1996 Fiscal Year Final Research Report Summary
DEVELOPEMENT OF MICROSTRUCTURE-CONTROLLED B2-ORDERED HIGH TEMPERATURE INTERMETALLICS
| Project/Area Number |
07555503
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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 | 試験 |
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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) |
1995 – 1996
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| Keywords | intermetallics / precipitation / dislocation / diffusion / coherency / strength / TEM / AEM |
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| Research Abstract |
A wide variation of microstructures can be obtained in B2-ordered intermetallicsdepending 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. The lattice misfits at interphase interfaces in NiAl (B2)-Ni_2AlTi (L2_1) and NiTi (B2)-Ni_2AlTi (L2_1) pseudobinary systems have been estimated by transmission electron microscopy (TEM). When the size of Ni_2AlTi precipitates is smaller than a critical value, the precipitates keep their lattice coherency with the NiAl and NiTi matrices. After longer periods of aging the Ni_2AlTi precipitates lose their coherency by introducing interface dislocations surrounding them. The coherency loss occurs catastrophically and the shape of the precipitates changes to a globular one after the loss of coherency, while keeping the cubic-cubic orientation relationship. The morphology of dislocations intr
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oduced by the deformation of B2-ordered NiTi containing fine precipitation of L2_1-ordered Ni_2AlTi is correlated with the yield strength variations during aging and deformation temperatures. The Burgers vectors of 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. With increasing the deformation temperature dislocations start to move as wavy single dislocations. In NiAl contaning 2 and 5 mol% of Hf, fine plate-like L2_1-type Ni_2AlHf precipitates are formed on the {111} planes of the NiAl matrix keeping the lattice coherency with the matrix lattice at the beginning of aging. By longer periods of aging Ni_2AlHf precipitates lose their coherency and change their morphology to the spherical ones surrounded by misfit dislocations. 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 obsernvations suggested 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. Less
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