On the use of B-alloyed MoSi2 particles as crack healing agents in yttria stabilized zirconia thermal barrier coatings

A new method for crack healing in thermal barrier coatings (TBCs) for turbine blades in the hot section of turbine engines relying on the oxidation of embedded spherical MoSi2(B) healing particles is reported. The oxidative decomposition at high temperatures of MoSi2(B) embedded in a TBC 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 healing agent and matrix material and results in a complete filling and sealing of the crack. Due to the oxygen transparency of ZrO2 matrix the decomposition reaction can take place even in the absence of cracks, leading to premature decomposition and undesirable filling of the pores in the TBC. For application in partially yttria stabilized zirconia (YSZ) thermal barrier coatings, the MoSi2(B) healing particles needs to be encapsulated with an oxygen impermeable shell.