Investigation on High-Temperature Oxidation Behavior and Mechanism of La2O3-Modified Hastelloy-C22 Coatings by Laser Cladding

Abstract

In this study, the high-temperature oxidation behavior and mechanism of Hastelloy-C22 coatings modified with La₂O₃ by laser cladding were systematically investigated. The microstructural morphology and oxidation product characteristics of the coatings were characterized through various analytical methods, including scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), x-ray diffraction (XRD), and laser confocal microscopy. The results indicate that La₂O₃ particles are primarily distributed along the grain boundaries of the coating, facilitating the entry of a solid solution of Cr, Mo, and Co into the γ-Ni lattice during the cladding process. With increasing La₂O₃ content, the content of the Ni-Cr-Co-Mo phases in the coating also increased. In the temperature range of 700-900 °C, the average thickness of the oxide layer of the coating with 1 wt.% La₂O₃ was reduced by 37%. After the addition of La₂O₃, the coating formed a La₄MoO₉ phase upon high-temperature oxidation. This phase effectively protects the metallic elements within the coating from oxidative attack, such as Ni, Cr, and Fe, resulting in optimal oxidation resistance for the coating. Furthermore, as the oxidation temperature increased, the mass of the C22-xLa₂O₃ coating gradually increased, displaying a parabolic relationship with the duration of oxidation.