Creep behaviour of two-phase lamellar TiAl: Crystal plasticity modelling and analysis

Two-phase (?2Ti3Al-k?TiAl) fully lamellar TiAl alloys show highly anisotropic creep behaviour. Depending on lamellar orientations, locally in the TiAl phases hard and easy deformation modes are active, which significantly influence the creep behaviour at a global scale. To obtain comprehensive understanding how the locally activated crystallographic deformation modes influence the macroscopic creep behaviour, a crystal plasticity (CP) model with modified hardening behaviour is proposed in this work. For this purpose, a softening parameter is introduced in the model that phenomenologically describes the threshold stresses for material softening depending on pile-up dislocation lengths during creep deformation. The model allows us to interpret the cause of creep anisotropy at macro-scale deformation based on the orientation dependent activation and interactions of slip systems at the TiAl phases. Comprehensive study was performed to validate the model and to predict creep parameters under different temperature and stress loading conditions. Comparing the experimental data with simulation results, we found that the proposed CP model captures creep behaviour in primary, secondary, and tertiary regime for all the lamellar orientations with good accuracy. This model can be further used for investigating microstructure-sensitive creep behaviour of a wide range of TiAl alloys.