Analysis of the multistage phase separation reaction in Fe–25 at%Co–9 at%Mo

Differential scanning calorimetry (DSC) has been used to characterize the phase reactions during age hardening of a Fe–25 at%Co–9 at%Mo alloy. The heat of reaction which can be accounted for the development of the hardening phase was further analyzed on the basis of the Kissinger method and a fit based on the JMA model. Additionally, the precipitation sequence was studied by in situ small‐angle neutron scattering (SANS) as well as in situ X‐ray diffraction (XRD) to gain knowledge on the chemistry and crystallography of the prevailing phases. As direct imaging techniques 3D atom probe (3DAP) and high‐resolution transmission electron microscopy (HRTEM) were used. The combination of these methods revealed that hardening in the investigated alloy starts with spinodally formed Mo‐rich clusters followed by precipitation of the intermetallic µ‐phase (Fe,Co)7Mo6.

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