Mössbauer Study on Crystallization Behavior of Glassy Fe58Co7Ni7ZrxB28-x (3 ≤x ≤18) Alloys with Variable Supercooled-Liquid Regions

Crystallization behavior of glassy Fe58Co7Ni7ZrxB28-x (3 ≤x ≤18) alloys was examined by means of X-ray diffraction and 57Fe Mössbauer spectroscopy in order to clarify the reason for the thermal stability against crystallization, where the thermal stability correlates strongly to the width of the supercooled-liquid region. Various crystalline phases appear in the specimens quenched from and annealed at temperatures 50 K higher than the crystallization temperatures. Crystalline Fe3B and Fe2B phases characteristic of the B-rich alloys appear along with Fe2Zr and unidentified Fe–Zr–B phases characteristic of the Zr-rich alloys in the quenched Fe58Co7Ni7Zr8B20 specimen that originally has the widest supercooled-liquid region of 66 K. The competitive frustration in the forming ability of these compositional short-range order is one of the reasons for thermal stability against crystallization. Both the quenched and annealed Fe58Co7Ni7Zr3B25 specimens do not contain any phase with the Zr constituent, while the glassy Fe58Co7Ni7Zr3B25 alloy has the supercooled-liquid region of 34 K. This fact implies that the Zr impurities in Fe3B- and/or Fe2B-type compositional short-range order also play an important role in the thermal stability of these glassy alloys.