Study of the Effect of Gas Shrouding on metallic coatings prepared via Atmospheric Plasma Sprayed

In present work modified gas shrouding was proposed to efficiently control the oxygen entrainment to the plasma jet. The shroud consisted of a nozzle assembly with 12 gas outlet nozzles blanketing the plasma jet. As a further improvement, a solid shell with shrunk opening was introduced to prevent the entrainment of ambient gas between the arranged shrouding nozzles. Enthalpy probe was employed to measure temperature and velocity of plasma jet. Simulation was also carried out for verifying the shrouding effect. Different powders were used for estimating the protecting effect. The element map and microstructure of coating were examined by EDX and SEM. The phase component of the coating was checked by XRD. The results show evident reduction of oxygen fraction in the coating. The plasma jet was well protected from the contact with ambient gas with slight influence of plasma velocity and temperature.