Effect Of Silicon On Corrosion And Passivation Behavior Of Iron-Chromium Based Amorphous Alloys

In this paper,based on the present situation of lacking in self-developed highly corrosion-resistant Fe-based amorphous alloys with independent intellectual property rights in China,a series of Fe-Cr-based amorphous alloys with high glass-formation ability,high thermal stability and excellent corrosion resistance have been developed.The effect of a small amount of Si on the stability of passivation film of Fe-Cr-based amorphous alloy was discussed preliminarily.At the same time,by comparing and analyzing the corrosion resistance and passivation behavior of the independently developed Fe₆₃Cr₈Mo_3.5Ni₅P₁₀C₄B₄Si_2.5 amorphous alloy with the famous Fe₄₈Cr₁₅Mo₁₄C₁₅B₆Y₂?SAM1651?amorphous alloy,the mechanism of Si on improving the corrosion resistance of Fe-Cr-based amorphous alloys was analyzed from the viewpoint of composition,distribution and electronic structure of passivation films.Fe-Cr-based metallic glasses?MGs?have attracted increasing interest in the past decade due to their superior corrosion and wear resistance to the conventional stainless steels.In this paper,we developed the Fe₄₃Cr₁₅Mo₁₄Ni₃P₁₀C_10-xB₅Si_x alloy system by addition of a small amount of Si on the basis of Fe-Cr-Mo-C-B amorphous alloy system,the effect of Si content on thermal stability,electrochemical corrosion and passivation behavior of Fe-Cr-based amorphous alloy was also studied.The results show that the addition of a small amount of Si have a beneficial effect on improving the thermal stability,corrosion resistance and stability of the passive films.But more addition of Si does not observably enhance the corrosion resistance,but decreases the thermal stability of the MGs.Based on the results of potentiodynamic polarization curves,potentiostatic tests,electrochemical impedance spectroscopy,Mott-Schottky,and XPS,we found that the optimum content of Si in the Fe-Cr-based amorphous alloy system is 2-4 at.%.In order to further explore the effect of Si addition on the mechanism of corrosion resistance of Fe-Cr-based amorphous alloy,the corrosion resistance of Fe₆₃Cr₈Mo_3.5Ni₅P₁₀C₄B₄Si_2.5?Cr₈?alloy and SAM1651 alloy were compared.But due to the difference in the composition of the elements in two alloys,the changing mechanism of corrosion resistance can not be obtained by the point of component alone.In this paper,through the characterization and quantification of the degree of difficulty in valence electron/ion transport and transfer in passivation films,the mechanism of a small amount of Si significantly improving the corrosion resistance of Fe-Cr-based amorphous alloys was studied.The results show that although the content of Cr and Mo in Cr₈amorphous alloy is very low,its stability of passive film and pitting corrosion resistance are better than SAM1651 amorphous alloy with high content of Cr and Mo.By analyzing the composition distribution and content of the passive film,it is found that the Cr and Mo enrichment layer of SAM1651 is thicker,and the uniform protective film of SiO2 and P2O3 on the surface of Cr8amorphous alloy is found.In addition,the densities of the states at the Fermi energy level of Cr8amorphous alloy is lower indicating that the Cr8 alloy has less electrons in the high-energy state,and the work function is higher at high potential,indicating that the energy required for electrons to disengage from the original orbit is stronger.So the electrons/ions in the passivation film are more difficult to transport and transfer.As a result,the stability of passivation film of Cr₈ amorphous alloy is better and the resistance to pitting corrosion is stronger.