The effect of nickel on the strength of iron nickel alloys: Implications for the Earth's inner core

We investigated the effect of nickel on the strength of iron-nickel (FeNi) alloys at high pressure. Using radial X-ray diffraction coupled with literature results from nuclear resonance inelastic X-ray scattering measurements we determined the bulk strength of two FeNi alloys (Fe0.88Ni0.12 and Fe0.8Ni0.2) at high pressures up to 70 GPa. When extrapolated to Earth's inner core conditions, the strength of these FeNi alloys is found to increase relative to pure Fe. For the likely composition and conditions of the inner core, we estimate that an FeNi alloy with ∼5.5 wt% Ni would have a strength that is ∼125% greater than estimates for pure Fe. As shear strength is a measure of a material's resistance to flow, our results have implications for understanding the deformation processes inside planetary interiors and support dislocation creep as the dominant mechanism in the Earth's inner core.