Thermal cyclic oxidation performance of plasma sprayed zirconia thermal barrier coatings with modified high velocity oxygen fuel sprayed bond coatings

Abstract

In this study, the Hastelloy-X superalloy samples were overlaid by a CoNiCrAlY bond coating using a high pressure high velocity oxygen fuel (HVOF) spray process. A thin platinum film around 7.5μm thick was further applied to the surface of CoNiCrAlY coating by the magnetron sputtering deposition. Then the superalloy coupons with bare bond coat and with Pt deposited bond coat were pack aluminized at 850°C for 4h to produce (Ni,Co)Al and PtAl2 phases on surfaces, respectively. After that, all samples were overlaid with the yttria-stabilized zirconia (YSZ) top coats by air plasma spraying (APS). Then specimens were subjected to a thermal cycling test at 1100°C. Thermal cycling tests were 1h at 1100°C followed by 10min of forced-air cooling to ambient temperature outside the furnace. The weights of all the specimens were measured every 2cycles. Then effects of aluminizing and Pt-aluminizing on the cyclic oxidation performance and microstructure evolutions of the coatings were evaluated. Scanning electron microscopy (SEM), X-ray diffractometry (XRD) and electron probe microanalyzer (EPMA) were used to identify crystalline phases and microstructures of each coating. The results proved that the roughness of the CoNiCrAlY coating was not changed after the aluminizing or the Pt-aluminizing process. The specific weight gain of the thermal barrier coatings (TBCs) with aluminizing or with Pt-aluminizing bond coating was lower than that of TBCs with only HVOF sprayed bond coat. The cyclic oxidation life of sprayed MCrAlY/ZrO2–Y2O3 thermal barrier coating can be improved effectively by either aluminizing or Pt-aluminizing treatment.