MICROHARDNESS ANALYSIS OF THIN METALLIC MULTILAYER COMPOSITE FILMS ON COPPER SUBSTRATES
2011
Composite systems of alternately electrodeposited nanocrystalline Ni and Cu
films on cold-rolled polycrystalline copper substrates were fabricated.
Highly-densified parallel interfaces which can give rise to high strength of
composites are obtained by depositing layers at a very narrow spacing. The
hardness properties of the composite systems were characterized using Vickers
microhardness testing with loads ranging from 1.96 N down to 0.049 N. Above a
certain critical penetration depth, a measured hardness value is not the
hardness of the electrodeposited film, but the so-called „composite
hardness“, because the substrate also participates in the plastic
deformations during the indentation process. Dependence of microhardness on
layer thickness, Ni/Cu layer thickness ratio and total thickness of the film
was investigated. Model of Korsunsky was applied to the experimental data in
order to determine the composite film hardness. The microhardness increased
with decreasing the layer thickness down to 30 nm and it is consistent with
the Hall-Petch relation. Layer thickness and layer thickness ratio are the
important parameters which are responsible for making decision of the total
film thickness.
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