Nanoscratch measurements

Nanoindentation and nanoscratch measurements were taken to determine hardness and modulus distributions with respect to depth as well as the shear strength and friction coefficient of the tribofilms on a nanometer scale [1, 32]. Both measurements were combined with in situ AFM observations to find a flat film area less influenced by roughness and to confirm the indent or scratch made on the tribofilms from topographic images after the test. In these observations, the same diamond tip was used as the stylus for indentation or scratching as well as the AFM probe for obtaining in situ AFM images. 

Since the early 1980s, the study of mechanical properties of materials on the nanometre scale has received much attention, as these properties are size dependent. The nanoindentation and nanoscratch are the important techniques for probing mechanical properties of materials in small volumes. Indentation load-displacement data contain a wealth of information. From the load-displacement data, many mechanical properties such as hardness and elastic modulus can be determined. The nanoindenter has also been used to measure the fracture toughness and fatigue properties of ul-... 

To measure the hardness and elastic modulus of thin films while avoiding the influence of the substrate, peak indentation depth cannot exceed about 30% of the film thickness.Because commercial nanoindenters can make a minimum penetration depth of 10-15 nm, hardness and elastic modulus of films thinner than 30 nm cannot be measured. Clearly, new techniques for fabricating sharper indenters and new nanoindentation theories are needed to extend this technique. For film thicknesses less than 30 nm, nanoscratch tests are widely accepted to evaluate the mechanical properties (discussed later). Alternatively, assuming the hardness and elastic modulus of a film do not change with thickness, thicker films can be used. 

Therefore, innovative layers composed of siloxane/cerium and deposited by atmospheric pressure plasma have been tested. In this study, HMDSO was atomised and introduced as a precursor in an atmospheric pressure DBD plasma. The hybrid coating was obtained by mixing liquid precursor and nanoparticles (HMDSO and nanoAlCeOs) before atomisation. The properties of these different coatings were studied by scanning electron microscopy (SEM) and interferometry measurements. Their corrosion resistance has been determined electrochemically and their self-healing properties have been demonstrated by a combination of electrochemical impedance spectroscopy (EIS) and a nanoscratch method. 

Figure 12.9 presents impedance spectra obtained on chromated (a), ppHMDSO (b) and ppHMDSO containing 3% AlCe03 (c) samples, in which an artificial defect was made by the introduction of a nanoscratch after 1 day of immersion. The samples were first immersed in NaCl solution for 24 h. After this period, a defect was created on the surface and new EIS spectra were measured. According to the literature, two kinds of behaviour can be expected. In the first [28], a decrease in impedance values after the creation of the defect is observed, but after more than 24 h of immersion,... 

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