Fabrication,Corrosion And Wear Properties Of Fe-Based Amorphous Coatings

In this paper, based on the shortage of well-known SAM series alloys, we developed a series of novel Fe-based bulk amorphous alloys with low cost, high glass-formation ability and corrosion resistance, and then investigated its corrosion mechamism by X-ray photoelectron spectroscopy（XPS）. Besides, we prepared high quality Fe₆₃Cr₈Mo_3.5Ni₅P₁₀B₄C₄Si_2.5 amorphous coatings by AC-HVAF and HVOF.Finally, the microstructure, corrosion and wear resistance of the coatings were comparatively studied using X-ray diffractometer（XRD）, differential scanning calorimetry（DSC）, scanning electron microscope（SEM）, electrochemical workstation, friction and wear testing machine, Vickers hardness tester and Raman spectroscopy.To reduce the content of Cr and Mo in the well-known SAM series alloys, a series of Fe_71-xCr_xMo_3.5Ni₅P₁₀B₄C₄Si_2.5（x = 0, 4, 8, 10, 12, 14 at.%） amorphous alloys have been fabricated successfully. Thermal stability of this alloy system increases slightly with appropriate Cr content. The minor alloying of Cr by 4 at.%can significantly increase the corrosion resistance in 3.5 wt.% NaCl solution. Further Cr addition will increase the corrosion resistance slightly with the best response obtained for the x = 12 alloy, which could be attributed to the formation of thick oxide film. More addition of Cr slightly decreases the thermal stability and corrosion resistance due tothe precipitation of（Fe, Ni, Cr, Mo）3（B, P） metastable phase. These Fe-based amorphous alloys show comparable corrosion resistance with the well-known SAM series amorphous alloys despite the low Cr and Mo content, making them good candidates as corrosion resistant coating materials.The Fe₆₃Cr₈Mo_3.5Ni₅P₁₀B₄C₄Si_2.5 coatings with almost fully amorphous structure have been successfully prepared by AC-HVAF and HVOF techniques. The AC-HVAF coating shows more superior corrosion resistance to the HVOF coating in3.5 wt.% NaCl solution, as evidenced by lower corrosion current density and passivecurrent density. Passivation properties have been studied in detail with comparing these two amorphous coatings by a series of electrochemical measurements. On the one hand, the faster formation of a thicker passive film on the AC-HVAF coating can provide greater protection performance against corrosive ions, compared to the HVOF coating. On the other hand, the AC-HVAF coating with less defective passive film exhibits higher pitting resistance and passivity stability than the HVOF coating.Moreover, the passive film formed on the AC-HVAF coating can be easier repassivated than that on the HVOF one, indicative of stronger self-repairing ability of the former.The wear mechanism for the both AC-HVAF and HVOF amorphous coatings is dominated by oxidation wear. However, the AC-HVAF coating shows more superior wear resistance than the HVOF coating during dry sliding conditions. The denser and fully amorphous microstructure achieved by AC-HVAF is beneficial for the formation of a more stable oxidized tribolayer and smoother worn surface, leading to the enhancement of the hardness and wear resistance with the wear volume being approximately 7 times less than the HVOF coating. The present results demonstrate that the AC-HVAF technique with less using-cost exhibits the superiority in making Fe-based amorphous coatings for wear applications.