Microstructure of Dense Thin Sheets of Γ-TiAl Fabricated by Hot Isostatic Pressing of Tape-cast Monotapes
A powder metallurgy route based on hot isostatic pressing (HIP) of tape-cast monotapes was used for the direct fabrication of dense thin sheets (250-300 μm thick) of gamma titanium aluminide (γ-TiAl). Polarized light microscopy revealed a fine-grained microstructure (average grain size not, vert, similar3 μm) but a few isolated larger grains (not, vert, similar20 μm) were also present. The primarily metastable α2 microstructure of the rapidly solidified starting powder transformed to the equilibrium near-γ microstructure during HIP at 1100 °C. Chemical analysis revealed that the dense sheet had a carbon content of 0.13 wt.%, which was only 0.04 wt.% higher than that of the starting powder, but the oxygen content was significantly higher, presumably introduced during the decanning step. The hardness measured using Vickers microindentation technique was 384 ± 9 HV. Manipulation of the as-HIPed microstructure was performed by heating for up to 1 h in flowing argon at temperatures (1170-1385 °C) below and above the alpha transus (1355 °C). Below 1250 °C, limited grain growth and no discernable change in the as-HIPed (near-γ) microstructure occurred. Sheets heated to 1320 °C and 1365 °C had a duplex microstructure of γ and α2 grains, with some lamellar grains. Except for a thin surface layer (20-30 μm thick), the microstructure of the heat-treated sheet was uniform, but a fully lamellar microstructure was not achieved even after heating for 1 h at 1385 °C.
A. G. Adams et al., "Microstructure of Dense Thin Sheets of Γ-TiAl Fabricated by Hot Isostatic Pressing of Tape-cast Monotapes," Materials Science and Engineering: A, Elsevier, Mar 2008.
The definitive version is available at http://dx.doi.org/10.1016/j.msea.2007.05.006
Materials Science and Engineering
Air Force Research Laboratory (Wright-Patterson Air Force Base, Ohio)
Keywords and Phrases
Gamma Titanium Aluminide; Hot Isostatic Pressing; Tape-Casting; Thin Sheet
Article - Journal
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