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 AuAgPdCuSiand AuAgPdCuGaSiby using fast differential scanning calorimetry, covering the whole timescale of the crystallization event of the metallic melt. In the case of AuAgPdCuSi, a typical crystallization nose was observed, whereas for the AuAgPdCuGaSi, a more complex crystallization behavior with two distinct crystallization noses was found. Even for the complex crystallization behavior of the AuAgPdCuGaSialloy 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 AuAgPdCuSiwas modeled using classical nucleation theory with the Johnson-Mehl-Avrami-Kolmogorov (JMAK) equation, enabling a determination of the interfacial energy.