Comparison of Nickel Nanoparticle-Assisted Diffusion Brazing of Stainless Steel to Conventional Diffusion Brazing and Bonding Processes

Transient liquid phase diffusion brazing is used in precision, hermetic joining applications as a replacement for diffusion bonding to reduce cycle times, reduce bonding pressure, and improve yields. In the present study, stainless steel 316L laminae are diffusion brazed with an interlayer of nickel nanoparticles and compared with samples joined by conventional diffusion bonding and electroplated nickel-phosphorous diffusion brazing. Comparison is made with regard to microstructural evolution, diffusional profile, and bond strength. All bonding was carried out in a uni-axial vacuum hot press at $1000°C$ with a heating rate of $10°C/min$⁠, a dwell time of 2 h and a bonding pressure of 10 MPa. Bond strength measurements show that the sample brazed with a nickel nanoparticle interlayer has the lowest void fraction at $4.8±0.9%$ and highest shear strength at $141.3±7.0MPa$⁠. Wavelength dispersive spectroscopic analysis of sample cross-sections shows substantial diffusion of Ni and Fe across the nickel nanoparticle bond line. Scanning electron micrographs show no secondary phases along the nickel nanoparticle bond line.