Fragments of blast media driven into the substrate surface, most common on soft metals such as aluminum, titanium and annealed steels, and with high pressures or broken-down grit. In a metallographic mount they show as dark angular particles at the coating interface. Specs often limit embedded grit because it lowers bond strength and can start fatigue cracks, especially in rotating aerospace parts.
Mount shows embedded grit all along the bond line on the titanium, drop to 40 psi and use fresh media.
Also heard as
- grit entrapment
- grit inclusion
Related terms
Grit blasting
Blasting a surface with angular abrasive to clean it and roughen it so the coating can grip.
Bond line
The interface between a sprayed coating and the substrate, or between two coating layers.
Mount
A polished cross section of a coated coupon set in resin, used to check structure under the microscope.
Bond strength
How hard you must pull to tear a coating off its substrate, measured by gluing and tensile testing.