Optimization of Low Pressure Plasma Spraying Coating for Aero Turbine Components Using Factorial Analysis

Thermal barrier coatings provide gas turbine engines with an enhanced operating temperature.  The increase in temperature is directly related to an increase in engine efficiency as well as performance.  The quality and design of the coating system is critical to maximize engine efficiency, performance and increase engine life between overhauls.  Thermodynamics and fluid dynamics of engines are subject to specific design parameters of coatings; i.e thickness, microstructure, roughness, porosity and density.  Substantial research dedicated to the coating development includes powders composition and substrate-coating interactions during component service life.  However, little published work is available on the understanding and most crucially the ultimate optimization of the fundamental elements of coating systems.  

This paper seeks to understand the optimized spray parameters for low pressure plasma spray (LPPS) bond coat application.  The integral properties of bond coat are critical to the life of the thermal barrier coating (TBC) system such as oxide content, un-melted particles, porosity and voiding and these have been optimized using a two-level full factorial analysis using chamber pressure, spray distance and gun power as variables. 

This paper delivers a high level description of LPPS systems and crucial indicators to a durable bond coat and their effects to TBC’s are described and evaluated using visual analysis, scanning electron microscopy and furnace cyclic testing. The data generated led to the formulation of a new methodology for bond coat application on aero turbine components.