Superplasticity of titanium aluminides

R. Imayev, V. Imayev

Abstract

In the present paper, processing methods and superplastic properties of fine-grained γ - TiAl+α2-Ti3Al based intermetallic alloys with varying alloy composition have been considered. It has been demonstrated that superplastic behavior is feasible in single-phase (γ-TiAl and α-Ti3Al), two-phase (γ-TiAl+α2-Ti3Al) and three-phase (γ-TiAl+α2-Ti3Al+β(B2)) alloys. Superplastic properties in the single-phase alloys were reached due to the fact that diffusion processes occur slower in intermetallic alloys in contrast to pure metals; this impeded dynamic grain growth during superplastic flow and promoted superplastic elongations. It has been revealed that processing required for manufacturing of a fine-grained condition is dependent on the alloy composition and can be simplified at transition from peritectically solidifying γ-TiAl+α2-Ti3Al based alloys to β-solidifying ones. The use of β -solidifying alloys, which are known to have better chemical homogeneity in contrast to peritectically solidifying γ-TiAl+α2-Ti3Al based alloys, provided enhanced superplastic characteristics. Highest superplastic elongations (up to δ=1000% at T=1000°C and εʹ≈10-3 s-1) were obtained for the β-solidifying alloy (Ti-45Al-5Nb-1Mo-0.2B, at. %) containing a small amount of the β(B2)-phase and subjected to single-step hot forging. Interestingly, superplastic properties were even attained in the as-cast β-solidifying alloy containing around 20 vol. % of the β(B2) phase without any prior hot working.

Accepted: 20 April 2015

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