Process and properties of dense and porous vertically-cracked yttria stabilized zirconia thermal barrier coatings

Abstract

Highly durable thermal barrier coatings (TBCs) are desired for various applications in hot sections of gas turbine engines. In this work, dense vertically-cracked (DVC) and porous vertically-cracked (PVC) yttria stabilized zirconia (YSZ) TBCs were produced using the air plasma spray process with a specially engineered powder. The effects of plasma enthalpy on the in-flight particle behavior and coating microstructures were investigated. Thermal conductivity, thermal cycling behavior, as well as, failure mechanisms of both DVC TBCs and PVC TBCs were evaluated. The thermal conductivity of PVC TBCs was found to be approximately 40%–50% lower than that of DVC TBCs due to their higher porosity. In addition, the thermal cycling life of PVC TBCs was demonstrated to be more than 1.8 times that of DVC TBCs with the same substrates and bond coats. PVC TBCs also showed excellent sintering resistance after 743 one-hour thermal cycles at 1125 °C. This work demonstrates that highly durable 8YSZ PVC TBCs with simultaneously high strain tolerance, low thermal conductivity, and high sintering resistance can be produced by the application of an engineered powder feedstock.