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Vol.56, No.5, 335 ~ 342, 2018
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| Title |
| Microstructural Evolution in Cast and HIP’ed Ingot Material of Beta Gamma TiAl Alloy by Two Step Cooling |
| 최광수 Kwangsu Choi , 김정민 Jeong Min Kim , 박준식 Joon Sik Park , 김영원 Young-won Kim |
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| Abstract |
| The beta gamma alloys of Ti - 43.8Al - 4Nb - 2Cr - 0.2B - 0.2C at % (9CN) were prepared using induction skull melted (ISM) cast ingots. In order to make a fine fully lamellar structure with some minor phases, two step cooling was performed using two furnaces after heat treatments in the α + β phase region. The heat-treatments produced an ~50 μm fully lamellar structure with α2 / γ + γ + B2 (HIP) → α + β (heating) → α / γ (FL) + γ + B2 → α2 / γ (FL) + γ + B2 phase change. For the two step heat treatment, the specimen was heat treated at 1340 ℃(or 1350 ℃) and transferred to another furnace, which was maintained at 950 ℃, in order to minimize any phase transformations between the temperatures. Fully lamellar specimens with some phases were compression-tested at RT, 700 ℃, 800 ℃, 900 ℃ and 1000 ℃, and showed excellent compressive strength at high temperature. The resultant material property determined via this cooling pr℃ess was superior to that of other materials such as Ni based superalloys or commercial TiAl alloys. The microstructures ass℃iated with the cooling effect were discussed in terms of materials properties and phase transformation. |
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| Key Words |
| TiAl, colony size, lameller structure, hall petch relation, two step cooling |
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