1996 Fiscal Year Final Research Report Summary
BEHAVIOR OF LATTICE DEFECTS IN MICROSTRUCTURE-CONTROLLED INTERMETALLICS
| Project/Area Number |
06402050
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| Research Category |
Grant-in-Aid for Scientific Research (A)
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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 | KYUSHU UNIVERSITY |
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Principal Investigator |
NEMOTO Minoru Kyushu Univ., Dpt.Mater.Sci.& Eng., Prof., 工学部, 教授 (90005265)
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| Co-Investigator(Kenkyū-buntansha) |
TIAN Wen-huai Kyushu Univ., Dpt.Mater.Sci.& Eng., Ass., 工学部, 助手 (50223631)
SANO Takeshi Kyushu Univ., Dpt.Mater.Sci.& Eng., Ass., 工学部, 助手 (70037810)
HORITA Zenji Kyushu Univ., Dpt.Mater.Sci.& Eng., Ass.Prof., 工学部, 助教授 (20173643)
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| Project Period (FY) |
1994 – 1996
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| Keywords | intermetallics / precipitation / dislocation / diffusion / coherency / strength / TEM / AEM |
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| Research Abstract |
Transmission electron microscope (TEM) investigations have been performed to investigate the characteristic features of phase decomposition and of interaction between dislocations and precipitates in L1_2-based, B2-based and T1_0-based intermetallics. Lattice site occupation and diffusivity in Ni_3Al and NiAl are measured by using an analytical electron microscope. A wide variation of microstructures including spinodal decomposition, zone formation, coherent and incoherent precipitation can be obtained depending on the chemical compositions and aging temperatures. The crystal anisotropy and the deviation from the stoichiometric composition play important roles in the microstructure and the strength variation during aging. One of the most typical features of the precipitation in intermetallics is the precipitation of disordered phases in the ordered matrices. L1_2-ordered Ni_3Al and Co_3 Ti harden appreciably by fine precipitates of coherent fcc disordered gamma upon aging after quenchi
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ng from solution annealing temperature. In these alloys superdislocations are effectively attracted to the disordered particles and extend their widths in the precipitates. The creep strengths of these alloys increase appreciably. A typical example of dislocation bypassing leaving loops surrounding hard precipitates has been observed in Ni_3Al and TiAl containing fine dispersion of carbides. TEM examination of phase decomposition and deformation induced dislocations in NiAl (B2)-Ni_2AlTi (L2_1) and NiTi (B2)-Ni_2AlTi (L2_1) pseudobinary systems have revealed that the glide dislocations are of a <100> type and shear the H-phase at the underaged state but by pass at the overaged state. In the underaged superdislocation pairs are formed by the deformation at room temperature. The lattice misfit between the Ni_2AlHf precipitate and the NiAl matrix is about four times as large as that of NiAl-Ni_2AlTi system. The high temperature strength as well as creep strength increase appreciably by the precipitation of fine Ni_2AlHf phase. TEM observations suggest that the attractive interactions for dislocations at the particle/matrix interfaces plays an important role to increase the high temperature strength of NiAl-based alloys. When intermetallic compounds precipitate in intermetallics, strengthening is dependent on the crystal structures of precipitates, Burgers vectors of glide dislocations and antiphase boundary energies formed during deformation. Less
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