Avaliação da resistência química e propriedades estruturais do sistema aço AISI M2 recoberto com TiN/MoS2

Abstract

The searching for new materials that may combine high resistance to mechanical stress, wear, corrosion, and oxidation proprieties, has been continuous pursued. Transition metals nitrides, such as TiN, are very important technological materials due to their excellent physical and chemical properties, such as high hardness and melt temperature, and also a good chemical stability. Therefore, TiN films have been applied as coatings in cutting and casting tools in order to improve mechanical devices lifetime and performance. Additionally, in order to achieve a new system presenting combined properties, solid lubricant MoS2 has been co-deposited with TiN. Even though it is known that the MoS2 incorporation reduces the friction coefficient of these systems, the MoS2 effect in the chemical resistance has not been completely elucidated yet. Hence, the main aim of this work was to evaluate the atmospheric corrosion and high temperature oxidation resistance of AISI M2 steel, as the substrate, coated with TiN and MoS2. For this purpose, four systems were obtained, using Magnetron Sputtering deposition technique: the uncoated M2 steel, and M2/TiN, M2/MoS2, and M2/TiN/MoS2 steel-coated systems. The results show that, when submitted to wet corrosion conditions, all the systems showed poor performance. This fact was associated with the films low adhesion and thickness. Steel M2 coated with TiN/MoS2 system presented best results in high temperature cyclical oxidation tests. This can be associated with the fact that MoS2 particles are inserted on TiN film columnar structure as clusters, which could retain the oxygen access to the substrate surface, delaying the oxidation effects.