Characterization of Multi-Material 316L–IN718 System Produced by Powder Binning in Laser Powder Bed Fusion

This study presents a detailed microanalysis and microstructural characterization of the multi-material 316L–IN718 system produced in a prior work by the powder binning method for Laser Powder Bed Fusion (L-PBF), in which these multi-material samples were fabricated in a single build and then mechanically tested. This effort extends the investigation by applying X-ray micro-computed tomography (Micro-CT), electron backscatter diffraction (EBSD), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) techniques to specimens produced under the baseline single-scan condition to examine the interface transition in volumetric porosity, crystallographic structure, and elemental composition. Micro-CT analysis revealed that the interface region exhibited the highest void volume ratio among the three analyzed regions, reaching 0.91%, compared to 0.32% for 316L and 0.37% for IN718. The interface also contained the largest defects, including the only voids with volumes exceeding 500,000 µm3, indicating that critical flaws, while not widespread, were concentrated at the dissimilar material boundary. EDS line scanning across four locations along the interface confirmed a diffuse compositional transition that closely and consistently supports the interface width independently reported via microhardness for the same material pairing in the original study. EBSD mapping showed a gradual grain structure transition with coarser equiaxed grains on the 316L side, and the entire scan indexed successfully with a single face-centered cubic structure file, with no secondary or intermetallic phases detected at the resolution of the measurement. Collectively, these results explain the failure behavior reported previously: the compositionally strengthened, defect-rich interface sheds plastic strain into the adjacent, softer 316L, which fails first due to its lower strength and coarser void population. Under monotonic tensile loading, improving binning-based multi-material performance therefore depends primarily on strengthening or targeting defect-reduction strategies at the weaker 316L constituent.