Investigation of the stability of glassy state in the Zr- and Hf-based glassy alloys correlated with their transformation behavior

The transformation behavior from glassy state was investigated in Zr- and Hf-based glassy alloys. The primary phases are metastable face-centered-cubic (fcc) Zr₂Ni and fcc Hf₂Ni phases in the Zr₆₅Al_7.5Ni₁₀Cu_17.5 and Hf₆₅Al_7.5Ni₁₀Cu_17.5 glassy alloys, respectively. By substitution of 5 at.% Pd for Cu, the primary phase changes to an icosahedral quasicrystalline phase in both alloys. It is found that the addition of elements, which have a positive or weak chemical affinity with one of the constitutional elements in the Zr–Al–Ni–Cu and Hf–Al–Ni–Cu glassy alloys, is effective for the precipitation of the icosahedral phase. It is suggested that Pd plays a dominant role in an increase in the number of nucleation sites. Since an icosahedron is contained as a structure unit in the icosahedral, fcc Zr₂Ni and fcc Hf₂Ni phases, it is implied that these phases are correlated with the local icosahedral order. The high-resolution transmission electron microscopy images of the as-spun Zr₆₅Al_7.5Ni₁₀Cu_7.5Pd₁₀ and Hf₆₅Al_7.5Ni₁₀Cu_12.5Pd₅ alloys reveal a possibility of the existence of the icosahedral ordered regions. It is therefore, concluded that the icosahedral short- or medium-range order exists and it stabilizes the glassy state in the Zr- and Hf-based multicomponent alloys.