Study On Structure And Properties Of FeCrBCSi Amorphous Nanocrystalline Alloy Coating Prepared By Wire Arc Spraying Process

In this study the effect of boron addtion on the Fe-Cr-B-C-Si amorphous alloy's amorphous content and nanocrystalline grain size during arc spraying process was invistigated based on the design amorphous/nanocrystalline alloy system. The relationship between amorphous content, nanocrystalline grain size and microstructure of the coatings was established, the corrosion and abrasive wear behavior of the amorphous/nanocrystalline alloy coatings were studied in details. The major results are summarized as follows:Fe-based coatings with different amorphous content and nanocrystalline grain size were prepared by arc spraying technology by adjusting the boron content in certain exten. The coating consisted of numerous flattened lamellae parallel to the substrate. The porosity was measured by the image analysis software and the value was about 3%. It was found that the optimum boron content in the alloy for the most amorphous content and nanocrystallin grain size was 26at%. The highest amorphous content was about 36.4%; and the smallest nanocrystalline grain size was 12.4 nm. With this composition the alloy possessed high thermal stability as the crystallization temperature exceeded 760K.It was found that the coatings possessed higher value of microstruture in the range of 865¹166HV0.1. The coatings abrasive wear resistance was 6¹3 times higher than that of the Q235 mild steel. In addition, fatigue abrasion form was observed on the surfaces of the coatings during abrasion testing processes. The wear resistance and hardness improved with the higher amorphous content and lower nano-grain size. The coatings annealed at the temperature of 923K expressed the greated thermal stability with relativly higher mircohardness and wear resistance. The amorphous/nanocrystalline alloy coatings showed excellent corrosion resistance in 3.5% NaCl solution, which were much better than Q235 mild carbon steel. Testing results shows that main corrosion mechinanism of coatings were pitting corrosion and uniform corrosion. Fe₆₂Cr₁₅B₂₀(CSi)₃ and Fe₅₆Cr₁₅B₂₆(CSi)₃ coatings after high-temperature corrosion at 923K for 100h, both the oxidation kinetics and the molten salt thermal etching kinetics showed a parabolic relationship. The coatings possess of high oxidation and thermal etching resistance with a final weight gain of 6mg/cm² and 10mg/cm² for each condition. Most of the products after high temperature oxidation and thermal etching were Fe₂O₃ and FeCr₂O₄. The existence of the passive film consist of these oxides gave a protection to the inner coating.