Vapor deposition on doublet airfoil substrates: Coating thickness control

Abstract

A combined simulation and experimental approach is used to investigate vapor deposition onto model doublet guide vane substrates found in gas turbine engines. These substrates contain surface regions that are not visible to the vapor source. Particular attention is given to coatings on interior surfaces of the doublet airfoil geometry, which are only accessible through the leading and trailing openings of the doublet airfoil substrate. Deposition of nickel is simulated for several flow conditions and vane separation distances, using a direct simulation Monte Carlo method. The simulated coating thickness predictions are then evaluated by comparison with experimentally deposited nickel coatings. Coating uniformity along interior surfaces was found to be highly sensitive to deposition conditions, and to the separation distance between the pair of airfoils. Coating thickness on these surfaces were found to vary with the ratio of laminar flow distance through the interairfoil channel to the transverse diffusion distance across the channel gap; a parameter which can be applied to optimize the coating of many interior channel-like substrate using gas jet assisted deposition concepts. V

Vapor deposition on doublet airfoil substrates: Control of coating thickness and microstructure

“…The design of the two individual airfoils was identical to that previously used in an investigation of single airfoil deposition 15,16 and a study of coating thickness on a doublet guide vane. 25 During the simulations, the doublet airfoils were assumed perfectly two-dimensional (taken to have infinite length in the out of plane direction). For experiments, the airfoils were 31.75 mm high in the out of plane direction and were capped on each side by a thin backing plate [ Fig.…”

“…1. 25 It is indicated that during vapor deposition onto a rotated guide vane substrate, the midregions of the interior convex and concave surfaces received a much smaller fraction of the evaporated flux than the outer surfaces, and led to significant disparities in coating thickness. The study in Ref.…”

“…The study in Ref. 25 found that the thickness uniformity along the curved inner channel surfaces could be improved by using a gas jet assisted deposition process. It is found that by increasing the chamber pressure to 10-40 Pa range, and using high velocity gas jet assisted vapor transport, the time for the vapor to be transported through the interairfoil channel could be made commensurate with that for transverse diffusion to the channel surface.…”

“…The variation in columnar growth angle and coating porosity as the deposition conditions were varied is then systematically investigated. Finally, the rotation optimization method previously proposed for controlling coating thickness uniformity 16,25 is investigated for reducing variations of coating microstructure between the inner and outer airfoil surfaces.…”

Modelling the EB-PVD thermal barrier coating process: Component clusters and shadow masks

“…Also, in addition to rotating and tilting actions, commercial EB-PVD chambers coat multiple blades in each batch [18]. of predicting vapour deposition have been discussed in the literature [7,[19][20][21][22]. Modelling of the degradation or failure mechanisms has also received attention [12,[23][24][25][26].…”