Nano-scratching

A nano scratch tester (CSEM) was employed to carry out the scratch test. A Rockwell diamond tip with a radius of 2 fim was used to draw at a constant speed 3 mm/min across the coating/substrate system under progressive loading of 130 mN maximum at a fixed rate 130 mN/min. The total length of the scratch scar is 3 mm. The critical load (L ) here is defined as the smallest load at which a recognizable failure occurs. The failure can be observed both by the built-in sensors and by the optical microscope. 

The same nano scratch tester was used to carry out the friction tests. The Rockwell diamond tip (radius 2 /u.m) was used to draw at a constant speed 3 mm/min across the sample surface under a constant load of 20 mN for which no scratches occurred for all the samples. Feedback circuitry in the tester ensures the applied load is kept constant over the sample surface. The sliding distance is 3 mm. The friction coefficient is defined normally as the ratio of the friction force and the applied load. 

With this background several measuring methods are currently being discussed in the automotive and paint industry with the objective to obtain a clear characterization of the scratch resistance of clearcoats. Especially procedures that create a single scratch have recently been developed (micro or nano scratch method) [1-8], These methods are different from more practically oriented procedures that are based on relatively simple methods to fly to test or even come close to reality (e.g. car wash brush method). 

A commercial instrument by the Swiss company CSEM (now CSM) was tested in the course of a project at the Research Institute for Pigments and Paints (Forschungs-institut fur Pigmente und Lacke e.V. (FPL)). This instrument is based on the method developed at the DuPont Marshall Lab. Objective of the project - where manufacturers of paints, raw materials and automobiles worked together - was the evaluation of the CSEM nano-scratch-tester regarding reproducibility, accuracy and applicability under the aspect of a realistic determination of scratch resistance. 

Atomic force microscopy has been combined with nano-indentation and nano-scratching studies [95]. The hardness (and, to a similar extent, the friction coefficient) of passivated titanium was three to four times higher under in situ conditions, this was assigned to a much faster repassivation process in the presence of the passivating electrolyte solution. Nanotribology, particularly surface friction forces mea-... 

Fig. 4 AFM image of the alignment of perpendicular lamellae of a thin PS-6-PChEMA film along a a grating and b near a locally functionalized nano-scratch (see text, 0.35 x 0.35 xm )...

EDX Energy-dispersive X-ray spectroscopy TEM Transmission Electron Microsoopry XRD X-ray Diffraction Nl Nanoindentations NIT Nano-Impact Test IT Impact Test ITMFS Impact Test with Modulated Force Signal BC Ball Cratering Test WLS White light scanning 3D measurements NT Inclined Impact Test S Scratch test NS Nano-scratch test RC Rockwell C OIF DiFfusion test OX Oxidation test TRM TRiboMeter... 

Hodzica A, Kimb J K and Stachurski Z H (2001) Nano-indentation and nano-scratch of polymer/glass interfaces. II. Model of interphases in water aged composite materials. Polymer 42 5701-5710. 

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