International Journal of Engineering and Technology

The surface of the austenitic 316 stainless steel was modified by using two processes, i.e, dc glow discharge plasma and RF magnetron sputtering. The plasma nitriding was carried out at 500°C under 3 mbar pressure for 5 h in presence of 4N2:1H2 gas mixture. A thin layer of TiN was coated on plasma nitrided samples by using RF magnetron sputtering.The phase formation, nitride layer, surface nanohardness and corrosion current density were evaluated by X-ray diffractogram, optical microscope and SEM, nanoindenter and electrochemical analyser. The untreated sample showed only Fe diffraction pattern while after nitridingCrN phase with Fe and after coating only TiN phase diffraction pattern is observed. The nitride layerof about 8-10 µm is observed in nitrided sample and TiN layer of about 200 nm is measured in TiN coated plasma nitridedsample.The untreated 316 steel shows the surface nanohardness about 1. 59 to 1.88 GPa. The nitriding improved the surface hardness about five times (8.45GPa) and TiN coating further enhanced the surface hardness about seven times (13.16GPa) than untreated sample. The corrosion potential (ECorr) of the plasma nitrided and TiN coated plasma nitrided 316 samples showing positive shift with reference to the untreated sample. The corrosion potential(ECorr) value of untreated, plasma nitride and TiN coated plasma nitrided 316 samples are -0.593 V, -0.443 V and 0.074 V, respectively. The corrosion current density (ICorr) is considerably enhanced after nitriding and TiN coating, i.e., 4.46 µAcm-2 and 2.24 µAcm-2 respectively than 15.13 µAcm-2 for untreated sample. The passivation current densities of samples measured at 0.6 V vs SHEare about 69.18 µAcm-2, 18.62 µAcm-2 and 3.16µAcm-2, respectively.