Ni self-diffusion in Zr-Ni(-Al) melts

Abstract

Abstract. We report on investigations on the atomic dynamics in melts of different binary ZrNi alloys and of the ternary glass-forming Zr 60 Ni 25 Al 15 alloy. The liquids are containerlessly processed in an electromagnetic levitator that is combined with quasielastic neutron scattering at the time of flight spectrometer TOFTOF of the FRM II. Ni self-diffusion coefficients are determined that exhibit an Arrhenius-type temperature dependence with comparatively large activation energies ranging between 0.64 and 0.90 eV. Although glass forming abilities and melting temperatures for these alloys exhibit large differences, the absolute values of the selfdiffusion coefficients are similar at same temperature. IntroductionAmong numerous multi-component alloys forming (bulk) metallic glasses [1], one important class of alloys is based on the binary Zr-Ni system. The solidification behaviour of melts and consequently the glass formation process is strongly affected by the the atomic dynamics in the liquid. While for glassforming Pd-(Ni-Cu-)P melts the viscosity is coupled with the diffusivity by the Stokes-Einstein relation above the critical temperature T c of mode-coupling theory [2], for Zr-Ti-Cu-Ni-Be melts viscosity and diffusivity are decoupled above T c and the liquidus temperature T L [3]. Moreover these liquids exhibit considerably smaller values of the Ni self-diffusivity as Pd-(Ni-Cu-)P alloys at similar temperatures. In this work we present investigations on the Ni self-diffusion in melts of different binary Zr-Ni alloys and of the ternary glass forming alloy Zr 60 Ni 25 Al 15 by quasielastic neutron scattering. In order to avoid reactions of the Zr-based melts with crucible materaials and in order to cover a large temperature range including the metastable regime of undercooled liquids at temperature below the melting temperature, the samples are containerlessly processed by application of the electromagnetic levitation technique.

Atomic dynamics in Zr-(Co,Ni)-Al metallic glass-forming liquids

“…T [8,26]. The Ni self-diffusion coefficients for Vit1 and Vit4 are also included for comparison [11,24].…”

Non-Equilibrium Solidification of Undercooled Metallic Melts

“…This may be understood by the fact that the Einstein-Stokes relation does not hold for Zr-based glass forming alloys [78]. As to a similar undercooled glass-forming Ni 50 Zr 50 alloy, from which a stoichiometric compound NiZr is crystallized, the self-diffusion coefficient of Ni D Ni was measured [79]. The activation energy for the atomic diffusion is determined as Q d = 0.73 ± 0.03 eV which is very close to the value inferred from the slope of the computed line in Figure 15, [80].…”

Atomic mobilities and diffusivities in Al alloys

“…The absence of a sample holder makes it not only possible to extend the accessible temperature range to high temperatures of up to 2300 K, but also into the metastable regime of the undercooled liquid several hundreds of Kelvin below the equilibrium melting point, due to the avoidance of heterogeneous nucleation at crucible walls [39]. The QNS in combination with EML was successfully used to determine diffusion coefficients of Ni in pure Ni [39], Si-Ni [40], Zr-Ni [41], and Zr-Ni-Al [41] melts.…”