Proceedings of SerbiaTrib '13

Fig. 9 shows the wear track obtained after 10cycles of ball-on-disc wear testing on the samplecoated with a single layer of Al 2 O 3 . It can beobserved that, even if the applied load is relativelylow, a wear track is clearly visible on the surface ofthe sample and, in particular, third body wear scarscan be observed. The pristine surface roughness ofthe sample has been completely removed from thesurface due to the tribological contact with the WCcounter-part.EDXS localized analysis shown that the ALDlayer has been completely removed from thesurface due to the tribological contact.It is possible that the clearly visible third bodywear on the surface of the sample has also beencaused by Al 2 O 3 particles detached from the samplesurface during testing.Increasing the number of cycles, it was possibleto observe the formation of a thick oxide layerinside the wear track, and strong adhesionphenomena, leading to a coarse wear track full ofirregular oxide depositions.applied to AISI 420 martensitic stainless steel usinga thermal ALD process based on H 2 O, TMA andTiCl 4 .The applied ALD layers and the substrate wheresuccessfully characterized using SEM, AFM,GDOES, stylus profilometer, electrochemicalequipment and an industrial tribometer in ball-ondiscconfiguration.The morphological characterization evidencedthat ALD layers are conformal and almost defectfreeeven at relatively high magnifications.GDOES testing correctly discriminated thepresence of the different ceramic layers on the AISI420 substrate.Adhesion testing showed that adhesion betweenAISI 420 and 200 nm ALD layers is relatively poorand cracks propagate from microhardness Vickersindentations.Electrochemical testing clearly showed that evenan ALD coating with a limited thickness of about200 nm is sufficient to strongly improve thecorrosion resistance of the martensitic stainlesssteel substrate, strongly reducing the corrosioncurrent densities and widening the passive range ofthis material.Wear testing results showed that ALD layersdeposited at the temperature of 120 °C onmartensitic stainless steel, are unable to granttribological resistance to the substrate, due to theirintrinsic brittleness and the relatively low hardnessof the substrate on which they were applied.REFERENCESFigure 10: wear track obtained after just 10 cycles forAl 2 O 3 /TiO 2 bi-layerFig. 10 shows the wear track obtained after 10cycles of ball-on-disc wear testing on the samplecoated with a bi-layer formed by Al 2 O 3 and TiO 2 .It can be observed that, as seen before for thesingle layer sample, the wear track is clearly visibleat 1000 magnifications. Scars of third body wearare present inside the wear track, even if the trackitself is smaller when compared to the trackobtained from the single layer sample.Even in this case, EDXS analyses shown that theALD layer has been completely removed from thewear track on the sample surface, due to thetribological contact with the WC counterpart.4. CONCLUSIONSNanometric ALD mono- and bi- layers, with atotal thickness of about 200 nm, were successfully[1] H. Zhang, Y.L. Zhao, Z.D. Jiang, Materials Letters59, 3370-3374; 2005.[2] P.J. Hidalgo, Surcae Technology 10, 193-208; 1980.[3] A. Turnbull, B. Nimmo, Environment-InducedCracking materials, 2008, 2, 483-492;[4] J.W. Boh, L.A. Louca, Y.S. Choo, Shreir’sCorrosion 3, 1802-1878, 2010.[5] D. Ferreno, J.A. Alvarez, E. Ruiz, D. Mendez, L.Rodriguez, D. Hernandez, Engineering FAilureAnalysis, 18, 256-270, 2011.[6] B. Fournier, M. Sauzay, C. Caes, M. Noblecourt, M.Mottot, A. Bougault, V. Rabeau, J. Man, O. Gillia,P. Lemoine, A. Pineau, International Journal ofFatigue 30 (10-11), pp. 1797-1812, 2008.[7] C. Liu, G. Lin, D. Yang, M. Qi, Surface and CoatingTechnology 200, pp. 4011-4016, 2006.[8] V.H.V. Sarmento, M.G. Schiavetto, P. Hammer,A.V. Benedetti, C.S. Fugivara, P.H. Suegama,[9] S.H. Pulcinelli, C.V. Santilli, Surface and CoatingsTechnology 204, pp. 2689-2701, 2010.[10] R. Di Maggio, L. Fedrizzi, S. Rossi, P. Scardi, ThinSolid Films 286, pp. 127-135, 1996.13 th International Conference on Tribology – Serbiatrib’13 175