Structural and tribological properties of Ti-TiN coatings obtained with a vacuum arc

Abstract

Abstract. In this work TiN and Ti-TiN bilayer coatings obtained with a vacuum arc on AISI 316 samples were proposed in order to improve hardness and tribological properties. The coatings were deposited with a DC cathodic arc running a 130 A current discharge between a Titanium cathode and the vacuum chamber employed as anode. The samples were placed 20 cm away from the cathode surface. TiN films were obtained employing a continuous nitrogen flux of ~ 20 sccm and a working pressure in the range of 3 10 -2 Pa. The structural and tribological properties were characterized by means of an optical microscope, scanning electron microscopy (SEM), x-ray diffraction (XRD), scratch test and fretting. The film thickness was about 0.5µm. Ti-TiN coatings presented better adhesion than TiN coatings and improved the fretting fatigue life compared to the untreated steel. IntroductionThe AISI 316L stainless steel is widely used in chemical, nuclear and food industry as well as in medical implants due to its excellent corrosion resistance and good biocompatibility. However, its low hardness, wear resistance and high friction coefficient limit the potential application of this material [1][2][3].A way of improving the corrosion resistance and the adhesive wear resistance or the friction coefficient could be to coat the surface with a ceramic film like TiN. These kinds of coatings are widely used for hardening cutting tools made of high speed steels [4][5][6]. In particular, cathodic arcs have proved to be very attractive to deposit TiN coatings because they promote the formation of dense nanostructured films with a good adhesion and a very high deposition rate. In cathodic arc devices, an electrical discharge of high current (~100 A) and low voltage (~20 V) runs between two electrodes in a vacuum chamber. From the surface of the metallic cathode, a beam of metallic ions is ejected with energies between 20 -100 eV; the ion current being approximately a 10% of the total discharge current. When a sample is exposed to the plasma, the surface is coated with a metallic film. If a reactive gas flows in the chamber, the substrate is covered with a metallic compound of the cathode material [7][8][9].

Influence of the Pre-Treatments and Process Temperature on the Adhesion of TiN Films Deposited by PBII&D Over Nitrided Austenitic Stainless Steel

“…There are also several studies about the benefits achieved with the deposition of thin Ti interlayer, as the inhibition of crack propagations and the reduction of surface residual stresses, among others, that improve the coating/substrate adhesion 11,22,23 . In a previous work, it was found that a Ti interlayer deposited onto the 316L improved the adhesion of PBII&D TiN coatings 24 .…”