Characterization of the high temperature deformation behavior of two intermetallic TiAl–Mo alloys

Abstract

Intermetallic titanium aluminides are promising candidates for high-temperature components in aero and automotive applications. To enable good processing characteristics with an optimized final microstructure, the hot-working parameters and the fraction of the β/βo-TiAl phase at deformation temperature are of particular interest. Therefore, the high-temperature deformation behavior of two γ-TiAl based alloys with the nominal compositions Ti–41Al–3Mo–0.5Si–0.1B and Ti–45Al–3Mo–0.5Si–0.1B, in at%, was studied. At room temperature both alloys contain the ordered phases γ-TiAl, βo-TiAl and small amounts of α2-Ti3Al. In order to investigate dynamic restoration during thermomechanical processing, isothermal compression tests were conducted on a Gleeble®3500 simulator and corresponding flow curves were measured. The tests were carried out at temperatures from 1150°C to 1300°C, applying strain rates ranging from 0.005s−1 to 0.5s−1, up to a true strain of 0.9. The deformed microstructural states of the multiphase alloys, particularly the dynamically recrystallized grain sizes, were characterized by means of scanning electron microscopy and electron back-scatter diffraction. To compare the microstructure right before and after deformation heat treatments were additionally performed at the same temperatures as the compression tests were carried out. The experimentally determined flow stress data were described with two different constitutive models (Sellars–McTegart model, Hensel–Spittel model). The experimentally determined dynamically recrystallized grain sizes of the hot-deformed microstructures were linked with the Zener–Hollomon parameter calculated from the simulation through a power law.