellar orientation is most important to improve the creep resistance of TiAI alloys. In the results of TEM analysis of creep specimen before and after creep test, it was found that no carbides were formed before creep test. But, after creep test, carbides were formed in γ lath, γ / γ interfaces, γ / α_2 interfaces and dislocations. In the case of creep test at 750℃, the quantity of carbides found in dislocations decreased as the load level increased. It was thought that superior thermal stability of Ti-46A1-1.5Mo-0.2C alloy suppressed the dynamic recrystallization and the coarsening of the lamellar microstructure, and the excellent creep resistance was maintained for long time due to this thermal stability.
α상분율의 변화가 층상조직 TiAl 합금의 열적안정성에 미치는 영향
金聖雄,이호년,吳明勳,山口正治,韋當文 대한금속재료학회 2002 대한금속·재료학회지 Vol.40 No.6
The thermal stability of lamellar microstructure in TiAl-Mo PST crystals containing C or Si was investigated. In addition, the variation of α-phase volume fraction in Ti-Al-Mo-(C, Si) systems was also investigated at several temperatures. It was found that Ti-46Al-1.5Mo-O.2C and Ti-46Al-1.5Mo-1.0Si alloys were very stable during heat treatments at various heating rates and temperatures. Moreover, the, α-phase volume fraction of Ti-46A1-1.5Mo-0.2C and Ti-46A1-1.5Mo-1.OSi alloys (stable composition) was less changed than those of Ti-47Al and Ti-46Al-1.5Mo alloys (unstable composition). From these results, the instability of the latter alloys was thought to be resulted from relatively higher variation of α-phase volume fraction during heating. Therefore, it could be suggested that the variation of α-phase volume fraction is an important factor that control the thermal stability of lamellar microstructure.
층상조직 TiAl 합금의 열적 안정성에 미치는 Si 첨가효과
이호년,김성웅,오명훈,山口正治,위당문 대한금속재료학회 2002 대한금속·재료학회지 Vol.40 No.11
Thermal stability of Si-doped TiAl alloys with the lamellar microstructure was investigated by partial melting in an optical floating zone(FZ) furnace to ascertain the possibility of usage as a seed material. The lamellar stability of TiAl and TiAl-X(X=Mo, Nb, W) alloys, which proved to be thermally unstable, was improved dramatically by Si addition. In the results of partial melting, it was found that there are two boundaries of Al content(low Al limit and high Al limit) which devide stable and unstable compositions. It is thought that when Al content is lower than low Al limit, recrystallization can be occurred by β-phase formation at high temperature, and when Al content is higher than high Al limit, the lamellar stability will be deteriorated by rapid variation of α/γ phase volume fraction during heating and cooling. The lamellar stability of TiAl-Si alloys can be predicted by drawing above two boundaries at TiAl-Si isothermal section. Moreover, the lamellar stability of TiAl-X-Si alloys can be also predicted by converting the compositions to TiAl-Si compositions. In addition, lamellar orientation control was successfully performed by directional solidification using the Ti-46Al-l.5Mo-1Si alloy as a seed material.
Seed 를 이용한 일방향 응고법에 의한 TiAl 합금의 층상경계방향제어
위당문,오명훈,이호년,Johnson, D . R .,건청행,산구정치 대한금속재료학회(대한금속학회) 1999 대한금속·재료학회지 Vol.37 No.11
The thermal stability of the lamellar microstructure and the orientation control of the lamellar microstructure in a cast TiAl alloys with Mo and C were investigated. The lamellar stability of the seed material up to the melting temperature is important in the orientation control of the lamellar microstructure by the directional solidification. First, the partial liquidus surface was constructed for TiAl-C ternary and TiAl-1.5Mo-C quaternary systems. The lamellar stability was determined by quickly heating specimens to a temperature just below the melting temperature, holding, and then cooling to room temperature. Ti-46Al-1.5Mo-0.2C alloy was found to be a promising composition as a seed materials and ingots with a lamellar microstructure aligned along the growth direction were successfully grown by directional solidification process using the seed alloy. From the result of tensile and compression tests, directionally solidified Ti-46Al-1.5Mo-0.2C (at.%) ingots were found to exhibit a high yield stress together with a reasonably good tensile elongation at room temperature and a high compression stress up to 1000℃.