Changes occurring in the friction and wear mechanisms
during a load-carrying capacity test, lubricated with cetane containing
a carboxylic acid, were investigated. The changes in
wear scar/track appearance and oxide coverage/composition
were analyzed during every load stage.
The main conclusions were as follows:
The breakdown in the protective oxide layer formed on the
opposing steel surfaces was found to be the prerequisite for
initiation of seizure.
The seizure load achieved during load-carrying capacity
testing quantifies the ability of the test fluid to prevent transition
to the adhesive wear regime.
The most severe surface damage was found to occur during
the first few seconds after test initiation. Desorption of
the adsorbed lubricant film and the subsequent removal of
the naturally occurring thin oxide layer results in the initial
period of adhesive wear.
Partial recovery to a state of acceptable friction occurs after
the period of initial seizure. During this period, the surface
coverage by the adsorption lubricant molecules and the oxide
coverage are sufficient to prevent severe adhesive wear
from occurring. Wear is primarily a combination of oxidative,
abrasive, and fatigue wear (all possible in the regions
of mixed friction and boundary lubrication).
Final lubricant breakdown and eventual seizure are initiated
when the oxide removal rate exceeds the oxide formation
rate resulting in severe adhesive wear followed by seizure.