Atmospheric Plasma Spraying of Environmental Barrier Coatings – A Parametric Study

Abstract

Abstract Environmental barrier coatings (EBCs) are required to protect SiC based composites in high temperature, steam containing combustion environments found in the latest generation of high efficiency gas turbine aeroengines. Ytterbium disilicate has shown promise as an environmental barrier coating, showing excellent phase stability at high temperature and a coefficient of thermal expansion close to that of SiC; however, its performance is dependent on the conditions under which the coating was deposited. In this work, a parametric study was undertaken to demonstrate how processing parameters using a widely used Praxair SG-100 atmospheric plasma spraying torch affect the phase composition, microstructure and mechanical properties of ytterbium disilicate environmental barrier coatings. Ytterbium disilicate coatings were deposited using 5 sets of spray parameters, varying arc current and secondary gas flow. The phases present in these coatings were quantified using X-ray diffraction with Rietveld refinement, and the level of porosity was measured. Using this data, the relationship between processing parameters and phase composition and microstructure was examined. Abradable coatings are used throughout gas turbine engines to increase efficiency in the compression and combustion phases of the turbine. Abradable coatings are soft enough to be worn away by turbine blade tips (without damaging the tip itself), allowing for tighter clearances to be used, limiting leakages and increasing efficiency. Using the optimum process parameter window determined in this work, a low density abradable Yb2Si2O7 layer will be deposited in future research.