News & Media

September 11, 2024 -                                                        One Minute Mentor

“The Bond Coat” and Why We Use It - By Ray Sinatra

A good thermal spray coating begins with proper surface preparation, and includes:

1)              Cleaning – by solvent or aqueous solution to remove grease and other organics

2)              Masking the adjacent coating areas.  Hard mask or tape

2)            Roughening - by grit blasting with aluminum oxide or other metallic grit.  Creating an “Anchor Profile”.

3)            Spraying - a bond coat of nickel aluminum like PMET 884 or PMET 885 or other bonding material

Grit blast preparation is still an important step for coating adhesion, but gaining good mechanical locking from the “keying” effect of grit blasting can be difficult with some substrate materials and geometries.  Also known as the Anchor Profile.

Bond coats were first developed in the 1960’s as a method of improving the adhesion of a thermal spray coating to a substrate. A bond coat provides added assurance that good coating adhesion occurs between the substrate and coating. A bond coat provides the ideal surface for a top coat to bond.

The classic Nickel Aluminum bond coat (PMET 884 or 885) is a formulated composite that undergoes an exothermic reaction during spraying and is self-bonding to many materials.

Typical bond coat thickness:       0.003 - 0.006 inch

• A bond coat thickness less than 0.003 inch may not provide complete coverage
• A bond coat thickness greater than 0.006” does not increase the bond strength but may be used as “filler” for thickness limited top coats.  And adds unnecessary cost.