Effect of Sealing Treatment of Modified Aluminum Phosphate Sealing Agent on Corrosion Resistance of Fe-Based Amorphous Coating

A modified aluminum phosphate sealing agent was prepared by using aluminum dihydrogen phosphate and silica sol as raw materials, and was used for sealing treatment of iron-based amorphous coating. The phase of sealing agent was analyzed by XRD. SEM and TG-DSC were used to characterize the surface morphology of the coating before and after sealing and the heat resistance of the sealing agent. The corrosion resistance of the sealing coating was evaluated by electrochemical measurements. The results show that the modified aluminum phosphate sealing agent has good heat resistance, and fine and close sealing layer was obtained, thus the corrosion resistance is significantly improved.

The Corrosion Resistance and Mechanism of AT13/Fe-Based Amorphous Composite Coatings

Due to high strength, high wear resistance and high corrosion resistance, the amorphous metallic glasses were investigated widely. In the present study, the corrosion resistance of amorphous coating and composite coatings with various proportions of AT13 (Al2O3–13 wt.% TiO2) ceramic as additions in 3.5 wt.% NaCl solution were studied. The corrosion resistance was improved obviously as the addition of AT13, and when the content of AT13 was 15 wt.%, the composite coating had the lowest corrosion current density (1.75 × 10−6 A cm−2) and the highest corrosion potential (−411 mV), which was 5.14 × 10−5 A cm−2 and −580 mV for Fe-based metallic glassy coating, respectively. The corrosion mechanism was proposed according to the long-time immersion corrosion test.

Numerical Analysis of High-Velocity Oxygen Fuel Thermal-Spray Process for Fe-Based Amorphous Coatings

High-velocity oxygen fuel (HVOF)-sprayed amorphous alloy coatings usually have advantages of a dense structure that improve their resistance to corrosion, wear, and fatigue in the substrate. The flame flow characteristics and particle behaviors during the spray process have a significant influence on the amorphous coating structure and properties. In this study, a computational fluid dynamics model is enforced to analyze the flame flow and Fe-based amorphous alloy particle behavior in an HVOF spray process. The flame flow temperature, velocity characteristics, and the Fe48Cr15Mo14C15B6Y2 Fe-based amorphous alloy particles’ velocities, temperatures, flight trajectories, and mass concentration distribution characteristics are simulated. Moreover, the effects of the oxygen/fuel ratio, particle morphology parameter, particle-injection rate, and angle on the particle behavior are also investigated. Judging from the simulation results, the optimum amorphous alloy particle size varies between 20 and 30 μm, the shape factor is within the range of 0.9–1, the optimum O/F ratio is 3.4, the optimum injection angle is 45°, and the optimum injection rate is 10 m/s. With these conditions, most of the particles settled toward the centerline of the spray gun and are in a semisolid or solid state before affecting the substrate, giving the materials optimal coating structure and performance.

Experimental Investigation and Numerical Simulation for Corrosion Rate of Amorphous/Nano-Crystalline Coating Influenced by Temperatures

A high-velocity oxygen fuel (HVOF) system was employed to prepare a Fe49.7Cr18Mn1.9Mo7.4W1.6B15.2C3.8Si2.4 amorphous coating on mild steel. The electrochemical behavior of the resultant coatings, namely as-sprayed coating and vacuum heat-treated coating (at 650 °C and 800 °C), were investigated in a 3.5% NaCl solution at variable temperatures using scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, optical microscopy (OM), and XRD diffraction. Moreover, COMSOL Multiphysics version 5.5 software were employed for predicting the galvanic corrosion of amorphous material immersed in an aqueous NaCl solution, using the software finite element kit. The experiments demonstrated that the coatings’ pitting resistance was significantly affected by temperature. The results also showed that temperature affected the pitting corrosion rate and changed the shape of the pits. However, the changes were not as extreme as those observed in stainless steel. Furthermore, there was no significant difference between the as-sprayed coating and the vacuum-heat-treated coating at 650 °C. At low NaCl concentrations at and temperatures below the critical pitting temperature, the resulting pits were significantly small with a hemisphere-like. By contrast, at a higher NaCl concentration at 70 °C, particularly in the case of heating at 650 °C, the pits appearing on the Fe-based amorphous coating were vast and sometimes featured a lacy cover.