Crystallization of an undercooled Zn-based glass forming alloy

Zn-based metallic glasses (Zn40Mg11Ca31+xYb18-x, x = 0 - 4) are strong glass forming alloys with low glass transition temperatures. While the crystallization onset temperature is also low, the nucleation behavior has not been examined and analyzed quantitatively. For a Zn40Mg11Ca31Yb18 metallic glass alloy, the crystallization behavior was determined based on the application of the Flash differential scanning calorimetry (DSC) with ultrafast heating and cooling rates. The critical cooling rate range was measured for glass formation at 1.6(+/- 0.2) x 104K/s. A temperature-time-transformation (TTT) diagram for the nucleation onset in an undercooled liquid was obtained by applying a series of isothermal exposures by fast heating from the glass state or fast cooling from the liquid state to the target temperatures. A heterogeneous nucleation analysis model was developed to interpret the experimental TTT diagram, which provided a further understanding of the nucleation in Zn-based metallic glasses.