Reactive magnetron sputter deposition of chromium nitride coatings

Chromium nitride coatings it,ere deposited by reactive D.C. magnetron sputtering on stainless steel substrates varying the substrate biasing voltage and nitrogen flow, rates and using chromium plated (>200 mum thick) stainless steel as the target (cathode). Coatings were characterised by X-ray diffraction analysis,for the phases present and surface hardness values were measured by Knoop indentor Electrochemical evaluation of the coatings was performed in deaerated I M H2SO4 solution at room temperature. CrN coatings had the typical hardness values ranging from 1300 1600 HK25. Increase in nitrogen flow, (to total gas) front 9.5 to 13% caused the corrosion resistance to increase rapidly (j(corr) reduced from 151.4 to 54 muA cm(-2)). Further increase in nitrogen flow ratio to 23% increased the corrosion resistance but very gradually. Increase in nitrogen flow, beyond 23% caused the corrosion resistance to decrease. Coatings with the minimum current in the passive region were found to be those deposited at a F-chi2/F-1 of 16.7%, the coating with the maximum hardness (1790 HK25) showed the presence of Cr2N as the major phase. Increase in substrate biasing (-50 to -250 V) resulted in an increase in corrosion resistance (j(corr). reduced from 159.6 to 18.4 muA cm(-2)).