Fast compression and pressure cycling alter phase transitions in iron-nickel alloys

In its early lifetime, Earth likely went through cycles of compression and decompression, buckling and eventually rebounding under the violent young solar system’s bombardment of asteroids and comets. Though we would never want to go back to this epoch, Zhang et al. have recreated similar conditions in a laboratory to help study our home’s history.

By combining fast compression of over 800 gigapascals per second with pressure cycling, the researchers monitored how iron-nickel (FeNi) alloys — the primary components of Earth’s core — change their structure in extreme conditions.

FeNi undergoes a phase transformation as it is compressed. At around 13 gigapascals, 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, however, the researchers found this transition mechanism changes; the phase transformation occurs at a lower pressure, and the hexagonal structures rotate in orientation.

“Overall, these interesting experimental observations can affect our understanding of how materials behave in the core during impact processes or during the evolution of the Earth,” said author Yanyao Zhang.

Though Earth’s early compression cycles occurred at even higher temperatures and pressures than the current experiments, they likely led to phase transformations similar to the ones seen here.

Beyond planetary core studies, understanding FeNi’s behavior under compression and pressure cycling can help design industrial materials with improved strength and ductility. The researchers hope to additionally evaluate the effects of shock compression, which can achieve compression rates of up to 10⁶ gigapascals per second.

“This is an exciting technique,” said Zhang. “We can really study how the compression rate can affect the transformation and stability of materials.”

Source: “Effect of pressure cycling and compression rate on the bcc-hcp transition in an FeNi alloy,” by Yanyao Zhang, Sebastien Merkel, Anna Celeste, Silvia Pandolfi, Matthew Ricks, Stella Chariton, Vitali Prakapenka, Arianna Gleason, and Wendy L. Mao, Applied Physics Letters (2025). The article can be accessed at https://doi.org/10.1063/5.0300182 .