[Kovove materialy - Metallic materials]
    Thu - November 07, 2024 - 19:37 No. of hits : 1796828 ISSN 1338-4252 (online) ISSN 0023-432X (printed)
© Institute of Materials and Machine Mechanics, Slovak Academy of Sciences, Bratislava, Slovak Republic

VOLUME 48 (2010), Issue 6

Long term microstructural stability of intermetallic Ti-46Al-8Ta alloy during ageing at temperatures of 700-800 °C
LAPIN, J., PELACHOVA, T., STANEKOVA, H., DOMANKOVA, M.
vol. 48 (2010), no. 6, pp. 337 - 343
DOI: 10.4149/km_2010_6_337

Abstract
The lamellar α2(Ti3Al) + γ(TiAl) microstructure of intermetallic Ti-46Al-8Ta (at.%) alloy is unstable and transforms to α2 + γ + τ type at temperatures ranging from 700 to 800 °C during long-term ageing up to 10000 h. TEM observations and selected area diffraction patterns show that the ternary τ phase with B82 type structure (space group P63/mmc) is preferentially formed along the grain and lamellar colony boundaries. Volume fraction of the τ and γ phases increase with increasing ageing time at the expense of decreasing volume fraction of the α2 phase at all ageing temperatures. The lattice parameters of the α2 and γ phases change during ageing when compared with those of the as received alloy. The ageing temperatures have no measurable effect on the lattice parameters of the coexisting α2, γ and τ phases after ageing for 10000 h. The Vickers microhardness decreases reaching a minimum after ageing for about 500 h and then increases to peak values with increasing ageing time. The ageing time longer than 1500 h leads to a continuous softening of the alloy at all ageing temperatures.

Key words
titanium aluminides, TiAl, phase identification, microstructure, diffraction

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Full title of this journal is bilingual: Kovové materiály - Metallic Materials.
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