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Unravelling the lamellar size-dependent fracture behavior of fully lamellar intermetallic γ -TiAl

A. Neogi, R. Janisch

Acta Materialia, 227, 117698, (2022)

DOI: https://doi.org/10.1016/j.actamat.2022.117698

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Strengthening of metals by incorporating nano-scale coherent twin boundaries is one of the important breakthroughs of recent years in overcoming the strength-ductility trade-off. To this effect, also twin boundaries in nano-lamellar lightweight Ti-Al alloys promise a great potential, but their contribution to the deformation and fracture behavior needs to be better understood for designing optimal microstruc- tures. To this end, we carry out linear elastic fracture mechanics informed large-scale atomistic sim- ulations of fully lamellar microstructures consisting of the so-called ”true twin” boundaries in γ -TiAl. We find that nano-scale lamellae are not only effective in improving the fracture toughness and crack growth resistance, but also that the lamellar size controls the crack tip mechanisms. We identify a critical lamella thickness in the region between 1.64 and 3.04 nm, above which the crack tip events are primar- ily dislocation-based plasticity and the critical fracture initiation toughness exhibits an increasing trend with decreasing lamella size. Below the critical thickness, a decline in fracture toughness is observed and the crack tip propagation mechanisms are quasi-brittle in nature, i.e. the cleavage of atomic bonds at the crack tip is accompanied by plasticity events, such as twin-boundary migration and dislocation nucleation. A layer-wise analysis of the unstable stacking fault energy, the energy barrier for dislocation nucleation, that the critical thickness is of a similar value as the distance from the twin boundary at which bulk properties are restored.

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{"type":"article", "name":"a.neogi20224", "author":"A. Neogi and R. Janisch", "title":"Unravelling the lamellar sizedependent fracture behavior of fully lamellar intermetallic \gamma TiAl", "journal":"Acta Materialia", "volume":"227", "OPTnumber":"", "OPTmonth":"4", "year":"2022", "OPTpages":"117698", "OPTnote":"", "OPTkey":"atomistic simulations; titanium aluminides; fracture mechanisms; twins; grain boundaries;", "DOI":"https://doi.org/10.1016/j.actamat.2022.117698"}
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