Low thermal conductivity and high reflectance thermal barrier coatings by EB-PVD for high temperature applications

Ceramic thermal barrier coatings have received increased attention for advanced gas turbine engine applications because of their ability to effectively protect engine hot section components. Achieving low thermal conductivity along with high reflectance and maintaining long-term high temperature stability are among the most critical requirements for developing advanced thermal barrier coatings (TBC). Zirconia and hafnia-based thermal barrier coating materials were produced by industrial prototype EB-PVD. Columnar microstructure of the thermal barrier coatings were modified with controlled micro-porosity and diffused sub-interfaces resulting in lower thermal conductivity (20-30% depending up on microporosity volume fraction), higher thermal reflectance (15-20%) and more strain tolerance as compared with standard TBC. The novel processed coating systems were examined by various techniques including scanning electron microscopy (SEM), X-ray diffraction, thermal conductivity, hemi-spherical reflectance and thermal cyclic tests. The test results showed the tailored-microstructure or modified composition TBC offered superior performance over the conventional thermal barrier coatings (ZrO ₂ -8 wt. % Y ₂O ₃).