Cavitation-resistant TiNi films deposited by using cathodic arc plasma ion plating

Abstract

TiNi intermetallic compound with superelasticity and corrosion resistance could have potential use in resisting sliding wear, rolling fatigue, corrosion, or erosion environments. TiNi is, however, expensive. A thin film coating of TiNi may enable low-cost materials such as plain steel to be used in the above applications. Thus, a study on the uses of TiNi coating is necessary. A cathodic arc plasma (CAP) ion plating process was used to deposit TiNi films onto plain steel using Ti 50Ni 50 target material. The substrate's bias voltage was changed to optimize the properties of the deposited film. Experimental results show that the deposited films have approximately the stoichiometry of Ti 40Ni 60. The nickel-rich composition may be caused by the ease of scattering of the titanium atoms or the thermalization of the background gas atoms during their flight to the substrate. Due to the higher migration ability of the surface adatoms, the films deposited at high substrate bias voltage possess a higher crystallinity. The major phase in such films is TiNi-B2. TiNi 3 and TiNi-B19′ coexist as the minor phases. Cavitation resistance of the specimen in freshwater was significantly increased to a 3-fold value in comparison with the uncoated plain steel. These promising results suggest that CAP ion plating is suitable for preparing cavitation-resistant TiNi films, if high substrate bias voltage is employed. The highly aggressive electrolyte develops a perfect Galvanic cell around the pits and the electrolyte accelerates the electrochemical dissolution of the anodically polarized substrate.