Structural properties, electronic structure, Fermi surface, and mechanical behavior of bcc Cr-Re alloys

The electronic structure and ground-state properties (lattice parameter, cohesive energy, bulk and tetragonal shear moduli) were calculated for bcc Cr and Cr-Re alloys over a wide range of Re concentration by the full-potential linear muffin-tin orbital method (FLMTO) with generalized gradient approximation (GGA). We show that the GGA predicts the commensurate antiferromagnetic Cr state as a ground state for the experimental volume with a small lower energy compared with the nonmagnetic state, but gives a large moment of (formula presented) In the Cr-Re system the magnetism becomes weak with Re concentration and for 25% Re the mean Cr moment is about (formula presented) Examining the Fermi surface of Cr-Re alloys within the modified rigid-band approximation, the electronic topological transition (ETT) is found to occur for 6% Re. A weakening of the Cr-Cr bonds near this ETT is considered as a possible microscopic reason for the “small” rhenium effect—the ductility enhancement in Cr(Mo, W)-Re alloys with small Re additions. As the mechanism for the “large” rhenium effect (near 25–35% Re) the formation of Cr-Re close-packed particles should play an important role together with the significantly weakened Cr-Cr bonding.