A comparative study between PVD-TiMgN and PVD-TiMgGdN sputtered coatings to evaluate the influence of Gd and its effect on the corrosion properties of the individual coatings

Abstract

DC-PVD TiMgGdN coatings with excellent corrosion properties have been successfully developed using a powder metallurgy TiMgGd target while maintaining the well known tribological properties of TiN. In this study, TiMgGdN coatings were compared with TiMgN coatings using identical deposition parameters to investigate the influence of Gd on the corrosion behavior. For this purpose, a TiMg powder metallurgical target was used with an identical Ti/ Mg ratio as the TiMgGd target. The coatings were comprehensively analysed by different analytical methods such as X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), X-Ray Photonelectron Spectroscopy (XPS) and Glow Discharge Optical Emission Spectroscopy (GDOES) regarding their chemical, structural and microstructural characteristics. The corrosion properties were investigated using the neutral salt spray test (NSS test) in 5 % NaCl solution as well as with potentiodynamic tests in 0.5 % NaCl solution saturated with Mg(OH)2.Based on the findings of this study, it can be concluded that the excellent corrosion performance along with the mechanical properties are supported by the Gd addition to the coatings. The TiMgN coatings show a change in chemical composition, microstructure as well as in hardness after corrosive exposure, which cannot be observed on TiMgGdN coatings. Consequently, alloying TiMgN with Gd maintains the stability of the coating during corrosive exposure. The analytical results show that the excellent corrosion performance and stability of the TiMgGdN coatings are due to a stable and stronger passivation layer by the formation of Mg(OH)2 and Gd2O3 on the TiMgGdN surface. Furthermore, the Gd2O3 contributes to a strong hydrophobic effect. Regarding the microstructure, TiMgGdN coatings are seemingly denser compared to the TiMgN coatings, which positively influences the corrosion resistance of this coating.