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International Journal of Corrosion
Volume 2011 (2011), Article ID 748168, 11 pages
http://dx.doi.org/10.1155/2011/748168
Research Article

Magnetron Sputtered NbN Films with Nb Interlayer on Mild Steel

1FRMS, MG, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India
2SES, MPD, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India
3Materials Group, Bhabha Atomic Research Centre, Trombay, Mumbai 400085, India

Received 16 March 2011; Revised 1 July 2011; Accepted 1 July 2011

Academic Editor: Ravin Kumar Dayal

Copyright © 2011 Kulwant Singh et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The aim of the study is to extend the NbN coating on MS with Nb interlayer to explore the benefits of hard nitride coatings on low-cost structural material and to compare the coating with NbN monolithic coating on SS. NbN on MS and SS was deposited by reactive d.c. magnetron sputtering at various N2/Ar flow ratios and substrate bias. Deposition rate decreased from 20 to 10 nm/min (without biasing) and from 16 to 8 nm/min (−50 V biasing) when 𝐹 N 2 / 𝐹 A r ratio was varied from zero to 70%. Deposition rate decreased with the increase in bias voltage. Coatings showed hexagonal β Nb2N, cubic δ NbN, and hexagonal δ′ NbN as major phases with the increasing N2 flow. Surface hardness reached a maximum of 2040 HK25 at a 𝐹 N 2 / 𝐹 A r of 20%. Critical loads, for cohesive and adhesive failure for coating on MS, were between 6–8 N and 9–12 N respectively; for coating on SS, the values were between 7–15 N and 12–25 N respectively. Duplex coatings were studied for hardness by Knoop microindentation, adhesion by scratch tester, and corrosion by potentiodynamic polarization technique. Hardness, adhesion, and corrosion resistance all improved when NbN coating was incorporated with Nb interlayer on MS.