In-situ neutron diffraction study on the relationship between mechanical response and post-build Hot Isostatic Pressing (HIP) of EB-PBF 316 L stainless steel

Hot Isostatic Pressing (HIP) post-processing is widely employed to enhance the performance of additive manufacturing components. However, its impact on Electron Beam Powder Bed Fusion (EB-PBF) 316 L stainless steel remains insufficiently understood. This study investigated the effects of HIP temperature on EB-PBF 316 L relative to the as-built (AB) and powder metallurgy (PM) conditions. In-situ neutron diffraction during tensile testing, with the loading direction parallel to the build direction, was combined with microstructural characterization to assess lattice strain evolution, crystallographic texture, dislocation density, local chemical heterogeneity, and the resulting mechanical response. The results revealed distinct microstructure-property relationships among the investigated conditions. Differences in microstructural features, including crystallographic texture, twinning, lattice-parameter evolution, and dislocation density, were correlated with the observed mechanical response. The PM product exhibited higher stiffness (193 GPa) than the AB EB-PBF product (120 GPa) while showing similar flow strength. Elastic-Plastic-Self-Consistent (EPSC) modeling demonstrated that crystallographic texture is the primary origin of the elastic modulus difference. SEM-BSE imaging and localized EDS analyses revealed Mo- and Cr-rich precipitates along cellular/subgrain boundaries in the AB EB-PBF product. Comparable precipitates were not observed after HIP at 1160 °C, indicating substantial precipitate dissolution and reduced local chemical heterogeneity. HIP treatment significantly influenced the stress-strain behavior of EB-PBF products, promoting recovery of the AM-induced defect structure and progressively reducing dislocation density, while the strong (200) texture remained largely unchanged. A strong correlation between flow strength and dislocation density was observed for the EB-PBF conditions, indicating that dislocation density is the dominant strength-controlling parameter within the investigated HIP temperature range. These findings decouple the roles of crystallographic texture, defect structure and solute redistribution in governing the elastic and plastic response of EB-PBF 316 L before and after HIP.