Abstract:
For many decades gas turbine engineers have investigated methods to improve engine
efficiency further. These methods include advances in the composition and processing
of materials, intricate cooling techniques, and the use of protective coatings. Thermal
barrier coatings (TBCs) are the most promising development in superalloy coatings
research in recent years with the potential to reduce metal surface temperature, or
increase turbine entry temperature, by 70-200°C.
In order for TBCs to be exploited to their full potential, they need to be applied to the
most demanding of stationary and rotating components, such as first stage blades and
vanes. Comprehensive reviews of coating processes indicate that this can only be
achieved on rotating components by depositing a strain-tolerant layer applied by the
electron beam-physical vapour deposition (EB-PVD) coating process.
A computer program has been developed in Visual c++ based on the Knudsen cosine
law and aimed at calculating the coating thickness distribution around any component,
but typically turbine blades. This should permit the controlled deposition to tailor the
TBC performance and durability. Various evaporation characteristics have been
accommodated by developing a generalised point source evaporation model that
involves real and virtual sources.
Substrates with complex geometry can be modelled by generating an STL file from a
CAD package with the geometric information of the component, which may include
shadow-masks. Visualisation of the coated thickness distributions around components
was achieved using OpenGL library functions within the computer model.
This study then proceeded to verify the computer model by first measuring the coating
thickness for experimental trial runs and then comparing the calculated coating
thickness to that measured using a laboratory coater. Predicted thickness distributions
are in good agreement even for the simplified evaporation model, but can be improved
further by increasing the complexity of the source model.
