Molecular dynamics simulations to identify atomistic deformationmechanisms in two-phase lamellar TiAl alloys

• Applicant: Privatdozentin Dr. Rebecca Janisch
• Subject Area: Computer-Aided Design of Materials and Simulation of Materials Behaviour from Atomic to Microscopic Scale
• Term: from 2018 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 404541620

• Final Report Year: 2022

Final Report Abstract

Different aspects of deformation and fracture in lamellar, two-phase TiAl microstructures have been investigated with molecular statics simulations. The focus of the investigation was two-fold. On the one hand, we determined the range of validity of micromechanical and continuum theory based models, such as the Hall-Petch relationship for hardening and toughening effects and the Griffith and Rice criteria for crack tip mechanisms and critical stress intensity factors. We could show, for instance, that the Hall-Petch regime only ends at a lamella thickness of a few nanometres. Another conclusion which should affect micromechanical modeling is the fact that the yield stress of twophase lamellar microstructures does not simply depend on the volume fraction of the phases involved, but the release of the coherency stresses by misfit dislocations provides new dislocation sources, the number of which scales with the number of interfaces in the structure, i.e. with the actual lamella spacing. On the other hand, we identified the atomistic mechanisms behind deformation and fracture in these microstructures, e.g. details of crack-tip interface interactions or dislocation nuleation at misfit dislocations in the semi-coherent interfaces. Thereby we could e.g. show that, locally, Schmid’s law holds for dislocation nucleation at misfit-dislocations, but not for the complex stress distribution in polycrystalline samples, where also the intersections between twin and grain boundaries come into play.

Publications

• Anisotropic failure behavior of ordered intermetallic TiAl alloys under pure mode I loading. Modelling and Simulation in Materials Science and Engineering, 28, 2020
  Anupam Neogi, Masud Alam, Alexander Hartmaier, and Rebecca Janisch
  
• Influence of lattice misfit on the deformation behaviour of α2 /γ lamellae in TiAl alloys. Materials Science and Engineering: A, 796, 2020
  Ashish Chauniyal and Rebecca Janisch
  
• On the role of preexisting defects in influencing hardness in nanoscale indentations - insights from atomistic simulations. Journal of the Mechanics and Physics of Solids, 154, 2021
  Ashish Chauniyal, Gerhard Dehm, and Rebecca Janisch
  
• Twin-boundary assisted crack tip plasticity and toughening in lamellar γ -TiAl. Acta Materialia, 213, 2021
  Anupam Neogi and Rebecca Janisch
  
• Unravelling the lamellar size-dependent fracture behavior of fully lamellar intermetallic γ -TiAl. Acta Materialia, 227:117698, 2022
  Anupam Neogi and Rebecca Janisch