Damage evolution in a self-healing air plasma sprayed thermal barrier coating containing self-shielding MoSi2 particles

A self-healing thermal barrier coating (TBC) system is manufactured by air plasma spraying (APS) and tested by thermal cycling. The ceramic topcoat in the self-healing APS TBC system consists of an yttria stabilised zirconia (YSZ) matrix and contains self-shielding aluminium containing MoSi2 healing particles dispersed close to the topcoat/bond coat interface. After spraying the healing particles the material was annealed to promote the formation of an oxygen impermeable Al2O3 shell at the MoSi2-TBC interfaces by selective oxidation of the aluminium fraction. The samples were subsequently thermally cycled between room temperature and 1100 degrees C. The study focussed on the spontaneous formation of the Al2O3 shell as well as the subsequent damage evolution in the APS produced TBC during thermal cycling. Experimental evidence showing characteristic signs of crack healing in the topcoat is identified and analysed. The study shows that while the concept of the self-healing APS TBCs containing self-shielding MoSi2 particles is promising, future study is needed to improve the protectiveness of the Al2O3 shells by further tailoring the aluminium content in the MoSi2 and the particle shape to avoid the premature oxidation of the healing particles and maximise crack healing efficiency.