What Does Interfacial Corrosion Mean?
Interfacial corrosion is a type of failure where silver-brazed joints in stainless steel are exposed to water or humidity in service. In these conditions joint failure may result along the stainless steel-brazing filler metal interface. This type of corrosion is frequently observed at water-air interfaces.
All types of stainless steel are susceptible to attack by interfacial corrosion. Nickel-free or low-nickel ferritic and martensitic-type stainless steels are most susceptible to interfacial crevice corrosion.
Interfacial corrosion is also known as crevice corrosion and knife-line attack.
Corrosionpedia Explains Interfacial Corrosion
Interfacial corrosion is a phenomenon involving corrosion along the interface between the brazing filler metal and the base metal. A brazed joint may be susceptible to interfacial corrosion depending on a number of factors, including:
- Types of base metal (stainless steel) and brazing filler metal used
- Brazing technique (using flux)
- Service environment (moisture exposure)
One very common occurrence involves the brazing of stainless steel using a flux and silver-based braze filler metal. During brazing, flux removes the surface oxide layer on the base metal at the brazed joint in order for bonding to take place. In metals that depend on a pacified layer (created by nickel or chromium) for corrosion resistance, this area (interface) at the brazed joint now has less corrosion resistance. During service, this area of reduced corrosion resistance is more susceptible to attack at the interface.
This type of corrosion can be prevented by using alloys containing nickel. When using 300 or 400 series stainless steels, a brazing filler metal containing a small amount of nickel can eliminate interfacial corrosion completely and cost effectively. The nickel-iron surface created is more resistant to corrosion than an iron surface, even in the presence of moisture and chlorides. Protection can also be provided by the application of a coating which prevents the service environment from coming in contact with the brazing alloy.