Numéro |
J. Phys. IV France
Volume 10, Numéro PR6, April 2000
The Sixth Japan-France Materials Science SeminarJFMSS-6 Microstructural Design for Improved Mechanical Behaviour of Advanced Materials |
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Page(s) | Pr6-9 - Pr6-14 | |
DOI | https://doi.org/10.1051/jp4:2000602 |
JFMSS-6
Microstructural Design for Improved Mechanical Behaviour of Advanced Materials
J. Phys. IV France 10 (2000) Pr6-9-Pr6-14
DOI: 10.1051/jp4:2000602
Microstructural design criteria of fully lamellar TiAl alloys for improved creep strength
K. Maruyama1, R. Yamamoto2 and G. Wegmann31 Department of Materials Science, Graduate School of Engineering, Tohoku University, Aoba-yama 02, Sendai 980-8579, Japan
2 Mitsubishi Heavy Industries Ltd., 2-1-1 Shinhama Arai-cho, Takasago 676-8686, Japan.
3 GKSS Research Centre, Institute for Materials Research, Max-Planck Strasse, 21502 Geesthacht, Germany.
Abstract
Grain size, volume fraction of constituent phases, lamellar spacing
and lamellar orientation are the major microstructural variables to be
considered in alloy design of fully lamellar TiAl alloys. Effects of the four
variables on creep strength of TiAl alloys were studied by using
polycrystalline specimens and PST (single grain) crystals. Creep rate of TiAl
alloys is independent of grain size, and insensitive to the phase volume
fraction (i.e. aluminum concentration). Grain size can be reduced down to
100[Math]m without loosing creep strength. Aluminurn concentration is essentially
free in the alloy design as far as creep strength is concerned. Creep rate of
the alloys decreases with decreasing lamellar spacing, suggesting that
refinement of lamellar microstructure is effective in improving creep
strength. However, the strengthening by lamellar refinement disappears at
low stress due to the increasing contribution of microstructural instability of
fine lamellar microstructure. Stabilization of lamellar microstructures is
necessary to prevent this loss of creep strength. Creep rate of the hardorientated
PST crystals, in which lamellar plates are aligned parallel or
perpendicular to the stress axis, is reduced by two orders of magnitude with
respect to the soft orientation. Creep strength of polycrystalline TiAl alloys
can be improved significantly by the control of their texture.
© EDP Sciences 2000