Thermal barrier coating deposition by rarefied gas jet assisted processes: Simulations of deposition on a stationary airfoil

Abstract

The uniform coating of a complex shaped substrate, such as a gas turbine airfoil, by collisionless physical vapor deposition processes requires rotation/translation of the substrate or sources and is inconceivable for regions on the substrate that are never in the line-of-sight of the vapor source. Recently developed directed vapor deposition processes use electron beam evaporation and inert gas jets to entrain, transport, and deposit metal oxide vapor in an environment where many vapor atom collisions occur prior to deposition. Direct simulation Monte Carlo simulations and experimental depositions of a rare earth modified thermal barrier coating are used to investigate fundamental aspects of the deposition process, including coating thickness and column orientation, over the surface of a nonrotated model airfoil substrate with substantial non-line-of-sight regions. The coating thickness uniformity was found to depend on the deposition chamber pressure and the pressure ratio between the low-pressure deposition chamber and high-pressure reservoir upstream of the gas jet forming nozzle. Under slow flow conditions, significant coating of the non-line-of-sight regions was possible. The growth column orientation is found to also vary over the substrate surface due to changes in the local incidence angle distribution of depositing vapor atoms. The variation in growth column orientation is not predictable by the Tangent rule widely used for predicting columnar growth orientation in physical vapor deposition processes. V

Vapor deposition on doublet airfoil substrates: Coating thickness control

“…Both airfoils were identical in design to that used in previous studies of deposition on single airfoil substrates. 33,34 The geometry and dimensions of the 2D doublet substrate are shown in Fig. 2.…”

“…[41][42][43] Both the DSMC simulation method, and its application to the simulation of vapor deposition have been described in detail elsewhere. 15,33,44 The simulation grid used here for the a ¼ 0 substrate orientation is shown in Fig. 4.…”

“…13 for a fixed channel width of 12 mm and pressure ratio of 5.0. The chamber pressure controls the rate of diffusion of the vapor atoms in the gas flow, 26,33 and has a large effect on both the magnitude and shape of the local deposition efficiency profile on all of the surfaces. Figure 13 shows that the most uniform deposition profiles on all surfaces occurred at the lowest chamber pressure of 1 Pa.…”

“…Gas jet assisted PVD methods offer the possibility of non-line-of-sight deposition while retaining the high deposition rates achievable with electron beam evaporation and sputtering methods. 15,32,33 For example, the electron beam directed vapor deposition process 15 uses a helium gas jet to entrain the vapor emitted during high power electron beam evaporation of a source. Deposition rates of many micrometers per minute are then possible.…”

A review of multiphase flow and deposition effects in film-cooled gas turbines

“…Generally, a second order central scheme with boundedness has been used for spatial discretization in quasi-DNS. In addition, Rodgers et al [53], simulated the deposition process by using direct simulation monte carlo (DSMC) method. Sreedharan et al [54] found that LES calculations were sensitized to temperature and ash composition for syngas ash deposition in the hot gas path.…”