Fig. 5 shows the results of the materials prepared by both process
paths, as well as a reference material without a plasma polymer film in
the cycling corrosion test according toVDA621-415. The combination of
a plasma polymer coating with the metallic overlay results in an
enhanced corrosion resistance.While, after 6 cycles, uncoated material
shows already N20–40% of red rust, both plasma polymer coated
materials still remain virtually free of red rust. First corrosion products
on the plasma polymer coated material are found after 10 cycles of VDA
621-415. Comparing the two process paths, the material produced by
process path B shows less red rust than the material produced by
process path A after the same number of test cycles. After 15 test cycles
the material produced by process path A formed N40–60% red rust,
while onthematerial processed by path B only N5–10% of the surface are
covered with red rust. After 20 cycles the samples of the first material
are completely covered with red rust,while the red rust on the samples
of second material remains at N40–60%. As it was discussed above, the
network structure and chemical composition of the plasma polymer
film becomes modified by the heat treatment. As a possible result of
these modifications pores or defects may be formed in the plasma
polymer thin film. These pores are possible pathways for the diffusion of
corrosive media to the interface between plasma polymer and metallic
coating. In thisway, the attack of themetallic part of the coating system
produced by process path A is stronger because of the less distinct
corrosion barrier properties of the heat-treated plasma polymer. In
comparison, the barrier properties of the plasma polymer structure
which did not undergo the heat treatment are improved.