Revealing solidification behaviour and phase transformations in Fe60Co25Ni10Mo5 and Fe63Co26Ni11 alloys by using high-speed video and in situ X-ray diffraction"?>

Abstract

A combination of time-resolved synchrotron X-ray diffraction (XRD), high-speed video and electromagnetic levitation (EML) enabled revealing the solidification path and phase transformations in Fe₆₀Co₂₅Ni₁₀Mo₅ and Fe₆₃Co₂₆Ni₁₁ alloys during heating and cooling. High-speed XRD provided direct evidence for nucleation of metastable δ-ferrite in undercooled liquid state and its quick transformation to γ-austenite. Addition of Mo clearly favours nucleation of δ-ferrite in Fe₆₀Co₂₅Ni₁₀Mo₅ melts undercooled by ΔT of about 100 K and more. In contrast, primary crystallisation of any of δ and γ phases appears to be possible in Fe₆₃Co₂₆Ni₁₁ melts at all levels of undercooling. Neither Ni nor Mo exhibit any notable effect on the growth behaviour of δ and γ phases, which remains close to the one in the Fe₆₀Co₄₀ base alloy. Alloying with Mo has a strong impact on the microstructure and solid state transformations in the Fe₆₀Co₂₅Ni₁₀Mo₅ samples such as grain refinement at ΔT < 200 K, incomplete transformation of γ-austenite to α-ferrite, and formation of martensite at ΔT ≥ 330 K.