Publication: pressure cycling and compression rate on the bcc-hcp transition in an FeNi alloy

In this work, our colleagues at Stanford University, led by post-doctoral fellow Yanyao Zhang, use fast compression of over 800 gigapascals per second with pressure cycling to monitor how iron-nickel (FeNi) alloys — the primary components of Earth’s core — change their structure in extreme conditions. The state of the sample is measured using in-situ X-ray diffraction at the Advanced Photon Source in the United States. The HotCore team then provided assistance with the analysis and interpretation of the experimental data in terms of texture, plastic deformation, stress, and phase transformation mechanisms.

FeNi undergoes a phase transformation as it is compressed. At around 13 GPa, its crystal structure changes from body-centered cubic to hexagonal close-packed, which alters its strength and how it deforms. With fast compression and pressure cycling, we found that this transition mechanism changes; the phase transformation occurs at a lower pressure, and the hexagonal structures rotate in orientation.

Overall, these experimental observations can affect our understanding of how materials behave in the core during impact processes or during the evolution of the Earth. Beyond planetary core studies, understanding FeNi’s behavior under compression and pressure cycling can help design industrial materials with improved strength and ductility. 

To know more:

• The full publication: Y. Zhang, S. Merkel, A. Celeste, S. Pandolfi, M. Ricks, S. Chariton, V. B. Prakapenka, A. E. Gleason & W. L. Mao. Effect of pressure cycling and compression rate on the bcc-hcp transition in an FeNi alloy, Appl. Phys. Lett. 127 261901 (2025) [doi: 10.1063/5.0300182].
• The corresponding science highlight, selected by the American Institute of Physics (AIP) journal editors: A. Bandari. Fast compression and pressure cycling alter phase transitions in iron-nickel alloys, Scilight 2026 011104 (2026) [doi: 10.1063/10.0042203].