1996 Fiscal Year Final Research Report Summary
Plastic Anisotropy and Fatigue Fracture Mechanism of TiAl Alloys under Cyclic Loading.
| Project/Area Number |
07455282
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Structural/Functional materials
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| Research Institution | Osaka University |
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Principal Investigator |
UMAKOSHI Yukichi Osaka University, Fac.of Engineering, Professor, 工学部, 教授 (00029216)
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| Co-Investigator(Kenkyū-buntansha) |
NAKANO Takayoshi Osaka University, Fac.of Engineering, Research Associate, 工学部, 助手 (30243182)
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| Project Period (FY) |
1995 – 1996
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| Keywords | fatigue / Intermetallics / fracture / Strength / TiAl / deformation / dislocation / high-temperature material |
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| Research Abstract |
The cyclic deformation and fatigue fracture behavior of TiAl polysynthetically twinned (PST) crystals were investigated, focusing on the effects of total strain amplitude, lamellar structure and the angle (phi) between the loading axis and the lamellar planes. Fatigue tests were performed in cyclic tension-compression mode at room temperature. Strong anisotropy in plastic behavior was observed at phi=0ﾟ and 45ﾟ.At phi=0ﾟ the stress amplitude incrteased with the number of cycles and the cyclic hardening became significant as the strain amplitude increased. Numerous dislocations and twins were activated depending on the types of gamma domain, and their motion was interrupted at the gamma/gamma domain and alpha_2/gamma lamellar boundaries resulting in an infomogeneous deformation substructure. Specimens with phi=45ﾟ showed weak cyclic hardening and broke without significant hardening. Fracture often occurred on the basal plane in the alpha_2 plates. Dislocations glided simply on (111) planes parallel to the lamellar planes and traveled a long distance since the gamma/gamma domain boundaries did not act as strong barrier to the motion of dislocations. Refinement of the lamellar structure is effective in achieving an increased fatigue life at both phi=0ﾟ and 45ﾟ.
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