Influence of Al content on thermal cycling behavior of HVOF-NiCrAlY+APS-nYSZ thermal barrier coatings

NiCrAlY is a commonly used metallic bond coat material for thermal barrier coating in gas turbines. This study investigates the effect of two NiCrAlY powders with different aluminum contents for gas turbine fabrication on the thermal cycling behavior of HVOF-NiCrAlY+APS-nanostructured YSZ (nYSZ) thermal barrier coatings (TBCs) within the temperature range from room temperature to 1150 ℃. The results show that the growth rate of the Al₂O₃ thermally grown oxide (TGO) on the surface of HVOF-Ni25Cr5Al0.5Y is lower than that of HVOF-Ni22Cr10Al1Y. Similar to the microstructured YSZ (mYSZ)/mYSZ interface, the nYSZ/mYSZ interface can also act as a crack initiation site, leading to the formation of a local crack network in the nYSZ layer. The failure mechanism of two HVOF-NiCrAlY+APS-nYSZ TBCs is consistent with that of the traditional APS/HVOF-MCrAlY (M=Ni and Co)+APS-mYSZ system, which is mainly attributed to the propagation and coalescence of cracks in the nYSZ layer adjacent to the HVOF-NiCrAlY/APS-nYSZ interface. The thermal cycling lifetime of the Ni25Cr5Al0.5Y+APS-nYSZ coating is slightly longer than that of the Ni22Cr10Al1Y+APS-nYSZ coating. Meanwhile, it can effectively improve the thermal cycling life of HVOF-MCrAlY+APS-YSZ TBCs to increase the bonding strength of the YSZ/YSZ interface in the APS-YSZ layer and avoid cracking at the YSZ/YSZ interface and the outer surface of the APS-YSZ.