The plasma transferred arc technique has been used for the production of high nitrogen surfaces on 2205 duplex stainless steel substrates. Nitrogen was introduced into the melt using Ar+5%N2 and Ar+10%N2 gas mixtures. The nitrided surfaces are austenitic–ferritic and have a thickness of 1140±35 and 1650±31 μm respectively. The change of the austenite crystal lattice, due to the absorption of nitrogen, was determined by X-ray diffraction. Pin on disc tests showed that the wear resistance was increased. The corrosion in 3·5%NaCl and 1 N H2SO4 aqueous solutions was also slightly improved. Significant improvement was, however, observed in the pitting corrosion resistance of the nitrided surfaces, with regard to the 2205 duplex stainless steel substrate.

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The present investigation focuses on the microstructure and the tribological properties of TiC/ steel composite coatings obtained on 2205 duplex stainless steel (DSS) substrate, by using the plasma transferred arc technique. Two different plasma and shielding gas mixtures have been used, namely (a) 100% Ar and (b) 95% Ar + 5%N 2 . The coatings obtained are defect-free and their thickness is 1.50 ± 0.05 mm. Both coatings consist of a dispersion of TiC x N y particles, with a volume fraction of about 18-22%, in an austenite-ferrite matrix. The austeniteto-ferrite volume fraction is 35/65% for the Ar coatings and it is found to increase to 40/60%, when nitrogen is used in the plasma and shielding gas. The hardness of the composite coatings is improved significantly (630-650HV on average) compared to the hardness of the substrate (250HV). The friction coefficient produced against an Al 2 O 3 counterbody has decreased considerably to 0.2-0.3 from 0.5 for the 2205/Al 2 O 3 pair and the wear rate was reduced at least by one order of magnitude with respect to the value of the 2205 DSS substrate.

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