Estimating the fracture resistance of functionally graded thermal barrier coatings from thermal shock tests

Characterizing the fracture resistance of thermal barrier coatings (TBC) is of technological importance in TBC design. It can enable coating designers predict the expected thermal fracture response under various thermo-mechanical loading conditions. A methodology is presented wherein results from previously reported laser thermal shock experiments are utilized in conjunction with principles of crack arrest to estimate the resistance to crack growth in a functionally graded yttria stabilized zirconia (YSZ) -bond coat (BC) alloy (NiCoCrAlY) TBC. Fracture resistance curves for cracks initiating at the TBC surface and propagating through its thickness are presented. The results show that fracture resistance increases with crack extension for the single-layer YSZ TBC as well as for the YSZ–BC alloy graded TBCs. Furthermore, the addition of BC alloy to the TBC layers (in the graded coatings) results in a substantial increase to their fracture resistance. The approach used provides a means of estimating the fracture resistance of such coatings at elevated temperatures.