2005 Volume 46 Issue 10 Pages 2282-2286
The physical significance of the glass transition observed by differential scanning calorimetry (DSC) in the metallic glasses was considered through the measurements of the heating-rate, β, dependence of the glass transition temperature, Tg, and the crystallization temperature, Tx, in the Zr70Cu30 and Zr70Ni30 amorphous alloys and X-ray study of their structures in as-quenched and crystallized states. Zr70Cu30 exhibits the glass transition before crystallization, but Zr70Ni30 is immediately crystallized at heating rates of conventional time scale in the DSC measurement. The heating rate βc at the intersection of the two linear curves of Tg and Tx against logβ provides us with a significant measure to determine the glass-forming ability or thermal stability of the metallic glasses. By heating at β larger than βc, the crystallization is suppressed and the glass transition is clearly observed even in Zr70Ni30. The thermal stability of the Zr70Cu30 amorphous alloy is caused by retardation of crystallization due to the amorphous structure that is different from the Zr2Cu crystalline phase. In contrast, the thermal instability of Zr70Ni30 is attributed to the structural similarity to the Zr2Ni crystalline phase. Thus, suppressing the crystallization is shown to be a key to enhance the thermal stability of the present amorphous alloys.