Microscopic view of structural phase transitions induced by shock waves

Area of Science:

• Materials Science
• Condensed Matter Physics
• Computational Materials Science

Background:

• Solid iron undergoes phase transformations under extreme conditions.
• Understanding shock-induced transformations is crucial for materials under dynamic loading.

Purpose of the Study:

• To investigate the shock-induced phase transformation of solid iron using large-scale simulations.
• To analyze the nucleation, growth, and dynamics of new crystalline phases under shock compression.

Main Methods:

• Multimillion-atom molecular-dynamics simulations.
• Simulating shock compression along different crystallographic directions.
• Analyzing the resulting microstructural evolution and shock wave structures.

Main Results:

• A critical shock strength was identified, above which body-centered cubic iron transforms to close-packed structures.
• Nucleation and growth of small grains occur on picosecond timescales.
• Observed split two-wave shock structures at lower strengths and single overdriven waves at higher strengths.
• Grain dynamics and orientation are dependent on shock strength and crystallographic direction.

Conclusions:

• Shock compression drives phase transformation in iron, forming new grains.
• The observed orientational relationships resemble those of temperature-driven martensitic transformations.
• Simulation results provide insights into the dynamic behavior of materials under extreme shock conditions.