Interface characterisation of IN825/309LSi stainless steel functionally graded material: grain structure and texture evolution

This study investigates the microstructure of functionally graded materials (FGMs) fabricated by wire arc additive manufacturing (WAAM) using Inconel 825 and 309LSi stainless steel. Electron backscatter Diffraction (EBSD) analysis revealed a heterogeneous dendritic morphology with ⟨001⟩, ⟨111⟩, and ⟨110⟩ texture components. A bimodal grain size distribution (2.9 and 247 µm) and an average grain size of 118 ± 136 µm were observed. High-angle grain boundaries (∼83.2%) dominated the interface region, indicating distinct grain boundary characteristics across the interface. Pole figure analysis confirmed orthotropic symmetry and directional solidification. These findings demonstrate WAAM’s capability to produce FGMs with tailored texture and grain boundary characteristics, providing a basis for future evaluation of mechanical and functional properties.