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Abstract

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 γ-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.