Formation and crystallization of Ti-Hf-Ni metallic glasses

The formation of a Ti₂₅Hf₅₀Ni₂₅ metallic glass and the phase evolution upon crystallization (devitrification) are reported. The glass is strongly metastable, with a 65°C separation between the glass transition temperature, T_g=335°C, and the onset temperature for primary crystallization to a nanoscale microstructure consisting of an icosahedrally symmetric ordered phase, that can not be reported as the icosahedral phase (i-phase). There is no distinction between an i-phase and a high-order crystal rational approximant for such small grains, since the unit cell size of a reasonable high-order approximant is of the order of the grain size. Upon annealing at higher temperatures, the metastable icosahedrally symmetric phase transforms to a stable Ti₂Ni-type crystal phase.