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

New high-performance engine concepts for aerospace and automotive application enforce the development of lightweight intermetallic gamma-TiAl based alloys with increased high-temperature capability above 750 degrees C. Besides an increased creep resistance, the alloy system must exhibit sufficient hot-workability. However, the majority of current high-creep resistant gamma-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 beta-solidifying gamma-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 degrees C and a strain rate regime of 0.005-0.5 s(-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 beta-phase and the contribution of particle stimulated nucleation of zeta-Ti5Si3 silicides and h-type carbides Ti2AlC enhance the dynamic recrystallization behavior during deformation within the (alpha+beta) phase field region, leading to refined and nearly texture-free alpha/alpha(2)-grains. In conclusion, robust deformation parameters for the refinement of critical microstructural defects could be defined for the investigated multi-phase gamma-TiAl based alloy. (C) 2014 Elsevier B.V. All rights reserved.