The influence of nitriding process on the corrosion resistance of the nickel alloy IN 718 produced by the Selective Laser Melting (SLM) method was studied in 3.5% NaCl of low pH. The nitriding process was carried out by the Plasma Assisted Chemical Vapor Deposition method (PACVD) in the nitrogen-hydrogen atmosphere (N2:H2=1:3). The observations of the microstructure of IN 718 nickel alloy were carried out using the light microscope and the scanning electron microscope. The corrosion resistance tests were carried out using an AutoLab PGSTAT302N potentiostat/galvanostat. A three-electrode set-up was used where the reference electrode was a silver chlorine electrode (Ag/AgCl/Cl−), the auxiliary electrode was a platinum plate and the working electrode was tested sample. The tests were carried out in a 3.5% sodium chloride (NaCl) solution with a reduced pH to 2.5 at the room temperature . The microhardness was measured by the Vickers method under a load of 200g. The nitriding process carried out by the PACVD method results in a formation of a layer containing the CrN phase. The surface of the nitrided layer is not homogenous, some particles that adhere well to the surface of the layer are observed. The nitrided layer is characterized by the high hardness of 800HV0.2 while the IN 718 nickel superalloy without the nitriding treatment has hardness of 370HV0.2. In Figure 1, the potentiodynamic curves recorded for the samples tested in a 3.5% solution of NaCl of pH 2.5 at the room temperature are shown. The printed IN 718 nickel alloy undergoes passivation as a wide passive domain up to the potential of 0.9 VAg|AgCl can be distinguished. The nitriding process actives the surface as in the test solution an active corrosion process manifested trough an abrupt increase of the current density in the anodic branch is observed. Then, the nitriding deteriorates the corrosion resistance of IN 718 nickel alloy in 3.5 % NaCl solution of low pH.
Fig. 1. Potentiodynamic curves of printed IN 718 nickel alloy before (dark blue curve) and after (light blue curve) nitriding recorded in 3.5 % NaCl of pH 2.5.
Souhaitez-vous présenter une affiche ?Corrosion resistance, CrN, Nickel alloy IN 718, Selective Laser Melting, PACVD
