In-situ synchrotron X-ray diffraction study of microstructure and strain evolution in brazed stainless steel joints under tensile loading

Brazed stainless steel joints are critical in heat exchanger applications but often suffer from residual stresses and brittle intermetallics. Using in-situ synchrotron X-ray diffraction and fluorescence at the DanMAX beamline, we investigated Fe-based filler joints in SS316 under tensile loading. Elemental mapping and phase analysis revealed distinct interfacial solidification zones (ISZ), athermal solidification zones (ASZ), and diffusion-affected zones (DAZ). Relative to the base composition, the ISZ showed an average Ni enrichment of 35%, while the ASZ exhibited localized Mo and Cr enrichment of up to 40% and 10%, respectively. The diffusion affected zone was strongly asymmetric, spanning approximately on one side of the wide joint and approximately on the other. Strain tensor mapping showed strong elastic anisotropy and stress localization at boride-rich zones, correlating with the observed fracture path. The results demonstrate the capability of synchrotron-based analysis to provide comprehensive insight into the interplay between chemical composition, microstructure, and stress in governing joint integrity, thereby informing strategies for improving toughness through process optimization. • In situ synchrotron X ray diffraction (XRD) and fluorescence (XRF) map brazed SS316 joints under tension. • X ray fluorescence and diffraction reveal chemical and microstructural asymmetry across the joint and the surrounding diffusion affected zone. • Full Debye Scherrer ring analysis reconstructs in plane strain tensor fields at micrometre resolution. • Strain localization correlates with boride rich regions and aligns with the observed crack trajectory.