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.
All Science Journal Classification (ASJC) codes
- General Computer Science
- General Chemistry
- General Materials Science
- Mechanics of Materials
- General Physics and Astronomy
- Computational Mathematics