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Ti/TiN multilayer coatings with multilayer periods in the range 550 nm and a final thickness of 2 µm were deposited on steel substrates by cyclic modulation of nitrogen gas flow into the chamber of a PVD sputtering device. Coating characterization was performed by cross-sectional transmission electron microscopy, glancing-angle X-ray diffraction and instrumental indentation testing. Individual a-titanium and titanium nitride layers were always observed, although for the finer microstructures, the TiN layers were thicker than the Ti layers by a factor three. The plastic hardness of the films increased steadily with decreasing layer spacing, following a HallPetch relationship. Finally, a hardness value of 42 GPa was reached, which is similar to that of a thick TiN monolayer, prepared under the same coating conditions.
Silica coatings filled with nanoscaled inorganic fullerene-like tungsten disulphide (IF-WS2) have been prepared through a solgel process on stainless steel substrates, and the structure and mechanical properties have been investigated. The precursor was prepared from a mixture of colloidal silica, 3-glycidoxypropyltrimethoxysilane (GLYMO), water and ethanol, adjusted to pH 4 with HNO3. In this solution WS2 is dispersed and in some cases immediately before coating ethylenediamine (ED) is added. The stainless steel substrates are dip-coated, dried in air and heat-treated in the temperature range of either 150360 °C in air or up to 900 °C in vacuum. The solidification process is followed by differential thermal analysis (DTA). The resulting brown coloured coatings have a thickness of 1.54 µm. Scanning electron microscopy investigations (SEM) show that the WS2 nanoparticles are embedded as small aggregates in a hybrid silica matrix. X-ray diffraction (XRD) measurements prove that most of the tungsten disulphide embedded in the matrix can be protected against oxidation even after curing the samples at temperatures up to 900 °C. Hardness and modulus of the hybrid silica films were measured through an instrumented indentation test. Increasing the temperature of the heat treatment yields an increase of hardness from 0.3 to 1 GPa and of modulus from 3 to 17 GPa. The amount of up to 10 wt.% WS2 in the coatings has no remarkable influence on hardness and modulus of the samples.
Force-deformation curves have been acquired using nanoindentation and atomic force microscopy on two amorphous polymer samples. The shape and size of the indenter tip was characterized using a white light interferometer and AFM. The measured nanoindentation curves were fitted with the Hertz equation to calculate the Young's modulus of the polymers. Once the Young's moduli of the polymers were known, AFM was used to acquire force-distance-curves on the same samples. We also used the Hertz theory for the analysis in this case. As a result, the tip radius of the AFM cantilever tip could be measured.
This procedure is proposed as a method to determine the shape and size of AFM tips for the quantitative characterization of surface forces through force-distance curves.
Thin polybutadiene/polystyrene blend films were deposited on glass substrates by spin-coating. The two polymers were chosen, as they are immiscible and differ strongly in their mechanical properties. The blend was characterized with Tapping Mode and force–distance curves. Several advantages of force–distance curves measurements compared to Tapping Mode are shown, most of all the capability of yielding quantitative information about several properties, such as Young's modulus and adhesion. Also the aging behaviour of the blend exposed to air could be observed, in particular the increase of the Young's modulus due to cross-linking and dewetting processes. Additionally, the sample was used to improve the resolution of force–distance curves up to 6 nm, which is to date the best resolution achieved with force–distance curves. Such an improvement resolves the major disadvantage of force–distance curves, compared to other scanning mode, i.e. its inferior resolution.