Abstract
The solidification structures of 12 alloys in the Ti-Al-Mo system with Al contents ranging from 44 to 50 at. pct and Mo contents ranging from 2 to 6 at. pct have been characterized metallographically and, for composition gradients, by electron probe microanalysis. All alloys solidify dendritically through sequences that fall into four distinct categories: alloys that solidify completely into the β phase field, alloys that solidify first into an L+β phase field and finally into an α+β phase field through an L+β+γ region, alloys that solidify first into a L+β phase field and finally form α+β+γ structures, and alloys that solidify into a L+α phase field. Postsolidification transformations occur as consequence of transitions from the high-temperature β, α+β, and α+γ phase fields to low-temperature α+β+γ or β+γ region. A variety of phase distributions result, such as Widmanstätten α 2+B2 structures from the α → α+β reaction followed by ordering, lamellar α 2+γ structures from the α → α+γ reaction followed by ordering of the α phase, eutectoid B2+γ structures from the α → B2+γ reaction, and platelike γ structures from the β → β+γ reaction. The former are observed in Al lean alloys, while the latter are present in Mo rich alloys.
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Singh, A.K., Banerjee, D. Transformations in α 2+γ titanium aluminide alloys containing molybdenum: Part I. Solidification behavior. Metall Mater Trans A 28, 1735–1743 (1997). https://doi.org/10.1007/s11661-997-0105-7
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DOI: https://doi.org/10.1007/s11661-997-0105-7