Surface properties of Ni/PTFE composite layers
Maria Trzaska, Beata Kucharska
Quarterly No. 4, 2009 pages 363-368
DOI:
keywords: nickel surface coatings, composite Ni/PTFE coatings, electrochemical method, surface roughness, roughness parameters, microhardness, static contact angle, scratch test
abstract The aim of the present research was to investigate the influence of process parameters on the structure and surface properties of nickel layers and composite layers Ni-PTFE deposited on the steel substrate (St3S) by the electrochemical reduction method. Electrochemical nickel coatings were also investigated to have a comparison with composite layers. The coatings were deposited from a small concentration of Watts bath modified by the organic additives- saccharine and sodium dodecyl sulfate. Polytetrafluoroethylen was used as a water disperse with nonionic surfactant of particle dimensions in the range of 0.1÷0.3 μm. The electrodeposition process was performed with constant current density (3 A/dm2) at different contents of PTFE disperse phase in the bath (5÷20 g/dm3). Structural analysis of produced layers was also performed. On that base the size of crystallites was calculated. The topography and morphology of produced layers are presented. Geometric profiles and rough-ness parameters were determined. That was observed that smoothing of the nanocrystaline nickel surface increases in comparison with surface of microcrystaline nickel layers. The microstructures of the coatings were examined by transmission electron microscope (TEM). The microhardness of the materials has been investigated by using the Vicker's method. It was observed that the hardness exhibit the layers deposited in the bath with saccharine and sodium dodecyl sulfate additives. Measurements of static contact angle (SCA) were applied in the investigations of surface properties of composite electrochemical Ni/PTFE coatings. The results of the investigations seem to be helpful in characterizing hydrophobic and antiadhesive properties of the produced coat-ings. Layers adhesion was evaluated by the scratch test. The morphologies of nickel and composite layers after scratch tests and diagram of acustic emision are presented. It was found that micro- and nanocrystaline nickel layers reveal perfect adhesion to the steel substrate. Increase of PTFE disperse phase in Watts bath causes deterioration of adhesive properties. Regarding the coating types it can be seen different locations of damages and loads being typical for such tests.