Janny Lindemann

Constitutive Analysis and Microstructure Evolution of the High-Temperature Deformation Behavior of an Advanced Intermetallic Multi-Phase γ-TiAl-Based Alloy

In the present study the high-temperature deformation behavior of a caste and subsequently HIPed β-solidifying γ-TiAl-based alloy with a nominal composition of Ti-43.5Al-4Nb-1Mo-0.1B (in at. %), termed TNM alloy, is investigated. At room temperature this alloy consists of ordered γ-TiAl, α2-Ti3Al and βo-TiAl phases. By increasing the temperature, α2 and βo disorder to α and β, respectively. In order to get a better understanding of dynamic recovery and recrystallization processes during thermomechanical processing, isothermal compression tests on TNM specimens are carried out on a Gleeble®3500 simulator. These tests are conducted at temperatures ranging from 1100 °C to 1250 °C (in the α/α2+β/βo+γ phase field region) applying strain rates in the range of 0.005 s-1 to 0.5 s-1 up to a true strain of 0.9. The evolution of microstructure along with the dynamically recrystallized grain size during hot deformation is examined by scanning electron microscopy (SEM). The flow softening behavior after reaching the peak stress in the true stress-true strain curve is attributed to dynamic recrystallization. By using the Zener-Hollomon parameter as a temperature-compensated strain rate the dependence of flow stress on temperature and strain rate is shown to follow a hyperbolic-sine Arrhenius-type relationship.

Constitutive Analysis of the Flow Curve Behavior of an Intermetallic b-solidifying γ-TiAl-based Alloy and Microstructural Characterization of the Deformed State

In the present study, the high-temperature deformation behavior of a cast and subsequently hot-isostatic pressed (HIPed) b-solidifying γ-TiAl-based alloy with a nominal composition of Ti-43.5Al-4Nb-1Mo-0.1B (in at.%), termed TNM alloy, is investigated. Isothermal compression tests on cylindrical specimens are carried out on a Gleeble 3500 simulator in order to investigate the dynamic recrystallization processes in the three-phase field region (α/α2+b/b0+γ−phase field) of the TNM alloy. The deformed microstructure along with the dynamically recrystallized grain size during hot deformation is examined by scanning electron microscopy (SEM). Two phenomenological-type constitutive models are presented and compared to experimental flow stress data.ZusammenfassungIn der vorliegenden Arbeit wird das Hochtemperatur-Verformungsverhalten einer gegossenen und anschließend heiß-isostatisch gepressten (geHIPten) b-erstarrenden γ-TiAl Legierung, mit einer nominellen Zusammensetzung von Ti-43.5Al-4Nb-1Mo-0.1B (in at.%), der sogenannten TNM-Legierung, untersucht. Isotherme Druckversuche an Zylinderproben erfolgen an einem Gleeble 3500 Simulator, um die dynamischen Rekristallisationsprozesse im drei-Phasengebiet (α/α2+b/b0+γ−Phasengebiet) der TNM-Legierung zu untersuchen. Die verformte Mikrostruktur wird zusammen mit der sich während der Warmumformung einstellenden dynamisch rekristallisierten Korngröße mittels Rasterelektronenmikroskopie (REM) untersucht. Zwei phänomenologische Konstitutivmodelle werden vorgestellt und mit den experimentell ermittelten Fließkurvendaten verglichen.