TEM study of an analogue of the Earth’s inner core ε-Fe

Metallurgists know that a hexagonal close-packed phase (ε-martensite) is formed by straining at low temperature or pressurization of nickel–chromium stainless steels. In many respects, the ε-martensite is similar to the hexagonal phase of iron thought to constitute the Earth’s inner core (ε-Fe), but, contrary to ε-Fe, it is metastable at atmospheric pressure. Observation of dislocations in ε-martensite in transmission electron microscopy (TEM) may thus provide information on the deformation mechanisms of the inner core alloy. s of 18 Cr–8 Ni austenitic stainless steel have been pressurized at 13 GPa and 800 °C, in a multi-anvil press and 30 GPa and RT, in a diamond-anvil cell. Subsequent TEM study shows that thin lamellae of ε-phase form on {1 1 1} planes of the fcc austenite. They were accompanied by crystals of bcc α′-martensite. In one case, a few dislocations were observed in a glide band of the ε-phase, compatible with second order pyramidal slip {1 1 2̄ 2}〈1 1 2̄ 3〉. servations suggest that ε-martensite, hence presumably ε-Fe, deforms by slip on the basal plane and second order pyramidal planes, as hexagonal cobalt.