Characterization and crystallization studies of melt-spun glassy Fe-22.5Al-10Zr Metal by analytical electron microscopy

Abstract

Melt-spun glassy Fe-22.5Al-10Zr metal (concentration in atomic percent) is an interesting material for high temperature oxidation study due to its high crystallization temperature, 650°C, and its capacity to form a protective oxide layer. We have applied analytical electron microscopy on cross-section samples to study the composition variation near the two surfaces of the melt-spun ribbon. An aluminum depleted layer was detected using X-ray energy dispersive spectroscopy ≈200 nm beneath the He-cooled surface. No composition variation was observed as a function of depth below the wheel-cooled surface. The crystallization behavior of this material both below and above the crystallization temperature was also studied. Crystallization begins with the nucleation of α-Fe particles via a primary crystallization mechanism followed by the formation of a metastable phase, Fe₈Al₃Zr, via polymorphic crystallization. At 700°C, above the crystallization temperature, the Fe₈Al₃Zr transformed to the equilibrium phase, Fe₁₀Al₄Zr₃, by solid state reaction.