Thermal shock behavior of YSZ thermal barrier coatings with a Ni-P/Al/Ni-P sandwich interlayer on AZ91D magnesium alloy substrate at 400 °C

Thermal barrier coatings (TBCs) consisting of yttria-stabilized zirconia (YSZ) as top coat and NiCrAlY as bond coat were deposited on AZ91D magnesium alloy substrate by atmospheric plasma spraying (APS). In order to improve the stability and prolong the thermal shock life of TBCs, a Ni-P/Al/Ni-P sandwich interlayer between the AZ91D magnesium alloy substrate and the NiCrAlY bond coat was fabricated by electroless plating for Ni-P layer and APS for Al layer. The thermal shock behavior of the YSZ TBCs with the Ni-P/Al/Ni-P sandwich interlayer quenched in water at 400 °C was investigated in detail. The results showed that the thermal shock life of YSZ TBCs with the Ni-P/Al/Ni-P interlayer on the AZ91D substrate was about 226 cycles. The failure of YSZ TBCs in thermal shock test was mainly induced by the corrosion of AZ91D substrate. The results of polarization tests and electrochemical impedance spectroscopy showed that the Ni-P/Al/Ni-P interlayer had better corrosion protection for the magnesium alloy substrate than the Ni-P interlayer, which thus enhanced the thermal shock life nearly two times as compared to that of YSZ TBCs with the Ni-P interlayer.