Dynamic heterogeneity in Pd40Ni40P20 glass-forming metallic melt and crystallization behavior probed by quasi-elastic neutron scattering and ultrafast scanning calorimetry

Abstract

The intrinsic heterogeneity of metallic glasses is hidden in long-range disordered structures. Due to the lack of a long-range ordered structure, it is difficult to construct the structure-property relationship in metallic glasses. However, relaxation dynamics provides a powerful approach to understanding metallic glasses. State-of-the-art quasi-elastic neutron scattering (QENS) and ultrafast scanning calorimetry are used to study the atomic relaxation dynamics, dynamic heterogeneity, diffusion coefficient and crystallization behavior of the Pd40Ni40P20 metallic glass. The presence of dynamic heterogeneity in the Pd40Ni40P20 glass-forming metallic melt is evaluated from the dynamic susceptibility, which is derived from the QENS self-intermediate scattering function. The dynamic heterogeneity increases gradually with decreasing temperature, and a dynamic crossover arises at approximately 1235 K, which is related to the cooperative motion of atoms. Ultrafast scanning calorimetry combined with conventional calorimetry provides heating and cooling rates over seven orders of magnitude, allowing us to study how the liquid thermal history affects glass formation, glass transition, and crystallization. The critical cooling rate required for glass formation is directly determined. A continuous-heating-transformation diagram for crystallization is constructed. This study will improve our understanding of the atomic relaxation dynamics mechanism and intrinsic heterogeneity in metallic glasses.