Oxide and TBC spallation in β-NiAl coated systems under mechanical loading

Thermal barrier coatings have been introduced in turbine blade technology to reduce surface temperature. But severe thermomechanical loading leads to TBC spallation and protection loss.In this work, damage localisation has been studied under thermo-mechanical solicitations on single crystal aluminide coated alloys, with and without TBC. Strong temperature dependencies have been observed for both systems. As expected, oxide spallation and TBC fracture appear to depend on the bond coat ability to accommodate strain mismatch between substrate and oxide layers. Strain triggers surface damage at low temperatures, whereas for high temperatures, bond coat relaxation slows the strain impact on damage, and modifies the rupture path.A kinematic multi-layer model has been proposed to explain the phenomenon. The substrate is assumed to impose mechanical strain to the other layers. Results are in agreement with experimental results.This work was undertaken by turbine manufacturer SNECMA (SAFRAN) and Mines ParisTech.