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

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 Fe 60 Co 25 Ni 10 Mo 5 and Fe 63 Co 26 Ni 11 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 Fe 60 Co 25 Ni 10 Mo 5 melts undercooled by Δ T of about 100 K and more. In contrast, primary crystallisation of any of δ and γ phases appears to be possible in Fe 63 Co 26 Ni 11 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 Fe 60 Co 40 base alloy. Alloying with Mo has a strong impact on the microstructure and solid state transformations in the Fe 60 Co 25 Ni 10 Mo 5 samples such as grain refinement at Δ T < 200 K, incomplete transformation of γ-austenite to α-ferrite, and formation of martensite at Δ T ≥ 330 K.