Investigation of carbides in Ti–45Al–5Nb–xC alloys (0 ≤ x ≤ 1) by transmission electron microscopy and high energy-XRD

• Published in: Intermetallics Vol. 33; pp. 44 - 53
• Main Authors: Gabrisch, Heike, Stark, Andreas, Schimansky, Frank-Peter, Wang, Li, Schell, Norbert, Lorenz, Uwe, Pyczak, Florian
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-02-2013
• Subjects: A. Intermetallics; A. Ternary alloy systems; Alloying; Alloys; B. Precipitates; B. Solid-solution hardening; Carbides; Carbon; Diffraction; F. Diffraction; Heat treatment; Imaging; Mechanical properties; Titanium base alloys; B. Solid-solution hardening; B. Precipitates; A. Intermetallics; A. Ternary alloy systems; F. Diffraction
• ISSN: 0966-9795; 1879-0216
• DOI: 10.1016/j.intermet.2012.09.023

The mechanical properties of γ-TiAl based alloys are often improved through alloying with niobium and carbon. Depending on composition and heat treatment the details of carbon distribution and the resulting consequences on mechanical properties vary greatly.
Here we present a study of the microstructure of Ti–45Al–5Nb alloys (in at.-%) with the addition of 0.5–1 at.-% of carbon. We use electron diffraction accompanied by energy dispersive spectroscopy and imaging in the TEM to characterize carbides. These studies are complemented by high-energy X-ray diffraction experiments using synchrotron radiation and by scanning electron microscopy. Carbides are identified in significant numbers in the alloys containing 1 and 0.75 at.-% of carbon but only rarely at 0.5 at.-% C. Our results show that in these alloys carbon in solid solution has a stronger effect on hardness than carbide precipitation.
► Solid solution hardening is acting strengthening mechanism in Ti–45Al–5Nb–xC. ► Carbon solubility in high Nb containing TiAl alloys near 0.5 at.-% (as HIPed state). ► Detection limit for carbides appr. 0.1 vol.-% by HERD.