Solution Precursor Plasma Spray of Yttrium Aluminum Garnet Thermal Barrier Coatings

Yttrium aluminum garnet (YAG) has a number of desirable properties for a thermal barrier coating, including high temperature phase stability and low density.  However it has  a relatively low coefficient of thermal expansion and tends to form an undesirable amorphous phase when plasma sprayed as a powder.  The Solution Precursor Plasma Spray (SPPS) process can readily produce fully crystalline coatings. In the present work, the SPPS process is used to produce thermal barrier coatings with stress relieving, through-thickness-cracks that solve the thermal mismatch problem and structured porosity that lowers the thermal conductivity.  Specific deposition conditions are necessary to achieve the desired microstructures.  Verification testing has included: cyclic furnace testing, sand erosion testing and initial calcium magnesium aluminum and silicon(CMAS) reaction studies.  Verification testing has produce promising results, which will be described.