Crack healing in yttria stabilized zirconia thermal barrier coatings

A new method for crack healing in thermal barrier coatings (TBCs) is presented, which can be applied to extend the lifetime of coatings that protect turbine blades in the hot section of turbine engines. The method relies on the oxidation of MoSi2(B) healing particles embedded in the top coat. The oxidative decomposition at high temperatures of MoSi2(B) leads to the formation of amorphous SiO2, which flows into cracks and establishes direct contact with the crack faces. The wetting of the crack faces is followed by a chemical reaction with the ZrO2-based TBC coating leading to the formation of solid ZrSiO4. This chemical reaction generates a strong bonding between the healing agent and the matrix material and results in a complete filling and sealing of the crack. A key ingredient in the proposed approach is the encapsulation of the MoSi2(B) healing particles with a shell impermeable to oxygen. The encapsulation is required since the ZrO2matrix is transparent to oxygen and the decomposition reaction of the MoSi2(B) particles can take place even in the absence of cracks, leading to premature healing and undesirable filling of the pores in the YSZ thermal barrier coating.