Investigation On Corrosion Behaviours And Erosion-corrosion Behaviours Of Metal Silicide Film Formed On Stainless Steel

In this paper, based on double-cathode glow discharge technique, a series of nanocrystalline (MoxCr1-x)₅Si₃(x=1.00, 0.82,0.75,0.65,0.56) films and a (Cr, Fe)3Si/Cr₁₃Fe₅Si₂ composite film have been prepared on Cr-alloyed AISI 316L stainless steel and AISI 316L stainless steel, respectively. The microstructure and phrases components of the nanocrystalline (MoxCr1-x)₅Si₃ ( x=1.00, 0.82,0.75,0.65,0.56) films and the (Cr, Fe)3Si/Cr₁₃Fe₅Si₂ composite film were analyzed by means of scanning electron microscopy(SEM) equipped with an energy dispersive spectroscope(EDS), X-ray diffraction(XRD), transmission electron microscope(TEM): (1)The results indicate that the nanocrystalline (MoxCr1-x)₅Si₃(x=1.00, 0.82,0.75,0.65,0.56) films consist of single (MoxCr1-x)₅Si₃ phase with the average grain size about 40nm. The as-deposited nanocrystalline (MoxCr1-x)₅Si₃(x=1.00, 0.82,0.75,0.65,0.56) films formed on Cr alloyed 316L stainless steel are uniform, compact and tightly bonded with the Cr alloyed 316L stainless steel. (2) (Cr, Fe)3Si/Cr₁₃Fe₅Si₂ composite film mainly contains (Fe, Cr)3Si phase and Cr₁₃Fe₅Si₂ phase, the film is well connected with the substrate and contains two layer, the deposition layer about 12μm and the diffusion layer about 15μm.The corrosion resistance of the nanocrystalline (MoxCr1-x)₅Si₃(x=1.00, 0.82,0.75,0.65,0.56) films were analyzed by polarization curve, electrochemical impedance spectroscopy (EIS). The nanocrystalline (MoxCr1-x)₅Si₃ films have much better corrosion properties than 316L SS, which is characterized by their much higher breakdown potential (Eb) and much wider passive range. The passive current density (ip) of nanocrystalline (MoxCr1-x)₅Si₃ films decrease with increasing the Cr concentration and the Ecorr increases with increasing the concentration of Cr in (MoxCr1-x)₅Si₃ films. The values of Rct increase with increasing concentration of Cr suggests that the corrosion resistance increases with increasing the amount of Cr in the sputter-deposited nanocrystalline (MoxCr1-x)₅Si₃ films. The excellent corrosion resistance of high Cr content nanocrystalline (MoxCr1-x)₅Si₃ film is due to quickly formation of a compact and protective passive film composed mainly of chromium (III) oxide and silicon oxides, and simultaneously the high chemical stability and strong inter-atomic bonds inherent to (MoxCr1-x)₅Si₃ intermetallic phases.The electrochemical corrosion behaviors of the (Cr,Fe)3Si/Cr₁₃Fe₅Si₂ composite coating compared with single alloying layer and AISI 316L stainless steel under static state and hydrodynamic conditions were characterized by potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS). In static 3.5% NaCl solution, the corrosion resistance of the (Cr,Fe)3Si/Cr₁₃Fe₅Si₂ composite coating was comparable to that of single alloying layer, but higher than that of AISI 316L stainless steel. However, under liquid impingement and liquid–solid impingement conditions, corrosion behaviors of the (Cr,Fe)3Si/ Cr₁₃Fe₅Si₂ composite coating were prominently superior to that of the reference materials. After 20 hours liquid–solid impingement test, the mass loss measurements indicated that the (Cr,Fe)3Si/Cr₁₃Fe₅Si₂ composite coating exhibited the lowest coupling effects of erosion and corrosion.