Ex- and in-situ high resolution microstructure investigations of additive manufactured parts

Additively manufactured robust complex metallic structures are very promising for field-specific applications in aerospace, automotive, energy, and medical implants. The micro- and nano-structure particularities of the materials for such specific applications are influenced by atomic scale effects. In particular, the very fast cooling rates during the additive manufacturing process affect the microstructure leading to grain refinement, disordered crystalline segregations at the grain boundaries, the formation of complex precipitates and amorphous phases. In order to understand and exploit these effects, advanced ex- and in-situ characterization methods are necessary.
This paper presents advanced correlative high-resolution microscopy studies performed on 3D-printed parts [1-3], providing information on morphology, chemical composition, and crystallinity from the micrometer scale down to the atomic scale. The studies were performed using scanning and transmission electron microscopy coupled with spectroscopic techniques such as electron energy loss spectroscopy and energy dispersive X-ray spectroscopy, which are key tools for localizing and identifying the alloying elements and their influence on stable and metastable phases.
The evolution of the microstructure was first studied in detail for the as-built and heat-treated parts to better understand the mechanical properties. In addition, in-situ heating measurements provided information on the evolution of nanometric phases and the coarsening/shrinkage of grains, the diffusion of alloying elements, and appearance of secondary phases at different temperatures.