The Anti-oxidizing Research Of Arc-sprayed Aluminum Bronze Coating Of High Temperature

Arc spray is a method of applying coatings, which is easy operating and with low cost. Arc-sprayed aluminum bronze coatings are widely used in many fields, while their corrosion properties at high temperature in oxidizing atmospheres are not yet studied or are rarely investigated. This work aimed at evaluating the anti-oxidation of the coatings and studying their protecting mechanism.In the work, aluminum bronze coatings were sprayed on low-carbon steel substrate. And then, continuous oxidation tests and circular oxidation tests were performed to investigate high temperature behavior of the coatings and to study anti-oxidation mechanism of them. An Cahn2000 hot balance was employed to measure the mass increment of the specimens respectively at 700 °C ,800 °C, 900°C. From those tests, oxidation dynamics curves were obtained. It was found that a protective oxide scale was easy formed on the surface of aluminum bronze coating at 900°C. To draw oxidation dynamics curves concerned with the conversion of coating surface area since original arc-sprayed coating surface was coarse. Using technique of roughness, the outline curves of arc sprayed surface was measured and the area ratio between the coarse surface and the smooth surface was approximately 2.3. Moreover, in comparison the coarse surface with the smooth surface, both of the oxidation dynamics properties of circular oxidation at 900 °C for 24 hours were discussed.The surface morphology and structure of the coatings were observed and the distribution of oxide component was analyzed using SEM, EDS. It was found that the aluminum oxide film covered the exterior surface of arc sprayed aluminum bronze coating. Alumina in the coatings played an important role of sealing pore spaces, which hindered oxygen into the coatings. Aluminum elements diffused to the interface and into the substrate in the course of heating and the continual oxide could protect the substrate from further oxidation. In order to compensate the aluminum element consumed in the coating and to prolong the anti-oxidation lifespan arcspraying aluminum bronze/ aluminum composite coatings were studied. By means of SEM and EDS analyzing it was found that there was a continual aluminum oxide layer bond in the interface of coating /substrate after circular oxidation at 900 °C for 48 hours, which revealed that the coatings provided a good oxidation-resistant effect.In the work, the forming mechanism of holes inside substrate near the interface was discussed, and the formula of oxidized vacancy was inferred. The diffusion coefficient of aluminum in copper was in the stage of pilot study and the mathematical model as a theory was established. The mechanical performance test gave a proof that the coating adherence to the substrate was conformed to the operating requirement and fit for the actual high temperature oxidation environment.