Time Resolved Transformation Kinetics of the BCC to HCP Transition in Iron Using Piezo- Driven Compression*

Understanding of the effect of kinetics on the behavior of phase transformations at high pressure is critical to interpreting experimental results but investigations have historically been hindered by limitations in compression rates and detector technologies. Current detector technologies, paired with the relatively rapid compression achievable by use of piezo-electrically driven dynamic diamond anvil cells (dDAC), have enabled time resolved diffraction experiments that can probe the effect of compression rate and overpressure on the kinetics of phase transitions. Iron, which experiences a pressure induced structural transition from BCC to HCP at approximately 13 GPa, has been extensively studied by both shock and static compression techniques. We examine the effects of fixed overpressure in iron by traditional Avrami style experiments, as well as the effects of compression rate, with rates on the order of 10^-3 to 10² GPa/s and assess the results in the framework of classical kinetic models to determine if better models for pressure induced transitions are required.