Abstract
The effect of heat treatment on the structure and mechanical properties of Co-Fe-Cr-Si-B/Fe-Cr-B/Fe-Ni-B amorphous alloys has been studied systematically. Melt-quenching (spinning method) was used for production of investigated amorphous alloys. The transmission electron microscopy (TEM) was used to study the structure transformations. The effect of temperature on deformation behavior (plasticity, microhardness, crack resistance, and the density and average length of shear bands) of the amorphous alloys was studied by bending and microindentation. It is shown that the ductile–brittle transition, which occurs at the stage of structure relaxation in amorphous alloys, is caused by two factors: a decrease in the susceptibility of the amorphous matrix to plastic flow and an abrupt decrease in the resistance to the development of quasibrittle cracks. It is established that the transition to a two-phase amorphous–nanocrystalline state upon annealing leads to substantial strengthening of the alloys and a partial recovery of their plasticity. It is proved that the strengthening of amorphous alloys at the initial stages of crystallization can be initiated by the difference in the elastic moduli of the amorphous matrix and the precipitated nanocrystals, as well as by the specific features of the interaction between nanocrystalline phase particles and shear bands propagating under external actions. It is established that the phenomenon of plasticization in amorphous alloys (the crack resistance can increase after annealing in a certain temperature range) is due to the effective retardation of cracks on nanoparticles.
Highlights
Amorphous alloys (AAs) exhibit unique and practically important properties due to an unusual structural state with a predominance of short-range order in the arrangement of atoms and the absence of translation symmetry over long distances [1,2,3]
It is shown that the ductile–brittle transition, which occurs at the stage of structure relaxation in amorphous alloys, is caused by two factors: a decrease in the susceptibility of the amorphous matrix to plastic flow and an abrupt decrease in the resistance to the development of quasibrittle cracks
It is proved that the strengthening of amorphous alloys at the initial stages of crystallization can be initiated by the difference in the elastic moduli of the amorphous matrix and the precipitated nanocrystals, as well as by the specific features of the interaction between nanocrystalline phase particles and shear bands propagating under external actions
Summary
Amorphous alloys (AAs) exhibit unique and practically important properties due to an unusual structural state with a predominance of short-range order in the arrangement of atoms and the absence of translation symmetry over long distances [1,2,3]. The uniqueness of amorphous–nanocrystalline structures resides in the fact that the phase components of the system are radically different in the nature of their atomic structure: on the one side, there is a crystalline constituent with a regular arrangement of atoms, in accordance with the laws of translational symmetry, and on the other side, an amorphous constituent with a disordered, statistical arrangement of atoms in space. This “symbiosis” leads to a number of effects that influence the mechanical behavior of these materials [9,11,12,18]. The aim of this work was a comprehensive study of the changes in the mechanical properties (plasticity, hardness, crack resistance) of the cobalt- and iron-based AAs in combination with their structure transformations occurring in a wide range of annealing temperatures
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