Modelling and Simulation of deformation and fracture of Titaniumaluminide alloys

Abstract

The two-phase Titaniumaluminide alloys show poor ductility and brittle fracture at room tempera-ture. The overall ductility and fracture behaviour depends on the intrinsic properties of the phases as well as on the morphology of grains and colony structures. During fracture mostly inter-granular fracture occurs at globular grains (consists of g-TiAl phases). However, fracture in lamellar colonies (consists of lamellar plates of a2-Ti3Al and g-TiAl phases) is much more complicated and often occurs by a single/combined action of inter-lamellar and trans-lamellar fracture, which is again highly dependent on the orientation of the lamellar interfaces with respect to the loading axis. Still today no numerical tool is available that can predict the microstructure dependent crack initiation and crack propagation, correlating them to the global failure of the material. Motivated by such issues we are developing numerical models to predict the generation of local and global plasticity at dif-ferent structural length scale as well as to predict the component failure based on micro-meso damages of the structure. In this presentation I will show a multiscale modelling approach that incorporates micro and meso scale structural description of a fully-lamellar TiAl alloy. The most important structural details, i.e., the vol.% of the phases, morphology of lamellar structure and orientation of the phases has been considered. The constitutive behaviour of the a2-Ti3Al -and g-TiAl-phases has been described in a crystal plasticity model where the mechanisms of crystallographic deformation (slip planes, slip di-rection and critical resolved shear stress) have been incorporated. Thus the model allows to predict the evolution of local plasticity in a realistic manner. In this work we also introduce fracture in the phases and colonies, which have been realized via “local-approach of damage mechanics” incorpo-rating decohesion at phase-boundaries (for inter-lamellar fracture) and splitting of phases (for trans-lamellar fracture). Development of this fracture model is in preliminary stage; therefore, only some fundamental results will be shown that may explain the quasi-brittle fracture of TiAl alloy at room temperature.