Diffusion brazed steel components with nickel-based filler metals are often used in applications where high strength and corrosive resistance are required at elevated operating temperatures. Example applications are turbine components, injection moulding tools or heat exchangers. To enable brazing temperatures significantly below the melting point of the steel, melting point depressant elements must be alloyed to the filler metal. The metalloids boron, silicon and phosphorus have proven to be particularly suitable for this purpose, so that brazing temperatures of nickel-based filler metals between 900 and 1,200 °C can be achieved. However, critical precipitation of brittle phases such as borides, silicides or phosphides can form in the diffusion-affected zone of the steel and within the brazing seam, which influence the mechanical and corrosive properties and thus, the lifetime of the joint. [1,2]

For 3D-reconstructions of these critical precipitates, large scale layer-by-layer removal of brazed joints were carried out using a focussed ion beam inside scanning electron microscope (FIB-SEM). Scans were generated using an in-lens detector and initially divided into different stacks for further processing. The relevant phases and pores were then segmented using a deep learning-based software. The segmented pixels were converted into voxels based on the layer distance and subsequently transformed into STL data. With the help of a CAD software, these were converted into volume components and joined together to form assemblies, which were rendered for better visualisation. Thus, for the first time, the 3D-morphology of the precipitates of diffusion brazed joints could be analysed, which enables a deeper understanding of properties and failure mechanisms as well as further investigations by FEM. [3]

References
[1] M. Way, J. Willingham, R. Goodall International Materials Review, 2020, 65, 257-285.
[2] M.A. Penyaz, A.A. Ivannikov, O.N. Sevryukov et al. Non-Ferrous Metals, 2021, 1, 41–56.
[3] J. L. Otto, L. M. Sauer, M. Brink et al. Materials and Design, 2023, 235, 112401, 1-10.