1996 Fiscal Year Final Research Report Summary
Formation Mechanism of Fracture Precursor Induced by Phase Transformation in beta Type Ti-Mo Alloy
| Project/Area Number |
07650769
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Physical properties of metals
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| Research Institution | Okayama University |
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Principal Investigator |
HIDA Moritaka Okayama University・Faculty of Engineering, Professor, 工学部, 教授 (90023134)
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| Co-Investigator(Kenkyū-buntansha) |
TAKEMOTO Yoshito Okayama University・Faculty of Engineering, Assistant Professor, 工学部, 助手 (60216942)
SAKAKIBARA Akira Okayama University・Faculty of Engineering, Associate Professor, 工学部, 助教授 (40033245)
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| Project Period (FY) |
1995 – 1996
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| Keywords | titanium molybdenum alloy / titanium nickel shape memory alloy / omega transformation / alpha transformation / martensitic transformation / {332} <113> twin / transition state / electron microscopy |
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| Research Abstract |
This study has been carried out mainly by electron microscopic observation. The summary is as follows :
1. It is well known that hardening and embrittlement of beta type Ti-14Mo alloy are caused by aged (1) -phase formation. According to the study on deformation bands formed during tensile test at the aging temperature, the reverse transformation ((1) *beta) in the band drove preferential plastic deformation (work softening) in the band. This was recognized as an origin of the inacroscopic embrittlement. It was also newly observed that the hardness of over-aged alloy decreased without changing (1) -particle size and brittleness. The transition state, (1) *alpha, prepared by a step-aging made the alloy ductile emitting bundles of needle -like alpha-phase into matrix during tensile deformation. The ductility was better than that of the alloy with large alpha-phase formed by direct aging.
2. It is well known that the as-quenched alloys show remarkable ductility with {332} twinning. The twinning mechanism which had not been cleared was determined by a model simulation of atom displacements to {332} twin from bee structure via alpha" martensitic transformation. Cutting and interaction between {332} twins maybe give rise to the local deformation at a kind of fractural precursors which are expected to be planar (1) -phase. The identification with TEM is now in progress.
3. In-situ observation on Ti-50.6% Ni shape memory alloy revealed that the deformation in plastic region multiplied the secondary martensitic plates between and/or from the primary ones which were formed during quasi-elastic deformation. Cutting and interaction between the plates led the sample to fracture.
4. Several cluster models of a given structure (beta, (1), alpha or alpha") were studied with DX-Xalpha method. The bond orders obtained seems to be effective in comparing the strength of stress induced products which stimulate work softening.
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