Sputtered NbN Films on MS with Cr and EN Interlayer

Objective of the present study was to explore the benefits of NbN coating on MS with Cr and EN interlayer. NbN films were deposited by reactive DC magnetron sputtering on MS, SS and MS with Cr and EN interlayer in 2, 4 and 10 µm thicknesses. N2/Ar flow ratio was varied 0-70%. Substrate biasing was varied from 0 to -150V. Effect of N2 flow and substrate biasing was studied on the deposition rate, crystal structure, hardness and adhesion. Cr was deposited by electroplating and EN was deposited by electroless plating. The duplex coatings were studied for the improvement with respect to surface hardness by Knoop micro indentation and corrosion performance by potentiodynamic polarization technique 1N H2SO4 solution at room temperature. Surface hardness increased from 1084HK25 (for NbN coating on MS) to 1672, 1985 and 2167HK25 respectively when Cr was incorporated as interlayer in 2, 4 and 10 µm thicknesses. EN increased the hardness to a lesser extent to 1436, 1564 and 1612HK25 respectively with 2, 4 and 10µm interlayer thickness. Cr was more effective in providing the load support. For corrosion protection, NbN coating alone could not protect the MS substrate effectively. However, when incorporated with either Cr or EN interlayer, there was an enormous increase in corrosion resistance. Icorr decreased from 150.2µA/cm2 (for NbN coating on MS) to 25.4, 12.3 and 2.5µA/cm2 with 2, 4 and 10µm thick Cr interlayer respectively. EN as interlayer was more effective and decreased the Icorr to 2.3, 0.37 and 0.35µA/cm2 with 2, 4 and 10 µm thick interlayer respectively.