Synchrotron X-ray study of vacuum brazed 316L stainless steel joints

Nickel phosphide is a valuable material in high-temperature brazing and joining applications, offering excellent thermal stability for temperatures up to 400°C. Nickel phosphide is used as powder form for joining applications and therefore it is imperative to study the formation as well as interaction of Ni2P particles with Brazing with nickel-chromium-based fillers is widely used to join stainless steel components in applications such as heat exchangers, where strong, corrosion-resistant joints are essential. Silicon and boron additives lower the filler melting temperature but can promote the formation of chromium-rich precipitates near the joint. This study characterizes such precipitates in AISI 316 stainless steel brazed with a Ni-Cr-Si-B filler using high resolution synchrotron hard X-ray fluorescence (XRF) and diffraction (XRD). XRF identified Cr-rich precipitates, while XRD revealed diffraction patterns consistent with space group number 70, with lattice parameters a = 4.26 Å, b = 7.38 Å, and c = 14.70 Å. Combined with SEM XEDS analysis, the results suggest the precipitates are Cr₂B or (Cr,Fe)₂B.