Comparative Study on Microstructure and Properties of Fe-Based Amorphous Coatings Prepared by Conventional and High-Speed Laser Cladding

Abstract

High-speed laser cladding (HLC) technology changes the position of laser and powder flow convergence focus, resulting in little heat input to the substrate and a faster cooling rate of the coating, which facilitates the preparation of cladding layers with low dilution and high amorphous content. In this study, Fe-based amorphous coatings were prepared by melting Fe47Cr15Mo14Co3C15B6 powder on AISI 1020 seamless steel tube substrate using conventional laser cladding (CLC) and HLC processes, respectively. The phase composition, amorphous content, cross-sectional microstructure, microhardness, and corrosion resistance of CLC and HLC coatings were compared. The experimental results showed that the CLC coating only had 55% amorphous phase content at the top of the layer. In contrast, the HLC coating had a more uniform distribution of amorphous phase content in the vertical direction, with the lowest amorphous phase content of 56% at the bottom and closer amorphous phase content of 66% and 68% at the middle and top, respectively. The microstructures of CLC and HLC coatings presented the same growth pattern, but the columnar crystal organization of HLC coating was finer, with an average height of only 7.6 µm. In the study, the Mo2C phase was generated only in the top region of the HLC coating, as the cooling rate of the HLC coating was much faster than that of the CLC. The hardness of the CLC coating was in the amorphous phase hardness range only at the top, with a hardness value of 1193 HV, while the HLC coating had a more even distribution of hardness values, all above 1300 HV. In summary, the HLC coating contains high amorphous phases that provide better mechanical properties and corrosion resistance.

Keywords: Laser cladding, Fe-based amorphous coating, microstructure, Corrosion resistance