Ni-P-TiO2-ZrO2 anti-corrosion coating on AISI 316 steel; Part Ι: effect of bath temperature

Austenitic stainless steels have been extensively used in various industrial areas such as chemical equipment, nuclear fusion equipment, and marine application, due to its excellent machinability, weld-ability, and non-magnetic property [1-3]. However, these kinds of alloys are very susceptible to pitting corrosion in chloride-containing environments. In particular, marine atmospheric environments have posed a great threat to the application of 316 SS due to the deposition of high chloride containing airborne sea salts on the metal surface [4]. In the present work electroplating method is used to preparation of Ni-P-TiO2-ZrO2 coating on AISI 316 stainless steel alloy in order to protection of substrate against corrosion in NaCl 3.5 %. For the direct current (DC) electrodeposition process, a one-compartment cell was used. Platinum foil was used as the anode and it was placed in the same compartment as the working electrode. Ammonia hydroxide or 20 vol% H2SO4 was used to adjust the electrolyte pH. Bath electroplating with composition of NiSO4 240 g/L + NiCl2 35g/L + H2NaO2P.H2O 25g/L + ZrO2 20 g/L + H3BO3 30 g/L + C7H5NO3S 1g/L at pH 4 and current density of 40 mA.cm-2 was used to electrodeposition of Ni-P-TiO2-ZrO2 coating. In order to investigate the corrosion behavior, an AutoLab Model 302N potentiostat was used for the corrosion studies. Measurements were carried out in a three electrode cell assembly containing a 3.5% Sodium chloride solution. A platinum foil and a saturated calomel electrode (SCE) were used as the counter and reference electrode, respectively. 14th Annual Electrochemistry Seminar of Iran Materials and Energy Research Center (MERC), 12- 13 Dec, 2018 240 The NOVA software was used to plot the polarization diagrams. In order to investigate the effect of TiO2 concentration on microstructure and corrosion behavior of coating, different amounts of TiO2 (10, 20 and 30 g/L) were inserted to the bath electrolyte. Figure 1 shows the polarization curves of coated 316 steel in NaCl 3.5 % in different amounts of TiO2. Table 1 shows the result of polarization. Data obtained from potentiodynamic polarization tests shows that the coated specimen at TiO2=30g/L had the highest polarization resistance (Rp= 12.3030MΩ) relative to other coatings.