Glass-liquid transition in a less-stable metallic glass

A stable metallic glass, SMG, is often viewed as an amorphous alloy exhibiting a reversible $\text{glass}\leftrightarrow \text{liquid}$ transition. Here we show experimentally that even in a less-stable metallic glass, LMG, which is prepared only by rapid melt quenching and promptly crystallized without glass transition at the ordinary heating rate, sufficiently rapid heating exposes the $\text{glass}\to \text{liquid}$ transition by suppressing crystallization. The experimental glass transition $T_{\mathrm{g}}$ and crystallization $T_x$ temperatures were plotted as a function of heating rate $\beta$, for ${\mathrm{Pd}}_{42.5}{\mathrm{Ni}}_{7.5}{\mathrm{Cu}}_{30}{\mathrm{P}}_{20}$ of SMG and for ${\mathrm{Zr}}_{70}{\mathrm{Ni}}_{30}$ of LMG. Two extrapolated curves, $T_g-\log \beta$ and $T_x-\log \beta$, intersect at a quite small $\beta$, e.g., $\sim {10}^{-4}°\mathrm{C}∕\min$, for SMG, whereas their intersection occurs at a large $\beta$, e.g., $\sim 10°\mathrm{C}∕\min$, for LMG. Such a large $\beta$ that is comparable to conventional heating rates makes it difficult to observe the reversible glass transition in LMG, and reflects low thermal stability of the glassy state.

Figure 1

(Color online) DSC profiles of ${\mathrm{Pd}}_{42.5}{\mathrm{Ni}}_{7.5}{\mathrm{Cu}}_{30}{\mathrm{P}}_{20}$ of SMG measured in the first (solid curve: For the amorphous phase) and the second (dashed curve: For the crystalline phases) heating runs at various heating rates $\beta$. Mark- ers indicate the onset temperatures of the glass transition $T_g$, crystallization $T_x$, and melting $T_m$.

Figure 2

(Color online) (a) DSC profiles of ${\mathrm{Zr}}_{70}{\mathrm{Ni}}_{30}$ at various $\beta$ obtained after subtracting the profile of second run from that of first run. The glass transition is clearly recognized at about and above $200°\mathrm{C}∕\min$. (b) DSC profiles of first run and second run at $\beta =500°\mathrm{C}∕\min$. For reference, the heat-capacity difference $\Delta C_p$ between first and second runs is also shown in the inset.

Figure 3

(Color online) Dependence of the onset temperatures of the glass transition and crystallization, $T_g$ and $T_x$, on the heating rate $\beta$ for ${\mathrm{Pd}}_{42.5}{\mathrm{Ni}}_{7.5}{\mathrm{Cu}}_{30}{\mathrm{P}}_{20}$ and ${\mathrm{Zr}}_{70}{\mathrm{Ni}}_{30}$ metallic glasses.