Corrosion protection of steel substrates by magnetron sputtered TiMgN hard coatings: Structure, mechanical properties and growth defect related salt spray test results

• Published in: Surface & coatings technology Vol. 349; pp. 82 - 92
• Main Authors: Balzer, Martin, Fenker, Martin, Kappl, Herbert, Müller, Th, Heyn, Andreas, Heiss, Alexander, Richter, Andreas
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 15.09.2018; Elsevier BV
• Subjects: Aluminum oxide; Coating effects; Corrosion; Corrosion effects; Corrosion prevention; Corrosion resistance; Defects; Growth defects; Magnesium; Magnetic properties; Magnetron sputtering; Mechanical properties; Morphology; Physical vapor deposition; Physical vapour deposition (PVD); Pinholes; Protective coatings; Salt spray tests; Statistical analysis; Statistical methods; Studies; Substrates; TiMgN; Titanium; Titanium alloys; Tribology; Wear resistance; Pinholes; Growth defects; Magnesium; Corrosion; Physical vapour deposition (PVD); TiMgN
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2018.05.037

Hard and wear resistant coatings deposited by PVD techniques have been characterized for decades for their capabilities to protect steel substrates from corrosion. In the present work the effect of Mg incorporated into TiN coatings is described in terms of the corrosion behavior as well as the mechanical and structural properties. TiN and TiMgN films with Mg contents between 10 and 35 at.% were deposited onto mirror polished 100Cr6 (1.3505) steel samples with 2.5 and 5 μm thickness by using DC magnetron sputtering. The corrosion protection capabilities of the coatings were characterized by neutral salt spray (NSS) test, considering the amounts and sizes of growth defects inherent in each coated sample as determined by a recently developed optical scan method (Large Area High Resolution mapping). The defect data were statistically analyzed for improved interpretation of NSS test results. Chosen growth defects were additionally analyzed by focused ion beam technique. Furthermore the coating composition and morphology, the hardness and the tribological behavior were characterized. Polished steel samples coated with 2.5 μm TiMgN containing about 35 at.% Mg were in the plane free of corrosion after 24 h in a NSS test. TiMgN with 10 or 20 at.% Mg only provided a slightly improved corrosion protection in relation to pure TiN coatings, which was limited to certain types of growth defects. The highest Mg containing coatings exhibited a decreased hardness down to 1200 or 1800 HV depending on type of deposition (HV 1200: Ti- and Mg-target with rotating substrate holder, 1800: Mg-plugged Ti-target with static substrate holder), but also showed a strongly improved wear resistance against Al2O3 related to pure TiN. By analyzing the NSS test results it was found that the corrosion behavior of the coated samples did not only depend strongly on the Mg content, but also on the sample individual defect concentrations. Therefore this subject is extensively discussed. [Display omitted] •Corrosion protection of steel is improved by increasing Mg content in TiMgN.•Good corrosion protection (salt spray test 24 h) for 2.5 μm TiMgN with 32 at.% Mg.•Even TiMgN with 10 at.% Mg shows active corrosion protection at certain defects.•Sample individual defect concentrations strongly affect the corrosion test results.•New general knowledge about corrosion tests of PVD coated samples deduced.