Diagnostics Of Plasma Jet And Coating Deposited By Very Low Pressure Plasma Spray

At all times, EB-PVD technology (Electron Beam-Physical Vapor Deposition) and Low Pressure Plasma Spray (LPPS) were considered very different from each other. The EB-PVD technology is used for getting YSZ coating with columnar structure used for engine blades, but it has very low deposition rates and large energy. LPPS can provide high deposition rates and low energy compared with EB-PVD. But the coating is formed by melting droplet with high roughness.Some researches showed that when using tri-cathode plasma gun and the vacuum arrives0.1kPa, we can obtain YSZ coating with columnar structure like EB-PVD method. Until now, because the VLPPS technology is so complex, the research for plasma jet characteristics and coating is just initial starting. The developments of these recent processes have been mainly based on empirical methods. The influences of parameters for plasma jet characteristics are very important for getting high quality coating.To make the low pressure plasma spraying processes more reliable and reproducible, further improvements are required, like the knowledge of physical properties of the plasma jet such as the temperature, flow velocity and plasma density.This thesis includes several parts:First of all, we used optical emission spectrum (OES) method to study the influence of parameters.It was found that the effect of pressure is more than the current intensity and hydrogen gas flux for emission spectrum intensity.By using Hα and Hβ spectrum, electron temperature has been obtained, and then changing powder size to study the influence of powder. We also used Stark method to get electron density of plasma jet and influence of plasma gun power.Then the enthalpy diagnostic method was used to get enthalpy,temperature and heat flux of plasma jet. In this condition, we obtained the highest enthalpy and temperature, and found that the enthalpy and temperature are much closed between50cm and60cm.It is certified that it has relationships with plasma jet structure.Finally, we used optimized parameters to deposit Cu and YSZ coating.But the coating has big particles.By changing injecting powder ways and using F100plasma gun. YSZ coating was well improved. While because of the limited power, the coating has mixed structure. By heating up the Cu, we obtained columnar structure thin film-like coating.It is certified that the evaporation and quantity of heat are very important for forming this structure.