Impact of sulfur on the liquid structure and dynamics of Ti-Ni-S and Pd-Ni-S glass forming

Abstract

Only very recently Sulfur has been discovered as an alloying element, which improves the glass forming ability of various binary base alloys. For example, in Titanium-based alloys without Beryllium, Sulfur addition allows the bulk glass formation for the first time [1]. It is also possible to produce Ni-Nb-based metallic glasses at very low levels of Sulfur addition, or Pd-based alloys using Sulfur as a substituent of Phosphor. The discovery of these new Sulfur-containing metallics glasses opens new possibilities for many different applications. However, the mechanisms of how Sulfur enhances the glass forming ability are still not well understood. In this study, we investigate the impact of Sulfur addition on the melt structure and dynamics of two ternary model systems: Ti-Ni-S, which is a transition metal-based alloy system, and Pd-Ni-S which contains a noble metal element. We employed state-of-art quasielastic neutron scattering as well as neutron and synchrotron X-ray diffraction, combined with containerless processing techniques like electromagnetic and electrostatic levitation. The latter allows also to access thermophysical proprieties of the alloys including melt viscosity and density. As show in Fig. 1, we found that in the Ti-Ni-S melts the liquid dynamics slow down already at a few atomic percent of Sulfur addition. This is, however, associated with a less densely packed liquid, observed consistently from average packing fraction and microscopic melt structure [2]. In contrast, the dynamics of the Pd-Ni-S seems to be less sensitive to the concentration of Sulfur. Yet, a large discrepancy between the measured Ni self-diffusion coefficient and that scaled from the melt viscosity has been observed, which indicates a potential dynamic decoupling at temperatures well above the liquidus temperature of the alloys [3]. Our findings show that the structure and dynamics of the Sulfur-containing alloys melts depends strongly on the interactions between alloy elements, indicating different mechanisms responsible for the glass formation in Ti-Ni-S and Pd-Ni-S melts. [1] A. Kuball, O. Gross, et al., Scri. Mater. 146 (2018) 73-76; [2] J. Wilden, F. Yang, et al., Appl. Phys. Lett., 117 (2020) 013702; [3] J. Wilden, F. Yang, et al., J. Phys.: Condens. Matter 33 (2021) 435101