Thermodynamic description and determination of nucleation rate and their application on the modeling of the glass formation of Pd-based alloys
Zusammenfassung der Projektergebnisse
Within this project, the glass-forming ability of Pd-based glasses as model systems for metallic glass formers has been assessed experimentally and compared to results that were calculated on the basis of a CALPHAD approach. A good agreement between experimental and calculation results was obtained for both, the critical cooling rate as a measure of glass forming ability as well as the dependence of the critical cooling rate on glass fluxing that presumably eliminates heterogeneous nucleation sites from the metallic melt. Minor alloying by similar transition metals (Co and Fe) as present in a base Pd-Ni-P glass-forming alloy showed, however, a significant impact of the alloying additions (that amounted to 1 or 0.6 at.%, respectively) on glass stability against crystallization, which is also often used as a measure for glassforming ability. Moreover, the alloying additions caused a strong impact on the mechanical properties of the glass: adding Co made the resulting glass even more ductile (in compression and bending), while the addition of Fe resulted in a brittle material that failed before reaching the plastic regime. Further analyses indicated the following results: • The numerical value of Poisson´s ratio does not describe the brittle or ductile behavior of metallic glasses. • The critical fictive temperature as described in literature does not account for the ductile or brittle behavior of metallic glasses. • The results indicate that the distribution of free volume and thus the distribution of local motifs is affected by minor alloying and controls the mechanical performance of a given metallic glass. Analyses of the transformation kinetics of an Au-based bulk metallic glass-forming alloy with sufficiently low melting temperature to allow repeated melting-freezing cycles to be applied within a fast scanning chip calorimeter resulted in a dataset on nucleation kinetics that covers almost the entire undercooling regime. At a rather sharply defined temperature that is intermediate between the glass transition temperature and the melting temperature, a kinetics transition indicated as a strong change of the activation enthalpy of crystallization was observed. This observation is tentatively interpreted as a signature of a dynamic cross-over in the deeply undercooled liquid, separating diffusive and collective dynamics as described by Mode-Coupling theory.
Projektbezogene Publikationen (Auswahl)
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Melt undercooling and nucleation kinetics. Current Opinion in Solid State and Materials Science, 20 (2015) 3-12
Perepezko, J.H., Wilde, G.
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Thermal expansion accompanying the glass-liquid transition and crystallization. AIP Adv. 5 (2015) 127133
Jiang, M.Q., Naderi, M., Wang, Y.J., Peterlechner, M., Liu, X.F., Zeng, F., Jiang, F., Dai, L.H. Wilde, G.
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Impact of micro-alloying on the plasticity of Pd-based bulk metallic glasses. Scripta Mater. 111 (2016) 119–122
Nollmann, N., Binkowski, I., Schmidt, V., Rösner, H., Wilde, G.
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Effect of copper addition on the glass forming ability in Pd-Si binary amorphous alloying system. AIP Adv. 7 (2017) 95108
Wang X., Zeng M., Nollmann N., Wilde G., Tian Z., Tang C.
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Effect of soda lime flux on evaluation of the critical cooling rate of Pd82Si18 amorphous ribbon. AIP Adv. 7 (2017) 95308
Wang X., Tian Z., Zeng M., Nollmann N., Wilde G., Tang C.
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Thermal stability and non-isothermal crystallization kinetics of Pd82Si18 amorphous ribbon. AIP Adv. 7 (2017) 65206
Wang X., Zeng M., Nollmann N., Wilde G., Wang J., Tang C.
