In-situ Neutron Scatteringstudy of crystallization behaviour in ternary bulk metallic glasses and its correlation to glass forming ability

Bulk metallic glasses (BMGs) are complex structural materials, which have potential in a variety of applications. To determine the nature of excellent glass-forming ability (GFA), it is desirable to investigate crystallization kinetics. Although considerable amount of works have been reported, most of them were carried out on multicomponent alloys with complex chemistry. In order to access the physics of crystallization, it is essential to simplify the chemistry. In this paper we report a time-resolved neutron diffraction study of crystallization kinetics in five ternary BMGs, Zr₅₆Cu₃₆Al₈, Zr₅₄Cu₃₈Al₈, Zr₄₈Cu₄₅Al₇, Zr₄₅Cu₄₉Al₆ and Zr₄₆Cu₄₆Al₈, with gradually enhanced GFA. The measurements were carried out using NOMAD at the Spallation Neutron Source, Oak Ridge National Laboratory (ORNL). The structural evolution in short- and medium- range order (SRO and MRO) during the amorphous-to-crystalline transformation for these BMGs has been well resolved with a time-resolution of ~ 2 minute. According to the property of their crystalline products and their crystallization pathways, these alloys can be divided into two types: Cu₁₀Zr₇-type and Zr₂Cu-type BMGs. For Zr₂Cu-type BMGs, i.e. Zr₅₆Cu₃₆Al₈ and Zr₅₄Cu₃₈Al₈, there is just one crystallization temperature (e.g. ~751 K for Zr₅₆Cu₃₆Al₈) on their Differential Scanning Calorimetry (DSC) curves, and total neutron diffraction patterns show highly-ordered crystalline phase after divitrification. For Cu₁₀Zr₇-type BMGs, i.e. Zr₄₈Cu₄₅Al₇, Zr₄₅Cu₄₉Al₆ and Zr₄₆Cu₄₆Al₈, two crystallization temperatures (e.g. ~ 776 K and ~ 778 K for Zr₄₆Cu₄₆Al₈) were identified, much like that in Zr₅₂.₅Cu₁₇.₉Ni₁₄.₆Al₁₀Ti₅ BMG (BAM-11), an excellent glass former. The crystalline phase of devitrified Cu10Zr7-type BMGs, with better GFA, is poorly ordered, also similar to BAM-11. These results suggest that the unique crystallization pathway for Cu₁₀Zr₇-type BMGs would be a distinctive feature of alloys with excellent GFA.