Evaluation of Ni interlayer effect on the diffusion bonding of Austenitic Fe-base alloys

Abstract

Micro-channel heat exchangers with high heat transfer area such as the printed circuit heat exchanger (PCHE) are likely to be adopted to next generation nuclear reactors such as Small Modular Reactor (SMR) and Sodium-cooled Fast Reactor (SFR) to ensure high thermal efficiencies and compact size. Diffusion bonding is a key technology for fabrication of such heat exchangers. In this study, Ni-foil interlayer was inserted into joint region in order to remove precipitates and induce grain boundary migration at the bond line to obtain better bond quality. Furthermore, application of post bond heat treatments on the diffusion-bonded specimens resulted in improved tensile properties and uniformity of Ni content across the bonding interface and performed corrosion behavior and stress corrosion cracking (SCC) analyses in $S-CO_2$ environment. The mechanical integrity of the diffusion bond joints was evaluated by tensile testing at room temperature, and $650^\circ C$. Moreover, the mechanical integrity and corrosion behavior of the diffusion bond joints will be discussed in view of the microstructural features at the joint region.