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 leads to less heat input to the substrate surface by changing the position of the convergence point of the laser beam and powder stream. The coating has a much faster cooling rate, which facilitates the preparation of coatings with low dilution and high amorphous content compared to conventional laser cladding (CLC). In this study, the Fe47Cr15Mo14Co3C15B6 powders were deposited on AISI 1020 seamless steel tube substrate by CLC and HLC processes, respectively. The phase composition, elemental distribution, amorphous content, cross-sectional microstructure, microhardness, and corrosion resistance properties of the CLC and HLC Fe-based amorphous coatings were compared. It can be seen that the thickness of the CLC coating was much thicker than that of the HLC coating, which was twice as thick as the HLC coating. Compared to the CLC coating, which had only 55 % amorphous phase content at the top, the HLC coating had a more uniform distribution of amorphous phases, with the lowest amorphous phase content of 56 % at the bottom and similar amorphous phase content of 66 % and 68 % at the middle and top, respectively. The microstructure of the CLC and HLC coatings shows the same growth law, but the microstructure in HLC was smaller and denser, and the columnar crystal areas were smaller, with an average height of only 7.6 µm. And only Mo2C was found at the top of the HLC coating. The cross-section microhardness of the CLC coating was only found in the amorphous hardness range at the top, at 1193 HV, while the microhardness of the HLC coating was more evenly distributed, all above 1300 HV. In addition, the corrosion resistance of HLC coatings was better than that of CLC coatings. As the amorphous phase content increased, the mechanical properties and corrosion resistance of the coatings became better.