Strain-rate effects on the fcc-to-hcp transition of Fe-10wt%Ni alloy at high-pressure and -temperature

Different strain rates during static and dynamic compression can lead to the observation of different transition pathways (e.g., Evans et al. 2007). Knowledge on the effects of strain-rate on phase transformation is thus important to our understanding of phase transition kinetics and natural impact events. As the most abundant component in the Earth’s core and a major component in iron meteorites, FeNi alloys undergo a face-centered cubic-to-hexagonal close-packed structure (fcc-to-hcp) transition at high pressure and temperature (P-T) with a fcc+hcp coexistence region based on previous static compression studies (e.g., Lin et al. 2002; Mao et al. 2006). Although shock wave experiments coupled with X-ray free electron laser probes to very high strain rates can provide insights into the transition kinetics of materials, the Hugoniot for FeNi alloys does not cross the fcc-to-hcp transition (Tecklenburg et al. 2021). Therefore, the transition kinetics remain unknown. Here, we investigate the fcc-to-hcp transition of Fe-10wt%Ni at different strain rates between 10 and 10³ GPa/s in dynamic diamond anvil cells (dDACs) using double-sides laser heating and in-situ synchrotron X-ray diffraction at millisecond timescales up to 80 GPa and 2000 K at 13ID-D beamline of the GSECARS in Argonne National Laboratory. Analysis of X-ray diffraction data shows strain rate effects on the fcc+hcp transition loop at high P-T conditions. Our results can shed new light on the mechanism of the fcc-to-hcp transition. We also apply our results to better understand shock metamorphism during iron meteorite impacts.

References

[1] Evans W.J., et al. 2007. Review of Scientific Instruments, 78(7), 073904.

[2] Lin J.-F., et al.  2002. Geophysical Research Letters, 29(10), 108.

[3] Mao, W.L., et al. 2006. Physics of the Earth and Planetary Interiors, 155(1-2), 146-151.

[4] Tecklenburg, S., et al. 2021. Minerals, 11(6), 567.