Direct simulation Monte Carlo modeling of metal vapor flows in application to thin film deposition

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

2015

Thermal barrier coating systems consisting of a metallic bond coat and ceramic over layer are widely used to extend the life of gas turbine engine components. They are applied using either high-vacuum physical vapor deposition techniques in which vapor atoms rarely experience scattering collisions during propagation to a substrate, or by gas jet assisted (low-vacuum) vapor deposition techniques that utilize scattering from streamlines to enable non-line-of-sight deposition. Both approaches require substrate motion to coat a substrate of complex shape. Here, direct simulation Monte Carlo and kinetic Monte Carlo simulation methods are combined to simulate the deposition of a nickel coating over the concave and convex surfaces of a model airfoil, and the simulation results are compared with those from experimental depositions. The simulation method successfully predicted variations in coating thickness, columnar growth angle, and porosity during both stationary and substrate rotated deposition. It was then used to investigate a wide range of vapor deposition conditions spanning high-vacuum physical vapor deposition to low-vacuum gas jet assisted vapor deposition. The average coating thickness was found to increase initially with gas pressure reaching a maximum at a chamber pressure of 8-10 Pa, but the best coating thickness uniformity was achieved under high vacuum deposition conditions. However, high vacuum conditions increased the variation in the coatings pore volume fraction over the surface of the airfoil. The simulation approach was combined with an optimization algorithm and used to investigate novel deposition concepts to tailor the local coating thickness. V

Section: Methodsmentioning

confidence: 99%

Microstructure of vapor deposited coatings on curved substrates

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

2015

“…Icarus uses the variable hard sphere (VHS) molecular collision model, which simulates gas molecules as hard spheres with velocity dependent radii. [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.…”

Section: Methodsmentioning

confidence: 99%

“…The VHS model has been used several times to model metal vapors with the DSMC methods. 42,43 Although the variable soft sphere (VSS) collision model is better suited for accurate simulation of diffusion-dominate flows, 40 VSS parameters have yet to be determined for the nickel metal vapor of relevance here.…”

Section: Methodsmentioning

confidence: 99%

Vapor deposition on doublet airfoil substrates: Coating thickness control

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

2015

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

“…DSMC is a statistical simulation method developed to analyze rarefied gas environments for which continuum computational fluid dynamics methods are difficult to apply. 27 It has been widely used to study conventional physical [28][29][30][31] and chemical vapor deposition processes [32][33][34][35] and has been employed to better understand the EB-DVD coating process. 7,25,[36][37][38] DSMC uses a subset of test particles within a grid to simulate the behavior of a much larger number of real gas particles (on the order of 1 test atom per billion real atoms).…”

Section: Introductionmentioning

confidence: 99%

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

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

2013

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