Virtual melting and cyclic transformations between amorphous Si, Si I, and Si IV in a shear band
arxiv(2024)
摘要
Virtual melting (VM) as alternative deformation and stress relaxation
mechanisms under extreme load is directly validated by molecular dynamics (MD)
simulations of the simple shear of single crystal Si I at a temperature 1,383 K
below the melting temperature. The shear band consisting of liquid Si is formed
immediately after the shear instability while stress drops to zero. A
thermodynamic criterion for VM, which depends on the ratio of the sample to
shear band widths, is derived analytically and confirmed by MD simulations.
With further shear, the VM immediately transforms to a mixture of low-density
amorphous a-Si, Si I, and IV, which undergo cyclic transformations a-Si to and
from Si I, a-Si to Si IV, and Si I to and from Si IV with volume fraction of
phases mostly between 0.2 and 0.4 and non-repeatable nanostructure evolution.
Such cyclic transformations produce additional important carriers for plastic
deformation through transformation strain and transformation-induced plasticity
due to volume change, which may occur in shear bands in various material
systems but missed in experiments and simulations.
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