Loading rate effect on lateral force measurements on nanostructured Ti and TiN thin films

Abstract

International audienceTribological properties of titanium and titanium nitride nanostructured thin films as well as of silicon substrate have been studied. We report onthe effect of lateral tip displacement direction and normal force loading mode on lateral force measurements. On hard coatings such as titaniumnitride thin films, we show that the tip's scratch direction has almost no effect on lateral force measurements. A completely different behaviour hasbeen observed on titanium films. In this last case, the measured lateral force is very dependent on the scratch direction.Concerning the effect of normal force loading mode, we will show how the loading rate, rather than the sliding speed, is a very importantparameter in the case of a ramping normal load. For this purpose we have performed two sets of six scratches, for each sample. Scratch length wasfixed to 10 μm in all cases.In the first set, the scratch length and duration were kept constant. In the second one, the scratch duration was tuned in order to achieve aconstant value of the normal loading rate dFzdt. In this last case, the experimental data leads to a unique curve. This means that during nanoscratchmeasurements, normal tip displacement is controlled by the normal force loading rate. Consequently, lateral displacement speed dxdtmust be tunedin order to obtain the required value of dFzdt. This behaviour seems to be universal and not related to material hardness and Young modulus.© 2005 Elsevier B.V. All rights reserved