Corrosion Resistant CrN_X Nanolayers Obtained by Low Temperature Ion Nitriding of Hard Chromium Coated AISI 1045 Steel

Chromium nitrides Cr_XN have attracted research interest due to their excellent wear and corrosion properties when are deposited on steels. Nevertheless, due to the considerable difference between Cr_XN and steel expansion coefficients, microcracks and delamination are still persistent problems. In this regard, this research addressed the generation of CrN_X nanolayers, through an ion nitriding process, carried out on hard chromium coated AISI 1045 steel. The effect of nitriding temperature (500°C-550°C) and nitrogen content in plasma (25, 50, and 75%) on corrosion performance and layer characteristics were studied. Grazing Incidence X-ray Diffraction analysis revealed that modified surfaces are composed of nanolayers, constituted by a mixture of CrN, Cr₂N, Cr, and Fe₄N. Rietveld quantification shows that the fraction of chromium nitrides in the region analyzed increased with increasing both temperature and nitrogen content in plasma, resulting CrN as the predominant phase for all evaluated conditions. The electrochemical behavior of the modified nanolayers was studied by potentiodynamic polarization technique, revealing an enhancement in corrosion performance of chromium coated 1045 steel by the nitriding treatment, showing a corrosion current density 10 times lower than the untreated sample and more positive corrosion potentials for the nitrided samples concerning chromium coated 1045 steel.

Keywords:
Ion nitriding; AISI 1045; Chromium nitrides; Hard chromium