Corrosion behavior of AISI 316L coated with Ti-TiN by vacuum arc deposition

L. VACA; M. FAZIO; A. MARQUEZ; S. BRÜHL

Congreso; SBPMat 2014; 2014

Sociedad Brasileira de Pesquisa de Materiales

Ti-TiN bilayer coatings on stainless steel have been proposed to improve not onlyhardness but also corrosion resistance. In this work the corrosion behavior ofnitride AISI 316L samples coated with Ti-TiN employing a vacuum arc ispresented, corrosion results obtained from only nitrided and non-treated samplesare compared.The samples were DC plasma nitrided at 430 °C with 24% nitrogen partialpressure and hydrogen. After that, they were coated by means of a DC cathodicarc running 125 A current discharge. The samples were placed 30 cm away fromthe cathode surface and one group of samples was grounded and another one wasconnected to 6kV negative bias voltage. TiN films were obtained employing acontinuous nitrogen flux of about 35 sccm and a working pressure in the range of1-3.10-2 Pa. The structural properties have been characterized by means of anoptical microscope, scanning electron microscopy (SEM) and X ray diffraction(XRD). The coatings adhesion was assessed by means of Scratch Test andRockwell C indentation. The corrosion behavior was evaluated etching thesamples with Marble reagent and by means of anodic polarization test in NaClsolution.The Ti and the TiN peaks can be distinguished in the XRD patterns of the coatedsamples, meanwhile, the XRD patterns of the nitrided samples showed theexpanded austenite phase, the SEM images showed the presence ofmacroparticles in the layer structure and the film thickness was about 1 μm. Allcoated samples resisted the Marble reagent attack and in the polarizationexperiment, the duplex coated samples presented the best behavior.