Home Kovove Materialy-Metallic Materials 2010 Metallic Materials Vol. 48 (2010), no. 6, pp. 337 - 365

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Metallic Materials Vol. 48 (2010), no. 6, pp. 337 - 365

Title: Long term microstructural stability of intermetallic Ti-46Al-8Ta alloy during ageing at temperatures of 700-800 °C

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.

Keywords: titanium aluminides, TiAl, phase identification, microstructure, diffraction
Year: 2010, Volume: 48, Issue: 6 Page From: 337, Page To: 343

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