Effect of La2O3 on resistance to high-temperature oxidation of laser clad ferrite-based alloy coatings

Ferrite-based alloy powders with different contents of La2O3 were laser-clad on AISI 1115 steel substrates. The oxidation kinetic of the coatings was studied by testing the weight gain. Cyclic oxidation tests were performed to determine the eventual weight loss due to spallation. The morphologies and phase structures of the coatings were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The experimental results showed that Cr2O3 was formed on all coatings after oxidation. The coatings with La2O3 exhibited excellent high-temperature oxidation behavior including low oxidation rates and high resistance to spallation. In addition, the effect of La2O3 was discussed. This included the change of transport mechanism in the oxide scales, the increase in the nucleation rate of the oxide, the release of stresses in the oxide scales by refining the oxide grains and the improvement of the adhesion of the oxide scales to the coatings by changing the scale growth mechanisms.