An Ordered Metallic-Glass Solid-Solution Phase That Grows From the Melt Like a Crystal
Lyle E. Levine, Karena Chapman, Leonid A. Bendersky, Gabrielle G. Long, John W. Cahn, Peter Chupas, Judith K. Stalick, Frederic Mompiou
We used high-energy synchrotron-based X-ray scattering to investigate the structure of an isotropic AlFeSi metallic glass that nucleates and grows from the melt during rapid cooling like a crystal. The glass is a noncrystalline homogeneous metastable phase in the full thermodynamic sense: it is distinct from the melt, and it coexists along typical interphase interfaces with clear partitioning of chemical elements with the melt from which it forms and with solid phases, both in reversible equilibrium and during heterogeneous phase changes. The pair distribution function reveals chemical ordering out to at least 12 Å that resembles that of a known crystalline intermetallic phase of neighboring composition. Under an isothermal anneal at 305 C, the glass first rejects Al, then persists for approximately an hour with no detectable change in structure, and finally transforms by a first order phase transition to a crystalline phase with different local ordering from that within the glass.