Microstructural Characterization, Porosity Anisotropy, and Residual Stress Fields in ADAM-Fabricated 17-4PH Stainless Steel

Abstract

This work presents an experimental characterization of 17-4PH stainless steel fabricated by Atomic Diffusion Additive Manufacturing (ADAM). The microstructure, porosity, local chemical composition, and residual stresses were investigated using optical microscopy, SEM-EDS, digital image analysis, and sin2ψ X-ray diffraction. Pronounced porosity anisotropy was observed, with a lower porosity area fraction in the transverse section (1.45%) than in the longitudinal section (3.48%), where elongated channel-like inter-layer defects were identified. Isothermal sintering at 1315 °C produced a predominantly martensitic microstructure with equiaxed morphology. Local chemical variations were detected in selected macro-voids and interfacial regions, including elevated concentrations of C, Cr, and Nb, reaching 1.61 wt.%, 42.58 wt.%, and 16.31 wt.%, respectively. These anomalies may be related to localized binder-derived residues or secondary phase formation, although their origin cannot be conclusively determined by EDS alone. Residual stress measurements at 12 surface locations revealed spatial variations, with maximum axial tensile stress of 185.6 ± 21.9 MPa and local compressive stress of −46.7 ± 10.9 MPa. All measured stresses remained below the reported yield strength. The findings highlight the importance of optimizing inter-layer bonding and thermal debinding conditions in ADAM.