[Kovove materialy - Metallic materials]
    Fri - March 29, 2024 - 05:41 No. of hits : 1736610 ISSN 1338-4252 (online) ISSN 0023-432X (printed)
© Institute of Materials and Machine Mechanics, Slovak Academy of Sciences, Bratislava, Slovak Republic

VOLUME 47 (2009), Issue 3

The effect of microstructure on mechanical properties of directionally solidified intermetallic Ti-46Al-8Nb alloy
LAPIN, J., GABALCOVA, Z., BAJANA, O.
vol. 47 (2009), no. 3, pp. 159 - 167

Abstract
The effect of microstructure on mechanical properties of directionally solidified (DS) intermetallic Ti-46Al-8Nb (at.%) alloy was studied. After directional solidification at constant growth rates V ranging from 5.56x10-6to 1.18x10-4 ms-1 and constant temperature gradients in liquid at the solid liquid interface GL from 3.5x103 to 8x103 Km-1, the DS samples contain several columnar grains aligned in a direction parallel or nearly parallel to the growth direction. The microstructure within the columnar grains is fully lamellar consisting of α2(Ti3Al)+γ(TiAl) lamellae. Mean α22 interlamellar spacing λ decreases with increasing growth rate V and increasing cooling rate. Room-temperature Vickers microhardness HVm and compressive yield stress σy at 700 °C increase with decreasing interlamellar spacing λ according to Hall-Petch relationship. High-temperature compressive yield stress depends on an angle Θ between lamellar boundaries and loading axis. Maximum values of the yield stress are measured at Θ = 90° and minimum values at Θ ranging from 30° to 60°. Columnar grain structure leading to a high anisotropy of mechanical properties can be transformed to fine equiaxed grains with convoluted type of α2+γ microstructure by appropriate heat treatments. Compressive yield stress of the specimens with equiaxed grain structure continuously decreases with increasing test temperature. A simple relationship is proposed for a prediction of the compressive yield stress at temperatures ranging from 20 to 900 °C.

Key words
titanium aluminides, TiAl, crystal growth, heat treatments, phase transformations, microstructure, mechanical properties

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