In situ TEM observations of thermally activated phenomena under additive manufacturing process conditions

Engineering components, fabricated via fusion based additive manufacturing (AM) processes, experience varying spatio-temporal thermal transients in the build process due to the localized high energy delivered by the heat source. The combination of extreme thermal gradients (10⁴ - 10⁶ K/m) and/or rapid thermal cycling (10²- 105 K/s) may result in metastable and directional microstructures that significantly affect part performance. In order to tailor the microstructure of AM builds to obtain desired properties in ‘as fabricated’ AM builds, it is necessary to understand the solid-state dynamic processes that govern the microstructural evolution under such extreme thermal conditions. Currently, this information can only be obtained through post-mortem characterization, e.g. by electron microscopy. Here, we performed in-situ electron microscopy studies using a modified heating device to simulate thermal AM conditions to observe the solid-state dynamic processes during phase transformations in Ti-6Al-4V and Haynes 282