Publications
Unravelling the lamellar size-dependent fracture behavior of fully lamellar intermetallic γ -TiAl
A. Neogi, R. Janisch.
Acta Materialia, 227, 117698, (2022)
Abstract
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.
Keyword(s): atomistic simulations; titanium aluminides; fracture mechanisms; twins; grain boundaries;
Cite as: https://www.sciencedirect.com/science/article/pii/S1359645422000775
DOI: https://doi.org/10.1016/j.actamat.2022.117698
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