TO 35-1-3 - Robins Air Force Base

TO 35-1-3
1.7.11 Fretting Corrosion. Fretting corrosion (see Figure
1-13) is a special form of concentration cell corrosion that
occurs in combination with surface wear. The corrosion products
increase the wear of the surface, and the wear exposes
additional bare metal surface to be corroded. The overall effect
is greater than the single effects of corrosion and wear added
together. It has the general appearance of galling, in which
chunks of metal are torn from the surface with corrosion at the
torn areas or ragged pits. This type of corrosion occurs on
faying surfaces of close tolerance and on parts under high
pressure in a corrosive environment when there is slight relative
movement of parts (such as that caused by vibration).
Fretting corrosion is normally encountered in heavily loaded
static joints that are subject to vibration and that are not sealed
to prevent moisture entry. Fretting corrosion is corrosion that
occurs between metals that are under load and subject to
vibration and/or slip. It appears as pits or grooves in the metal
surrounded by corrosion products. Fretting corrosion can be
very destructive in that it loosens mated parts and close tolerance
fittings that in turn lead to stress or fatigue failures. In the
case of iron alloys, brown to red iron oxide will be visible
from the area or interface experiencing fretting corrosion. On
aluminum alloys, a black corrosion product is evident. Fretting
corrosion is most commonly found in heavily loaded joints
that are subject to vibration such as press fitted ball bearing
races, bolted flanges, fayed surfaces, electrical connections,
and riveted areas.
Figure 1-12. Example of Filiform Corrosion
Figure 1-13. Illustration of a Fretting Corrosion Cell
1-12