1. Tensile specimens prepared from diffusion bonded block of 316/316L SS
2. Micrograph showing good grain growth across the diffusion bond
3. Small defects in bond area may not impact overall strength but could lower design life due to crevice corrosion
Diffusion Bond Characterization
- Diffusion bond strength, defects, and corrosion behavior must be understood before they can be reliably used in reactor systems.
Diffusion Bond Process
- Plates were chemically cleaned and electroplated with nickel to prevent surface oxidation which would impair bonding process
- Actual process variables are proprietary to the subcontractor
- 24 plates were diffusion bonded (25 bond interfaces)
- Corner sample was removed and inspected
Diffusion Bond Metallography
- 316L alloyed with nickel plating (dark vertical line is nickel enriched from plating)
- Microstructure growth across nickel layer indicates good diffusion migration
- Remaining nickel layer ~40-50µm in thickness
- 24 of the 25 bonds had this bond quality
- Energy Dispersive Spectroscopy (EDS) indicates that at locations outside of the electrodeposited nickel bulk properties of the steel are preserved.
- Nickel and iron formed an intermetallic, while some places in the bond are chromium deficient.
- Porosity and voiding were observed in one bond (see arrow above for location)
- In regions of porosity poor diffusion occurred (microstructures do not extend across nickel deposition zone)
- It is unclear if the entire plate bond surface is poor or only the region near this corner
- Diffusion Welding and Brazing, Welding Handbook, 7th ed., American Welding Society, 1980, p 311–335
Corrosion and Erosion Behavior in Supercritical CO2 Power Cycles