First Results of Cavitation Erosion Behavior of Plasma Nitrided Niobium: Surface Modification

This work presents the first results of the plasma nitriding study performed in pure niobium in order to increase its cavitation erosion resistance. Samples were prepared from 98.9% purity and 90% reduction cold-rolled niobium bars. Annealing treatment of the cold-worked niobium samples was carried out in vacuum furnace at 1.33 Pa pressure, in the temperature of 1000 [degrees]C, for a time of 60 min. Annealed samples showing hardness of 80 HV were cut to dimensions of 20 x 30 x 4 mm super(3). Nitriding treatment was conducted at 1080 [degrees]C, gas mixture of 90% N sub(2)+ 10% H sub(2), flow rate of 5 x 10 super(-6) Nm super(3) s super(-1), and pressure of 1200 Pa (9 Torr), for a total time of 4 h comprised by two treatment steps of 2 h each. For comparison purpose, results for nitrided and non-nitrided niobium are confronted. Samples were characterized by XRD, nanoindentation, microhardness, SEM, and 2D surface topography and 3D interferometry profile analysis techniques. Cavitation testing was conducted according to ASTM G32-09. Comparatively, promising results based on the formation of niobium nitride phases in treated surfaces are presented and discussed in the present work.