Influence of scanning speed on microstructure and corrosion resistance of Fe-based amorphous coatings by high-speed laser cladding

Fe-based amorphous coatings were prepared on the surface of the AISI 1020 steel pipe by high-speed laser cladding technique. This study is aimed to investigate the influence of scanning speed on the microstructure, hardness, amorphous content and corrosion resistance offered by the Fe-based amorphous coatings. The results showed that, the coating obtained at 50 mm/s exhibited a distinct three-layer hardness distribution, with the second layer displaying the highest hardness. This phenomenon was primarily ascribed to amorphous strengthening, fine-grain strengthening, and martensitic strengthening. The bottom region of the coatings contains budding crystals, with prominent aggregation of elemental Fe. Away from the budding regions, a transition from columnar to dendritic crystals was observed. The amorphous content of the coatings exhibited an initial rise followed by a decline with increasing scanning speed. Among these, the amorphous phase content of 130 mm/s coating was up to 95 %. Differential Scanning Calorimetry (DSC) test results confirmed the presence of amorphous phases in the bottom and middle regions of the 50 mm/s coating. Electrochemical experiments underscored the exceptional corrosion resistance of the 130 mm/s coating, evidenced by its maximum corrosion potential (−0.471 V), minimal corrosion current density (2.7 × 10−6 A/cm2), and highest polarization resistance value (22,149 Ω·cm2). This superior performance was attributed to the presence of the amorphous phase and the Cr oxide layer formed on the surface, providing robust protection to the substrate.