Impact of minor sulfur additions on the structure and dynamics of Ni-Nb melts

Abstract

Bulk metallic glasses feature an amorphous structure, which results in exceptional properties as engineering materials. Typically alloying additional components improves the glass forming ability (GFA). Beside adding non-metallic elements like P, B, C, recently sulfur has been found to facilitate bulk metallic glasses formation at different concentration levels [1]. This makes them promising candidates for commercialization, where the alloy composition can be tuned according to applications. In the case of the binary Nig2Nb3g glass forming alloy, it has been found that an optimal enhancement of the GFA can be achieved by alloying only 3 at% S. Such kind of minor alloying effects cannot be understood by applying the common empirical rules like a denser packing of the melt, or the formation of deep eutectic compositions. Employing electrostatic levitation combined with in-situ synchrotron diffraction, we studied impacts of sulfur on the structure and dynamics of Ni-Nb based alloys, as well as on the solidification behavior from undercooled melt. First results show that small, but notable changes can be observed in the measured liquid structure factor upon an addition of 3 at% S. In particular, in the obtained X-ray total structure factor the position of the first structure factor maximum appears to shift towards lower g values. The structure changes are analyzed with the help of the partial structure factors of the binary Ni-Nb alloy [2]. It has been also observed that the initial phases solidified from the undercooled melt seem to be different with and without S. The implication of these changes on the glass forming behavior is discussed together with the melt viscosity measured using the oscillating drop technique. References: [1] A. Kuball, O. Gross, B. Bochtler, R. Busch, Scr. Mater. 146, 73-76 (2018). [2] D. Holland-Moritz, F. Yang, J. Gegner, T. Hansen, M. D. Ruiz-Martin, and A. Meyer, J. Appl. Phys. 115, 203509 (2014).