| Iron-based amorphous coatings have attracted keen interest due to their high hardness, promising wear- and corrosion-resistance. However, the relatively poor bonding strength and toughness have largely restricted their industrial applications. To conquer this problem, the amorphous composite coating with reinforcements have been payed increasingly attentions in recent years. However, how the addtion of second phases would affect the corrosion behavior and mechanism of Fe-based amorphous coating remained unclear. In this thesis, effects of 316 L stainless steel reinforcement and sealing treatments on the corrosion behavior of Fe Cr Mo CBY amorphous coatings were systematically investigated. The microstructures of the coatings were characterized through X-Ray diffraction(XRD), scanning electron microscope(SEM) and transmission electron microscopy(TEM), while the electrochemical behavior were systematically studied through potentiodynamic, electrochemical noise, in-situ observation and scanning Kelvin probe(SKP) tests.Early research had shown that 316 L stainless steel as a second phase could improve the bonding strength and toughness of amorphous coatings effectively. In this thesis, the influence of 316 L stainless steel second phase on the corrosion behaviors and pitting mechanism of Fe-based amorphous coatings in simulated seawater environment was investigated. It was found that 8 vol% stainless steel reinforcement phase in the amorphous coating increased the corrosion weight loss for 3 times, indicating deterioration in corrosion resistance. Potentiodynamic and electrochemical noise tests revealed an obvious decrease in passivation property and a higher pitting initiation rate of composite coatings. Through in-situ observation of corrosion morphology, the pitting was found to initiate preferentially at the boundary between stainless steel phase and amorphous matrix. However, it was proved that no strong galvanic corrosion effect existed between these two phases by open circle potential and scanning Kelvin probe tests. Further study by high-resolution transmission electron microscopy confirmed the existence of nano-scale Fe3O4 crystal, and that the corrosion behavior was induced by this oxide formed at the boundary of stainless steel particles during the spray process. The present work suggests that the oxidation resistance of reinforce phase plays an important role in affecting the corrosion property of amorphous coatings, bringing some new recommendations to the design of new amorphous composite coatings in the future.On the other hand, the effect of sealing treatments on the corrosion behavior and mechanical properties of Fe-based amorphous coating was also studied. Two kinds of sealants, aluminium phosphate and polysiloxane were chosen. It was revealed that the porosity was 0.44% for the coating sealed by aluminium phosphate, and 1.46% by the polysiloxane, indicating a better porosity sealing effect of aluminium phosphate. Results of potentiodynamic and impedance spectroscopy tests confirmed a better corrosion property for the coating sealed by aluminium phosphate than the original coating and coating sealed by polysiloxane. Long-term immersion test in the simulated seawater confirmed that the corrosion resistance of the coating sealed by aluminium phosphate was better than the original one. Furthermore, it was found that these two sealants had little effects on the hardness of amorphous coatings(remain 730 Hv and over for treated coating), but did change the wear property greatly. For example, coefficients of friction rose from 0.2 to 0.8. This was resulted from the preferential abrasion of sealants during the wear test which hindered the process of friction. Above research results confirm that amorphous coatings after porosity sealing have out-standing long-term corrosion resistance and high coefficients of friction, showing a promising application as nonskid coatings for ships. |
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