Corrosion resistance of aluminum alloys with a titanium nitride coating

Abstract

The ion-plasma method of depositing refractory coatings makes it possible to treat parts at temperatures of about 200~ Since these temperatures correspond to aging regimes of heat-treatable high-strength aluminum alloys, it becomes possible to combine the process of deposition of a wear-resistant coating with toughening treatment of them that consists of quenching and aging. The present paper concerns results of a study of the tribotechnical properties and corrosion resistance of titanium nitride coatings deposited by the ion-plasma method on alloys DI6, PV90, and 1420.The high hardness and melting temperature of carbides and nitrides of transition metals are determined by the presence of a complex combination of covalent and metallic bonds in them. In addition to these two types of bonds carbides and nitrides have to a slight degree an ionic bond. For the metal-nonmetal bonds, octahedral surrounding of C or N atoms by the metal atoms is preferable.To deposit a wear-and corrosion-resistant coating it is expedient to choose carbides and nitrides of transition metals of group IV. Additional stresses in the transition zone can be prevented by providing a minimum difference in the atomic radii of the treated material and the material of the cathode. This makes titanium carbide (TIC) and titanium nitride (TIN) the most suitable wear-resistant coatings for aluminum alloys.Like other carbides of transition metals, titanium carbide possesses low chemical activity and is quite resistant to oxidation. This carbide has a high hardness and, unfortunately, a high brittleness, which diminishes its applicability as a wearresistant coating for plastic aluminum alloys.Titanium nitride is characterized predominantly by metallic properties, namely, a high electrical conductivity, hardness, and melting temperature. Although very hard, titanium nitride possesses a higher plasticity than titanium carbide. It should also be noted that the lattices of aluminum and titanium nitrides have a size and structural correspondence.Its set of physicochemical properties makes titanium nitride the most expedient wear-and corrosion-resistant coating for aluminum-base alloys.We studied aluminum alloys D16, PV90, and 1420 (Table 1) with coatings of titanium nitride.The coatings were deposited in a modernized installation of the Plazmennyi Kotel type that made it possible to separate plasma flows and obtain coatings free of the microdrop phase [1,2].The wear resistances of aluminum alloys coatinged with titanium nitride were compared by a special method used for determining the tribotechnical properties of thin-film coatings.The tests were conducted under conditions of dry endface friction on a laboratory machine under an axial load of 3 N/mm 2 that was created by a pneumosystem and controlled by a manometer. The counterbody was fabricated from a fluoroplastic reinforced by glass fiber of grade F4S 15. The friction area with a coefficient of overlapping Kov = 0.17 was 0.5 cm 2. The constancy of the rotation frequency of the specimen (v = 0.31 m/sec) w...