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

Abstract

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 (∼9nm) and in-house synthesized nanoparticles. Syringe pump deposition of ∼9nm NiNP ink and diffusion brazing at 900°C for 30min under 2MPa resulted in a hermetic joint up to the tested pressure of 70psi. 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±0.9nm. An as-synthesized suspension of NiNPs was patterned onto 316L stainless steel laminae via automated dispensing to a thickness of ∼3μm and bonded at 800°C for 30min at a pressure of 2MPa. The diffusion-brazed test article was also found to be hermetic up to 70psi. An examination of the bond line using scanning electron microscopy (SEM) showed good uniformity and continuity.