A promising route to overcome the strength-ductility trade-off in metallic alloys is the incorporation
of nano-scale twin boundaries in the microstructure. However, to design optimum microstructures,
the contribution of the twin boundaries to the deformation and fracture behavior still needs to be
better understood.
To this end, molecular statics simulations were performed in conjunction with a linear elastic
fracture mechanics based analysis, to characterize the crack advancement at and across internal
twin-boundaries in lamellar $\gamma$-TiAl alloys, namely true-twins (TTs), rotational boundaries (RBs),
and pseudo-twins (PTs). It was confirmed that nano-scale lamellae are effective in improving the
fracture toughness and crack growth resistance, at which both interface type and spacing influence
the crack tip mechanisms of inter-lamellar cracks. Furthermore, these cracks exhibit prominent
crystallographic direction sensitivity. For trans-lamellar cracks the tip shows plastic deformation
and toughening at all interfaces.
The overall fracture initiation toughness in a microstructure of TTs exhibits an increasing trend with
decreasing lamellar size down to a critical thickness, below which the crack advances via a quasi-
brittle manner, and the fracture toughness drops again.
These phenomena and their origins, as well as their impact on multiscale modeling strategies and
materials design concepts will be discussed in the presentation.