Failure mechanism of ZrO2-8%Y2O3 thermal barrier coatings on aluminum alloy with electroless plating interlayer
To relieve the thermal mismatch stress between coatings and substrate, Ni-P and Ni-Cu-P electroless platings were fabricated onto 2A70 aluminum as interlayers. Subsequently, the specimen with plating was covered by CoNiCrAlY bond coat and ZrO2-8%Y2O3(8YSZ) top coat (mass fraction), then a novel thermal barrier coating (TBC) was produced. The thermal shock resistance of TBCs was evaluated by heat cycle test. The results indicate that the lifetimes of TBC with Ni-P interlayer and Ni-Cu-P interlayer are about 1000 cycles and 500 cycles, respectively. The interdiffusion of Ni and Al results in the formation of diffusion layers and island particles at the interface between interlayers and substrate. The connection between particles and diffusion layers improves the adhesion of coatings with substrate, while isolate particles are harmful to the lifetime of coatings due to their poor deformation ability under alternative stress. Crack initiation happens at the interfaces between particles and substrate, which leads to coatings spallation.
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