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

•The elastic properties of C15 NbCr2 Laves phase are calculated.•NbCr2 Laves phase with mechanical properties beyond Pugh’s criterion.•Other Laves phases and other compounds also with mechanical properties beyond Pugh’s criterion.•New insights into Pugh’s B/G criterion are discussed.

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 NbCr2, suggesting the ductility of NbCr2 according to Pugh’s criterion. However, experiments indicate that NbCr2 is a brittle phase at room temperature with the fracture toughness of 1.0–1.4 MPa m1/2. NbCr2 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.

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