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Korean Journal of Metals and Materials > Volume 56(5); 2018 > Article
Korean Journal of Metals and Materials 2018;56(5): 335-341. doi: https://doi.org/10.3365/KJMM.2018.56.5.335
Cast 와 HIP 으로 제작된 베타 감마 TiAl 합금의 열처리 후 2단계 냉각법을 통한 미세구조의 변화
최광수1, 김정민1, 박준식1, 김영원2
1한밭대학교 신소재공학과
2Gamteck LLC
Microstructural Evolution in Cast and HIP’ed Ingot Material of Beta Gamma TiAl Alloy by Two Step Cooling
Kwangsu Choi1, Jeong Min Kim1, Joon Sik Park1, Young-won Kim2
1Department of Materials Science and Engineering, Hanbat National University, Daejeon 34158, Republic of Korea
2Gamteck LLC, Beavercreek, Oh 45431, USA
Correspondence  Joon Sik Park ,Tel: +82-42-821-1276, Email: jsphb@hanbat.ac.kr
Received: 29 November 2017;  Accepted: 19 February 2018.  Published online: 8 May 2018.
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 oC(or 1350 oC) and transferred to another furnace, which was maintained at 950 oC, in order to minimize any phase transformations between the temperatures. Fully lamellar specimens with some phases were compression-tested at RT, 700 oC, 800 oC, 900 oC and 1000 oC, and showed excellent compressive strength at high temperature. The resultant material property determined via this cooling process was superior to that of other materials such as Ni based superalloys or commercial TiAl alloys. The microstructures associated with the cooling effect were discussed in terms of materials properties and phase transformation.
Keywords: TiAl, colony size, lameller structure, hall petch relation, two step cooling
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