Corrosion of TiN, (TiAl)N and CrN hard coatings produced by magnetron sputtering

Abstract

Metallic components like moulds, dies and machinery can be subjected to intensive degradation during plastic transformation processes, namely when working with fibre filler materials and plastics which release F, S or Cl during transformation. The degradation is attributed to the combined erosive and abrasive wear by the filler material and corrosive attack of agents. This degradation reduces the lifetime of the components considerably and has a direct impact on process productivity and surface finish of the final products.Nitride based hard coatings like TiN, (TiAl)N, BN, etc. have proved their capability to increase tool lifetime when exposed to abrasive and corrosive environments found in plastic transformation processes (halogenated polymers, acrylics, polyesters, fibre reinforced plastics, etc.).Within the frame of this work we produced TiN, (TiAl)N, CrN hard coatings, with and without a metallic interlayer, by DC and RF reactive magnetron sputtering, with a thickness of about 2 µm. The aqueous corrosion behaviour of the coatings was studied in saline and acidic environments by potentiodynamic and open circuit potential (OCP) measurements. The oxidation resistance during annealing in air was also studied.In saline (NaCl 9%) and acid (HCl 3.4 %) environments we found that a metallic interlayer of Ti or Cr in the case of TiN / (TiAl)N coated samples and CrN coated samples, respectively, generally improve the corrosion resistance. Best results for all tested nitride coated samples were obtained for the Ti .27 Al .73 N coating. The OCP vs. Saturated Calomel Electrode (SCE) (60 min) measurements indicated that most samples were nobler than the un-coated substrate. The mentioned potentials depend on the deposition conditions and the film microstructure. Most of the coatings lose some of

Pitting corrosion of TiN-coated stainless steel in 3 % NaCl solution

“…11,[16][17][18][19][20][21] Based on Figure 12, it was concluded that the semiconductor layer formed on the TiN-coated substrate was n-type (presumably TiO 2 ), in agreement with the literature. 11,21 The Mott-Shottky equation on page 127 in 20 was used to determine the flat band potential and the density of the charge (density of donors for n-type semiconductor) in the space-charge region.…”

“…In the literature, the single phase of the TiN coating was generally obtained with various N 2 pressures, since TiN was stable across a wide stoichiometric range. [11][12][13][14][15][16][17][18][19] The grain morphology of the TiN coating was columnar (Figure 4). The columnar grain boundaries in the TiN coatings, aligned perpendicularly from the topmost surface down to the substrate/coating interface (Figure 4), were considered to be an easy path for the penetration of the electrolyte.…”

“…[9][10][11][12][13][14][15][16] Even though the widely accepted pitting corrosion mechanism of the TiN-coated substrate in the literature was local galvanic corrosion through the galvanic coupling of the TiN coating and the substrate, there remain questions about the mechanism of pitting formation and the growth of the pitting corrosion. One of the key parameters for galvanic corrosion is defects in the coatings, such as pin holes and micro and macro porosities in the coatings.…”

“…The defects in the coatings provide the electrolyte with a path to the coating/ substrate interface. [9][10][11][12][13][14][15][16] Martensitic stainless steels (EN 1.4034 was used in this work) that are generally used for the blades in kitchen appliances were coated for both decorative and wear-resistance requirements. The pitting corrosion of the TiN coating deposited by arc PVD on a stainlesssteel substrate was studied in detail with the corrosion potential (Cor.Pot), the polarization resistance (PR) and electrochemical impedance spectroscopy (EIS) techniques.…”

From Ti–Al- to Ti–Al–N-sputtered 2D materials

“…12. Dense columnar morphology is the most reported in the literature for Ti 1 -x Al x N coatings [32,33,38,39,41,49].…”