Phase field crystal simulation of stress induced localized solid-state amorphization in nanocrystalline materials

Prior research has shown that localized solid-state amorphization (SSA) occurs in nanocrystalline materials under stress. Established knowledge includes the role of grain boundaries and dislocation density in structural changes. However, the exact mechanisms linking strain rate, temperature, and grain size to SSA remain unclear. No prior work had resolved how these variables interact during uniaxial deformation. This gap motivated the use of advanced computational models to simulate SSA dynamics. Existing studies often lack detailed thermodynamic and kinetic analysis of SSA. The need for a method that captures both atomistic and macroscopic behavior is evident. The phase field crystal (PFC) method offers a promising approach to bridge this gap.

This study aimed to investigate how localized SSA occurs in polycrystalline materials under uniaxial tensile deformation. The specific problem addressed is the interplay between strain rate, temperature, and grain size in triggering SSA. The motivation stems from the lack of a unified model that captures both kinetic and thermodynamic factors. The authors propose using the PFC method to simulate SSA processes. This approach allows for tracking lattice distortion and atom rearrangement. The study seeks to clarify the role of dislocation density and free energy in SSA. By calculating critical diffusion-time steps and amorphous region areas, the authors aim to quantify SSA dynamics. This work provides a framework for understanding stress-induced amorphization at the nanoscale.

The phase field crystal (PFC) method was applied to simulate localized solid-state amorphization. The model incorporates uniaxial tensile deformation and tracks structural changes. Variables included strain rates, temperatures, and grain sizes. The simulation captures lattice distortion and grain boundary evolution. Dislocation density was monitored as a key indicator of structural instability. Thermodynamic factors like Helmholtz free energy were calculated. The model also tracks atom rearrangement and interface energy changes. The PFC method allows for analyzing both kinetic and thermodynamic aspects of SSA.

The highest strain rate caused significant lattice distortion and grain collapse. This led to a sharp increase in dislocation density, triggering localized SSA. At higher temperatures, atoms became more active and left their original positions. This increased atom rearrangement and interface free energy. Small grain sizes raised the percentage of grain boundaries in the system. This increased the Helmholtz free energy, promoting SSA. The critical diffusion-time step was calculated to determine amorphization onset. Amorphous region areas were quantified to assess the extent of SSA. These results suggest that strain rate, temperature, and grain size all influence SSA dynamics.

The PFC method successfully simulated localized SSA under uniaxial deformation. Strain rate, temperature, and grain size were identified as key factors. High strain rates caused lattice distortion and dislocation density increases. Thermodynamically, higher temperatures increased atom activity and interface energy. Small grain sizes raised Helmholtz free energy, aiding amorphization. Dislocations and free energy acted as seeds and driving forces for SSA. The model calculated critical diffusion-time steps and amorphous region areas. These findings confirm the PFC method's effectiveness in studying SSA processes.