A study on the vacuum kinetic spray deposition mechanisms of particles based on a finite element and microstructural analysis

Abstract

The vacuum kinetic spraying (VKS) is a new kinetic spray coating process by which utilizes the pressure gap between powder hopper and vacuum coating chamber for successful ceramic coating formation. This technique has high potentials for industrial applications such as blocking layer of dye-sensitized solar cell (DSSC), solid oxide fuel cell (SOFC) interconnector, and artificial bone because of higher deposition rate, and lower price than conventional thin film deposition such as physical vapor deposition (PVD), and chemical vapor deposition (CVD). The ceramic coating formation of VKS is related to the dynamic fragmentation of ceramic particles upon impact. However, exact coating formation mechanisms have not been clarified yet, although it is an important issue to tailor the process conditions, microstructure, and properties. This study presents the possible Al2O3 coating formation mechanisms of VKS through a finite element analysis (FEA) and experimental methods. Mechanical ball milling of the powder was performed to produce the defects, e.g., dislocations, in the powder without shape and size changes. The as-received and ball-milled powders were applied to VKS process, and their coating formation behavior and microstructures, e.g., grain size were analyzed. The defects of the ball-milled powder promoted the fragmentation and coating formation during VKS process. On a basis of FEA and microstructure analysis, the deposition mechanisms of Al2O3 coating were discussed. In addition, single Al�2O3 particle impacts under various impact velocities were simulated. The mass loss and shape change were analyzed as a function of various impact velocities to show the deposition optimized velocity zone (DOVZ) of the particles. At last, to estimate the particle velocity upon impact onto glass substrate, computer simulation was utilized, and the results were similar to the conventional experimental results. Furthermore, during coating experiment, the pressure of the coating chamber was proportional to the gas flow rate. Therefore, the particle velocity could be decided by the gas flow rate which is the experimental variable.