Homogenization of Coating Properties in Atmospheric Plasma Spraying - New Results of a DFG (German Research Foundation)-Funded Research Group

In order to homogenize the properties of APS sprayed coatings by employing 3-cathode technologies the spray process was investigated using numerical simulations combined with innovative diagnostic techniques. Thus the process was subdivided into three areas: the plasma torch, the free jet and the coating formation allowing the development of individual numerical models. By simulating these areas separately and combining the results, appropriate process parameters for homogenized coatings were to be obtained. A numerical model coupling fluid dynamic, electro-magnetic and thermal phenomena for a 3-cathode torch was developed to investigate the plasma and the dynamic electric arc behavior inside the torch. For a comprehensive computation of coating formation, which, besides the impact, flattening and solidification of the particles, includes the mechanical properties of the coating, a “Volume of Fluid” algorithm (VOF) is coupled with a “Finite Element Method” (FEM). In order to verify the modeling of the plasma jet and to provide input data for the coating formation the diagnostic efforts were concentrating on measuring the gas temperature of the plasma as well as particle shape, velocity and temperature. The results of spatially resolved 3D analysis employing an innovative tomography system for most of the mentioned parameters are presented and compared with the numerical results.