The corrosion behaviour of macroparticle defects in arc bond-sputtered CrN/NbN superlattice coatings

• Published in: Surface & coatings technology Vol. 126; no. 2; pp. 279 - 287
• Main Authors: Wang, H.W, Stack, M.M, Lyon, S.B, Hovsepian, P, Münz, W.-D
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 24.04.2000; Elsevier
• Subjects: Applied sciences; Arc bond-sputtering; Condensed matter: structure, mechanical and thermal properties; Corrosion; Droplets; Exact sciences and technology; Macroparticles; Metals. Metallurgy; Other nonelectronic physical properties; Physical properties of thin films, nonelectronic; Physics; PVD coatings; Surfaces and interfaces; thin films and whiskers (structure and nonelectronic properties); Droplets; PVD coatings; Corrosion; Arc bond-sputtering; Macroparticles; Thin films; Corrosion resistance; Polarization; Chromium nitrides; Physical vapor deposition; SEM; Corrosion testing; Experimental study; Coatings; Niobium nitrides; Sputtering
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/S0257-8972(00)00554-5

The investigation concerned the corrosion behaviour of macroparticle and growth defects in PVD CrN/NbN superlattice coatings formed by arc bond-sputtering (ABS) process on a mild steel BS6323. The electrochemical behaviour of the coatings was firstly studied by potentiodynamic polarising in de-aerated 0.5 M (Na 2CO 3–NaHCO 3) buffer and 5% NaCl solutions, respectively. The coating and defects were then examined in planar view and cross-section by scanning electron microscopic analyses and the results were compared with those prior to the electrochemical measurement. It is found that the overall coating/substrate corrosion process is closely related to the deleterious effect of the macroparticles and growth defects in the PVD coatings. It is further demonstrated that for through thickness macroparticle inclusions, corrosion initiates by galvanic or crevice corrosion between the defect and the coating matrix, subsequently permitting solution access to those defects with eventual substrate pitting and corrosion at the coating/substrate interface. On the basis of the experimental findings and the macroparticle formation theory, the mechanisms of the growth defect-related coating/substrate corrosion are finally proposed.