Fully lamellar structures of powder metallurgy (PM), investment cast, and directionally solidified (DS) TiAl alloys containing ß stabilizer were produced after stepped cool heat treatment, and interface ß precipitates were formed after aging at 950°C In addition, a columnar grain structure combined with a fully lamellar structure aligned with the load direction and interface ß precipitates were formed by directional solidification and subsequent heat treatments. Creep test results of PM TiAl indicate that controlling the initial microstructures is also critical for balancing the primary and steady-state creep resistance during short and long-term tests. DS TiAl alloy exhibits a significant reduction of the primary strain and creep rate compared to polycrystalline TiAl due to the unique DS microstructure. Therefore, a DS microstructure with proper lamellar orientation and controlled interface ß precipitation is the ideal if maximum time to a relatively small (<0.5%) strain is the design criterion of merit.

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Department of Mechanical and Aerospace Engineering

Seo, D.Y., Saari, H, Au, P., & Beddoes, J. (2007). Microstructure and creep of γ-TiAl containing ß stabilizer.