Improvement in the Corrosion Resistance of Austenitic Stainless Steel 316L by Ion Implantation

Abstract

In the present work, austenitic stainless steel 316L (SS316L) samples were implanted with Ni and Ni-Cr. A nickel-rich layer about 100 nm in thickness and a Ni-Cr enriched layer about 60 nm thick are formed on the surface of SS316L. The effects of ion implantation on the corrosion performance of SS316L are investigated in a 0.5 M H2SO4 with 2 ppm HF solution at 80°C by open circuit potential (OCP), potentiodynamic and potentiostatic tests. The samples after the potentiostatic test are analyzed by XPS . The results indicate that the composition of the passive film change from a mixture of Fe oxides and Cr oxide to a Cr oxide dominated passive film after the potentiostatic test. The solutions after the potentiostatic test are analyzed by inductively coupled plasma atomic emission spectrometry (ICP-AES). The results reveal that Fe is selectively dissolved in all cases and a proper Ni and Ni-Cr implant fluence can greatly improve the corrosion resistance of SS316L in the simulated polymer electrolyte membrane fuel cells (PEMFCS) environment. They are in agreement with the electrochemical test results that the bare SS316L has the highest dissolution rate in both cathode and anode environments and the Ni and Ni-Cr implantation reduce markedly the dissolution rate. When nickel implanted with a dose of 3 h, the corrosion potential (Ecorr) moved from -0.293V vs SCE to -0.05 V vs SCE in the accelerate anode environment and the passivation current density in the cathode operation potential (0.6 V vs SCE) reduced to 7 μAcm. For Ni-Cr co-implanted with a dose of 2h, the corrosion potential (Ecorr) is shifted from -0.293 V vs SCE to -0.06-0.09 V vs SCE and more positive than the PEMFC anode operation potential, and the passivation current density diminishes to 6.7 μAcm after ion implantation (Fig. 3). It reveals that Ni and Ni-Cr implantation could greatly improve the corrosion resistance of SS316L in both anode and cathode environment. After the potentiostatic test the interfacial contact resistance (ICR) values are also measured. Ni and Ni-Cr are enriched in the passive film formed in the simulated PEMFC cathode environment after ion implantation thereby providing better conductivity than that formed in the anode one. It shows that the ICR values after ion implantation having a reduction of by more than 11 folds (Fig. 6). A significant improvement of ICR is achieved for the SS316L implanted with Ni and Ni-Cr as compared to the bare SS316L, which is attributed to the reduction in passive layer thickness caused by Ni and Ni-Cr implantation. The ICR values for implanted