EFFECT OF La2O3 ON HIGH-TEMPERATURE OXIDATION RESISTANCE OF ELECTROSPARK DEPOSITED Ni-BASED COATINGS

The oxidation tests of electrospark deposited Ni-based coatings without and with 2.5 wt.% La2O3 were conducted at 960°C in air for 100 h. The oxidation kinetic of the coatings was studied by testing the weight gain. The phase structures and morphologies of the oxidized coatings were investigated by XRD and SEM. The experimental results show that the coatings with 2.5 wt.% La2O3 exhibits excellent high-temperature oxidation resistance including low oxidation rate and improved spallation resistance, due to the formation of a denser and more adherent oxide scale compared with that without La2O3. The effects of La2O3 on the oxidation resistance include the following two aspects: First, refinement of the coating grains promotes the selective oxidation of Cr, leading to the formation of protective chromia scale in a short time, and second, refinement of the oxide grains enhances the high-temperature creep rate, resulting in decrease of inner stress and improvement of spallation resistance of the oxide layer.