Theoretical study of the devitrification of the metallic glassNi80B20

The devitrification of ${\mathrm{Ni}}_{80}{\mathrm{B}}_{20}$ metallic glass has recently been investigated experimentally by two different groups with contradictory results. Rojo et al. interpret their data as showing that devitrification occurs in two successive processes separated by a state in which pure amorphous Ni is present. By contrast, Riveiro et al. have suggested that the “intermediate” state consists of two crystalline phases. Using a semiempirical treatment which combines classical elasticity theory and Miedema’s model for the heat of formation of alloys, we have constructed the free energy diagram for Ni-B. We found that it supports Riveiro et al.’s account of the devitrification of ${\mathrm{Ni}}_{80}{\mathrm{B}}_{20}$ glass rather than Rojo et al.’s.