Hermetic joining of 316L stainless steel using a patterned nickel nanoparticle interlayer

This paper evaluates the use of a nickel nanoparticle (NiNP) interlayer for making hermetic joints in 316L stainless steel substrates via diffusion brazing. Different NiNP inks were prepared using commercial nanopowder (～9 nm) and in-house synthesized nanoparticles. Syringe pump deposition of ～9 nm NiNP ink and diffusion brazing at 900 °C for 30 min under 2 MPa resulted in a hermetic joint up to the tested pressure of 70 psi. In-house synthesis of NiNPs was carried out in ethylene glycol by the reduction of NiCl₂·6H₂O in the presence of hydrazine (N₂H₄) as a reducing agent. X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM) results confirm the presence of pure fcc-Ni with an average particle size of 5.4 ± 0.9 nm. An as-synthesized suspension of NiNPs was patterned onto 316L stainless steel laminae via automated dispensing to a thickness of ～3 μm and bonded at 800 °C for 30 min at a pressure of 2 MPa. The diffusion-brazed test article was also found to be hermetic up to 70 psi. An examination of the bond line using scanning electron microscopy (SEM) showed good uniformity and continuity.