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Microstructure evolution in tial alloys with b additions: Conventional solidification

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Abstract

Solidification microstructures of arc-melted, near-equiatomic TiAl alloys containing boron additions are analyzed and compared with those of binary Ti-Al and Ti-B alloys processed in a similar fashion. With the exception of the boride phase, the matrix of the ternary alloy consists of the same α2 (DO19) and γ (Ll0) intermetallic phases found in the binary Ti-50 at. pct Al alloy. On the other hand, the boride phase, which is TiB (B27) in the binary Ti-B alloys, changes to TiB2 (C32) with the addition of Al. The solidification path of the ternary alloys starts with the formation of primary α (A3) for an alloy lean in boron (∼1 at. pct) and with primary TiB2 for a higher boron concentration (∼5 at. pct). In both cases, the system follows the liquidus surface down to a monovariant line, where both α and TiB2 are solidified concurrently. In the final stage, the α phase gives way to γ, presumably by a peritectic-type reaction similar to the one in the binary Ti-Al system. Upon cooling, the α dendrites order to α2 and later decompose to a lath structure consisting of alternating layers of γ and α2.

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Authors and Affiliations

  1. Materials Department, College of Engineering, University of California, 93106, Santa Barbara, CA

    M. E. Hyman (Research Assistant), C. McCullough (Assistant Research Engineer), J. J. Valencia (Assistant Research Engineer), C. G. Levi (Associate Professor of Materials and Environmental and Mechanical Engineering) & R. Mehrabian (Professor of Materials and Dean of Engineering)

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  1. M. E. Hyman
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  2. C. McCullough
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  3. J. J. Valencia
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  4. C. G. Levi
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  5. R. Mehrabian
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Hyman, M.E., McCullough, C., Valencia, J.J. et al. Microstructure evolution in tial alloys with b additions: Conventional solidification. Metall Trans A 20, 1847–1859 (1989). https://doi.org/10.1007/BF02663215

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  • DOI: https://doi.org/10.1007/BF02663215

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