Fcc-Based Superstructure in CrCoNi System Induced by Annealing of Amorphous Cr-Co-Ni-Si-B-P Alloy.

Chemically ordered face-centered cubic (fcc) phases consisting mainly of Cr, Co, and Ni were synthesized by annealing a Cr_26.7Co_26.7Ni_26.7Si₁₀B₅P₅ amorphous alloy. The annealed Cr_26.7Co_26.7Ni_26.7Si₁₀B₅P₅ sample was composed of Cr_4.5BP₂, Cr₃ Co₅Si₂, and fcc phases. Synchrotron radiation anomalous X-ray scattering (AXS) measurements confirmed that the annealed Cr_26.7Co_26.7Ni_26.7Si₁₀B₅P₅ sample had superlattice reflections from an L1_0-, and/or L1_2-, and D0₂₂-type ordered structure. The diffraction intensities of the superlattice reflections observed in the AXS measurements indicated strong dependence on the incident X-ray energy. The diffraction intensity of the superlattice reflection increased at the X-ray energy near the K-edge of Cr, suggesting that Cr is mainly ordered in the L1_0- and D0₂₂-type structures. Microstructural analysis using scanning transmission electron microscopy (STEM) revealed crystal grains with diameters of approximately 20 nm, showing diffraction spots corresponding to superlattice reflections of 001 and 110, in addition to a two-dimensional diffraction pattern corresponding to the fcc structure. Simultaneous STEM--energy dispersive X-ray spectroscopy analysis indicated that the grains had a higher Cr concentration than the mother alloy composition of Cr_26.7Co_26.7Ni_26.7Si₁₀B₅P₅. [ABSTRACT FROM AUTHOR]