| Great attention has been attracted to amorphous materials for its superior properties. Although the bulk amorphous can be made at present, its extensive application is limited by the high cost and hard preparation condition of these materials. With rapid cooling rate of the deposition particles, thermal spraying becomes a low cost and high efficiency method to fabricate amorphous coatings. This makes it possible for wide application of amorphous materials. For this reason, a Fe-based amorphous coating was fabricated by plasma spraying. The influences of spraying parameters and heat treatment on Fe-based amorphous coating structure, wear and corrosion resistance were investigated systematically. The evolution mechanisms in structure, wear, and corrosion of the coatings were discussed. In view of the adverse effects of pores in the coating on its properties,both Mo-based alloy addition and lasrer remelting treatment were applied to Fe-based amorphous coating to reduce or eliminate pores with in the coating and enhance the bond strength of the coating. Moreover, the influences of Mo-based alloy addition and lasrer remelting treatment on structure and properties of Fe-based amorphous coating were studied. Main research results are summarized as follows:It is showed that spraying power is a significant factor for the formation of Fe-based amorphous coating. High spraying power is helpful to form a dense structure and a amount of crystallization phase as well. However, it is not obvious for the influence of the flow rate of main gas(Ar) on formation of Fe-based amorphous coating. The optimization plasma spraying parameters are 50 V voltage, 300 A current, 0.7 MPa main gas pressure, 80 L/min main gas flow rate and 100 mm spray distance. The highest amorphous content in amorphous coatings is up to 93%. Structural relaxation was found in the coating annealed at 573 K, and no crystallization phase produced during heat treatment under this condition. XRD pattern showed that Fe3 B, Fe2O3, and B0.44C1.41Cr3 appeared in the coating annealed at 873 K with a decrease in the amorphous content. It is found that these formed crystals have small size(about 60 nm in diameter), which results in a enhancement in hardness and wear resistance of the coatings by a refined-crystalline strengthening mechanism. However, when the heat treatment was operated at 1023 K, the amorphous phase crystallized and resultant grains grown up to micron scale. The wear resistance of the coatings is deteriorated by the surface cracks occurred during heating and cooling. Salt spray and wear tests show that the corrosion of Fe-based amorphous coating takes place at pores and exihibits a crevice corrosion characteristic. The wear is derived from the fracture and delamination of the splats in the coating and the plough cutting by hard particles.With increase of Mo-based powders addition, the porosity of the composite coating decreases significantly and bond strength enhances about 10 MPa due to the self-adhesive character of Mo alloy. As a result, the fractures and delaminations of the splats decrease and the wear resistance is improved. At the same time, the crevice corrosion is restrained.The porosity of Fe-based amorphous coating is eliminated by laser treatment. The coating bonds on substrate surface metallurgically when the depth of molten pool exceeds the coating thickness. Though extremely fine pores and few cracks appear on the surface of remelted coatings, corrosion potential of the coating are enhanced and corrosion current density are reduced by 20 times in NaCl and HCl solution compared with that of Fe-based amorphous coating. Thus it can be confirmed that the remelted coating has high corrosion resistance in both solutions. Compare to as-sprayed coatings, the wear resistance of the remelted coating is improved under dry sliding condition. The wear mechanism of the remelted coatings is dominated by hard particles cutting and furrow formed. However the wear mechanism of as-sprayed coating was fractures and delaminations of the splats around pores apart from hard particles cutting.The result indicates that the microstructure of laser treated Fe/Mo composite coating become denser than that of Fe/Mo composite coating. Mo-based particles fuse completely with Fe-based particles, and the pores within the composite coating disappears. XRD analysis shows that much crystallization phases appear in the remelted composite coatings. In addition, the elements Mo and Ni and reduced porosity can promote the formation of stable passivation film in NaCl and HCl solutions, resulting in low current density and high corrosion resistance. |
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