Access to Optimum Working Voltage of Plasma Electrolytic Nitridation of Tantalum Alloys

Abstract

Recently, efficient coatings with excellent adhesion to the substrate have been applied to metals through the plasma electrolytic nitriding (PEN) method, which is a cathodic atmospheric plasma process with a high deposition rate. The structure, microhardness, and corrosion resistance of coatings after cathodic PEN with different critical and plasma-formation voltages were investigated. The characterization of the layer phases and their microstructure were studied via optical microscopy, X-ray diffraction, and scanning electron microscopy. The corrosion resistances of the coated metal samples were also investigated. It was found that various voltages provided different phases of Ta4N, TaN0.43, TaN, Ta4N5, and a nitrogen solid solution in tantalum. The PEN process with critical and plasma-formation voltages of 185 and 220 V, respectively, had the best uniform coating, with sharp peaks of tantalum nitride high corrosion resistance and microhardness of about 1200 VHN, which was selected as the optimum sample for nitriding process.