Proceedings of SerbiaTrib '13

coated and uncoated region after adhesive taperemoval.The ALD coating was deposited using a TFS500 reactor (Beneq Oy, Finland): Al 2 O 3 layers wereobtained using trimethylaluminium (Al(CH 3 ) 3 ) andH2O precursors and TiO 2 layers were obtainedusing titanium tetrachloride (TiCl 4 ) and H 2 Oprecursors. Both depositions were performed at atemperature of 120 °C. The low temperatureprocesses were chosen in order to obtain anamorphous structure for both layers. The number ofprecursor cycles for each deposition was calculatedusing a growth rate per cycle (GPC) of ~0.1nm/cycle for TiO 2 and a GPC of ~0.15 nm/cycle forAl 2 O 3 .The samples were coated using different ALDconfigurations, with an overall coating thickness ofabout 200 nm.2.2 MorphologyMorphological characterization was carried outusing Veeco’s Digital Instrument’s Nanoscope IIIaatomic force microscope (AFM) in tapping modeconfiguration, using a Bruker SCM-PIT tip(Antimony (n) doped Si, frequency: 60-100 kHz,elastic constant: 1-5 N/m, PtIr coated) and CarlZeiss EVO-40 scanning electron microscope (SEM)with an operating voltage of 20 kV. Analyses wereperformed on the stainless steel substrate and oncoated samples. In particular, SEM was used inorder to scan the surface of the sample andinvestigate the presence of deposition defectsand/or surface anomalies. AFM was mainly used toinvestigate the presence of surface morphologicaldefects on the coating that were supposed to behardly visible using SEM due to the coatingtransparency. AFM was also used at the interfaceregions between coated and uncoated substrate afteradhesive tape removal in order to obtaininformation about the overall thickness of thedeposits and confront it with the theoreticaldeposition rates values and the results obtainedfrom GDOES analyses.2.3 CompositionIn-depth compositional analyses were carriedout using Horiba Yobin-Yvon’s RF – GD ProfilerGDOES. Due to the difficulties in calibration ofGDOES for the analysis of Titanium andAluminum oxides, only qualitative compositionalanalyses were performed, even if a keen calibrationwas performed in order to obtain reliable singlelayer thickness values. GDOES technolnique isstrongly influenced by surface roughness, whichwas relatively high.2.4 Mechanical propertiesIn order to evaluate the resistance todelamination of the different ALD configurations,Vickers indentations were applied to the samplesunder different load conditions (HV0.1-0.2-0.5-1.0-2.0) and the delaminated areas have been thenmeasured using a specific image post-processingsoftware (Wayne Rasband, ImageJ 1.44p). As allindentation hardness tests, Vickers indentation aredependant from the mechanical characteristics ofthe substrate and can only be used to comparedifferent coatings applied on the same substrate andnot results from different substrates. As adhesion isstrictly connected to the surface roughness [33-35],Vickers adhesion tests will give reliable results onlyfor substrates with similar surface finishing.2.5 Electrochemical propertiesElectrochemical characterization of the differentsamples was performed using PotendiodynamicPolarizations. An AUTOLAB PGSTAT-20potentiostat was used in a standard three electrodesconfiguration. The reference electrode wasAg/AgCl and the counter electrode was a 99.99%pure Platinum wire. All measurements have beenperformed in a pH 6.5, 0.2 M solution of NaCl. Allpolarization curves were obtained using a scanspeed of 0.2 mV/s after 10 minutes of immersion ofthe samples, in order to stabilize the OCP. Thepotential has been increased from -200 mV respectto the OCP to a measured current density of about10-3 A/cm 2 .2.6 Wear propertiesWear properties were investigated using anindustrial CETR UMT tribometer in ball-on-discconfiguration, using a WC counter-material. Weartesting was performed for 1, 10 and 100 cyclesunder dry conditions, at a relatively low rotatingspeed (1 rps) and at different diameters (15 mm, 18mm, 21 mm). After testing, the wear tracks wereobserved using SEM and the volume losses werethen estimated using a stylus profilometer.3. EXPERIMENTAL RESULTS3.1 MorphologySEM resulted to be an inadequate technique forthe analysis of ALD layers, since no morphologicaldifferences were found between images obtained oncoated and uncoated regions and no morphologicalproperties of the ALD layers could be correctly13 th International Conference on Tribology – Serbiatrib’13 171