What is it about?
A dedicated in situ heating setup in a scanning electron microscope (SEM) followed by an ex situ atomic force microscopy (AFM) and electron backscatter diffraction (EBSD) is used to characterize the nucleation and early growth stages of Fe-Al intermetallics (IMs) at 596°C. A location tracking is used to interpret further characterization. Ex situ AFM observations reveal a slight shrinkage and out of plane protrusion of the IM at the onset of IM nucleation followed by directional growth. The formed interfacial IM compounds were identified by ex situ EBSD. It is now clearly demonstrated that the θ-phase nucleates first prior to the diffusion-controlled growth of the η-phase. The θ-phase prevails the intermetallic layer.
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Why is it important?
It is well established that the brittleness of the IM phases increases with increasing at.% Al content. However, the Al-rich IMs (especially the η- and θ- phases) spontaneously form during various manufacturing processes, e.g. welding, coating, sintering, aluminum casting with ferrous inserts, hot-dip aluminizing, etc. Therefore, understanding the formation mechanism of the η- and θ- phases is crucial to avoid their undesirable formation during manufacturing processes. During these processes, the local temperature at the interface rapidly changes with time, which could play a significant role in the sequence of IM phase nucleation.
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This page is a summary of: High temperature in situ SEM assessment followed by ex situ AFM and EBSD investigation of the nucleation and early growth stages of Fe-Al intermetallics, Scripta Materialia, July 2021, Elsevier, DOI: 10.1016/j.scriptamat.2021.113910.
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