1995 Fiscal Year Final Research Report Summary
Development of Directionally Solidified TiAl/Ti3Al Alloys
| Project/Area Number |
06555203
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| Research Category |
Grant-in-Aid for Developmental Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
Structural/Functional materials
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| Research Institution | KYOTO UNIVERSITY |
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Principal Investigator |
YAMAGUCHI Masaharu Kyoto Univ., Grad.School of Eng., Prof., 工学研究科, 教授 (90029108)
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| Co-Investigator(Kenkyū-buntansha) |
INUI Haruyuki Kyoto Univ., Grad.School of Eng., Res.Asso., 工学研究科, 助手 (30213135)
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| Project Period (FY) |
1994 – 1995
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| Keywords | Intermetallic compounds / TiAl / Directional solidification / Lamellar structure / Structure control / strength / Toughness / Crystal growth |
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| Research Abstract |
Directionally solidified ingots containing only one lamellar orientation for the complete ingot can be produced. Unfortunately, the lamellar microstructure in these ingots was perpendicular to the growth direction. However, since only one orientation was observed, microstructural control may be achievable by using a seed crystal during directional solidification. There are two requirements that must be met if the orientation of the lamellar microstructure is to be controlled by using a seed crystal. The first is that the alpha phase must nucleate first from the liquid. The basic idea is to control the orientation of the alpha phase upon nucleation. Since the lamellar microstructure forms with the (111) gamma// (0001) alpha orientation relationship, once the orientation of the alpha phase is determined, the orientation of the lamellar microstructure is also determined. Secondly, upon heating or cooling, either the alpha phase or the alpha-2 phase must be thermodynamically stable. That is, upon heating or cooling, the alloy must not pass through the gamma single-phase region since recrystallization may occur. These two requirements are met in the TiAl-Si system. Within the composition range of 40-50 at%Al, the addition of Si to TiAl shifts the primary alpha region towards much lower Al content. At a composition of Ti-43Al-35Si, either alpha or alpha-2 is stable from the melting temperature to room temperature and the orientation of the lamellar microstructure can be controlled using a seed material. The room temperature mechanical properties were determined by tensile tests and by three point bend tests. From bend specimens oriented with the notch parallel to the lamellar microstructure, the Ti-43Al-3Si alloy was found to have a greater fracture toughness than a TiAl-PST crystal of the same orientation.
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