An entropy driven liquid-liquid transition (LLT) from a fragile (less ordered) to a strong (highly ordered) liquid occurs in the phase during undercooling. In this work, we show that this ordering transition as well as the applied shear rate affect the onset of crystallization. By recording simultaneously melt viscosity and temperature profiles, we quantitatively determine the shift in the upper part of the time-temperature-transformation diagram of Vit1 to shorter times with increasing shear rate. This acceleration in nucleation rate can be explained by the classical nucleation theory of crystals only if we take into consideration the effect of both shear flow and equilibrium viscosity. A critical assessment of the results concludes that shearing must first trigger the nucleation of the strong liquid from the fragile liquid and that the crystallization proceeds in a second step from the strong liquid. The fragile-to-strong transition decreases the configurational entropy of the liquid leading to a smaller interfacial energy between liquid and crystal, thus reducing the activation barrier for crystallization.
Keywords: TTT diagram; bulk metallic glass; crystallization; liquid–liquid transition; shear; viscosity.
© 2021 IOP Publishing Ltd.