Dresden 2017 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 56: Topical session: Dynamics, relaxation and deformation in deeply supercooled metallic liquids and glasses - kinetic transitions

MM 56.2: Vortrag

Donnerstag, 23. März 2017, 10:45–11:00, IFW A

Structural origins of the boson peak in metals: From high-entropy alloys to metallic glasses — •Karsten Albe, Tobias Brink, and Leonie Koch — Fachgebiet Materialmodellierung, Technische Universität Darmstadt, Germany

Virtually all amorphous materials exhibit a boson peak, which is an excess of vibrational modes at low frequencies compared to the phonon spectrum of the corresponding crystal. Until recently, the consensus was that it originated from “defects” in the glass. However, the boson peak was also attributed to the first van Hove singularity of crystal lattices in alternative theories. A recent viewpoint is that the van Hove singularity is simply shifted by the decreased density of the amorphous state and is therefore not a glass-specific anomaly. In the current contribution, we aim to resolve this question for metallic systems. Using molecular dynamics computer simulations of high-entropy alloys and metallic glasses of the same composition, we show that the boson peak consists of additional modes which only arise in structurally disordered, softened regions [1]. Consistent with theoretical models, these regions are characterized by reduced stiffness and can be regarded as “soft spots”: The boson peak can serve as an indicator for the amount of such regions. This is consistent with observations that find an increased boson peak signal in mechanically deformed glasses in which an increase of the boson peak originates in the shear band [2].
[1] Brink et al., PRB, accepted (2016)
[2] Bünz et al., PRL 112, 135501 (2014)