High-temperature Oxidation Behavior and Mechanism of Hybrid Twin-wire Supersonic Arc Sprayed Coatings

Because of its low cost, easy operation, and high deposition efficiency, supersonic arc spraying technology is extensively used in the field of preparation and repair of protective coatings. Hybrid twin-wire arc spraying technology is a process that employs two kinds of metal wires with distinct compositions to prepare composite coatings. Nonetheless, little research has been conducted on the high-temperature oxidation resistance of iron-based coatings made with the hybrid twin-wire method. The work aims to adopt two kinds of wire materials with similar but different components to solve the problem of the large difference in melting point of hybrid twin-wire arc spraying. Three kinds of ultrasonic arc-sprayed iron-based coatings were prepared on 45 steel substrates by hybrid and homogeneous twin-wires. The microstructure, surface morphology, chemical composition and phase composition of the coatings before and after high-temperature oxidation at 700 ℃ were characterized by optical microscope (OM), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), and X-ray diffraction (XRD). The porosity of the coatings was measured by Matlab software, and the microhardness of the coatings was measured by a microhardness tester. The porosity of the three coatings was all lower than 10%, which could meet the requirements of arc spraying. The microhardness of the three coatings reached above 400HV, among which the hybird FeAlCrMoVC/FeAlNiMoCrC composite coating had the lowest porosity of 5.00% and the highest microhardness of 456.91HV. The high-temperature oxidation results showed that the mass gain/area of FeAlCrMoVC, FeAlNiMoCrC, and FeAlCrMoVC/FeAlNiMoCrC coatings reached 10.67, 3.32 and 2.02 mg/cm2, respectively. Notably, the oxidation kinetics of the three coatings conformed to the classical parabolic law, and the parabolic rate constants (kp) were 3.08×10−10, 2.20×10−11 and 5.60×10−12 g2•cm−4•s−1, respectively. According to the scanning electron microscopy (SEM) images after high-temperature oxidation, compared with the coating prepared by homogeneous twin-wires, the coating prepared through hybrid twin-wire was mainly composed of three dense morphologies. Combined with EDS and XRD analysis, it was inferred that they were primarily composed of Fe3O4, Fe2O3, Cr2O3 and Al2O3, and spinel NiCr2O4. Cross-section analysis demonstrated that the FeAlCrMoVC/FeAlNiMoCrC composite coating made by homogeneous twin-wires showed the thinnest internal oxidation and surface oxidation films of 5.3 μm, 24.7 μm and 118.2 μm. EDS element mapping results showed that oxygen and aluminum in the coating aggregated and overlapped with each other in the pores, which indicated that the internal oxidation mainly generated dense aluminum oxides. In addition, the internal oxidation of the coating started from defects including pores and oxidation inclusions, and the dense oxides generated could enhance the oxidation resistance of the coating. Three kinds of coatings prepared by supersonic arc spraying have good high-temperature oxidation resistance, while the FeAlMoCrC/FeAlNiMoCrVC composite coatings prepared by hybrid twin-wire method exhibit much better high-temperature oxidation resistance. This indicates that the supersonic arc spraying coating prepared by hybrid twin-wire method is the alternative way to improve the oxidation resistance in high temperature. © 2024 Chongqing Wujiu Periodicals Press. All rights reserved.