3D EBSD and EDS characterization of additively manufactured Inconel 718

Additive manufacturing plays an important role in the development of prototypes and small series or for the repair of defective components. In the FAFil project, funded by the European Union, a platform for the additive manufacturing of large-format components by coaxial wire feed laser metal deposition (LMD-W) was developed and set up. In the wire fusion process, a metal wire made of the desired material is coaxially fed through a laser head and then melted onto the substrate. The advantage is, compared to powder bed fusion, the complete use of the metal wire to build up the component without the need to recycle waste material. In order to be able to realize complex component shapes, the laser-wire unit must be mounted on a robot arm that can move in six axes.

Among the materials used in the aerospace industry, Inconel 718 is one of the most successful advanced alloys, which has attracted a large number of studies over the years. Recently, the production of Inconel 718 using LMD-W showed promising results as large zones of fine equiaxed grains were found at the bottom of the melt pools in the remelting regions of each layer. The equiaxed grains form from an ISRO (Icosahedral Short-Range Order) mediated nucleation mechanism, which induces a significant reduction in grain size.

In the present work, the fine grained region was characterized using Xe-PFIB serial section tomography. Electron backscatter diffraction (EBSD) and x-ray spectroscopy (EDS) were integrated into the serial section process to characterize the grain structure and grain orientation as well as the chemical composition of the individual regions. It is shown that titanium carbide particles play a key role in the ISRO-mediated nucleation in Inconel 718.