Hot-working behavior of an advanced intermetallic multi-phase γ-TiAl based alloy

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2014-09, Vol.614, p.297-310
• Main Authors: Schwaighofer, Emanuel, Clemens, Helmut, Lindemann, Janny, Stark, Andreas, Mayer, Svea
• Format: Article
• Language: English
• Subjects: Alloying additive; Applications; Applied sciences; Automotive engineering; Deformation; Elasticity. Plasticity; Engineering techniques in metallurgy. Applications. Other aspects; Exact sciences and technology; Failure; Fractures; Hardening. Tempering; Heat treatment; Hot working; Intermetallics; Mathematical models; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Microstructure; Production techniques; Recrystallization; Surface layer; Synchrotron X-ray diffraction; Texture; Thermomechanical processing; Titanium aluminides; Titanium base alloys
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2014.07.040

New high-performance engine concepts for aerospace and automotive application enforce the development of lightweight intermetallic γ-TiAl based alloys with increased high-temperature capability above 750°C. Besides an increased creep resistance, the alloy system must exhibit sufficient hot-workability. However, the majority of current high-creep resistant γ-TiAl based alloys suffer from poor workability, whereby grain refinement and microstructure control during hot-working are key factors to ensure a final microstructure with sufficient ductility and tolerance against brittle failure below the brittle-to-ductile transition temperature. Therefore, a new and advanced β-solidifying γ-TiAl based alloy, a so-called TNM alloy with a composition of Ti–43Al–4Nb–1Mo–0.1B (at%) and minor additions of C and Si, is investigated by means of uniaxial compressive hot-deformation tests performed with a Gleeble 3500 simulator within a temperature range of 1150–1300°C and a strain rate regime of 0.005–0.5s−1 up to a true deformation of 0.9. The occurring mechanisms during hot-working were decoded by ensuing constitutive modeling of the flow curves by a novel phase field region-specific surface fitting approach via a hyperbolic-sine law as well as by evaluation through processing maps combined with microstructural post-analysis to determine a safe hot-working window of the refined TNM alloy. Complementary, in situ high energy X-ray diffraction experiments in combination with an adapted quenching and deformation dilatometer were conducted for a deeper insight about the deformation behavior of the alloy, i.e. phase fractions and texture evolution as well as temperature uncertainties arising during isothermal and non-isothermal compression. It was found that the presence of β-phase and the contribution of particle stimulated nucleation of ζ-Ti5Si3 silicides and h-type carbides Ti2AlC enhance the dynamic recrystallization behavior during deformation within the (α+β) phase field region, leading to refined and nearly texture-free α/α2-grains. In conclusion, robust deformation parameters for the refinement of critical microstructural defects could be defined for the investigated multi-phase γ-TiAl based alloy.