Deposition and oxidation behavior of atmospheric laminar plasma sprayed Mo coatings from 200 mm to 400 mm under 20 kW: Numerical and experimental analyses

A stable laminar plasma jet with a jet length of above 600 mm was adopted to deposit molybdenum coatings to investigate the behavior of high-melting point metal, molybdenum, and particles during laminar plasma spraying process. The temperature, velocity, and species distribution of the plasma jet were calculated by numerical simulation. In the experiment, the temperature and velocity distribution of the in-flight particles were measured, and the microstructure and properties of the coatings were analyzed. Combining the results of the simulation and experimental results, the deposition behavior and oxidation mechanism of the coatings prepared at the spray distance from 200 mm to 400 mm were discussed. The results indicate that both the laminar plasma jet and injected particles exhibit high temperature and low velocity, and low temperature and velocity gradients. The microstructure of the coatings shows a high similarity and hardly changes when the spray distance exceeds 250 mm. When the spray distance is 200 mm, post-deposition oxidation occurs due to the heating effect of the long plasma jet on the substrate. In contrast, when the spray distance is longer, the particles undergo severe in-flight oxidation, and the oxide formed is uniformly distributed in the coating improving the hardness from 500 HV_0.3 to 700 HV_0.3.