Ultrafast scanning calorimetry of newly developed Au-Ga bulk metallic glasses

The isothermal crystallization times and critical cooling rates of the liquid phase are determined for the two bulk metallic glass forming alloys Au₄₉Ag_5.5Pd_2.3Cu_26.9Si_16.3and Au_51.6Ag_5.8Pd_2.4Cu_20.2Ga_6.7Si_13.3by using fast differential scanning calorimetry, covering the whole timescale of the crystallization event of the metallic melt. In the case of Au₄₉Ag_5.5Pd_2.3Cu_26.9Si_16.3, a typical crystallization nose was observed, whereas for the Au_51.6Ag_5.8Pd_2.4Cu_20.2Ga_6.7Si_13.3, a more complex crystallization behavior with two distinct crystallization noses was found. Even for the complex crystallization behavior of the Au_51.6Ag_5.8Pd_2.4Cu_20.2Ga_6.7Si_13.3alloy it is shown that the minimal isothermal nose timeτx*does allow for a quantification of the macroscopic critical thickness. It is discussed in contrast to the critical cooling rate, which is found to allow less exact calculations of the critical thickness and thus does not correlate well with the critical cooling rate from macroscopic experiments. Additionally the crystallization data of Au₄₉Ag_5.5Pd_2.3Cu_26.9Si_16.3was modeled using classical nucleation theory with the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation, enabling a determination of the interfacial energy.