Friction and Wear Behavior of Multilayer [Al/AlN]_n Coatings Deposited on AISI52100 Steel

Abstract: In this study, a set of multilayer hard nanocrystalline coatings of Al/AlN with 35, 55 and 75 bilayer were prepared by DC magnetron sputtering on AISI 52100 steel specimens at nitrogen fractions of 35 and 65% in the Ar + N₂ discharge. X-ray diffraction analysis indicates a polycrystalline structure of AlN + Al and AlN phases for 35% N₂ and 65% N₂ fraction, respectively. Nanoindentation tests showed hardness values from 11 to 19 GPa and elastic modulus of ~200 GPa almost independent of the bilayer number for both, 35% N₂ and 65% N₂. Tribological tests evaluated with a CSM pin-on-disk tribometer showed a reduction in the wear rate compared to AISI 52100 steel specimens. Multilayer coatings deposited at 35% N₂ fraction presented a lower friction coefficient than those coatings deposited at 65% N₂. The origin of such a decrease in the coefficient of friction was associated with the presence of the Al phase in the coatings deposited at 35% N₂. The wear mechanism for both 35 and 65% N₂ were different. For the first case, the wear is controlled by plastic flow and abrasive wear, while in the second case, is dominated by adhesive wear.