Ultrafast dynamic compression technique to study the kinetics of phase transformations in bismuth

Area of Science:

• Materials Science
• Condensed Matter Physics
• High-Pressure Physics

Background:

• Understanding material behavior under extreme conditions is crucial for various scientific and engineering applications.
• Dynamic loading conditions, such as shock compression, can induce unique material responses not observed under static conditions.
• Bismuth (Bi) exhibits complex phase transformations that are sensitive to pressure and temperature.

Purpose of the Study:

• To investigate the structural phase-transformation kinetics of bismuth (Bi) under dynamic loading.
• To explore the influence of high strain rates on phase boundary deviations.
• To determine if the transformation is consistent with a thermally activated process.

Main Methods:

• Preheated bismuth samples (296-532 K) were subjected to ramp compression.
• Compression was achieved with 15-35 nanosecond (ns) rise times to a peak stress of approximately 11 Gigapascals (GPa).
• High strain rates (epsilon > 5 x 10^6 s^-1) were achieved during compression.

Main Results:

• Deviation from equilibrium phase boundaries was observed at high strain rates.
• The observed deviations suggest that compression time scales are comparable to the incubation period of the new phase.
• The relationship between pressure change over thermal energy (DeltaP/kT) and strain rate (epsilon) was consistent with a thermally activated transformation.

Conclusions:

• Dynamic compression of bismuth at high strain rates leads to deviations from equilibrium phase boundaries.
• The kinetics of phase transformation in bismuth under dynamic loading are influenced by the incubation period of the new phase.
• The transformation process is consistent with a thermally activated mechanism, providing insights into material behavior under extreme conditions.