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A. Naveira-Suarez, A. Tomala, R. Pasaribu, R. Larsson, I. Gebeshuber:
"Evolution of ZDDP-Derived Reaction Layer Morphology With Rubbing Time";
Scanning, 32 (2010), 5; 294 - 303.

Functional additives, particularly
extreme pressure and antiwear additives, in formulated
oil will compete to adsorb and function in
tribological contacts. A low-polarity commercial
base oil, poly-a-olefin (PAO), blended with zinc
dialkyl dithiophosphates (ZDDP) has been studied.
The tribological performance was evaluated using
a ball-on-disk test rig under mixed rolling-sliding
conditions in the boundary lubrication regime at
901C. An adapted in situ interferometry technique
was used to monitor the additive-derived reaction
layer formation. The thickness of the reaction layer
evolves with rubbing until reaching a limiting
thickness value of approximately 70 nm. The evolution
of the topography and mechanical properties
of the ZDDP-derived reaction layer with
rubbing time were studied using Atomic Force
Microscopy. A constant roughening and hardening
of the additive-derived layer with rubbing time is
observed and related to the different tribological
performance of the layer at different rubbing
times.

additives, AFM, atomic force microscopy, boundary layers formation, boundary lubrication, morphology, nanowear, reaction layer, ZDDP