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

Abstract

Electron beam-physical vapour deposition (EB-PVD) is a commonly employed process for the production of thermal barrier coatings (TBCs), used in high performance applications such as gas turbines high-pressure aerofoil blades for the aerospace industry. Computer modelling can contribute to improved control of the coating process, important to support a continuous drive for increased efficiency. This paper considers two aspects associated with the EB-PVD coating of TBCs for commercial application: firstly, that clusters of blades are coated simultaneously in commercial coaters and, secondly, that these parts possess a complex geometry, such that shadow masks need to be taken into account. In this context, a computer model that calculates coating thickness distribution along the surface of different engine components, based on the analysis of the vapour deposition flux around complex geometries, is presented. To validate the predictive capability of the computer model two deposition trials were performed. Firstly, a cluster of components was simulated using three rotating cylinders, as a simple representation of coating multiple blades. Secondly, the effect of shadow masks was studied with an arrangement in which flat plates were welded, in the form of a U-shaped component, but with one side shorter than the other. The predicted results generated by the computer model compare favourably with those measured in the experimental runs presented. For the cluster of three cylinders, an error of 4% was obtained whilst the divergence was around 20% for the simulated shadow mask due to the fact that overall coating thickness was significantly reduced. In spite of this, the results obtained from the model were promising with respect to the degree of fit of the inverse square law. It is thought that a virtual source may be responsible for measurements being generally higher than those predicted by the model.

Finite element modeling of coating thickness using heat transfer method

“…For the three-pin model, same as in Ref. [4], the center of the disk is used as the point of rotation of the three-pin structure. The rotation axis is parallel to the disk's normal.…”

“…The model is firstly validated using disk and cylinder shaped components, followed by a three-pin component as in Ref. [4]. The validation studies show that the developed model results are in good 4 agreement with either the analytical model or experimental measurements.…”

“…Schiller et al proposed generic analytical models to predict the coating thickness on simple shaped workpieces, such as plate and cylinder [3]. Pereira et al presented a model that calculates coating thickness considering the shadow effect [4]. Pereira's model is based on the analysis of the vapor deposition flux, and the predicted coating thickness distribution in a three-pin rotatory component is in good agreement with experimental measurement [4].Although the above ray-tracing based method has been widely used, its computational cost is usually prohibitively high, due to calculating individual ray.…”

Convection–Diffusion Model for the Synthesis of PVD Coatings and the Influence of Nanolayer Parameters on the Formation of Fractal and Hierarchical Structures

“…In particular, the studies proposed the coating thickness uniformity model [8,9], the cosine analytical and generic computational model [10], and the inverse power law relationship between thickness and source-to-substrate distance was considered [11]. Recent studies also applied true line-of-sight models, based on the inverse square law and also taking into account the effect of shadow masks [12]. In [13], the computational level set method was also applied for tracking topographic change of a surface.…”

On evaporation via an inclined rotating circular lift-off shadow or stencil mask

“…Determining the topographic profile of the deposition when the wafer contains arbitrary geometry, high-aspect-ratio openings, under rotation and inclination is not trivial 22 -with several solutions having been proposed which make use of numerical methods. [23][24][25][26][27][28][29][30][31][32][33] The main parameters in this process are: the resist thickness, the resist opening width, the resist profile, the evaporation angle, the evaporated material thickness, the lateral sidewall and vertical evaporation onto the mask itself.…”