C15 NbCr2 Laves phase with mechanical properties beyond Pugh’s criterion.

Pugh’s criterion in terms of the bulk/shear modulus ratio ( B / G ) is widely used to distinguish the ductility and brittleness of metals, with the recommended B / G ratio of 1.75 for the boundary ratio between ductility and brittleness. The present first-principles calculations yield a B / G = 3.69 for the C15 Laves phase NbCr 2 , suggesting the ductility of NbCr 2 according to Pugh’s criterion. However, experiments indicate that NbCr 2 is a brittle phase at room temperature with the fracture toughness of 1.0–1.4 MPa m 1/2 . NbCr 2 is hence a compound with its ductile and brittle behavior beyond Pugh’s criterion, and this finding also validates for other Laves phases and compounds. New insight into Pugh’s B / G criterion is also discussed. [ABSTRACT FROM AUTHOR]