Application of High Resolution Jet-Miniaturized HVOF Spray Systems for the Development of Bond Coats for TBCs

In the context of high temperature protection of hot sections of gas turbine engines, recently developed miniaturized thermal spray torches offer new capabilities in creating protective thermal barrier coatings (TBCs) in space restricted components at normal spray angles. In this work, novel miniaturized HVOF systems of hydrogen fueled SprayWerx ID-Nova and liquid fueled Praxair JPid, with high resolution spray jets of few millimeters width, were employed for the deposition of NiCoCrAlX (X=Y,HfSi) bond coats. The coatings were applied at short standoff distances on both external and internal surfaces of cylinders with ≥140 mm diameter. Inert gas was added to the spray jet to reduce the flame temperature and increase in-flight particles’ kinetic energy, thus minimizing oxidation while improving coating density. Spray parameters and feedstock powders were selected to overcome challenges imposed by the compact torch designs. Yttria-stabilized zirconia top coats were subsequently applied by air plasma spraying, and the resulting TBC systems were evaluated by high frequency furnace cycle testing (50 min dwell time at high temperature / 10 min cooling) at 1150°C in air. Oxidation behavior and thermal cycle performance of these newly developed TBCs for space restricted applications will be discussed.