ISOTHERMAL BEHAVIOR OF MULTILAYER THERMAL BARRIER COATING WITH POROSITY FORMER

Rare earth pyrochlores(A2B2O7 have shown improved performance over standard yttria stabilized zirconia(YSZ) with low thermal conductivity, better phase stability and improved resistance to infiltration of CMAS( calcium magnesium alumino silicates). However, due lower co - efficient of thermal expansion (CTE) and lower fracture toughness has limited the use of pyr ochlores. Drawbacks of single layer configuration can be overcome by Multilayer configuration with conventional YSZ along with pyrocholre. Present study uses four configuration of TBC including single and multilayer produced with suspension plasma praying . However, two samples with bi - layer configuration having porosity former with dense top coat were prepared. Denser top coat provides fracture toughness and intermediate with polymer porosity former reduces conductivity to restrict CMAS penetration. Micros tructural evaluation was done using scanning electron microscope (SEM) before and after isothermal oxidation for 20hrs. Columnar microstructure with vertical cracks was observed, these cracks and pores reduces due to narrowing after oxidation whereas dense r layer show non columnar microstructure. Porosity was measured using water intrusion and image scanning method. Thermal conductivity was obtained from laser flash analyzer. By weight gain and SEM analysis samples with porosity former shown low weight gain and high porosity and thermal conductivity was observed low. Erosion rate of denser top layer was found lower compared other specimens. Bi - layer TBC with intermediate porous layer and dense top coat found better performing among other configuration of TBC .