Ni self-diffusion in glass forming Pd–Ni–S melts

Johanna Wilden,Gerrit Günther,Andreas Meyer,Ralf Busch,Margarita Russina,Alexander Kuball,Fan Yang

doi:10.1088/1361-648x/ac1968

Abstract

The Ni self-diffusion in glass forming Pd40Ni40S20, Pd37Ni37S26 and Pd31Ni42S27 melts was probed by incoherent, quasielastic neutron scattering over a temperature range between 773 and 1023 K. The Ni self-diffusion coefficients are on a 10−10 m2 s−1–10−9 m2 s−1 scale and barely change with composition. Each composition exhibits an Arrhenius-type temperature dependence of the Ni self-diffusion coefficients, which results in activation energies ranging from E A = 348 ± 16 meV for Pd40Ni40S20 to E A = 387 ± 6 meV for Pd37Ni37S26. The structural relaxation shows a stretched exponential behavior even far above the liquidus temperatures. In addition, the viscosity of the Pd37Ni37S26 melt was measured under reduced gravity conditions. The diffusion calculated from the viscosity reveals a significant deviation from the measured Ni self-diffusion by a factor between 4 and 8. This may indicate a dynamic decoupling between the atoms within the Pd–Ni–S equilibrium melts.

Highlights

Ni–P-based alloys are very well explored bulk metallic glass formers
For all temperatures the self-diffusion coefficients are constant over the entire q-range, which confirms the diffusive nature of the melt dynamics
The Ni selfdiffusion coefficients were derived from the structural relaxation times and correspond to 3.75–5.60 ×10−10 m2 s−1 at the liquidus temperature, which is about one order of magnitude slower than for monatomic metallic melts (e.g. Ni [8])

Summary

Introduction

Ni–P-based alloys are very well explored bulk metallic glass formers. Within the ternary Pd–Ni–P system, Pd40Ni40P20 represents the best glass former [1,2,3,4] and enables the casting of glassy cylinders with 25 mm in diameter by fluxing in dehydrated B2O3 and subsequent water quenching [4]. The authors came to the conclusion that the atomic motion is determined by the packing fraction [8, 9] This implies that these melts behave like monatomic metallic melts above the critical temperature of mode coupling theory [10]. The decrease of the packing fraction upon S-addition indicates the occurrence of directional bonds, which may develop a pronounced chemical short-range-order This could be the origin for the improved glass formation in Ti–Ni–S. Besides the reduced packing fraction, the decoupling of the self-diffusion coefficients indicates the occurrence of a chemical short-range order. In order to estimate whether a dynamic decoupling occurs in Pd–Ni–S melts above the liquidus temperature like in Zr-based melts, the viscosity of Pd37Ni37S26 was measured under reduced gravity conditions by electromagnetic levitation. The correlation between self-diffusion and packing fraction in Pd37Ni37S26 melts was crosschecked

Experimental

Results and discussion

Conclusion

Data availability statement