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Journal Articles

Hydrostatic compression behavior and high-pressure stabilized $$beta$$-phase in $$gamma$$-based titanium aluminide intermetallics

Liss, K.-D.*; Funakoshi, Kenichi*; Dippenaar, R. J.*; Higo, Yuji*; Shiro, Ayumi*; Reid, M.*; Suzuki, Hiroshi; Shobu, Takahisa; Akita, Koichi

Metals, 6(7), p.165_1 - 165_22, 2016/07

https://doi.org/10.3390/met6070165
 Times Cited Count：20 Percentile：67.57(Materials Science, Multidisciplinary)

Titanium aluminides find application in modern light-weight, high-temperature turbines, such as aircraft engines, but suffer from poor plasticity during manufacturing and processing. Huge forging presses enable materials processing in the 10 GPa range and hence, it is necessary to investigate the phase-diagrams of candidate materials under these extreme conditions. Here we report on an in-situ synchrotron X-ray diffraction study in a large-volume-press of a modern ($$alpha_{2}$$ + $$gamma$$) two-phase material, Ti-45Al-7.5Nb-0.25C, under pressures up to 9.6 GPa and temperatures up to 1686 K. At room temperature, the volume response to pressure is accommodated by the transformation $$gamma$$ $$rightarrow$$ $$alpha_{2}$$ rather than volumetric strain, expressed by apparently high bulk moduli of both constituent phases. Crystallographic aspects, specifically lattice strain and atomic order are discussed in detail. It is interesting to note that this transformation takes place despite an increase in atomic volume, which is due to the high ordering energy of $$gamma$$. Upon heating under high pressure, both the eutectoid and $$gamma$$-solvus transition temperatures are elevated, and a third, cubic $$beta$$-phase is stabilized above 1350 K. Earlier research has shown that this $$beta$$-phase is very ductile during plastic deformation, essential in near-conventional forging processes. Here, we were able to identify an ideal processing window for near-conventional forging, while the presence of the detrimental $$beta$$-phase is not present under operating conditions. Novel processing routes can be defined from these findings.

Journal Articles

Phase stability and mechanical properties of irradiated Ti-Al-V intermetallic compounds

Sawai, Tomotsugu; Wakai, Eiichi; Jitsukawa, Shiro; Hishinuma, Akimichi

Journal of Nuclear Materials, 307-311(Part1), p.389 - 392, 2002/12

https://doi.org/10.1016/S0022-3115(02)01206-0
 Times Cited Count：3 Percentile：23.20(Materials Science, Multidisciplinary)

A Ti-35Al-10V alloy was fabricated from mechanically alloyed powder by a hot-isostatic-pressing. The microstructure consists of $$alpha$$2, $$gamma$$, and $$beta$$ phases. Specimens were irradiated in Japan Research Reactor No. 3 Modified (JRR-3M) up to 3.5 $$times$$ 10$$^{25}$$ n/cm$$^{2}$$ at 400$$^{circ}$$C and 600$$^{circ}$$C. Unirradiated tensile specimens showed total elongation of 3 to 15 % at 400$$^{circ}$$C-tests, while 400$$^{circ}$$C-irradiated or 600$$^{circ}$$C-irradiated specimens showed no plastic deformation before fracture. At 600$$^{circ}$$C tensile tests, unirradiated specimens showed total elongation of more than 60 %, while irradiated ones showed 10 % or less elongation. The low ductility of irradiated specimens suggests embrittlement due to phase decomposition, but electron diffraction using a transmission electron microscope results of irradiated specimens will be also discussed.

Journal Articles

Development and irradiation behavior of TiAl-based intermetallic compounds

Hishinuma, Akimichi; ; Sawai, Tomotsugu; Tabuchi, Masayuki*

Physica Status Solidi, 167(2), p.521 - 529, 1998/00

no abstracts in English

Journal Articles

Ductilization of TiAl intermetallic alloys by neutron-irradiation

Hishinuma, Akimichi; Fukai, Katsumaro; Sawai, Tomotsugu;

Intermet., 4, p.179 - 184, 1996/00

no abstracts in English

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