Tribological Behavior of Thermal Spray Coatings, Deposited by ...

A. Lanzutti at al., Tribology in Industry Vol. 35, No. 2 (2013) 113‐122a)b)micro‐particles leads to a microstructurecolumnar with a slight modification oforientation, caused probably by the deviation ofelectrical field in proximity of ceramic particlesthat are in non‐conductive material. On thecontrary, the addition of nanoparticles gives agrain refinement and a multi‐orientation ofcolumns. The SiC amount is higher in the microcompositecoatings compared to the nanocompositeone. The addition of particles leads toa noticeable microhardness increase due to boththe presence of the particles and the grainrefinement.All the analysed samples showed a surfaceRoughness Ra of about 0.5µm, obtained after thesurface’ grinding.b. Tribological characterizationAll the wear tracks obtained for both bare steel,thermal spray and composite electrodeposits atboth room temperature and 300 °C are shown inFigs. 4‐6.c)In Fig. 4 the top views of the wear tracksobtained for gr. 22 steel are shown, tested atboth room temperature and 300 °C.Room temperature 300°CFig. 3. SEM images and microstructuralcharacterization of electrodeposited coatings:a) pure Ni, b) Ni/µSiC and c) Ni/nSiC.The microstructure of the electrodeposits iscolumnar. In the case of the pure Ni the metalcolumns are oriented along the direction ofelectrical fields. The addition of SiC microparticlesleads to a slight modification of the Nicolumns orientation and size. On the other hand,the codeposition of SiC nano‐particles leads tothe formation of a fine grained deposit in whichthe Ni columns are not oriented. The addition ofFig. 4. SEM images of the wear tracks obtained for thebare steel at both RT and 300 °C.The steel is subjected to triboxidative wear atboth room temperature and 300 °C. At roomtemperature the oxide produced is adherent tometal substrate and very homogeneus. At 300 °Cthe oxide produced is concentrated on the weartrack’ sides. This phenomenon is related to theloss of mechanical properties of the substratesthat permits the countermaterial to destroy theoxide layer that is thus deposited on the sides ofthe wear track. At 300 °C are highlighted the117