Abstract
The effect of fatigue on ZrCuAl amorphous metals induced by mechanical cyclic loading is investigated using inelastic neutron scattering and the pair density function analysis of neutron diffraction data. With cooling, the local atomic structure undergoes reorganization under fatigue that is directly related to the number of fatigue cycles. Also under fatigue, suppression in the atomic dynamics is observed as well. A structural restructuring occurs within a 4 Å radius and intensifies with increasing the compression cycles, whereas the vibrational density of states is attenuated as the intensity shifts towards the elastic, zero-energy transfer peak. The combined static and dynamic structural effects are a signature of the microscopic changes brought about by fatigue, and together may be the onset for subsequent behaviors following extended cyclic loading such as fracture. Even after the load is removed, the structural changes described here remain and increase with repeated cyclic loading which is an indication that the lattice deforms even before shear bands are formed.
Highlights
Amorphous metals are solids devoid of periodicity, prepared by the very fast cooling of a viscous liquid to avoid crystallization
The suppression of these excitations, to the suppression of the boson peak [36] by external stimuli, may be linked to the structural re-organization that we observed in the local structure
A connection is present between the changes observed in the local structure and the dynamics in the solid state
Summary
Amorphous metals are solids devoid of periodicity, prepared by the very fast cooling of a viscous liquid to avoid crystallization. One anomaly is the observation of excess vibrational density of states manifested in the so-called boson peak, and observed by techniques such as neutron [14] and Raman scattering [15] This is manifested in an unusual low temperature behavior of the heat capacity, CP, as well, in which CP deviates from the T3 Debye law expected of a typical metallic solid with cooling. A local reorganization of the atom packing is observed, where the changes intensify as the number of compression cycles increases This is best observed by cooling the system down to low enough temperatures that reduces the smearing induced by thermal vibrations. Associated with these changes in the static structure is a softening of the lattice dynamics. The attenuation implies an increase in the sound velocity, suggesting that the glass becomes stiffer and more likely brittle under fatigue
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